Background: Press-On Optics™ and OPTX 20/20™ removable bifocal segments were evaluated in three areas: optical quality, effects on vision, and stability under simulated environmental conditions.
Methods: OPTX 20/20™ segments -generate optical power using smooth front and back surfaces with differential radii; Press-On Optics™ segments use Fresnel groves. To evaluate optical quality of the segments, sphere, cylinder, and spherical equivalent powers were measured in center, right, and left portions of 10 segments of each type with powers of + 1.00, + 1.50, +2.00 and +2.50 D. A Data Optics Ann Arbor Distortion Tester was used to grade optical distortion in the central portion of each segment and across the entire segment. To evaluate the effects on vision, monocular near visual acuity and contrast sensitivity were measured while 23 subjects wore +2.00 D Press-On Optics™, OPTX 20/20™, and molded CR-39 segments. To evaluate the effects of environmental conditions, plano CR- 39 carriers with mounted segments were heated to 140° F (60° C), cooled to oo F (-18° C), subjected to a water stream, and exposed to intense light.
ResuIts: With regard to optical characteristics of the segments, 12 out of 20 OPTX 20/20™ segments and 6 out of 20 Press-On Optics + 1.00 and + 1.50 D segments failed to pass ANSI ophthalmic lens standards because of unwanted cylinder powers of -0.25 to -0.50 D. Marked powers of the OPTX 20/20™ segments were significantly more accurate than those of the Press-On Optics™ segments. OPTX 20/20™ segments produced substantial distortion near their upper edges, but the implications of this distortion for wearability are unknown. In their central portions, higher power OPTX 20/20™ segments typically produced less distortion and had better optical characteristics than did the Press-On Optics™ segments. With regard to vision, +2.00 D OPTX 20/20™ segments provided a one Snellen line advantage in near acuity as compared to the Press-On Optics™ segments for a majority of subjects. Contrast sensitivity for low and mid-spatial frequencies was not significantly different for +2.00 0 OPTX 20/20™ or Press-On Optics TM segments. All of the segments retained their attachments to CR-39 carriers during heating, cooling, and water stream tests. Following prolonged exposure to intense light, optical transmission decreased by 7% for the OPTX 20/20™ segments and 2% for the Press-On Optics™ segments.
Conclusions: Both the OPTX 20/20™ and Press-On Optics™ segments have relative advantages and disadvantages. For higher powers, the optical characteristics of the OPTX 20/20™ segments are better and provide better visual acuity. For lower powers, distortion and small amounts of unwanted cylinder reduce the optical quality of the OPTX 20/20™ segments. It is unknown whether the cylinder and distortion are of sufficient magnitude to produce asthenopia if the segments were used for extensive near
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