Performance of the dot visual acuity test with uncorrected ametropia resulting in target blur

The dot visual acuity test is used to test the acuity of children between the ages of 2 and 4 years who do not respond to the tumbling E test. Because the test involves the detection of a black dot on a white background it is appropriate to ask if the detection threshold is lowered artificially in the presence of target blur. Twenty-one children (42 eyes) were used in the study. Refractive errors were fully corrected and each subject's lag of accommodation was measured. A monotonic decrease in acuity was found with increasing amounts of optical blur. The explanation for the decreased acuity is found in the reduced retinal image contrast of the blurred target.