Characterization of a new model of focal cone degeneration induced by a Light-emitting-diode (LED).

Abstract

Purpose: To establish a new model of focal light emitting diode induced phototoxicity (LEDIP) in rats.

Methods: Adult female Sprague-Dawley rats (n=7) were dark adapted overnight. The next day the animals were anesthetized under dim red light and their left pupil was dilated with topical 1% tropicamide. The animal bodies were placed over a heated pad and their heads were secured with a head-holder in order to maintain the same eye orientation for all animals. The left eye was then exposed during 10 s to 200 lux of blue light (430nm) emitted by a 10V LED placed at 1mm of the corneal apex. Focal retinal damage was analyzed using Spectral Domain Optic Coherence Tomography (SD-OCT; Spectralis, Heidelberg Engineering) at 12, 24, 36, 48, 72 hours, 5 and 7 days after LEDIP. One week after LEDIP, the animals were processed and their retinas dissected as whole mounts and immunoreacted for S-opsin and L-opsin demonstration. The numbers of S- and L-cones were automatically counted within a circular area (with a radius of 1.3 or 1 mm for S-cones or L-cones, respectively) centered on the lesion and in a similar corresponding region of the right control retinas.

Results: Retinal damage was circumscribed to a circular region whose center was located at approximately 2.4 mm from the optic disc in the superotemporal retina (the region with highest L-cone density). The diameter of the lesion was measured with SD-OCT and decreased from 24 hours (1,842.4±84.5µm) to 7 days (1,405.4±76µm) after LEDIP. There was a progressive decrease in retinal thickness in the centre of the lesion from 12 hours (183.4±5µm) to 7 days (114.6±6µm) after LEDIP, while the thickness in the periphery was maintained from 12 to 72 hours (200.5±5µm-193.1±9µm) and then decreased at 7 days (161.2±10µm) after LEDIP. Whole-mounted retinas showed the lesion as a small circular area that lacked S- and L-opsin immunofluorescence at its center. The mean numbers (±SD) of S- or L-cones in the circular area measured (that comprised the lesion) were 655±139 and 7,118±842 in the left retinas and 2,235±179 and 14,040±1,860 in the right control retinas, respectively.

Conclusions: LEDIP results in a focal lesion that shows with severe loss of both S- and L-cones. This model of cone degeneration is reproducible and quantifiable and may thus be used to study cone degeneration and neuroprotection.

Keywords: 615 neuroprotection • 648 photoreceptors • 688 retina