Electrophysiological evaluation in normal-tension glaucoma suspects: a pilot study

Abstract

Purpose: To evaluate the variations of intraocular pressure (IOP), morphometric papillary characteristics, perimetric indices and electrophysiological parameters (Pattern electroretinogram and visual evoked potentials) before and after topic hypotonization therapy in patients with suspect normal tension glaucoma.Methods: we evaluated 38 eyes of 20 patients with intraocular pressure < 21 mmHg (measured with Goldman applanation tonometry), initial glaucomatous optic neuropathy (valued with HRT: retinal fiber layer (RNFL) and/or linear cup/disk (linear C/D), minimal visual defects (Octopus 101: G2 program), visual acuity more than 15/20 with best correction and pathological electrophysiological parameters (valued with pattern electroretinogram and visual evoked potentials), free of systemic or other ocular diseases. All parameters were evaluated at the beginning of the study (T0) and after 12 months from the beginning of the therapy (T12). A randomized normal control group (27 eyes of 14 subjects) with apparent larger disc cupping underwent all exams at initial of study and after 12 months. Results:At T0, P100 Latency VEPs in LTG was slightly increased either at 15’ (12,9 msec) and 30’ (8,9 msec). At T0, P100 Amplitude VEPs in LTG group were reduced compared to normal subjects, with average differences of: -6.4 µV (95% C.I.: (-9.8, -3.0) µV) for 15'; and: -5.4 µV (95% C.I.: ( -8.9, -2.0) µV) for 30’. P50N95 complex amplitude PERG was reduced at T0 in LTG, with average differences: -0.9 (95% C.I.: ( -1.4, -0.4) µV), -0.8 (-1.3, -0.3) µV) for 15’ and 30’, respectively; than it improved after therapy, with average differences between T12 and T0 of 0.3 µV (95% C.I.: (0.1, 0.6) µV) and 0.5 µV (95% C.I.: ( 0.2, 0.8) µV). So IOP decreased at T12 in LTG group, with an average difference between T12 and T0 of -5.2 mmHg (95% C.I.: (-5.9, -4.4). mmHg). Finally, CRT was slight delayed in LTG group at T0. Conclusion: In a viewpoint of an integrated diagnostic, electrophysiological tests (VEPs and PERG) could provide a more sensitive measure of retinal ganglion cell integrity and help to distinguish between suspect normal-pressure glaucoma patients before perimetric alterations are evident and normal subjects with apparent larger disc cupping.