Prevalence of Plateau Iris Syndrome among Patients Presenting with Primary Angle Closure and Primary Angle-Closure Glaucoma in a Tertiary Eye Care Hospital.

PURPOSE: Glaucoma is a leading cause of visual impairment worldwide, and plateau iris syndrome (PIS) is the most common nonpupillary block mechanism of angle closure. This study aims to assess the prevalence of PIS among Saudi population.
METHODS: It is a prospective observational study that examined patients previously diagnosed with chronic angle closure. Those patients already underwent peripheral laser iridotomy (PLI) and were assessed clinically and by ultrasound biomicroscopy (UBM).
RESULTS: A total of 147 eyes in 77 patients were included in this study. The mean age among subjects was 61.2 years, and almost 69% were females. Chronic angle closure was noted to be bilateral in 91% of patients, whereas 5% had their left eye involved and 4% had right eye involved. The mean intraocular pressure (IOP) before PLI and after laser treatment was 19.3 and 16.2, respectively. The mean visual acuity before and after PLI was 0.3 logMAR. After UBM examination, plateau iris was found in 41.5% of subjects. The anterior chamber (AC) depth was noted to be deeper in PIS patients (P = 0.046). Other risk factors were observed in our study including place of residency (P = 0.048) and preintervention IOP (P = 0.032).
CONCLUSION: PIS is the most common mechanism of nonpupillary block angle closure. In addition to clinical findings, UBM is important to reach the appropriate diagnosis. This study reviewed the prevalence of PIS with the aid of UBM; it was found consistent with previous reports. In addition, PIS risk factors included AC depth, place of residency, and preintervention IOP. Copyright:

Introduction

Glaucoma is the second leading cause of blindness worldwide accounting for 12.3% of total blinding causes. The prevalence of visual impairment in Saudi Arabia was noted to reach up to 15%, where glaucoma was a leading cause of visual impairment.[12345] Primary angle-closure glaucoma (PACG) is the most common form of glaucoma in Saudi Arabia, followed by primary angle closure (PAC).[6] Peripheral laser iridotomy (PLI) is a major procedure in the management and treatment of PACG and PAC. However, nonpupillary block mechanisms of angle closure play a role when LPI is not sufficient to alleviate the condition.[789]

Plateau iris is a nonpupillary block mechanism that causes angle closure. It leads the iris plane to be flat, and the anterior chamber (AC) not to be shallow axially. Plateau iris syndrome (PIS) is a postoperative state in which peripheral iridotomy is patent releasing the relative pupillary block. However, angle closure is noted on gonioscopy without AC shallowing.[1011] The prevalence of PIS in angle closure varies among populations and it ranges from 22% to 56%.[1112131415161718] These numbers raise a concern and motivate researchers to conduct further investigations. Unfortunately, there is neither enough documentation nor research in Saudi Arabia regarding the prevalence of PIS.

This research aims to assess the frequency of PIS in Saudi population presented with PAC or PACG, describing the pattern of PIS in Saudis and situating it among global patterns. This will increase awareness among physicians, help to prevent further damage to one's eyes and reduce the cost of applying unnecessary medical and/or surgical interventions.

Methods

This observational study was conducted in accordance with the Declaration of Helsinki with the approval of the Institutional Review Board at King Saud University. Eligible patients with previously diagnosed primary angle closure (PAC) and PACG were consented and recruited. All the participants went through PLI at least 4 weeks before recruitment, and a full ophthalmic evaluation was conducted to determine their eligibility. Patients were 35 years old or above. The clinical indices investigated include intraocular pressure (IOP) by Goldmann tonometry, visual acuity test, AC depth, indentation gonioscopy by Zeiss four-mirror gonioscope, and optic-to-disc ratio. As the presence of PAC and PACG is the determinant of eligibility, clear and specific characteristics were used to confirm the diagnosis and declare eligibility. PAC is identified based on the following characteristics: Iris whorling, excessive pigment deposition on the trabecular surface, high IOP, and the presence of peripheral anterior synechiae; it occurs without glaucoma signs. On the other hand, PACG is identified as PAC in addition to the evidence of glaucoma occurrence such as optic nerve neuropathy (vertical cup-to-disc ratio >0.7).

Subjects were examined by ultrasound biomicroscopy (UBM) under topical anesthesia in a supine position and a dark room, using 50-MHz transducer. The probe was vertical in position to prevent the compression of the globe by the eyecup. Four quadrants had been scanned in each examined eye, and one clear image in each quadrant was analyzed. The presence of ciliary sulcus had been evaluated as it was defined as a clear space between the iris and the ciliary body anteriorly. A subject was diagnosed with plateau iris when the following characteristics had presented in at least two quadrants: An anteriorly pointed ciliary body where the ciliary proses is parallel to the trabecular meshwork, irdioangle contact, steep iris root from its point of insertion, followed by a downward angulation from the corneoscleral wall (plateau of the iris) and the absence of ciliary sulcus [Figure 1].

Figure 1

Ultrasound biomicroscopy of one of the patients with plateau iris syndrome

Any subject with secondary angle closure, previous intraocular surgeries, and/or any previous penetrating eye injury were excluded from the study.

One hundred and forty-seven eyes out of 77 patients having PAC with or without glaucoma were included in the study. All subjects had been clinically examined, and each UBM image had been analyzed separately at different times by an experienced glaucoma consultant. Furthermore, the UBM study was performed on subjects by an expert ophthalmic technician. The glaucoma consultant and the UBM technician were blinded to the patients. All candidates have signed an informed consent before being involved in the study.

Results

A total of 147 eyes out of 77 patients were included in this study. The gender distribution was 24 males (31.1%) and 53 females (68.9%). The mean age in years was 61.2 (ranging 36–82). PAC and PACG were noted to be bilateral in seventy patients (90.9%), whereas seven patients (9.1%) had unilateral disease. Of these seven patients, four had their left eye involved and three patients had right eye involved [Table 1].

Table 1

Patients demographics (n=65 persons)

Characteristic	n (%)
Gender
Male	20 (30.8)
Female	45 (69.2)
Laterality
Bilateral	62 (95.4)
Unilateral	3 (4.6)
Family history	5 (7.7)
Chronic diseases
HTN	35 (53.8)
DM	38 (58.5)
Hyperlipid	1 (1.5)
Hypothyroidism	2 (3.1)
Asthma	4 (6.2)
Smoking	1 (1.5)
Age (years), mean (SD) (range)	61.2 (9.1) (43-82)

DM: Diabetes mellitus, SD: Standard deviation, HTN: Hypertension

In the studied eyes, the mean IOP before PLI was 19.3 (range 10–40), whereas after PLI the mean IOP went down to 16.2 (range 7–25) (P ≤ 0.001). The mean visual acuity logMAR before PLI was 0.3 (range 0–2) and it was similar even after PLI.

After examination with UBM, plateau iris was found in 32 (41.5%) subjects. Of these, 23 (71.8%) candidates had bilateral disease, 5 (15.6%) had left eye involvement, and 4 (12.6%) had right eye disease. All patients with PIS had closed angles on gonioscopy and they fulfilled the inclusion criteria of diagnosis with UBM. However, AC was found deep in 83.9% of PIS patients (P = 0.046). Furthermore, with multivariate analysis, a conduct of binary logistic regression revealed that both residency (P = 0.048 (95% confidence interval [CI]: 0.060–0.965]) and preintervention IOP (P = 0.032, (95% CI: 1.049–4.848]) were statistically significant. The further characteristics of candidates and their association with PIS are presented in Table 2.

Table 2

Patients characteristics and risk factors

Variable	Category	PIS		P
		Yes, n (%)	No, n (%)
Age	≤60	13 (41.9)	22 (48.9)	0.550
	>60	18 (58.1)	23 (51.10)
Gender	Male	8 (25)	16 (35.6)	0.324
	Female	24 (75)	29 (64.4)
Residency	Urban	27 (84.4)	31 (68.9)	0.120
	Rural	5 (15.6)	14 (31.1)
Glaucoma	PACG	26 (81.3)	31 (68.9)	0.223
	PAC	6 (18.8)	14 (31.1)
Laterality	Unilateral	2 (6.3)	7 (15.6)	0.210
	Bilateral	30 (93.8)	38 (84.4)
Family history	Yes	1 (3.1)	5 (11.1)	0.198
	No	31 (96.9)	40 (88.9)
AF	Yes	1 (3.1)	0	0.233
	No	31 (96.9)	45 (100)
Asthma	Yes	1 (3.1)	3 (6.7)	0.490
	No	31 (96.9)	42 (93.3)
DM	Yes	20 (62.5)	23 (51.1)	0.321
	No	12 (37.5)	22 (48.9)
HTN	Yes	20 (62.5)	21 (46.7)	0.170
	No	12 (37.5)	24 (53.3)
Hypothyroidism	Yes	0	2 (4.4)	0.227
	No	32 (100)	43 (95.6)
Smoking	Yes	1 (3.1)	0	0.233
	No	31 (96.9)	45 (100)
Preintervention IOP (mmHg)	≤20	26 (83.9)	27 (90)	0.478
	>20	5 (16.1)	3 (10)
Preintervention VA	≤20/40	15 (88.2)	17 (85)	0.774
	>20/40	2 (11.8)	3 (15)
Visual field	Normal	8 (34.8)	12 (41.4)	0.627
	Abnormal	15 (65.2)	17 (58.6)
CDR	<0.5	22 (71)	22 (73.3)	0.837
	≥0.5	9 (29)	8 (26.7)
Gonioscopy (angle)	Open	6 (20.7)	9 (36)	0.210
	Closed	23 (79.3)	16 (64)
AC depth	Shallow	5 (16.1)	11 (39.3)	0.046*
	Deep	26 (83.9)	17 (60.7)

* Significant P value ≤ 0.05, AF: Atrial fibrillation, DM: Diabetes mellitus, IOP: Intraocular pressure, VA: Visual acuity, CDR: Cup-to-disc ratio, AC: Anterior chamber, PIS: Plateau iris syndrome, HTN: Hypertension, PAC: Primary angle closure, PACG: PAC glaucoma

Discussion

PACG and PAC are the most common forms of glaucoma in Saudi Arabia, and they are managed by PLI. Nevertheless, LPI could not be sufficient as solely procedure to treat PACG and PAC when the condition is caused by nonpupillary block mechanism.[6789]

PIS is one of the causes of nonpupillary block angle closure where peripheral iridotomy is patent, but the angle is noted closed without AC shallowing.[101119] Clinically, under darkroom setting, the AC depth is centrally normal and the iris surface is flat with a patent peripheral iridotomy. On gonioscopy, the angle is noted narrow or closed, and a double hump sign is seen.[111920] UBM is an important tool to aid in diagnosing PIS. Eyes with PIS show normal AC depth with flat iris interface and narrow angles in the absence of anterior bowing of the iris. The ciliary processes are situated anteriorly in comparison to normal subjects and to patients with angle closure caused by pupillary block. Furthermore, iridotrabecular contact is noted, and the processes are positioned closely adjacent to posterior peripheral iris closing the ciliary sulcus.[11121921]

PIS is the most common nonpupillary block mechanism found in 56% of patients in a comprehensive analysis.[18] In our review, we studied the prevalence of PIS among PAC and PACG patients who underwent PLI by UBM analysis, and we found PIS represented 41.5% of our patients. This falls within the range and matches with the previous studies which reported the prevalence of PIS in eyes with angle closure. In a study by Kumar et al.[12] to determine the prevalence of plateau iris in PAC suspects by UBM in subjects over 50 years of age, plateau iris was found in 32.3% of PAC suspects after LPI. This study demonstrated female predominance and the mean age was 63.2; it is consistent to our report where 68.9% of our patients are females and the mean age was 61.2 years. Another study investigated the prevalence of plateau iris in Asian population by UBM in subjects with PACG, where plateau iris was diagnosed in 36 (32.4%) out of 111 PACG eyes with female predominance as well.[13] Moreover, in Japanese patients, plateau iris was found in 17.6% based on UBM imaging.[15] In another study using UBM analysis, plateau iris was observed in 31.68% in PACG eyes.[16] In addition, in a published article investigating angle closure in young population where PIS was the main cause of angle closure in individuals younger than 40 years, 52.2% of subjects were diagnosed with PIS.[14] Furthermore, in another study, the prevalence of PIS in patients younger than 60 years with recurrent angle closure in spite of iridotomy or iridectomy was found to be 54%.[17]

Risk factors of developing PIS are not well reported in the literature. Our study investigated patients’ characteristics including demographics, family history, systemic diseases, and ocular examination. The only risk factor found in our study was the AC depth where it was deeper in patients with PIS compared to nonPIS patients. In addition, multivariate logistic regression found place residency and preinterventional IOP was significant. However, further studies are warranted in regard of PIS risk factors.

The ideal treatment of PIS is not established because of the lack of randomized controlled trials. The use of pilocarpine has been suggested, but the proposed definitive treatment is argon laser peripheral iridoplasty. However, further interventions are required including lens extraction and filtration surgery.[11222324] Furthermore, no clear criteria have been established to diagnose PIS. The diagnosis of plateau iris with gonioscopy is subjective and possibly underestimates the condition. The use of UBM is more objective, but there is no consensus on UBM diagnostic criteria.[121325] We used our diagnostic criteria based on the reported findings in UBM in at least two quadrants, and we tried to standardize the imaging. Future studies to assess trabecular-ciliary process distance and iris thickness before and after LPI is advised to review its significance in the assessment which may help objectifying and standardizing the diagnostic criteria further.

Conclusion

In brief, glaucoma is a leading cause of vision loss worldwide, and angle closure is the dominant form in our area. PIS is the most common mechanism of nonpupillary block in angle closure. In addition to clinical findings, UBM is important in nonpupillary block angle closure to guide to an appropriate diagnosis and an appropriate treatment plan. We reviewed the prevalence of PIS and found it was within the range of what is previously reported.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.