SOFT MULTIFOCAL CONTACT LENS FITTING

Introduction

The essential optics of center-distance (CD) multifocal soft contact lenses, used to correct presbyopia or control myopia, are often misaligned with a patient’s visual axis, thereby reducing visual quality. This study compares two of these CD multifocal lens designs: one with geometrically centered optics and one with offset optics. Centered optics indicates that the center of the multifocal optic is positioned at the midpoint of the overall lens diameter, equidistant from all points along the lens edge. In this study, offset optics are optics that have been repositioned over each subject’s visual axis. Both lenses were custom-made.

Custom Offset Optics

Thirty-four adults with myopia were fitted bilaterally with centered optics and then with offset optics in multifocal lenses sharing identical designs, differing only in optic location. The amount and direction of lens decentration from the visual axis were measured using corneal topography maps over a plano lens with geometrically centered optics. Figure 1 and Figure 2 present the topography scans for one subject’s right eye, displaying the centered optics lens and the offset optics lens, respectively. Visual performance, ocular aberrations, and subjective viewing questionnaires were recorded.

Figure 1. Topography scan of a GCO lens over the subject’s right eye (“+” indicates pupillary center, “✰” indicates visual axis).

Figure 2. Topography scan of an OFO lens over the subject’s right eye (“+” indicates pupillary center, “✰” indicates visual axis).

Offset Preference

Our findings suggest that the lathe-cut, prism-ballasted multifocal lenses with centered optics used in this study were decentered superior-temporally from the visual axis in both eyes (Figure 3). The anterior optics of the offset lens design are positioned closer to the subject’s visual axis, thereby lowering the optical aberration of coma, resulting in improved visual outcomes. As expected, spherical aberration increased with the offset lens however, it remained within an acceptable range (<0.3 µm). The offset lenses focus the distance and near optics in closer proximity to the center of the foveola, resulting in improved visual performance. There was a significant improvement in visual performance under glare conditions. Most of the subjects preferred the offset lenses over the geometrically centered lenses, with less physical discomfort. Figure 3. Amount of offset lens deviation for both right and left eyes of each subject. (A) shows the amount of deviation between two lenses in the right eye for all subjects. (B) shows the amount of deviation between the two lenses in the left eye for all subjects. The circle indicates the optic location of the GCO lens, while the arrow shows the final optic position of the OFO lens. Axis (0,0) represents the visual axis. Different colors are used to distinguish among subjects.

Conclusions

Multifocal lenses that incorporate offset optics (optics positioned over the visual axis) offer better optical alignment, reduced aberrations, and improved glare-related visual performance, making them more often preferred over lenses in which the optics are positioned at the geometric center. The results of this study indicate that customized offset multifocal optics significantly lowered ocular aberrations, enhanced vision clarity, and improved physical comfort. These changes may benefit patients who want presbyopia correction or myopia control management. Further work is needed to more precisely determine the amount and direction of offset required to position the complex multifocal optics over our patients’ visual axis or line-of-sight.

Figure 3. Amount of offset lens deviation for both right and left eyes of each subject. (A) shows the amount of deviation between two lenses in the right eye for all subjects. (B) shows the amount of deviation between the two lenses in the left eye for all subjects. The circle indicates the optic location of the GCO lens, while the arrow shows the final optic position of the OFO lens. Axis (0,0) represents the visual axis. Different colors are used to distinguish among subjects.

​