Incisional refractive procedures
Radial Keratotomy (RK), Astigmatic Keratotomy (AK) and Limbal Relaxing Incisions (LRIs)

Radial keratotomy (RK) is a refractive procedure for myopia (nearsightedness) that has enjoyed tremendous success, but has largely been supplanted in the past decade by excimer laser procedures such as PRK, LASIK, Intra-LASIK, and now the phakic IOLs.  RK was performed on approximately one million Americans over a ten-year period beginning in the early 1980’s, but rapidly began to lose its place in the refractive surgery arena in 1996, following FDA approval of the first excimer laser in the U.S.

The RK procedure entails placing radial incisions in the peripheral cornea, which results in relaxation and flattening of the central cornea. RK is best for low myopes (e.g., -1.00 to –3.00 diopters) and is still offered by a very few refractive surgeons for patients in this range of refractive error. The procedure has the advantage of being safe, with rapid results and high predictability in the low range of myopia. Drawbacks include the fact that the procedure may result in significant glare, starburst patterns around lights at night, and a theoretical risk of wound rupture with blunt trauma to the eye. These risks are minimal for patients with few incisions, however, the greater the nearsightedness, the more incisions required to produce the desired effect. 

Illustration courtesy of www.JirehDesign.com

In general, for the above stated reasons, RK has fallen into disfavor for most ophthalmologists. Furthermore, other procedures such as LASIK, Epi-LASIK, Intra-LASIK, and phakic IOLs have the potential to safely treat much greater degrees of refractive error (including farsightedness) without any structural weakening of the eye.

Astigmatic Keratotomy (AK)

Astigmatic keratotomy (AK) is similar to RK in that deep incisions are placed in the cornea, albeit in this case for the purpose of reducing astigmatism.  With AK, the incisions are placed in an arcuate pattern, at 90 degree angles to the radial incisions (in patients who have or had both RK and AK) and in the steep axis of the astigmatism.  The effect of the AK incisions is to flatten the steeper axis of astigmatism, thereby making the cornea more spherical in nature.  This ultimately provides better vision without glasses.  As with RK, AK has largely fallen into disfavor since FDA approval of the excimer laser and its associated procedures, which treat astigmatism very successfully.

Limbal relaxing incisions (LRI)

Limbal relaxing incisions (LRI) are truly a modification of astigmatic keratotomy (AK), which is a procedure to treat astigmatism. LRI’s, however, are incisions that are placed on the far peripheral aspect of the cornea (the limbus), rather than directly on the cornea itself (as in AK), which ultimately results in a cornea that is more spherical. The astigmatism is thus reduced and uncorrected vision is improved.  Unlike AK, LRIs do not result in glare, starburst, or a weakened cornea, and the incisions heal rapidly without a weakening effect on the eye.

The procedure can be completed in a few seconds after numbing the eye with anesthetic drops. There is usually little if any post-operative discomfort. Furthermore, the cornea is usually stable within two to four weeks, indicating that visual fluctuations have typically resolved by that time interval. 

Limbal relaxing incisions have gained widespread acceptance among cataract surgeons where the procedure is often combined with cataract surgery to reduce pre-existing astigmatism. This results in improved uncorrected visual acuity postoperatively and reduced dependence on corrective eyewear.