OCT Imaging of Glaucoma Drainage Implants in the Rabbit Model

Abstract

Purpose: : To image the position of draining tubes in the rabbit model using optical coherence tomography.

Methods: : A Stratus OCT–3 (Zeiss–Humphrey, CA) was modified with a custom–built adjustable stage and an animal carrier with 2 degree of rotation to allow examination of the angle structures of rabbits. 5 NWZ rabbit eyes implanted with silicone rubber (polydimethylsiloxane, PDMS, Dow Corning, Midland MI) drainage tubes (outer diameter = 0.64mm, lumen=0.3mm) or SIBS [poly(styrene–b–isobutylene–b–styrene), MiDi, InnFocus LLC, Miami FL], drainage tubes (outer diameter = 0.25mm, lumen = 0.07mm) were scanned. In order to visualize the implant, the animals were anesthetized and the OCT objective adjusted to its maximum forward setting to focus the OCT beam on the surface of the eye. No optical modification was required to acquire images.

Results: : The tube position and its relationship with the corneal vault, limbus and iris plane could be scanned and measured in all eyes. Cysts under the conjunctiva–Tenon surface that were difficult to visualize with the slit–lamp were recorded with OCT. In all animals, OCT was able to detect the presence of shallow blebs which could not be identified with the slit–lamp. With OCT we were able to check the patency of PMDS tube’s lumen even when buried beneath conjunctiva–Tenon tissues. Incorrect positioning of the tube distal end was observed in one animal, and thinning of the conjunctival–Tenon tissues overlaying the implant in another animal. OCT could not detect thin fibrin bridges linking the iris to the implant at the angle that could be seen with the slit–lamp at 40x.

Conclusions: : Optical coherence tomography is a useful tool for the follow–up of animal models implanted with glaucoma drainage implants.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)