THE
DOCTOR'S
CORNER
By Richard A. Lewis, M.D.
THE
READERS'
FORUM
Questions answered on:
RP in one eye
Cataracts
RP and childbearing
Vision loss and anesthesia
RP and Ushers Syndrome
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The RP Messenger Archives
Q. Can a person have RP in
one eye only?
A. By the usual medical definitions and conventions, retinitis
pigmentosa is the descriptive
name for a group of disorders, all
of which are genetic (that is,
caused by altered genes), and
each of which may be transmitted
differently in different families
(dominant, recessive, X-linked,
and no family history or "isolated"). These disorders may
number between 35 and 50. In the
usual situations, we consider
retinitis pigmentosa characterized by difficulty with dim
light or night vision, progressive
loss of peripheral or side vision,
ultimate involvement of central or
reading vision, and associated
with a characteristic process that
involves the nerve tissue in the
retina and the retinal pigment
epithelium (which is the glue that
bonds the retina to the inside
lining of the eye).
Thus, retinitis pigmentosa is
a single name for a group of
disorders which are typically
bilateral (both eyes involved),
progressive (that is, invariably get
worse over time), and genetically
determined. Scattered through
the ophthalmic and medical
literature, there are occasional
reports of individuals with
"retinitis pigmentosa" in only one
eye (sometimes called "unilateral
retinitis pigmentosa"). Interestingly, these diagnoses are based
typically on the characteristic
appearance of pigment
degeneration inside the eye, the
loss of both central and
peripheral vision in one eye,
which does not occur in the other
eye. Thus, something which looks
remarkably similar to retinitis
pigmentosa in some individuals
and is described as a complication of trauma to the eye (such as
a blunt injury), as following a
complete retinal detachment with
spontaneous retinal
reattachment, as following
certain infections or parasitic
infiltrations of one eye only, and in
many instances, unassociated
with any other recognizable
feature.
However, in no instance has
unilateral retinitis pigmentosa
ever occurred in more than one
individual in a family, and in no
instance has anyone with
unilateral retinitis pigmentosa
ever proceeded to have a child
with retinitis pigmentosa.
As such, it is assumed, by the
best available medical
information, that there is no truly
genetic disorder called "unilateral
retinitis pigmentosa" nor does
unilateral pigmentary degeneration which resembles RP place
the individual or the family at any
higher risk to have another
individual with RP in the family in
present or future generations
than the expected risk in the
general population. Occasionally,
true retinitis pigmentosa can be
slightly asymmetrical between the
two eyes and thus one might
mistakenly think one eye was
relatively uninvolved. However,
careful observation by a diligent
observer will reveal most of the
characteristics of RP, clarifying
that, indeed, this is a bilateral
disease.
In summary, unilateral
retinitis pigmentosa in the usual
sense of our use of the term does
not exist as a genetic disorder,
but rather mimics RP, because of
the appearance of the retinal
degeneration caused by some
other insult.
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Q. I have been told that many
people who have had cataracts
removed and receive a lens
implant have trouble with the
membrane later. Why? And what
can be done to prevent complications?
A. There has been a great deal
of recent interest, publicity, and
misinformation concerning lasers
and cataract surgery. A laser is
simply a narrow intensified beam
of light which can produce a tiny
burn or hole in tissue. There are
several kinds of lasers. Each type
of laser may produce a different
effect according to the material
used to produce the laser beam.
The laser that we use after
cataract surgery is commonly
nicknamed the "YAG" laser (its
real name is neodymium:yttrium
aluminum garnet or Nd:YAG
laser). The "YAG laser" beam is
used to open gray or white membranes or scars. Many patients
ask that their cataracts be
removed with laser surgery. This
cannot be done by any surgeon at
this time. Cataracts are removed
surgically by conventional
methods, usually by removing all
the cataract except the back wall
or shell (also called the "capsule")
of the human lens. Thus, the laser
is not used for the removal of
ordinary (primary) cataracts.
However, the YAG laser is
useful for the treatment of what
we call "secondary cataracts" or
"secondary membranes". A
secondary membrane is a cloudy
film that forms in an eye months
or years after surgical removal of
a primary cataract. Prior to the
YAG laser, such membranes had
to be cut with a knife through a
surgical incision.
Not all patients who have had
cataracts removed by
conventional (extracapsular)
surgery, even with an artificial
lens implant, will need to have this
remaining membrane opened; the
opening made only if the
membrane become optically
cloudy (much like a sheet of wax
paper or a frosted window pane).
Thus, if you have had cataract
surgery and you experience a
slow but progressively decreased
vision because of a secondary
cataract, the laser can promptly
restore your vision with a simple
outpatient procedure to cut a hole
in the secondary membrane.
However, since this procedure is
done with a highly focused form of
light energy, there is no cutting
into the eye and no risk of
infection, bleeding, or many other
complications.
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Q. Is there a relationship
between child-bearing and
deterioration of vision?
A. Several historical anecdotes
suggest that women who have
retinitis pigmentosa and become
pregnant experience an
acceleration of their RP, that is,
an increased rate of visual field
loss or an accelerated loss of
central vision. However, the
documentation of such claims is
non-existent. Furthermore, there
is no experience to suggest that
women creating artificial states of
pregnancy, such as with birth
control pills, fertility hormones,
and so forth accelerate the rate of
changes of their retinitis
pigmentosa.
Investigators in the
numerous academic Retinitis
Pigmentosa Centers distributed
around the United States have
volunteered to collect data from
women with RP who plan a
pregnancy. Any reproductive
age-group female with RP who
plans a pregnancy should contact
one of these investigators well
before, so that baseline visual
acuities, visual fields, and where
appropriate, electrophysiologic
responses can be assessed and
then monitored during pregnancy
and afterward. However, in the
absence of any documentation,
most specialists in retinitis
pigmentosa do not admonish
reproductive age females against
pregnancy nor advise those
women that there is an
acceleration of their disease
during pregnancy.
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Q. I belong to a support group and
two of my friends have lost more
vision as a result of having
unrelated surgery that required
anesthesia. Is there a connection?
A. This question is
unanswerable. One would need
to know the nature of the visual
impairment, the specific
diagnosis of the type of retinal
dystrophy, the visual status
before the surgery, including
visual acuity and visual field, the
nature of the surgery, the nature
of the anesthetic, and certain
other factors including the
duration of the procedures. In
addition, the visual acuity after
surgery and other parameters
would need to be assessed.
There is no known relationship or
risk to RP patients undergoing
local or general anesthesia.
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Q. I have been told that the
eyes of someone with RP are
different from the eyes of
someone who has Usher
syndrome. What is the difference
in the rate of visual loss for the
two types of disorders?
A. A loose and generic
definition of retinitis pigmentosa
is mentioned in the answer to
Question #1 above. Usher
syndrome was described by
Charles Usher, M.D., an
ophthalmologist from Scotland
who studied visual impairments
among families at institutions for
the hearing impaired in Southern
England and initially reported his
findings in 1913. He noted two
groups of families: in one the
children were hearing impaired
from birth, never learned to
speak, and developed a retinal
dystrophy similar to retinitis
pigmentosa beginning between
the ages of five and ten years; in a
different set of families, children
experienced hearing impairment
of a milder degree, learned to
speak, but developed pigmentary
retinal dystrophy similar to
retinitis pigmentosa roughly from
age 10 to age 20. The techniques
for analyzing Usher's families
have changed substantially since
his original observations, since
neither audiograms nor clinical
electroretinograms were possible
until the late 1940s. Nonetheless,
we call those individuals with
severe congenital hearing
impairment who never speak
(because they never hear) and
develop a "retinitis
pigmentosa"-like retinal
dystrophy in the first decade of
life Usher Syndrome Type I. Usher
Syndrome Type II refers to the
milder form of retinal dystrophy
associated with a milder form of
congenital hearing impairment
which is compatible with speech
and conversation, but with a
characteristic flat or nasal
pattern. In each instance, as best
we can judge, the hearing impairment is stationary throughout life
or only very minimally
progressive. The retinal disease
in each type is progressive.
When an ophthalmologist
looks inside the eye of a person
with Usher syndrome or with
retinitis pigmentosa, the appearances can be remarkably similar.
However, unless there is some
other event occurring in the
family, hearing impairment does
not occur in typical retinitis
pigmentosa, whereas in the Usher
syndromes, both hearing impairment and a progressive
pigmentary retinopathy always
occur together. (On the other
hand, I have seen an occasional
individual who inherited RP from
one parent and a form of deafness
from another parent, and thus had
two independent and unrelated
genetic diseases at the same
time. Those individuals do not
have Usher syndrome but rather
have two diagnoses.) Both Usher
Syndromes are always inherited
as autosomal recessive traits.
The genes for Usher Syndrome
Type I have been mapped by
various investigators to Chromosome 14, the long arm of Chromosome 11, the short of
Chromosome 11, and possibly
one or two other places. The gene
for Usher Syndrome Type I has
been mapped only to the long arm
of Chromosome 1, but the specific
gene defect has not yet been
identified.
There is no good information
about the differing "rates" of
visual or visual field loss, since
there are at least two different
forms of Usher Syndrome; there
may well be at least three different genes for Usher Syndrome
Type I, each of which presumably
would have its own rate of
progression, even within different
families. It is not yet possible to
assess how many different forms
of retinitis pigmentosa there are,
but their rates of progression and
loss of both peripheral vision and
visual acuity would be moderated
at least by the different genetic
events and by the different
mutations or alterations of the
same genetic type(s).
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©1997,2000 Texas Assn of Retinitis Pigmentosa Inc
This page last updated 12/11/97 8:32:50 PM
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