Role of Pattern Electroretinogram (PERG) and Visual Evoked Potentials (PEV) in Glaucoma: Morphological and Functional Correlations

Purpose to assess the correlation between visual function (studied by visual field-VF-, PERG and VEP), and anatomical damage (detected by confocal laser polarimetry, GDx-VCC). Methods 35 eyes of 18 glaucoma patients were selected and classified, on the basis of VF defect, in early, moderate, and advanced (21, 6, and 8 patients, respectively). All patients underwent a complete ophthalmic examination to determine the presence of: clear optical media, best corrected visual acuity > 0.8, no macular disease, open angle. All subjects were submitted to the following examinations: VF, GDx-VCC, PERG and VEP. These parameters have been considered: the average of the 16 central threshold values Central Mean Differential Light Sensitivity (DLS) for VF; the Nerve Fiber Indicator (NFI) for GDx; P50 and N95 latency for PERG, and P100 for VEP. The Pearson correlation coefficient has been applied as a measure of the correlation among different parameters. Results All the patients with moderate or advanced VF defect presented abnormal DLS and pathological VEP P100; NFI and PERG values were discordant since NFI resulted normal in 28,5% of these patients, and both PERG P50 and PERG N95 were normal in 57,1% and 42,8% of patients, respectively. A good correlation was found between NFI and VEP P100 (r=0,48, p=0,07 for latency, and r=0,71, p=0,003for amplitude).About function, all early glaucoma patients presented normal DLS values, but only 28,6% had a normal VEP P100, and 19% recorded normal PERG P50 and N95. About anatomy, NFI was normal in 50% of patients. Anatomical and functional data did not correlate in early glaucomatous.All the patients with an evident asymmetry (7 subjects out of 18) between the eyes (early defect in one eye and advanced defect in the other) presented abnormal PERG N95 but normal NFI. Conclusions Electro-functional tests may play a role in the diagnosis of glaucoma. PERG records the ganglion cell response and is therefore able to detect early defects in these cells that are principally and early involved in the glaucomatous opticopathy. Our data pointed out that PERG N95 is able to record a retardation before the defect is detectable anatomically.The function is altered before the anatomy in glaucoma patients? Our data seem to suggest this consideration. Further studies with more patients are required.