Abstract
Purpose: :
To determine factors that predispose to a positive 45 minutes prone dark room provocative test (DRPT) in patients with plateau iris after laser iridotomy (LI).
Methods: :
In this retrospective observational cohort study, patients diagnosed with narrow angles persisting following LI (performed between March 2003 and June 2007) were submitted to a DRPT. Subjects were subsequently subdivided to form a positive (an increase of IOP of 6 mmHg or more) and a negative (maximum increase 3mmHg) DRPT group. Eyes of patients were imaged in 4 quadrants using an ultrasound biomicroscope. Quantitative assessment of UBM images was made by a blinded observer using research software. Measurements obtained included the anterior chamber depth (ACD), angle opening distance at 500 micrometers (AOD 500), angle recess area (ARA), anterior chamber angle (ACA), trabecular-ciliary process distance (TCPD), iris thickness (IT), iris-ciliary process distance (ICPD), height of plateau, distance of iris-cornea contact, and number of open quadrants. Demographic/clinical data were obtained from the patient charts. Comparisons of UBM measurements (mean and most open quadrant), clinical and demographic data were made using a t test or a khi-2 test accordingly. Correlation between UBM measurements and a positive DRPT was studied using Pearson correlation.
Results: :
35 eyes of 35 patients were studied : 17 had a positive DRPT (group A) with a mean increase in IOP of 11.1 ± 3.5mmHg and 18 had a negative DRPT (group B) with a mean increase in IOP of 0.9 ± 0.1mmHg. Mean patient age was 57.9 ± 10.5yrs and 57.3 ± 10.8yrs in groups A and B (p=0.9). There was a significant difference in sex distribution (58% men in group A and 83% women in group B, p=0.01). Mean refraction was 3.41 ± 2.27D in group A and 2.60 ± 2.06D in group B (p=0.3). There was no statistically significant difference between the two groups in any UBM measurement. However, on indentation gonioscopy, patients in group A had significantly more synechial angle closure (35% vs. 0%, p=0.008) and more frequent double hump sign (59% vs. 11% p=0.005).
Conclusions: :
UBM measurements could not predict a rise in IOP after DRPT in patients with narrow angles following iridotomy. However, the presence of synechial angle closure and double hump sign on indentation gonioscopy was associated with a positive DRPT. While plateau iris is known to be more prevalent in women, men may be at higher risk of developing a positive DRPT.
Keywords: anterior segment • intraocular pressure • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)