Customizing a Cryolite Glass Prosthetic Eye

Summary

This manuscript shows each step of customizing a cryolite glass prosthetic eye including some major advantages of the use of cryolite glass for manufacturing an eye prosthesis compared to poly(methyl methacrylate). In addition, this manuscript gives ophthalmologists better insight into the ocularistic care that could improve interprofessional collaboration.

Abstract

In Germany, Austria, and Switzerland, over 90% of ocularists still manufacture customized prostheses using cryolite glass from Thuringia. The present manuscript demonstrates this long-forgotten technique in detail. This manuscript shows some major advantages of manufacturing prosthetic eyes using cryolite glass in comparison to poly(methyl methacrylate) (PMMA). These advantages include a lighter weight of the prosthesis, higher levels of patient satisfaction, and only one appointment necessary for the customized manufacturing. Potential risk of breakage seems not to be a critical disadvantage for glass prosthetic eye wearers. However, in some patients, manufacturing a well-fitting prosthetic eye is not possible or reasonable due to anophthalmic socket complications such as post nucleation socket syndrome, scarred fornices, or an orbital implant exposure. This article gives ophthalmologists a better insight into ocularistic care in order to improve the essential interprofessional collaboration between ocularists and ophthalmologists.

Introduction

The purpose of the present manuscript is to comprehensively demonstrate the technique of manufacturing a customized cryolite glass prosthetic that is long forgotten outside the German-speaking countries (Figure 1). This manuscript also focuses on major advantages of this technique. These include a very smooth surface of the prosthesis due to fire polishing, the light weight of the prosthesis due to the hollow design, high levels of patient satisfaction, and the need of only one appointment for manufacturing of the customized prosthesis^1,2,3,4,5. This article also gives ophthalmologists better insights into ocularistic care in order to improve essential interprofessional collaboration^1,2,3,4,5.

In 1832, the glassblower Ludwig Uri Müller from Thuringia, Germany, developed the cryolite glass prosthetic eye based on the class-leading models made in France⁴. Benefits of cryolite glass included a better look, better tolerability, easier processing, and longer durability than previous glass eyes^4,6,7,8. Herman Snellen, a Dutch eye surgeon, used this cryolite glass to produce a lightweight hollow prosthetic eye in 1880^4,6,7,8. This lightweight prosthetic eye, the Snellen ‘reform eye’, increased the volume of prosthetic eyes, resulting in better fitting into larger eye sockets following the introduction of enucleation procedures made possible by the development of anesthesia and asepsis^4,8. Twenty years later, cryolite glass had become the most commonly used material for prosthetic eyes. Germany developed into the manufacturing center of prosthetic eyes globally^2,4,5,7,8. At the start of the second world war, German cryolite glass eyes became unavailable outside of the German-speaking area. Therefore, (poly)methyl methacrylate (PMMA) became a substitute material for prosthetic eyes^4,7,8, and today PMMA is the most commonly used material for prosthetic eyes globally^4,5,8. Notwithstanding, in German speaking countries, over 90% of ocularists still manufacture customized prostheses using the cryolite glass from Thuringia^{2,3,4,5,7,8,9,10,11,12,13}. Each customized cryolite glass prosthetic eye is produced in two major steps: the first step is to produce a "half-done" cryolite glass eye that conforms to a white sphere with an iris and a pupil (Figure 2). The second and decisive step is to customize the "half-done" cryolite glass prosthetic eye for the respective patient. To that end, a "half-done" cryolite glass eye is selected from thousands (Figure 3) based on the best matching iris color to the patient's healthy fellow eye.

The following protocol presents customizing a selected "half-done" cryolite glass eye for a specific patient. This step lasts about 25–35 min.

Protocol

All procedures performed in the following protocol involving human participants were in accordance with the ethical standards of the institutional research committee of the University of Cologne and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

1. Prosthetic eye customization

1. Select one of the "half-done" cryolite glass eyes based on the best matching iris color to the healthy fellow eye of the patient (Figure 3).
2. Examine the fitting of the current prosthetic eye. To do so, let the patient look straight ahead. Pay special attention to the retention of the prosthesis, the viewing direction, the eye lid contour (ptosis, entropion, and ectropion), as well as to the size and volume (exophthalmos and enophthalmos) of the current prosthesis.
3. Remove the current prosthetic eye with help of a contact lens suction cup for hard contact lenses.
4. Examine the anophthalmic eye socket without the prosthesis and pay attention to a potential inflammation of conjunctiva, the volume filling of the orbital implant, if the orbital implant is visible through the conjunctiva, and if the fornices and sulci are deep enough for a good fitting prosthesis. If there are any major concerns regarding one of these points, an examination by an ophthalmic surgeon should be performed before manufacturing a new prosthesis.
5. Take the selected "half-done" cryolite glass eye with the ocularist forceps and in the other hand take a hollow skewer that will be used later as a mouthpiece for blowing the glass prosthesis. Heat both slowly to 600 °C with a Bunsen burner while continuously rotating it, and melt the skewer at the open end of the "half-done" cryolite glass eye. Open the forceps and lay it down.
6. Heat the "half-done" cryolite glass eye continuously (Figure 4). Using the healthy fellow eye as a model for the color, shape, and quantity of the conjunctival vessels, draw the vessels on the white sclera with heated glass stems in different colors (mostly red, brown, or yellow) (Figure 5).
7. Heat the whole "half-done" cryolite glass eye while continuously rotating it so that the drawn vessels merge with the white cryolite glass and to produce a very smooth surface.
8. Modify the shape and the volume of the of the cryolite glass prosthetic eye by suction and blowing in the mouthpiece. Keep rotating the glass eye in the flame of the Bunsen burner from time to time. Use the old prosthesis as a template for this step, but if necessary, modify the shape and the volume of the new prosthesis based on the findings of the previous examinations.
9. Heat a transparent glass stem and melt it at the pupil of the cryolite glass prosthetic eye while continuously rotating the glass eye (Figure 6).
10. While continuously rotating the "half-done" glass prosthetic eye, melt the glass at the rear of the prosthesis (Figure 6 and Figure 7) and reduce the volume of the rear by suction with help of the mouthpiece so that the back side shape is nearly equal to the sample prosthesis or the desired shape.
11. Melt the glass stem at the front side away and heat the front side of the prosthesis again to produce a very smooth surface (Figure 8).
12. Take the front side of the prosthesis with the forceps again, form the final shape of the back side with help of the skewer (Figure 9), and then melt the skewer away (Figure 10).
13. Heat the whole prosthesis for fire polishing again, especially at the back side and rotate the prosthesis until the surface is very smooth all over.
14. Put the prosthesis in a preheated metal container and let it slowly cool down (Figure 11).
15. Insert the prosthesis and check the fitting as described in step 1.2 (Figure 12).
16. If necessary, modify the shape of the prosthesis again (repeat steps 1.8–1.15).

Results

Optimal results include a new prosthetic cryolite glass eye that fits very well, is comfortable, has a good motility, and the appearance with the prosthetic eye, including the eye lid contour, is nearly symmetrical to the healthy fellow eye (Figure 12).

Suboptimal results can result if the new prosthetic cryolite glass eye fits and is comfortable, but there are concerns regarding the cosmetic results. If a prosthesis does not fit perfectly, the appearance, includi...

Discussion

Following enucleation with an orbital implant, a conformer has to be inserted for two weeks (Figure 1) in order to prevent scarring of the conjunctival fornices and subsequent inserting of a prosthesis^{2,3,4,7,12,13}. Because an early ocular prosthesis insertion improves quality of life after enucl...

Materials

Name	Company	Catalog Number	Comments
Bunsen burner with gas and air flow over a fire-resistant worktop made from anodised stainless steel
Hollow skewer
Ocularist forceps
Preheated metal container to 500 degree celsius
Pre-produced "half-done" cryolite glass eye
Transparent glass stem
Various preproduced glass stems in different colors