Purpose: To evaluate clinical aspects of patients with the diagnosis of plateau iris (PI) or pseudoplateau iris (PPI) made by ultrasound biomicroscopy (UBM) in order to determine if there are any clinical factors that can help differentiate between these two entities.
Method: A retrospective cohort of consecutive UBM patients with the diagnosis of PI or PPI. The diagnosis of PI was based on an anteriorly positioned ciliary body that abutted the peripheral iris, a narrow (<10°) or closed angle for at least 180°, and the anterior portion of the iris positioned anterior to scleral spur. The diagnosis of PPI was similar to plateau except that large or a cluster of small cysts had to be present in the iridociliary sulcus.
Results: There were a total of 76 patients (29% male), 21 with PPI and 55 with PI. Patients with PPI were more likely to be male (p = 0.005), slightly younger (51.5 (SD 10.7) vs 57.9 (10.2) p = 0.0190), have a “bumpy” peripheral iris appearance (p = 0.003), have greater trabecular meshwork pigmentation (2.0 (0.7) vs 1.3 (0.6) p = 0.004) and have fewer clock hours of gonioscopic angle closure versus plateau iris patients (5.1 (4.3) vs 9.2 (4.2) p = 0.0009). Spherical equivalent was not significantly different between groups (0.50D (1.69) PPI vs 1.33D (2.42) PI; p = 0.187).
Conclusions: In patients being referred to a UBM clinic for evaluation of angle-closure mechanism, younger males with a bumpy peripheral iris have a higher likelihood of having a diagnosis of pseudoplateau iris. However, clinical factors do not appear to discriminate well between PPI and PI. UBM is extremely helpful in confirming underlying mechanism and guiding therapy.
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Glaucoma is the second leading cause of blindness worldwide.1 Angle-closure glaucoma constitutes approximately one-quarter of this glaucoma burden.1 The diagnosis of ACG requires an assessment of the anterior chamber angle through gonioscopy to determine if the trabecular meshwork is blocked by the peripheral iris. Various mechanisms can lead to appositional and/or synechial closure of the angle, and of these, plateau iris (PI) syndrome is well recognised and considered a rare entity.2 The mechanism of angle closure in PI is thought to be due to a ciliary body that is anteriorly positioned, thus bolstering the peripheral iris and leading to angle closure. Pseudoplateau iris (PPI) syndrome, an even rarer cause of angle-closure glaucoma, is often difficult to distinguish from plateau iris syndrome, even though the underlying mechanism is different, as both may have an s-shaped configuration of the peripheral iris upon indentation gonioscopy. In PPI, iridociliary sulcus cysts can cause secondary angle closure.3 As these cysts enlarge, they displace the iris forward, resulting in a narrowing of the anterior chamber and angle closure.4 In the past, the diagnosis of plateau iris and PPI syndrome has been based on clinical examination with gonioscopy. Patients with PPI appear to have a bumpy peripheral iris on slit lamp and/or gonioscopic examination; however, this is not always the case, and so confirmation by ultrasound biomicroscopy (UBM) is required to make a definitive diagnosis.
It is important to distinguish between PI and PPI as causes of angle closure as the treatment approach may differ. In particular, PPI may be treated with rupture of large iridociliary cysts,5 although these may recur. The purpose of this study was to evaluate the demographics and clinical information of patients with the diagnosis of PPI or PI encountered in a tertiary UBM clinic setting in order to determine if there are any criteria that help clinically differentiate between these two causes of angle-closure glaucoma. If distinctive features could be highlighted, this would be helpful to assist in an earlier and more definitive diagnosis as well as permit a rationale treatment approach based on underlying mechanism.
A retrospective cohort of consecutive UBM patients with the diagnosis of PI or PPI was undertaken. All UBM diagnoses were made at either the University of Ottawa Eye Institute or at Maisonneuve-Rosemont Hospital, University of Montreal. The UBM used at the University of Ottawa was the Ultrasound Biomicroscope System Model 840 by Humphrey Zeiss Instruments. Patients referred to these UBM clinics were done so for analysis of angle-closure mechanism. The diagnosis of plateau iris was based on an anteriorly positioned ciliary body that abutted the peripheral iris, a narrow (<10°) or closed angle for at least 180°, and the anterior portion of the iris positioned anterior to scleral spur. The diagnosis of PPI was similar to plateau except that large or a cluster of small cysts had to be present in the iridociliary sulcus.
Clinical information that was collected included epidemiological factors such as age, gender, and ethnicity. As well, pertinent medical and ocular history was reviewed, including any history of hypertension, diabetes, thyroid problems and a list of medications as well as any history of ocular trauma, eye surgery and family history of glaucoma. Features on examinations that were documented included best corrected visual acuity, refractive error, highest intraocular pressure, and most recent recording of intraocular pressure. Various other parameters were also measured, including peripheral anterior chamber depth (Van Herick technique), gonioscopy (angle status, degree of angle pigment, the number of clock hours of angle closed, the number of hours of PAS) and degree of nuclear sclerosis in the lens. Other features noted were the degree of cataract, and the vertical cup-to-disc ratio.
Ultrasound biomicroscopy (UBM; Paradigm, Salt Lake City, UT) was performed with the 50 MHz ultrasound probe. Patients were examined in a supine position, and topical anaesthesia was used before placing a cup designed for UBM on the eye. Fluid is required to produce a coupling medium, and 2.5% methyl cellulose was used to fill the cup. The images were obtained with the beam perpendicular to the structures being examined. The mark on the probe indicates the plane of the scanning motion and corresponds to the left side of the screen. The superior aspect of the image correlates to the face of the transducer. Radial sections were obtained with the marker toward the sclera. Thus, the left side of the screen corresponds to the scleral side and the right side to the corneal side. A full 360° examination was performed; however, four images were stored as a record of the exam (superior, nasal, inferior and temporal).
The data were tabulated in an Excel spreadsheet. Care was taken to ensure dim room light illumination during ultrasonography.
The objective of analysis was to compare the characteristics of PPI and PI patients. Variables were classified as dichotomous, categorical or interval. A chi-square test was used to compare the dichotomous variables and a Kruskal–Wallis test was used for categorical variables with more than two categories. The normality assumption was checked for each continuous variable before an unpaired two-sample Student t test was carried out. Continuous variables found not to have a Gaussian distribution were subjected to a Wilcoxon rank-sum (Mann–Whitney) test, the non-parametric equivalent of a Student t test, for comparison of the plateau and pseudo-plateau iris groups. The level of significance was 0.05.
The sample population consisted of 76 patients (21 PPI and 55 PI) aged 26–88 years; 93.4% were Caucasian and 29% male (22/76). Of the 21 patients with a diagnosis of PPI syndrome, 10 were female, and 11 were male (see fig 1 for a representative UBM scan of pseudoplateau iris). Of the 55 diagnosed as having plateau iris syndrome, 44 were female 11 were male (see fig 2 for representative UBM scan of plateau iris). The age range for PPI was 26–69 with a mean of 51.5, and for PI 39–88 with a mean of 57.9. The spherical equivalent was not significantly different between groups (0.50D (SD 1.69) PPI vs 1.33D (2.42) PI; p = 0.187).
Table 1 summarises the comparisons of the PPI and PI groups. Variables that were statistically significant were that patients with PPI were more likely to be younger, to be male, to have a bumpier peripheral iris appearance, to have a greater degree of trabecular meshwork pigmentation, and to have fewer clock hours of chronic angle closure.
Our study examined a series of patients with pseudoplateau iris as well as plateau iris configuration referred to a UBM clinic for evaluation of angle-closure mechanism, and found that it is difficult to distinguish between the two based on clinical grounds. We found that younger males with a bumpy peripheral iris have a higher likelihood of having a diagnosis of pseudoplateau iris. This is consistent with the literature that suggests patients with true plateau iris tend to be female, are less often hyperopic and often have a family history of angle-closure glaucoma.6 As well, patients with PI had a mean age that was notably older than for PPI, and they were all more likely to present with a chronic course or be asymptomatic. In our study, the spherical equivalent was not statistically significant; however, the variance was high, and so if there were more patients in this study, the number may be statistically significant.
It was also interesting to observe that patients with PPI had a heavier degree of trabecular meshwork pigmentation on average than patients with PI. This raises the possibility that the iridociliary sulcus cysts (which are lined with pigment epithelium) may disperse pigment as part of their pathophysiology.
It is important to distinguish between PI and PPI, as the approach to treatment can vary depending on the underlying mechanism. The first published description of plateau iris appears to be by Shaffer in 19607 8 as a configuration capable of angle closure despite a patent iridotomy either spontaneously or after dilation.9 Historically, it was identified as a postoperative condition in which iridectomy has removed the relative pupillary block, but gonioscopically confirmed angle closure occurs with a flat iris plane such that the iris remains in a position that allows it to occlude the angle.8 10 In this situation, the dilated pupil is still capable of closing off the trabecular meshwork;5 the mechanism is thought to be related to an anteriorly located ciliary body which bolsters the peripheral iris and thus leads to acute and/or chronic angle closure. A presumptive diagnosis can be made prior to iridotomy on gonioscopy in which a normal central anterior chamber depth, flat iris configuration and steep iris insertion are noted.11 With indentation gonioscopy, the central iris typically moves posteriorly, while the peripheral and mid-iris remain positioned anteriorly, that is, there is a positive sigma or sine wave sign. Provocative testing with phenylephrine (ie, a pure mydriatic)12 and prone dark room testing have also been described.13
In contrast to PI, the mechanism of angle closure with pseudoplateau iris is related to multiple cysts located in the iridociliary sulcus. An early description was published by Chandler and Braconier in 1958, and since then others have published on this subject.4 Much like the anteriorly located ciliary body in PI, the cysts, if large enough, support the peripheral iris and lead to angle closure. An autosomal dominant familial pattern of PPI has also been described.19
The advent of UBM has enabled high-resolution images of the angle region and anterior chamber, and thus has been instrumental in differentiating the cause of angle-closure.11 14–17 UBM uses high-frequency ultrasound (50–100 MHz) to produce images of the anterior segment at a high resolution (20–50 um)10 14 that allows structural details of the angle and the ciliary body to be microscopically visualized.10 15 18 In addition to confirming the diagnosis of PPI and PI, UBM may be very helpful in ruling out other posterior peripheral iris push mechanisms such as an anterior uveal effusion and a ciliary body tumour—for example, diffuse ciliary body melanoma. Therefore, it is especially suitable for diagnosis and research on the various mechanisms of angle-closure glaucoma.14 18
Recognition and management of cases of plateau versus pseudoplateau iris are outlined in fig 3. Treatment of plateau iris is generally reserved for cases deemed to be at high risk for acute and/or chronic angle closure. This can involve dilute (eg, 1%) Pilocarpine at bedtime and/or laser gonioplasty.21 The latter is quite effective at flattening out the peripheral iris and thus preventing iridocorneal apposition and angle closure. Although medical and laser gonioplasty methods can also be applied to PPI, direct treatment of iridociliary cysts including surgical intervention can also be effective in opening portions of the angle.6 22 Puncturing of the cysts can be done with an Nd: YAG laser (iridocystotomy) or a needle.6 23 This treatment, however, requires accurate localisation of the cyst, results in pigment dispersion and carries the potential risk of cyst recurrence and inflammation.20 Further medical management may also be required.
Some of the limitations of this study include the fact that it is a retrospective cohort study, and so data were not collected systematically. As well, there is likely an ascertainment bias, as patients were obtained from UBM referral clinics rather than from a population-based study.
In patients being referred to a UBM clinic for evaluation of angle-closure mechanism, younger males with a bumpy peripheral iris have a higher likelihood of having a diagnosis of pseudoplateau iris rather than plateau iris. However, clinical factors do not appear to discriminate well between PPI and PI. UBM is extremely helpful in confirming underlying mechanism and guiding therapy.
We thank Dr S El-Defrawy for referring patients with PI and PPI to the UBM clinic.
Competing interests: None declared.
Ethics approval: Ethics approval not required.