Time Course of IOP Elevation, Electroretinographic Changes and Retinal Ganglion Cell Loss in a Rat Model of Glaucoma Induced by Laser

Abstract

Purpose:: To evaluate the time course of intraocular pressure (IOP) elevation, electroretinographic changes and retinal ganglion cell (RGC) loss in a rat model of glaucoma induced by photocoagulation of the trabeculum and the episcleral and limbal veins.

Methods:: Male Sprague Dawley rats were used at 6 weeks of age. At least 3 of the episcleral veins, the trabeculum and the limbal veins were photocoagulated with a laser at 532nm (Quantel Medical, Vitra) in one eye of the animals. IOP and electroretinogram (ERG) were monitored every 2 weeks during 11 weeks after photocoagulation. Three months after laser photocoagulation, the RGC population was identified with a 5% Fluorogold solution applied to both superior colliculi. Seven days after labelling, retinas were whole-mounted and examined with a fluorescence microscope equipped with a motorized stage. The population of Fluorogold retrogradely-labelled RGCs was counted for each retina using image analysis software (Image Pro Plus).

Results:: IOP significantly increased in the laser-treated eyes as soon as one week after photocoagulation (32 mmHg versus 18 mmHg in control eyes) and remained at high values up to 7 weeks after treatment. The ERG b-wave amplitude of the treated eyes started to decline 9 weeks after photocoagulation and was half of that observed in the control eyes after 11 weeks. No differences were observed in the ERG b-wave latencies. The population of RGCs in lasered retinas was reduced to approximately 70% of the values observed in their contralateral control eyes.

Conclusions:: Laser photocoagulation of the trabeculum, episcleral and limbal veins induces chronic elevation of the IOP, and this result in functional alterations of the inner retina as well as the loss of retinal ganglion cells. Thus, the methodology employed in these experiments reproduces several of the characteristics of glaucoma.

Keywords: ganglion cells • electroretinography: non-clinical • intraocular pressure