Long-Term Effect of Laser-Induced Ocular Hypertension on the Cone Electroretinogram and Central Macular Thickness in Monkeys

Objective: The purpose of this study was to investigate the long-term effect of laser-induced ocular hypertension on the cone electroretinogram (ERG) and retinal thickness in monkeys. Background data: Degeneration of retinal nerve fiber layer (RNFL) and loss of retinal ganglion cells in the primate glaucoma model have been confirmed by histological studies and optical coherence tomography (OCT) images. However, it remains unclear whether the outer retina distal to the RGCs (e. g., photoreceptors) is involved in histological studies and in functional test. Materials and methods: Subjects were five monkeys with high intraocular pressure (IOP) induced in the right eye by laser. Six years after the laser coagulation of the mid-trabecular meshwork, RNFL, ganglion cell complex (GCC), central macular thickness (CMT), and the thickness of outer retinal layer (ORL) were measured by OCT. The photopic responses of ERG were recorded in response to red flashes on a blue background. The maximum cone amplitude (R-cone) and cone sensitivity (Scone) were calculated. Results: Enlarged cup-to-disc (C/D) ratio was found in the lasered eyes. RNFL and GCC were significantly thinner in the lasered eyes (p < 0.05), but no significant differences were found in CMT and the thickness of ORL compared with fellow eyes (p > 0.05). Mean amplitude of the photopic negative response (PhNR), Mean R-cone were significantly lower in the lasered eye (p < 0.05), and no significant differences of Scone were found between the two eyes (p > 0.05). Conclusions: Long-term ocular hypertension induced by laser affects the function of cone photoreceptor in monkeys.