Optotype Test Research Articles

Clinical assessment of contrast sensitivity

Visual system transfers information at both high and low contrastlevels. It has been customary to assess visual function by measuring visual acuity although it has been well documented for over ten years' time that measurement of contrast sensitivity may reveal loss of visual function that is not detected by measurement of visual acuity.There are several commercially available clinical tests that are used in Scandinavian countries for assessment of visual transfer function in low contrast domain. We have chosen six of them for comparison: Cambridge Low Contrast Gratings, Vistech's contrast sensitivity tests for distance and near, PelliåRobson's low contrast letter chart, Vistest's LH‐5 contrast visual acuity test, and Mentor's computer based device for measurement of both contrast sensitivity and low contrast visual acuity.Each of the commercial tests measures low contrast vision in slightly different way. In order to have an overview of the function of these tests we have assessed vision of visually impaired patients and normally sighted subjects using all tests during one visit. In general the grating tests result inslightly higher contrast sensitivity values than the optotype tests. Contrast sensitivity values measured with grating tests are difficult to assess because the size of the stimulus affects the values.Based on our results, we recommend assessment of low contrast visual transfer using an optotype test as the basic test and a grating test in order to assess vision for orientation and mobility. The grating test should be used at two different distances resulting in approximately two and ten degree stimuli.

Contrast sensitivity in amblyopia. IV. Assessment of vision using vertical and horizontal gratings and optotypes at different contrast levels.

The contrast sensitivity of 49 amblyopic children (mean age 9 years) was measured in the beginning and at the end of a treatment period using both vertical gratings and optotypes (LH-4 contrast test) at 2, 3, 5 and 75% contrast. The contrast sensitivity of 37 patients was also measure using horizontal gratings. The contrast sensitivity of the dominant eyes measured with vertical gratings was generally higher than when measured with horizontal gratings. The difference was statistically significant at spatial frequencies 1 and 6 c/deg. A similar difference was present in the amblyopic eyes only at the spatial frequency 1 c/deg both before and after the treatment. Individual variation was great; in a given patient the relationship between the two measurements varied from one spatial frequency to the next. It has been shown in earlier investigations that contrast sensitivity measurements using gratings reveal important new information in the study of amblyopia. Both tests, used in this investigation, measure visual function in the low contrast domain and improve follow-up of the changes in vision during treatment of amblyopia when used in addition to visual acuity measurements. Low contrast optotype test seems to measure contrast sensitivity in amblyopia closely similarly to the grating test. The slight difference in detecting a 'hidden occlusion amblyopia' at the intermediate spatial frequencies needs further study.

Pre‐school visual acuity tests

A number of visual acuity tests are available for both the literate and the preliterate child. This paper compares the results obtained with five different visual acuity tests; Illiterate E, Landolt C, Bailey-Hall Cereal test, Lighthouse Flash Cards and Stycar Five Letter test, for 43 children between the ages of three and five years. The linear Illiterate E test appears to be the test of choice; it will detect amblyopia, and the results are not significantly different from those obtained for the single optotype tests. No significant differences were found between the results for the different single optotype tests used in this study. The Landolt C test results are significantly different from those for the other tests and we do not recommend this test for young children.