A new edge contrast chart (60x60 cm) has been designed to use in a population study and for contrast sensitivity assessment in visually impaired people. The chart contains 16 circular test targets (diam. 8 cm), one half of each target has a lower reflectance than the other half and a sharp transition edge in between. Edge contrasts vary between 40 and 0.7% in steps of about 0.15 log units. Normal population data are collected at viewing distances of 6, 3, and 1 meter and at illumination levels of 65, 500, and 2000 lux. The GECKO contrast sensitivity scores of normal subjects are 0.25 log units lower than the maximal contrast sensitivity scores obtained with the Vistech VCTS 6500 wall chart (3 meter viewing distance); in visually impaired people with widely varying visual acuities and contrast sensitivities this difference is smaller (1 meter viewing distance). Disability glare has been measured as the loss of log (contrast sensitivity) caused by using the Mentor Brightness Acuity Tester (BAT) at the medium and high luminance settings in normal subjects. The GECKO chart in combination with the BAT is used in a population screening study and in a rehabilitation institute. Its use is easy to explain, both to the test leader and to the subjects. In visually impaired persons assessment of contrast sensitivity and disability glare is less tiring and much quicker to perform than a sine-wave modulated contrast sensitivity test and an intra-ocular straylight test. Subjects who could not see the targets of the Vistech chart (1 meter) or of the straylight test, succeeded in doing the GECKO-BAT test.
Samenvatting