Myopia and contrast sensitivity function.

PURPOSE

to measure the contrast sensitivity function of varying degrees of myopia with two types of optical correction (spectacle lens and contact lens).

METHODS

One hundred and five myopic eyes and twenty-eight emmetropic eyes were collected. The myopic group included 105 eyes corrected with spectacle lenses and 71 eyes of them corrected with contact lenses, too; all had corrected vision acuity of 20/20 or better. The myopic eyes were divided into four groups: group 1 (-1D to -3D), low myopia; group 2 (-3.25D to -6D), medium myopia; group 3 (-6.25D to -12D), high myopia; and group 4 (> -12D), severe myopia. Spatial contrast sensitivity was measured using the OPTEC 2000 Contrast Sensitivity System.

RESULTS

In groups 1 and 2, no statistically significant difference was found between myopes and emmetropes. In group 3, statistically significant loss of contrast sensitivity at higher spatial frequencies was found for myopic subjects corrected with spectacle lens, but not for myopes corrected with contact lens. In group 4, myopic subjects corrected with spectacle lenses showed significantly reduced contrast sensitivity function at all spatial frequencies; subjects corrected with contact lenses showed statistical sensitivity losses at 6, 12, 18 cycle/degree spatial frequencies.

CONCLUSIONS

1. We may suppose that low and medium myopes (groups 1 and 2), who showed normal contrast sensitivity functions, had no retinal dysfunction. 2. For high myopes, contact lens correction could reduce optical defocus and improve contrast sensitivity function in high spatial frequencies. 3. As retinal function disturbances occurred in severe myopes, the diminished contrast sensitivity was not fully compensated by contact lens correction. 4. Loss of contrast sensitivity might be interpreted as evidence for early retinal function disruption before retinal pathological events occur in severe myopes.