Ocular Hypertension In The Adult Rat Retina Results In Protracted Loss Of S- And L-cones

Abstract

Purpose: : To evaluate the long term effects of laser-induced ocular hypertension (OHT) in the innermost and outer retinal layers, we have quantified and examined the topological distribution of retinal ganglion cells (RGCs) and the two types of cone photoreceptors, the S- and L-cones.

Methods: : In adult female Sprague-Dawley rats, the left eyes were treated with laser photocoagulation (LP) of limbal and episcleral veins (Salinas-Navarro et al.,2010 Exp. Eye Res.). Intraocular pressure was recorded with a Tono-lab® at various survival intervals. Wholemount retinas were analysed one and six months after injury. RGCs were identified with Fluorogold® applied to both superior colliculi one week prior to sacrifice. S- and L-cones were doubly immunodetected with specific antibodies against these opsins. The three retinal neuronal populations were automatically quantified and their spatial distribution was assessed by constructing isodensity maps (Ortín-Martínez et al.,2010 IOVS).

Results: : There were typical pie-shaped retinal areas preferentially located in the dorsal retina, that varied from a small sector to several retinal quadrants, showing focal absence of FG+RGCs, The lack of FG+RGCs at one month was comparable to that observed by 6 months and approximates to 75-80% of the total RGC population. S- and L-opsin expression in cones decreased to 65% and 80%, respectively, at one month, and to 20% and 35% respectively at six months. The loss of cones was observed throughout the retina, and highest densities of surviving cones were located around the periphery.

Conclusions: : LP-induced OHT result in the loss of RGCs that is present already by 1 month and does not progress further with time. However, the two types of cones show a progressive loss that amounts to 65-80% by six months after LP.

Keywords: intraocular pressure • photoreceptors • retina