Competing defocus stimuli of opposite sign produce opposite effects in eyes with intact and sectioned optic nerves in the chick
Wildsoet, Christine F. & Collins, Michael J. (2000) Competing defocus stimuli of opposite sign produce opposite effects in eyes with intact and sectioned optic nerves in the chick. Investigative Ophthalmology and Visual Science, 41, S738.
Purpose: Experimental studies of refractive development have traditionally used single focus lenses which are worn continuously. While such studies provide convincing evidence that ocular growth is sensitive to defocus, they only poorly simulate the dynamic state of natural viewing conditions. Here we made use of a novel lens design to create a dynamic defocus situation. Methods: Multifocal lenses were used to present competing defocus stimuli of opposite sign: power combinations of (i) +10/-10, (ii) +5/-10, (iii) +10/-5D were presented in alternate 0.5mm wide rings across the 12mm total lens diameter. The average defocus for the 3 lenses were 0, -2.5 and +2.5D respectively. The lenses were fitted monocularly to 1 week old chicks which were measured after 1 week. For some of the chicks, the lens-treated eyes underwent optic nerve section (ONS) 5 days earlier. Results: Chicks with intact optic nerves consistently showed a hyperopic bias (interocular difference means, SDs: (i) +8.41, 1.96D; (ii) +4.20, 1.72D; (iii) +7.70, 0.27D) although from average defocus data this bias is predicted for only one lens (+10/-5D). In contrast, ONS chicks showed myopic biases (means, SDs: (i) -2.79, 7.87D; (ii) -5.86, 7.36D; (iii) -1.09, 5.82D and the total changes in these eyes over the lens-wearing period are even larger (means: -6.88, -9.61, -4.71D respectively) because these eyes were initially more hyperopic than normal. The ONS data also showed increased scatter. Interocular differences in refraction correlated well with differences in vitreous chamber depth and choroidal thickness differences (p<0.05), except for the ONS group and the choroid where the poor correlation reflects the limited capacity of the choroid to thin in eyes becoming myopic. Conclusions: That normal eyes became hyperopic rather than myopic with the lenses rules out form deprivation due to poor vision as an explanation. These results imply that myopic defocus effects are more robust. That ONS eyes exhibited myopic rather than hyperopic changes suggests that accommodation is required to distinguish between myopic and hyperopic defocus.
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|Item Type:||Journal Article|
|Additional Information:||For more information, please refer to the journal’s website (see hypertext link) or contact the author.|
|Subjects:||Australian and New Zealand Standard Research Classification > MEDICAL AND HEALTH SCIENCES (110000) > OPTOMETRY AND OPHTHALMOLOGY (111300)|
Australian and New Zealand Standard Research Classification > MEDICAL AND HEALTH SCIENCES (110000) > OPTOMETRY AND OPHTHALMOLOGY (111300) > Vision Science (111303)
Australian and New Zealand Standard Research Classification > MEDICAL AND HEALTH SCIENCES (110000) > OPTOMETRY AND OPHTHALMOLOGY (111300) > Optical Technology (111302)
|Divisions:||Current > Research Centres > Centre for Health Research|
Current > QUT Faculties and Divisions > Faculty of Health
Current > Institutes > Institute of Health and Biomedical Innovation
|Copyright Owner:||Copyright 2000 Association for Research in Vision and Ophthalmology|
|Deposited On:||25 Jan 2008|
|Last Modified:||22 Apr 2010 01:58|
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