In vivo evaluation of Schlemm’s canal in experimental glaucoma monkeys

Abstract

Purpose : To determine the effect of pupillary changes on Schlemm’s canal (SC) in normal and experimental glaucomatous monkey eyes in vivo.

Methods : chronic ocular hypertension (OHT) was unilaterally induced in 18 Cyno monkeys by laser trabecular photocoagulation. The effect of 300 µg Pilocarpine, 600 µg Azopt®, or Phenylephrine and Mydriacyl® on intraocular pressure (IOP) in both eyes was evaluated in conscious animals using an applanation pneumatonometer post a single topical ocular dose. The effect of same treatments on pupil and SC area was evaluated in sedated animals with Spectralis SD optical coherence tomography (OCT). Pupil diameter (PD) was measured in OCT images. The size of SC in a series of 49 OCT B-scan images obtained in the temporal limbal region was measured by three masked readers using AMIRA (V.5.5) image analysis software.

Results : Pilocarpine maximally decreased IOP by 23±3% at 1h post-dose in OHT eyes and 14±3% in the fellow normal eyes. The baseline IOP (±SEM) was 33±1 mmHg and 24±1 mmHg in OHT and normal eyes, respectively. The pupil diameter in both eyes was decreased similarly by about 70% compared to pre-dose reading (3.8±0.3 and 3.5±0.3 mm). The SC area was significantly increased by 218±122% in OHT eyes and 122±57% in normal eyes. There was a positive correlation between reduced PD and IOP reduction (r=0.889 in OHT eye and r=0.670 in normal eye) but not with PD vs. SC and IOP vs. SC. Azopt® maximally reduced IOP by 13±5% at 6h post-dose in OHT eyes and by 4±2% in normal eyes. Azopt® did not significantly alter pupil size or SC area. There was no correlation between IOP and SC area. Maximal pupil dilation with mydriatic treatment increased IOP by 9.0±9.3% in OHT eyes and 36.5±12.6% in normal eyes at 1 hour post dose. The area of SC did not change in OHT eyes. However, the area of SC significantly decreased (-34%) in normal eyes at 1 hours post dose.

Conclusions : SC in the monkey eye can be noninvasively assessed with OCT. The area of SC measured in the temporal quadrant is passively changed along with pupillary responses to miotic or mydriatic treatment. Pupil constriction induced A. greater change in SC size and IOP than that following pupil relaxation and B. a greater effect on SC size in OHT eyes compared to normal eyes. Pupil relaxation induced greater changes on SC and IOP in normal eyes than that of OHT eyes.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.