G. van Tiel, and W.J.M. van Damme

de Blauwe Kamer Theofaan Group,
Nijmegen,
The Netherlands

Existing methods of assessment of visual acuity use optotypes in a standard luminance condition (for example the projector at 6m which gives about 400 cd /m2). Visual impaired people prefer different (often higher) lighting conditions, so the assesment of visual acuity often occurs at sub-optimal lighting levels. To give an optimal advice with respect to low-vision devices however, it is necessary to know the visual acuity at optimal lighting conditions. How valid is the assessment of visual acuity of visually impaired people using the standard procedures for normally sighted people?

We used a standard EDTRS chart illuminated from behind by 9 fluorescence tubes of 18W each and variabele luminance conditions (up to 4500 cd/m2). For comparison, a halogene-lamp, 200W placed at 2m of the chart leads to 600 cd/m2. Commercially available cabinets are restricted to about 1000 cd/m2. We measured visual acuity with the high-luminance chart and with the standard method at 6m with the projector for a number of clients at the low-vision institute in Nijmegen.

We present results and comparisons with the two methods of assessment and indicate the advantages and disadvantages of using this method as a standard procedure in low-vision practice.