Prevalence and clinical profile of glaucoma patients in rural Nigeria-A hospital based study.

PURPOSE: To determine the prevalence and clinical presentation of participants with glaucoma attending a public eye care facility in Nigeria.
METHOD: Hospital based retrospective study of glaucoma participants aged 50 years and above seen over a 5-year period. Descriptive statistics summarized the demographic, clinical characteristics and treatment of the participants and determined the association of variables with gender and age. Prevalence of the glaucoma by type, and their 95% confidence intervals (CI) were also calculated. RESULT: Of the 5482 case files that were reviewed, 995 (18.15%, 95% Cl 17.15-19.19%) had glaucoma particularly primary open angle glaucoma (11.55%, 95%CI 10.73-12.42%) and were mostly females (564, 56.7%) aged 69 ± 12 years (range, 50-103 years). In contrast to other glaucoma types, the prevalence of primary angle closure glaucoma (3.68, 95%CI 3.22-4.22) increased by 15% over 5 years. The mean intraocular pressure ranged from 15-50 mmHg but higher in females than males (27.8 ± 6.1mmHg versus 26.6 ± 6.0 mmHg, P <0.05) who had comparable VA (0.58 ± 0.4 Log MAR) and cup-disc ratios (P >0.05). On presentation, the glaucoma hemi field test (GHFT) was outside the normal limits in 45.5% and 54.5% of males and females, respectively. The type of visual field defect was associated with glaucoma type (P = 0.047). Arcuate scotoma was most common (35.5%) across glaucoma types, paracentral scotoma more common in Secondary glaucoma while Seidel scotoma was highest in NTG (19.3%). Beta-blocker was the mainstay of management (42.2%) but more likely to be prescribed to males while more females received carbonic anhydrase inhibitors.
CONCLUSIONS: The high prevalence of glaucoma in older people remains a public health problem in Nigeria. The fact that about half of the participants presented with visual field defect suggests there is a need for public health messages to emphasize on early glaucoma screening, detection and management.

Introduction

Glaucoma is a group of disorders characterized by a progressive optic neuropathy resulting in characteristic appearance of the optic disc, and/or irreversible visual field defect that are associated either with elevated intraocular pressure or normal pressure [1]. It is a public health problem accounting for 8% of world blindness and the second leading cause of blindness after cataract [2]. Globally, an estimate of 60.5 million people have glaucoma and about 8.4 million had become blind from the condition [2].

The number of people (aged 40–80 years) with glaucoma has been projected to increase to 111.8 million by 2040 [3,4]. Blindness due to glaucoma can be avoided if the glaucoma is detected early and managed appropriately [5]. The prevalence of glaucoma worldwide is about 1% in older people (aged >50 years) and increases with age [3,6]. A review of relevant population based surveys of glaucoma, visual impairment and blindness in Sub- Saharan Africa indicate that glaucoma affects about 4% adults aged 40 years and above and accounts for 15% of blindness [5]. The prevalence ranges from 0.66% to 1.79% in Eritrea, Liberia, Ghana, South Africa and Malawi [7-9]. Primary open angle glaucoma (POAG) is the most common form of glaucoma among Africans [5] and contributes to 8.4 million cases of bilateral blindness even in developed countries with half of the cases still undiagnosed [10]. In Nigeria, 1,130,000 individuals’ ≥40 years are blind and 4.25 million have moderate to severe visual impairment [11].

Various studies [12-14] in different parts of Nigeria have shown that glaucoma is one of the leading causes of blindness in the country and the prevalence is slightly higher in the Southeastern part of the country compared with other regions. In a 1995 population based cross sectional survey conducted in Dambatta local government area (LGA), Kano state, Northwestern Nigeria, the authors reported that 15% of the blindness and 7% of the visual impairment they found, were attributable to glaucoma [15]. Murdoch et al [16] reviewed population based studies published between 1966 to September 2012 on posterior segment eye diseases (PSEDs) in sub-Saharan Africa. They found that in Nigeria, the prevalence of glaucoma was 1.02% in those aged >45 years and noted that African-based studies are needed to help estimate present and future needs and plan services to prevent avoidable blindness.

Nigeria is divided along three main ethnic groups with the Igbos in the Eastern region, Yorubas in the Western region and Hausas in the Northern region. Each ethnic group has its unique culture and the lack of ethnic specific data on sight-threatening diseases such as glaucoma makes it difficult to extrapolate the one group’s findings due to differences in cultural and socio-economic activities. There is a need to understand the demographic and clinical presentation of glaucoma in different regions in Nigeria for effective management. Evaluating the epidemiological and clinical profile of glaucoma patients seen at the Federal Medical Centre Eye clinic Gusau, Zamfara State will shed light on inter-ethnic and regional variations of glaucoma prevalence in Nigeria. It will also provide a useful background information for planning epidemiological surveys on glaucoma in this region as well as other parts of Nigeria with similar socio-demographic and ecological characteristics. Therefore, this study was aimed to assess the epidemiological characteristics and clinical presentations of glaucoma patients’ ≥50 years seen at a referral center in Nigeria.

Materials and methods

Study setting

This retrospective study of adult participants who attended the glaucoma referral center of the Federal Medical Centre (FMC) Gusau, Zamfara State, Nigeria between, January 2011 and December 2016 (5-year period). The eye clinic is one of the two public/government established eye clinics that serves as a primary health care center for over 3 million residents of Zamfara State and its environs. The region is made up of largely Muslims of Hausa ethnic group many of who (60%) are subsistence farmers that live in rural areas and live in rural areas on less than a dollar per day [17]. There is low literacy level in the region [5,17,18]. Life expectancy in this region is less than 50 years, there is high poverty rate and the region has ill-equipped hospitals and infrastructure in terms of roads, public transport and access to health care services are relatively poor [18].

Study design and sampling

This was a hospital-based study of participants diagnosed with glaucoma over 5 years. A non-probability convenience sampling method was utilized because all patients with glaucoma who visited the center during the study period were eligible.

Inclusion and exclusion criteria

Data for all participants aged 50 years and over who presented for the first time to this referral center and were diagnosed with glaucoma at the eye clinic during the study period were included. This includes those who had undergone filtration surgery. Participants with ocular hypertension, who did not have changes in optic nerve head or visual function abnormalities were excluded. Also, those with any history of ocular disease that could affect the validity of the ocular fundus examination including macular degeneration, retinitis pigmentosa, hypertensive retinopathy, diabetic retinopathy; those with refractive error of ± 4 Diopter (D) sphere, and/or astigmatism of 3D; participants with significant cataract that affect vision as well as glaucoma participants with incomplete records of C/D ratio, visual field assessment were excluded.

Techniques for determination of clinical indices of glaucoma

The hospital does not have electronic records, coding, and database registry. It still operates in hard copy system for storing patients’ records’ therefore all case files of adult patients diagnosed with glaucoma from 2011 to 2016 were first requested from the hospital administrator and retrieved from the archives with the assistance of the eye clinic department secretary.

Data collection involved the use of a data extraction sheet to extract information on demographics, and clinical profile directly from the patients’ files. The data on demographics of patients included gender, age at presentation, ethnic group, religion, and occupation. The clinical profile recorded included presenting visual acuity, intraocular pressure (IOP), vertical cup-to-disc ratios (VCDR), type of glaucoma, glaucoma hemifield test, type of visual field defect and method of management. Visual acuity was measured in Snellen notation and subsequently converted to logMAR notation for the purpose of analysis. Glaucoma hemifield test (GHFT) was performed with automated Humphrey visual field analyzer (Humphrey 740; Carl Zeiss Meditech, Dublin, CA) but global indices including pattern deviation, mean deviation, pattern standard deviation were not documented in the patients ‘files at the time; hence, the global indices were not included in the study. IOP was measured using the Goldmann applanation tonometer mounted on a slit lamp bimicroscope and as a routine practice, were taken between the hours of 8 am to 4 pm when the IOP are most stable [19].

For diagnosis of glaucoma, gonioscopy using a Goldmann 3-mirror and fundus eye exam with the Welch-Allyn (Welch-Allyn Inc., Skaneateles Falls, New York, USA) ophthalmoscope was conducted. The hospital used International Society for Geographical and Epidemiological Ophthalmology (ISGEO) for the diagnosis and classification of glaucoma. Similar diagnosis criteria has been used in other hospital based studies [20-22]. Glaucomatous optic disc atrophy was confirmed by stereoscopic examination of the optic disc with a +90D lens on the slit lamp. A measuring eyepiece graticle (Haag Streit) was used in measuring the vertical optic diameter and cup diameter. Also noted were the presence of notching on the disc rim and any violation of the ISNT rule. The vertical cup-to-disc ratio (VCDR) was used as an index of structural glaucomatous damage. There was no ocular coherence tomography (OCT) in the hospital at the time of data collection, hence retinal nerve fiber layer (RNFL) loss and central corneal thickness (CCT) were not collected.

Glaucoma diagnosis criteria. The criteria for the classification of glaucoma at this hospital are described below: Criterion 1 Diagnosis (Structural and Functional Evidence) included eyes with a VCDR of 0.7 or more and less than 0.9 and/or VCDR asymmetry of 0.2 or more or a neuroretinal rim width reduced to less than or equal to 0.1 VCDR (between 11 and 1 o’clock or 5 and 7 o’clock) that also showed a definite visual field defect consistent with glaucoma. Criterion 2 Diagnosis (Advanced Structural Damage With Unproved Field Loss) included participants who could not satisfactorily complete the visual field test but had eyes with VCDR of 0.9 or more and/or VCDR asymmetry of 0.3 or more. Criterion 3 Diagnosis (Optic Disc Not Seen, Field Test Impossible) was given if it was not possible to examine the optic disc, and eyes had visual acuity less than 20/400, presence of relative afferent pupillary defect with IOP of 26 mm Hg or higher, and/or evidence of glaucoma surgery or medical records confirming glaucomatous visual morbidity [23].

Glaucoma types

Primary Open Angle Glaucoma (POAG) was defined as open and normal appearing angle with IOP ≥21 mmHg associated with either glaucomatous optic disc abnormalities (cupping) or glaucomatous visual field abnormalities or with both. Normal tension glaucoma (NTG) was defined as open and normal appearing angle with IOP ≤ 21 mmHg at all times, with glaucomatous optic neuropathy or IOP ≤ 21 mmHg at all IOP measurements on record. Primary angle closure glaucoma (PACG) was defined as an eye with an occludable drainage angle and features indicating trabecular obstruction by the peripheral iris, such as peripheral anterior synechiae, irido-corneal contact, elevated intraocular pressure (IOP of 21 mmHg or more), together with evidence of glaucomatous optic nerve damage and visual field (VF) loss. Secondary glaucoma (SG) was defined as raised IOP with glaucomatous optic neuropathy or IOP ≥21mmHg associated with positive history and ocular findings of pathologies such as trauma, previous surgery, neovascularization, inflammation, or any other abnormal ocular or systemic findings that could have caused prior or current IOP elevation. In addition, glaucoma, patients with a history of use of topical steroids (6 months), a history of trauma or ocular surgery, chronic uveitis, evidence of pseudo exfoliation or pigment dispersion on slit lamp examination, and those with hyper mature or intumescent cataract were grouped under secondary glaucoma.

Variables description

The type of Glaucoma (POAG, NTG, PACG and SG) [24] and the clinical indices of glaucoma were the dependent variables at each time. The changing in frequency of different subtypes of glaucoma was gotten by calculating the total number of people with a particular glaucoma type divided by the total number with glaucoma in that year multiplied by 100. The independent variables included epidemiological characteristics of age, gender, occupation, ethnic groups and religion and clinical indices including type of VF defect, vertical cup-disc ratio (VCDR), IOP, GHFT, VA in logMAR and treatment of the glaucoma (surgery, medications and combinations). Similar to previous paper [25] and for purposes of analysis, participants with counting finger at 2 feet were considered to have a visual acuity of 2/200 or 20/2000. Those with hand movement at a distance of 2 feet were considered to have an equivalent Snellen acuity of 20/20,000. Also, these were converted to logMAR. Light perception (LP) with or without projection and no light perception (NLP) are not VA measurements but merely the ability to detect a stimulus. Therefore, these factors were excluded from the analysis [26].

Ethics

Approval for this study was obtained from the Institutional Review Board of Madonna University, Nigeria. The study adhered to the tenets of the Declaration of Helsinki and permission to access the patient records was obtained from the management of the Federal Medical Centre (FMC) Gusau, Zamfara State.

Statistical analysis

All data analysis were performed using the IBM SPSS Statistics for Windows, Version 25.0 (IBM Corp., Armonk, NY, USA). Normality distribution of the data was assessed using Kolmogorov–Smirnov test. Data was presented using descriptive statistics using frequencies for categorical variables and mean (±standard deviation, SD; range) for continuous variables. One-way analysis of variance (ANOVA) and chi-square test were performed to assess the differences between groups for the continuous and categorical variables respectively. The differences in the proportion diagnosed with different types of glaucoma by year of diagnosis was also assessed using chi-square test. Univariate analysis was conducted to assess the effects of gender on the clinical indices. The level of statistical significance was set at 5%.

Results

Demographic characteristics of the participants with glaucoma

Of the 5482 casefiles of participants aged 50 years and over who attended this hospital over 5 years period, 995 participants were diagnosed with glaucoma. Table 1 presents the characteristics of this study population indicating that nearly all were Muslims, females (56.7%) and of Hausa origin. The mean age of the participants was 69 ± 12 years (mean ±SD), and about 61% were farmers. The clinical indices, glaucoma hemifield test classification, type of visual field defect, glaucoma type and treatment in this study population has been shown in Table 1. The table also shows the mean values for the clinical profiles such as IOP, cup-to-disc ratios, visual acuities and the others.

Table 1

Descriptive statistics of measured variables among glaucoma participants.

Variables	n (%)
Demography n(%)	995/5482 (18.2%)
Age, mean (SD)	69.2 (11.8), 50–103
Gender
Male	431 (43.3)
Female	564 (56.7)
Ethnic group
Fulani	183 (18.4)
Hausa	631 (63.4)
Others	178 (17.9)
African Traditional	9 (1.0)
Christian	84 (8.4)
Islam	901 (90.6)
Occupation
Employed	90 (9.0)
Farming	613 (61.6)
Retired	181 (18.2)
Self employed	111 (11.2)
Clinical index, mean (SD), range
Visual acuity (RE)	0.58 (0.40), 0–2.8
Visual acuity (LE)	0.55 (0.38), 0–2.8
Cup-disc ratio (RE)	0.69 (0.11), 0.30–0.90
Cup-disc ratio (LE)	0.69 (0.12), 0.3–0.9
Intraocular pressure (RE)	27 (6), 15–45
Intraocular pressure (LE)	27 (6), 15–50
Glaucoma Hemifield Test
Borderline	231 (23.2)
Outside Normal Limit	541 (54.4)
Reduced Sensitivity	55 (5.5)
Within Normal Limits	168 (16.9)
Visual field Defects
Arcuate	353 (35.5)
Paracentral	52 (5.2)
Ring	224 (22.5)
Seidel	98 (9.8)
Tunnel	268 (26.9)
Glaucoma type
Normal tension	57 (5.7)
Primary angle closure	202 (20.3)
Primary open angle	633 (63.6)
Secondary	103 (10.4)
Treatment
Surgery only	18 (1.8)
Trabeculectomy + Alpha 2 agonist	49 (4.9)
Trabeculectomy + prostaglandin analogues	10 (1)
Trabeculectomy + Beta-blocker	43 (4.3)
Prostaglandin analogue	112 (11.3)
Carbonic anhydrase inhibitor	78 (7.8)
Beta blocker	420 (42.2)
Alpha 2 agonist	265 (26.6)

VA was recorded in Log MAR = logarithmic minimum angle of resolution; SD = standard deviation; RE = right eye; LE = left eye.

Of clinical indices, VA was drastically reduced with mean VA of 0.58 ± 0.4 logMAR indicating visual impairment. There were 23 (2.31%) and 6 participants (0.60%) whose VA in either or both eyes respectively was recorded as counting finger (n = 1, 4.3%), hand movement (n = 9, 0.90%), and light perception (15, 1.5%). For 375 participants (37.7%), VA in the better Seeing Eye was worse than 0.5logMAR indicating either low vision (n = 315, 31.6%) or blindness (n = 60, 6.0%) according to the WHO definition for blindness as a best-corrected visual acuity worse than 1.3 logMAR.

The mean IOP in this study group ranged from 15–50 mmHg with an average cup-disc ratio of 0.7. For majority of the participants, beta-blocker was the mainstay of therapy (42.2%) and about 1.8% had glaucoma filtration surgery done. Arcuate and ring scotomas were the predominant visual field defect among the participants consisting of about 58% of the reported visual field defects.

Hospital prevalence of glaucoma

Fig 1 shows the hospital prevalence by glaucoma type over 5 years in this rural referral hospital. Over the five-year study period, 18.15% [95% Confidence interval CI 17.15–19.19] had glaucoma in this referral hospital. The highest prevalence was for POAG, which was more than three times higher than that of PACG. The lowest prevalence was for NTG.

Fig 1

Prevalence of glaucoma by type over 5 years.

Error bars represent 95% confidence intervals.

Analysis of glaucoma type

Chi-square analysis revealed no significant association between the type of glaucoma and the demographic factors of gender (P = 0.122), occupation (P = 0.169), and ethnic group (p = 0.408), but age and year of glaucoma diagnosis were associated with glaucoma type in this study group (P <0.0005, for both). Participants who were diagnosed with NTG were younger (57 ± 9 years) than those in PACG (71 ± 11 years), PAOG (70 ± 12 years), and SG (69 ± 12 years) groups (P <0.0005, for all comparisons).

Fig 2 presents the glaucoma types by year of diagnosis showing that except for PACG, which increased by about 15% over the five-year period, all other glaucoma types showed a decline in the proportion diagnosed over 5 years. Overall, 50% fewer cases were diagnosed with glaucoma in 2016 compared with 2011, in this rural hospital.

Fig 2

Percentage distribution of glaucoma type by year of diagnosis.

The type of visual field defect was also associated with glaucoma type (P = 0.047) as shown in Fig 3, with arcuate scotoma (35.5%) being the most predominant visual field defect across all types of glaucoma, followed by tunnel vision. Although fewer people had paracentral scotoma, it was more among those diagnosed with SG and POAG. Seidel scotoma was highest among those diagnosed with NTG (19.3%).

Fig 3

Percentage distribution of the visual field defect by glaucoma type.

Analysis of the clinical profiles and treatment types

The mean values for the clinical profiles by gender is shown in Table 2. The mean IOP (27± 6 mmHg) was significantly higher in females than males (27.8 ± 6.1mmHg versus 26.6 ± 6.0 mmHg, P <0.05) who had comparable VA and cup-disc ratios (P >0.05). For more than half of the participants (n = 541, 54.4%), the glaucoma hemi field test was outside the normal limit and it was within normal limits for 16.9% of the participants (Table 1) and comparable between gender (Table 2, P = 0.136).

Table 2

Clinical indices and treatment of glaucoma participants aged 50 years and over.

Variables	Male	Female	P -Value
Clinical index, mean (SD), range	RE/LE	RE/LE
Visual acuity (RE)	0.58 (0.42)/0.56 (0.40)	0.57 (0.39)/0.55 (0.35)	0.799, 0.661
Cup-disc ratio	0.68 (0.11)/0.68 (0.11)	0.69 (0.10)/0.69 (0.12)	0.268, 0.322
Intraocular pressure (RE)	26.6 (6.0)/26.3 (5.9)	27.8 (6.10)/27.4 (5.97)	0.002, 0.006
Glaucoma Hemi field Test, n (%)
Borderline	103 (44.6)	128 (55.4)	0.136
Outside Normal Limit	246 (45.5)	295 (54.5)
Reduced Sensitivity	18 (32.7)	37 (67.3)
Within Normal Limits	64 (38.1)	104 (61.9)
Treatment, n (%)
Trabeculectomy only	10 (2.3)	8 (1.4)	0.021
Trabeculectomy + Alpha 2 agonist	27 (6.3)	22 (3.9)
Trabeculectomy + prostaglandin analogues	4 (0.9)	6 (1.1)
Trabeculectomy + Beta-blocker	24 (5.6)	19 (3.4)
Prostaglandin analogue	51 (11.8)	61 (10.8)
Carbonic anhydrase inhibitor	44 (10.2)	34 (6.0)
Beta blocker	169 (39.2)	251 (44.5)
Alpha 2 agonist	102 (23.7)	163 (28.9)

VA was recorded in Log MAR = logarithmic minimum angle of resolution; SD = standard deviation; RE = right eye and LE = left eye were for clinical index only.

The treatment type varied significantly between males and females. Males were more likely to be treated with Alpha 2 agonist and beta-blockers, while females were more likely to receive carbonic anhydrase inhibitors (Table 2). About 12.1% of participants had done glaucoma filtration surgery (Trabeculectomy) for control of intraocular pressure and more in males than females (n = 55, 15.1% versus n = 47, 9.8%).

Discussion

In the present study, epidemiological and clinical profile of glaucoma patients 50 years and above seen at a health care facility for a period of 5 years were evaluated. There was a high prevalence of glaucoma particularly open angle glaucoma, especially among females, Muslims and farmers. Whereas there was a decline in prevalence for other types of glaucoma, the prevalence of PACG in this underserved community increased by 15% over 5 years. Contrary to a previous report [27], the prevalence of PACG exceeded that of NTG by about 4 folds. The type of visual field defect varied significantly with the glaucoma type but arcuate scotoma was most common in all glaucoma types. Although, beta-blocker was the main drug of choice of glaucoma treatment in this hospital, men were more likely to receive this treatment than women who were more likely to receive carbonic anhydrase inhibitors. At the time of this study, about a quarter of the participants, more men than women (15% versus 10%) already had Trabeculectomy as a surgical procedure for control of their intraocular pressures.

The prevalence of glaucoma reported in this region was considerably higher than previous estimates from survey studies (ranging from 1% to 8.6%) in other parts of the country [14,23,28-30]. Such high prevalence is expected since this region has only two primary health care centers that provide eye care services; therefore high influx of patients will be expected at this center. The fact that our study was in the northern part of Nigeria where majority of the participants were of Hausa ethnic group (less educated) may contribute to the difference in prevalence compared with other studies which included the more educated ethnic groups (Yorubas and Igbos) [23,29]. Also, the lack of awareness and poor utilization of eye care services reported in some parts of Nigeria [31-33] could be the reason for the reduced prevalence recorded. There is a need for more awareness to be created and more eye care outlet established in underserved communities in Nigeria to encourage utilization of eye care services.

Similar to the present report, high prevalence of POAG has been reported in the black race including among African Americans and Afro-Caribbean [5] and in other studies [4,34-39]. It is possible that the prevalence reported in our study may have been underestimated as POAG is usually asymptomatic and people only seek for medical attention when it becomes severe and affect vision. Although the prevalence of POAG observed in this study was higher than previous reports from Nigeria [5,14,18,29,30,40], it was much lower than the 91.2% recorded in another hospital based study from Benin City [41]. Considering the rurality of this community, there is a high possibility that many remain cases of PAOG remain undetected in this population.

The present finding of a significant increase in PACG prevalence during the study period is in agreement with the projected global increase in the prevalence of PACG (from 23–32 million over the next 2 decades [42]. Also, the prevalence of PACG in this Northern hospital exceeds the 1.7% that was reported in Southern hospital studies [14,30]. The study found a marked reduction in the prevalence of all other glaucoma types including POAG, which might not necessarily reflect reduction in glaucoma prevalence but rather a decrease in the utilization of eye care services triggered by insurgency and civil unrest predominant in this region [18]. In addition to these factors, poor awareness of glaucoma and low life expectancy in Nigeria could play a role in the decline in glaucoma prevalence [18,43]. Contrary to our findings, a hospital-based study in Benin City recorded a monthly increase in glaucoma prevalence from 10 to 27% [41] but failed to distinguish between glaucoma types. This increase might be attributed to greater glaucoma awareness, and higher socioeconomic status of the participants since data was from a private owned hospital. However, in another study conducted in a South Korean public hospital, a 54% annual increase in glaucoma prevalence was observed over 5 years. This increase could be attributed to the improvement in glaucoma detection techniques at this hospital, as well as increase in access to eye care services (increased by 9%) and the life span of people in the region (increased by 14.28%) [39].

There are mixed reports on the effect of gender on glaucoma prevalence. The present study found no significant difference in glaucoma prevalence between male and females, which was similar to previous studies from Ghana [44,45]. In contrast, studies from Nigeria [5,40,41], Ghana [46] and South Korea [44] reported a higher prevalence in men than women. Moreover, gender predilection of glaucoma has not been established suggesting the need for more studies to determine the association of glaucoma with gender. Age is a risk factor for glaucoma [47-50] and this was also associated with glaucoma type in this study. Participants with NTG were younger than other glaucoma types even though the overall mean age of participants in this study was similar to previous studies [14,30,41,51-53]. This finding further confirms the importance of visual field and optic nerve assessment as part of the early screening of glaucoma in this population.

The mean VCDR recorded in this study was similar to that of the national eye survey in Nigeria [54], but less than the VCDR recorded among participants in Oyo State Nigeria [23], Tanzania [55] and Netherland [56]. There is a limited information on the distribution of VCDR among Nigerian population; although those from Igbo ethnic group have larger optic disc area and cup than other ethnic groups [5]. The visual field defect, which is one of the hallmark used in the diagnosis of glaucoma, occurs as a result of optic disc cupping. For a good number of the participants in the present study, the glaucoma hemi field test was outside the normal limit field. Uncontrolled IOP due to late presentation could be the reason for the increased visual field loss recorded in this study [20]. Furthermore, the rate of progression of the visual field defect varies in patients, and treatment of the glaucoma may not completely stop the visual field loss as some patients still progress despite treatment. Early screening for glaucoma is highly indicated in this region. Majority of the participants in this study presented to the clinic at the late stage of glaucoma with many already having significant visual field loss leading to tunnel vision or blindness in at least one eye, which confirms the findings of other studies in Africa [18].

That a good number of participants in this study had severe visual impairment and blindness on first presentation to the clinic was in line with previous reports from Nigeria [5,11,33,40,57] and Saudi Arabia [58]. In North-eastern Nigeria, a study found that about 76% were already blind at hospital presentation. Old age, poor knowledge of glaucoma, rural residence and living far from the hospital were attributed to the late presentation of glaucoma patients in Nigeria [18,57]. In addition, the report of earlier age of onset of glaucoma among Africans or black population may contribute to the high rate of blindness in this population since they would have had the disease for a longer time [40]. Public eye health education and glaucoma screening programs in the rural communities in Nigeria cannot be over emphasized. The Nigerian government should consider ameliorating programs aimed at reducing cost for glaucoma management especially in this region.

The uptake of glaucoma surgery in this region was low and could be attributed to the reported low success rate of Trabeculectomy among black patients [6]. Inadequate access, high cost of surgery, superstition and socio-cultural beliefs may contribute to the preference for medical treatment rather than surgery [59]. In Ethiopia, authors reported a high uptake of glaucoma surgery [60] as ophthalmologists in the country choose surgery over medications due to patients’ non-compliance. Similar to a study in Ghana [51], we found that beta-blockers such as timolol were the mainstay of treatment. This could be explained by the fact that it is more affordable and readily available than other classes of drugs including prostaglandin analogues (latanoprost), which are considered the first line of treatment for lowering IOP [61]. In addition, prostaglandin analogues have ocular adverse effects like pruritus, conjunctival hyperemia, ocular irritation, ocular pain, burning, and cilia alteration which may not be pleasant in older people.

Strengths and limitations

The study has some limitations. First, as a single hospital-based study, the findings are better representatives of the clinical situation compared with population studies but the findings cannot be representative of the general population in Northern Nigeria or the country at large. A population based study is needed with a larger number of patients, to substantiate information obtained from this study. Also, we did not assess associations with other ocular conditions like myopia and comorbid conditions which would require further investigation with additional hospital based data. Retinal nerve fibre layer loss and central corneal thickness were skipped in the diagnosis due to the unavailability of OCT data at the hospital during the period of data collection. Also, global indices were not recorded in the patients’ files and this further limits the study. The fact that OCT was not used in the glaucoma diagnosis could have affected the low prevalence of NTG. Normal tension glaucoma (NTG) may be very difficult to detect without OCT and/or pachymetry because it occurs with normal IOP. Despite the limitations, our study is the first to highlight the epidemiology of glaucoma in this region and the key findings were comparable with results from other studies.

Conclusion

This study found that among people aged 50 years and above in this underserved community, the prevalence of glaucoma was higher than previously reported in other parts of Nigeria. Although primary open angle glaucoma (POAG) showed a decline, it remains a public health problem in Nigeria together with the added burden from the increasing rate of angle closure glaucoma in this community. The fact that majority of the participants with glaucoma in this region still present late when their ganglion cells and vision have already been severely affected calls for urgent public health measures for glaucoma control in this region. Public health messages emphasizing on early glaucoma screening, detection and management are needed.

(XLSX)

Click here for additional data file.

20 Aug 2021

PONE-D-21-21579

Prevalence and clinical profile of glaucoma patients in rural Nigeria -  A hospital based study

PLOS ONE

Dear Dr. Osuagwu,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

The manuscript sheds some light and provides useful information about the demographics of glaucoma in Nigeria. However, the manuscript needs meticulous revision regarding the visual field findings to be consistent. In addition, the authors need to address whether he studied population would representative of a single or different ethnic groups.

Please submit your revised manuscript by Oct 04 2021 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Ahmed Awadein, MD, Ph.D, FRCS

Academic Editor

PLOS ONE

Journal Requirements:

When submitting your revision, we need you to address these additional requirements.

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and

https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

2. We note that your paper includes detailed descriptions of individual patients/participants. As per the PLOS ONE policy (http://journals.plos.org/plosone/s/submission-guidelines#loc-human-subjects-research) on papers that include identifying, or potentially identifying, information, the individual(s) or parent(s)/guardian(s) must be informed of the terms of the PLOS open-access (CC-BY) license and provide specific permission for publication of these details under the terms of this license. Please download the Consent Form for Publication in a PLOS Journal (http://journals.plos.org/plosone/s/file?id=8ce6/plos-consent-form-english.pdf). The signed consent form should not be submitted with the manuscript, but should be securely filed in the individual's case notes. Please amend the methods section and ethics statement of the manuscript to explicitly state that the patient/participant has provided consent for publication: “The individual in this manuscript has given written informed consent (as outlined in PLOS consent form) to publish these case details.

3. In the ethics statement in the manuscript and in the online submission form, please provide additional information about the patient records used in your retrospective study, including: a) whether all data were fully anonymized before you accessed them; b) the date range (month and year) during which patients' medical records were accessed; c) the date range (month and year) during which patients whose medical records were selected for this study sought treatment. If the ethics committee waived the need for informed consent, or patients provided informed written consent to have data from their medical records used in research, please include this information.

4. Thank you for stating the following financial disclosure:

[Not applicable].

At this time, please address the following queries:

a) Please clarify the sources of funding (financial or material support) for your study. List the grants or organizations that supported your study, including funding received from your institution.

b) State what role the funders took in the study. If the funders had no role in your study, please state: “The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.”

c) If any authors received a salary from any of your funders, please state which authors and which funders.

d) If you did not receive any funding for this study, please state: “The authors received no specific funding for this work.”

Please include your amended statements within your cover letter; we will change the online submission form on your behalf.

5. We note that you have indicated that data from this study are available upon request. PLOS only allows data to be available upon request if there are legal or ethical restrictions on sharing data publicly. For information on unacceptable data access restrictions, please see http://journals.plos.org/plosone/s/data-availability#loc-unacceptable-data-access-restrictions.

In your revised cover letter, please address the following prompts:

a) If there are ethical or legal restrictions on sharing a de-identified data set, please explain them in detail (e.g., data contain potentially identifying or sensitive patient information) and who has imposed them (e.g., an ethics committee). Please also provide contact information for a data access committee, ethics committee, or other institutional body to which data requests may be sent.

b) If there are no restrictions, please upload the minimal anonymized data set necessary to replicate your study findings as either Supporting Information files or to a stable, public repository and provide us with the relevant URLs, DOIs, or accession numbers. Please see http://www.bmj.com/content/340/bmj.c181.long for guidelines on how to de-identify and prepare clinical data for publication. For a list of acceptable repositories, please see http://journals.plos.org/plosone/s/data-availability#loc-recommended-repositories.

We will update your Data Availability statement on your behalf to reflect the information you provide.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Partly

Reviewer #2: No

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: No

Reviewer #2: Yes

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: No

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: No

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: This manuscript requires revision in order to make it useful to the reader.

Introduction.

Lines 81-4: An explanation is required as to how this study will shed light on inter-ethnic and regional variations in glaucoma prevalence in Nigeria, as the study was based in a particular hospital (single centre). Was the population multi-ethnic?

Methods. The authors need to state how cases of glaucoma were identified: was there a database, registry, or coding system that allowed such identification, other system employed?

Was VA measured in logMAR directly or in Snellen and subsequently converted? See later as well (lines 76=9)

What type of prevalence was this, and how was it determined (lines 221-4)? As the authors are aware, hospital prevalence is totally different from population prevalence, and have different implications.

How was the changing frequency of different subtypes of glaucoma determined? How do the authors explain the falling frequency of glaucoma over time?

The Discussion could be slightly focused.

Other comments

Line 44, 123.202 and elsewhere: 'hemi-field'

Line 45 and elsewhere: p value with lower case 'p'

Line 576: insert 'and/or' preceding 'irreversible'

Line 111: replace ';' with stop, and commence a new sentence to read 'Further, those with a history....'

Line 120: define 'IOP' at first use in the manuscript (I cant find it)

Line 136: 'VCDR previously defined in line 120; adopt abbreviation subsequently throughout

Line 174: 'logMAR'

Lines 76-9: define these levels of VA in logMAR. Similarly HM, CF and PL have logMAR notations?

Reviewer #2: The authors are not clear with their unit of analysis.they reported that 995 patients with glaucoma were diagnosed over the 5 years of their study and they proceeded to present field defects of 995 patients however they didn't mention which one of the patient was selected for analysis and what criteria was used in the selection of the eye. Furthermore, they stated in line 209 to 211 that 15 patients had visual acuity of light perception in both eyes and that these patients were excluded from analysis (line 177 to 179) then how did they arrive at 995 visual defect results when 15 of the 995 had only light perception bilaterally. Additionally, it is impossible for HVF machine to report GHT results without reporting the global indices.As a glaucoma specialist who has been treating glaucoma patients in Nigeria,I know it is almost impossible to see only 995 glaucoma patients in 5 years.The glaucoma definition the author's quoted in the study is applicable only in prevalent survey not for hospital based study.

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

Submitted filename: PONE-D-21-21579 PLOS ONE.pdf

Click here for additional data file.

10 Oct 2021

PONE-D-21-21579R1

Prevalence and clinical profile of glaucoma patients in rural Nigeria - A hospital based study Dr Uchechukwu Levi Osuagwu

Dear Dr. Osuagwu,

We've checked your submission and before we can proceed, we need you to address the following issues:

1. Thank you for stating the following financial disclosure:

[Not applicable].

At this time, please address the following queries:

a) Please clarify the sources of funding (financial or material support) for your study. List the grants or organizations that supported your study, including funding received from your institution.

b) State what role the funders took in the study. If the funders had no role in your study, please state: “The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.”

c) If any authors received a salary from any of your funders, please state which authors and which funders.

d)

e) If you did not receive any funding for this study, please state: “The authors received no specific funding for this work.”

Please include your amended statements within your cover letter; we will change the online submission form on your behalf.

Reply: Done. See cover letter and wording was revised in the manuscript to reflect this. Thanks for changing the online submission on our behalf

2. In the ethics statement in the manuscript and in the online submission form, please provide additional information about the patient records used in your retrospective study, including:

a) whether all data were fully anonymized before you accessed them;

Reply: This has been included in the manuscript.

“…..Only the researcher (CO) has access to identifiable participant data in order to extract the required variables. However, the researcher de-identified the data once the variables were extracted.

[line 116-118]”

b) the date range (month and year) during which patients' medical records were accessed.

Reply: This was already in the manuscript lines 100-101 and read: ….January 2011 and December 2016

If the ethics committee waived the need for informed consent, or patients provided informed written consent to have data from their medical records used in research, please include this information.

Reply: Done. Line 201

3. We note your updated Data Availability Statement: “All relevant data are within the manuscript and additional information can be obtained on reasonable request by the Corresponding author"

Please address the following:

a. We note that you state that all relevant data are within the manuscript. Please confirm at this time whether or not your submission contains all raw data required to replicate the results of your study. Authors must share the “minimal data set” for their submission. PLOS defines the minimal data set to consist of the data required to replicate all study findings reported in the article, as well as related metadata and methods (https://journals.plos.org/plosone/s/data-availability#loc-minimal-data-set-definition).

For example, authors should submit the following data:

- The values behind the means, standard deviations and other measures reported;

- The values used to build graphs;

- The points extracted from images for analysis.

Authors do not need to submit their entire data set if only a portion of the data was used in the reported study.

If your submission does not contain these data, please either upload them as Supporting Information files or deposit them to a stable, public repository and provide us with the relevant URLs, DOIs, or accession numbers. For a list of recommended repositories, please see https://journals.plos.org/plosone/s/recommended-repositories.

Reply: The data has been uploaded as supporting information file and revised the availability of data and material section.

“Availability of data and material: The data that support the findings of this study are included in the manuscript. In addition, the de-identified data required to replicate all study findings reported in the article are included as supplementary file”

b. We also note that additional data will be available from the corresponding author. PLOS only allows data to be available upon request if there are ethical, legal, or third-party restrictions on sharing a de-identified data set. Please also note that in the interest of long-term data availability, PLOS data policy states that it is not acceptable for an author to be the sole named individual responsible for ensuring data access. (https://journals.plos.org/plosone/s/data-availability#loc-acceptable-data-access-restrictions)

If there are restrictions, please explain them in detail (e.g., data contain potentially sensitive information, data are owned by a third-party organization, etc.) and who has imposed them (e.g., an ethics committee). Please also provide contact information for a data access committee, ethics committee, or other institutional body to which data requests may be sent. If data are owned by a third party, please indicate how others may request data access.

This information will be helpful in updating your Data Availability Statement. We look forward to hearing from you.

Reply: The statement has been revised and raw data that is required to replicate all results presented have been uploaded as supplementary file. I have also included it in the cover letter.

Kind regards,

Osuagwu Uchechukwu Levi

Corresponding Author

Submitted filename: PONE review response.docx

Click here for additional data file.

26 Oct 2021

PONE-D-21-21579R1Prevalence and clinical profile of glaucoma patients in rural Nigeria -  A hospital based studyPLOS ONE

Dear Dr. Osuagwu,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

==============================

ACADEMIC EDITOR:I cannot find a point-to-point response to reviewers' comments, nor changes in the manuscript in response to these comments. The authors only addressed the changes needed by the journal, but not the reviewers.

==============================

Please submit your revised manuscript by Dec 10 2021 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Ahmed Awadein, MD, Ph.D, FRCS

Academic Editor

PLOS ONE

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

28 Oct 2021

Rebuttal letter: Response to reviewers’ comments

Dear Editor, thanks for the comments. We had earlier addressed all the reviewers’ comments and those of the editor and we were surprised that you didn’t receive that even though it was in our attached submission. I have again attached the response file for your perusal and highlighted the sections that addressed the reviewers concerns. In addition, we have worked on the recent comment as shown below

New file

PONE-D-21-21579R1

Prevalence and clinical profile of glaucoma patients in rural Nigeria - A hospital based study

PLOS ONE

Dear Dr. Osuagwu,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

==============================

ACADEMIC EDITOR:

I cannot find a point-to-point response to reviewers' comments, nor changes in the manuscript in response to these comments. The authors only addressed the changes needed by the journal, but not the reviewers.

==============================

Response: Thanks for the comment. We have addressed all comments in the manuscript and provided a point by point response to all comments in the attached rebuttal letter. It came as a surprise that the reviewer could not find that in the merged document. Below are the responses and all changes in the manuscript have been highlighted in different fonts

Please submit your revised manuscript by Dec 10 2021 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

• A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

Done

• A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

Done

• An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

Done

Reviewers' comments:

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

Response: Done

Old file

Response to Reviewer #1 comments:

This manuscript requires revision in order to make it useful to the reader.

Introduction.

Lines 81-4: An explanation is required as to how this study will shed light on inter-ethnic and regional variations in glaucoma prevalence in Nigeria, as the study was based in a particular hospital (single centre).

Response

Various studies [12-14] in different parts of Nigeria have shown that glaucoma is one of the leading causes of blindness in the country and the prevalence is slightly higher in the Southeastern part of the country compared with other regions. In a 1995 population based cross sectional survey conducted in Dambatta local government area (LGA), Kano state, Northwestern Nigeria, the authors reported that 15% of the blindness and 7% of the visual impairment they found, were attributable to glaucoma [15]. Murdoch et al [6] reviewed population based studies published between 1966 to September 2012 on posterior segment eye diseases (PSEDs) in sub-Saharan Africa. They found that in Nigeria, the prevalence of glaucoma was 1.02% in those aged >45 years and noted that African-based studies are needed to help estimate present and future needs and plan services to prevent avoidable blindness.

Nigeria is divided along three main ethnic groups with the Igbos in the Eastern region, Yorubas in the Western region and Hausas in the Northern region. Each ethnic group has its unique culture and the lack of ethnic specific data on sight-threatening diseases such as glaucoma makes it difficult to extrapolate the one group’s findings due to differences in cultural and socio-economic activities. There is a need to understand the demographic and clinical presentation of glaucoma in different regions in Nigeria for effective management. Evaluating the epidemiological and clinical profile of glaucoma patients seen at the Federal Medical Centre Eye clinic Gusau, Zamfara State will shed light on inter-ethnic and regional variations of glaucoma prevalence in Nigeria. It will also provide a useful background information for planning epidemiological surveys on glaucoma in this region as well as other parts of Nigeria with similar socio-demographic and ecological characteristics. Therefore, this study was aimed to assess the epidemiological characteristics and clinical presentations of glaucoma patients’ ≥50 years seen at a referral center in Nigeria. (Line 73-94).

Reviewer’s comment

Was the population multi-ethnic?

Response

No, the population was mostly Hausa because the study was done in the north where majority of the population are Hausas. However, there was still a good proportion of people from other ethnic groups. The relevant information from the study was mainly to highlight the prevalence of glaucoma among Hausa ethnic groups in this region so as to compare with the findings from other regions including studies done in the South East and South West where majority of the population are of Igbo and Yoruba ethnic groups respectively.

This was also highlighted in the result. The relevant section reads: Table 1 presents the characteristics of this study population indicating that nearly all were Muslims, females (56.7%) and of Hausa origin.

Reviewer’s comment

Methods. The authors need to state how cases of glaucoma were identified: was there a database, registry, or coding system that allowed such identification, other system employed?

Response

Done. This has been added to the manuscript for clarification (Line 123-129).

The hospital does not have electronic records, coding, and database registry. The hospital still operates in hard copy system for storing patients’ records’ therefore all case files of adult patients diagnosed with glaucoma from 2011 to 2016 were first requested from the hospital administrator and retrieved from the archives with the assistance of the eye clinic department secretary. Data collection involved the use of a data extraction sheet to extract information on demographics, and clinical profile directly from the patients’ files.

Reviewer’s comment

Was VA measured in logMAR directly or in Snellen and subsequently converted? See later as well (lines 76=9).

Response

All VAs were measured in Snellen and subsequently converted to logMAR. It was previously explained in the old version as stated below:

for purposes of analysis, participants with counting finger at 2 feet were considered to have a visual acuity of 2/200 or 20/2000. Those with hand movement at a distance of 2 feet were considered to have an equivalent Snellen acuity of 20/20,000. Also, these were converted to logMAR. Light perception (LP) with or without projection and no light perception (NLP) are not VA measurements but merely the ability to detect a stimulus (Line 187-192).

Reviewers comment

What type of prevalence was this, and how was it determined (lines 221-4)? As the authors are aware, hospital prevalence is totally different from population prevalence, and have different implications.

Response

The prevalence of glaucoma reported in this study was a hospital prevalence as only those who attended the hospital and were diagnosed with glaucoma participated in the study. We also made this clear in the previous version of the manuscript (line 113-115) as stated below:

Data for all participants aged 50 years and over who presented for the first time to this referral center and were diagnosed with glaucoma at the eye clinic during the study period were included.

We have also made it clearer in the subtitle: Hospital Prevalence of Glaucoma

Reviewer’s comment

How was the changing frequency of different subtypes of glaucoma determined?

Response

The changing in frequency of different subtypes of glaucoma was gotten by calculating the total number of people with a particular glaucoma type divided by the total number with glaucoma in that year multiplied by 100. It has also been added to the manuscript (184-186).

Reviewer’s comment

How do the authors explain the falling frequency of glaucoma over time?

Response

The study found a marked reduction in the prevalence of all other glaucoma types including POAG, which might not necessarily reflect reduction in glaucoma prevalence but rather a decrease in the utilization of eye care services triggered by insurgency and civil unrest predominant in this region [18]. In addition to these factors, poor awareness of glaucoma and low life expectancy in Nigeria could play a role in the decline in glaucoma prevalence [18, 43]. This was previously explained in the old version of the manuscript (line 316-321).

Reviewer’s comment

The Discussion could be slightly focused.

Response

The discussion has been revised to be more focused.

Reviewer’s comment

Other comments

Line 44, 123.202 and elsewhere: 'hemi-field'

Response

All hemi-field have been corrected to hemifield

Reviewer’s comment

Line 45 and elsewhere: p value with lower case 'p'

Response

All p value have been changed to P

Reviewer’s comment

Line 576: insert 'and/or' preceding 'irreversible'

Response

The revision has been added in the manuscript (Line 57).

Reviewer’s comment

Line 111: replace ';' with stop, and commence a new sentence to read 'Further, those with a history....'

Response

The semicolon has been replaced with a full stop (Line 117).

Reviewer’s comment

Line 120: define 'IOP' at first use in the manuscript (I cant find it)

Response

IOP has been defined appropriately at first use as intraocular pressure (IOP) in the manuscript (Line 131).

Reviewer’s comments

Line 136: 'VCDR previously defined in line 120; adopt abbreviation subsequently throughout.

Response

VCDR abbreviation has been modified throughout.

Reviewer’s comment

Line 174: 'logMAR'

Response

LogMar has been changed to logMAR in the manuscript.

Reviewer’s comment

Lines 76-9: define these levels of VA in logMAR. Similarly HM, CF and PL have logMAR notations?

Response

The section has been revised and the levels of VA has been explained.

Similar to previous paper [25] and for purposes of analysis, participants with counting finger at 2 feet were considered to have a visual acuity of 2/200 or 20/2000. Those with hand movement at a distance of 2 feet were considered to have an equivalent Snellen acuity of 20/20,000. Also, these were converted to logMAR. Light perception (LP) with or without projection and no light perception (NLP) are not VA measurements but merely the ability to detect a stimulus. Therefore, these factors were excluded from the analysis [26].

Reviewer’s comment

Response to Reviewer #2 comments

Reviewer’s comment

The authors are not clear with their unit of analysis. they reported that 995 patients with glaucoma were diagnosed over the 5 years of their study and they proceeded to present field defects of 995 patients however they didn't mention which one of the patient was selected for analysis and what criteria was used in the selection of the eye.

Response

All the 995 participants with glaucoma were included in the analysis and no participant was excluded.

Reviewer’s comments

Furthermore, they stated in line 209 to 211 that 15 patients had visual acuity of light perception in both eyes and that these patients were excluded from analysis (line 177 to 179) then how did they arrive at 995 visual defect results when 15 of the 995 had only light perception bilaterally.

Response

No participant was excluded in the analysis as that was written in error.

Reviewer’s comment

Additionally, it is impossible for HVF machine to report GHT results without reporting the global indices.

Response

It is true that Humphrey visual field test report GHT and global indices. However, in this hospital it is not common practice for ophthalmologists to record global indices in patients’ files. So we recorded only data found in patients’ files. This limitation has also been included in the manuscript (Line 386-387).

Reviewer’s comment

As a glaucoma specialist who has been treating glaucoma patients in Nigeria, I know it is almost impossible to see only 995 glaucoma patients in 5 years.

Response

We have now indicated that this was a hospital prevalence and we agree with the reviewer that it might not be the true reflection of prevalence of glaucoma in Nigeria. However, the prevalence of glaucoma recorded was based on the record given to us by the hospital.

Reviewer’s comment

The glaucoma definition the author's quoted in the study is applicable only in prevalent survey not for hospital based study.

Response

The glaucoma definition used was based on the information obtained from the hospital which was confirmed in other studies (line 144-145).

Submitted filename: Responses to the reviewers for PLOS ONE journal.docx

Click here for additional data file.

22 Nov 2021

Prevalence and clinical profile of glaucoma patients in rural Nigeria -  A hospital based study

PONE-D-21-21579R2

Dear Dr. Osuagwu,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at http://www.editorialmanager.com/pone/, click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Ahmed Awadein, MD, Ph.D, FRCS

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

24 Nov 2021

PONE-D-21-21579R2

Prevalence and clinical profile of glaucoma patients in rural Nigeria – A hospital based study

Dear Dr. Osuagwu:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

If we can help with anything else, please email us at plosone@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Ahmed Awadein

Academic Editor

PLOS ONE