Impact of experimental glaucoma severity on structural and functional outcomes after internal limiting membrane peel for retinal ganglion cell replacement in nonhuman primates

Abstract

Purpose : Restoring vision for those blinded by glaucoma is a long-term goal of our studies. Advancing approaches for retinal ganglion cell (RGC) replacement requires development of translational strategies for donor cell engraftment to the inner retina. This study characterizes structural (by optical coherence tomography, OCT) and functional (by electroretinogram, ERG) consequences of transplantation procedures in nonhuman primates (NHP) with moderate-to-severe experimental glaucoma (EG).

Methods : OCT scans (Spectralis) were acquired bilaterally under anesthesia at baseline (BL), before (PRE) and after surgery (POST) in rhesus macaques (ages 5-17 y) with unilateral moderate (N=4) and severe (N=5) EG. Bilateral multifocal (mfERG, VERIS) and full-field (ffERG, BigShot, LKC) ERGs were recorded to assess retinal function, including RGC-driven parameters (mfERG high-frequency components, HFCs and ffERG photopic negative response, PhNR) at BL, PRE, and POST timepoints. The surgery was vitrectomy and internal limiting membrane (ILM) peel with delivery of a suspension containing human stem cell-derived RGCs to the retinal surface (N=7), sub-retinally (N=1), or done without cells as sham surgery (N=1). Frequency of structural abnormalities PRE vs. POST surgery was compared between severity groups using Fisher’s exact test. ERG parameters were compared over time and between EG and fellow control eyes using 2-way ANOVA and mixed-effects models.

Results : Retinal nerve fiber layer loss at PRE was 25% ± 1% (mean ± s.d.) in moderate EG and 66% ± 11% in severe EG eyes. Increased frequency of structural abnormalities PRE vs. POST was associated with EG severity (p=0.04). All EG eyes exhibited significant loss of mfERG HFCs at PRE (Fig1A, p=0.02), but no further loss at POST. PhNR amplitude was significantly reduced by EG at PRE (Fig1B, p=0.01); the slight further reduction to POST was not significant. No significant differences were found in light-adapted or dark-adapted ffERG a-wave or b-wave amplitudes (Fig1C,D) at any time point. mfERG revealed subtle, local dysfunction in ILM peel areas.

Conclusions : ILM peel for RGC replacement in NHP with EG caused localized structural damage, which was exacerbated by more severe EG. ERG changes manifested only as those typical of RGC dysfunction in EG with other subtle changes localized to the ILM peel.

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