OCT/A Optic nerve head changes with flicker in NHP eyes with experimental glaucoma.

Abstract

Purpose : Light flicker is known to increase retinal and optic nerve head (ONH) blood flow, a reflection of neurovascular coupling. Alterations in blood flow can affect vascular caliber and, hence, thickness measures obtained using optical coherence tomography (OCT). This study aimed to determine if control and experimental glaucoma eyes in the nonhuman primate (NHP) have altered vascular and ONH morphological responses to flicker.

Methods : Data were collected from 6 healthy adult NHPs with unilateral, laser-induced experimental glaucoma. Prior to imaging, animals were sedated with ketamine and xylazine, and pupils dilated with 1% tropicamide. Six high-speed 384x384 (15°x15°) OCT Angiography scans (Spectralis, Heidelberg Engineering) and three laser speckle flowgraphy videos (LSFG-LITE, Softcare) centered on the ONH were acquired from both eyes with and without 8.7 Hz white light flicker. OCT scan volumes were imported into Matlab, scaled using ocular biometry, and segmented using a neural network-based algorithm. Changes in LSFG mean blur rate (MBR) and OCT measures of circumpapillary retinal nerve fiber layer (RNFL) thickness, minimum rim width (MRW), neuroretinal rim (NRR) volume, and associated vascular volume measures were used for paired analysis.

Results : Mean RNFL and MRW measures were reduced in experimental eyes (RNFL:98±21µm, MRW:231±82µm) compared to the fellow controls (RNFL:125±7µm, MRW:344±34µm, P<0.02). OCTA vascular volume of the NRR and circumpapillary NFL was reduced in eyes with experimental glaucoma (P<0.05). There was a correlation between MBR and OCT measures of RNFL thickness and MRW (R²>0.44, P<0.02). With flicker, there was an increase in MBR, which was similar for both control (5.6±1.6) and experimental glaucoma eyes (5.1±2.5, P=0.66). The increase in NRR vascular volume with flicker was linearly related to the change in NRR tissue volume (R²=0.64, P<0.01). In addition to MRW (9±5µm, P<0.01), both control and experimental eyes had an increase in circumpapillary RNFL thickness (4±2µm, P<0.01) with flicker.

Conclusions : Flicker induced increases in blood flow and OCTA vascular volume were similar in experimental glaucoma and control eyes in the NHP. In addition to changes in blood flow, flicker results in an increase in both NRR and circumpapillary tissue thickness.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.