Good suture technique can minimise astigmatism in refractive corneal transplantation

By Ana Hidalgo-Simon MD, PhD

BARCELONA - Good trephination is imperative but the importance of good suture technique in refractive corneal transplantation should not be underestimated, a New York-based specialist says.

Post-transplant refractive control has improved with the extensive use of LASIK and will continue to get better as custom ablation improves, said Olivia Serdarevic MD at the 4th International Course on Corneal Pathology held in conjunction with the 6th Winter Refractive Surgery Meeting of the ESCRS.

She noted that post-keratoplasty astigmatism associated with the wound healing response continues to be a problem despite considerable progress in recent years in controlling the refractive effects of corneal transplantation.

The excitement and research of the early 90s focused on growth factors which many investigators hoped would allow modulation of wound healing. But results have not translated into clinical improvements.

"Selection of donor tissue based on preoperative measurements is one important step towards controlling postoperative astigmatism. We have tried to get tissue banks to do it but it is still not routinely done.

"Considering current trends - more and more patients are now undergoing refractive surgery - there will be additional donors who underwent LASIK procedures and eye banks will have to start looking at the donor corneas. That will help us to improve our refractive results," Dr Serdarevic of the Manhattan Eye and Ear Infirmary in New York explained.

Keratconus patients do very well
She reported excellent refractive results in patients with keratoconus when the whole area of the cone was included in the trephination.
However, in cases in which the cone extends too far out, the risk of graft rejection is too high and a full inclusion is just not possible.

"In these cases, lamellar keratectomy improvements may play a much larger role than in other types of patients. But lamellar keratectomy does not achieve the results that I can achieve with penetrating keratoplasty," she remarked.

A well-chosen surgical technique can improve the intraoperative control of astigmatism. Mechanised trephination has improved the control, but adequate suction is essential.
This can be especially difficult with keratoconic patients and while some have recommended flattening the cone before trephination, that approach can make some patients hyperopic.

Most keratoconic patients are myopic and are not happy to find themselves hyperopic postoperatively.

Suction loss may result in non-complete removal of the lips of the stroma. If these are not removed, the risk of astigmatism is elevated. The effects become apparent when the sutures are removed.

Dr Serdarevic stressed that suturing and intraoperative suture adjusting have a clear impact on the control of astigmatism, although the quality of trephination determines the long-term impact of suturing factors.

In her experience, a single running suture with 20 to 24 short bites can be adjusted more easily intraoperatively and leads to faster visual rehabilitation than interrupted sutures.

"The astigmatic results with interrupted sutures after selective suture removal can be just as good in the long term, but more postoperative visits are required since only one suture should be removed at any one visit.

"My retrospective analyses showed that refractive stability and improvement of best-corrected visual acuity are achieved more rapidly with a single running suture adjusted intraoperatively than with interrupted sutures selectively removed postoperatively," she explained.

Suturing techniques
Dr Serdarevic's prospective, randomised clinical studies compared different running suture techniques. In those randomised studies, intraoperative suture adjustment of a single running suture permitted earlier refractive stability and more rapid visual rehabilitation than postoperative adjustment of a running suture.

Best-spectacle corrected visual acuity was better with intraoperative suture adjustment at all times until suture removal and demonstrated no significant change between month one and month 15 (three months after suture removal).

Intraoperative suture adjustment allowed significantly better astigmatism results and more corneal regularity from one month up to one year after surgery.

The differences were not significant between the intraoperatively and postoperatively adjusted groups after the sutures were removed, although they still tended to be better in the intraoperatively adjusted group.

"It is here that your trephination starts to play a large role. <If you don't have a good trephination you are going to have large increases in astigmatism after suture removal> even if there has been intraoperative or postoperative adjustment.

"Keratoconus patients also obtained excellent long-term astigmatism results with this approach, as long as a large part of the cone did not remain after trephination," she said.
Dr Serdarevic predicted that both lamellar keratoplasty and PKP would be refined with the use of wavefront analysis of postoperative astigmatism.

She said there has been little advancement in trephine design over more than a decade but improvements in instrumentation are needed to continue to improve refractive and optical results of both lamellar and penetrating grafts.

Top