Abstract
Purpose :
Although approximately 30-50% of aqueous outflow resistance lies distal to Schlemm’s canal (SC), the morphology of the aqueous outflow pathway distal to SC has not been thoroughly examined. This study investigated the morphology of the outflow pathway from SC to the intra-scleral veins (ISVs) in an experimental model of glaucoma in cynomolgus macaques.
Methods :
Argon laser photocoagulation was used to create burns to ~270 degrees of the trabecular meshwork (TM) of one eye (n = 6) or both eyes (n = 2) of each monkey until intraocular pressure was consistently elevated. Discrete regions of the TM were left untouched. Contralateral eyes (n = 5) were used as controls. Monkeys were sacrificed at 60 months or more after the last treatment. Eyes were enucleated and perfused at 15 mmHg for 30 min to measure outflow facility, perfusion-fixed with Karnovsky’s fixative for 1 hr, and then immersion-fixed overnight. Anterior segments of each eye were cut into 24 to 36 radial wedges and embedded in Epon-Araldite. Semi-thin sections (2 µm) of select wedges were cut, stained, and imaged. Width, height, and cross-sectional area (CSA) of SC of non-lasered regions of laser-treated eyes and control eyes, as well as number and CSA of ISVs of non-lasered and lasered regions of laser-treated eyes and control eyes were compared. Statistical analyses were conducted using R.
Results :
Mean outflow facility was significantly decreased in laser-treated eyes (0.12 μL/min/mmHg; n = 8) compared to control eyes (0.34 μL/min/mmHg; n = 5; P = 0.02). Median CSA, width, and height of SC were not different between non-lasered regions of laser-treated eyes and control eyes (P > 0.05). SC was partially or completely obliterated in lasered regions. Median number of ISVs was significantly decreased in lasered regions (1.4 ISVs) compared to non-lasered regions (3.7 ISVs) of laser-treated eyes (P ≤ 0.01) and control eyes (6.0 ISVs; P ≤ 0.01). Median CSA of ISVs did not differ between groups (P > 0.05). Lasered regions displayed looser, more disorganized scleral stroma in the region surrounding the TM.
Conclusions :
Partial or complete obliteration of SC, decreases in ISV number, and changes in scleral composition may account for a portion of the increased outflow resistance in SC and the distal aqueous outflow pathway in monkey eyes with laser-induced OHT.
This is a 2021 ARVO Annual Meeting abstract.