Encyclopedia of Health and Medicine

prosthetic eye 109
Eyeglasses
The conventional treatment for presbyopia is reading
glasses, which are magnifying lenses that
enlarge near objects to allow the eyes to focus on
them. Many retail and optical stores sell standard
reading glasses that come in common magnifications
typically ranging from +1.00 to +3.00 in gradations
of 0.25 power. This is often the least
expensive and most convenient option. An optometrist
also can prescribe custom-strength lenses.
People whose eyes otherwise do not require
refractive correction wear reading glasses as
needed for close vision. People who have other
REFRACTIVE ERRORS, such as myopia or ASTIGMATISM,
and wear eyeglasses require bifocal or trifocal COR-
RECTIVE LENSES that provide multiple levels of correction
to accommodate both the refractive
correction and the magnification for close vision.
Eyeglass lenses may be progressive, in which there
are no discernible lines on the lens to mark the
transition from one level to another. People who
wear contact lenses to correct refractive errors
often choose to wear reading glasses as needed
with the contacts for close vision, or may choose
to switch to eyeglasses.
Contact Lenses
Contact lenses may also have multiple levels of
refractive correction (multifocal contact lenses).
Another approach using contact lenses is monovision,
in which one eye, typically the dominant
eye, wears a lens that fully corrects for refractive
error and the other eye wears a lens that undercorrects.
The BRAIN learns to distinguish which eye
to use for close and for distant focusing, automatically
shifting as necessary. It may take a week or
two for the brain to make the adjustment and for
monovision to feel comfortable. However, some
people do not adjust to monovision at all. Monovision
results in some loss of depth perception,
which some people find barely noticeable and
other people find intolerable.
Surgery
In the United States, the two most commonly
used surgical methods to correct presbyopia are
conductive keratoplasty and LASIK (an acronym
for laser-assisted in situ keratomileusis), both done
as ambulatory procedures that require no
overnight hospital stay. In conductive keratoplasty,
the ophthalmologist uses radiofrequency
energy applied in a concentric pattern around the
base of the CORNEA to shrink corneal collagen. This
constricts the cornea’s base, causing the center of
the cornea to thicken and rise, which improves
close focus. It may take several weeks to experience
the full effect. In LASIK, the ophthalmologist
uses an excimer laser to reshape the cornea. There
is little recovery time with LASIK, and effects are
apparent almost immediately.
Each surgical method establishes a permanent
degree of monovision. Depending on the age of
the person and the anticipated progression of the
presbyopia, the ophthalmologist may leave a margin
of correction to allow for future changes.
Many ophthalmologists recommend a trial of
monovision with contact lenses before surgery to
determine whether the approach produces acceptable
results. The risks of surgical correction for
presbyopia include INFECTION, vision that still
requires corrective lenses even after surgery, and,
rarely, worsened vision. Some people may have
other eye conditions, vision problems, or general
health conditions that exclude them from surgery
as an option to correct presbyopia.
See also HYPEROPIA; REFRACTIVE SURGERY; SURGERY
BENEFIT AND RISK ASSESSMENT.
prosthetic eye A cosmetic replacement, also
called an ocular prosthesis or artificial EYE, for a
surgically removed (enucleated) eye. A specialist
called an ocularist designs the prosthetic eye to be
as close a match in appearance as possible for the
remaining natural eye.
The most common type of prosthetic eye
attaches to a spherical implant the same size and
shape of the eye that the surgeon places in the
orbit (eye socket) after removing the eye. As the
HEALING process takes place, other tissues and
blood vessels grow into and around the implant,
anchoring it firmly within the orbit. Once healing
is complete, the surgeon drills into the front of the
implant to attach a small post. The post then holds
the prosthetic eye, a “facing” that fits over the
front of the implant. The muscles of the orbit
move the implant in coordination with the movements
of the healthy eye, providing a natural
appearance to the prosthetic eye.