Testing VA : Do symmetrical charts make a difference?

Elaine Cornell, DipAppSc (Cumb) MA (Macq)
Nathan Moss, BSc (Qld) PhD (UNSW)

Data on 117 subjects over seven years of age were obtained whether there is a difference in the results obtained from visual acuity charts that use only lateral symmetry and those that use a combination of letters with and without this symmetry. Subjects with acuities of 6/9 or better were used to overcome the problems associated with difference in letters on the 6/60 to 6/18, such as the number of letters, their spacing on a line, and the spacing between lines.
The results showed a highly significant statistical difference (p=0.0001) between the two charts, with the charts that use only letters with lateral symmetry giving a better result of on average 0.49 letters. This means that on approximately every second test, an eye tested on a chart with lateral symmetry would read one more letter than one tested on a chart with letters with and without symmetry. It is unlikely that clinical decisions would be based on this small difference. These findings should only be generalised to subjects with good visual acuity.