As the protective window that controls the entry of light into the eye, the cornea plays an important role in enabling us to see.

But should things go wrong, the Singapore National Eye Centre’s (SNEC) team of corneal ophthalmologists are well-versed in providing medical and surgical care to treat patients with corneal disorders.

We take care of patients who need:

1. Corneal transplantation
2. Contact lens-related eye problems
3. Infectious keratitis (corneal ulcers)
4. Ocular surface disorders requiring reconstruction
5. Treatment for dry eye
6. Artificial corneal transplant

The Singapore Corneal Transplant Programme was initiated in 1991 and since then, SNEC has been performing over 350 corneal transplants a year, with an overall graft survival rate exceeding 90%. Nearly 3,500 transplants have been performed to-date.

WHO WOULD BENEFIT FROM A CORNEAL TRANSPLANT?

Individuals with poor vision due to a diseased or cloudy cornea, with healthy optic nerve and retina, may benefit from a corneal transplant to see well.

Whenever vision is reduced from corneal disorders like infections, corneal injuries/scars and degenerative diseases, a corneal transplant can be an effective means of restoring vision.

HOW IS A CORNEAL TRANSPLANT PERFORMED?

There are several types of corneal transplant procedures that are performed in SNEC. Broadly, these include:

1. full-thickness corneal transplants or penetrating keratoplasty (PLK),
2. partial thickness corneal transplants or lamellar keratoplasty (LK) [viz: anterior lamellar keratoplasty (ALK)], and
3. endothelial keratoplasty (EK) (Figure 1).

1. Penetrating keratoplasty (PK)

PK is a form of microsurgery in which the central 7-8 mm portion of the diseased cornea is removed and replaced with a clear and healthy donor cornea. The donor cornea is held in place with very fine microsurgical nylon sutures.

2. Lamellar keratoplasty (LK)

In LK, only diseased corneal layers are replaced, preserving healthy corneal tissue. When only the anterior layers (corneal stroma) of the cornea are replaced, the procedure is called anterior lamellar keratoplasty (ALK).

Deep anterior lamellar keratoplasty (DALK)

DALK is one such form of ALK in which most of the anterior layers of the cornea are removed sparing the posterior corneal layer [Descemet membrane (DM) and endothelium].

About 40% of corneal transplants at SNEC are performed with DALK procedures. SNEC today is one of the few transplant centres in the world that offers these new and advanced techniques of LK to our corneal patients.

3. Endothelial keratoplasty (EK)

When only the diseased posterior layers of the cornea (DM and endothelium) are replaced, the procedure is called endothelial keratoplasty (EK).

EK today includes:
a) DSAEK – Descemet Stripping Automated Endothelial Keratoplasty
b) DMEK – Descemet Membrane Endothelial Keratoplasty.

a) DSAEK

In DSAEK, only the inner layer of the donor cornea, about a 10th of a millimeter thick, is transplanted onto the patient’s own cornea through a small 4-5 mm incision at the side of the cornea.

The Tan EndoGlide

SNEC and SERI’s team of scientists have been working on continually improving the technique of DSAEK and were the first to pioneer a surgical device, the Tan EndoGlide, in 2009, to perform DSAEK. Licensed to a UK surgical company, the EndoGlide is the first FDA-approved device for DSAEK.

This device enables donor insertion into the patient’s eye with ease and minimises donor trauma that can occur while inserting into the eye through a small incision.

It has been the most successful surgical device to implant this donor tissue through a keyhole incision. It has the best published safety record compared to other devices, and over 5,000 corneal transplants using this device have been performed around the world to-date.

The Tan Endoglide was first used in 2009 as part of the SNEC DSAEK EndoGlide Clinical Trial. We have reported our results using this device and have achieved very good visual outcomes and lower rates of endothelial cell loss as well as reduced risks of complications (Khor WB et al).¹ Similar good outcomes have also been reported from another centre that has successfully adapted this device for DSAEK surgery (Hollick E et al).²

SNEC is the regional centre in Asia for DSAEK surgery and more than 40% of transplants in SNEC are DSAEKs. DSAEK is probably the most significant advance in the field of corneal transplants.

b) DMEK

DMEK is the latest innovation in the form of minimally invasive, sutureless, corneal transplant surgery. Instead of implanting a 10th mm thick donor in DSAEK, this new complex procedure now just replaces the actual damaged corneal endothelial cell layer which is just 1/100th mm thick.

In selected patients, this has the advantage over DSAEK in that patients have the possibility of attaining 6/6 vision within a few weeks after surgery. Additionally, it may be associated with a lowered risk of rejection as suggested by a recently published article (Anshu et al).³

Currently however, DMEK is suitable for milder forms of corneal oedema and may not be suitable for all patients.

WHERE DOES THE DONOR CORNEA COME FROM?

All corneas transplanted at our Centre are of excellent quality and procured by the Singapore Eye Bank (SEB). SEB gets corneas from local donors in Singapore, as well as from internationally accredited eye banks in the United States of America and other international eye banks around the world. Because the SEB is very successful in procuring corneal tissue, one usually has to wait only a couple of weeks to receive a donor cornea. SEB also provides corneas for non-Singaporeans undergoing corneal transplants in Singapore. Singapore is a leading transplantation Centre in Asia, with many international patients successfully undergoing transplantation surgery here.

WHAT ARE OUR OUTCOMES WITH THESE CORNEAL TRANSPLANT PROCEDURES?

The success rate for uncomplicated corneal transplants is about 91% in the first year. However, complications can occur following a transplant. The more common complications that can occur include raised intra-ocular pressure, which can cause damage to the optic nerve (glaucoma), and corneal graft rejection.

Most of the complications occur in the first year after transplantation, but most can be treated successfully if detected early.

There are very few countries that have long-term followup, and our Singapore Corneal Transplant Study (SCTS), which spans more than 20 years, is one of the largest transplant databases worldwide.

Our results in Singapore show that the results in Asian eyes in our Centre are equivalent to that of Caucasian eyes in the West, and ours is the only major database monitoring success in Asian eyes.

Anterior Lamellar Keratoplasty (ALK)

Nearly 40% of corneal transplants in SNEC are LKs. Because ALK retains the innermost corneal layer, it greatly reduces the risk of corneal graft rejection, a significant cause of corneal transplant failure.

Compared with the 20% overall risk of rejection after PK, rejection risk following ALK is less than 1%.⁴ There is also better long-term graft survival following ALK. Our SCTS results show that the overall 1-year graft survival for ALK in SNEC is 94%.

In terms of recovery of vision, we have been able to achieve equal if not better visual outcomes following ALK as compared with PK performed for similar indications.⁵

Endothelial Keratoplasty (EK)

In SNEC, more than 100 cases of EK are performed yearly, and SNEC leads the field in EK surgery in Asia. EK offers several advantages over a full-thickness procedure like PK in patients with selective damage to the inner layers of the cornea (endothelium):

1. No suture-related problems: Because EK does not involve any donor suturing onto the patient’s cornea, it does not have the risk of suture-related problems like suture- related abscess. There is also reduced astigmatism, resulting in better vision when compared with PK.
2. Lower risk of graft rejection: Early results have shown that the risk of rejection is much lower with EK. Compared with the 20% overall risk of rejection after PK, rejection risk following EK is just 7.6% in the first year.⁵
3. Very good graft survival: Graft survival appears to be excellent in our SNEC series, with very few failures occurring to date. Graft survival appears to be better than conventional PK surgery. This may be related to the lower risk of graft rejection.
4. Faster visual recovery: The visual recovery is much faster following an EK procedure with reduced astigmatism compared with PK.

GPs can call for appointments through the GP Appointment Hotline at 6322 9399.

By: Dr Arundhati Anshu, Senior Consultant, Department of Cornea and Refractive Surgery and Department of General Cataract and Comprehensive Ophthalmology, Singapore National Eye Centre

Dr Arundhati Anshu is a Senior Consultant in the Departments of Cornea and Refractive Surgery as well as General Cataract and Comprehensive Ophthalmology of the Singapore National Eye Centre (SNEC).

She is also the Associate Program Director of fellowships in SNEC and Adjunct Assistant Professor in the NUS Yong Loo Lin School of Medicine (NUS-YLLSoM) as well as Duke-NUS Medical School, Singapore. She has been actively involved in research and teaching for over a decade.

References

1. Khor WB, Mehta JS, Tan DT. Descemet stripping automated endothelial keratoplasty with a graft insertion device: surgical technique and early clinical results. Am J Ophthalmol. 2011 Feb;151(2):223-32.
2. Gangwani V, Obi, A, Hollick EJ. A prospective study comparing Endoglide and Busin glide insertion techniques in descemet stripping endothelial keratoplasty. Am J Ophthalmol. 2012 Jan;153(1):38-43.
3. Anshu A, Price MO, Price FW. Risk of corneal transplant rejection significantly reduced with Descemet membrane endothelial keratoplasty. Ophthalmology 2011.
4. Tan et al. Penetrating keratoplasty in Asian eyes - The Singapore Corneal Transplant Study. Ophthalmol 2008;115:975-82.
5. Tan and Anshu et al. Visual acuity outcomes after deep anterior lamellar keratoplasty - A case control study. British J of Ophthalmol 2010.