BLOG: We have two eyes for a reason: Binocularity in presbyopia correction
The conventional wisdom is that if a patient is already accustomed to monovision, either with contact lenses or as a result of prior laser vision correction, then it makes sense to replicate that with IOLs following cataract surgery. Our practice has evolved over the years to convert habitual monovision patients to binocularity where appropriate. Blended vision still has a place in our LASIK practice and in select refractive IOL patients; however, more and more our aim is to restore binocularity when possible.
My thinking on this was influenced by Dan Durrie’s American Ophthalmological Society thesis evaluating the effects of different levels of anisometropia in contact lens monovision. In this study, he identified a sweet spot for what would come to be termed “blended vision,” which is a refractive target of plano in the dominant eye and between –1.25 D to –1.5 D in the nondominant eye, or about half the amount of defocus in traditional monovision. Another important finding in this paper is that as little as 0.75 D difference between the eyes results in a statistically significant decrease in stereoacuity. Contrast sensitivity also declined with increases in anisometropia.
Although blended vision is an important tool in the refractive surgeon’s toolbox, diminished stereoacuity and contrast sensitivity can have an impact on functional vision, even when patients’ objective acuity is excellent. In Durrie’s paper, for example, patients subjectively reported that their ability to judge distances was increasingly impaired with larger amounts of anisometropia. As patients age, accurate perception of depth of field and three-dimensional spatial relationships are important considerations. With that said, we will utilize a blended vision approach in our laser vision patients and select IOL patients.
Increasingly, I am convinced that, given its role in overall visual performance, binocularity deserves prioritization in our refractive cataract surgical decision-making. In my habitual monovision patients (either prior laser vision correction or contact lens users), I recommend a binocular solution with a personalized vision approach with a combination of a Tecnis Symfony EDOF lens in the dominant eye with a mid-add diffractive bifocal such as the Tecnis multifocal +3.25 in the nondominant eye (both Johnson & Johnson Vision), or bilateral extended depth of focus IOLs, particularly in post-refractive patients or if toric correction is needed.
Either of these approaches gives patients the benefits of binocular summation, which we have long recognized can improve uncorrected visual acuity (at every distance) by about one line. With modern presbyopia-correcting IOLs, we can now give our habitual monovision clients back something that they have not had in years — full stereoacuity and what are likely the synergistic positive effects of binocular vision for uncorrected distance acuity, reading acuity and contrast sensitivity.
Durrie DS. Trans Am Ophthalmol Soc. 2006;104:366-401.
Disclosure: Waring reports he is a consultant for Johnson & Johnson Vision and a member of the Johnson & Johnson Vision Optics Advisory Board.