Eye Care Blog

Orthokeratology

The term orthokeratology comes from the words ortho, meaning “straight,” and keratology, relating to the cornea. It should come as no surprise then that this form of vision therapy seeks to actually change the curvature of the cornea—in order to lessen the refractive error. Using much the same principle as an orthodontist employs when using braces to correct the position of wayward teeth, orthokeratology utilizes a series of relatively flat, hard PMMA contact lenses to mold the cornea gradually into the desired shape.

The process is a long and costly one. The success rate is quite low, the process may be very uncomfortable, and there are no guarantees. Even when successful the result is fleeting unless “retainer” lenses are worn periodically to prevent the elastic cornea from “bouncing back” to its natural shape. Most ophthalmologists object to this practice, citing the inadvisability of altering such a sensitive part of the anatomy (especially when so many safer alternatives are available.) There is also the possibility of permanently damaging the cornea. Nevertheless orthokeratology does have its advocates, and experimentation and research continue.

There are three methods, highly controversial and still experimental, that can correct errors of refraction:

Radial Keratotomy

This surgical procedure may be performed on those nearsighted people who cannot or do not wish to wear eyeglasses or contact lenses. The process consists of making a series of eight to sixteen radial incisions in the cornea, much like the spokes of a wheel. The incisions are about half the thickness of the cornea, and do not meet in the center, thus sparing the pupillary zone. The scored cornea flattens in shape as the incisions heal, a process that takes approximately six to eight weeks. The result is a reduction of myopia. Each patient undergoing this procedure has to be carefully selected as to degree of myopia and the thickness and condition of the cornea. Like other forms of surgery, radial keratotomy cannot be guaranteed, and complications such as scarring and perforations in the cornea can occur. The surgery can be performed as an outpatient procedure under local anesthesia. The average cost is two thousand dollars. A national investigational study is under way to determine the efficacy of radial keratotomy.

Keratophakia

Only aphakia and hyperopia can be corrected using this method, which involves the use of a human corneal donor button. The donor cornea is frozen and lathe-cut and shaped by computer technology. A portion of the recipient cornea is removed surgically and the donor button is sutured onto or placed in a center pocket of the recipient cornea. The resultant combination corrects the refractive error.

Keratomileusis

Still another experimental surgical technique utilizes a vibrating microkeratome (tiny surgical knife), which removes a 1mm-thick slice from the patient’s cornea. The slice is promptly frozen and a computer-controlled cryolathe fashions the underside of the slice to obtain the desired correction of the refractive error. After thawing out, the newly shaped corneal slice is sutured back onto the patient’s cornea. In essence the patient’s own corneal tissue has been made into a permanent contact lens.

Possibly related posts: (automatically generated)
Eye Surgery as a Means to Correct Vision Refractive Errors

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