From the Elite School of Optometry (SU, SBG, SS), Medical Research Foundation; and Sankara Nethralaya (MB, BS, LV), Medical and Vision Research Foundation, Chennai, India.
The authors have no financial or proprietary interest in the materials presented herein.
Address correspondence to Mani Baskaran, Medical and Vision Research Foundation, Sankara Nethralaya, 18 College Road, Nungambakkam, Chennai – 600 006, India.
Primary angle closure glaucoma (PACG) is the leading cause of bilateral blindness in Asia. Relative pupillary block is the main mechanism of angle closure, whereas the plateau iris syndrome is characterized by narrow angles, anteriorly situated ciliary processes, and narrow ciliary sulcus in ultrasound biomicroscopy (UBM), described as a post-iridotomy condition. Plateau iris configuration (PIC) is described as a preoperative condition with angle closure, flat iris plane, and a relatively deeper central anterior chamber, whereas convex iris configuration (CIC) is described as a convex iris plane with a shallower anterior chamber seen in a classic relative pupillary block mechanism.1,2 UBM studies have revealed that plateau iris syndrome is common in angle closure eyes.3,4
The gold standard for angle assessment is gonioscopy. However, it is subjective and varies depending on lighting conditions and the amount of corneal indentation.5–7.
The anterior segment optical coherence tomography (ASOCT) is non-contact, gives reproducible optical imaging of the anterior segment in dark conditions. ASOCT can provide information on the dynamic changes of the angle not provided by gonioscopy.8,9
The purpose of this pilot study was to quantify the dark–light dynamic changes of the angle and to differentiate PIC from CIC.
Design and Methods
This retrospective study included 45 eyes of 26 narrow angle patients (14 CIC and 12 PIC), who were referred for anterior chamber angle assessment using ASOCT during the period of March 2007 to July 2008 from the glaucoma clinic in a tertiary care hospital. Four mirror gonioscopy (Posner gonio prism, Ocular Instruments, Bellevue, WA) were used for diagnosis, and ASOCT (Visante TM Model 1000; Carl Zeiss Meditec, Dublin, CA) was advised for documentation and confirmation. Narrow angles were defined as posterior trabecular meshwork not seen for at least 180º on gonioscopy. Gonioscopic criteria for PIC were (1) greater force required for opening the narrow angle; and (2) iris angulating forward and then deepening centrally with sine wave sign when using indentation gonioscopy.1,2 The rest were classified as CIC for the purpose of the study. No attempt was made to differentiate the CIC into a combined mechanism because the study was conducted in pre-iridotomy eyes. Patients with signs of secondary angle closure were removed from the study. The images included were taken before laser peripheral iridotomy (LPI), first in the dark and then in bright illumination, and those with poor scleral spur identification were excluded. Patients on anti-glaucoma medications that would alter the iris configuration were also excluded from analysis.
The angle opening distance (AOD) was measured in all the included images. AOD500 was calculated as the distance from the corneal endothelium to the anterior iris surface perpendicular to a line drawn at 500 μm from the scleral spur, whereas a distance of 750 μm was used for AOD750. AOD500 and AOD750 were measured in nasal and temporal quadrants, using the irido-corneal angle tool provided in the ASOCT after manual selection of the scleral spur.
Statistical analysis was performed with SPSS 12.0 for Windows. The Kolmogorov Smirnov test showed that all the values were normally distributed and hence we used Student’s paired t test for comparing the AOD parameters in dark and bright conditions. The statistical significance was kept at P < .05.
There were 13 men and 13 women subjects, with the spherical equivalent refraction of −6.00D to +5.75D in the right eye and −6.00D to +6.00D in the left eye. The mean age group was 50.96 ± 10.9 years. Of 45 eyes, 38 were diagnosed as “primary angle closure suspects (PACS)” and 7 had “primary angle closure glaucoma (PACG).”
PIC eyes did not show significant change in dark and light conditions (Table 1; Figs. 1 and 2), whereas CIC eyes showed significant change in the nasal AOD500 and AOD750 and temporal AOD750 as given in Table 2 (Figs. 3 and 4).
Table 1: Dark-Light Changes in Plateau Iris
Figure 1. Anterior Segment Optical Coherence Tomography (ASOCT) Image of the Angle in Plateau Iris Configuration with Dark Condition.
Figure 2. ASOCT Image of the Angle in Plateau Iris Configuration with Room Light Condition.
Table 2: Dark-Light Changes in Convex Iris
Figure 3. ASOCT Image of the Angle in Convex Iris Configuration with Dark Condition.
Figure 4. ASOCT Image of the Angle in Convex Iris Configuration with Room Light Condition
We had demonstrated the dark–light changes in the anterior chamber angle using quantifiable parameters in CIC and PICs using ASOCT in a pilot study for the first time in literature. The angle configuration in PIC did not change significantly when compared with CIC.
Gonioscopy is the gold standard for anterior chamber angle assessment. The amount of illumination to visualize the angle, the changes in angle on placing the goniolens over the cornea, and the interobserver variability are the disadvantages with gonioscopy. Precise angle assessment and quantitative measurements were not possible with gonioscopy. However, literature describes differentiation of relative pupillary block when compared with plateau iris.1,2
UBM was used to visualize and quantify the angle. However, being a contact technique, the cup placed over the eye could cause artificial widening of the angle.7 Moreover the examiner must be very careful as to which clock hour of the eye was examined, which often led to reduced interobserver and intraobserver reproducibility in angle assessment especially in narrow angles.10,11
Studies analyzing the dynamic dark–light changes using UBM had reported differences in angle parameters.5,6 ASOCT studies also reproduced the results in narrow angles.8,9 All these studies used mainly AOD500 for quantifying the changes and found that it was greater in light than in dark.
Our results showed that neither AOD500 nor AOD750 produced significant change for PIC in both the nasal and temporal quadrants of the angle. Both AOD500 and AOD750 in CIC showed significant difference for the nasal quadrant and AOD750 for the temporal quadrant. AOD500 in the temporal quadrant failed to show significant change marginally, possibly due to the effect of the small sample size.
The findings of the study suggest that PIC did not change significantly to the room illumination. The possible reason could be that greater force was needed in indentation gonioscopy to open the PIC iris angle than relative pupillary block angles due to anteriorly displaced ciliary processes.1,2 Our study did not utilize UBM to confirm the position of the ciliary processes in these eyes; however, these patients were pre-iridotomy patients with PIC based on gonioscopy. It could have been possible that many of these eyes with CIC may have residual angle closure after LPI due to combined mechanism; however, we did not analyze this aspect in this study.
Due to the residual apposition of the angle in plateau iris postiridotomy, it is essential to diagnose plateau iris accurately. The parameters utilized so far were the goniscopic and UBM findings in literature, which need a certain amount of subjectivity in classification of plateau iris from convex iris eyes.12–14
The quantitative parameter using the dynamic changes could be utilized clinically as a reproducible, objective parameter in the diagnosis or confirmation of PICs with further refinements. We did not assess the changes in superior and inferior quadrants because lid and tear meniscus influence these quadrants to produce artifacts. The images where scleral spur was not identified and excluded from the analysis could be a potential bias. A Larger sample size is required to see if more quadrants show such differences and to standardize cut-off levels of AOD measurements between the PIC and CIC, before and after iridotomy and in comparison with UBM parameters for plateau iris syndrome.
This study can be a precursor to further refine the dynamic changes between PIC and CICs future studies as suggested above may be able to elucidate dynamic anterior segment quantitative measures that go along with the underlying mechanism of angle closure. Such an approach can be useful in refining the diagnosis of angle closure objectively to enable clinicians to adhere to appropriate treatment approaches.
This pilot study showed that the PIC did not show significant change in angle configuration with dark–light changes using ASOCT and the parameters; especially AOD500 and 750 could be of clinical interest in the diagnosis of this condition.
- Wand M, Grant WM, Simmons RJ, et al. Plateau iris syndrome. Trans Am Acad Ophthamol Otolaryngol. 1977;83:122–129.
- Ritch R. Plateau iris is caused by abnormally positioned ciliary processes. J Glaucoma. 1992; 1:23–26. doi:10.1097/00061198-199204000-00006 [CrossRef]
- Razeghinejad MR, Kamali-Sarvestani E. The plateau iris component of primary angle closure glaucoma: Developmental or acquired. Medical Hypotheses. 2007; 69:95–98. doi:10.1016/j.mehy.2006.11.025 [CrossRef]
- Yeung BY, Ng PW, Chiu TY, et al. Prevalence and mechanism of appositional angle closure in acute primary angle closure after iridotomy. Clin Exp Ophthalmol. 2005;33: 478–482. doi:10.1111/j.1442-9071.2005.01065.x [CrossRef]
- Woo EK, Pavlin CJ, Slomovic A, Taback N, Buys YM. Ultrasound biomicroscopic quantitative analysis of light–dark changes associated with pupillary block. Am J Ophthalmol. 1999;127:43–47. doi:10.1016/S0002-9394(98)00283-9 [CrossRef]
- Ishikawa H, Esaki K, Liebmann JM, Uji Y, Ritch R. Ultrasound biomicroscopy dark room provocative testing: a quantitative method for estimating anterior chamber angle width. Jpn J Ophthalmol. 1999;43: 526–534. doi:10.1016/S0021-5155(99)00139-2 [CrossRef]
- Ishikawa H, Inazumi K, Liebmann JM, Ritch R. Inadvertent corneal indentation can cause artifactitious widening of the iridocorneal angle on ultrasound biomicroscopy. Ophthalmic Surg Lasers. 2000;31: 342–345.
- Dacosta S, Fernandes G, Rajendran B, Janakiraman P, Assessment of anterior segment parameters under photopic and scotopic conditions in Indian eyes using anterior segment optical coherence tomography. Indian J Ophthalmol. 2008;56:17–22 doi:10.4103/0301-4738.37591 [CrossRef]
- Kai-shun Leung C, Yim Lui Cheung C, Li H, et al. Dynamic analysis of dark–light changes of the anterior chamber angle with anterior segment OCT. Invest Ophthalmol Vis Sci. 2007;48:4116–4122. doi:10.1167/iovs.07-0010 [CrossRef]
- Tello C, Liebmann J, Potash SD, Cohen H, Ritch R. Measurement of ultrasound biomicroscopy images: intraobserver and interobserver reliability. Invest Ophthalmol Vis Sci. 1994;35:3549–3552.
- Ramani KK, Baskaran M, George R, Roy J, Vijaya L. Intraobserver and interobserver reliability of measurements of ultrasound biomicroscopy images in primary angle closure suspects. Asian J Ophthalmol. 2007;9: 13–16.
- Nolan WP, See JL, Chew PT, et al. Detection of primary angle closure using anterior segment optical coherence tomography in Asian eyes. Ophthalmology. 2007;114:33–39. doi:10.1016/j.ophtha.2006.05.073 [CrossRef]
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Dark-Light Changes in Plateau Iris
|Parameter||Dark (μm)||Light (μm)||P|
|Nasal AOD500||0.177 ± 0.121||0.186 ± 0.116||.381|
|Temporal AOD500||0.188 ± 0.118||0.187 ± 0.104||.666|
|Nasal AOD750||0.294 ± 0.181||0.306 ± 0.172||.207|
|Temporal AOD750||0.346 ± 0.175||0.310 ± 0.161||.531|
Dark-Light Changes in Convex Iris
|Parameter||Dark (μm)||Light (μm)||P|
|Nasal AOD500||0.156 ± 0.072||0.186 ± 0.084||0.025|
|Temporal AOD500||0.111 ± 0.062||0.127 ± 0.060||0.068|
|Nasal AOD750||0.235 ± 0.082||0.280 ± 0.097||0.000|
|Temporal AOD750||0.192 ± 0.078||0.213 ± 0.086||0.039|