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Ocular implants

Top left - the porous implant. Top right - an artificial eye. Main picture: A girl with an artificial eye.

 

This article was written for the 'Global Eye' - newsletter of Daisy's Eye Cancer Fund - by Manoj Parulekar, consultant paediatric ophthalmologist and retinoblastoma specialist with the retinoblastoma team at Birmingham Children's Hospital, to whom we are grateful for allowing us to republish on our website.

Between 70-80% of children with retinoblastoma undergo life-saving surgery to remove their cancer-filled eyes.  Ocular implants are used in combination with artificial eyes following enucleation surgery.

 

1. What is the difference between an implant and an artificial eye?

After removal of the eye (enucleation), it is desirable to replace the lost volume of the eye, as well as restore the appearance to match the colour, shape and size of other eye. This is usually achieved with a combination of an orbital implant and an artificial eye (prosthetic eye, prosthesis).

An implant is usually ball shaped, made of synthetic material, and is used at the time of surgery to restore the volume previously occupied by the eye. It may be inserted at the same time of eye removal (primary implantation), or at a later date as part of a second surgical procedure (secondary implantation). The implant is placed into the position previously occupied by the eye, and the tissues closed over it. The eye muscles are usually surgically attached to the implant so that the movement of the muscles is transmitted to the implant. The implant is buried under the pink lining tissue (conjunctiva), and should stay there permanently. It does not need to be replaced, unless it gets exposed or infected.

An artificial eye (prosthesis) on the other hand is made of acrylic, shaped like a portion of an eggshell, and painted to match the white (sclera) and coloured part (iris) of the other eye. It is worn over the conjunctiva which overlies the implant. It is not a permanent fixture and is removed and cleaned periodically.

When the fellow eye moves, the muscles similarly move the implant. This movement is transmitted to the artificial eye which is worn over the implant, separated from it by a layer of tissue.

 

2. What type of implants are there, and what pros/cons do they have?

The three broad categories of implants are:

Integrated - such implants are made of porous material. The body tissues grow into the porous structure of the implant.

Examples are hydroxy-apatite (coral like), porous polyethylene (Medpor) and Aluminium oxide (Alumina). A recent development is coated implants such as Bioeye, where the implant has a soft absorbable coating to which the muscles can be attached during surgery. These implants can be pegged.

Pros: confer excellent mobility, remain in the same position, rarely migrate, can be pegged

Cons: risk of infection and extrusion higher than non integrated, expensive

Semi-integrated - such implants are not porous but have large gaps- at surgery, the muscles are pulled through gaps in the implant and tied over. The Allen implant is the best known semi-integrated implant.

Pros: Inexpensive, good mobility

Cons: risk of exposure higher due to irregular surface rubbing against the prosthetic eye

Non integrated - usually made of acrylic, often ball shaped. Often get encased in a capsule of tissue due to the body's healing response. There is little or no contact with the muscles, and movement is not as good as integrated implants.

Example is the acrylic ball implant.

Pros: Inexpensive, very low risk of exposure

Cons: Less movement than integrated or semi-integrated implant, can migrate within the orbit

 

3. I heard of a child having a fat graft instead of an implant.  What is that exactly?  Is it better than a regular implant?

The fat (correctly termed dermis fat graft) is an alternative means of restoring the lost volume after enucleation. The dermis fat graft is usually taken from around the groin, navel (umbilicus) or the buttock and placed into the space previously occupied by the eye. It comprises the deep layers of skin, and the fat below it, measuring approximately 2cm in length width and depth.

The technique of fat graft placement is similar to that for an implant. However it is not possible to attach the muscles to the fat graft, unlike with an implant.

Dermis fat grafts have some advantages over orbital implants:
- There is no risk of rejection as it is the patient's own tissue
- Dermis fat grafts in children have been reported to grow with the child, thus matching the growth of the other eye.
- If an exposed/infected orbital implant has to be removed, it can be successfully replaced with a dermis fat graft.

There are some disadvantages as well
- The movement may not be as good as is expected of an implant as the muscles are not attached to the fat graft. However, in some cases, the movement may be surprisingly good.
- Dermis fat grafts in adults do not grow, and often shrink (atrophy) with time. The resulting volume deficiency might be cosmetically unsatisfactory

 

4. Does the type of implant impact the quality of the artificial eye?

No. The quality of the artificial eye is independent of the type of implant , and depends on the skills of the ocularist.

 

5. How much motility can an enucleated patient expect?

Motility after enucleation is better with an implant than without. Typically the range of movement with an implant expressed as a % of normal ie compared to the other eye is 30% upgaze, 50% side to side, and 70% downgaze.

 

6. I was told peg-implants are inappropriate for Rb survivors as they can mask recurrences. Is this true? And if many years down the road your risk of recurrence gets really low, can you change your implant into a peg implant for better motility?

No, peg implants can be used for Rb. It is possible to differentiate between recurrent Rb and the imaging features of a pegged implant.

Implant exchange is not an easy procedure, and carries risks. It is best avoided, especially with buried integrated implants that get enmeshed in surrounding tissues. Non-integrated implants are easier to remove and could be considered for implant exchange. However, the motility with a pegged implant may be marginally better than non pegged. The risks outweigh the benefits and it is a procedure best avoided.

It may however be possible to drill a hole into some types of implants at a later date, converting it into a pegged implant.

 

7. Will the socket grow normally with an implant rather than a real eye?

There is good evidence that sockets with an implant grow better than without. However, the absence of an eye will undoubtedly have a negative influence on growth of the orbit, and the growth of enucleated orbits (with or without implant) usually lags behind an orbit with a real eye.

 

8. What does "migration of the implant" mean, and how is it treated?

The enucleated orbit undergoes changes with time. There is downward movement of the orbital fat, and there may be movement of the implant within the orbit.

The implant can migrate downwards and forwards, resulting in shallowing of the gap behind the lower eyelid (lower fornix), making it difficult to fit and wear the prosthesis. There is usually associated deepening of the upper eyelid sulcus (hollowing out of the upper lid), and the prosthetist often has to keep adding bulk to the upper half of the artificial eye to compensate for this change.

The implant can also migrate back deeper into the orbit, resulting in volume deficiency and reduced movement.

 

9. Can a tear in the surgery scar or a hole in the implant repair itself, and if so, how long does this take?

A tear in the surgery scar or a breakdown of the tissues (conjunctiva) overlying the implant may result in exposure of the implant. This is a cause for concern as it provides an entry point for bugs (bacteria) that may result in infection of the implant. Such infections are often difficult to eradicate- prevention is therefore the key.

Such a break in the conjunctiva can repair itself but can takes several weeks to months.

 

10. Do antibiotic drops help to prevent oozing from the implant?

Antibiotic eye drops may be used to prevent and/or treat infections during the healing of an exposed implant.

It is important to differentiate between the ooze (often coloured yellow, sometimes blood tinged) from an infected implant, and the whitish discharge that usually occurs from a healthy socket.

 

11. What are some typical indications that there's an infection in the implant?

The typical features of implant infection are:
- Visible exposure of the impant- appears white in contrast to the surrounding healthy conjunctiva which looks pink.
- Blood tinged/yellow coloured discharge from the socket
- Foul smelling discharge

 

12. When should an implant be replaced?

Recurrent, long standing or extensive implant exposure with implant infection that is resistant to conservative treatment is an indication for implant removal. The implant is rarely replaced at the same sitting. It is more usual to perform a second operation several months later to replace the implant with another implant (secondary implantation) or with a dermis fat graft.

Volume deficiency is not an indication for replacement of implant. Such cases do well with volume augmentation procedures (orbital floor wedge implants, or injectable fillers)

The implants last for life, and a healthy covered implant will never need replacement.

 

13. My child does not have an implant because the doctors here do not use them.  Is this bad for his socket?  Will it become infected?

It is desirable to have an implant as it will stimulate the orbit to grow at a similar rate to the other healthy orbit. Another reason is that absence of an implant may result in shrinkage and downward displacement of the unsupported orbital fat. This may result in shallowing of the gap behind the eyelid (conjunctival fornices), making prosthesis fitting difficult.

Absence of an implant does not increase the risk of infection.

 

14. What will happen to a socket as the child grows older if there is no implant or prosthetic?

Absence of an implant may result in shrinkage and downward displacement of the unsupported orbital fat. This may result in shallowing of the gap behind the eyelid (conjunctival fornices), making prosthesis fitting difficult.

 

15. Can we do anything to protect the socket where there is no implant?

It is important to wear a prosthetic eye to maintain the gap behind the eyelids (conjunctival fornices) as this gap is likely to shrink if left unsupported.

 

Other sections on artificial eyes

Children and adults with artificial eyes

See our gallery of children and adults with artificial eyes.

Artificial eyes

How to prepare your child’s school for looking after a child with an artificial eye.

Monocular vision

An explanation on how your child’s sight may be affected.

Sports goggles/protective glasses

Advice on protecting your child’s eyes.

Dino/Tino/other toys to help your child

Toys to help your child adapt.

What shall I tell my child’s school?

Advice on what your child’s teacher needs to know.