Myopia, Radial Keratotomy 

Approximately one fourth of the world's population is myopic. Radial keratotomy (RK) for myopia has developed slowly over the last century. Since it was first performed in the United States, the operation has been the subject of interest and lively debate among ophthalmologists and patients with myopia.

The use of corneal incisions to alter corneal curvature began in the late 19th century.

Choi et al^[1] reported the following:

The earliest report of using an incision to alter the shape of the human cornea was in 1885, when the Norwegian ophthalmologist Schiotz used a limbal relaxing incision in a patient who underwent cataract surgery. Schiotz observed that the placement of the incision in the steep meridian of the patient's cornea resulted in flattening in the incised meridian. In 1894, Bates made the observation that traumatic peripheral corneal scars flattened the cornea in the meridian of the scar without affecting the meridian that was 90 degrees away. His observation advanced the idea that anterior corneal incisions could affect shape in a way to create more symmetry in astigmatic corneas.

Modern surgery for myopia was initiated by the original ideas and experiments of the late Professor Tsutomu Sato of Juntendo University, Tokyo. In 1939, he observed that spontaneous breaks in the Descemet membrane in keratoconus produced flattening of the cornea as the breaks healed. This observation provided hints of his idea of posterior corneal incisions. He also observed that injury to the Descemet membrane was greater than that induced by injury on the Bowman layer, suggesting that surgery on the posterior cornea would be more effective than surgery on the anterior cornea. In the late 1940s, anterior incisions were added to enhance the effect of the posterior incisions after experimental studies on radial and tangential incisions in rabbits to correct astigmatism. Myopic surgery was performed most frequently in Japan in the early 1950s.

As the contributions of Sato and his colleagues to the development of keratotomy wilted and died in Japan, they took root and blossomed in the former Soviet Union. There, ophthalmologists (first, Yanaliev, who performed 426 incisional refractive surgery cases between 1969 and 1977, and, later, Fyodorov and Durnev) found identical conclusions to Sato's over thousands of operations. Anterior radial incisions were not very effective, and posterior incisions were necessary for the desired effect. They concluded that the effect of the surgery was contingent on the length, the distance from the limbus, and the depth of the transverse incisions.

During the 1970s and 1980s, Fyodorov and his colleagues in Moscow made important contributions to modern anterior refractive keratotomy. Fyodorov started performing surgery in humans in 1974 using a freehand razor blade fragment in a blade holder, checking the depth of the incision with a depth gauge and deepening the incisions as needed.

The intense interest in RK in the United States in 1979 and 1980 triggered a stampede of ophthalmologists traveling to Moscow to learn the technique from Fyodorov. At that time, he reported "99% successful results" after refractive keratotomy and stated "there have been no more than one or two complications in tens of thousands of cases."

The clinical and scientific development of keratotomy in the United States involved the experience, insights, and studies of dozens of ophthalmologists working rapidly in an unstructured setting. Identifying who was responsible for which innovations and advances is difficult.

Frequency

The introduction of RK to the ophthalmologist's arsenal of surgical procedures sparked criticism and controversy.

RK for myopia was the most commonly performed refractive procedure in the late 1970s and 1980s. Most patients who elected to have RK did so to avoid being dependent on glasses or contact lenses. Other patients sought the surgery for occupational, athletic, or cosmetic reasons.

Hundreds of thousands of RKs were performed by ophthalmic surgeons around the world during that period, but now they are rarely, if ever, performed. New techniques with fewer complications and adverse effects have supplanted RK in the 1990s, starting with photorefractive keratoplasty (PRK) and followed by laser in situ keratomileusis (LASIK).

RK is considered an elective surgery because the surgery is not necessary to achieve functional emmetropia. The most common motivation for patients to have RK is to see well without having to depend on spectacles and contact lenses.

The refractive error is typically the first item used to screen patients. Those patients with myopia less than 1.00-1.50 diopters (D) and greater than 10.00 D are eliminated from consideration, as are patients with hypermetropia. Best results were found on individuals with myopia from 1.50-6.00 D.

In patients who have less than 1.50 D of myopia, the danger for overcorrection is usually high, and, in those patients who have more than 6.00 D of myopia, a decreased probability of an acceptable result exists.

The second most common criterion used to screen patients is age. Individuals younger than 21 years should not have the procedure performed because their refraction may not be stable.

Individuals who cannot be corrected better than approximately 20/40 with spectacles are seldom considered for RK, including patients with amblyopia, maculopathies, myopes with previous retinal detachment, and higher myopes with macular degeneration.

The cornea protects the intraocular contents and refracts the light. It is approximately 550 µm thick centrally and 700 µm thick peripherally and has, on average, a 12-mm diameter horizontally and an 11-mm diameter vertically.

The human cornea has 5 primary layers, as follows: epithelium, Bowman layer, stroma, Descemet membrane, and endothelium.

Knowing the corneal thickness is fundamental in keratotomy surgery because it forms the basis for setting the length of the knife blade in an attempt to make uniformly deep incisions through approximately 90% of the cornea.

RK works by altering cornea anatomy to create a new shape, flatter in the center and steeper in the periphery. The incisions cut a graded amount of corneal stroma, allowing the biomechanical forces to produce a gaping of the incisions and repositioning of the uncut corneal tissues.

Contraindications include abnormal corneal thickness or topography, keratoconus, inflammatory corneal disease, glaucoma, herpes simplex keratitis, pathologic myopia, pregnancy, active systemic diseases, atopy, and connective tissue diseases.