The concept of using a different sized diameter corneal graft and host bed has been used in ophthalmology for many years.
In what cases of corneal transplantation do you use a disparate sized graft? What is the difference in size between the donor and the recipient bed? Are there conditions such as keratoconus where you would not use disparate-type grafis? If you had experience with the newer mechanized-type trephines such as the Hanna and the Krumeich-type trephine, have you modified the size of the donor recipient bed? If so, why have you modified the difference with these new trephines?
Question provided by Miles H. Frledlander, MD
Before answering the question, a brief overview of the origins of this technique may assist the reader to better understand the response. The first use of a disparate sized (larger) graft was probably by Jose Barraquer in the 1950s to obtain a better fit in the bed of a lamellar keratoplasty. I was introduced to his technique by his brother Joaquin and acquired a set of the special trephines he had made by Greishaber with 0.1 and 0.5 mm diameter differences in addition to the usual 1.0 mm diameter differences of the standard set. In the early 1970s when Kaufman introduced corneal cryopreservation, it became necessary to cut the donor button from the endothelial surface by punching it on a block of paraffin or Teflon, a technique originally advocated by Amsler. As this technique produced graft buttons more reliably than the whole eye technique I had been using, I began to employ it routinely. However, it soon became evident that the postoperative corneas, with all sutures removed, were excessively flat, inducing unwanted corneal hyperopia in phakic eyes and sometimes severe anisometropia, as well the need for excessively high corrections in aphakic eyes. The punched buttons were being undercut, making their anterior diameter less than the stated diameter of the trephine and the recipient opening. When I used 0.1 mm, 0.5mm, even 1.0 mm larger diameter Barraquer-Grieshaber blades to cut the donor button, I was able to obtain significant average corneal steepening and reported this with Kelly at the 1976 World Congress of the Cornea in Washington, DC. I further detailed the rationale and technique together with a specially designed adjustable trephine and corneal punch to fit multiple blade diameters required in my 1977 book on The Cornea: Optics and Surgery.1
Disparate sized grafts should be routinely employed when using a combination of posterior punch cutting of the donor button and anterior cutting of the recipient opening with any manual, motorized, or suction trephine. In my opinion, however, the diameter difference should not exceed 0.2 or 0.25 mm, the object being today to achieve an average keratometric power of approximately 43 diopters. Only in the case of a preoperative corneal or axial anisometropia where the eye to be grafted is significantly flatter or axially disparate (?-scan confirmed) than the fellow normal eye should a iarger diameter - 0.5 to 1.0 mm - be considered. The use of a 0.5 to 1.0 mm disparate diameter (larger) graft in pseudophakia or a triple procedure is counterproductive since the steeper cornea induced will result in a "dioptric surprise" unless of course the fellow eye has already had a too large diameter graft. In addition, diameter differences larger than 0.2 or 0.25 mm seem to be productive of higher degrees of postkeratoplasty astigmatism.
Using differences of 0.5 to 1.0 mm in a normally curved or steeper (such as keratoconus) cornea will result in a myopic (steeper than average 43 D) cornea and also can induce an annoying anisometropia. An exception could be to prevent anisometropia when too large a diameter graft has been used on the fellow eye. Although in 1977 I advised to use the same sized donor for keratoconus, I now use a 0.2 mm larger donor button which, when employed with my "Standard Keratoplasty Technique" described in Troutman and Buzard's recent textbook,2 results in an average K of 42.95 D. However, should a keratoconus with a significant axial myopia (?-scan confirmed) be encountered, and this in my experience is rare, a same size or smaller diameter graft may be considered to reduce the postoperative myopia and, provided the fellow eye had or will have the same procedure, so as not to induce a corneal anisometropia.
For the past 4 years, since we have had available the Krumeich anterior chamber and recipient cornea trephine system, Belmont and I no longer employ disparate sized grafts for penetrating keratoplasty. In our hands this system, which uses an 8.0millimeter trephine blade to cut both donor and recipient, has significantly reduced postoperative astigmatism to less than 3 D (AEVO Poster 1992), while maintaining a 43 D average K with all sutures out (ARVO Poster 1991). We have used the Hanna recipient suction trephine and corneal punch set but have not yet been able to evaluate his new artificial anterior chamber for cutting the donor button. According to Parel, the Krumeich and the Hanna instruments cut significantly better donor and recipient (in the case of the Krumeich System) and recipient (in the case of the Hanna instrument) than other trephines he has evaluated.
I would like to qualify that our results are based on the use of a "Standard Keratoplasty Technique"2 which includes surgical-keratometer-controlled rotational matching of the graft to the recipient bed and through and through (full thickness) suturing with a 10-0 monofilament nylon suture using opposing continuous antitorque closure2,3 adjusted to approximate sphericity, again under surgical keratometer control. Final evaluation and reporting of residual postkeratoplasty astigmatism and average keratometry with the Topographic Modeling System is done only after all sutures have been removed and interval stable readings are obtained.
1. Troutman RC. Microsurgery of the Anterior Segment of the Eye. The Cornea: Optics and Surgery. St Louis, Mo: CV Mosby Co; 1977;2:357.
2. Troutman RC, Buzard KA. Corneal Astigmatism: Etiology, Prevention and Management. St Louis, Mo: Mosby Yearbook; 1992:506.
3. Troutman RC. Microsurgery of the Anterior Segment of the Eye: Introduction and Basic Techniques. St Louis, Mo: CV Mosby Co; 1974:324.
RICHARD C. TROUTMAN, MD
New York, NY
The need for larger donor trephines arose with the preservation of isolated corneas, which necessitates punching the donor button from the endothelial side. This results in a slightly smaller corneal button than trephination from the epithelial side. I use a 0.25millimeter larger donor trephine in all cases except keratoconus, where I use the same size. Although it is true that the larger the disparity between donor and recipient trephines, the steeper the graft, the final graft curvature also depends on the trephine system used. For instance, I obtained a mean corneal curvature of 46.00 diopters after all sutures were removed using a 0.20-mUIimeter larger donor with a modified Lieberman punch and a Katena trephine for the donor and a Hessburg-Barron suction trephine for the recipient. On the other hand, I obtained grafts several diopters flatter (often a preferable result from a "mean k" standpoint) with essentially the same nominal trephine disparity (0.25 mm) using disposable Storz trephines and a Castroviejo handle for the recipient and the Iowa press for the donor. The final result also may vary with the individual surgeon and with the preoperative curvature of the recipient cornea. The newer mechanized trephines may decrease this variability, but I do not have enough "sutures out" results with them yet for comparison.
WILLIAM M. BOURNE, MD
The principle of my trephine, the Guided TVephine System, is to create identical dimensions of donor button and recipient's bed.
After close to 400 perforating grafts with this system using no disparate grafts but identical sizes for donor and recipient, the clinical results confirm the theoretical approach.
The rationale behind oversizdng buttons comes from necessity. As long as free hand cutting trephines are used and create necessarily ovals, oversizing was necessary to compensate for the induced tissue difference. The same is true for the direction of the cut. As long as corneal punches are used to cut the donor button from the endothelial side, we have a tissue gap at the endothelial side. To counteract these gaps, oversizing has been necessary, too. Cutting both donor and recipient from the epithelial side under the same pressure creates the same amount of undercut and a fit without intracorneal tension.
Results for all indications indicate that no disparate grafts are necessary and may be disadvantageous, except maybe keratoconus in which the results show rather steep radii so that this indication may still be in discussion regarding graft size.
JÖRG H. KRUMEICH, MD
The concept of using disparate size grafts is not new. Over 30 years ago, it was recognized that when the donor cornea is obtained by punching from the endothelial surface with a trephine, one obtains a different size diameter than is obtained by using the same diameter trephine from the epithelial surface.
In the last 10 years, numerous publications have cited the mean corneal power in cases that underwent a donor corneal transplant that was obtained with a trephine labeled 0.25 mm or 0.20 mm larger in diameter than the diameter of the trephine used to remove the opaque host tissue. This is a so-called 0.25-millimeter or 0.20-niillimeter disparate diameter graft. Similarly, 0.50-millimeter and 0.75millimeter disparate grafts have been reported. "Same size" grafts usually mean that the surgeon has used the same diameter trephine for the donor and recipient. However, studies by Olson and others have demonstrated that the diameters actually achieved may not be what is labeled on the trephine because the trephines vary in their labeling, their sharpness, and because the mechanics of trephining can produce different wound morphologies. Any or all of these factors tend to. produce diameters smaller than the stated diameter on the trephine.
Although surgeons have been aware of these facts for many years, recently Girard has suggested that surgeons use donor corneas smaller in diameter than the recipient hole to reduce the myopia that is common with keratoconus. These so-called undersized grafts are actually achieved when one uses the same diameter trephine for the donor and recipient, but Girard purposely uses a donor trephine used for the host. I personally have been using same size and 0.25-millimeter oversized grafts for keratoconus cases that had been highly myopic. I try to avoid using same size grafts in short eyes with keratoconus.
Since 1986, I have been using the Guided Trephine System (distributed by Katena Instruments) designed by Dr Jörge Krumeich. I have found this trephine to be the best I have ever used to produce a recipient wound. I have been unable to use it on donor corneas because the eye banks will not supply a large enough corneal scleral rim which is needed for the artificial anterior chamber that goes with the instrument. For this reason, I have used only an 8-millimeter diameter recipient hole and have varied the diameters of my donor trephines using disposable WECK, Ine trephines and the Troutman punch.
As an aside, I found that the same donor recipient combinations with the Guided Trephine System produced statistically steeper mean corneal powers then when I had used other trephines with the same donor recipient combinations.
PERRY S. BINDER, MD
San Diego, Calif
I prepare my donor button by punching from the endothelial side. This creates a button that is slightly smaller than the stated diameter on the trephine because of compression of the tissue during punching. Therefore, I select a donor trephine that is 0.25 mm larger in diameter than the host, but in fact I am putting in a "same size" graft in reality. In keratoconus, I usually use trephines with a 0.25millimeter smaller diameter for the donor than the host, which makes the resultant donor curvature flatter.
I have used the Hanna mechanical suction trephine for the host and the Hanna donor punch for the donor almost exclusively for 3 years; I have not modified the size of the diameter trephines that I use. If the host trephine is used to cut into the anterior chamber, it leaves no posterior lip and there is a small angle of undercut. Surgeons accustomed to having a posterior lip on the host may find this a somewhat difficult transition and may find a need to use a larger diameter donor button than they are used to.
GEORGE O. WARING, III, MD, FACS
I use disparate sized grafts in almost all corneal transplants. For aphakia, Pseudophakie bullous keratopathy, and triple procedures where corneal transplants and cataract extractions are being done, combined with posterior chamber lenses, I use a 0.50-millimeter different size graft. I usually use 8.00 for the host and 8.50 for the donor button in 90% of these cases. For patients who are phakic such as stromal dystrophies, corneal opacities, or trauma, the disparate size is .25 mm.
If the patient has keratoconus and if a corneal transplant has been done on the other eye with resultant high myopia, I will use the same size corneal transplant. I have not used smaller transplants than the donor although I have heard that some surgeons have done this if there is resultant high myopia with previous transplants for keratoconus. Unfortunately, if the same size or even a smaller graft is done for keratoconus, the resultant corneal transplant is very flat and makes contact lens fitting very hard. As more than 50% of the patients require contact lenses after corneal transplantation for keratoconus, I do not like to do the same size or smaller grafts for this disease.
I have not used the Hanna and Krumeich-type trephines.
PETER R. LAIBSON, MD
New Orleans, La