I Know Why Refractive Surgeons Wear Glasses - EyeKnowWhy - Refractive Surgery Options
I Know Why Refractive Surgeons Wear Glasses
Refractive Surgery Options
EyeKnowWhy - Refractive Surgery Options Updated: 9/14/97 Bugs?

Update Status: Discussions of Surgical Options are Added as Appropriate

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Refractive Surgery Options

For those who decide they wish to go through with refractive surgery, and have chosen a procedure, there are decisions to be made before having the surgery. In some cases, a patient may need to decide if they should have additional surgery on each eye. This section discusses these options and their advantages and disadvantages.

  1. Monovision

    Monovision refers to a strategy to prevent the onset of presbyopia. The theory is to undercorrect one eye at least one diopter (-1 D), often more. This, in theory, would allow the patient to have fairly good near vision after forty and use this for reading as presbyopia develops. There are problems with this technique. First, the accuracy of the refractive surgery procedure itself may result in unintended refractive errors. For example, an eye that was 'targeted' for emmetropia may end up slightly farsighted or slightly nearsighted, while the eye that was intended to be slightly nearsighted may end up more nearsighted than intended or emmetropic or slightly farsighted. The most recent PRK studies show improved accuracy and the 'targeted' results are achieved more precisely than in previous studies. Let's assume that the targeted results can be achieved. Would you be happy with monovision? Some people just cannot tolerate monocularity. People with monovision may develop the same symptoms as people with anisometropia, since monovision is 'planned' anisometropia. One of the drawbacks is the loss of depth perception in distance vision. That is, since only one eye would have sharp vision, the depth that results from the brain reconciling two sharp images is not available.

    Studies of monovision indicate that somewhere between 30% and 60% of refractive surgery patients do not tolerate monovision well long term. Additional studies of monovision's effectiveness need to be done. How large of a refractive difference is tolerated? Obviously, the greater the difference, the greater the risk of intolerance and symptoms of anisometropia. How many patients are happy with monovision at six months, one year, etc.?

    You can simulate (somewhat) monovision's effects prior to making a decision. Have your prescriptions adjusted to simulate monovision. This can be most easily done with contacts, but eyeglasses can also be used. Be sure to try monovision consistently for at least one week, then decide. Some refractive surgeons may tell you that a second surgery can be performed on the eye 'targeted' for residual nearsightedness to make it more closely match the other eye if you are not happy with the result, but this has drawbacks. It's an additional surgery, with all the risks, side effects and complication possibilities of the first surgery. See below (Repeat Surgery).

  2. Bilateral or Sequential Surgery

    Should you have both eyes done at the same time (bilateral) or wait a period of time between the first eye and second (sequential)? Bilateral surgery is controversial because of the additional risk. If both eyes are done at the same time, and an infection occurs in one eye, there is a good chance the infection may spread to the other eye. (The risk of infection is greatest the first month after surgery.) Likewise, other complications may occur bilaterally that may have been avoided. Still, this does have the advantage of 'getting it over with', and avoiding anisometropia that patients who have sequential surgery experience.

    Some have argued that sequential surgery has the advantage of greater accuracy since the second eye's surgery can be 'fine tuned' based on the results of the first surgery. This may or may not be true since final visual acuity has not 'stabilized' until months after the surgery, and most people are unwilling to wait a year to learn the results in the first eye. Sequential also has the drawback of causing moderate to severe anisometropia until the second eye is done. This can be alleviated best with a contact lens in the unoperated eye. Another question to ask, is it better to experience the trauma of eye surgery in one fell swoop or sequentially? Only a few studies have been done regarding bilateral surgery and you should review them if possible.

  3. Repeat Surgery

    Additional surgery or repeat surgery known as 'enhancement' surgery is a difficult decision to make. Repeat surgery after RK was troubling. It was rarely effective, caused additional scarring, and was problematic.

    Repeat surgery after PRK has had better results and is sometimes necessary to improve complications after the initial surgery. If a person experiences regression (i.e., becomes nearsighted again to the point that glasses are needed to function) but still has a clear cornea and no other complications, the person may elect to have repeat surgery in an attempt to bring the acuity back to Snellen 20/40 or better withougt glasses. This is a hard decision since it is elective. Some surgeons advocate cornea topical drug treatments (steroids and other drugs) to reverse regression before attempting a repeat laser procedure. These drugs seem to inhibit collagen formation and thickening of the epithelium.

    You should read studies regarding the results of repeat surgery. In some cases, there are no improvements, regression recurs or the patient may end up farsighted (undesirable) or experiences additional haze. Significant haze is usually associated with regression, but not always.

    If a person develops severe haze/scarring that interferes with vision or has central islands that reduce spectacle visual acuity, a repeat surgery may improve their situation. But repeat surgery carries all the risks, complications, side effects, and prolonged healing of the first surgery. People who have significant haze or central islands should defer repeat surgery if possible and see if they resolve on their own as wound healing progresses. This is especially true if they did not regress back into myopia. Studies from Europe show that patients who had Grade 2+ haze at one year had significant improvement in haze density three years later. Likewise, central islands tend to be 'eroded away' by the cornea's wound healing response in many cases. These decisions will have to be made with your refractive surgeon if these complications develop in your corneas.

    Some refractive surgeons have advocated a 'therapeutic' ablation for patients with 'rough' transition zones with circular scarring and signifant GASH (glare, arc, starburst, halo) complaints or eccentric ablations that also increase GASH.

    If you are overcorrected and become farsighted, there are no proven treatments to resolve this. Some have advocated using the holmium thermal surgery (Laser Thermal Keratoplasty - LTK) to burn spots around the ablation wound. These spots result in shrinking of the collagen within the spots, producing a 'cinch' effect and 'steepening' the cornea. This is experimental and the results, safety and stability are unknown. Others have advocated scaping the epithelium and the underlying stroma with a blade to reactivate the wound healing response. In this case, the surgeon hopes this will stimulate the cornea to produce more collagen or thickening of the epihelium thus 'steepening' the cornea, and reducing the farsightedness. Results have been mixed.

    All of the above apply to LASIK with the additional risk of lifting and reseating the flap.

If you have any questions or comments, please contact eyeknowwhy@aol.com.