|Year : 1982 | Volume
| Issue : 4 | Page : 347-350
Recent advances in corneal transplantation
VK Raju, Bruce Mathalone, IV Rao
West Va. Univ. Med. Ctr., Dept. of Ophthal., Morgantown, and Royal Eye Hospital, Surbiton, Surrey, England, United Kingdom
V K Raju
Dept. of Ophthalmology, WVU Medical Center, Morgantown, WV 26506
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Raju V K, Mathalone B, Rao I V. Recent advances in corneal transplantation. Indian J Ophthalmol 1982;30:347-50
Corneal transplantations enjoy the highest success rate of any of the organ transplants. Although these tissues have been transplanted on a relatively large scale since the 1930's, their success rate has soared with major advances occurring in the early 1960's. Prior to that time aphakic transplants were nearly always unsuccessful. However, with the advent of anterior vitrectomy, aphakic transplants can now be performed with greater success. Other major advances associated with corneal transplants concern the introduction of cryo preservation in 1965 and the subsequent development of the technique of preserving corneas in recipient serum.
Further major advances have taken place in the last decade to improve prognosis and ultimate visual acuity for patients undergoing corneal transplantation.
| Corneal preservation|| |
In 1973. McCarey and Kaufman introduced a new and simple technique for short term preservation of the donor cornea, by placing the donor cornea having a 3mm scleral rim in tissue culture medium 199 and 5% dextran. (MK medium) Their immediate results in animals and later in man very were encouraging. Further reports substantiated their findings,. Most corneal surgeons recommend preservation of donor cornea as soon as possible after death at+ 4° C. The cornea is removed from the medium and donor button is punched out over a teflon block from the endothelial side. Punching out from the endothelial side allows more endothelial cells to be transplanted, compared with excision of donor button with scissors. Contamination of corneas has occasionally been reported with disastrous results. Today most corneal surgeons recommend the addition of gentamycin at a concentration of 40-100 μgrams/ml. to MK medium. It is extremely important to sterilize the donor globe completely before excising the cornea. Comparison of MK medium storage with moist chamber storage has demonstrated the better quality of the endothc lium which had been stored in the MK medium. Another advantage of the MK medium is the ability to store the tissue for periods up to 96 hours, compared with the limited time of 36 hours of most chamber storage. The advantages of increased storage time are obvious. Another approach is to store the entire cornea at 37° C in a more nutritive medium (organ culture). Doughman and coworkers reported their results of organ cultured corneas at 37° C in 1973 and have since published numerous reports discussing their techniques and results. They have preserved human corneas up to an average of 13 days post mortem with successful results. Although they have been working at a temperature more prone for contamination, they have reported only one instance of infection.
| Selection and handling of donor tissue|| |
In 1975 Leibowitz and Laing and in 1976 Bourne and Kaufman introduced the clinical utilization of the corneal specular microscope originally designed by Maurice. Specular microscopy of the cornea allows one to evaluate endothelial cell morphology and density before and during preservation, as well as after transplantation. The presently available specular microscope views 0.02-0.04mm. of the entire endothelial surface which measures over 100 mm in area. Hence we are able to sample a very small area of the corneal endothelium. Newer specular microscopes are being manufactured which can scan larger areas of the endothelium. King set forth some of the criteria fir donor selections, most of which are maintained today. [Table - 1] As we have learned more about endothelial physiology and preservation, certain of these criteria have been modified in recent times.
| Sutures and suturing techniques|| |
The development of the 10-0 monofilament nylon suture greatly improved many aspects of transplantation. Many different combinations of suturing techniques have been recommended from the simple interrupted and running suture to a combination of both interrupted and running, double running and anti-toric sutures. The nylon sutures are non-reactive and elastic and can close a full thickness corneal wound when placed at the level of Descemet's membrane, and it has even been recommended that such sutures be used for eompleme through and through suturing. During the suturing of the corneal graft the anterior chamber is usually not formed and the iris and lens rub on the corneal endothelium damaging the cells. It was shown that more cell loss occurs at the time of phakic than aphakic transplantation.
| Removal of sutures|| |
What is the optimal time for removal of sutures following corneal transplantation? Every surgeon has different indications for this procedure. Too early removal would lead to wound dehiscence, graft failure and possible infection, while delay may lead to vascularization of the wound and donor cornea. The more vascularization of the giaft, the greater incidence of graft rejection. A running suture in an avascular recipient (keratoconus, bullous keratopathy) should remain in place for at least 6 montns. Interrupted sutures in these cases are usually removed earlier as they stimulate wound healing faster than running suture. Indications for interrupted suture removal include wound vascularization, suture abcess, visible wound scar, loose suture or graft rejection.
| Post keratoplasty glaucoma|| |
The cause of this postoperative glaucoma in patients with aphakic corneal transplants is not known. It is a major problem following aphakic keratoplasty, or combined keratoplasty and cataract extraction in patients with no history of glaucoma before surgery. This type of glaucoma is probably short-lived but it may compromise the donor corneal endothelium. When medical treatment to control the pressure fails, cyclocryotherapy is the choice. Recently Olson and Kaufman have presented a hypothesis suggesting that the trabecular sheets and the openings into Schlemm's canal are compromised during keratoplasty leading to decrease in the outflow facility. They also suggested that placement of 0.5mm larger donor button will improve the outflow facility.
| Astigmatism|| |
One cannot predict how much corneal astigmatism will develop after the removal of the sutures. Wound dehiscence may occur if the sutures are removed early and delayed removal may lead to vascularization of the cornea, irregular wound scarring and graft rejection. Use of a surgical keratometer during operation may minimize corneal distortion and subsequent astigmatism. In cases of postoperative high astigmatism, wedge resection of peripheral cornea may be beneficial. At present most surgeons favour accurate radial placement of cardinal sutures in combination with a running suture using 10-0 monofilament nylon with a GS-9, 14, 15 or 16 needle.
| Graft rejection|| |
In the past, the avascular cornea was considered to reside in a privileged site free of recognition as foreign tissue. However, it is now clear that rejection can occur at almost anytime following transplantation. The incidence of rejection in the avascular corneas is much lower than the incidence in the vascularized corneas. There is some evidence to suggest that matching patients with vascularized corneas with compatible donors may decrease the incidence and severity of the rejection.
| Macular edema|| |
Despite meticulous surgical technique, good donor cornea, glaucoma control, and rejection process, patients may still not recover good visual function owing to macular edema. This is particularly true in aphakic corneal transplants as most of these eyes have had manipulation of the vitreous during surgery. There is no satisfactory treatment for postoperative macular edema. One could possibly prevent this complication by performing all combined cataract extractions by the extracapsular technique.
| Summary and conclusions|| |
In summary, the prognosis for corneal transplantation has tremendously improved in the last decade. In our own recent series of 60 cases of penetrating corneal transplants, [Table - 2] excellent results were obtained in Group I fair to good results were obtained in Group II, and poor results were obtained in Group III. Follow up period ranged from 1 year to 3 1/2 years. In the near future we will see better techniques of corneal storage, improved suturing techniques and will be able to tissue type prospective donors and recipients, all contributing to ultimate success of corneal transplantation.
| References|| |
Barraquer, J., 1962 : Highlights of Ophthalmol., 5 : 320.
McCarey, B.E., Kaufman, H.E., 1974, Invest. Ophthalmol 13 : 165.
Stark, W.J., Maumenee, A.E., and Kenyon, K.R., 1975, Amer. J, Ophthalmol. 79 : 795.
Aquavella, JA., Van Horn, D.L., and Haggarty, C.J., 1975, Amer. J. Ophthalmol., 80 :791.
Doughman, D.J., Van Horn, D.L.1 Harris, J.E. et al. 1273 : Trans. Am. Ophthalmol. Soc., 71 304.
Laing, R.A., Sandstron, M.M. and Leibowitz, H.M., 1975, Arch. Ophthalmol. 93 : 143.
Bourne. M., anc Kaufman, H.E., 1976, Amer. J. Ophthalmol, 81 : 319.
King, J.H., Jr, 1970, Intl. Ophthalmol. Clin,, 10 , 313.
Batehelor, J.R. 1974, Lancet, 1 : 651.
[Table - 1], [Table - 2]