Control of chart memory for retesting acuity.
BACKGROUND: Enhancement of visual acuity has been demonstrated when retesting takes place within 24 hours and appears to be due to chart memory. Significant chart letter subset memory has been found after a single acuity measurement and can still be present 10 days after an examination involving several acuity measurements. Control of chart memory may increase the precision of acuity measurement. METHOD: A single acuity measurement was used to establish chart letter subset memory. Retroactive interference methods for the inhibition of chart letter memory have been compared using a letter recognition memory test. The experimental methods used to promote forgetting included a spelling backward exercise and near acuity assessment using a contra-chart. The contra-chart is constructed from the 16 letters not involved in the distance chart that was used to establish chart memory. RESULTS: Assessment of near vision using a contra-chart was found to inhibit chart letter memory. CONCLUSIONS: The contra-chart appears to have research and clinical applications that require control of measurement imprecision due to chart memory. Contra-charts obviate the need to use equivalent charts, which have the disadvantages of being difficult to use and control only for memory of letter sequences. The contra-chart can be included easily in an examination protocol for research or in a clinical examination sequence for which it will have the additional purpose of providing a guide to near vision performance.