Lamellar Keratoplasty

Definition

Refractive surgery is any operation intended to alter the refractive state of the eye. Refractive corneal surgery refers to operations on the cornea that are intended to alter the refractive state of the eye. This type of surgery is popularly referred to as refractive keratoplasty, an appropriate term since keratoplasty means "to mold the cornea."

Lamellar refractive keratoplasty involves the placement of a lenticule on or within the cornea to alter its refractive power, usually by changing its anterior curvature.

Description

Lamellar keratoplasty involves replacement of the patient's diseased anterior corneal stroma and Bowman's membrane with donor material. Host endothelium, Descemet's membrane, and a part of the deep stroma are preserved. The donor corneal disc becomes repopulated with host fibroblasts, and the recipient epithelium usually covers the anterior corneal surface. This procedure is technically more difficult than penetrating keratoplasty.

Lamellar keratoplasty has the advantage of being primarily an extraocular (outside the eye) procedure that preserves the host endothelium. The risk of rejection is therefore markedly diminished. The risks of wound leaks or flat anterior chambers associated with an intraocular procedure may be eliminated.

Microsurgical techniques have vastly improved the technique of lamellar keratoplasty, but they have also substantially improved the results with penetrating keratoplasty. The use of conjunctival flaps and therapeutic soft contact lenses has reduced the indications for lamellar keratoplasty.

Procedure

There are at least three major lamellar refractive keratoplasty techniques:

1. keratomileusis ("carving the cornea") in which a disk of the patient's anterior cornea is removed with a microkeratome, ground into a new shape on a cryolathe, and sutured back into place

2. epikeratoplasty ("graft on the top of the cornea") in which a human donor lenticule - either lyophilized or fresh - is ground into a new shape on a cryolathe and is sutured to a groove in the de-epithelialized surface of the cornea

3. keratophakia ("lens within the corneal stroma") in which a human donor or synthetic plastic lenticule is placed within the corneal stroma

Deep keratectomy ("excision of a piece of the cornea") is used to remove diseased corneal stroma. Usually this procedure is performed along with a conjunctival transplant procedure or with a lamellar graft.

Indications for lamellar keratoplasty may be optical or tectonic (relating to variation in the structure of the eye).

Optical reasons for a lamellar graft include advanced or recurrent pterygium; anterior and stromal dystrophies; superficial post-traumatic or post-infective leukoma; or high risk of postoperative penetrating keratoplasty rejection.

A tectonic lamellar graft is used to support thinned or weakened corneal tissue. In many cases, tectonic lamellar keratoplasty is a precursor to a more definitive procedure such as penetrating keratoplasty. Specific tectonic indications for lamellar keratoplasty include generalized corneal thinning; localized corneal thinning; or peripheral thinning such as in Terrien's marginal degeneration.

All of the above optical and tectonic conditions are relative indications for lamellar keratoplasty.

Postoperative Care

Postoperative care involves use of appropriate quantities of topical antibiotics and corticosteroids. During the few weeks the sutures are left in place, an antibiotic such as 0.3 percent tobramycin drops 4 times daily may be given. The sutures are removed when they become loose, when vessels bridge the wound from host to donor, or when healing is apparent.

Since lamellar keratoplasty does not usually involve penetration into the eye, most complications are not serious. Premature loosening of sutures, ingrowth of vessels, infection, or later appearance of the original disease may all occur.

Perhaps the major complication is the inherent slow recovery of vision in most cases of lamellar keratoplasty because of haze at the interface.

Questions to Ask Your Doctor

What is the problem with the cornea?

Is surgery needed?

Is there a non-surgical option?

What type of surgery is indicated?

How will this be performed?

What are the possible complications?

Will further surgery be required at a later date?

Will full sight be regained?