Introduction
Enucleation and evisceration reduce the volume of the tissues within the orbit. To achieve a cosmetic result this volume must be replaced. A large artificial eye may appear satisfactory at first but with time the lower eyelid will stretch under its weight. The redistribution of orbital fat which follows, results in the familiar appearance of the ‘postenucleation socket syndrome’ – a deep sulcus in the upper eyelid, ptosis or lid retraction, enophthalmos and downward displacement of the eye.
This uncosmetic appearance is prevented by the insertion of a buried orbital implant at the time of removal of the eye. If this is not done an implant is often needed at a later date. In an adult socket a 22 mm diameter implant is ideal. If the implant is wrapped a 20 mm diameter implant is usually adequate. A smaller implant may need to be inserted if a 20 to 22 mm implant appears too large for the socket; however, a degree of inadequate volume replacement may become evident postoperatively.
Improved movement is possible with integrated implants such as hydroxyapatite and other porous implants which link the implant with the prosthesis more directly.
If the volume replacement within the orbit is inadequate, despite the presence of an implant, a secondary implant may need to be added, usually on the orbital floor, or as additional fat within the muscle cone.
Finally, contraction of the conjunctival lining of the socket may prevent the artificial eye being worn at all until the fornices are reconstructed with grafts of oral mucosa.
Primary implants
Choice of operation
As soon as an orbit has been made anophthalmic by enucleation or evisceration of the eye an orbital implant should be inserted. Little extra dissection is required to insert such primary implants and the risk of shallowing the fornices is relatively small. Following enucleation a spherical implant ( 13.1 ) provides reliable volume replacement with little late orbital fat reabsorption but a small risk of extrusion. The traditional covering has been donor sclera. However, an alternative such as autogenous fascia lata or temporalis fascia, or a nonautogenous material such as Vicryl mesh or Mersilene mesh is now preferred because of the small risk of transmitted infection from donor sclera. The covering usually encloses an acrylic sphere but hydroxyapatite ( 13.2 ), porous polyethylene, or several other possible implant materials are popular, although often expensive, alternatives.
A motility peg for articulation with the prosthesis may be inserted into a hydroxyapatite or polyethylene implant at approximately 6 months postoperatively. The implant must be fully vascularised and the technique is different for hydroxyapatite and polyethylene implants. Many patients decide against this second procedure because of satisfactory cosmesis without it. Surgeons, increasingly, also choose not to insert a peg because of the relatively high risk of complications at the site of the peg. The techniques for peg insertion and fitting a prosthesis will not be described but see Further Reading.
The dermofat graft ( 13.3 ) loses volume from reabsorption during the first 6 to 9 months but has a very low extrusion rate. Because the conjunctiva is sutured to the edges of the dermofat graft, the fornices are shallowed less than with other implants.
A primary implant should also be inserted following evisceration. An acrylic ball, or one of the alternatives, may be used. No covering is needed and the sclera is closed anteriorly to cover the implant (see 12.1m–o ).
13.1
Primary spherical implant with Vicryl mesh wrap
The spherical implant is covered with a wrap to which the rectus muscles are attached to improve motility. Vicryl mesh is widely used.
Assess the space in the socket with sizers or by the trial insertion of different sized acrylic spheres. Select an implant of the appropriate size. If a wrap is to be used it will add up to 1 mm to the diameter of the implant.
Donor sclera is an alternative. It was the original material used to wrap implants and its appearance gave rise to the name ‘baseball’ implant. Sclera is now used less because of the very small risk of transmitted infection. However, it is still a satisfactory alternative. The principles of implantation are the same.
Place the implant well posteriorly in the socket. An introducer facilitates posterior placement (see also Figs 12.1j,k ).
Attach the rectus muscles to the implant in their natural positions. The inferior oblique muscle may be attached to the belly of the lateral rectus.
Close Tenon’s capsule and the conjunctiva in two layers with 6/0 or 7/0 Vicryl sutures with the knots buried. Fit a plastic conformer to maintain the shape of the fornices until a temporary prosthesis can be fitted after 1 to 2 weeks. A final, moulded, prosthesis may be fitted after about 2 months.
The fornices, especially the lower fornix, may be shallowed if there is inadequate conjunctiva or if the closure over the implant draws too much conjunctiva out of the fornices. If a prosthesis cannot be fitted or worn satisfactorily deepen the fornix with oral mucosa ( 13.12 ).
Exposure of the implant may lead to extrusion if it is not dealt with promptly ( 13.10 ). If extrusion occurs allow the socket to heal and reassess with a view to a secondary implant (Sect. B ). Migration of the implant, often inferiorly and laterally, makes the fitting of a satisfactory prosthesis difficult. Remove the migrated implant and insert a secondary implant in the correct position within the muscle cone.
13.2
Primary porous implant with a scleral wrap
Assess the size of implant needed with plastic spheres or sizers ( 13.1aA and 13.1aB ). Soak the appropriate hydroxyapatite ball in gentamicin and place it into a donor sclera. Close the sclera around the hydroxyapatite and suture it, leaving a gap. This will be the posterior aspect of the implant. Cut small rectangular windows anteriorly for insertion of the rectus muscles about 5 mm from the anterior pole of the implant. A fifth window may be cut for the inferior oblique muscle.
Complications and their management are the same as those for the wrapped acrylic implant.
Exposure rates are higher than acrylic implants. In addition, the vascularisation of the hydroxyapatite may be inadequate and drilling the implant to insert a peg may also result in exposure or extrusion of the implant.
13.3
Primary dermofat graft
General anaesthesia is used and the patient is placed in the left lateral position if the dermofat graft is to be taken from the buttock. Alternative donor sites include the groin, abdominal wall and lateral thigh (see 13.9 ).
Dermofat is not a common primary implant because of the tendency to lose volume. It has the advantage of deepening the fornices and may be considered as an autogenous graft.
Mark a sickle-shaped ellipse approximately 6 cm in its long axis and 2.5 cm across, convex posteriorly, in the middle third of the buttock and following the curve of the buttock. Incise the epidermis around the edge of the graft and inject saline intradermally. Carefully remove the epidermis with a curved scalpel blade (Bard Parker no. 10 or 15) to the depth of a moderate split skin graft. The skin removed should not be paper thin and translucent but moderately opaque, leaving multiple focal haemorrhages and scattered small foci of exposed fat on the donor site. Large globules of exposed fat indicate too deep a dissection.
Gently remove the dermofat graft. (Note – The sciatic nerve is approximately halfway between the greater trochanter of the femur and the ischial tuberosity, deep to the lower part of the gluteus maximus muscle, so it is relatively well protected during this operation.)
Close the defect with two or three layers of a 4/0 absorbable suture to close the fat and subcutaneous tissues and use interrupted 4/0 sutures to close the skin. Use a supporting Elastoplast dressing for about 5 days and remove the sutures in 10 days.
Trim the graft if necessary. Suture the four rectus muscles to the edge of the dermis with 6/0 absorbable sutures. The conjunctiva does not need to cover the whole graft but it should be sutured to its anterior surface to cover the edge using a 6/0 absorbable suture. Place a conformer. Epithelialisation occurs within about a month.
The fat in the graft reduces in volume during the first 6 to 12 months. The absorption is greater when this graft is used as a secondary implant. However, the advantage to the fornices is not lost (see Choice of Operation ).
If the split-thickness skin removed from the surface of the graft is too thick fat will be visible through the remaining dermis and epithelialisation may be delayed. Complete cover will eventually be achieved.
If the skin removed is too thin adnexal remnants may lead to keratinisation and the growth of hairs on the surface of the graft. These result in discomfort as soon as a prosthesis is fitted. If they persist, cryotherapy as a double freeze–thaw to –20°C will usually eliminate hair growth but keratinised areas may need to be removed surgically.
If the edge of the graft separates from the host conjunctiva fat will prolapse. If this is small wait for epithelialisation to occur. If the prolapse is large resuture the edge of the graft. Sweat gland remnants or conjunctival ingrowth can lead to cyst formation.
Primary implants
Choice of operation
As soon as an orbit has been made anophthalmic by enucleation or evisceration of the eye an orbital implant should be inserted. Little extra dissection is required to insert such primary implants and the risk of shallowing the fornices is relatively small. Following enucleation a spherical implant ( 13.1 ) provides reliable volume replacement with little late orbital fat reabsorption but a small risk of extrusion. The traditional covering has been donor sclera. However, an alternative such as autogenous fascia lata or temporalis fascia, or a nonautogenous material such as Vicryl mesh or Mersilene mesh is now preferred because of the small risk of transmitted infection from donor sclera. The covering usually encloses an acrylic sphere but hydroxyapatite ( 13.2 ), porous polyethylene, or several other possible implant materials are popular, although often expensive, alternatives.
A motility peg for articulation with the prosthesis may be inserted into a hydroxyapatite or polyethylene implant at approximately 6 months postoperatively. The implant must be fully vascularised and the technique is different for hydroxyapatite and polyethylene implants. Many patients decide against this second procedure because of satisfactory cosmesis without it. Surgeons, increasingly, also choose not to insert a peg because of the relatively high risk of complications at the site of the peg. The techniques for peg insertion and fitting a prosthesis will not be described but see Further Reading.
The dermofat graft ( 13.3 ) loses volume from reabsorption during the first 6 to 9 months but has a very low extrusion rate. Because the conjunctiva is sutured to the edges of the dermofat graft, the fornices are shallowed less than with other implants.
A primary implant should also be inserted following evisceration. An acrylic ball, or one of the alternatives, may be used. No covering is needed and the sclera is closed anteriorly to cover the implant (see 12.1m–o ).
13.1
Primary spherical implant with Vicryl mesh wrap
The spherical implant is covered with a wrap to which the rectus muscles are attached to improve motility. Vicryl mesh is widely used.
Assess the space in the socket with sizers or by the trial insertion of different sized acrylic spheres. Select an implant of the appropriate size. If a wrap is to be used it will add up to 1 mm to the diameter of the implant.
Donor sclera is an alternative. It was the original material used to wrap implants and its appearance gave rise to the name ‘baseball’ implant. Sclera is now used less because of the very small risk of transmitted infection. However, it is still a satisfactory alternative. The principles of implantation are the same.
Place the implant well posteriorly in the socket. An introducer facilitates posterior placement (see also Figs 12.1j,k ).
