Evaluation of damaged photoreceptors in a macaque model of viral vector induced retinal degeneration using an AOSLO

Abstract

Purpose : Efforts to test efficacy of vision restoration methods can benefit by use of non-human primates, but progress is needed in developing useful models of photoreceptor degeneration. Although clinical imaging such as OCT can be used to assess such models, imaging with an adaptive optics scanning light ophthalmoscope (AOSLO) enables cellular-scale tracking of not only photoreceptor structure but also function. Here, photoreceptor damage in a macaque model of retinal degeneration is characterized using 3 AOSLO imaging modalities: confocal reflectance, two-photon autofluorescence (TPAF), and multi-offset detection (MOD).

Methods : An AAV construct designed to locally damage photoreceptors was administered by subretinal injection into 2 macaque retinas. Pre- and post-injections, OCT images were acquired (Heidelberg Spectralis). In one retina, photoreceptors were imaged with an AOSLO (λ=730nm) in the 3 modalities aforementioned. Confocal reflectance was used to evaluate changes in photoreceptor structure. TPAF (λ_em=400-550nm), thought to originate primarily from retinol in outer segments (OS), was collected to assess function of photoreceptors. As previously shown, TPAF increase in response to the imaging light demonstrates production of retinoids required for visual function. MOD combined images from orthogonal offset aperture positions to visualize photoreceptor inner segments (IS).

Results : Post injection, OCT showed regions of decreased intensity in the outer retina, suggesting photoreceptor damage. AOSLO images revealed presence of both normal and damaged photoreceptors in regions with decreased intensity in OCT (Fig 1). TPAF was decreased in damaged photoreceptors by 75 ± 3% when compared to normal photoreceptors. Furthermore, there was no detectable increase in TPAF at light onset, unlike normal photoreceptors (Fig 2). MOD images indicated that photoreceptor IS remained in damaged photoreceptors.

Conclusions : Three distinct AOSLO imaging modalities and OCT, taken together, are consistent with loss of photoreceptor OS while IS are preserved. This model of retinal degeneration shows potential for testing efficacy of vision restoration methods, especially those such as optogenetics that capitalize on remaining photoreceptor structure.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.

 

Damaged (upper) and normal (lower) photoreceptors imaged with 3 AOSLO modalities

 

TPAF response to imaging light in damaged and normal photoreceptors