Scleral shell prostheses fit over existing eyes and are often a better alternative to prosthetic contact lens because they are more stable. Scleral shell prostheses are more akin to prosthetic eyes than prosthetic contact lens in that they cover the entire globe and are made from (poly) methyl methacrylate (PMMA). They are also custom made in New Zealand and qualify for a subsidy from the Ministry of Health. They generally produce a better cosmetic result than prosthetic contact lenses. Scleral shell prostheses are indicated in cases where the eye is pthisical (shrunken) or where the direction of gaze is misaligned (strabismus), or where a prosthetic contact lens is unable to centre over a distorted cornea.
The process for making and fitting scleral shell prostheses involves four clinical sessions interspersed with laboratory processing. The four clinical sessions are usually completed over the course of a single day to minimize patient inconvenience and travel costs. Patients are free to explore the local environs and drink lots of coffee between sessions.
An impression of the eye is taken and this forms the base for the construction of a blank initial shell. The impression procedure is painless as eyedrops numb the eye while the impression is taken inside a preformed shell.
The blank initial shell is tried in and modified by polishing it thinner or by adding wax to make it thicker according to the size and eyelid contour required to match the companion eye. The modified trial shell is then invested in a two-part mold and duplicated in white (poly) methyl methacrylate ((PMMA) which forms the body of the final prosthesis. A layer of material is removed from the anterior surface of the duplicated shell leaving minimal thickness.
The trimmed shell is inserted and the position of the iris is marked with a waterproof marking pen. The shell is removed and a circular iris shape is painted directly onto the surface using oil paints mixed with a fast setting paint medium. The shell is then re-inserted and the position and size of the painted iris circle is checked and modified as necessary. When satisfactory, the painted iris is thoroughly dried and the pupil and extra iris colours are added to match the companion eye. The scleral colours and veins are added next and the shell is returned to the original mold for a clear acrylic veneer to be processed over the top.
When processing is complete, the shell is polished to a high standard of finish.
The completed scleral shell is inserted and Instructions are given for removing, inserting and cleaning the shell.
Follow up appointment
A follow-up session is recommended after one month to check the fit and to answer any questions.
An impression of the eye
A blank shell painted to match the companion eye
A clear veneer is packed over the shell in a mould
Semi translucent scleral shell prosthesis – .08mm thick
Rubber suction cups used for inserting and removing scleral shells