Comparison of Crowded Single Optotypes with Linear Acuities in Amblyopes

Megan Williams, BappSc(Syd)
Tiffany Wong, BappSc(Syd)
Helen Goodacre, MHlthScEd(Syd), DipAppSc(Orth)

In order to evaluate the effectiveness of the letter matching test (LM test) in the detection of the crowding phenomena, the authors compared it to two conventional test, the linear Snellens/Sheridan Gardiner test and the Sheridan Gardiner Singles test. The LM test differs from conventional tests in that the less complex singles test has been enhanced by the addition of four ‘crowding bars’ to increase sensitivity to the crowding phenomena. To find out if the LM test provides an accurate equivalent to the linear charts, visual acuities were compared in amblyopic patients (n=15) and a control group of normal with no history of amblyopia (n=30). The amblyopic group was found to have significantly different acuities when comparing results in the singles tests with the results in both the linear and LM test. In addition there was no significant difference found between the linear and LM test acuities. These findings are consistent with the hypothesis that the crowding bars contained in the LM test provide contour interactions which are similar to the linear chart, therefore providing a reliable alternative method to single optotypes in the measurement of vision in the young.