Sir,

We read the paper by Buckle et al1 with great interest but would respectfully disagree with the authors assertions that ‘the limitations of certification data to estimate the true incidence of blindness and visual impairment have been demonstrated repeatedly’. Clearly much is dependent upon one’s definition of blindness and when considering certification data it is essential to understand that it reflects the number of individuals whose vision has fallen to a particular threshold and whose ophthalmologist offers certification, and who accept this offer. Geurin et al2 have commented upon difficulties in interpreting who is and who is not eligible for certification which has led to development of a CVI app which readers are encouraged to explore. (https://play.google.com/store/apps/details?id=com.cviapp.cviapp) (https://itunes.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=969850184&mt=8) A systematic review by Tate et al3 showed that certification figures were more robust than suggested by cross-sectional surveys which will always be unreliable because of fluctuation of vision over time. As readers will be aware, CVI (Certificate of Vision Impairment) figures due to age-related macular disease are now a public health indicator and are accessible to all on www.phoutcomes.info (albeit currently only from 2010/11). These data are provided by the Certifications Office (email correspondence from Certifications office on the 25th March 2015) which operates under the auspices of the Royal College of Ophthalmologists. During the years ending 31 March 2009 and 2010, respectively, there were 23 and 24 CVIS for AMD in the over 50-year olds in Gloucester compared with Buckle’s figures of 22 and 30, respectively, a finding suggesting perhaps greater accuracy in certification figures than anticipated.