Imposed retinal image size changes--do they provide a cue to the sign of lens-induced defocus in chick?

Schmid, Katrina L., Strang, Niall C., & Wildsoet, Christine F. (1999) Imposed retinal image size changes--do they provide a cue to the sign of lens-induced defocus in chick? Optometry and Vision Science, 76(5), pp. 320-325.


BACKGROUND: Young chicks can adjust their eye growth to compensate for both imposed hyperopia and myopia (using negative and positive spectacle lenses); the rate of eye elongation increases in the former and slows in the latter case. This emmetropizing behavior implies that the eye can distinguish the sign and magnitude of defocus, although the identity of the cue(s) involved is unknown. As the spectacle lenses used in these studies generally introduce significant retinal image size differences that are in opposite directions for negative and positive lenses (minification vs. magnification), we asked whether retinal image size might provide the required sign information. METHODS: This question was addressed by manipulating retinal image size while keeping lens power constant. We also investigated the effect of eliminating other potential cues, accommodation and chromatic aberration, under these conditions. Three negative "size" lenses of approximately -11 D optical power were used, with 2 of the lenses producing magnification rather than minification as typical of negative lenses (i.e. +1.9% and +6.9% compared to -2.9%). The lenses were fitted monocularly to 7-day-old chicks, which were subsequently measured at 9 and 11 days of age (refractive error and axial dimensions). The same lens-wearing schedule was applied to two other groups of chicks that had monocular ciliary nerve section surgery to prevent accommodation 2 days posthatching; one of these groups was reared under monochromatic yellow light instead of white light. RESULTS: Near-perfect refractive compensation was seen by the end of the treatment period with all three lenses, for all three treatment groups, and there was also little difference in the rate of compensation among the various groups. In all cases, the typical responses of axial (mainly vitreous chamber) elongation and myopia were observed. CONCLUSIONS: That manipulations to retinal image size, which either decrease or reverse the usual effects of negative lenses, did not disrupt compensation to the imposed hyperopic defocus, even in the absence of accommodation and chromatic aberration cues, argues against imposed retinal image size changes being the directional cue to defocus in experimental emmetropization.

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12 citations in Web of Science®
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ID Code: 4190
Item Type: Journal Article
Refereed: Yes
Additional Information: The contents of this journal can be freely accessed online via the journal's web page (see link) 12 months after publication. For more information, please refer to the journal’s website (see link) or contact the author. Author contact details:
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Keywords: Fixation, Ocular/, physiology, Refractive Errors/, physiopathology, Retina/, physiopathology, Accommodation, Ocular, Animals, Animals, Newborn, Chickens, Comparative Study, Contact Lenses/adverse effects, Disease Models, Animal, Male, Photic Stimulation, Refraction, Ocular, Refractive Errors/etiology, Research Support, Non, U, S, Gov't
ISSN: 1538-9235
Subjects: Australian and New Zealand Standard Research Classification > MEDICAL AND HEALTH SCIENCES (110000) > OPTOMETRY AND OPHTHALMOLOGY (111300)
Divisions: Current > QUT Faculties and Divisions > Faculty of Health
Current > Institutes > Institute of Health and Biomedical Innovation
Copyright Owner: Copyright 1999 Lippincott, Williams and Wilkins
Deposited On: 15 Jun 2006 00:00
Last Modified: 10 Aug 2011 17:39

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