Radial keratotomy

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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

File:RK2.png
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

File:Epiplugs.png
Cross-section schematic of postsurgical epithelial plugs. Example of a desirable outcome left, and an undesirable outcome right.

The healing corneal wounds are comprised 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]

Increasing altitude can cause partial blindness in radial keratotomy patients, as discovered by mountaineer Beck Weathers (who had had the surgery) during the 1996 Mount Everest disaster.

References

  1. http://elliseye.com/chapter_3.html
  2. 2.0 2.1 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. 4.0 4.1 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.