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

To measure visual acuity (VA) on Early Treatment Diabetic Retinopathy Study (ETDRS) charts with a modified faster procedure (ETDRS-Fast), based on adaptive psychophysics methods and to assess the method's validity and reproducibility.

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 downward, 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 sessions to assess validity and reproducibility.

In both sessions the correlation between the two procedures was high (intraclass correlation coefficient 0.95), confirming the validity of the ETDRS-Fast procedure. Reproducibility was good for both procedures, with intraclass correlation coefficients of 0.94 for the standard and 0.96 for the ETDRS-Fast method. The ETDRS-Fast procedure allowed a significantly shorter test duration (-30%; P < 0.0001).

Adaptive procedures allow accurate and fast determination 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 applied to optotype chart reading allow adaptation to each patient'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.