Indications

The main indications for primary enucleation are large tumor size, neovascular glaucoma, optic nerve invasion, blind painful eye, localized extrascleral extension, and patient preference. Enucleation is also considered for the treatment of medium-sized choroidal melanoma with poor vision (<20/400) or absence of potential for visual recovery. Functional status of the other eye and patient preference are also important considerations in the decision-making process. The indications for secondary enucleation are local treatment failure and ocular pain secondary to radiation-related complications.

Implant description

An ideal implant should restore volume, transmit motility, possess a low complication rate, and demonstrate cost-effectiveness.¹⁰ To transmit motility, the extraocular muscles should attach to the implant directly or surround the implant indirectly.¹⁰ An implant of proper size restores volume.¹¹ Current orbital implant designs fall into two general categories: solid spheres and porous, integrated implants. Solid spheres include silicone and polymethyl methacrylate (PMMA), while porous implants include coralline hydroxyapatite and porous polyethylene.¹⁰ Bioceramic and other implants also exist.¹⁰ Porous materials allow for fibrovascular ingrowth which may induce epithelialization of a drill hole to accept a prosthesis coupling peg to improve motility. Pegged hydroxyapatite implants offer subjective improved motility over unpegged implants and vascular ingrowth possesses some theoretical advantages, including decreased rates of infection, exposure, and extrusion.^10,12

Coralline hydroxyapatite (HA) is a porous, nontoxic implant composed of inorganic, nonreplenishable marine coral.¹³ High-density porous polyethylene is a porous, synthetic implant that can be molded into various shapes.¹⁴ Hydroxyapatite has a brittle nature, which precludes direct suturing to the implant surface.¹⁵ Pore sizes and interconnectivity vary, which could affect vascularization.¹⁶ Some surgeons drill holes into porous implants to facilitate integration.¹⁷ The use of porous materials adds additional costs of the implant, wrapping material, and imaging studies, and possesses higher complication rates.¹⁸

Some surgeons wrap porous implants to protect the anterior tissues from hydroxyapatite bone spicules and to facilitate muscle attachment and implantation. However the perceived benefits have not been proven.¹⁵ Wrapping materials include donor sclera, autogenous fascia or polyglycolic acid mesh. While some surgeons wrap porous polyethylene implants, the extraocular muscles can be directly sutured to polyethylene.^19,20 Wrapping materials may pose infection risk and decrease vascularization rates.¹⁷

When surveyed in 1995, the majority (56%) of the American Society of Ophthalmic Plastic and Reconstructive Surgeons (ASOPRS) preferred hydroxyapatite implants and human donor sclera wrapping in enucleations.²¹ When resurveyed in 2002, the majority (43%) of ASOPRS surgeons preferred porous polyethylene and only 27% preferred hydroxyapatite.¹⁸ In the later survey, most implants (60%) were not wrapped and only 25% were wrapped in human donor sclera.¹⁸ The majority (92%) of implants were left unpegged.¹⁸ In 2007, a survey from the UK supported these trends, demonstrating that 55% of surgeons used porous implants, 57% wrapped the implant (with autogenous sclera being most popular; 20%), and only 7% pegged the implants.²² Custer demonstrated no significant difference in motility between unpegged hydroxyapatite and solid implants.²³ The potential advantages of using porous implants and wrapping materials should be weighed against the risks, morbidity, and additional cost.²⁰ If the surgeon does not plan to peg, if the patient has systemic illnesses or factors that may limit fibrovascular ingrowth, or if a porous implant may not improve a patient’s quality of life, the surgeon should give consideration to a solid implant.

Implant sizing

Proper implant sizing is essential for cosmesis, volume restoration, and to minimize extrusion, exposure, and sulcus deformities. Most adult patients require at least a 20 mm implant. Traditionally, surgeons use a set of sizing spheres to individualize implant size and use standard volume tables to maximize volume restoration. Alternatively, orbital implant size can be determined using the contralateral eye axial length measurements subtracted by 2 mm, or by 3 mm for hyperopia.¹¹ Another algorithm subtracts the volume of an ideal 24 mm eye by the volume of sclera and 2 mL to determine implant volume.²⁴