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.
Semi translucent scleral shell prosthesis – .08mm thick
The process for making and fitting scleral shell prostheses involves four clinical sessions interspersed with laboratory processing. An impression of the eye is taken during the first session and this forms the basis for the construction of a clear initial shell.
The initial shell is tried in at the second clinical session and modified by grinding 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 or semi translucent (poly) methyl methacrylate (acrylic) 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.
At the third clinical session, 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 and inserted at the forth and final clinical session. Instructions and training are given for removing, inserting and cleaning the shell at this visit.
A follow up session is recommended after one month to check the fit and to answer any questions.
This woman’s disfigured right eye is slightly shrunken.
The right scleral shell prosthesis masks the disfigured iris and restores the eyelids to their correct position.