Vanishing optotypes: is single presentation superior to chart exposure?

A study comparing single optotype presentation vs entire chart exposure (with spacings of either 1.5 or 3.0 times the optotype width) was conducted on 46 subjects divided into two groups in order to evaluate how the mode of presentation affects visual acuity measurements made with medium-pass filtered vanishing optotypes. There were no significant differences in either group between the two modes of presentation. However, in the individual cases in which a decrease in percent correct responses greater than 20% was observed in either mode of presentation, there was a slight tendency towards superiority of the entire chart exposure mode.