ETDRS-fast: implementing psychophysical adaptive methods to standardized visual acuity measurement with ETDRS charts

PURPOSE. To measure visual acuity (VA) on Early Treatment Diabetic Retinopathy Study (ETDRS) charts with a modified faster procedure (ETDRS-Fast), based on adaptive psychophys- ics methods and to assess the method’s validity and reproduc- ibility. METHODS. Whereas the standard method for measuring VA with the ETDRS charts requires that the subject read all the letters beginning with the top row, in the ETDRS-Fast procedure, the subject is asked to read only one letter per row until a mistake is made. Then, following simple rules, the examiner finds a row from which the subject can begin reading all the letters down- ward, thus making the method identical with the standard method near threshold. VA determination was performed twice with both methods in 57 subjects in two separate ses- sions to assess validity and reproducibility. RESULTS. In both sessions the correlation between the two procedures was high (intraclass correlation coefficient 0.95), confirming the validity of the ETDRS-Fast procedure. Repro- ducibility was good for both procedures, with intraclass cor- relation coefficients of 0.94 for the standard and 0.96 for the ETDRS-Fast method. The ETDRS-Fast procedure allowed a sig- nificantly shorter test duration ( 30%; P 0.0001). CONCLUSIONS. Adaptive procedures allow accurate and fast de- termination of psychophysical thresholds by reducing the number of stimulus presentations when the subject is far from threshold. In the ETDRS-Fast method a few simple rules ap- plied to optotype chart reading allow adaptation to each pa- tient’s level of VA. The ETDRS-Fast procedure significantly reduces test time and still yields results that are as accurate as those obtained with the standard method.