Extreme anisometropic pseudophakic monovision treats cataracts, diplopia

Robert H. Osher, MD, reports his experience in intentionally creating extreme pseudophakic monovision in patients with stable diplopia undergoing cataract surgery. All 12 patients showed improved unaided distance and near vision while eliminating or reducing awareness of pre-existing diplopia. Dr. Osher and his co-authors recommend further studies in order to confirm that this new surgical approach is a worthwhile option for patients with bilateral cataracts and symptomatic diplopia secondary to longstanding acquired strabismus.

All patients were 62 years or older, with longstanding diplopia secondary to a stable ocular misalignment. IOL selection was targeted for emmetropia in one eye and at least 3.0 D of myopia in the fellow eye.

In nine of the patients, a myopic defocus of at least 3.0 D was achieved, which resolved pre-existing diplopia. In the remaining three patients, in whom the achieved myopic defocus was between -2.0 D and -3.0 D, diplopia symptoms were diminished but occasionally evident. All patients achieved excellent UDVA and UNVA, and none reported being dissatisfied.

The authors note that accurate biometry and keratometry along with a high confidence in IOL formula interpretation are desirable in achieving the refractive target. Because lower degrees of anisometropia may yield the advantage of traditional monovision and the retention of some degree of fusion, it is necessary to accurately create extreme anisometropia to completely eliminate pre-existing diplopia. They say that when selecting the IOL, it is prudent to aim for a greater rather than lesser disparity in refractive error between eyes.

Controlling astigmatism is essential to the success of the procedure because it is necessary to achieve unaided vision in each eye. The authors theoretically could place the cylindrical correction by itself (no sphere) in the patient's glasses; however, their goal has been to achieve spectacle freedom. They have tried to reduce pre-existing astigmatism by modifying the incision location, performing limbal relaxing incisions or astigmatic keratotomy, and more recently, by implanting toric IOLs. They say that removing the cataract through a small incision is the best prophylaxis against surgically-induced astigmatism.