Abstract
Purpose: :
Contrast sensitivity (CS) measurement in clinical practice is routinely performed with the Pelli–Robson chart, which has become established as the gold standard. Two new clinical tests of contrast sensitivity that have recently become commercially available are the hand–held Mars chart and the computer–based Test Chart 2000. The purpose of this study was to compare the repeatability of these new contrast sensitivity charts and their agreement with the Pelli–Robson charts, in a cohort of hospital patients with and without visual impairment.
Methods: :
Subjects were recruited from the low vision and refraction clinics at Moorfields Eye Hospital. Contrast sensitivity was measured in the right eye only with the optimal refractive correction using two versions of the Mars chart (Mars Perceptrix Inc, Chappaqua, NY), two presentations on the Test Chart 2000 (Thomson Software Solutions, Hatfield, UK) and two versions of the Pelli–Robson chart (Haag–Streit, Harlow, UK). Corrections were made to allow for the test working distance. Tests were presented in a counterbalanced order. Bland–Altman techniques were used to assess repeatability and agreement.
Results: :
52 subjects were recruited with visual acuity from 20/12 to 20/240. Coefficient of repeatability was 0.180 for the Pelli–Robson chart, 0.120 for the Mars chart and 0.238 for Test Chart 2000. Limits of agreement with the Pelli–Robson chart were –0.28 to 0.16 log units for the Mars chart and –0.31 to 0.78 log units for the Test Chart 2000. For the subgroup of patients with contrast sensitivity poorer than 1.70 log units, the Test Chart 2000 had limits of agreement of –0.37 to 0.24 log units.
Conclusions: :
In a population of hospital ophthalmology patients, coefficient of repeatability is better for the Mars chart and worse for the Test Chart 2000 when compared to the Pelli–Robson. The electronic test chart does not agree well with the Pelli–Robson chart. It appears that this is due to the performance of the Test Chart screen at low contrast levels (CS better than 1.70 log units). Contrast sensitivity measured with the Mars chart agrees moderately well with that measured with the Pelli–Robson chart.
Keywords: contrast sensitivity • low vision