We welcome the latest estimates of global visual impairment (VI). (1) Posterior segment eye diseases (PSED): Glaucoma; Age-Related Macular Degeneration (ARMD); and Diabetic Retinopathy (DR) are now recognised as a major cause of VI worldwide and are more prevalent than infectious causes of VI such as trachoma and corneal ulcers. The majority of data collated in the last ten years from which these figures are estimated likely underestimate the true prevalence of PSED for three reasons: (a) The majority of surveys used the WHO coding instructions, which use the "principal disorder responsible for visual loss in the individual after considering disorders in either eye which are most amenable to treatment or prevention"(2), i.e. if a patient has co-existent PSED with cataract it will be deemed that cataract is the primary cause of VI. Therefore most VI prevalence data available in which cataract is the primary cause will underestimate the actual prevalence of PSED; (b) The Rapid Assessment of Avoidable Blindness (RAAB) methodology, which forms one of the most employed methods of gathering VI data in the last ten years (20 published from Africa, Latin America and Asia) does not allow for accurate diagnosis of PSED or differentiation between PSED; and (c) VI surveys have been designed to diagnose the cause of disease in those with varying degrees of visual impairment (?6/18 Snellen acuity) and thus pre-visually impairing disease is not detected. This is particularly important in the detection of PSED where cessation rather than cure is currently our only realistic management option. If VISION 2020: The Right to Sight's aims of alleviating suffering from avoidable blindness is to be met, the growing impact of PSED needs to be a focus of policy makers.

Conflict of Interest:

None declared