Keratomileusis — classical

eratomileusis, and Keratophakia are lathing procedures that had their beginnings in 1949 with the work of J. I. Barraquer, M.D. of Bogota, Columbia, South America. The technique of Keratomileusis (KM) consists of the temporary removal of a lamellar section of the patients cornea. This is done by placing a specially constructed suction ring upon the eye after the eye (or the patient) has been thoroughly anesthetized. This ring is fitted with dove-tail guides on its front surface which serve to guide the footplate of a device called a microkeratome. When suction is applied to the ring, it holds the eye against it tightly. A clear plastic applanation lens is placed upon the eye to check the diameter of the tissue disk to be resected. If the disk is too large or too small, a different ring is substituted until the size is correct.

Guided by previous experience and the effect desired, the microkeratome is prepared by inserting a special plate into the bottom section. The thickness of this plate and to a lesser extent the pressure induced by suction controls the thickness of the resected tissue. The microkeratome is equipped with a special blade which is oscillated at approximately 10,000 RPM and is controlled through a footswitch.

The sequence of events then is as follows: the ring is applied to the eye and suction begun. The microkeratome is advanced across the cornea until the blade is clear. The resected tissue disk is grasped gently with forceps and transferred to the thickness gauge. Both the diameter of the tissue and its thickness are entered into a computer program. The tissue is then placed into a preservative solution. The patients cornea is then scrubbed by irrigating with Balanced Salt Solution and wiping with a Sable Brush. A plastic cap is then placed over the eye to prevent the introduction of dust particles. Gloves are not worn during these procedures to avoid the introduction of talc and other particulate matter into the interface.

The tissue is then placed in a preservative for one minute. From there it is transferred to a special, sterilized lathe and the tissue is re-shaped while frozen. The tissue is then thawed an replaced onto the patients eye where it is sutured into place. Many people get frightened when we talk about lathing. However, the operation works very well and thousands of patients have benefited from this technique. It takes a little longer for vision to get clear again than it does for RK, but the success rate is about the same. The effective range for this surgery is from -6 to -17 diopters of myopia and +5 to +16 diopters of hyperopia (Figure).

Myopic Keratomileusis (MKM)

Keratomileusis performed for myopia. In these cases, tissue is removed (lathed) from the center of the resected disc to form a concave lenticule. When this is sutured back into the resection bed, the front of the cornea becomes flatter thereby increasing the focal length of the eye.

Hyperopic Keratomileusis (HKM)

Keratomileusis performed for hyperopia. In these cases, tissue is removed (lathed) from the periphery of the resected disc forming a convex lenticule. When this is sutured back into the resection bed, the front of the cornea becomes steeper thereby decreasing the focal length of the eye.

Keratomileusis-In-Situ

(see also: ALK) In this technique a large but thin section (7.25 mm/135 µm is first removed and stored in a moist chamber. Then, another, smaller section is removed in the same manner. The previously removed tissue is then replaced onto the eye and sutured in place. That's all there is to it! Recovery with this method is much more rapid because no freezing of the tissue is required. This newer method should not be confused with the so-called “BKS” method which was an unsuccessful attempt at cutting the tissue without freezing — but OFF THE EYE.

The complications of this surgery are those that can be expected of any non-penetrating surgical procedure. Infection is usually rare and confined to the corneal stroma and is generally localized. It responds well to topical antibiotics but some may require sub-tenons injection. Cases of severe intraocular infection have been reported with a few cases of endophthalmitis leading to visual loss having occurred. Induced astigmatism is by far the most common complication occurring with this surgery and occurs in about 4% of the cases tending to group in the higher myopia ranges.

Occasionally, epithelial cells (the cells covering the cornea) will be introduced into the interface during this surgery. These cells can grow and spread to the point of producing large plaques or sub-lenticular fluid obscuring vision. In these cases the lenticule has to be removed, cleaned, and replaced -- suturing it back into place. Re-epithelialization is generally rapid after this surgery. However, rarely epithelialization may not occur. In these cases a new lenticule must be made from donor tissue and replaces the old one. A trial of topical cysteine drops may be warranted based on recent reports.

The success rate of this surgery within its indicated range is high (89%) — comparing favorably with other techniques. Because of its technical complexity the surgery is reserved for myopia cases higher than 6 diopters with a practical upper limit of 15 diopters in autoplastic cases and 19 diopters in homoplastic (donor tissue) cases. In low hyperopia the range is from 4 diopters to 9 diopters. Above that the technique of Keratophakia can be used. Astigmatism cannot be treated directly with this technique. Attempts to produce toric lenticules have all failed due to the elasticity of the tissue.

Hyperopic Lamellar Keratotomy (HLK)

This method was originated by Luis Ruiz, MD and Leo D. Bores, MD; Dr. Bores performed the first of these procedures specifically for over-corrected RK's in the mid-1980's. In this procedure, a predetermined diameter corneal disk of approximately 70% thickness is resected using the microkeratome and immediately resutured to the eye. The sutures can be removed in 10 to 15 days. An amount of relative corneal ectasis (bulging) occurs post-operatively, proportional to the diameter of the resected disc. This procedure is more uniform than the hexagonal procedure and is also more predictable — though technically difficult to perform. In addition, the corneas are extremely stable and smooth post-operatively.

Automated Lamellar Keratotomy (ALK)

(See Keratomileusis-in-situ.) The only difference between ALK and KMIS is that ALK is done with an automated microkeratome which moves itself across the cornea. In most instances the corneal cap is hinged and is not sutured in place.

Laser Augmented In-situ Keratomileusis (LASIK)

(See LASIK.)