What's New in Refractive Surgery

David I.Geffen, OD, and James V. Aquavella, MD
JUNE 1998

Refractive surgery has come a long way. Here's a review of the latest terms, tools and techniques to bring you up-to-date.

The surgical correction of ametropia has gone through a period of development that seems to parallel that of the computer. Although surgical techniques evolved slowly through the 1970s and 1980s, the pace has increased considerably within the past couple of years, and the future shows great promise for continued innovation.

The Old and The New

Radial keratotomy (RK) had its day in the sun. With the advancements of laser technology, RK is now primarily used as an enhancement technique for very low prescriptions. In the future, even this minimal use may become obsolete.

Astigmatic keratectomy (AK), which works very well to correct astigmatism up to approximately 5.00D is still a widely used procedure. It's an excellent choice for correcting residual astigmatic errors after laser treatment and for reducing astigmatism in corneal transplant patients (Figs. 1a & 1b).

FIG. 1a: Astigmatic keratectomy to reduce astigmatism post-PK

. FIG. 1b: Close-up of eye shown in Fig. 1a.

Photorefractive keratectomy (PRK) is currently the most widely used refractive surgery procedure. However, it is rapidly declining in popularity due to the growing preference of laser assisted in situ keratomileusis (LASIK) by surgeons. With currently approved excimer lasers, PRK is effective for correcting up to approximately 7.00D of myopia and 5.00D of astigmatism.

All About LASIK

LASIK has become the procedure of choice for most refractive surgeons. Refractive surgery specialists are reporting that LASIK accounts for anywhere from 70 to 95 percent of their surgeries. Three diopters and greater of myopia appears to be the typical cut-off to recommend LASIK, but many surgeons are using it to correct as little as
-1.00D. LASIK is an excellent procedure for correcting up to approximately 12.00D of myopia. Beyond this, optical aberrations dramatically increase. In the future, we'll probably use phakic intraocular lens implants, which should be able to extend the range of corrections to between approximately �20.00D. Although early studies are showing very promising results, there may be much greater risks involved with this type of refractive surgery. The incidence of cystoid macular edema is of major concern, as is the uncertainty about how the corneal endothelium will be affected. Other potential risks include retinal detachment, scleral perforation, infection and hemorrhaging. Many questions need to be answered before full acceptance of intraocular lenses is seen.

Patients prefer the LASIK procedure because of the fast recovery and minimal discomfort, doctors prefer it because of the minimal follow-up care involved. The results at six months are almost identical to those of PRK for the majority of patients. With the ability to perform astigmatic procedures at the same time, the surgeon can completely correct the patient's ametropia with greater ease. The clear lure of the LASIK procedure is that the patient is comfortable and enjoys corrected acuity within several hours after the surgery. With PRK, these benefits take time to surface.

Nevertheless, the LASIK procedure is more invasive, and requires an operating room approach. If the number of refractive surgery procedures per year is to be numbered in the millions as opposed to the hundreds of thousands, further improvements will be necessary in both PRK and in LASIK.

New developments in microkeratomes (Fig. 2) will make LASIK a more efficient procedure. The ability to make a vertical cut may decrease complications with the cap. New power supplies may eliminate the wires attached to the keratome. Disposable microkeratomes may make the procedure quicker and more efficient with less technician dependence.

Correcting Hyperopia

Hyperopic PRK and hyperopic LASIK are currently in the final stages of FDA approval. The study results are excellent for corrections of up to approximately +5.00D. Astigmatism can also be corrected at the same time as the hyperopia. Hyperopia is corrected by ablating a doughnut shape into the cornea. Microkeratomes that will cut a larger cap are desired for hyperopic procedures. Several manufactures are working on new, larger microkeratomes. Monovision laser correction for hyperopes opens a whole new group of potential patients for refractive surgery.

Intrastromal Corneal Ring

The intrastromal corneal ring is close to approval. In its final stage of studies, the ring has proven to be a good technique for treating low myopia. The biggest advantage of the ring is its potential reversibility. In theory, the cornea will return to the presurgical state once the ring is removed. Due to its limited range and inability to correct astigmatism, this procedure may be a choice for younger patients whose refractive error is still changing.

Up-and-Coming

New excimer lasers are on the verge of approval and will be offering features that should improve results. The increased competition can only be beneficial to practitioners and patients in ultimately reducing the cost of the technology, as well as promoting future technological innovations. Presumably, the new lasers will offer a smoother ablation via the so-called scanning technology. While it's clear that these new lasers will do a better job of blending, thereby increasing the regularity of the ablated surface, we don't yet know whether this improvement will result in improved visual acuity or improved predictability.

A second innovation is the ability of the laser to track with eye movements. While this should be a significant advantage, the evidence that it will translate into improved visual results is not yet available.

The future looks bright for refractive surgery. In the interim, refractive surgeons have two excellent techniques at their disposal, and continued innovations can only improve technical results and patient satisfaction.