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Parameters of accommodative and vergence systems and the development of late-onset myopia
1College of Optometry, University of Houston, TX 77204-6052, USA.
Purpose:
To evaluate whether the characteristics of the oculomotor system are related to the development of late-onset myopia.
Methods:
Forty-four college students were followed for 2 to 3 years. When recruited, 33 of the 44 subjects had emmetropia whereas the remainder (N = 11) had late-onset myopia (LOM). For each subject, dark-focus, dark-vergence, response AC/A, and CA/C ratios, and manifest refraction were measured at 6-month intervals.
Results:
The mean dark-focus and AC/A ratios for the subjects (N = 6) who started with emmetropia and became myopic were higher than for the subjects (N = 25) who remained emmetropic. These higher values presented before the refractions exceeded -0.50 D. Interestingly, 7 of 11 subjects with LOM whose myopia increased displayed higher mean AC/A and dark-vergence values and lower mean dark-focus values than the subjects who remained emmetropic.
Conclusion:
The lower dark-focus values found among subjects with LOM seems to be a consequence of the development of myopia. However, myopia might eventually develop in a person with emmetropia with a relatively high AC/A and/or dark-focus values. Therefore, AC/A and dark-focus values may be predictors of the development of myopia.