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Successful RK is a shared responsibility
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My experience with incisional refractive surgery includes thousands of cases beginning in 1986. Now, since Food and Drug Administration approval of the less invasive excimer laser, I rarely perform radial keratotomy (RK). For the purpose of this discussion, however, we will review RK.
The burden of excellence demanded by the refractive surgery patient is shared by the optometrist accepting the responsibility of comanagement. The visual result of all refractive cases, either incisional or laser based, is ultimately determined by the components of an equation that calculates for a predicted surgical response.
To create a precise response, the preoperative comanagement assessment is as vital a component to the surgical equation as the operation itself. Comanaging the postoperative period implies caring for the surgically traumatized eye, nurturing it, guiding its response and, thus, directing the final outcome.
Patient history first
My involvement begins well before we enter the operating room. A complete medical and ocular history is necessary to ensure an appropriate healing response. We discuss the patient's visual requirements and determine if an element of night myopia exists. Certain systemic factors should be focused on, such as a negative history of rosacea, psoriasis, hypertrophic scar or keloid, and autoimmune disease, to name a few.
The age, gender and even the eye color of the patient must be factored into the surgical equation. For example, a young, blue-eyed woman with a thin cornea responds less to the same intervention than a deeply pigmented man with an average corneal pachymetry.
Preop assessment
The preoperative assessment of any refractive patient includes the uncorrected and best-corrected visual acuity, as well as a stable refraction for more than 1 year. A precise manifest refraction should always be performed and adjusted for a 20-foot lane. This is then compared to a cycloplegic refraction using 1% cyclopentolate HCl. For darker pigmented irises, we use 2% cyclopentolate HCl every 5 minutes three times and wait at least 40 minutes.
We "push the plus" and, for precision, "tune" the refraction by using a trial frame with the patient looking out of a window. Contact lenses must be discontinued and the final refraction postponed until the topography stabilizes. Clearly, the success of any refractive procedure is based on the accuracy of a stable refraction.
Eye exam next
We perform a complete eye exam, concentrating on those particular aspects of the myopic eye in preparation for refractive surgery. Unsuccessful contact lens wearers may have a subepithelial basement membrane abnormality with poorly adherent epithelium. Patients who are unable to tolerate contact lenses may have been suffering from contact lens-induced microabrasions and perhaps will not respond appropriately to the RK incisions.
Another cause of poor outcome following a perfect surgical procedure is an inadequate tear film. A Schirmer's tear test and a tear break-up time must be performed to rule out a dry eye. Diuretics, as well as cold and allergy remedies, must be discontinued prior to surgery and the lid margins must be carefully inspected for blepharitis.
Corneal topography has become the "standard in the community" prior to any refractive surgery procedure. Topography not only rules out corneal dystrophies, such as keratoconus, but will also define astigmatism, unmasking any asymmetric patterns.
This can be especially important in incisional refractive cases where asymmetric surgery can be performed. Four-quadrant pachymetry is noted not only to adjust the depth of penetration of the diamond blade, but also because a thin cornea responds less than expected. Because myopic eyes generally have a longer than average axial length, they have a higher incidence of peripheral retinopathy, and a detailed depressed retinal exam should be performed.
Current RK method
My current RK method has evolved over the years into the DuoTrack (Chiron) system for the radial incisions and a "heavy" 45° back cutting blade for the astigmatic arcuate cuts. We begin Voltaren (diclofenac sodium, Ciba Vision) the morning of surgery to develop a tissue medication level, as well as TobraDex (tobramycin dexamethasone, Alcon). In my experience, Voltaren reduces postoperative pain better than other nonsteroidal anti-inflammatory.
The astigmatic arcuate incisions are performed at the 7-mm optical zone before the radials using a thick blade that will resist a "swimming" serpentine-like pass. In my hands, a thick blade yields the straightest incision at the expense of depth precision. For the astigmatic cuts, however, depth is not a critical issue. The length and position of each astigmatic incision is guided by the symmetry or asymmetry seen on topography.
The radial incisions are then made after the astigmatic cuts. They can either be adjacent, that is, on either side of the astigmatic incisions, or in line with them, "jumping" the arcuate cuts. Depending on the amount of astigmatism to be corrected, jumping an arcuate incision will enhance the effect of the astigmatic correction. The radial and astigmatic incisions should never connect.
Safe, efficient cuts
The DuoTrack technique for the radial incisions provides the incisional safety of an American centrifugal cut with the efficient depth of a Russian centripetal cut. The radial incision should achieve 90% penetration depth at the central optical zone.
The DuoTrack is constructed as a 60° angle diamond blade. The back surface of the blade is sharp all along the edge, allowing the tissue to be incised as the blade is pulled from the central optical zone toward the limbus. The front surface is sharp only along the lower 200 µm; above this, the blade is dull and will not cut tissue. This blade design will permit the blade only to deepen a cut that has already been created.
To perform a DuoTrack incision, the surgeon places the diamond blade into the cornea at the predetermined central optical zone, waits for the tissue to equilibrate, then pulls radially, stopping 2 mm to 3 mm before reaching the limbus. The surgeon then pushes the blade forward back along the same path toward the central optical zone, where the incision is squared off.
Because only the lower 200 µm of the front of the blade is sharp, the forward Russian-style incision will cut only the base of the incision trough, deepening the previous cut. Because this blade cannot pass into tissue that has not already been cut, the central clear optical zone is not threatened, hence the safety. The centrifugal course of the forward uphill cut provides greater incision depth; consequently, a shorter incision length yields the expected effect.
Additionally, by resetting the blade extension for each quadrant around the cornea, surgical efficiency can be achieved by creating the shortest incision to achieve the desired goal.
Know the limits
Knowing when to not operate is perhaps the most important concept a surgeon can learn. We should all understand the limits of each particular surgical intervention and respect them.
Should the opportunity arise to do an RK today, I would not create an optical zone smaller than 4 mm or use more than eight incisions with a single zone. If correction could not be achieved using these parameters, I would defer to excimer laser correction or recommend the patient continue enjoying good spectacle-corrected vision.
Postop treatment
Postoperatively, TobraDex and Voltaren are both continued four times a day until the epithelial defects heal. Artificial tears are then applied four times a day for the next 4 weeks. Patients should experience a refractive overcorrection for the first week of about 1 D to 1.25 D. As corneal edema resolves and the epithelium grows into the incisions, the refractive error stabilizes.
Overcorrection that is greater than expected may be pharmacologically reduced to prevent consecutive hyperopia by continuing the Voltaren four times a day for a few weeks and adding pilocarpine 1% to 2% four times a day. This seems to "tighten" the wounds by creating a fibrosis and lowering intraocular pressure.
Conversely, I have not found prolonged steroids to be of any permanent benefit for an undercorrection. I prefer to wait 6 to 8 weeks and enhance the result surgically with additional incisions.
As stated earlier, I prefer the excimer laser for corrections within its approved range. The only advantages to incisional refractive surgery today would either be economic, and that would be a questionable justification, or as an enhancement to a previous surgery.
My concern with RK is that in the best case, it is still a procedure based on an oxymoron known as "controlled ectasia." I believe if we induce an ectasia by weakening the structural integrity of the cornea, we no longer have control. In the past, by remaining conservative and with no better approach available, I was able to achieve very good results with RK. Today, with the less invasive excimer caser, we correct an even greater range of ammetropia without relying on corneal ectasia.
My greatest concern with RK is consecutive progressive hyperopia. I have seen eight-incision moderate myopes remain stable for more than 10 years, and I have also seen low myopes corrected with four perfect incisions develop an uncontrolled hyperopic shift.
The final outcome
The optometrist comanaging a refractive patient, by virtue of the preoperative exam, determines the foundation from which the ophthalmologist bases the surgical intervention. The postoperative comanagement care develops the final outcome.
Problems should be corrected before they occur. The history and ocular examination should be designed to unmask and eliminate any potential occurrences. Consequently, the comanaging optometrist is burdened with as much responsibility to the outcome of the case as the ophthalmic surgeon.
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For Your Information:
- Alexander P. Hatsis, MD, FACS, is a board-certified ophthalmologist in practice in Rockville Centre, N.Y. He is the director of refractive surgery and senior attending for resident training at Nassau County Medical Center, State University of New York, and is also board certified in incisional refractive surgery by the American College of Eye Surgeons. Dr. Hatsis specializes in LASIK surgery and is currently investigating phakic implants for the correction of high hyperopia and high myopia. He may be contacted at 2 Lincoln Ave., Suite 401, Rockville Centre, NY 11570; (516) 763-4106; fax: (516) 763-5216. Dr. Hatsis has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any company mentioned.