| Abstract |
It is generally recognized that the «aspheric» multifocal design, although it improves depth-of-focus and the range of functional vision compared to uncorrected vision, often results to reduced, compared with best spectacle-correction, visual acuity (VA) for both near and distance.
Aim: The aim of this study is to evaluate the visual performance of multifocal CLs by measuring the visual acuity in different levels of defocus (0 D – 3 D), and estimate the depth of focus in different artificial pupils (3 and 6mm) with monocular/binocular observation.
Method: The protocol included 12 young and healthy (Average age: 27 years, S.D: 5 years) emmetropes or myopes with no history of any ophthalmological disorder or ocular surgery e.g. refractive surgery. The average refractive error in the form of spherical equivalent of the dominant eye was -2.24 D ± 2.22 D. Presbyopia is simulated with the use of cycloplegic drops (CYCLOGYL 1%). In order to assess the effect of “simultaneous vision” on these tests, different levels of “multifocality” are applied. This was achieved by using the three designs of Aqua multifocal CLs, each having a different power distribution profile that provides correction for low (LO ADD), medium (MED ADD) and high (HI ADD) near demands, correspondingly.
High Order Aberrations were measured by using the topographer-aberrometer, i-Trace by TRACEY. The estimations refer to a 6mm pupil diameter without CL correction.
Distant binocular and monocular visual acuity (4m) was recorded with best-spectacle distance correction (if needed), during the progressive increase of the defocus by using logMAR charts (Plainis et al., 2007). Two different artificial pupils (of 3mm and 6mm) were used.
Binocular subjective depth-of-focus for near and distance testing was estimated by “defocus curves”. This was performed with the use of minus lenses (0.00 D- 3.00 D in 0.50 D steps), placed in front of the best-spectacle distance correction + CL. A criterion of functional vision has been set for this purpose (0.10 logMAR acuity).
Results: Depth of focus is greater through the binocular viewing in any case. It also appears that the depth of focus is increased by the use of the 3mm pupil compared to the 6mm pupil. An analysis of variance (ANOVA) on these data reveals a significant effect (p< 0.001) of viewing condition (monocular- binocular). Moreover, it is appeared a statistically significant effect (p=0.002) of the artificial pupil diameter and the refractive power of any contact lens that was used in this study (p=0.002). However, there was no statistically significant effect of the combination of all factors that has been mentioned earlier (p = 0.881).
7
The mean (±S.E.) depth of focus of the “naked” eye, created by using a 3mm artificial pupil was 1.55 D ± 0.22 D and 1.76 D ± 0.22 D through the monocular and binocular viewing, respectively. Similarly, the average depth of focus during the application of the LO ADD contact lens was 1.60 D ± 0.23 D and 1.86 D ± 0.22 D, respectively. The average depth of focus during the application of the MED ADD contact lens was 2.03 D ± 0.25 D and 2.40 D ± 0.23 D, respectively. The average depth of focus during the application of the HI ADD contact lens was 2.42 D ± 0.28 D and 2.66 D ± 0.27 D respectively. However, the average depth of focus of the “naked” eye by using a 6mm artificial pupil during monocular observation seemed to be 1.30 D ± 0.23 D, while binocular observation was 1.60 D ± 0.24 D. The average depth of focus by using the LO ADD contact lens was 1.41 D ± 0.24 D and 1.71 D ± 0.25 D, respectively. Similarly, the average depth of focus during the application of the MED ADD contact lens was 1.71 D ± 0.28 D and 2.39 D ± 0.26 D. The average depth of focus by applying the HI ADD contact lens was 2.19 D ± 0.29 D and 2.57 D ± 0.24 D, respectively.
The average depth of focus created by using “positive” lenses and a 3mm artificial pupil, without the application of a contact lens was 0.96 D ± 0.14 D and 1.37 D ± 0.17 D, through the monocular and binocular observation, respectively. Correspondingly, the average depth of focus, in 6mm artificial pupil, during monocular observation without the application of contact lens was 0.76 D ± 0.43 D, while the binocular observation was 1.05 D ± 0.45 D.
The mean spherical aberration calculated for the dominant eye, was equal to 0.073 ± 0.041κm, while the binocular observation (mean spherical aberration of both eyes) resulted to 0.072 ± 0.038 κm.
Conclusions: In this study it was observed that both VA at near and depth-of-focus improve with MFCLs (LO, MED and HI ADD design) with the effect being more pronounced for small pupils and binocular compared to monocular vision. Coupling of ocular spherical aberration with the aberration profiles provided by MFCLs possibly contributes to their functionality.
|
Search
