Short-Term Changes in the Photopic Negative Response Following Intraocular Pressure Lowering in Glaucoma

Area of Science:

• Ophthalmology
• Neuroscience
• Retinal Electrophysiology

Background:

• Glaucoma is a progressive optic neuropathy characterized by vision loss.
• Inner retinal function is crucial for visual processing and can be affected by glaucoma.
• The photopic negative response (PhNR) is an electroretinogram (ERG) parameter sensitive to inner retinal function.

Purpose of the Study:

• To assess short-term alterations in inner retinal function using PhNR following intraocular pressure (IOP) reduction in glaucoma patients.
• To investigate the impact of IOP-lowering therapy on specific PhNR parameters.

Main Methods:

• A cohort of glaucoma patients undergoing new or additional IOP-lowering therapy (treatment group) and a control group with stable glaucoma were recruited.
• Intraocular pressure (IOP), visual field, retinal nerve fiber layer thickness, and ERGs were measured at baseline and follow-up (3 ± 2 months).
• An optimized protocol for a portable ERG device was used to record PhNR, analyzing parameters like Vmax, Vmax ratio, K, and Naka-Rushton slope.

Main Results:

• The treatment group achieved a significant IOP reduction (28 ± 3%) compared to the control group (2 ± 3%; P < 0.0001).
• PhNR Vmax showed a significant difference over time (P = 0.019), with the treatment group exhibiting improvement (mean difference, 1.23 µV) while the control group did not.
• Improvement beyond test-retest variability was observed in 17% of the treatment group versus 3% of the control group (P = 0.007).

Conclusions:

• An optimized PhNR measurement protocol can detect short-term functional improvements in a subset of glaucoma patients after IOP reduction.
• The majority of patients did not exhibit significant changes in PhNR parameters despite IOP reduction.
• These findings suggest that PhNR may serve as a sensitive indicator of early functional changes in response to glaucoma treatment.