Radial Keratotomy (RK)

What it is

adial keratotomy is an established surgical procedure whose purpose it is to remove or reduce ametropia resulting from myopia and/or myopic astigmatism. The whole point of RK is to reduce the central corneal curvature sufficiently so as to move the cornea’s focus back onto the retina. Like all surgery, it has its limitations and hazards. Its limitations are that it cannot be expected to completely eliminate myopia over -7.00 diopters nor astigmatism much in excess of -4.00.

Its hazards are the usual of any partially invasive procedure on the cornea, namely: infection (both of the cornea and the eye); irregular healing; as well as others. Temporary glare, and photophobia are frequent as well. It is not expected that the surgery will cause loss of vision in the absence of serious infection and/or scarring. Serious scarring is not expected unless the incisions are so made as to promote certain inevitable healing responses. Infection is likewise prevented by the administration of antibiotic drops post-surgery.

The surgery works by causing temporary weakening of the peripheral stroma of the cornea such that the prevailing intraocular pressure of the eye acts to reshape the weakened area (by steepening its curvature) which in turn acts to flatten the central uncut or visual portion of the cornea - increasing the focal length of the eye. The amount of flattening of the center of the eye is directly dependent upon a number of factors, most of which are controlled by the surgeon. For example: as the surgical clear zone (OZ) gets smaller, all else being equal, the amount of flattening will increase; this effect appears to be non-linear. That is, as the zone gets smaller, the amount of flattening increases almost exponentially. If the OZ is kept constant, the amount of flattening can be increased in 3 ways: 1) by increasing the number of incisions, and 2) by increasing the depth of the incisions, or 3) both.

The weakening of the peripheral cornea allows the internal pressure within the eye to cause this weakened area to bulge outward. This outward bulging places tension on the edge of the uncut central optic clear zone causing it to flatten. RK therefore works by increasing ocular area through tissue weakening — not by adding tissue as some believe.

This peripheral weakening is controlled by the length, depth, and number of incisions made. Other factors have an effect on the outcome causing the surgeon to make an adjustment in the first three factors. These affecting factors are: age, gender, and degree of curvature of the central cornea.

Generally speaking males get more effect for a given combination of factors than do females (up to age 40); and younger individuals usually get less effect under the same circumstances. This influence cannot be quantified but cannot be ignored either.

If the incisions are grouped or clustered, more weakening will occur in that area than in any other. This fact was used in the original “L” procedure designed to correct myopic astigmatism. Today, tangential or “T-cuts” are used to effect the astigmatism. (see also AK)

© Leo D. Bores, MD - 2002