The Hydroxyapatite Orbital Implant (Coral Implant)

What is Hydroxyapatite?

Porous hydroxyapatite is a complex calcium phosphate salt, made from coral, which is similar to human cancellous (spongy) bone with interconnecting tunnels and no dead-ends. When implanted into the socket, porous hydroxyapatite is not treated as a foreign substance by the body in contrast to most other implants used in the past, but becomes ingrown with blood vessels and  tissue. As a result of this integration with the orbital tissues, the implant resists migration and rejection.

            The porous hydroxyapatite implant can be directly coupled with the artificial eye some months after insertion to improve movement by means of a small peg. This fits into a hole drilled through the conjunctiva (the pink membrane which lines the socket) and into the buried implant. The conjunctiva then grows down the sides of this drilled hole.  This occurs because the implant by then contains blood vessels that support growth of this tissue. This secondary procedure is, however, only undertaken for patients in whom the degree of movement of the artificial eye is deemed unsatisfactory following the first stage. Nowadays the second stage is rarely required.

A coral implant	A diagram of a coral implant viewed from the side	A drilled coral implant showing a well-healed motility peg hole

Following successful human clinical trials the US Food and Drug Administration authorised the use of these orbital implants in September 1989. Porous hydroxyapatite orbital implants have now become the implants of first choice amongst the leading oculoplastic surgeons world-wide. By January 2005 over 1200 patients had received this implant under Dr. Leatherbarrow's care in Manchester.

This implant offers a number of advantages over other implants currently being used. These advantages are as follows:

1. Once the implant has been accepted by the body and has a blood supply it cannot come out (extrude)
   
   
2. The risk of migration of the implant into an abnormal position within the orbit is much reduced
   
   
3. The implant can permit better movement of the overlying artificial eye
   
   
4. The implant has a low risk of complications after the operation when used by a suitably trained and experienced surgeon.

It is necessary for the hydroxyapatite implant to be fully ingrown with blood vessels (vascularised) prior to the drilling procedure for the fitting of the motility peg.

The hydroxyapatite orbital implant can be used:

1. An extruding implant

   At the time of enucleation (removal of an eye). This is known as a primary orbital implant.
   
   
2. For those patients without an implant in their socket. This is known as a secondary orbital implant when no implant was previously placed in the socket.
   
   
3. Or as an exchange implant for those patients dissatisfied with the movement of their artificial eye or whose implant has moved causing fitting problems of the artificial eye. It may also be used as an exchange implant for the patient with an old fashioned implant which is coming out (extruding).

Are there any disadvantages associated with this implant?

The implant has a number of disadvantages:

The additional costs involved, namely the cost of the implant, the requirement and expense of the 2nd stage drilling procedure, and the required modifications to the artificial eye.

Additional expense may also be incurred if scans are used to determine whether or not the implant is vascularised and safe to drill. An alternative is to allow a long period of time before proceeding to the second stage (6 months in primary cases and 12 months in secondary/exchange cases). This is favoured by Mr. Leatherbarrow and in no case to date have we encountered problems with failure of vascularisation when drilling has been performed.

Although there are no specific contraindications to the use of this implant, some patients are not suitable for implantation due to severe contracture of the socket tissue due to previous serious infections, trauma, or the use of radiotherapy (X-ray treatment). A simple examination of the socket and eyelids by your surgeon can determine your suitability for this procedure.

A patient who has undergone a left secondary hydroxyapatite orbital implant procedure with placement of a motility peg

How good are the results of this procedure?

The results of primary implantation tend to be very good indeed. The results of secondary implantation are less predictable as the socket anatomy has been disrupted and the eye muscles are retracted, scarred and difficult to locate at the time of surgery. In experienced hands, however, the results are usually good but the degree of movement is very variable from patient to patient.

This is always a possibility. Sometimes the size of implant used is insufficient to overcome a sunken appearance or hollow appearance in the upper eyelid. If this is unsatisfactory a second type of implant can be used (or fat cells taken from the buttock area can be injected into the socket depending on the patient's wishes). This is referred to as a subperiosteal implant and is placed beneath the lining of the bone at the bottom of the orbit through a small skin incision in the laughter lines at the outer corner of the eye under general anaesthesia. Approximately 5-10% of patients require this. Sometimes a graft (a mucous membrane graft) is taken from the inside of the lower lip at the time of implantation if the tissue lining of the socket is insufficient to safely close the wound without undue tension. Eyelid surgery to deal with a droop to the upper eyelid (ptosis) or sagging of the lower eyelid is occasionally required under local anaesthesia at a later date.

Patient with right ptosis and artifical eye	Same patient following ptosis surgery

The majority of patients in the past received these implants wrapped in donor sclera - the white of the eye left over from eyes donated for corneal transplants. A wrapping material is important as the implant is very hard and the eye muscles cannot otherwise be attached to the implant. At present our preferred technique is to wrap the implant in a synthetic material which dissolves over a period of a few weeks (vicryl mesh). We often remove a small piece of tissue from the temple behind the hairline (temporalis fascia) to cap the implant as this markedly reduces the risk of the overlying tissues breaking down and exposing the implant. The stitches or staples in this small wound are removed after a week. The choice of material will also depend on your own wishes.

No operation is free from risk. There are risks common to all operations performed under general anaesthesia. The risks are kept to an absolute minimum e.g. the risk of postoperative infection is minimised by a strict aseptic surgical technique and by the use of intraoperative and postoperative antibiotics. Complications in our hands are rare and to date have been minor. In a secondary situation a potential problem is placement of the implant into an eccentric position which may require repositioning.

No. If you are happy with the results of the initial procedure the second stage drilling procedure may be omitted. Approximately 5% of our patients choose to proceed with the drilling procedure.

Approximately 1 hr 30 mins.

Few patients experience much pain after the first 24-48 hours although for some patients (approximately 1 in 10) the pain can be more severe and last for a few days. Pain is usually controlled very well with simple analgesics but stronger ones can be provided. Pain is associated with movement of the normal eye and this can be avoided by simply moving your head instead of your eyes. If you experience much pain or sickness following the surgery an extra night in hospital will be arranged. The postoperative dressing should be worn for 5 days to reduce postoperative bruising and swelling. Should it become uncomfortable, however, a new pad can be easily applied. It is wise to advise your family and friends, including children, that you will be wearing a head bandage, and that when it is removed the eyelids may be quite bruised and the upper eyelid will be swollen and very droopy. You may remove your own dressing to save another journey to the hospital. You will be given written instructions on aftercare before you are discharged home.

Usually you will be admitted on the day of surgery and discharged home the following day.

Occasionally a further night in hospital is required in the event of excessive sickness from general anaesthesia. It is wise to plan for a 2 night stay if you have far to travel home. Medicines are available which can reduce feelings of nausea.

This very much depends on your individual circumstances and the type of work you do. Most people take at least the first week after surgery off. It is wise to take off more time if your work is not in a clean environment. You will be discharged home with a pressure dressing in place and a bandage around your head to keep bruising and swelling to a minimum. This should be kept in place for a week. When it is removed a week later the eyelids may be quite bruised and the upper eyelid will be swollen and droopy. Often the eyelids have been sewn together with a nylon suture over small red rubber bolsters. This helps to prevent any excess swelling. The suture is usually removed after 2-3 weeks. The appearance can be camouflaged with dark glasses or with tape stuck over the lens of a pair of ordinary glasses. A temporary eye pad may be applied to go home with but this should not be worn continuously.

The socket has to heal fully before a new artificial eye is fitted. This usually takes a minimum of 8 weeks. If all is well after surgery your ocularist may proceed with fitting arrangements. Please take note that the time this process takes may be longer depending on your own postoperative progress and the demands made on the service.

At 1-3 weeks after surgery a visit may be required for a surgical shell to be fitted by your ocularist. This is a clear plastic shell or conformer which is inserted into the socket to prevent shrinkage. Occasionally this will have been fitted in the operating theatre.

The typical appearance of an artificial eye	The modified back surface of the artificial eye

How is the second stage drilling procedure performed?

This is performed in the operating theatre under local anaesthetic on a day case basis. Some sedation can be provided if required or a general anaesthetic can be given if preferred by the patient. A few days before the drilling a wax template is made by your ocularist with a hole in the desired position. This is used to mark the surface of the implant to ensure that the drill hole is made in the best possible position.

A drilling template	A temporary motility peg being placed	A permanent peg in position

You will be given a local anaesthetic injection through the lower eyelid. The drilling takes a few minutes to perform but the whole procedure, taking into account preparation time, make take approximately 30 minutes. A temporary peg with a flat head is inserted into the hole and the artificial eye replaced in the socket.

This will not fit correctly until adjusted. You should take note of this as it will affect your appearance until the necessary modifications have been made later. A permanent round headed peg is then placed and the back of the artificial eye modified to accept the head of the peg.

The latest motility peg is made of titanium and, although more expensive, it can be more easily screwed into the implant avoiding the need for any drilling. This is simpler to perform but can be more painful requiring a short general anaesthetic.

Your artificial eye

This will be made by your Ocularist, Robin Brammar. Each artificial eye (ocular prosthesis) is specially made for you, to fit your individually shaped socket and to conform to the shape of your irnplant. It will be hand painted in your presence to match your natural eye colouring. There will be no pain during the procedures and anaesthetics will not be necessary. You will be required to return for three appointments:

First appointment

An impression is obtained of your socket by introducing cream which will set to a very soft, rubbery consistency and will record the shape of your socket. A painting to match your remaining eye is usually made at this stage. This is competed in your presence to obtain the best possible colour match. This appointment usually lasts one hour.

Second appointment

A wax pattern will by now have been produced to fit the plaster model resulting from the impression of your socket obtained during your first appointment. This wax pattern will be tried in the socket and modified by careful sculpturing until an ideal compromise between fit, comfort, mobility, lid-line and contour is achieved. Lastly, the iris/cornea unit is positioned to match the remaining natural eye. This appointment will take about one hour.

Third appointment

This is usually a simple matter of collecting your artificial eye prosthesis. There may be some minor adjustments necessary.

Your artificial eye need only be cleaned occasionally. You may sleep with your artificial eye in, in fact it is advisable to do so. However, when it is removed, it should be cleaned by using hard contact lens cleaner, as the most common problem is irritation and watering caused by a protein build up.

If not cleaned correctly this protein will collect upon the surface of the artificial eye as a crystalline coating which will eventually make the artificial eye feel gritty. The socket lining and the inner surface of the eyelids may become inflamed and sore with discharge in extreme cases.

Annual check ups and replacements

You are advised to return annually for a check up when any small fitting changes will be assessed and your artificial eye will be re-polished to remove deposits and any scratches. You will be advised when your prosthesis needs to be replaced. This can be required every two to five years as your body is constantly changing but this time-scale varies considerably from patient to patient.

1. Discontinue the use of aspirin and products containing aspirin for three weeks before your scheduled surgery unless instructed otherwise. This may include a number of arthritis medications. These medications can cause excessive bleeding.
   
   
2. As your operation is planned to be done under a general anaesthetic (when you will be asleep), you may have some blood tests done and an ECG (heart tracing) prior to surgery. Please bring all your tablets/medications in their original, labelled bottles. Also provide information on any known allergies.
   
   
3. It is important that you follow instructions about food and drink prior to surgery.

1. You will awaken in the recovery room in the theatre.
   
   
2. You will be returned to the ward usually after a period of up to 30 minutes in the recovery room.
   
   
3. You may go to the bathroom with assistance.
   
   
4. Your usual medications may be continued. Resume aspirin, blood thinners, and arthritis medications 72 hours after surgery unless otherwise instructed.
   
   
5. You may experience difficulty wearing your glasses because of the dressings.
   
   
6. If a graft was taken from your lower lip use Difflam mouthwash 4-5 times a day and eat a soft diet.
   
   
7. You will be given antibiotics to take postoperatively, usually Cephadroxyl 500mg twice a day (or Erythromycin if you are allergic to Penicillin) for 7 days. Please ensure that you complete the course and do not omit a dose.
   
   
8. You will also be given a 2 week course of anti-inflammatory tablets, Diclofenac 50mg 3 times a day. You should not take these if you have a history of ulcer problems or if you experience heartburn. These should be taken with food. They also act as a painkiller. You may also be prescribed Kapeke tablets to take home. These are painkillers. If simple analgesics are sufficient use these instead.
   
   
9. Apply antibiotic drops four times a day to the socket for 5 weeks after the dressings have been removed. Use sterile cotton wool balls and saline to keep the eyelids clean of any discharge 2-3 times a day.
   
   
10. The stitches used to close the wound in the socket are absorbable and will drop out in 3-4 weeks.
    
    
11. It may be necessary to remove and clean your conformer. You will be shown how to do this.