In today’s modern contact lens practice, there are numerous contact lens options for patients who have presbyopia. Depending on the contact lens modality and the lens design chosen for an individual patient, the effective add that the patient receives may or may not meet his or her near vision needs. As patients mature in their presbyopia and require increasing amounts of plus in the add portion of the lens, there may be too much of a disruption to the distance vision for patients to successfully wear the contact lenses.
As this occurs, one potential troubleshooting technique is to break away from the traditional spectacle prescribing habits in which the add powers are identical in each eye. The rationale is to increase the add in only one eye in an effort to provide patients with enough add power to perform the near activities necessary yet not provide so much plus that it disrupts their distance vision. Depending on the lens design chosen, this recommendation of utilizing dissimilar adds between the eyes may even be in the manufacturers’ fitting guides. The question, though, is over which eye to place the increased add.
Generally, it is advocated to place the higher add over a patient’s nondominant eye. Some of the techniques used to determine ocular dominance include having patients first extend their arms and make a hole with their hands, then sight a letter on the Snellen chart through the hole; if you cover an eye and they can still see the letter through the hole made by their hands, they are looking through their dominant eye. If they can no longer see the letter, then it is the nondominant eye.
A similar technique is to have patients hold up their finger so that they see it pointing to a letter on the Snellen chart. If you cover an eye and they no longer see their finger pointing to the letter, the dominant eye is covered. If they still see their finger pointing to the letter, then the nondominant eye is covered.
These are simple and efficient ways to identify sighting dominance. However, what we really need to determine is over which eye patients will accept more plus.
Introduce Plus to Each Eye
Another method to determine over which eye patients will accept plus is to first optimally correct their distance vision with either single-vision contact lenses or their habitual spectacles. Then, while patients use both eyes to view a group of letters on the Snellen chart that are near the limit of their acuity, hold a loose trial lens of +1.25D or +1.50D over one eye at a time and ask what happens as you move the lens from one eye to the other. If patients report significantly worse vision in one eye versus the other, this is the eye over which you do not want to place the increased plus power (Figure 1).
A similar technique is to use the phoropter; after the final manifest refraction, toggle between the +1.50D retinoscopy lens.
Finalizing the Prescription
Once ocular dominance has been identified, patients can attempt to trial a lens with increased add power over the eye in which they seem to accept more plus. The goal is to improve their overall visual experience with contact lenses at near without overly sacrificing their distance vision. CLS