FOR SOMEONE WHO constantly cares for keratoconic, transplanted, and otherwise diseased corneas in the medically necessary contact lens environment, people are often surprised to hear my claim that the hardest thing I do in clinical practice is multifocal contact lens prescribing for the presbyopic patient.
The project seems beguilingly simple—give the presbyopic patient a lens with multifocal optics so that they can see clearly at all distances. What could go wrong with that? In a word: everything.
Don’t get me wrong. The current batch of multifocal contact lenses is the best the market has ever had.
As all practitioners are painfully aware, the issue being solved with static lens powers is what the patient did dynamically through the process of accommodation. As the accommodative reserve declines, the depthfield becomes more important to providing clarity in the near environment. This is Optics 101. In fact, the realization of the importance of an extended depth of focus (EDOF) to seeing clearly at near compelled intraocular lens (IOL) designers to move away from the more exaggerated multifocal designs in favor of more subtle EDOF designs (Kanclerz et al, 2020).
The multifocal design splits the light rays into discrete bundles focused at different distances, while the EDOF lenses elongate the focal point to make seeing clearer across a wide distance easier. Several properties are associated with the EDOF concept. One of the most important is the pinhole effect. Another is the use of spherical aberration (Kanclerz et al, 2020).
The greater the distance for the nodal point of the eye to the optics are, the greater the defocus on the retina, which limits the benefit of EDOF lenses. That is why it is easier to design EDOF IOL lenses than it is to design contact lenses and glasses (Kanclerz et al, 2020).
So, are there alternatives in the contact lens market? Yes. While they were originally designed to reduce the defocus of the peripheral image shell in degenerative myopia, they work well for the presbyopic patient (Sankaridurg et al, 2019; Bakaraju et al, 2018). In my practice, I have found them to help, especially in early presbyopia.
Another way of improving the performance of many multifocal contact lenses is the adjunctive use of the newer miotic EDOF medications. Currently, 4 are approved for this use by the US Food and Drug Administration.
Two versions of low-dose pilocarpine act cholinergically to cause miosis through contraction of the iris sphincter muscle. The other 2 use different drugs to act selectively only on the sphincter muscle without stimulating the ciliary muscle, which can cause a myopic shift, as well as headaches (Haghpanah and Alany, 2022). They take some experimenting, and they need full disclosure of the side effects prior to use, but I have found them helpful.
REFERENCES
1. Kanclerz P, Toto F, Grzybowski A, Alio JL. Extended depth-of-field lenses: an update. Asia Pac J Ophthalmol (Phila). 2020;9(3):194-202. doi: 10.1097/APO.0000000000000296
2. Sankaridurg P, Bakaraju R, Naduvilath T, et al. Myopia control with novel central and extended depth of focus contact lenses: 2-year results from a randomized clinical trial. Ophthalmic Physiol Op. 2019;39(4):294-307. doi: 10.1111/opo.12621
3. Bakaraju R, Tilia D, Sha J, et al. Extended depth of focus contact lenses vs. two commercial multifocals: Part 2. Visual performance after 1 week of lens wear. J Optom. 2018;11(1):21-32. doi: 10.1016/j.optom.2017.04.001
4. Haghpanah N, Alany R. Pharmacological treatment of presbyopia: a systematic review. Eur J Transl Myol. 2022;32(3):1078. doi: 10.4081/ejtm.2022.10781