Fundus autofluorescence and OCT thickness evaluation in P23H rats

Abstract

Purpose: The aim of this study was to evaluate fundus autofluorescence (FAF) and OCT changes in an animal model of Retinitis Pigmentosa, the P23H rat and to investigate retinal and choroidal vascularization using fluorescein and indocianin green angiography.

Methods: Twenty albino homozigous P23H line 1 rats aging from 18 postnatal days (P18) to 27 months and albino wild-type Sprague-Dawley (SD rats) (2 and 15 months old) were used for this study. Normal pigmented Long Evans (LE) 2 months old were used to compare FAF findings. Scanning laser ophthalmoscopy (SLO) imaging and Optical Coherence Tomography (OCT) were acquired using a Spectralis HRA OCT system (Spectralis, Heidelberg Engineering, Heidelberg Germany). For checking FAF, fluorescence was excited using diode laser at 488 nm. A single OCT line was performed passing through the optic nerve of the rat. Thickness measurements were evaluated avoiding the ones close to the optic nerve. Immunohystochemistry (ICC) was performed to correlate with the findings of OCT and AF changes.

Results: FAF in LE rats showed no findings. In SD and young P23H rats choroid was seen by transparence. During the course of P23H degeneration, the FAF pattern varied from not findings in young animals, some spotting at 2 months old to a mosaic of hyperfluorescent dots in the rats of 6 months or older. Retinal thicknesses diminished during the time. Young SD rats showed thickness values higher than old ones (205.2 vs 183.18 μm, at 2 and 15 months old respectively). P23H rats showed great changes in morphology in advanced ages, with no clear limit between the retina and the choroid. Mean retinal thickness values varied from 189.88 μm to 73.55 μm at 2 months old and 11 months old respectively, lowering till 58.15 μm at 27 months old. Retinal vascular plexus were diminished with time, and vessels exhibiting an abnormal, tortuous morphology could be observed. Arteries did not change in their diameter.

Conclusions: Autofluorescent ophthalmoscopy is a non-invasive procedure that can detect changes in metabolic activity at the RPE in animal models of retinal degeneration in vivo. Hyperautofluorescent changes appeared with the course of the degeneration with a diminution of retinal thickness. Retinal vascular plexus changes are clear with aging.

Keywords: 688 retina • 551 imaging/image analysis: non-clinical • 695 retinal degenerations: cell biology