Accommodation and the Stiles-Crawford effect: theory and a case study.
OBJECTIVE
Fincham (The accommodation reflex and its stimulus. Br. J. Ophthalmol. 35, 381-393) was the first to suggest that the Stiles-Crawford effect (Type I) might provide a stimulus for accommodation, but the possibility has not been investigated experimentally. The present paper outlines a theoretical basis for such a mechanism, and includes a case study on a subject with a nasally decentred Stiles-Crawford (S-C) function.


METHODS
Accommodation to a monochromatic sine grating was monitored continuously with the natural S-C function intact, or with apodising filters imaged in the subject's pupil to neutralise, reverse or double the natural S-C function.


RESULTS
Mean accommodative gain was not reduced significantly when the normal S-C function was either neutralised or reversed.


CONCLUSIONS
For the present subject, the average S-C effect does not mediate the accommodation response to defocus, but more subjects should be examined. Other methods by which directionally sensitive cone receptors could detect light vergence are discussed.
Kruger
P B
PB
Schnurmacher Institute for Vision Research, State College of Optometry, State University of New York, NY 10036, USA. pkxx@aol.com
López-Gil
N
N
Stark
L R
LR
D000065:Accommodation, Ocular / Q000502:physiology*; D000328:Adult; D005246:Feedback; D005584:Fovea Centralis / Q000502:physiology; D006801:Humans; D008297:Male; D008954:Models, Biological; D011601:Psychophysics; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology