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Rizwan Malik, Richard A. Russell, David P. Crabb, David F. Garway-Heath; How Does A Change In The Visual Field Index Relate To Pointwise Visual Vield Progression?. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4152.
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Visual field (VF) global indices are less variable than point sensitivities in patients at risk of glaucoma and may assist the clinician to identify progression. The aim of this study was to assess whether a change in pointwise VF sensitivity is accompanied by a change in the Visual Field Index (VFI) in patients with Ocular Hypertension (OHT).
Humphrey 24-2 Full-threshold VFs were analyzed from a longitudinal series of 194 patients with OHT at Moorfields Eye Hospital from 1992-2000. The VFI was computed for each time-point and overall change evaluated by linear regression analysis. Pointwise VF progression was defined by linear regression of sensitivity over time, progression was flagged if the slope was less than -1 dB / year (p<0.05) for ‘central points’ or less than -2 dB / year (p<0.05) for ‘edge points’. The change in VFI (slope, %/year) was computed and the correlation between the number of progressing points and VFI slope assessed, Figure 1.
The median (IQR) age of the patients at baseline was 63 (56-71) years, with median follow-up of 6.0 (5.4-6.5) years. The results are summarised in Figure 1. There was a highly significant correlation between the change in VFI and the number of progressing points (Spearman's rank correlation rho =-0.59, p<0.001%). In some patients, pointwise sensitivity decline was associated with an improvement in VFI.
On average, in OHT patients, pointwise sensitivity decline was accompanied by a decline in VFI. A change in VFI may assist the clinician in identifying patients with VF progression; however, VF progression may be missed if only VFI is considered, so pointwise sensitivity data should also be carefully examined.
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