Abnormalies of scotopic electroretinography in rats with laser-induced ocular hypertension

Abstract

Scotopic threshold response (STR) and negative response (NR) in flash electroretinography (ERG) have been found to be related to the response from inner retina. These are useful indicators to assess the functional changes in inner retina of animal ocular hypertension models which always involve the damage of retinal ganglion cells (RGCs). In the present study, ERG was used to investigate the functional changes of retina in a laser-induced ocular hypertension model. Ocular hypertension was induced unilaterally using Argon laser photocoagulation of the episcleral veins and limbal veins in Sprague-Dawley adult rats. Intraocular pressure (IOP) was measured with a calibrated tonopen. For studying the number of RGC loss at different time-points, the RGCs were labeled with FluoroGold four days before sacrifice of the animals. ERG was measured in these animals before the laser treatment, at two weeks, four weeks and eight weeks after the laser treatment. The animals were under general anesthesia during all the experimental procedures. There was about 1.6-fold increase of intraocular pressure (IOP) in the experimental eyes after the laser photocoagulation compared to those of the control eyes and the elevated IOP could be maintained at a quite steady level for at least eight weeks. The amplitudes of STR and NR were markedly attenuated together with the progressive loss of RGCs after the induction of ocular hypertension. This indicates that the elevation of IOP in this ocular hypertension model causes functional impairments in inner retina and this result is beneficial to future glaucoma studies using this model. Acknowledgement: This study was supported by the award from The University of Hong Kong, the donation from the late Mr. And Mrs. Ma Yip Seng, the research grant from the Research Grant Committee of the Hong Kong Special Administrative Region and the research grant (G-T506) from The Hong Kong Polytechnic University.