Effect Of Experimental Glaucoma On The Non-Image Forming Visual System

Abstract

Purpose: : Glaucoma is a major cause of blindness characterized by progressive and irreversible damage of the optic nerve. The degenerative loss of retinal ganglion cells (RGCs) and the visual deficit associated with glaucoma have been extensively studied. The aim of the present study was to examine the non-image forming visual system in an experimental model of glaucoma in rats induced by weekly injections of chondroitin sulphate (CS) in the eye anterior chamber.

Methods: : Animals were unilaterally or bilaterally injected with CS or vehicle for 6 or 10 weeks. Melanopsin levels were assessed by Western blotting and immunohistochemistry, whereas superior collicular RGCs were retrogradely labeled from the superior colliculus with Fluorogold. The pupil light reflex (PRL) was measured after exposing eyes to a 30-s light flash, whereas pineal melatonin content was analyzed by radioimmunoassay after exposure to white or blue light for 20 min at night (nocturnal melatonin suppression test). In addition, light-induced c-Fos expression in the suprachiasmatic nuclei was assessed by immunohistochemistry.

Results: : A significant decrease in melanopsin levels was observed in the retinas from eyes injected with CS. CS injections induced a similar decrease in the number of melanopsin-containing cells and superior collicular RGCs. Experimental glaucoma induced a significant decrease in the afferent (but not efferent) PRL. White light significantly decreased nocturnal pineal melatonin content in control and glaucomatous animals, whereas blue light decreased this parameter in vehicle- but not in CS-injected animals. Moreover, a significant decrease in light-induced c-Fos expression in the suprachasmatic nuclei was observed in glaucomatous animals.

Conclusions: : These results indicate the glaucoma induced significant alterations in the non-image forming visual system.

Keywords: ganglion cells • pupillary reflex • melatonin