The optics of multifocal contact lenses are pretty complex. With the many combinations of center-near, center-distance, aspheric, and concentric designs, it can be hard to remember the design type with which you are working and what choices to make when the lens evaluation yields unexpected results.
First, the lens has to fit. Keep lens fitting basics in mind, and yes, that includes soft frequent replacement lenses. Larger corneas need larger-diameter and often deeper (in sagittal depth) soft lenses, whereas smaller corneas need smaller diameters and usually shallower lenses. If a soft lens is decentered, it is unlikely that the optics will have a chance to line up with a patient’s line of sight.
Loose lenses are essential in multifocal over-refractions to enhance binocularity and to maintain pupil size. Consider using the phoropter only when needing to determine whether residual astigmatism is limiting a lens’ performance. My initial goal in fitting multifocal lenses is to get patients to a point at which they feel comfortable driving so that they can actually wear the lenses and allow some adaptation to occur. Through adaptation, vision improves at both distances the more that patients wear their lenses, and fine tuning at near can be done at a follow-up visit.
The Dominant Eye
Upon applying the lens, first allow the reflex tearing to decrease and initial lens movement to settle down. Next, attempt to clear distance vision in the dominant eye by working through the following steps:
- Rule out over-minus. With both eyes open, present a small amount of plus to the dominant eye first. You’d be surprised at how often a little (or more) plus is accepted, which goes a long way in improving near vision.
- If no plus is accepted and a patient’s acuity needs improvement, present a small amount of minus to the dominant eye. If vision is then acceptable, update the lens power.
- If a significant amount of minus is needed to improve acuity, consider trying another lens design, especially if the amount of minus essentially negates the add power in the lens. This finding could mean that a patient isn’t able to use the distance power in the lens and is looking through mostly near optics. In a custom lens, practitioners can change zone size and add power; in a mass-produced lens, however, they may need to select a lens design that has a smaller add zone to allow for adequate distance vision.
- Lastly, a single-vision distance lens may be needed if multiple multifocal designs are unsuccessful.
The Nondominant Eye
Use these steps to determine best distance power and design selection. When sticking with the same lens design, move to the nondominant eye assessment:
- Again, present plus at distance to rule out being over-minused. If plus is accepted or it does not seem to affect vision quality, show a little more plus, and adjust lens power based on over-refraction.
- Once the most plus is determined (i.e., the most comfortable distance vision), assess near, aiming for about 20/40 or better on a reduced Snellen chart. If patients are there, educate them on a great first visit and schedule a follow-up visit.
- If plus is not accepted and better near acuity is needed, increase the add power of the lens in the nondominant eye.
The key to success with multifocals is confidence in lens selection, patience during the initial process, and allowing the lenses to go to work through the process of patient education and adaptation. CLS