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Experimental myopia in a diurnal mammal (Sciurus carolinensis) with no accommodative ability
N A McBrien1, H O Moghaddam, R New
1Department of Optometry and Vision Sciences, University of Wales, College of Cardiff.
The Journal of Physiology
|September 1, 1993
Summary
Grey squirrels lack functional accommodation but have strong iris muscles. Monocular deprivation induced myopia, showing accommodation isn't needed for experimental myopia in their eyes.
Area of Science:
- Ophthalmology
- Animal Physiology
- Neuroscience
Background:
- The grey squirrel's visual system and accommodative capabilities are not fully understood.
- Investigating intra-ocular muscle function is key to understanding visual processes in mammals.
Purpose of the Study:
- To investigate the functional morphology of intra-ocular muscles in the grey squirrel.
- To determine the role of accommodation in myopia development in this species.
Main Methods:
- Pharmacological agents (phenylephrine, carbachol) and histological analysis were used to assess iris sphincter, dilator, and ciliary muscles.
- Streak retinoscopy, coincidence optometry, and high-resolution ultrasonography measured ocular refraction and intra-ocular dimensions.
- Monocular deprivation (MD) was employed to induce experimental myopia.
Main Results:
- Grey squirrels lack a functional accommodative system, evidenced by no refractive or dimensional changes with carbachol.
- Pharmacological agents caused significant pupil diameter changes, and histology confirmed well-developed iris muscles but a poorly developed ciliary muscle.
- Monocular deprivation of pattern vision led to significant experimental myopia through axial elongation of the vitreous chamber.
Conclusions:
- The grey squirrel's depth of focus may explain its near viewing habits.
- A functional accommodative system is not required to induce experimental myopia in the grey squirrel.
- These findings offer insights into myopia development and visual adaptations in non-human mammals.