Monovision is a strategy used to compensate for presbyopia by correcting one eye for distance vision and the other for reading. Because producing two eyes with unequal correction creates a compromise, there is controversy regarding this treatment option. Are our patients capable of making the decision to compromise distance vision for near vision? If our patients choose monovision, can we be sure that we have screened them adequately to ensure success and patient happiness? Herein lies the difficulty in creating monovision for our patients. Because the success rates with contact lens monovision range from 50% to 70%, at least half of the patients who try it may be unhappy with the results. Although monovision should be part of every refractive surgeon's armamentarium, knowing its limitations and carefully selecting patients are paramount.

Interocular blur suppression is the adaptive mechanism that allows monovision to succeed. If this mechanism is not adapted, the patient may experience reduced binocular visual acuity and reduced depth perception, especially early on. As with most adaptive mechanisms, the brain needs time to adapt to this new visual function before it embraces the visual compromise that is monovision.

During the 10 years I have performed cataract and refractive surgery, I have compiled the following list of monovision's limitations. I hope that it will help other physicians to select monovision patients more carefully and avoid the pitfalls I have experienced. Whether we practice cataract or refractive surgery or general medical ophthalmology, understanding monovision and its limitations is the key to success and happy patients with this treatment.

1. PATIENT SELECTION CAN BE DIFFICULT
Patient education is the key to success with monovision, and it requires your time and patience. Explaining how the monovision optical system works will save you time in the long run, especially if the patient is unhappy because he did not understand what monovision meant. This process also allows you more time to get to know your patient and assess his visual needs and personality type.
2. REDUCED BINOCULAR VISUAL ACUITY
I find that my post-LASIK patients require 20/20 vision in their dominant eye and at least J2 in their reading eye or they may not be satisfied. Increased amounts of anisometropia accentuate this effect, as this decreases the synergy for binocular visual acuity. In order for a 60-year-old patient to achieve this quality of vision, the reading eye may require -1.5 D to -2.0 D of myopia. As we age, the myopia that we need for excellent reading vision increases. When inducing monovision, we must compensate for this by adding more myopia in the reading eye, which will further reduce distance vision in this eye. Increased amounts of anisometropia accentuate this effect and decrease the synergy for binocular visual acuity.
3. EXTENDED READING REQUIRES BRIGHTER LIGHTS
We have all occasionally treated an emmetropic 50-year-old patient who can read without aid in bright-light conditions. We have also seen the 50-year-old monovision patient who, despite a “good” refractive result, may require bright light to read comfortably. During the monovision education process, it may be wise to suggest to the patient that higher intensity light may be necessary to enjoy monovision to the fullest.
4. PATIENTS MAY STILL NEED GLASSES
I recommend distance glasses for night driving and other visually demanding events such as theatrical performances or spectator sports. Make sure to state this information clearly to the patient before the surgery.
5. DIFFICULTY IN CHOOSING THE CORRECT AMOUNT OF MONOVISON
There is a fine balance in providing the patient with excellent reading vision while minimizing anisometropia and maximizing binocular visual acuity. I try to never induce more than 1.5 D in difference between the two eyes.
6. OCCASIONAL REVERSALS/ENHANCEMENTS
Despite perfect technique and surgical outcomes, patients may not adapt to monovision and therefore want reversal in the form of converting the reading eye to distance. I recommend waiting at least 3 months to allow the patient an adequate trial with his new monovision, and to allow the eye a chance to heal adequately after surgery. If after this trial he is still unhappy, I proceed to reverse the monovision in order to achieve our ultimate goal: patient satisfaction.
7. TEST CONTACT LENSES FIRST
Proceed cautiously with monovision in patients who have not tried it in the past with contact lenses. Encourage a trial to ensure the patient's ultimate success and happiness with the result. For many of our patients, comfort while wearing contact lenses is difficult to achieve due to contact lens intolerance, but encourage them to ignore the discomfort and emphasize whether “visual comfort” is either achieved or possible.
8. REDUCTION IN STEREO ACUITY/DEPTH PERCEPTION
While this effect usually improves following adaptation, I will rarely perform monovision on patients who require excellent stereo acuity. I proceed cautiously with (1) patients who are marginally ambulatory or disabled and at high risk of falling, (2) patients whose hobbies include golf, tennis, and baseball, and (3) pilots, truck drivers, or law enforcement officers.
9. HIGHER COST FOR THE SURGEON
Because the enhancement rates for monovision are higher, the cost to perform the procedure is higher as well. In addition to requiring more preoperative chair time, monovision demands a postoperative result of at least 20/20 in the distance eye and J2 in the reading eye. Although the cost of enhancement is actually the same as the original surgery, rarely do we charge full price for an enhancement or reversal. In essence, this ends up being a “free trial” if the patient fails to adapt to monovision. The time we spend in counseling, the examination, in surgery, and postoperatively is often the same as for an enhancement. The good news is that we expend no marketing dollars and have no keratome blade cost.
10. COMPROMISE
Monovision entails concessions from both the surgeon and the patient. The “wow factor” is lessened with monovision, rendering these patients slightly less satisfying to work with and more demanding. The measure of “success” in each monovision patient is different and difficult to define. The key to a successful outcome is preoperative counseling and staightforwardness prior to surgery. To each of my monovision patients, I state that monovision is a compromise: “You will give up something (binocular balance/acuity) to get something else (ability to read).” Only the patient knows whether the advantages of monovision will outweigh the disadvantages.
IN SUMMARY

Perhaps in no other situation does the patient's occupation, personality type, goals, age, and visual demands play as large a role as when we educate our patients to help them make informed choices regarding monovision. In these situations, we must reinforce the idea of “compromise” so that patients understand that certain aspects of their vision may be compromised to gain reading vision.

Timothy L. Schneider, MD, specializes in refractive and anterior segment surgery and is in private practice at Schneider Eye Associates and Laser Center, Jacksonville, Florida. Dr. Schneider may be reached at (904) 371-0000; jaxeye.net or eyefixu@aol.com.