Peripheral defocus does not necessarily affect central refractive development.
OBJECTIVE
Recent experiments in monkeys suggest that deprivation, imposed only in the periphery of the visual field, can induce foveal myopia. This raises the hypothesis that peripheral refractive errors imposed by the spectacle lens correction could influence foveal refractive development also in humans. We have tested this hypothesis in chicks.


METHODS
Chicks wore either full field spectacle lenses (+6.9 D/-7 D), or lenses with central holes of 4, 6, or 8mm diameter, for 4 days (n=6 for each group). Refractions were measured in the central visual field, and at -45 degrees (temporal) and +45 degrees (nasal), and axial lengths were measured by A-scan ultrasonography.


RESULTS
As previously described, full field lenses were largely compensated within 4 days (refraction changes with positive lenses: +4.69+/-1.73 D, negative lenses: -5.98+/-1.78 D, both p<0.001, Dunnett's test, to untreated controls). With holes in the center of the lenses, the central refraction remained emmetropic and there was not even a trend of a shift in refraction (all groups: p>0.5, Dunnetts test). At +/-45 degrees , the lenses were partially compensated despite the 4/6/8mm central holes; positive lenses: +2.63 / +1.44 / +0.43 D, negative lenses: -2.57 / -1.06 / +0.06 D.


CONCLUSIONS
There is extensive local compensation of imposed refractive errors in chickens. For the tested hole sizes, peripherally imposed defocus did not influence central refractive development. To alter central refractive development, the unobstructed part in the central visual field may have to be quite small (hole sizes smaller than 4mm, with the lenses at a vertex distance of 2-3mm).
Schippert
Ruth
R
Section of Neurobiology of the Eye, University Eye Hospital Tuebingen, Calwerstrasse 7/1, 72076 Tuebingen, Germany.
Schaeffel
Frank
F
D000065:Accommodation, Ocular / Q000502:physiology; D000818:Animals; D001699:Biometry; D002645:Chickens; D005123:Eye / Q000000981:diagnostic imaging / Q000473:pathology; D005139:Eyeglasses; D005584:Fovea Centralis / Q000254:growth & development*; D008297:Male; D009216:Myopia / Q000209:etiology / Q000503:physiopathology; D012029:Refraction, Ocular / Q000502:physiology; D012030:Refractive Errors / Q000209:etiology* / Q000503:physiopathology; D014463:Ultrasonography; D014794:Visual Fields / Q000502:physiology