Commentary: Multifocal versus modified monovision contact lens correction for presbyopia – A synopsis

In this article of Indian Journal of Ophthalmology, the authors have studied use of two commercially available brands of contact lenses among presbyopes and have compared their visual outcomes when used as multifocal versus their modified monovision counterpart. The lenses used were PureVision 2 and Clariti contact lenses. High- and low-contrast distance visual acuity, near visual acuity, stereopsis, contrast sensitivity, and glare acuity were studied among 19 presbyopes with low distance refractive errors and moderate near add requirements. Modified monovision lenses were seen to be better when high-contrast distance visual acuity was measured. Multifocal contact lenses were better when stereopsis was considered. Uniform performance was noted with both the corrections in parameters like low-contrast distance visual acuity, near acuity, and contrast sensitivity.[1]

Presbyopia is an aging disease characterized by weakening of the ciliary muscles, hampering accommodation and thus unaided near vision in phakics. It is treated symptomatically by giving appropriate refractive addition lenses for near, be in the form of spectacles (as bifocals or progressive lenses) or more recently multifocal contact lenses.[2] Multifocal contact lenses are available in two designs – simultaneous vision and segmented. Segmented lenses are just like bifocal/trifocal presbyopic glasses with superior designated area for distance vision and inferior designated area for near vision. They are available as rigid lenses, rest over the tear film, and are independent of ocular vertical movements to allow vision through the respective designated areas during distance and near vision, much like bifocal spectacles. Simultaneous vision lenses, on the other hand, have concentric demarcated/nondemarcated rings of different powers for distance and near vision. Depending on the refractive state of the central zone supposed to overly the constricted pupil, simultaneous vision lenses are further classified as center-near or center-distance lenses.[3] Clarity and PureVision2 contact lenses used in the above study are both center-near lenses, which differ in that the former is a progressive lens and the latter a 3-zone form.

Due to a common light beam being split at different foci, enabling anunaided multifocal vision, these lenses have their own set of limitations, which are light-reduced contrast sensitivity, haloes, reduced brightness perception, and so on, compared to reading glasses. Monovision using contact lens emerged as a concept to partially overcome these problems. The subject is fitted with distance monofocal lens over the dominant eye and near monofocal lens over the nondominant eye, exploiting uniocular blur, fooling the brain to ignore the image that is out of focus/interest. Monovision overcomes the problems of haloes/reduced brightness, but falls short when binocularity/stereopsis is considered since ocular input from one eye is completely shut down at a given time.[4] Modified monovision combines best of both worlds. It involves using the following:

1. monofocal distance contact lens over the dominant eye, multifocal over the nondominant eye, allowing binocularity for distance;

2. multifocal with low add for the dominant eye for distance and intermediate vision, multifocal with high add for the nondominant eye for distance and near vision, allowing binocularity for distance and intermediate vision; and

3. center-distance multifocal for the dominant eye, center-near multifocal for the nondominant eye, allowing binocularity for intermediate vision.

Allowing binocularity, modified monovision gives some form of stereoacuity over its predecessor concept of monovision. It reduces haloes and gives better brightness perception and distant acuity when compared to binocular application of similar multifocal lenses. But the latter definitely has an edge considering stereoacuity, since binocularity is maintained for all distances while modified monovision still depends on uniocular suppression for some distances.[5] The subjects can choose from the two available treatment modalities depending on what suits their life and workstyle.