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L. M. Ventura, F. Venzara, V, V. Porciatti; Rates of Visual Field and PERG Changes Over 4 Years in Early Glaucoma. Invest. Ophthalmol. Vis. Sci. 2007;48(13):221.
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© ARVO (1962-2015); The Authors (2016-present)
To compare changes of visual sensitivity and Retinal Ganglion Cell (RGC) activity over time in patients with early glaucoma.
Ninety-six patients (mean age 60.3 ± 11.6 years, 128 eyes) with normal corrected visual acuity (≥20/20) and free from retinal diseases, but with either suspicion of glaucoma (GS) or early manifest glaucoma (EMG) were repeatedly (n > 6 times) tested over 4.1 ± 0.6 years with both Standard Automated Perimetry (SAP) and PERG (Porciatti and Ventura, Ophthalmology 2004). GS patients had optic disc abnormalities and one or more risk factors for glaucoma. EMG patients had either repeatable mild to moderate SAP defects or signs of progressive disc changes. Mean intraocular pressure was 15.9 ± 4.3 mm Hg, and mean vertical cup-to-disc (C/D) ratio was 0.54 ± 0.18. PERG amplitude and phase were expressed as dB deviations from age-predicted values. Mean PERG and SAP deviations for the 4-year observation period, as well as rates of change (linear regressions in dB/year) were calculated and compared.
Mean deviations were: SAP MD -1.28 ± 1.77 dB; PERG amplitude -1.26 ± 1.55 dB; PERG phase -0.19 ± 0.33 dB. SAP and PERG amplitude MDs were weakly correlated (R=0.35). PERG amplitude and phase MDs were not correlated. The number of significant (p<0.05) abnormalities depended on the different tolerance intervals (TI) of the normal population for different measures. Assuming a -3 dB lower 95% TI for SAP MD, and -2dB and -0.38 dB for PERG amplitude and phase, respectively (Porciatti and Ventura, Ophthalmology 2004), the percent of eyes with abnormal deviations were: SAP MD: 12%, PERG amplitude MD: 31%; PERG phase: 24%. Mean rates of change were: SAP: -0.09 ± 0.54 dB/year (not significantly different from zero), PERG amplitude: -0.28 ± 0.38 dB/year (different from zero, p<0.001); PERG phase: -0.03 ± 0.07 dB/year (different from zero, p<0.001). The percent of eyes with significant (p<0.001) regressions were: SAP 1%; PERG amplitude: 6%; PERG Phase: 5%.
While SAP and PERG amplitude display similar average MDs, there is a greater percentage of eyes with abnormal deviations for PERG amplitude and phase than SAP. Compared to SAP, the rate of change for PERG amplitude and phase is more skewed towards negative values, which reaches statistical significance in a substantial percent of eyes. The PERG offers promise to signal RGC dysfunction and its progression in early glaucoma. It remains to be established if progressive PERG changes predict future SAP changes in early glaucoma.
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