GP MULTIFOCALS can be a great option for presbyopes, whether a corneal, hybrid, or scleral design is chosen. In particular, they offer crisp optics and can be a better alternative for pickier or higher astigmats bothered by rotation-induced reduction in acuity with soft toric designs.
Corneal multifocal lenses come in a lined-bifocal (translating) style and in aspheric designs (simultaneous vision). Aspheric lenses can have the aspheric (add-generating) surface on the front or the back of the lens (or both). Front-surface aspherics are probably the most straightforward to fit, as the base curve selection and fitting process is nearly the same as for single-vision lenses. Back-surface aspherics also work well and typically lid attach less and center better.
CASE EXAMPLE
A patient had worn corneal GP lenses since her teens. Now, in her mid-40s, she needed reading help. This solution is usually an easy transition into a front-surface aspheric. A potential complicating factor in this case was that her habitual lens had a fairly high position, which could present a problem with getting best distance vision with an aspheric multifocal. The first multifocal was fit about 0.1mm steeper than her habitual lens to try to avoid centration issues.
Figure 1 shows the appearance of the first lens, with the lens position still a little too high. The patient noted that distance vision suffered a bit, but she was very happy with her near vision. Distance VA varied between 20/20 and 20/40, depending on where the lenses were positioned, and near acuity was easily achieved to a 4pt font. Distance was very clear when she used her lids to push the lenses to a more central position, but her vision was too variable with normal blinking.
What options could improve this situation? The issue is that the patient was looking through the more plus-powered midperiphery and wasn’t getting the full minus central power of the lens for distance. A quick over-refraction of –0.50D over each eye improved distance vision but did not adversely affect near viewing, so lenses were reordered with this change.
If this does not prove sufficient, the next option would be to try to move the lens more centrally, such as by steepening the lens more, increasing the diameter, or changing to a back-surface aspheric. Increasing the size of the distance zone could also help to move the start of the near power zone a bit farther peripherally.
GP multifocals are typically very straightforward to fit, and each manufacturer has a fitting guide with fitting steps and troubleshooting pearls. Aspheric designs can often be fit empirically, and your lab consultant can guide you throughout the fitting process. Consider one of these designs for your next patient with particular vision needs.
