Quantification of Iridotrabecular Contact in Primary Angle Closure Disease.

PRECIS Iridotrabecular contact, a measure of angle closure can be quantified along with other angle parameters on ASOCT. Hence, angle changes and angle closure mechanisms can be detected predicting efficacy of iridotomy. PURPOSE To assess 360° iridotrabecular contact (ITC), and ocular parameter changes after laser peripheral iridotomy, in primary angle closure disease (PACD) subgroups. METHODOLOGY This was a prospective observational study including ninety subjects, thirty each of primary angle closure suspect (PACS), primary angle closure (PAC) and primary angle closure glaucoma (PACG). Anterior segment OCT parameters were measured before and three weeks after laser peripheral iridotomy (LPI) - ITC, central anterior chamber depth, lens vault, angle opening distance, angle recess area, trabecular-iris space area, trabecular-iris angle at 500 μm and 750 μm from scleral spur. RESULTS ITC was highest in PACG, 81.43±22.39%, followed by PAC, 28.53±21.30%, and PACS 10.76 ± 8.54%, (P 0.011). There was a significant decrease in ITC in all three groups after iridotomy (P<0.001), with a residual ITC of 68.56±26.44% in PACG, 18.23±15.98% in PAC and 5.13±5.11% in PACS. A significant positive correlation was seen between extent of ITC, baseline intraocular pressure (IOP) and visual field index. ITC was highest in eyes with exaggerated lens vault, 77.3±32.03% as compared to eyes having a plateau iris configuration or relative pupillary block configuration, P<0.001. CONCLUSION Iridotomy at any stage of PACD shows a significant decrease in ITC, with areas of residual ITC. Even in PACG, iridotomy is effective in exposing parts of the trabecular meshwork which had contact earlier. Greater baseline ITC and post laser ITC are a biomarker for higher IOP and greater visual field damage, which need lifelong review and appropriate management.