New cornea transplants a cut above

MsSimren's eyeballs had begun to take on a cone-shaped appearance, due to a disorder called keratoconus. She underwent a cornea transplant for her right eye using a method called Dalk last year and is happy with the result.
MsSimren's eyeballs had begun to take on a cone-shaped appearance, due to a disorder called keratoconus. She underwent a cornea transplant for her right eye using a method called Dalk last year and is happy with the result.PHOTO: LIMYAOHUI FOR THE STRAITS TIMES

They tend to result in longer graft survival and lower rejection rates

Her eye troubles surfaced during a routine check at the optician's.

Fifteen-year-old Simren Kaur Gurdip Singh was told that the device used to assess myopia "could not capture any eye power".

"I went to a few other shops to check, thinking that their machine was spoilt," said Ms Simren, now 19.

But it turned out she had a problem that glasses could not correct. Her eyeballs had begun to take on a cone-shaped appearance, due to a disorder called keratoconus.

 

WORTH THE TRAINING

There is a definite learning curve, which varies for different surgeons, but it is definitely worthwhile to get through this phase.

DR POR YONG MING, a consultant eye surgeon at Mount Elizabeth Novena Hospital, noting that it took about 12 to 18 months to get "very comfortable" operating using the newer procedures.

"When I looked at my eye from the side in the mirror, I noticed that it was protruding," she recalled.

  • EYE-CATCHING STATISTICS

  • TRANSPLANTS (2014)

    • 446 cornea transplants nationally

    • 362 cases done by the Singapore National Eye Centre (SNEC), 86 per cent involving the use of new techniques

  • DONORS (2014)

    • 483 cornea donations

    • 127 local, 356 foreign

  • GRAFT SURVIVAL

    Patients at SNEC whose new cornea survived for at least five years after transplant

    • Penetrating keratoplasty (traditional methodreplacing the entire cornea): 67 per cent

    • Deep anterior lamellar keratoplasty (replacingouter corneal layer): 93 per cent

    • Descemet's stripping automated endothelialkeratoplasty (replacing inner corneal layer): 93 per cent

  • VISUAL OUTCOME

    Patients at SNEC who achieve 6/12 vision or better after the operation, which is the best possible result

    • Penetrating keratoplasty (traditional method): 53 per cent

    • Deep anterior lamellar keratoplasty: 74 per cent

    • Endothelial keratoplasty: 81 per cent

    SOURCE: SINGAPORE NATIONAL EYE CENTRE

The abnormal shape of the cornea, the transparent layer covering the front of the eye, caused her vision to be distorted. To fix the problem, she underwent a cornea transplant on her right eye at the Singapore National Eye Centre (SNEC) in 2014.

But instead of the conventional way of replacing her entire cornea, the inner-most layer was left intact. Only the outer, misshapen layers of her cornea were removed and replaced with donor tissue.

This method, called deep anterior lamellar keratoplasty (Dalk), is among the newer cornea transplant procedures being adopted by the SNEC.

In fact, about 86 per cent of cornea transplants at the centre in 2014 were performed using new techniques - likely the highest proportion worldwide, based on latest figures provided by the eye centre.

Other countries with a high adoption rate of new techniques are Brazil, Sweden and the United States.

It was not too long ago, in 2006, that the majority of cornea transplants at SNEC were carried out using the traditional method called penetrating keratoplasty - a standard operation for many years.

This paradigm shift, in which selected layers of the cornea are replaced instead of the whole cornea, is the future of cornea surgery, said Professor Donald Tan, senior consultant cornea surgeon and Arthur Lim Professor of Ophthalmology at SNEC and Duke-NUS Medical School.

And this has translated into better outcomes for patients.

Generally, they enjoy a longer graft survival, lower rejection rates and complications, as well as better vision after the operation.

These results were shown in the Singapore Corneal Transplant Study, which tracks all cornea transplants done by SNEC since 1991.

For instance, an analysis of 2,330 cornea transplants between 2000 and 2011 revealed that 93 per cent of grafts survived at least five years when performed using the newer Dalk method.

The corresponding figure for transplants done with the conventional method was 67 per cent.

"Our transplant success has improved tremendously following our early adoption of these new forms of selective lamellar transplantation," said Prof Tan.

In another method, Descemet's stripping automated endothelial keratoplasty (Dsaek), the inner layers of the cornea are replaced, leaving the external layers intact.

Replacing only selected layers of the cornea results in a lower risk of rejection, as some of the patient's own cells are retained.

"The rejection rate is lower as we have compartmentalised the cornea into segments," said Prof Tan.

Improving graft success is important for another reason: Cornea transplants depend on donations.

In 2014, 446 cornea transplants were performed in Singapore - a 31 per cent rise from 2010, when there were 341 transplants.

However, the number of local cornea donations dropped from a five-year high of 187 in 2011 to 127 in 2014. They make up one in four donor corneas used, with the majority sourced from abroad.

"The local donor rates are not sufficient, which is why we need to rely on overseas sources," said Adjunct Associate Professor Lim Li, deputy director of the Singapore Eye Bank.

"Improving graft success rate will reduce the need for repeat corneal transplants. This would reduce the demand for corneas, and enable the corneas to be available to other needy patients," said Prof Lim, who is also the head (clinical) of the cornea and external eye disease department at SNEC.

Most transplant cases are linked to age-related degeneration, which turns the inner corneal layer cloudy. Others, like Ms Simren's, are disorders that affect the cornea.

Before her operation, Ms Simren could detect only hand movements with her right eye. Today, she can make out numbers in the distance with that eye. "The difference was great," said Ms Simren, who is from Malaysia and now a Singapore permanent resident. "Despite the transplant, I did not have to alter my lifestyle much after the operation."

Currently, the nursing student at Ngee Ann Polytechnic wears hard contact lenses in both eyes because of astigmatism. Her left eye is also affected by keratoconus and may require a transplant years later.

However, she is able to go swimming, wear eye make-up and rub her eyes without problems.

Besides such day-to-day conveniences, patients like Ms Simren can look forward to several long-term benefits, one being that they may not need immunosuppressive eyedrops for life.

This is the case for Dalk, which "virtually eliminates" the most serious type of rejection that is a major cause of graft failure for patients who underwent the standard method, said Dr Por Yong Ming, a consultant eye surgeon at Mount Elizabeth Novena Hospital.

"There is a lot less worry in the long term. As anti-rejection steroids are not needed for a long period of time, the risk of steroid-use side effects like glaucoma and cataracts is also reduced," said Dr Por, who performs two-thirds of cornea transplants using the newer techniques.

Patients who had endothelial keratoplasty - of which Dsaek is the most common - can also expect to recover "much faster" than if they were to undergo the standard method. This is because doctors do not need to stitch up the cornea.

The standard method requires about 16 corneal stitches to hold the donor tissue in place; these are removed only six months to a year after the surgery, he explained.

In contrast, endothelial keratoplasty is done through a small incision. "The eye is stronger and the risk of serious eye injury in the future is lower," said Dr Por.

However, these recent methods are generally more challenging for surgeons to perform.

Depending on the method, the duration of the surgery may be longer, and donor corneas may need to be cut in a special way before surgery.

Surgeons also have to adapt to the Asian eye, which tends to be smaller and more difficult to operate on, said Prof Tan.

SNEC has been training doctors in the newer techniques. So far, it has taught more than 100 surgeons from 23 countries.

Dr Por said he took about 12 to 18 months to get "very comfortable" performing the newer procedures.

"There is a definite learning curve, which varies for different surgeons, but it is definitely worthwhile to get through this phase."

A version of this article appeared in the print edition of The Straits Times on January 26, 2016, with the headline 'New cornea transplants a cut above'. Print Edition | Subscribe