Tree Shrew and Rat Models Imaged With 3d 1050nm Optical Coherence Tomography and Simultaneous Electrophysiology

Abstract

Purpose: : To monitor nerve fiber layer thickness changes in animal models of acute intraocular pressure (IOP) increase and to demonstrate an instrument combining visual field stimulus, optical coherence tomography (OCT), and electrophysiological recording.

Methods: : Acute IOP increases were induced by the injection of paramagnetic beads in the anterior eye of rats and tree shrews to occlude the trabecular outflow pathway. Contralateral eyes served as controls. Intraocular pressure pressures were monitored by rebound tonometry. Selected tree shrews were prepared as paralysed -anesthetised preparations for electrophysiological recordings from the lateral geniculate nucleus. All animals were sacrificed and examined by histology.The custom OCT combined thigh resolution (4um axial), high speed (up to 47,000 A-scans per second) at 1050nm and incorporated a digital light projector for the presentation of visual stimuli. A field programmable gated array coordinated OCT spectral acquisition, scan pattern, and simultaneous collection of analog signals. The ECG and respiratory cycle could be monitored during imaging and used to optimize the alignment of OCT signals.

Results: : Retinal nerve fiber layer thickness (RNFLT) was monitored by OCT at 1 week pre and at 1 and 2 weeks post induction of experimental glaucoma. OCT tomograms could be obtained in all animals, including those in which the optical clarity was compromised by glaucoma induction. Both models showed progressive thinning of the RNFLT following elevation of the intraocular pressure. In the tree shrew, the scleral lamina cribrosa could be resolved in its entire thickness as a hyperintense meshwork (230um thick).

Conclusions: : High resolution OCT imaging at 1060 provides high quality and robust delineation of optic nerve head structures in small animal models of glaucoma. The combination of stimulus and imaging arms in a single device has the potential for both structural and functional characterization of the retinal and optic nerve head changes in these models.

Keywords: nerve fiber layer • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • electrophysiology: non-clinical