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Experimental myopia in a diurnal mammal (Sciurus carolinensis) with no accommodative ability
1. We examined the functional morphology of the intra-ocular muscles of the grey squirrel using pharmacological and histological methods. Using sympathomimetic (phenylephrine) and parasympathomimetic (carbachol) agents, administered by transcorneal iontophoresis, the response of the iris sphincter a...
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Published in: | The Journal of physiology 1993-09, Vol.469 (1), p.427-441 |
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Main Authors: | , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that cite this one |
Online Access: | Get full text |
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Summary: | 1. We examined the functional morphology of the intra-ocular muscles of the grey squirrel using pharmacological and histological
methods. Using sympathomimetic (phenylephrine) and parasympathomimetic (carbachol) agents, administered by transcorneal iontophoresis,
the response of the iris sphincter and dilator muscles and the ciliary muscle were recorded. Measurement techniques included
both streak retinoscopy and coincidence optometry for measurement of ocular refraction and high resolution ultrasonography
to monitor changes in the intra-ocular component dimensions. 2. The grey squirrel was found not to possess a functional accommodative
system. No change in ocular refraction or intra-ocular dimensions could be induced with 40% carbachol. Marked changes in pupil
diameter occurred with topical application of both phenylephrine (dilation) and carbachol (constriction). Histological findings
were in agreement with pharmacological findings in showing well developed iris sphincter and dilator muscles but only a poorly
developed ciliary muscle. 3. Calculation of the depth of focus of the grey squirrel eye reveals that this could be sufficient
to account for the behavioural observations of near viewing habits. 4. We then determined whether we could induce axial elongation
of the vitreous chamber and a consequent myopia by monocular deprivation (MD) of pattern vision. 5. Monocular deprivation
of pattern vision produced a significant experimental myopia due to axial elongation of the vitreous chamber in the deprived
eye. 6. The results demonstrate that a functional accommodative system is not necessary to induce experimental myopia in the
grey squirrel eye. |
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ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1113/jphysiol.1993.sp019821 |