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E. Drouyer, E. WoldeMussie, L. Wheeler, G. Ruiz, W. de Vanssay, C. Chiquet, P. Denis, H.M. Cooper; Reduction of Retinal Projections in a Rat Model of Glaucoma . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3335.
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Purpose: Laser photocoagulation of episcleral and limbal veins has been shown to induce elevated intraocular pressure and induce significant loss (up to 45%) of retinal ganglion cells in a rat model of glaucoma (IOVS, 42: 2849-2855). This study is aimed to evaluate the alteration of retinal projections to different visual structures in this experimental model. Methods: Albino Wistar rats were laser operated unilaterally (at 1, 10, 60 days) and intraocular pressure (IOP) was subsequently monitored by tonometer over a four month period. Animals subsequently received an intraocular injection of Cholera toxin (CTb) anterograde tracer coupled with the fluorochrome dye Alexa 488 (green) in one eye, and CTb coupled Alexa 594 (red) in the other eye. The density of retinal projections was analysed between the operated and unoperated control eye. Results: IOP increased two-fold and remained elevated in the operated eye over the study period. Retinal projections to visual structures from the glaucomatous eye were reduced from 10-70%, depending on the individual and the visual nucleus as compared to projections from the unoperated eye. Reduction was observed in all structures, including the dorsal and ventral geniculate, superior colliculus, pretectum and suprachiasmatic nucleus. The degree of reduction was greatest in the regions corresponding to the representation of the inferior visual field (superior quadrants of the retina). Conclusions: The results show that chronically elevated IOP can lead to a severe reduction of the retinal projections to all visual structures. These results suggest that in addition to the reduction of visual field extent and acuity, a broad range of visual functions including the pupillary reflex (pretectum) and circadian responses to light (SCN) can potentially be affected by ganglion cell loss associated with glaucoma.
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