To evaluate near stereoacuity
(SA) with Focus Progressives and PureVision Multifocal simultaneous vision
In a cross-over study design, 20 presbyopic subjects were fitted with either the Focus Progressives or PureVision Multifocal lenses. After 1 month, SA was measured with the vectographic Titmus, Random dot stereotests, and the Howard-Dolman apparatus under photopic conditions (85 lux) at 40 cm. Binocular high-contrast visual acuity at distance and near was examined. Subjects were then refitted with the alternative correction and the procedure was repeated.
Mean SA with the Focus Progressive was 21 ± 7 sec arc, 54 ± 17 sec arc, and 51 ± 21 sec arc, with the Howard-Dolman, Titmus, and Random dot sterereotests, respectively. These values were 25 ± 9 sec arc, 74 ± 26 sec arc, and 82 ± 26 sec arc with the PureVision Multifocal, respectively. SA was better with the Focus Progressives compared with the PureVision using the Howard-Dolman (4 sec arc of difference; p = 0.001), Titmus (2 sec arc of difference; p = 0.001), and Random dot (31 sec arc of difference; p < 0.001) tests. Binocular mean high-contrast distance visual acuity was similar for the Focus Progressives and PureVision Multifocal: −0.01 ± 0.07 and +0.02 ± 0.08 logMAR, respectively (p = 0.074). At near vision, these values were +0.01 ± 0.07 and +0.06 ± 0.06 logMAR, respectively, being statistically significant different (p = 0.004).
Both the Focus Progressive and PureVision Multifocal contact lenses provided good visual acuity preserving stereopsis. Focus Progressives had slightly better near acuity and better SA than the Purevision Multifocal contact lenses. Differences found between the lens types may be related to asphericity, near addition of the contact lens, or even visual acuity differences between the two eyes that were not measured in this study but could conceivably have contributed to SA measure differences. SA measurement with a Howard-Dolman apparatus reveals better SA than vectographic tests.