The Amsler chart: absence of evidence is not evidence of absence

Early detection of the onset or progression of macular disease is likely to become increasingly important as new treatment modalities are introduced. Current best practice involves issuing patients with an Amsler chart for daily or weekly observation with the instruction to attend for immediate assessment should any new distortion be perceived. However the sensitivity of Amsler charts in detecting macular disease can be less than 50%, implying that presentation may be delayed in over half of patients with advancing disease relying on the Amsler chart to detect progression. A likely explanation for this is the phenomenon of perceptual completion whereby regular objects are "filled-in" across the scotoma. Although alternative tests have been developed and shown to have greater sensitivity, at present no straightforward, cheap, home-based test of macular disease progression is available. The development of such a self-diagnostic tool should be a research priority.