Purpose. This study aims to determine the accuracy and repeatability of visual acuity measurements taken with the LEA Numbers Low Vision Book (LNLVB) and the Feinbloom chart in visually impaired subjects.
Methods. Distance visual acuities were taken with the LNLVB, the Feinbloom chart, and the Early Treatment of Diabetic Retinopathy Study (ETDRS) chart, then repeated 15 to 30 min later to evaluate for inter-test repeatability. To determine threshold, participants were encouraged to guess until they could not identify any optotypes. The total number of correctly identified optotypes was recorded and extrapolated to logMAR on all three charts. The Feinbloom chart and LNLVB were evaluated for correlation to ETDRS. Nine visually impaired children and nine visually impaired adults participated in the study.
Results. In comparing the LNLVB to ETDRS, the 95% limits of agreement were +0.099/−0.240, and the correlation coefficient (R) was 0.953 (p < 0001). The same comparison for the Feinbloom chart vs. ETDRS was +0.169/−0.322 with r = 0.905 (p < 0.0001). On test–retest comparisons, the ETDRS was highest with the 95% limits of agreement of +0.117/−0.128. LNLVB and Feinbloom were nearly identical at +0.159/−0.200 and +0.184/−0.202, respectively. The R value for ETDRS was 0.976, LNLVB was 0.954, and Feinbloom was 0.942 (p < 0.0001 on all three).
Conclusions. The results of our study indicate that there is a slight advantage, in terms of agreement with ETDRS, of LNLVB over the Feinbloom chart when testing visually impaired patients. The two tests proved nearly identical in terms of repeatability in a low-vision setting. Both handheld charts measured slightly worse acuity than the ETDRS chart, but overall proved to be suitable alternatives when the ETDRS chart is not available or practical in certain clinical situations.
Northeastern State University, Oklahoma College of Optometry, Tahlequah, Oklahoma.