PENETRATING KERATOPLASTY

Full thickness grafts retain their usefulness in select cases

Lamellar keratoplasty (LKP) techniques are continuing to gain wider acceptance but there will likely remain a place for penetrating keratoplasty (PKP) for the foreseeable future, said ESCRS president Jose Güell MD, Autonomous University of Barcelona, Barcelona, Spain, in a keynote lecture at the 15th ESCRS Winter Meeting's Cornea Day.

He noted that there is an urgent need for improved keratoplasty techniques. Cornea transplants are the most common solid organ transplants performed in the world. However, although the success rate is 90 per cent in low-risk patients, it is only 30 per cent to 50 per cent in more complex, higher risk cases, and overall, 30 per cent of cases have a rejection episode. Moreover, re-grafting has become the most common indication for corneal transplantation in the US and some places in Europe.

The more recently developed LKP techniques are designed to overcome some of the problems of corneal transplantation by leaving as much of the healthy cornea in place as possible. For example, endothelial keratoplasty procedures replace only the endothelium but leave the patient's cornea's refraction fairly intact, he noted. Anterior lamellar keratoplasty, on the other hand replaces all or nearly the entire cornea except Descemet's membrane and the endothelium, which all but grossly eliminates the chance of immune rejection.

'Techniques that substitute only the damaged corneal layers have obvious theoretical advantages over penetrating surgery, but these advantages must be demonstrated through properly designed comparative long-term studies, the results from which are not yet available, and they must be superior to the better known and more widely practised techniques,' he said

Lamellar graft update

Dr Güell noted that, regarding endothelial keratoplasty, the data available to date suggests that despite much better postoperative refraction and more rapid functional rehabilitation, the visual acuity is still slightly better after PKP, in some series probably as a result of issues related to the interface between host and donor tissue. In addition, early endothelial cell loss is also greater after endothelial keratoplasty techniques than after PKP, although rejection rates are similar with the two techniques.

The cases where endothelial keratoplasty may not be the best option include eyes where the anterior stroma is seriously compromised, and eyes that are likely to need multiple intraocular procedures, Dr Güell added.

Eyes that have undergone deep anterior lamellar keratoplasty (DALK) techniques have, as expected, a greatly reduced incidence of rejection and a better-preserved endothelium than is the case with PKP.

Generally fewer patients achieve a visual acuity of 20/20 with DALK than do with full thickness grafts, he said. However, visual acuity and visual quality following DALK is partly dependent on the surgeon's success in baring Descemet's membrane in the host and removing Descemet's membrane and the endothelium in the donor button.

Apart from obvious endothelial disease, contraindications for DALK include doubts about endothelial health as in some cases of herpetic disease, where there may be difficulty in evaluating the posterior corneal layers, and also some cases of keratoconus where the cornea is very thin after an hydrops episode. Moreover a certain percentage of cases must be converted to full thickness procedures because of peri-operative complications.

Eyes with penetrating corneal injuries are also unsuitable for lamellar approaches, as are many cases with chemical burns, which frequently require limbal transplants to facilitate post-grafting rehabilitation. In paediatric keratoplasty cases the use of posterior or anterior lamellar surgery is possible but the endothelial layer's postoperative transparency is less reliable.

Case reports

Dr Güell described several cases where he considered full thickness grafts to be the best option. One was a patient who developed a severe case of infectious keratitis following a LASIK procedure. The infection penetrated through most of the cornea's layers and may have compromised the endothelium.

'In cases like this we are unable to consider any lamellar option but we need to do full thickness transplantation usually combined with some other reconstructive surgery, as in this case, trying to avoid any surgical damage to the iris tissue and the crystalline lens,' Dr Güell said.

He described another case of severe infection where it was necessary to wait until the eye was quiet, at which point the cornea's posterior layers could not be properly evaluated. In this particular case, a full thickness keratoplasty procedure was necessary in combination with an amniotic membrane transplant because of epithelialisation problems.

In another case, the patient's eye had longstanding endothelial failure because of silicone oil tamponade and central band keratopathy, which ruled out both endothelial keratoplasty and DALK. In this case, Dr Güell first used a temporary keratoprosthesis to enable the vitreoretinal surgeon to take out the silicone oil and finally repair the retina and afterwards he replaced the keratoprosthesis with a full thickness graft.

Another reason some surgeons might prefer to use PKP is lack of training and experience in lamellar techniques, he noted. However, such surgeons may serve their patients best in many cases by referring them to surgeons experienced in lamellar techniques. Exceptions to that would include practices in remote locations and emergency situations.

The situation with lamellar keratoplasty techniques is similar to the situation that once prevailed regarding phacoemulsification and ECCE, when many surgeons were slow to adopt the newer technique, he said. However, he pointed out that PKP is not a static technique, but continues to evolve just as does endothelial keratoplasty and DALK.

'Penetrating keratoplasty will continue to improve with technological advances involving femtosecond lasers, bioadhesives, and biological approaches such as regular HLA matching and the use of new immunosuppressants. So until the 'artificial cornea' becomes a reality, the corneal surgeon must be trained to use the best surgical approach for every single case,' Dr Güell concluded.