Quantitative and functional influence of surround luminance on letter contrast sensitivity function

JUAN ANTONIO APARICIO; ISABEL ARRANZ; BEATRIZ MATEZANZ; JUAN VIZMANOS; L PADIERNA; V. GONZÁLES; JUAN MENÉNDEZ; SANTIAGO MAR; LUIS ISSOLIO

Ophthalmic and Physiological Optics

Blackwell Publishing

Año: 2010 vol. 30 p. 188 - 199

0275-5408

This work reports data on the influence of surround luminance on the letter contrast sensitivity function. A clinical study has been performed on 31 young and ocularly healthy individuals whose binocular contrast sensi¬tivities were measured with letters of sizes calculated to obtain the targeted fundamental frequencies of 3, 10, 20, and 30 c/deg respectively at a viewing distance of 5.2m and surround luminances from 1 to 1000 cd/m2 always with a luminance test chart background of 200 cd/m2. Results revealed that letter contrast sensitivity increases with surround luminance up to 100 cd/m2 and decreases when surround luminance increases from 100 to 1000 cd/m2. These increments are higher for greater fundamental spatial frequencies while decrements are similar for all frequencies. To analyse pupil size influence, results were com¬pared with theoretical predictions obtained by combining different ocular MTFs with a typical neural function, being pupil size constriction the responsible for the letter contrast sensitivity increments and veiling luminance the responsible for the observed decrements. Other possible optical or neural factors that influence these values have also been discussed. As a final conclusion, letter contrast sensitivity function depends on surround luminance and this influence should be considered in future standardized directives.