Abstract
Purpose: To evaluate the variations of intraocular pressure (IOP), morphometric optic nerve head characteristic, perimetric indices and electrophysiological parameters (pattern electroretinogram and visual evoked potentials) before and after topical IOP lowering in patients with early normal-tension glaucoma.Methods: we evaluated 38 eyes of 20 patients with IOP < 21 mmHg, initial glaucomatous optic neuropathy (valued with HRT: retinal nerve fiber layer thickness (RNFL) and linear cup/disk ratio (linear C/D ratio)), minimal visual field defects (Octopus 101: G2 program), best correct visual acuity more than 15/20 and pathological electrophysiological parameters (valued with pattern electroretinogram (PERG) and visual evoked potentials (VEPs)), free of systemic or other ocular diseases. All parameters were evaluated at the beginning of the study (T0) and after 12 months of therapy (T12). A randomized normal control group (27 eyes of 14 subjects) with apparent larger disc cupping underwent all exams at initial of study (T0) and after 12 months (T12).Results: Among electrophysiological parameters, at the beginning of the study NTG P100 VEPs latency is slightly increased and P100 amplitude is reduced compared to normal subjects. There are not significant variations after 12 months. P50 PERG latency in NTG is quite similar respect normal and do not modify after therapy. P50N95 complex PERG amplitude in NTG is reduced compared to normal subjects and slightly increases after 12 months (1.8 vs 1.5 ; 2.4 vs 1.9 micronvolts, with different checkboard spatial frequency). Cortical retinal time (CRT) is slightly delayed in NTG and does not modify. Among visual field indices, MD and CLV is slightly higher in NTG and do not significantly modify after therapy. Among morphometric optic nerve head characteristics, linear C/D and RNFL thickness are quite similar in NTG and do not modify. IOP is quite similar between NTG and control group and modifies in NTG after therapy.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 early normal-pressure glaucoma patients with no or minimal visual field alterations and normal subjects with apparent larger disc cupping.
Highlights
Glaucoma is a multifactorial optic neuropathy characterized by progressive loss of retinal ganglion cells, changes in optic disk morphology and visual field defects
Up of 30% of retinal ganglion cells loss is associated with statistically significant changes in visual field sensitivity:[8] visual field is not impaired in ocular hypertension (OHT) or in early manifest glaucoma and it is important to early diagnosis, before visual field defects are evident
We evaluate functional (visual field indices; electrophysiological (VEPs and Pattern electroretinogram (PERG)) parameters) and morphometric optic nerve head characteristic, before and after topical IOP lowering in patients with early normal-tension glaucoma
Summary
Glaucoma is a multifactorial optic neuropathy characterized by progressive loss of retinal ganglion cells, changes in optic disk morphology and visual field defects. Pattern electroretinogram (PERG) is a useful tool for detection of open-angle glaucoma, but is not a routine diagnostic exam. It is a direct indicator of retinal ganglion cell function.[5] PERG reflects diffuse RCG damage but not focal,[6] so one should not necessarily find correlations between alterations of PERG and visual field.[7] Up of 30% of retinal ganglion cells loss is associated with statistically significant changes in visual field sensitivity:[8] visual field is not impaired in ocular hypertension (OHT) or in early manifest glaucoma and it is important to early diagnosis, before visual field defects are evident. Several authors in human studies found PERG as a predictive value to identify those patients with elevated IOP who develop a glaucoma before visual field changes occur.[11,12]
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