Quantification of Iridotrabecular Contact in Primary Angle-Closure Disease

Precis: Iridotrabecular contact (ITC), a measure of angle closure, can be quantified along with other angle parameters on anterior segment optical coherence tomography (ASOCT). Hence, angle changes and angle closure mechanisms can be detected predicting the efficacy of iridotomy. Purpose: To assess 360-degree ITC and ocular parameter changes, after laser peripheral iridotomy (LPI), in primary angle-closure disease (PACD) subgroups. Methodology: This was a prospective observational study including 90 subjects, 30 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 3 weeks after LPI ITC: central anterior chamber depth, lens vault, angle-opening distance, angle recess area, trabecular iris space area, trabecular iris angle at 500 and 750 mu m 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 3 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 the extent of ITC, baseline intraocular pressure, and visual field index. ITC was highest in eyes with exaggerated lens vault (77.3%+/- 32.03%), as compared with eyes having a plateau iris configuration or relative pupillary block configuration (P<0.001). Conclusions: Iridotomy at any stage of PACD shows a significant decrease in ITC, with areas of residual ITC. Even in PACG, the iridotomy is effective in exposing parts of the trabecular meshwork that had contact earlier. Greater baseline ITC and postlaser ITC are a biomarker for higher intraocular pressure and greater visual field damage, which need lifelong review and appropriate management.