Contact Lenses for Presbyopia
Presbyopia affects virtually everyone older than 40 years. Thus, as contact lens wearers age, their accommodation needs must be considered. Three options are available for these patients: (1) use of reading glasses with contact lenses, (2) monovision, and (3) bifocal contact lenses.
The first option, using reading glasses over contact lenses, has the advantages of being simple, inexpensive, and effective.
Figure 5-11 Evaluating lens rotation in fitting soft toric contact lenses using the LARS rule of thumb (left add; right subtract). The spectacle prescription in this example is –2.00 –1.00 ×180°.
(Modified with permission from Key JE II, ed. The CLAO Pocket Guide to Contact Lens Fitting. 2nd ed. Metairie, LA: Contact Lens Association of Ophthalmologists; 1998. Redrawn by Christine Gralapp.)
The second option, monovision, involves correcting one eye for distance and the other eye for near (see BCSC Section 13, Refractive Surgery). Many patients are satisfied with this correction, tolerating the reduced binocular acuity and depth perception. Typically, the dominant eye is corrected for distance. For driving and other critical functions, overcorrection with glasses may be necessary. A temporary trial of monovision contact lenses is often useful when considering a permanent monovision option with laser refractive surgery or lens implant surgery.
The third option for patients with presbyopia is to use bifocal contact lenses, either soft or RGP. There are 2 types of bifocal lenses: alternating vision lenses and simultaneous vision lenses. Alternating vision bifocal contact lenses are similar in function to bifocal spectacles in that there are separate areas for distance and near, and the retina receives a focused image from only 1 object plane at a time (Fig 5-12). Segmented contact lenses have 2 areas, top and bottom, like bifocal spectacles, whereas concentric contact lenses have 2 rings, 1 for far and 1 for near. For alternating vision contact lenses, the position on the eye is critical and must change as the patient switches from distance to near viewing. The lower eyelid controls the lens position, so that as a person looks down, the lens stays up, and the eye’s visual axis moves into the reading portion of the lens. The need for this “translation” of the lens in downgaze makes RGP lenses work well for these designs.
Figure 5-12 Alternating vision bifocal contact lenses. A, Segmented lens. B, Concentric (annular) lens.
Simultaneous vision bifocal contact lenses, in soft multifocal lenses and some RGP, provide the retina with focused images of near and far simultaneously. This requires the patient’s brain to ignore one or the other and accept the reduction in contrast (Fig 5-13). These lenses have various optical designs, with rings of differing focal lengths to provide a bifocal or multifocal effect. The most central portion may be used for either near or distance. Another strategy is to have less add for the dominant eye, so that it has better distance vision, and more add in the nondominant eye.
Avoiding amblyopia is a major goal in the management of aphakia in infants and young children. When contact lens wear is not feasible, intraocular lens placement is considered for the initial surgery (see BCSC Section 6, Pediatric Ophthalmology and Strabismus).
Excerpted from BCSC 2020-2021 series : Section 3 - Clinical Optics. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.