The effect of different monovision contact lens powers on the visual function of emmetropic presbyopic patients (an American Ophthalmological Society thesis).

PURPOSE: To evaluate the effects of three increasing powers of monovision contact lenses on both objective and subjective vision in emmetropic presbyopic patients.

METHODS: A prospective single-center study was conducted on 50 emmetropic presbyopic patients with a mean age of 55.4 +/- 4.3 years (range, 50 to 66). Each patient wore for 1 week a +0.75 D, +1.50 D, and +2.50 D contact lens in the nondominant eye. Objective testing after each week included near and distance visual acuity, distance stereopsis, distance contrast sensitivity, and measurement with two different aberrometers of spherical equivalent, defocus, spherical aberration, and total higher-order aberrations. Subjective testing included questionnaire responses regarding vision under various conditions after 1 week with each lens power. Statistical tests were performed to determine significant differences from pretreatment.

RESULTS: Binocularly, mean uncorrected near visual acuity increased in both eyes (P < .01) with each increase in contact lens power. Monocular distance vision decreased significantly with each increasing lens power, but binocular distance vision remained unchanged from pretreatment. Distance stereopsis decreased significantly with increasing contact lens powers (P < .01 with the +2.50 D lens power). Photopic and mesopic distance contrast sensitivity decreased significantly with progressive increase in power. Wavefront analysis showed a change in defocus in the myopic direction, but no increase in higher-order aberrations.

CONCLUSIONS: In emmetropic presbyopes, near vision improved with increased lens power, but distance vision was degraded objectively and subjectively. The +1.50 D power provided optimal near and distance vision for monovision contact lens wear, as measured by a patient questionnaire and a series of eight tests for evaluating various aspects of visual function. The objective and subjective tests used in this study will provide a baseline for evaluation of surgical procedures performed for near vision enhancement.