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Stuart K. Gardiner, Chris A. Johnson, Shaban Demirel; Adjusting for Visual Acuity to Remove the Potential Confound of Cataract Development when Assessing Visual Field Change in Early Glaucoma. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5496.
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Automated perimetry remains the gold standard for functional testing in glaucoma. However, contrast sensitivity (perimetric sensitivity) is affected not just by glaucoma, but also by developing cataract. The Visual Field Index (VFI) aims to provide a global index that is less affected by cataract development. However, it is insensitive to early glaucomatous change, signaling "100% of normal vision" even when generalized loss or very early localized loss are present. This study aims to identify predictors of the rate of sensitivity loss after adjusting for potential cataract development, without excluding early glaucomatous change.
Data were taken from the ongoing Portland Progression Project, a longitudinal study of participants with early or suspected glaucoma. The rate of change of Mean Deviation (MD) over sequences of six visual fields was predicted based on the initial neuroretinal rim area (from confocal scanning laser ophthalmoscopy), intra-ocular pressure (IOP; the maximum recorded during the series), treatment (the proportion of the six visits at which the patient self-reported taking IOP-lowering medication), and the rate of change of logMAR-equivalent visual acuity during the series. A first-order autoregressive multivariate linear generalized estimating equation model was used, to adjust for multiple series from the same participant.
1232 series of six visits were included, from both eyes of 145 participants, averaging 4.2 series per eye. At their first visit, 84% of participants had VFI>98; 31% had VFI=100. Series began with an average MD of -2.0dB; VFI of 98.3; IOP of 18.1mmHg; and acuity of -0.01 logMAR equivalent. Only 8% had a rate of change of VFI worse than -1/year, while 29% had MD change worse than -0.33dB/year (both approximately 1% of the available range). Rate of change of MD was predicted by Rim Area (p=0.003), rate of change of acuity (p=0.027), Treatment (p<0.001) and IOP (p=0.008). Similar models predicted rate of change of MD using optic nerve head cup volume (p=0.001), and cup-to-disc ratio (p<0.001).
Adjusting for change in visual acuity allows the rate of glaucomatous progression to be assessed, without discarding information about early glaucomatous change. Clinically, considering the rate of change of MD together with acuity may allow better detection of change than using the trend of VFI in early glaucoma.
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