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Radial Keratotomy Myopia

  • Author: Mounir Bashour, MD, PhD, CM, FRCSC, FACS; Chief Editor: Hampton Roy, Sr, MD  more...
 
Updated: Mar 03, 2014
 

Background

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.

Optical zones and pupil dilation discussed by radi Optical zones and pupil dilation discussed by radial keratotomy surgeons.
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History of the Procedure

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.

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Epidemiology

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).

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Indications

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.

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Relevant Anatomy

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.

  1. 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
  2. The Bowman membrane is structureless and acellular
  3. 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
  4. 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
  5. 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.

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Contraindications

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.

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Contributor Information and Disclosures
Author

Mounir Bashour, MD, PhD, CM, FRCSC, FACS Assistant Professor of Ophthalmology, McGill University Faculty of Medicine; Clinical Assistant Professor of Ophthalmology, Sherbrooke University; Medical Director, Cornea Laser and Lasik MD

Mounir Bashour, MD, PhD, CM, FRCSC, FACS is a member of the following medical societies: American Academy of Ophthalmology, American Association for Pediatric Ophthalmology and Strabismus, American College of International Physicians, American College of Surgeons, American Medical Association, American Society of Cataract and Refractive Surgery, American Society of Mechanical Engineers, American Society of Ophthalmic Plastic and Reconstructive Surgery, Biomedical Engineering Society, Canadian Medical Association, Canadian Ophthalmological Society, Contact Lens Association of Ophthalmologists, International College of Surgeons US Section, Ontario Medical Association, Quebec Medical Association, Royal College of Physicians and Surgeons of Canada

Disclosure: Nothing to disclose.

Specialty Editor Board

Simon K Law, MD, PharmD Clinical Professor of Health Sciences, Department of Ophthalmology, Jules Stein Eye Institute, University of California, Los Angeles, David Geffen School of Medicine

Simon K Law, MD, PharmD is a member of the following medical societies: American Academy of Ophthalmology, Association for Research in Vision and Ophthalmology, American Glaucoma Society

Disclosure: Nothing to disclose.

Louis E Probst, MD, MD Medical Director, TLC Laser Eye Centers

Louis E Probst, MD, MD is a member of the following medical societies: American Academy of Ophthalmology, American Society of Cataract and Refractive Surgery, International Society of Refractive Surgery

Disclosure: Nothing to disclose.

Chief Editor

Hampton Roy, Sr, MD Associate Clinical Professor, Department of Ophthalmology, University of Arkansas for Medical Sciences

Hampton Roy, Sr, MD is a member of the following medical societies: American Academy of Ophthalmology, American College of Surgeons, Pan-American Association of Ophthalmology

Disclosure: Nothing to disclose.

Additional Contributors

Daniel S Durrie, MD Director, Department of Ophthalmology, Division of Refractive Surgery, University of Kansas Medical Center

Daniel S Durrie, MD is a member of the following medical societies: American Academy of Ophthalmology, Association for Research in Vision and Ophthalmology

Disclosure: Received grant/research funds from Alcon Labs for independent contractor; Received grant/research funds from Abbott Medical Optics for independent contractor; Received ownership interest from Acufocus for consulting; Received ownership interest from WaveTec for consulting; Received grant/research funds from Topcon for independent contractor; Received grant/research funds from Avedro for independent contractor; Received grant/research funds from ReVitalVision for independent contractor.

Acknowledgements

Mirelle Benchimol, MD Consulting Staff, Benchimol Eye Clinic

Disclosure: Nothing to disclose.

References
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Optical zones and pupil dilation discussed by radial keratotomy surgeons.
 
 
 
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