The prevalence of visual disorders in Iranian students: A meta-analysis study and systematic review.

BACKGROUND: Visual defects have dramatic effects on health, self-esteem, and educational function of students, and delayed diagnosis will cause complications, like academic failure and psychologic disorders.
OBJECTIVE: The present study aimed to investigate the prevalence of ocular disorders in Iranian students in a systematic review.
METHODS: We searched databases, including PubMed, SID, Magiran, Google Scholar, and Iranmedex using the following keywords in Persian and English: disorders, vision, amblyopia, refractive errors, astigmatism, student, and Iran with all the possible combinations, important, chief, and sensitive words. Search resulted in 28 articles, conducted during a period from 1996 to 2014 in Iran and their data was analyzed using meta-analysis and random effects model. Heterogeneity of studies was assessed using I2 index, and data was finally analyzed with R Software and STATA (Version 11.2).
RESULTS: Total number of subjects in the study was 1,117,274, aged 2 to 18 years. The prevalence of disorders related to amblyopia, refractive error, and strabismus was 8%, 7% and 1%, respectively. The greatest amount of refractive error was related to astigmatism (19%) followed by myopia (17%).
CONCLUSION: According to the study results, the prevalence of visual disorders among Iranian students indicated the critical necessity of screening programs for prevention of visual disorders in this age group.

1. Introduction

About 75% of an individual’s general information is obtained through the visual system (1). The visual system of children does not take its final evolution up to the age of 10 years and the most important factor for growth and development of this system is clear stimuli (2). If the child’s eye is deprived of receiving these stimuli, for any reason, the development of the visual system will be impaired (3). Visual acuity is of great importance in children for clear vision in writing and education, especially in school training ages (1). Visual disorders have dramatic effects on health, self-esteem, and educational function of students and if diagnosed with delay, it will cause complications, like academic failure and mental difficulties for the student (4). Also, delay in diagnosis of visual difficulties can decrease the treatment success (5). Most visual disorders are preventable at an early age. Therefore, a comprehensive study of visual problems in students is of great importance. According to studies, the most common cause of visual disorders in children include refractive errors (1–11%), amblyopia (1–5%) and strabismus (3.8%) (6). Unfortunately, there is no comprehensive statistical information available in Iran and only sparse data have been reported from cities in national scientific sources (7). Considering the importance of research about visual problems in children and differences in the prevalence of visual disorders in different parts of Iran, the present systematic review and meta-analysis aimed to determine the prevalence of common visual disorders in Iranian students.

2. Material and Methods

The present systematic review and meta-analysis study was carried out in 2015, and articles published since 1996 to 2014, related to the prevalence of visual disorders in Iranian children, in Farsi and English were searched in national and foreign databases, including SID, Magiran, IranDoc, IranMedex, MedLib, PubMed, ISI, and Google Scholar. Mentioned databases were searched using the following keywords in Persian and English: disorders, vision, amblyopia, refractive errors, astigmatism, student, and Iran with all the possible combinations, important, chief, and sensitive words. Also, the titles resulted through search and references of the selected articles were used as additional search tools. All descriptive cross-sectional or group studies that had investigated the prevalence of visual disorders in Iran were considered. Articles were selected based on three steps of title, abstract and full text. Studies with insufficient information or non-descriptive cross-sectional studies, congress abstracts, studies published in other languages than English and Persian, review and meta-analysis studies, and duplicates were excluded from the analysis. For all studies, the following data were extracted: the first author, publication year, study year, study location, sample size, and mean age, sex and the prevalence of each visual disorder (Table 1). The major inclusion criteria for including various articles into this study was mentioning visual disorders and exclusion criteria of the studies from the present research were: lack of reference to the prevalence of visual disorders, unrelated studies, and low quality of articles. The researcher collected all articles related to visual disorders first and prepared a list of abstracts after finishing the search. In this step, 86 articles were listed, which mentioned “The prevalence of visual disorders in Iran”. Then, each article was independently evaluated. In this step, 14 articles were eliminated because of duplication, and among a total of 72 articles, 16 articles were omitted because of low quality, and 4 because of the unavailability of the full text, and 24 articles were deleted due to differences in the types of criteria. Finally, 28 articles were appropriate to enter meta-analysis (Figure 1). A checklist of necessary information was prepared for all studies primarily evaluated. Then, a checklist containing several parts was designed, including researcher’s name, publication year and place, sample size, age, visual disorders, prevalence of visual disorders, etc. Then, fundamental data needed for research entered the chart for analysis. For calculation of variance of each study, binary distribution and for combination of prevalence of visual disorders among various studies, mean weight was used. Each study was weighed proportional to the reverse of its variance. With attention to the great difference in the prevalence among different studies (heterogeneity of studies) and significance of Heterogeneity index (I2), Random Effects Model was used in the meta-analysis. And finally, the data was analyzed by R Software and STATA (Version 11.2). The level of significance (P value) was considered less than 5%.

Table 1

General information of studies included in the meta-analysis

Ref. no.	Publication year	Study year	Age of cases (year)	Male (n)	Female (n)	n (total)	City
9	2014	2013	3–6			1,126	Bojnoord
6	2006	2000	7–12	2,348	2,185	4,533	Kermanshah
11	2009	2005–2006	14–18	216		216	Tehran
12	2004	1999–2000	3–6			8,427	Ardebil
28	2008	2006		1,208	942	2,510	Mashhad
13	2010	2004	11–17	3,635	913	4,548	Ardebil
14	2007	2004	6	436	379	815	Shahrood
8	2009	2007	7–18			957,582	Iran
2	1999	1996	7			2,000	Shahrekord
3	2014	2011–2012	2–6	8,297	8,302	16,599	Bandar Abbas
15	2016	2012	2–6	1,160		75,173	Ardebil
16	2012	2011	7–15			1,551	Bojnourd
17		2010	14–18			1,133	Varamin
18	2014			5,641	6,180	11,821	Qazvin
19	2010	2008	<15	1,191	1,941	3,132	Mashhad
20	2015	2012	7–12			320	Zahedan
21	2013	2010	7–14	643	898	1,551	Bojnourd
22	2016	2013		2,127		4,106	Iran
23	1996		7–8	951	775	1,726	Kerman
24	2007		12–16			1,830	Mashhad
25	1997	1996	7–12			1,275	Zanjan
26	2007	2004–2005	7–15			3,673	Dezful
26	2007	2004–2005	14–18			1,871	Dezful
27	2014		14–21	212	222	434	Aligoudarz
28	2008	2006–2007	7–15			1,163	Mashhad
28	2008	2006–2007	14–18			947	Mashhad
29	2015	2013–2014	6–15	631	520	1,151	Dezful
30	2010	2008–2009	7–15	1,002	870	1,872	Shiraz

Figure 1

Flowchart of the stages of the systematic review and meta-analysis

3. Results

Basic information of studies that entered meta-analysis, including the author’s name, year of publication, study place, the sample size, based on gender and age range are shown in Table 1. The total number of subjects was 1,117,274, in the age range of 2 to18 years old. The raw data on prevalence of ocular disorders in different studies are demonstrated in Table 2. In Figure 2, the prevalence of strabismus in Iranian students is shown based on the random effects model. In this graph, the resultant prevalence of strabismus was 1% (CI 95%: 1–2%). In Figure 3, the total prevalence of refractive errors in Iranian students is shown based on the random effects model. It has been shown that the prevalence of refractive errors was an estimated 7% (CI 95%: 5–9%). Moreover, the prevalence of amblyopia in Iranian students was 8% based on random effects model (Figure 3) (CI 95%: 7–10%). The overall prevalence of visual disorders has been shown in Table 3. Based on the results of this study, the overall prevalence of visual disorders in Iranian students was 5% (Table 3), in which the prevalence of amblyopia was 8% [Girl 2% (CI 95%: 1–3%), boy 1% (95% confidence interval: 1–2%)], refractive error was 7% [Girl 8% (CI 95%: 6–10%), boy 6% (95% confidence interval: 4–7%)], and the prevalence of strabismus was an estimated 1% (Table 3). The prevalence of amblyopia in Iranian students, based on random-effects model was shown in the Figure 4. The greatest amount of astigmatism-related refractive error was 19% [girls 27% (CI 95%: 6–61%) and boys 28% (CI 95%: 5–51%)], followed by myopia with a prevalence of 17% (Table 3). Details of the prevalence of refractive errors are shown in Table 3.

Table 2

Prevalence of ocular disorders in studies included in the meta-analysis

Ref. no.	Astigmat. Prev.	Estrab. Prev.	Ref. Eror Prev.	Amb. prev.	Total prev.	Anisometropia	Hyperopia Prev.	Myopia Prev.	Astigmat. Prev. Boys	Astigmat. Prev. female	Refractive Eror Prev. male	Refractive Eror Prev. female	Amblyopia prev. male	Amblyopia prev. female
9		1.8	4.61	11.8							2.66	1.9	6.21	5.59
6	1.78		5	0.33	5.7		0.61	2.6	1	0.8			0.21	0.45
11	21.3	17.1
12		0.55	3.59	1.25	7.21
28	11	3.1		1.9		30.6							1.7	2.1
13	27	0.9	11.4	2.63	2.63	59	17						2.8	1.9
14					6.4
8					4.6
2		0.55		9.9	2.55	1.5							12.5	14.8
3		0.27	2.72	1.01
15		0.34	0.074	0.14									0.17	0.12
16		2		2.3									2	2.5
17	10.5	1.5		2.1		3.8	6.1	33.2
18	8.37			6.34		5.45	19.8	66.2	48.48	51.52			44.73	55.27
19	15.34					5.84
20	3.4					21.3	5.8	6.3	1.8	5	55.6	73.1
21	22		6.2				18	40			4.8	7.1
22	17.43						6.2	3.04	15.46	19.54
23			7.5	1.7							6.2	9.4	1.4	2
24	5.02		24.97				4.97	3.77
25	2.03	0.47	8.4	7.8		1.33	2.1	3.5
26	18.7						16.6	3.4	18.5	18.9
26	18						2.1	33	18.5	18.9
27	20.7					4.6	1.2	29.3	25.9	15.8
28	9.8					3	87.9	2.4
28	11.8					5.6	8.4	24.1
29	45.3						12.9	14.9	48.5	41.5

Figure 2

The prevalence of strabismus in Iranian students, based on random-effects model.

Figure 3

The prevalence of refractive errors in Iranian students, based on random-effects model.

Table 3

The prevalence of visual disorders in Iranian students; derived from meta-analysis study

Visual disorder (Prevalence %)	I2%	p-value	Prevalence (CI 95%)	Studies number
Myopia	99.9	0.000	0.17 (0.09–0.25)	16
Hyperopia	99.9	0.000	0.16 (0.10–0.22)	17
Anisometropia	99.8	0.000	0.11 (0.06–0.17)	13
Amblyopia	99.8	0.000	0.08 (0.07–0.10)	14
strabismus	97.2	0.000	0.01 (0.01–0.02)	12
Astigmatism	99.9	0.000	0.19 (0.06–0.32)	20

Figure 4

The prevalence of amblyopia in Iranian students, based on random-effects model.

4. Discussion

One of the goals of the WHO (world health organization) is to prevent visual disorders in children by the year 2020 (31). According to studies, visual disorders, especially refractive errors, strabismus and amblyopia are higher in students than in other groups (34–36). Amblyopia occurs in the first decade of life and if diagnosed at this age, it can be treated, and prevention of further development can be done by appropriate treatment measures (32, 33). In the present study, the prevalence of amblyopia among Iranian students was 8%, while based on similar studies in developed countries, the prevalence of amblyopia in preschool children has been reported as 1–5% (48–50). The overall prevalence of visual disorders, including amblyopia, strabismus, refractive errors and other ocular diseases in children, was 2.4–6.1% in various articles (51). In the present study, the prevalence of visual disorders in students was 5%, which was higher compared with many developed countries (37–41). Of course, differences in the various reports could be due to taking into account the different diagnostic criteria, different characteristics of the study population, and skills and expertise of the examiners (2, 52–60). In the present study, the prevalence of strabismus was 1%, which is consistent with the findings of previous studies, however differences in the prevalence of different types of strabismus (phoria or tropia, exo, or eso) are likely, but given that in most of the selected studies, the type of strabismus was not specified, it was not possible to compare the prevalence of different types. The overall prevalence of strabismus in studies conducted in different parts vary from 0.5 to 2% (2, 16, 17). Another common cause of visual disorders among this age group was refractive errors, which was 7% in the present study. Numerous studies are conducted worldwide in the field of refractive errors in the age groups at risk, including children and students, and prevalence of these disorders are highly variable in different regions (17–24, 26–29). According to most studies conducted in the world, myopia is introduced as the most common refractive error among students (63, 64). Also, in some comprehensive studies out of Iran, the prevalence of myopia has been reported higher than hyperopia (65). This difference in the prevalence needs to be confirmed by further studies.

5. Conclusions

Various reports have questioned screening for visual disorders in Iran, and on the basis of these studies (64, 65), these programs are not sensitive enough to detect and refer patients to seek appropriate treatment, on the other hand, given that most parents rely on the results of these examinations, and do not pay attention to the possible complaints of their children, identification of these disorders are delayed and their treatment becomes more difficult (43, 44). Therefore, it is suggested to increase the awareness of parents, use highly-experienced staff in screening programs, and increase the validity and sensitivity of the examinations by more professional methods.