Primer

A Tooth for an Eye

To regain vision using one's own tooth is a boon for people who lose their eyesight, especially through chemical
accidents and allergic reactions. K Deepalakshmi finds out why this method scores over the conventional ones

S Rajendran (52) would have never thought his allergy to penicillin would deprive him of his vision. Given penicillin for an ailment, he developed Stevens Johnson syndrome - a life-threatening condition arising from an allergic reaction, affecting the skin and eye. A skin-like layer formed over his eyes, resulting in the loss of his eyesight. His tear glands stopped functioning and his eyes became dry and difficult to open. Help came from an unexpected quarter, his tooth. His canine tooth was used in a procedure called Osteo Odonto Keratoprosthesis (OOKP) that restored his vision. This is a technique used to replace damaged corneas in blind patients for whom conventional corneal transplantation is impossible.

Rajendran finally saw the light after three long years when he underwent OOKP surgery at Sankara Nethralaya in 2005. Based in Kolkata, he now enjoys 6/6 vision but has a check-up every year without fail.
"For a person who can appreciate the difference between darkness and light, OOKP surgery gives 6/6 vision, just like any normal eye, provided the other structures of the eye are normal," informs Dr Geetha Iyer, Associate Consultant, Cornea services, Sankara Nethralaya, Chennai, adding, "OOKP surgery is performed for bilateral end stage ocular surface disorders most commonly caused by chemical injuries and Stevens Johnson syndrome. It is not for those who are blind from birth." The person should have had vision for at least the first four to five years of life and should be older than 17 for the tooth to be extracted.

"For a person who can appreciate the difference between darkness and light, OOKP surgery gives 6/6 vision" - Dr Geetha Iyer Associate Consultant Cornea Services Sankara Nethralaya Chennai

"The two-stage surgery can stretch to a three-stage process in some cases, where the first stage is done in two parts" - Dr Srinivas K Rao Consultant Rajan Eye Care Hospital Chennai

OOKP Modality

OOKP was developed some 40 years ago by Italian surgeon Benedetto Strampelli and uses the patient's own tooth root and alveolar bone to support an optical cylinder. It was, however, sidelined because of poor results. Later, his student Prof Gian Carlo Falcinelli revived the technique after extensive research and several modifications. Today, the technique is known as modified OOKP.

OOKP is performed in two stages. In the first stage, the retina and optic nerves are checked for any damage. A canine tooth is extracted with the alveolar bone from the mouth. This tooth acts as a lamina, fashioned by sawing through the root of the tooth in a longitudinal fashion to expose the dentine and the root canal.

The pulp in the root canal is scraped off and a hole is drilled in the widest part of the root — to a size of three to four mm depending on the width of the root at that point. An appropriate sized plastic cylinder of appropriate power, which is determined from the axial length of the eye, is then glued to the hole using dental cement.
A subcutaneous pocket is created in the tissues of the cheek into which the lamina-cylinder complex is placed, and the pocket is sutured and closed. This is done to develop blood supply in the lamina. A three to four cm diameter circular flap of mucous membrane is extracted from the cheek. In the eye, the symblephara are released, and scar tissue is excised. A superficial keratectomy is performed to expose the bare corneal stroma after which the cheek mucosa is placed over the cornea and sutured to sclera, also covering the muscle insertions. Stage I takes about five to seven hours or even longer depending upon the patient.

Two-staged Procedure

Stage II is performed two to three months later to allow time for a connective tissue cover to develop around the lamina implanted in the cheek. During the second stage surgery, the lamina is retrieved from the subcutaneous location and excess connective tissue is removed from the two ends of the optic cylinder, and trimmed over the rest of the lamina.

The mucosal graft on the ocular surface is incised superiorly and reflected from the superior sclera and cornea, in a downward direction. The inferior attachment of the mucosal graft is left undisturbed to ensure that the blood supply is retained.

A flieringa ring is sutured in place and a 3 mm opening is created in the centre of the cornea. Three radial incisions are made in the cornea extending till the limbus. The iris is torn at the root.

The lens is then cryoextracted and the corneal radial cuts are sutured to close. The lamina is then placed over the cornea, such that the posterior part of the optic cylinder is in the anterior chamber —entering through the central corneal opening.

The lamina is sutured into position using the connective tissue covering and episcleral bites. The lamina is placed over the eye, positioned so that a part of the cylinder protrudes inside the eye. After the cylinder and lamina are satisfactorily placed, the mucosal flap is replaced and a small opening is created over the optic cylinder to allow the anterior portion of the cylinder to protrude through the mucosa. The superior edge of the mucosal flap is sutured in place and this completes the operation.

"There is a possibility of the mucosal graft melting and the prosthesis becoming unstable in some cases" - Dr Sonia Nankani Consultant, Ophthalmology Bombay Hospital Mumbai

"OOKP is a good advancement in ophthalmology and it is a boon for people who lose their eye-sight" - Dr S Natarajan Chairman and Managing Director Aditya Jyot Eye Hospital Mumbai

Not without Risk

Dr Iyer cautions, "This procedure could be associated with complications involving the mucous membrane and the lamina, requiring minor revision procedures, although the risk of extrusion is minimal when compared to other prostheses," and adds, "Glaucoma is one of the leading problems associated with chemical injuries. Of the 38 eyes operated on at Sankara Nethralaya, in one eye continued progression of glaucomatous changes led to deterioration of vision following OOKP, while endophthalmitis caused loss of vision in another."

"There is a possibility of the mucosal graft melting and the prosthesis becoming unstable in some cases," warns Dr Sonia Nankani, Consultant, Ophthalmology, Bombay Hospital, Mumbai.

Medication like antibiotics and ointments are required for about a week. After that the person can have a routine just like any other person after surgery. But lifelong follow up and monitoring is essential since the procedure involves a plastic cylinder, tooth bone and mucous membrane.

"Unlike cataract where you don't meet nearly 999 of your 1000 patients again, a routine follow up every three months initially, twice a year and then once every year is needed for these patients," says Dr Srinivas K Rao, Consultant, Rajan Eye Care Hospital, Chennai.

Multi-disciplinary Needs

Despite the advantages, OOKP surgery is complicated. Terming the surgery "a multi-disciplinary approach," Dr Iyer explains, "It demands considerable infrastructure and specialists from areas apart from ophthalmology." Apart from a team of corneal surgeons, specialists involved include a dentist, anaesthetists, and radiologist with inputs from glaucoma, oculoplastic and vitreoretinal surgeons. "The two-stage surgery can stretch to a three-stage process in some cases, where the first stage is done in two parts," Dr Rao points out. Each stage would take five to seven hours and the whole process would take nearly six months to complete for a single eye.

This is one of the reasons why the surgery is not practiced in many centres in India. Dr S Natarajan, Chairman and Managing Director, Aditya Jyot Eye Hospital, Mumbai, says, "OOKP is a good advancement in ophthalmology and it is a boon for people who lose their eye-sight," however, "It is a complicated and time-consuming process. The cost factor is also a hurdle." He feels the lack of trainers in India to teach OOKP is another reason for scarcity in OOKP centres.

Indigenising

The average cost of this procedure ranges between Rs 1.5 lakh and Rs 2 lakh for one eye. The cost has been considerably reduced since the plastic cylinder is now being manufactured in India by Appasamy Associates. "We are currently giving the patients a comfort level. We collect as much as they can afford," avers Dr Sujatha Mohan, Associate Medical Director, Rajan Eye Care. However, the hospitals in question have done the operation at a subsidised rate and even free for some deserving cases.

Advancements

Of further advancements in the procedure, Dr Rao says, "Prof Falcinelli has evolved it over 40 years and has near perfected it. However, there can be small differences in each case."

One interesting area of advancement in OOKP is the cosmetic aspect. A cosmetic shell has been developed abroad, which can be fixed over the operated eye a few months post surgery for a near-natural look. These shells have not been used in India yet, as each one has to be custom-made for every eye, increasing the overall cost.
Dr Mohan opines, "Most of the patients are almost blind. Considering that we are able to give vision to people who are not able to see, it doesn't really make a difference."

While Rajan Eye Care plans to fix cosmetic shells in future, Sankara Nethralaya is trying to work out if the shell can be made in India, just like the plastic cylinder.

There are some other areas of research too. One such area is to attempt to reduce the incidence of glaucoma or find means to control it better. Increasing the field of vision by practically feasible modifications in the cylinder design is being actively researched all over.

OOKP is just the tip of the iceberg as extensive research could deliver more such techniques to bring back life to many people who yearn for vision.

k.deepalakshmi@expressindia.com