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The susceptible period for deprivation-induced myopia in tree shrew
1Department of Physiological Optics, School of Optometry, University of Alabama at Birmingham, AL 35294-4390, USA. jsiegwart@icare.opt.uab.edu
Insights
The juvenile tree shrew eye is most susceptible to myopia development from deprivation between 15 and 45 days after opening. Recovery from this induced myopia is complete within 48 days of normal binocular vision.
Area of Science:
- Ophthalmology
- Developmental Biology
- Animal Models
Background:
- Myopia, or nearsightedness, is a significant global health concern.
- Understanding the developmental periods susceptible to myopia induction is crucial for prevention strategies.
- Animal models are essential for studying the complex mechanisms of eye growth and refractive error development.
Purpose of the Study:
- To determine the susceptible period for deprivation-induced myopia in tree shrews (Tupaia glis belangeri).
- To investigate the recovery process from myopia after removal of the visual stimulus.
- To explore potential changes in ocular structures like the choroid during myopia development and recovery.
Main Methods:
- Monocular deprivation for 12 days in tree shrew pups at various ages post-eye opening.
- Measurement of refractive error and axial length (vitreous chamber elongation).
- Assessment of recovery after occluder removal and subsequent binocular visual experience.
Main Results:
- Significant myopia and axial elongation were induced by monocular deprivation across all tested age groups.
- The peak susceptibility period for myopia induction was observed between 15 and 45 days post-eye opening.
- Complete recovery from deprivation-induced myopia occurred within 48 days of binocular visual experience, with reduced elongation rates in previously deprived eyes.
Conclusions:
- Visually guided emmetropization occurs in tree shrews during a developmental period analogous to human juvenile development.
- The juvenile phase, characterized by slower axial elongation, represents a critical window for myopia susceptibility.
- The findings suggest that the eye possesses mechanisms for correcting refractive errors induced by visual deprivation during development.
Abstract:
To examine the susceptible period for deprivation-induced myopia, six groups of tree shrew pups (Tupaia glis belangeri) were monocularly deprived for 12 days with an opaque occluder starting 7, 15, 21, 33, 48, or 63 days after natural eyelid opening. Compared to the untreated fellow control eye, significant myopia and vitreous chamber elongation were produced by the deprivation in all six groups. The effect was greater in the middle three groups in comparison with the youngest and the two oldest groups and the amount of induced myopia and axial elongation was not proportional to the normal rate of axial growth. The peak period of susceptibility was between approximately 15 and 45 days after eye opening during the juvenile, slow-elongation phase of ocular development when the eye is within 7% of its adult axial length. Significant myopia and axial elongation were also induced in adult animals by 70 days of monocular deprivation. To examine recovery from deprivation-induced myopia, the occluder was removed at the end of the 12 day deprivation period. After an additional 48 days of binocular visual experience, no significant myopia was present in the previously deprived eyes in any experimental group. During the recovery period, the elongation rate of the previously deprived eyes was reduced in comparison with the control eyes while normal corneal flattening and lens development continued, thus reducing the myopia. No difference in corneal curvature, relative to the untreated control eyes, was found after deprivation or after the recovery period. Data are presented which suggests that changes in the thickness of the choroid may occur in this mammal during deprivation and recovery that are in the same direction, but of smaller magnitude, than those reported in the chicken. The results of this study provide evidence that visually guided emmetropization occurs in this mammalian species during a period of ocular development analogous to the juvenile period in humans.