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Radial Keratotomy

Definition

Radial keratotomy (RK) is a type of eye surgery used to correct myopia (nearsightedness). It works by changing the shape of the cornea—the transparent part of the eye that covers the iris and the pupil.

Description

In a person with clear vision, light passes through the cornea and the lens of the eye and focuses on a membrane lining the back of the eye called the retina. In a person with myopia, the eyeball is usually too long, so light focuses in front of the retina. Radial keratotomy reduces myopia by flattening the cornea. This reduces the focusing power of the cornea allowing light to focus further back onto the retina (or at least closer to it), forming a clearer image.

A surgeon performing RK uses a very small diamond-blade knife to makes four to eight radial incisions around the edge of the cornea. These slits are made in a pattern that resembles the spokes of wheel. As the cornea heals, its center flattens out.

Radial keratotomy is usually performed in an ophthalmologist's office. Before the surgery begins, the patient may be given medicine to help him or her relax. A local anesthetic—usually in the form of eye drops—is used to numb the eye, but the patient remains conscious during the procedure. The surgeon looks through a surgical microscope while making the slits. The treatment usually takes no more than 30 minutes.

Some ophthalmologists will perform RK on both eyes at once but others prefer to do one eye at a time. It once was thought that surgeons could use the results of the first eye to predict how the well the procedure would work on the second eye. However, a study published in 1997 found that this was not the case. The authors of the study cautioned that there might be other reasons not to operate on both eyes at once, such as increased risk of infection and other complications.

The cost for RK depends on the surgeon, but usually ranges from $1,000–$1,500 per eye. Medical insurance usually does not cover RK, because it is considered an elective procedure—one that people choose to have done.

— Nancy Ross-Flanigan


 
 
Dictionary: radial keratotomy

n. (Abbr. RK)

Keratotomy involving a radial pattern of incisions, used to reduce or correct myopia.


 
Dental Dictionary: radial keratotomy

n

A surgical procedure in which a series of tiny, shallow incisions are made on the cornea, causing it to bulge slightly to correct for nearsightedness. The operation is performed using local anesthesia and requires only a few minutes. Hospitalization is not necessary. Radial keratotomy usually corrects mild to moderate myopia.

 
Wikipedia: radial keratotomy

Radial keratotomy (RK) is a refractive surgical procedure to correct myopia.

Discovery

The procedure was discovered by accident by Svyatoslav Fyodorov who removed glass from the eye of one of his patients who had been in an accident. A boy, who wore eyeglasses, fell off his bicycle and his glasses shattered on impact, with glass particles lodging in his eyes. A procedure was performed consisting of making numerous radial incisions which extended from the pupil to the periphery of the cornea in a pattern like the spokes of a wheel. After the glass was removed (by this method) and the cornea healed, he found that the patient's eyesight was significantly improved.[1]

Procedure detail

Schematic diagram of RK, with incisions drawn in orange.
Enlarge
Schematic diagram of RK, with incisions drawn in orange.

In radial keratotomy (RK), incisions are made with a precision calibrated diamond knife. It has been found that incisions that penetrate only the superficial corneal stroma are less effective than those reaching deep into the cornea,[2] and consequently incisions are made quite deep. One study cites incisions made to a depth equivalent to the thinnest of four corneal-thickness measurements made near the centre of the cornea.[3] Other sources cite surgeries leaving 20 to 50 micrometres of corneal tissue unincised (roughly equivalent to 90% of corneal depth based on thickness norms).[2]

Arcuate keratotomy is still popular to correct astigmatism. It is also done with a diamond knife but in these cases, cuts are made circumferentially, parallel to the edge of the cornea.

Postsurgical healing

Cross-section schematic of postsurgical epithelial plugs. Example of a desirable outcome left, and an undesirable outcome right.
Enlarge
Cross-section schematic of postsurgical epithelial plugs. Example of a desirable outcome left, and an undesirable outcome right.

The healing corneal wounds comprise of newly abutting corneal stroma as well as fibroblastic cells and irregular fibrous tissue. Closer to the wound surface lies the epithelial plug, a bed of the cells that form the normal corneal epithelium, which have fallen into the wound. Often this plug is three to four times as deep as the normal corneal epithelium layer. As the cells migrate from the depth of the plug up to the surface, some die before reaching the surface, forming breaches in the otherwise healthy epithelial layer. This consequently leaves the cornea more susceptible to infection.[4][5][6] This risk is estimated to be between 0.25%[7] and 0.7%[8] Healing of the RK incisions is very slow and unpredictable, often incomplete even years after surgery.[9] Similarly, infection of these chronic wounds can also occur years after surgery,[10][11][12] with 53% of ocular infections being 'late' in onset.[13] The pathogen most commonly involved in such infections is the highly virulent bacterium Pseudomonas aeruginosa.[14]

Side effects

Large epithelial plugs may cause more scattering of light, leading to symptoms of flare and 'starbursts'. This can happen especially in situations like night driving, where the stark glare of car headlights abounds. These dark conditions cause the pupil to dilate, maximizing the amount of scattered light that enters the eye. In cases where large epithelial plugs lead to such aggravating symptoms, patients may seek further surgical treatment to alleviate the symptoms. [4]

References

  1. ^ http://elliseye.com/chapter_3.html
  2. ^ a b Bashour M, Benchimol M. (2005) Myopia, Radial Keratotomy. Emedicine. Viewed 12 October 2006. <http://www.emedicine.com/oph/topic669.htm>
  3. ^ Waring G, Moffitt S, Gelender H, Laibson P, Lindstrom R, Myers W, Obstbaum S, Rowsey J, Safir A, Schanzlin D, Bourque L. (1983) ‘Rationale for and design of the National Eye Institute Prospective Evaluation of Radial Keratotomy (PERK) Study’. Ophthalmology 90(1):40-58
  4. ^ a b Bergmanson J, Farmer E. (1999) ‘A Return to Primitive Practice? Radial Keratotomy Revisited’. Contact Lens and Anterior Eye 22(1):2-10
  5. ^ Bergmanson J, Farmer E, Goosey J. (2001) ‘Epithelial plugs in radial keratotomy: the origin of incisional keratitis?’ Cornea 20(8):866-72
  6. ^ Deg J, Zavala E, Binder P. (1985) ‘Delayed corneal wound healing following radial keratotomy’. Ophthalmology 92(6):734-40,
  7. ^ Waring G, Lynn M, McDonnell P. (1994) ‘Results of the prospective evaluation of radial keratotomy (PERK) study 10 years after surgery’. Arch Ophthalmol 112:1298-1308
  8. ^ Holler K, Darin J, Pettit T, Hofbaner J, Elander R, Levenson J. (1983) ‘Three years experience with radial keratotomy: the UCIA study’. Ophthalmology 90:627-636
  9. ^ Binder P, Nayak S, Deg J, Zavala E, Sugar J. (1987) ‘An ultrastructural and histochemical study of long-term wound healing after radial keratotomy’. Am J Ophthalmol 15;103(3 Pt 2):432-40.
  10. ^ McClellan K, Bernard P, Gregory-Roberts J, Billson F. (1988) ‘Suppurative Keratitis: a late complication of radial keratotomy’. J Cataract Refract Surg 14:317-320
  11. ^ Mandelbaum S, Waring G, Forster R, Culbertson W, Rowsey J and Espinal M. (1986) ‘Late development of ulcerative keratitis in radial keratotomy scars’. Arch Ophthalmology 104:1156-1160
  12. ^ Wilhelmus K, Hanburg S. (1983) ‘Bacterial Keratitis following Radial Keratotomy’. Cornea 2:143-6
  13. ^ Jain S, Azar D. (1996) ‘Eye infections after refractive keratotomy’. J Refract Surg 12:148-155
  14. ^ Heidemann D, Dunn S, Chow C. (1999) ‘Early- versus late-onset infectious keratitis after radial and astigmatic keratotomy: clinical spectrum in a referral practice’. J Cataract Refract Surg 25(12):1615-9.


Surgery - eye surgery
Eyelids Blepharoplasty
Lacrimal system Dacryocystorhinostomy
Cornea Radial keratotomy - LASIK - Keratomileusis - Epikeratophakia - Corneal transplantation - Photorefractive keratectomy
Iris, ciliary body, sclera, and anterior chamber Trabeculectomy - Iridectomy
Lens Phacoemulsification - Cataract surgery - Capsulorhexis
Retina, choroid, vitreous, and posterior chamber Vitrectomy
Orbit and eyeball Enucleation

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Medical Encyclopedia. © 2006 through a partnership of Answers Corporation. All rights reserved.  Read more
Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved.  Read more
Dental Dictionary. Mosby's Dental Dictionary. Copyright © 2004 by Elsevier, Inc. All rights reserved.  Read more
Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Radial keratotomy".  Read more

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