Clinical Cornea Research
Tests of corneal function
The Cornea and External Eye Disease Service at Mayo Clinic, Rochester, MN, is evaluating the optical function of the cornea, the front clear window of the eye, in response to various corneal surgeries, including corneal transplantation and laser vision correction of refractive errors (such as myopia and astigmatism).
The ability to see is the result of complex interactions involving all layers of the eye and the brain. Typically, vision (visual acuity) is measured by using an eye chart, but a true evaluation of visual function is much more difficult to assess. Our service is involved in measuring how the cornea contributes to overall visual function. This is done using instruments that measure of the cornea's curvature, clarity, and thickness, and with the microscopic analysis of the cellular layers of this clear tissue. These measurements are correlated to the patient's visual function as measured by his/her ability to see fine detail and contrast. These analyses require an array of testing devices and microscopes that result in some of the most detailed studies of human corneal function performed in the United States. Our service occasionally recruits subjects with normal, abnormal or post-surgical corneas to obtain baseline or preliminary data with these various testing methods.
Corneal transplantation (grafting) is one of the most commonly performed transplants of human tissue, and has a high rate of success. Very recently, new surgical techniques have been developed that allow transplantation of specific layers (i.e. the diseased layers) of the cornea (lamellar corneal graft) as an alternative to traditional full-thickness transplants (penetrating graft). The potential advantages and disadvantages of this new lamellar grafting technique are being studied in a prospective randomized trial for patients with corneal swelling due to diseases such as Fuchs dystrophy or bullous keratopathy. We are actively recruiting interested patients, who would be randomly assigned by a computer to have either a full thickness or partial thickness corneal transplant. As part of their routine postoperative visits, we employ our corneal testing facility to evaluate the structure and function of the healing cornea. With this ongoing study, we hope to help the ophthalmology community decide the ongoing debate regarding which of these two procedures is indicated for which patients.
Fuchs corneal dystrophy
Fuchs dystrophy is a common, inherited disease affecting the corneal endothelium, which is the inner lining of the cornea. This thin and fragile layer is responsible for maintaining the cornea's clarity. Diseases of the corneal endothelium can result in the cornea becoming swollen and cloudy, thereby causing the individual's vision to become poor. In Fuchs dystrophy, corneal endothelial cells are gradually lost during a patient's lifetime and replaced by thickened, irregular bumps (guttae). Even though this is a common disease, the gene (or genes) causing the condition is uncertain. As part of an NIH supported multicenter study, we are attempting to identify the gene or genes responsible for this disease. Identification of the genetic cause would assist in early identification of affected patients, genetic counseling of affected families, and ultimately may lead to treatment in which gene therapy could alter the course of this progressive condition. We are actively recruiting families (ideally, but not exclusively, affected sibling pairs or families with several affected members) with Fuchs dystrophy to participate in the study, which involves an eye examination and blood testing for each affected member. One affected member of the family must have had a corneal transplant.
Laser vision correction
Refractive surgery, or laser vision correction, is currently the most commonly performed corneal surgery in the United States. Individuals with refractive errors, such as myopia or astigmatism, may be candidates for laser vision correction, enabling them to see better without spectacles or contact lenses. This type of surgery has been performed with great success over the last decade, but the longer term consequences of these elective procedures are still unknown.
At Mayo Clinic, we are continuing to study a small group of patients who had the most common types of refractive surgery (LASIK and PRK) in 1998, when the service was first introduced. The longevity of these studies and the detailed prospective evaluation of the cellular effects of laser corneal surgery are unique to Mayo Clinic. As a result of these studies, we recently completed enrollment for a randomized-controlled trial of LASIK, comparing the bladeless and blade techniques for this surgery. This will help to answer new questions that were generated by the original study, and will provide a new detailed study of the cornea's response to newer laser technology. Similarly, we are currently recruiting patients for a randomized-controlled trial of PRK, comparing PRK to its variant procedure known as LASEK. PRK and LASEK are refractive surgery procedures that do not involve the creation of a flap (as with LASIK). Instead, the cells from the corneal surface (epithelium) are removed, and laser treatment is applied to the underlying corneal stroma. PRK and LASEK only vary by the method of removal of the surface cells. We will be studying the cellular response to the different methods of surface cell removal by using our corneal testing facility, in an attempt to answer frequently debated questions in the refractive surgery community, and to provide new long-term data for these procedures.
Laboratory Cornea Research
Donor corneas from donors who have consented to donate their eyes after death can at present be preserved for about 1 week in U.S. eye banks. Permanent corneal storage could be obtained by cryopreservation at very low temperatures, but to date this method has not proved satisfactory for clinical use. We are performing laboratory studies aimed at developing a useful method for corneal cryopreservation, which would then allow permanent storage and true eye "banking."
Increasing the number and quality of donor corneas
Donor corneas need a sufficient number of endothelial cells, which are responsible for corneal clarity, to qualify for successful transplantation, and many donor corneas cannot be transplanted because they do not meet this criterion. These cells are needed because they do not normally divide, so that their numbers cannot be replaced after transplantation. In these laboratory studies, we are developing methods to stimulate these cells to divide during donor corneal storage in order to increase their numbers so that more corneas would qualify for transplantation. This will increase the supply of donor corneas for transplantation.
Experimental corneal transplantation
We have developed an experimental model of corneal transplantation. This allows us to test the effectiveness of new methods of corneal storage before they are used in people. We also can test new techniques of transplantation, such as the use of lasers, in the laboratory. Use of this model increases the safety of our transplantation techniques.