Abstract
Purpose :
During postnatal development, the visually guided emmetropization mechanism actively regulates eye growth and refractive state, but the neurophysiological basis of this mechanism remains unclear. We asked if myopia induced by imposing a negative lens (lens-induced myopia) produces alterations in retinal electrophysiology responses in tree shrews.
Methods :
At 24 days of visual experience (DVE), five juvenile tree shrews (small mammals close to primates) housed in broadband colony light (100-300 lux) wore goggles with a -5.00 D lens on the right (treated) eye while the left (control) eye had unrestricted vision. Non-cycloplegic refractive error and axial ocular dimensions were measured every other day starting at 24 DVE. A hand-held, portable RETeval system (LKC Technologies, MD, USA) was used to record electroretinogram (ERG), including flash, 30 Hz flicker, photopic negative response, S-cone, and ON-OFF ERGs before (24 DVE), during (30 DVE), and after treatment (35 DVE). In addition, flash and flicker ERGs were repeated twice in the same session.
Results :
At the onset of treatment, the refractive state was near emmetropia (mean±SEM, treated eye: 0.63±0.33, control eye: 0.29±0.33, p=0.52). At the end of treatment, the treated eye became significantly myopic (-4.75±1.00 D), while the control eye remained near emmetropic (0.04±0.40 D); these refractive changes were consistent with changes in vitreous depth (treated eye: 0.10±0.01 mm, control eye: -0.01±0.02 mm, p=0.02). Tree shrew ERGs exhibited well-defined and robust waveforms similar to human ERGs, with excellent intersession (r≥0.98; bias (mean±95% limits), amplitude: 17±32 µV, peak time: -0.12±0.81 ms), and intrasession repeatability (r≥0.99, bias: -0.1±4.6 µV, -0.03±0.08 ms). There was no effect of age (DVE) (p>0.05) or treatment (p>0.05) on ERG parameters (Figure 1).
Conclusions :
The RETeval measures of ERGs in tree shrews were robust, repeatable, and consistent with human ERGs, demonstrating the reliability of the RETEval system in measuring retinal function in tree shrews. The retinal electrophysiology responses remained relatively stable and unaffected during treatment with a myopiagenic stimulus, which suggests that the retinal circuits of photopic ERGs may not be involved in the emmetropization mechanism, at least in this species.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.