The good news about cataract surgery is that often the replacement lenses can be chosen to correct near-sightedness or far-sightedness. So if you've worn glasses or contact lenses for years, you may not need them once you're old enough for this procedure. But there are some decisions to be made. In young people, the natural lenses of the eyes can change focal length to produce clear images at a range of distances. This is called accommodation. All of us lose this ability in a slow process that starts about age 40 and ends sometime in our 60's, after which time our natural lenses have become single focus lenses.
Cataracts are cloudy or opaque natural eye lenses. Today it is standard practice to replace them with clear plastic lenses. Different focal lengths are available, so the patient and surgeon together can select the distance for perfect vision in each eye. Multifocal and accommodative lenses have been developed with some success, but these are expensive and not all patients are able to adjust to them.
Monovision is the technique of correcting one eye for distance vision and the other for near vision. This has been done with contact lenses since 1958. Recently it has been extended to refractive surgery (LASIK and similar procedures). Cataract surgeons and their patients often choose this option as well. The major benefit is good focus for the entire visual field of each eye. The disadvantages are loss of stereoscopic vision and reduced visual acuity in the intermediate distance range.
A study in the medical literature in 2009 reported a high rate of satisfaction with monovision in cataract surgery patients. The 38 participants answered a questionnaire about the following visual challenges without glasses:
1. Driving at night
2. Reading small print
3. Watching television
4. Seeing steps, stairs, or curbs
5. Reading traffic signs, street signs, or store signs
7. Fine handwork such as sewing, knitting, or carpentry.
The overall satisfaction with monovision was 97 percent. Of the 38 patients, only two asked for optical correction: one used glasses only for extensive reading and was satisfied with the procedure; the other was unsatisfied and received contact lenses plus reading glasses.
The authors conclude that monovision is a “viable and alternative technique”.
Marques FF et al, “Evaluation of visual performance and patient satisfaction with pseudophakic monovision technique”, Arq Bras Oftalmol. 2009; 72(2): 164-8.
Linda Fugate is a scientist and writer in Austin, Texas. She has a Ph.D. in Physics and an M.S. in Macromolecular Science and Engineering. Her background includes academic and industrial research in materials science. She currently writes song lyrics and health articles.