Abstract
Purpose: :
To assess variability of refracted and non-refracted visual acuity (VA) measurement in a consecutive series of AMD patients undergoing treatment with Ranibizumab. Loss of 5 or more letters of VA may be considered as an indication for Ranibizumab (Lucentis) reinjection as suggested by the European Summary of Product Characteristics.
Methods: :
LogMAR visual acuity was recorded in the setting of AMD clinics where patients attended 1 or more times over 1-10 day period for their monthly Lucentis schedule. At each scheduled follow up refracted LogMAR visual acuity was measured by an optometrist refraction by a standard protocol. If the appointment was split in 2 episodes unrefracted logMAR visual acuity was measured by a nurse. The change of mean visual acuity from baseline to 12 months was plotted using the refracted and non-refracted logMAR VA values. In addition, a retrospective review of a sample of 114 eyes of 57 consecutive patient records was undertaken to directly compare the LogMAR VA measured with and without refraction. Bland-Altman plot of VA measurement disagreement and analysis of variance was carried out (ANOVA).
Results: :
Analysis of changes of the mean visual acuity from baseline revealed overall comparable mean values but greater variability of non refracted logMAR VA measurements. Of the 314 episodes available for direct comparison 62% (195) had differences of the non-refracted and refracted logMAR VA within 5 letters. In 27% (85) and 11% (34) episodes the non-refracted VA differed more than -5 and +5 letters respectively from the refracted VA (range -24 to +29 letters). However, the mean visual acuity was not significantly different between the two methods (p=0.28).
Conclusions: :
Non-refracted and refracted measurements achieved comparable mean logMAR visual acuities. There was greater variability of non-refracted VA measurements, with a clinically significant large difference in terms of anti-VEGF retreatment decisions in a high proportion of follow ups. Whilst unrefracted visual acuity measurements may be satisfactory for audits caution should be taken when using them to make Ranibizumab re-treatment decisions.
Keywords: age-related macular degeneration • clinical (human) or epidemiologic studies: treatment/prevention assessment/controlled clinical trials • visual acuity