Taking an Impression for a Custom Prosthetic Eye
Taking an impression of a patient’s eye is an art and should be performed by experts only. A poor impression can traumatize a patient or child, and doom the ability to create a good prosthesis. Impressions can be taken of a wide range of eyes, including eyes with vision, as well as traumatized eyes such as cases of eviseration or enucleation. The eye is one of the most sensitive areas on the body and the impression is an invasive and unusual procedure. Experience is critical in obtaining a good impression as many factors can affect the impression which is obtained. First the eye socket must be examined thoroughly prior to an impression looking for anything that could cause a problem such as exposed sutures or an exposed implant. Then the proper impression material needs to be chosen.
Alginate and Polyvinyl siloxane are popular impression materials taken from the dental industry and adapted for ocularistry. Polyvinyl siloxane is a relatively new material in ocularistry, it causes minimal irritation to the patient and the impression does not degrade with time so it may be referenced later if needed. Alginate impressions are the traditional impression material used since the 1940’s. Alginate eye impressions gently release from problem areas of an eye socket, however alginate causes significantly more irritation to the eye socket, and alginate begins shrinking within minutes after the impression is taken so moving quickly is necessary to maintain detail from the impression.
Next an impression tray needs to be chosen. Often we use the patients’ old eye as the tissues have settled around that shape and an impression will reveal where the geometry of the prosthesis needs to be altered to fill the volume of the eye socket properly. If a patient is having trouble with their current shape or if a patient is getting their first impression, we often will begin with an impression tray that mirrors the shape of the patient’s good eye on the front side, and the impression is used to fill in the space on the backside. This method can quickly achieve a very close final shape for the patients’ prosthesis because the detail of the inside of the patients’ eye socket is captured and can be reproduced in detail unique to the patient’s eye socket.
Following the impression the shape is reproduced and used for fitting the prosthesis. We prefer to duplicate the impression in clear acrylic so we can see through the template prosthesis and determine if the template prosthesis is fitting properly. Once the prosthesis is fitting properly and the lids are opened as symmetrically as possible, then the fitting of the prosthesis can begin.