Radial Keratotomy Myopia
- Author: Mounir Bashour, MD, PhD, CM, FRCSC, FACS; Chief Editor: Hampton Roy, Sr, MD more...
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. See the image below.
History of the Procedure
The use of corneal incisions to alter corneal curvature began in the late 19th century.
Choi et al 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.
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.
- The epithelium is a stratified squamous nonkeratinized epithelium (5-6 layers of cells) it is highly sensitive due to numerous nerve endings and has excellent regenerative power
- The Bowman membrane is structureless and acellular
- The substantia propria (stroma) forms 90% of the cornea's thickness; fibrils of the stroma criss-cross at 90º angles, and these fibrils are of types I, III, V, and VII collagen
- The Descemet membrane is structureless, homogeneous, and measures 3-12 microns; it is composed of the anterior banded zone and the posterior nonbanded zone; the Descemet membrane is rich in type IV collagen fibers
- The endothelium is a single layer of simple cuboidal and hexagonal cells that line the inner surface of the cornea; the endothelium is derived from the neural crest and functions to transport fluid from the anterior chamber to the stroma; Because the cornea is avascular, its nutrients are derived mainly from diffusion from the endothelium layer
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.
For more information about the relevant anatomy, see Eye Globe Anatomy.
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.
Choi DM, Thompson RW Jr, Price FW Jr. Incisional refractive surgery. Curr Opin Ophthalmol. 2002 Aug. 13(4):237-41. [Medline].
Reinstein DZ, Archer TJ, Gobbe M. Very high-frequency digital ultrasound evaluation of topography-wavefront-guided repair after radial keratotomy. J Cataract Refract Surg. 2011 Mar. 37(3):599-602. [Medline].
Reinstein DZ, Archer TJ, Gobbe M. Epithelial thickness up to 26 years after radial keratotomy: three-dimensional display with Artemis very high-frequency digital ultrasound. J Refract Surg. 2011 Aug. 27(8):618-24. [Medline].
Forister JF, Sun A, Weissman BA. Progress report on a post-radial keratotomy patient 20 years after surgery. Eye Contact Lens. 2007 Nov. 33(6 Pt 1):334-7. [Medline].
Gibson CR, Mader TH, Schallhorn SC, Pesudovs K, Lipsky W, Raid E, et al. Visual stability of laser vision correction in an astronaut on a Soyuz mission to the International Space Station. J Cataract Refract Surg. 2012 Aug. 38(8):1486-91. [Medline].
Bourque LB, Lynn MJ, Waring GO 3rd, Cartwright C. Spectacle and contact lens wearing six years after radial keratotomy in the Prospective Evaluation of Radial Keratotomy Study. Ophthalmology. 1994 Mar. 101(3):421-31. [Medline].
Charpentier DY, Garcia P, Grunewald F, Brousse D, Duplessix M, David T. Refractive results of radial keratotomy after 10 years. J Refract Surg. 1998 Nov-Dec. 14(6):646-8. [Medline].
Cinal A, Yasar T, Demirok A, Simsek S, Yilmaz OF. A comparative study on the effect of radial keratotomy in patients who live at sea level and high altitude. Eye. 1999 Jun. 13 (Pt 3a):339-44. [Medline].
Creel DJ, Crandall AS, Swartz M. Hyperopic shift induced by high altitude after radial keratotomy. J Refract Surg. 1997 Jul-Aug. 13(4):398-400. [Medline].
Gwon A. Prospective Evaluation of Radial Keratotomy (PERK) Study 10 years after surgery. Arch Ophthalmol. 1995 Oct. 113(10):1225-6. [Medline].
Heidemann DG, Dunn SP, Chow CY. Early- versus late-onset infectious keratitis after radial and astigmatic keratotomy: clinical spectrum in a referral practice. J Cataract Refract Surg. 1999 Dec. 25(12):1615-9. [Medline].
Kemp JR, Martinez CE, Klyce SD, Coorpender SJ, McDonald MB, Lucci L, et al. Diurnal fluctuations in corneal topography 10 years after radial keratotomy in the Prospective Evaluation of Radial Keratotomy Study. J Cataract Refract Surg. 1999 Jul. 25(7):904-10. [Medline].
Kozuch O, Mayer V. Pig kidney epithelial (PS) cells: a perfect tool for the study of flaviviruses and some other arboviruses. Acta Virol. 1975 Nov. 19(6):498. [Medline].
Mahanti R, Shapiro D. Complications of small clear zone radial keratotomy. Ophthalmology. 2000 Jun. 107(6):1023-6. [Medline].
McDonnell PJ, Nizam A, Lynn MJ, Waring GO 3rd. Morning-to-evening change in refraction, corneal curvature, and visual acuity 11 years after radial keratotomy in the prospective evaluation of radial keratotomy study. The PERK Study Group. Ophthalmology. 1996 Feb. 103(2):233-9. [Medline].
Nizam A, Waring GO 3rd, Lynn MJ, Ward MA, Asbell PA, Balyeat HD, et al. Stability of refraction and visual acuity during 5 years in eyes with simple myopia. The PERK Study Group. Refract Corneal Surg. 1992 Nov-Dec. 8(6):439-47. [Medline].
Panda A, Sharma N, Kumar A. Ruptured globe 10 years after radial keratotomy. J Refract Surg. 1999 Jan-Feb. 15(1):64-5. [Medline].
Rowsey JJ, Balyeat HD, Monlux R, Holladay J, Waring GO 3rd, Lynn MJ. Prospective evaluation of radial keratotomy. Photokeratoscope corneal topography. Ophthalmology. 1988 Mar. 95(3):322-34. [Medline].
Rowsey JJ, Waring GO 3rd, Monlux RD, Balyeat HD, Stevens SX, Culbertson W, et al. Corneal topography as a predictor of refractive change in the prospective evaluation of radial keratotomy (PERK) study. Ophthalmic Surg. 1991 Jul. 22(7):370-80. [Medline].
Schanzlin DJ, Santos VR, Waring GO 3rd, Lynn M, Bourque L, Cantillo N, et al. Diurnal change in refraction, corneal curvature, visual acuity, and intraocular pressure after radial keratotomy in the PERK Study. Ophthalmology. 1986 Feb. 93(2):167-75. [Medline].
Wang JQ, Zeng YJ, Li XY. Influence of some operational variables on the radial keratotomy operation. Br J Ophthalmol. 2000 Jun. 84(6):651-3. [Medline].
Waring GO 3rd, Lynn MJ, Fielding B, Asbell PA, Balyeat HD, Cohen EA, et al. Results of the Prospective Evaluation of Radial Keratotomy (PERK) Study 4 years after surgery for myopia. Perk Study Group. JAMA. 1990 Feb 23. 263(8):1083-91. [Medline].
Waring GO 3rd, Lynn MJ, McDonnell PJ. Results of the prospective evaluation of radial keratotomy (PERK) study 10 years after surgery. Arch Ophthalmol. 1994 Oct. 112(10):1298-308. [Medline].
Waring GO 3rd, Lynn MJ, Nizam A, Kutner MH, Cowden JW, Culbertson W, et al. Results of the Prospective Evaluation of Radial Keratotomy (PERK) Study five years after surgery. The Perk Study Group. Ophthalmology. 1991 Aug. 98(8):1164-76. [Medline].
Waring GO 3rd, Moffitt SD, Gelender H, Laibson PR, Lindstrom RL, Myers WD, et al. Rationale for and design of the National Eye Institute Prospective Evaluation of Radial Keratotomy (PERK) Study. Ophthalmology. 1983 Jan. 90(1):40-58. [Medline].