Continued exploration of multiple corneal and ocular surface surgical approaches bodes well for good treatment outcomes

IMPROVEMENTS in tissue engineering, synthetic polymers, mechanical and laser devices, pharmacological agents and diagnostic equipment are bringing us closer to
breakthroughs in the treatment of corneal and ocular surface disorders.

Presentations at the XX ESCRS Congress demonstrated how these improvements are facilitating current re-exploration of decades-old techniques, such as lamellar keratoplasty, amniotic membrane transplantation and artificial replacements of
damaged corneas.

Innovations in microkeratome technology in refractive surgery and small-incision techniques in cataract surgery have influenced anterior and posterior procedures and provided more options in the treatment of corneal disease.

Recent technical progress has led to improved optical results and decreased complications with these procedures. However, although indications for these procedures are increasing, the procedures themselves have not improved sufficiently to supersede penetrating keratoplasty (PK) in many cases.

Deep anterior lamellar keratoplasty (DALK) requires dissection at the level of Descemet's membrane to obtain optimal optical results. Multiple studies have documented poorer optical results when DALK is not performed at this level.

Endothelial damage precludes the use of lasers for DALK at the level of Descemet's. Cleavage at this level has been facilitated with different techniques of fluid, air and viscoelastic dissection, but perforation of Descemet's membrane still occurs even with experienced surgeons.

This complication can lead to secondary anterior chamber formation and increased risk of graft failure in the early postoperative period, as documented in published studies and again at the Nice Congress.

Khandwala and associates reported on Descemet's perforation resulting in a graft failure rate of 6.25% during the first six months after DALK with fluid and air dissection in keratoconus patients.

We need to develop safer and more reliable dissection methods before DALK can be considered the procedure of choice in patients, without increased risks of wound dehiscence or rejection.

Although the risk of a rejection episode is about 10 times lower after lamellar keratoplasty than after PK, we must remember that rejection does occur after lamellar procedures.

It should also be emphasised that most rejection episodes after both lamellar and penetrating keratoplasties are mild and easily treated with topical therapy in patients with pathologies such as keratoconus.
Multiple studies have documented five-year full-thickness graft survival rates of up to 90% to 100% in keratoconus patients.

Posterior lamellar keratoplasty is evolving quickly through the innovative work of Melles and others. Most recent approaches include increasing the posterior lamellar disc diameter to maximise the number of endothelial cells implanted. Techniques that allow insertion through small limbal incisions created mechanically or with lasers are being developed. Techniques should minimise endothelial damage from folding or touch.
Ideal donor and recipient diameter disparities need to be determined to best balance tight-sealing wounds with minimal inducement of unwanted sphere or cylinder.

PK is still the primary procedure for treating corneal blindness. Additions to our diagnostic armamentaria are enabling more complete assessment of visual function after PK and correlation with surgical factors.

New developments in mechanical and laser trephine designs have been very limited for many years because of the surge of interest in refractive surgery. Improvements in trephination systems are needed to further improve refractive results after corneal transplantation.

Re-exploring laser trephination
Several surgeons noted at the Nice Congress that there has been more interest in the ophthalmic industry over the past year in re-exploring laser trephination.
After my first use and development of the excimer laser for PK, only the German groups of Lang, Naumann and Seitz pursued clinical use for many years. Hopefully, recent advances in both laser and mechanical device technologies will be applied to
keratoplasty.

The quest for artificial replacements for human corneas continues. Despite the availability of more synthetic polymers and chemical modifications to enhance biocompatibility and biocolonisation, long-term stability remains problematic.

Although we have not yet achieved much better long-term clinical results than with some keratoprostheses developed decades ago, experimental work with newer approaches to support epithelialisation are promising. Ultimately, it is hoped
tissue-engineered corneal substitutes will provide better results.

Increasing experimental success in culturing and transplanting corneal cells, as well as in combining polymeric scaffolds with cells derived from stem cells or from corneal epithelial, stromal and endothelial cell lines, offer exciting prospects for treatment.

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