Many options exist for the correction of presbyopia. The simplest is the use of low-powered convex lenses—reading glasses. Sometimes referred to as “cheaters,” there is unfortunately no way to cheat the reality that the correction of presbyopia involves a compromise. Reading glasses bring near objects into focus, but they make distance objects out of focus. With any given pair of “monofocal” glasses, one can have clear distance vision or clear near vision—but not both. Benjamin Franklin recognized this problem and created the first pair of bifocal glasses. In doing so, he traded the benefit of a full field of vision for the convenience of not having to change glasses to see both near and far.
Fundamentally, “accommodative vision loss” or “dysfunctional lens syndrome” arises from the loss of a dynamic process: accommodation. Until we are able to restore true dynamic accommodation, the correction of presbyopia will remain a balance of compromises. For a patient to see multiple ranges without having to change optical devices, a compromise needs to be made in at least one of three categories: (1) binocularity, (2) visual field, or (3) contrast sensitivity and night vision symptoms.
Monovision is a common approach for the correction of presbyopia. Whether through contact lenses, corneal refractive surgery, or lenticular refractive surgery, simply adjusting the target refraction can provide many patients with an acceptable compromise to achieve a broader range of vision. The loss of depth perception at near, a sense of imbalance, and the loss of visual redundancy at any given distance (if the one eye gets blurry, the entire distance or near field becomes blurry) are the trade-offs with monovision. Additionally, the loss of binocular summation, which typically improves visual acuity by 1.5 lines, may affect overall patient satisfaction as well.
VISUAL FIELD COMPROMISE
Bifocal glasses and multifocal contacts use a portion of the visual field (typically inferior) for near vision and the rest of the visual field for distance vision. Difficulty finding the proper zone of vision, aesthenopic symptoms, and quality of vision issues are common side effects of bifocal glasses and contact lenses. The difficulties and dangers of ambulation and climbing stairs while wearing bifocal glasses are well known.
CONTRAST SENSITIVITY, NIGHT VISION SYMPTOM COMPROMISE
IOLs offer the unique ability to increase depth of field with diffractive optics. By creating two simultaneous images in both eyes, distance and near vision can be achieved without loss of binocularity or visual field. In this category, the compromise comes in the area of contrast sensitivity and night vision symptoms, or halos. Depending on the specific IOL material and design, quality of vision and night vision symptoms may be side effects of multifocal IOLs.
To address presbyopia, patients are variably accepting of modalities from each of the three categories described above. Some patients adapt and function well, while others are less tolerant of the compromise made. Until a fully accommodative solution provides us with the ability to cure presbyopia without compromises of binocularity, field, or contrast (perhaps during the careers of the millennials), forward-thinking physicians will continue to work with industry to create varied and improved options that balance some combination of these compromises.
Ultimately, each patient’s needs and motivation will help to determine which option would work best for them. For the practicing ophthalmologist, our job is to find the solution that provides the best set of compromises to meet the needs of each individual patient.