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Cosmetic Optics: Hydroxyapatite Orbital Implants Raise Standards and Expectations for the Anophthalmic Patient
Recent developments in orbital prosthetics, and the orbital implants that support them, have greatly improved the rehabilitation of the anophthalmic patient. Leading these developments is a novel orbital implant composed of marine coral (converted to hydroxyapatite) known as the Bio-eye Hydroxyapatite Orbital Implant. This implant has the ability to completely integrate with the tissues of the orbit. Once ingrown with tissue, it will actually bleed if cut and can be drilled to accept a motility/support peg, which allows transfer of all implant movement directly to the artificial eye. Traditional implants cannot be pegged, and therefore may fail to deliver lifelike movement to the eye while also causing sagging of the lids due to chronic, unsupported weight of the artificial eye on the lower lid.
The new peggable orbital implant has set new standards and expectations for motility of the artificial eye and for preservation of the delicate structures of the lids. These higher standards also present greater challenges to the various eye care professionals concerned with rehabilitation of the anophthalmic patient: the ophthalmic surgeon must alter his surgical technique and choice of orbital implant to allow a direct connection, via a motility/support peg, between the artificial eye and the implant; the ocularist must fashion an artificial eye that accepts a motility/support peg while still maintaining adequate anterior chamber depth to give a natural appearance; and the optometrist must select lenses that protect and improve the vision of the natural eye while also employing special techniques, known as "cosmetic optics," to give the best cosmetic result for the artificial eye.
The optometrist may not realize that he represents the last link in the chain of cosmetic rehabilitation for the patient. The condition of the socket following disease (or injury) and surgery may not allow even the most skilled surgeon-ocularist team to produce a completely natural-looking artificial eye. Even with the peggable Bio-eye Hydroxyapatite Orbital Implant, damage to the rectus muscles or lids may not be reversible, and the patient's last best hope for cosmetic rehabilitation may be an optometrist who understands and employs cosmetic optics to optically distort the appearance of the artificial eye to better match that of the natural eye.
When an ocularist fits an artificial eye he does so without the patient's eye glasses in place. The eye is fit to match the companion side, taking into account the lid opening, the position of the iris in relation to the lid opening, and the size of the iris itself. When the eye is painted, the matching of the iris color, pupil size, and scleral details is completed without eye glasses in place. Thus, when the patient wears his glasses, the cosmetic effect is largely determined by the prescription in the glasses. If the lenses in the glasses are the same prescription, the visual appearance of the natural eye and prosthetic eye should have the same balanced look as when the patient is not wearing glasses.
The art of cosmetic optics comes into play when optical differences are intentionally built into the lens for cosmetic reasons. Obviously, glasses that have plus power in them will appear to make both eyes larger to the observer; and minus power lenses will make the eyes appear smaller. But beyond these simple starting points are many, less-obvious effects and techniques. Below is a brief guide for applying the art of cosmetic optics to the anophthalmic patient.
Adjusting Iris Size
If the iris of the artificial eye appears larger than that of the natural eye, add a minus sphere power to the lens over the artificial eye to reduce the apparent diameter of the iris. As the power is increased, the iris will continue to get smaller. Adding one diopter of minus will reduce the image size by about 0.3 mm. Likewise a smaller iris size can be increased in apparent size by adding plus spherical power.
Adjusting the Lid Opening
In cases of a too-narrow or too-wide lid opening, the use of a cylinder lens, by itself or in combination with plus or minus power lenses, will change the apparent shape of the lid opening. If the patient's lid opening is too wide, start by holding a -3.00 cylinder over the patient's artificial eye at axis 180, and then rotate the lens slightly in different directions. You will see the lid shape change and take on a more narrow look. Holding the lens at axis 90 will produce the opposite effect. The use of a minus cylinder to narrow the lid opening can also cause the iris to look smaller. In such cases, adding plus sphere power will neutralize this effect.
Adjusting Orbit Height
Anophthalmic patients often appear to have a sunken socket due to lower lid sag (from an unpegged artificial eye), an inferior orbit "blow-out" fracture, or from atrophy of orbital tissues. In such cases, a prism can be used to raise the apparent height of the orbit.
One diopter of prism base down will raise the orbit by 1.0 mm. However, since the prism may add significant weight to the lens, special consideration should be given to frame selection. A frame that is too large will result in a thick edge and a heavy look. It is definitely possible to raise the orbit with prism, but if the end result is unacceptable, then the benefit is lost.
Ocularists, especially those with a background in optometry, are often aware of the specific methods of cosmetic optics that should be tried in order to produce the best cosmetic results. Good communication between all participants in the chain of cosmetic rehabilitation of the anophthalmic patient is essential to ensure the best results.
© Copycopyright 1996 Jim Cahill