Characterization of retinal morphology in the naturally occurring hypopigmented 13-lined ground squirrel

Abstract

Purpose : The cone-dominant 13 lined ground squirrel (13-LGS) is an emerging model for vision research. Here, we sought to characterize a naturally occurring hypopigmented 13-LGS model using non-invasive imaging.

Methods : Six (5M, 1F) 13-LGS from the same hypopigmented pedigree were anesthetized and underwent non-invasive retinal imaging and axial length measurement. Near infrared reflectance (NIR), Near infrared autofluorescence (NI-AF), and short wavelength autofluorescence (SW-AF) scanning laser ophthalmoscopy (SLO) imaging was used for qualitative assessment. Optical coherence tomography (OCT) scans were obtained to quantify retinal thickness. Adaptive optics scanning light ophthalmoscope (AOSLO) images were acquired along vertical strips from the optic nerve head (ONH) inferior to the visual streak. Regions of interest were then selected at 0.75° increments along this strip to estimate cone density. Quantitative metrics were compared to eccentricity matched data from one-year-old wildtype animals (OCT: n = 12 eyes, AOSLO: n = 6 eyes).

Results : SLO imaging revealed variable choroidal visualization in all animals. Two animals had substantially shorter axial length values (5.87 and 5.90 mm; normal range = 8.53 - 8.9 mm). These two animals had significantly increased total retina, inner retina, outer retina, and choroidal thicknesses, while thickness values for the other 4 animals were within normative ranges (see Figure). AOSLO imaging was not possible in the two short-eyed animals due to poor image quality. In remaining hypopigmented animals, density measurements fell within ± 2 SD of the normative eccentricity matched mean values (c.f., at 6.25 degrees eccentricity, normal mean ± 2SD: 534.98 ± 115.46 cones/deg²; hypopigmented range: 522.37 – 594.09 cones/deg²).

Conclusions : While some of the hypopigmented 13-LGS present similarly to wildtype animals, the decreased axial length, abnormal OCT, and altered SLO observed in two of the hypopigmented animals present similarly to that of human albinism patients. This supports continued examination of the hypopigmented 13-LGS pedigree as an emerging model to study human albinism.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.

 

Figure 1. Comparison of hypopigmented 13-LGS retinal thickness measurements to wildtype normative range (shaded region). Open symbols are from two short-eyed animals, remaining symbols are from the other four hypopigmented animals.