Quantitative and functional influence of surround luminance on the letter contrast sensitivity function.
OBJECTIVE
To determine the influence of surround luminance on the letter contrast sensitivity function.


METHODS
The binocular contrast sensitivities of 31 young and ocularly healthy individuals were measured with letters of sizes calculated to obtain the targeted fundamental frequencies of 3, 10, 20, and 30 c deg(-1), respectively; with surround luminances from 1 to 1000 cd m(-2), always with a test chart background luminance of 200 cd m(-2).


RESULTS
The letter contrast sensitivity increased with surround luminance up to 100 cd m(-2) and decreased when surround luminance increased from 100 to 1000 cd m(-2). These increments are larger for higher fundamental spatial frequencies, while decrements are similar for all frequencies. To analyse pupil size influence, results were compared with theoretical predictions obtained by combining different ocular MTFs with a typical neural function, where pupil size decrease leads to letter contrast sensitivity increments and veiling luminance causes the observed decrements. Other possible optical or neural factors that influence these values have also been considered.


CONCLUSIONS
Letter contrast sensitivity function depends on surround luminance and this influence should be considered in future standardized directives.
Aparicio
Juan A
JA
Departamento de Optica, Universidad de Valladolid, P. Prado de la Magdalena s/n, Valladolid, Spain. apa@opt.uva.es
Arranz
Isabel
I
Matesanz
Beatriz M
BM
Vizmanos
Juan G
JG
Padierna
Lidia
L
González
Víctor R
VR
Mar
Santiago
S
Menéndez
José A
JA
Issolio
Luis
L
D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology*; D005260:Female; D006801:Humans; D008029:Lighting; D008297:Male; D011680:Pupil; D014787:Vision Tests; D015348:Vision, Binocular / Q000502:physiology; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult