ONE OF MY favorite types of corneal GP lens fits is when we refit a patient with aspheric multifocal (MF) GPs, especially if the patient has just begun to need reading glasses. Although this type of lens is typically straightforward to fit, there are some design details to understand that can increase your success with these lenses.

ADD LOCATION MATTERS

MF GPs can have the aspheric curve (which creates the add power) on the front, back, or both surfaces. My general preference is to use a front-surface aspheric. This makes the back surface spherical, which makes the lens fit and move on the eye like a standard GP. This is particularly helpful when the patient is changing from a distance-only lens, because there isn’t much to change about the base curve, diameter, etc. Sometimes a back-surface aspheric can help to force a contact lens to center better, and higher adds can be generated with asphericity on both surfaces; however, my general preference is to use a front-surface aspheric.

ZONE SIZE MATTERS

Changing the add zone size of a MF contact lens can really tailor it to the patient’s needs. Since corneal GP designs are usually distance-center, the impact of the add can be changed by altering the size of the center distance zone. A smaller zone will move the add power closer into the pupil, enhancing the MF effect, or it can be made larger to improve distance vision.

A common mistake is to overly increase the add power itself when a patient has a near-vision problem. In reality, the distance zone is likely too large. If the near over-refraction suggests a much higher add than the spectacles, think about using a smaller distance zone instead.

LENS POSITIONING MATTERS

Aspheric MF GPs do not depend on translation (vertical movement) for their add effect, but they do benefit some from it. In general, the GP lens should center vertically in straight-ahead gaze for the best distance vision (Figure 1). The patient is looking through aspheric optics, so they do get the MF effect if the lens still centers while doing near tasks. However, the lens will often translate upward a little when the patient looks down for near tasks, moving the more-plus periphery over the pupil and boosting the add effect.

Thinking back to zone sizes, zone size may need to be tailored to how the contact lens positions. If it is more lid-attached than centered, a larger distance zone may be needed to prevent the patient from always looking through the peripheral add zone.

WRAP-UP

The tips in this article should help practitioners understand why the fitting guide may make certain recommendations for troubleshooting. It should also make discussing changes with the lab consultant more helpful. Aspheric GP MFs are a fantastic optical choice for presbyopes, and they don’t need to be intimidating for the fitter. CLS