Purpose
To compare the functional changes on Multifocal ERG (MFERG) and visual fields by standard automated perimetry (SAP) with structural changes on Cirrus Spectral domain optical coherence tomography (SD-OCT) in all severities of glaucoma.
Methods
Retrospective review of consecutive patients with different severities of adult glaucoma. Data collected for analysis included age at diagnosis, baseline clinical variables like intraocular pressure, visual field indices including mean deviation and pattern standard deviation and diagnosis (type of glaucoma). OCT variables including Retinal nerve fibre layer thickness (average and quadrant analysis) and N1P1 amplitudes (average and 4 quadrant analysis). Association between visual field indices with demographic, SD-OCT and N1P1 amplitudes were evaluated by regression statistics and clustered analysis in early (MD>-6dB), moderate (-6 to -12dB) and advanced glaucoma (<-12dB).
Results
Ninety seven eyes of 49 patients were included with a mean age of 54±11.2 years, including 22 early, 32 moderate and 43 with advanced glaucoma. While superior RNFL thickness differed between early (92±22.9 microns) , moderate (88±22.4 microns) and severe (52±22.6 microns), p=0.02, N1P1 amplitudes were not statistically significant between early-severe glaucoma subtypes, p=0.2. Visual field index correlated significantly with the superior (r=0.6, p=0.01), inferior (r=0.7, p=0.02) RNFL thickness and superonasal N1P1 amplitude(r=0.6, p=0.02). Multivariate linear regression identified significant relationship between VFI and superior RNFL thickness (β=1.5, p=0.002), inferior RNFL thickness (β=1.6, p=0.004) and superonasal N1P1 (β =1.2, p=0.02) only in severe glaucoma (R2=0.85) while N1P1 amplitudes did not correlate significantly with visual field damage variables in earlier stages of glaucoma.
Conclusions
Functional damage on visual field correlates well with MFERG functional impairment only in advanced glaucoma. This suggests that focal abnormalities seen in moderate and early glaucoma may not be picked up by MFERG whereas diffuse abnormalities as seen in advanced glaucoma may be monitored for functional changes using MFERG.
Keywords: 507 electrophysiology: clinical •
568 intraocular pressure •
642 perimetry