MACULAR DEGENERATION
This
information page has sections on Macular Degeneration and several
related diseases. Click on the following links to find out more
about the condition which is of interest to you.
Macular
Degeneration occurs in 2 forms. These are "involutional" (DRY) which
is age related and "neovascular" (WET). Both forms affect central vision
causing loss of the ability to read and recognise faces.
People with macular degeneration usually retain
enough peripheral vision to care for themselves and remain active, but
reading a clock, a street sign, the destination particulars on a bus
even telling the difference between a bus and a truck is difficult
without central vision.
Reading, driving, sewing and any tasks that demand
fine visual discrimination require a healthy macula. Without it, the
world is visible but only in an imprecise way. However, macular
degeneration seldom leads to total blindness.
Symptoms
of Macular Degeneration
Macular Degeneration is characterised by loss, blurring or distortion
of central vision caused by progressive deterioration of the macula, the
small central area of the light-sensitive cells making up the eye's
retina. A dark grey spot may appear in the central part of vision or the
size of an object may appear different for each eye. It is the visual
acuity which is most affected.
Diagnosis and Treatment
Although there are no symptoms in the early stages, an
ophthalmologist can detect the condition during a medical eye
examination before the symptoms appear.
Use of the "Amsler grid" at home can also lead to early detection
(Test your sight with
the
Amsler grid
)
A person with macular
degeneration can be helped.
Laser surgery can help conserve sight in the early stages of the
neovascular form of macular degeneration. Vision aids in the forms of
magnifying lenses and reading machines for close work and telescopic
lenses for distance can greatly assist many individuals with macular
degeneration to continue a relatively normal life. A wide range of
vision aids is available from Low Vision Centres but referral by an
ophthalmologist is required.
Involutional macular degeneration is the technical
name for what is often more simply described as "age-related" because it
is commonly associated with aging. What happens with age-related macular
degeneration is that the macula progressively thins and dries that is,
it progressively atrophies as part of the aging process. Consequently,
this condition is also labelled "dry" macular degeneration. This
involutional or age-related form is by far the most prevalent form of
macular degeneration, accounting for 90 percent of all cases.
Why the macular thins and dries in some older
people and not in others is yet not known, although two things appear to
be fairly clear. One is that some families seem to have a predisposition
to age-related macular degeneration, meaning that family members are
more prone to it. If someone in a family has macular degeneration, an
ophthalmologist should examine annually all family members over 40.
Additionally, there is now clear evidence that smoking can contribute to
the development and progress of the condition.
Treatment
Medical or surgical treatment for age-related
macular degeneration is not yet available, though experimental research
is in progress and hopefully treatments will result. However, not only
may vision be helped by vision aids but, with appropriate counselling,
people can learn to use some of their peripheral vision to help them see
more clearly and continue to cope with the practical tasks of everyday
life.
The earlier macular degeneration is detected, the
better are the chances of maintaining useful vision. Compensation by an
unaffected eye often masks early symptoms. When symptoms do
appear, they vary.
Neovascular macular degeneration is also labelled
"wet" macular degeneration because it is fluid from leaking blood
vessels in the retina that causes the light-sensitive cells of the
macula to sicken and die. This can occur at any age but is still more
common as age increases.
Symptoms
Noticeable visual
symptoms usually accompany this process. Straight-lines look wavy and
later blank spots may appear in your vision. If untreated much of the
nerve tissue in the macula may be killed or injured within a few weeks
or months. This damage cannot be repaired because nerve cells in the
macula do not grow back once they have been destroyed.
Although only a small percentage of people with macular degeneration
develop this
form, they may make up the majority of those
who suffer serious vision loss as a result of macular degeneration.
Treatment
If leaking blood vessels characteristic of
neovascular macular degeneration are detected early enough and are not
located in the centre of the macula, a treatment called laser
photocoagulation can reduce the risk of severe vision loss by more than
half.
In this procedure, the ophthalmologist aims a
focused beam of laser light at the leaking blood vessels. On contact,
the laser light turns into heat and destroys (photocoagulates) the
leaking blood vessels. A sophisticated photograph, called a fluorescein
angiogram, maps the affected area and allows the ophthalmologist to aim
the laser beam precisely.
Although the laser treatment does not restore lost
vision, distortion usually disappears and, more importantly, further
vision loss is retarded. Recently, laser therapy has been combined with
a drug, Visudyne, which helps focus the laser in the macular. Advice
should be sought from your ophthalmologist.
As with the more prevalent involutional form of
macular degeneration, vision aids can be a great help, as can training
in how to make more effective use of peripheral vision.
Does Macular Degeneration run in Families?
For most people with age-related macular
degeneration, there is no hereditary predisposition. However, if someone
is diagnosed with this condition before the age of 50, there is an
increased risk for other family members and they should be encouraged to
seek medical advice.
There are several other diseases which are more
clearly genetic and in which the macula is damaged.
Click
here for Genetic Inheritance
Stargardt Disease is the most common form of Inherited Macular
Degeneration in patients under the age of 20. It is usually first
noticeable between the ages of 8 and 12.
Diagnosis and cause
In this condition, the cone cells (at the macula) deteriorate in
function and eventually die, while the rod cells generally remain
intact. The diagnosis is usually made as a result of deterioration in
visual acuity and typical appearances around the macula when the
ophthalmologist looks into the eye. Electrical tests - such as the
electro-retinogram (ERG), electro-oculogram and dark adaption testing -
can measure the progress of the disease but are not usually necessary
for its diagnosis.
Symptoms
Patients with previously normal vision develop
irregularly shaped yellowish-white flecks or spots in the macula. This
causes decreased central vision, reading and fine handwork may become
difficult which eventually deteriorates to 6/60 as the flecks in the
macula grow. In late stages of the disease, there may also be some
impairment of colour vision.
In some, this deterioration is rapid, while in
others it is much slower. There is no way to detect how fast this
deterioration will occur in any individual. By the age of 50, about half
will have a visual acuity of 6/60 or worse (defined as "legal
blindness").
People with Stargardt disease do not usually have
a problem with peripheral vision, and hence usually have little problem
with bumping into objects when moving around. They may however
experience difficulties in adjusting to light.
This is mainly inherited as autosomal recessive.
The gene for this disease has been located to the
shortarm of Chromosome 1. The gene has recently been identified as the
ABCR gene. The protein produced by this gene is involved in the energy
transport to and from the photoreceptor cells.
Occasionally, it can be inherited as autosomal dominant.
click
here for Genetic Inheritance
Treatment
There is no cure, but research on this and other
related diseases may identify a form of treatment
Fundus Flavimaculatus is a condition similar to
Stargardt Disease but varies in its age of onset and severity. When
there is macular damage, vision can deteriorate to 20/200, although it
usually remains between 20/50 and 20/80. Damage to the macula first
appears in the adolescent and early adult years, and the area of damage
may gradually spread.
PERIPAPILLARY (pericentral) CHOROIDAL
DYSTROPHY
Peripapillary (pericentral) Choroidal Dystrophy is
a condition, which causes wasting of the blood vessels that surround the
optic nerve. Patients first notice symptoms in the late adult years,
when the macula is affected.
Stationary cone disorders are present at birth and
have symptoms decreased acuity, decreased colour vision, sensitivity to
light - that do not worsen with age. There are several types of
stationary cone disorders (for example, cone monochromatism, blue cone
monochromatism, dichromatism, trichromatism) with differing prognoses
for visual acuity.
Pigment Pattern Dystrophy, which describes a group
of disorders that includes Butterfly shaped Pigment Dystrophy of the
fovea, North Carolina Macular Dystrophy, Macro reticular (Spider)
Dystrophy and Sjogren Reticular Pigment Epithelium Dystrophy. The
macular changes in these patients can occur at any age, but usually
first appear in childhood. Many patients do not experience symptoms and
may have visual acuities in the 6/6 to 6/24 range. Some of the genes
have been identified for these disorders and are located on chromosome
6.
X-linked Cone-Rod
Dystrophy is a rare disorder, and patients present with decreased
central vision, may have a bull's eye lesion in the macula, a fine
nystagmus, and no or very little pigmentary change in the fundus, until
advanced stages of the disease. The visual field loss is slower than in
x-linked RP, the ERG shows a cone-rod pattern if the ERG is recordable,
which is often the case: unlike x-linked RP, in which the ERG is
severely affected early in the disease.
Best disease (also known
as vitelliform macular dystrophy) is an inherited form of macular
degeneration characterised by a reduction of central vision.
CLINICAL DESCRIPTION
Best disease affects the macula, the central part
of the retina responsible for fine visual detail and colour perception.
The retina and its component photoreceptor cells are essential to vision
as they convert light into electrical impulses and then transfer these
impulses to the brain via the optic nerve.
Although the age of onset of Best disease can
vary, it is usually diagnosed during childhood or adolescence. In the
initial stages, a bright yellow cyst (fluid-filled sac) forms in the
retinal pigment epithelium (RPE) beneath the macula. On examination, the
cyst looks like a sunny-side-up egg. Despite the presence of the cyst,
visual acuity may remain normal or near normal (between 6/9 and 6/18)
for many years. Peripheral (side, upper and lower) vision usually
remains unaffected.
In many individuals with Best disease, the cyst
eventually ruptures. Fluid and yellow deposits from the ruptured cyst
spread throughout the macula. At this point the macula has a scrambled
egg appearance. Once the cyst ruptures, the macula and the underlying
RPE begin to atrophy causing further vision loss. As a result, central
vision tends to deteriorate to about 6/36 late in life. However, Best
disease does not always affect both eyes equally. Many individuals
retain useful central vision in one eye with a visual acuity of about
6/12 in the less affected eye.
In some cases, Best disease does not progress far
enough to cause significant central vision loss. However, retinal
specialists can still detect the disease using sophicated diagnostic
tests that measure the function of the RPE and the retina. Individuals
with Best disease are also often farsighted which can be corrected with
glasses.
INHERITANCE
Best disease is genetically passed through
families by the autosomal dominant pattern of inheritance.
(click
here for Inheritance Pattern)
TREATMENT
Currently, there is no treatment for Best disease.
Ongoing scientific research is directed at understanding the cause of
Best disease. A gene for Best disease has already been mapped (located
to a specific region) to a human chromosome. Next, this gene will be
identified and its function in the retina determined as the first step
in developing means of treatment and prevention.
Individuals with Best disease may benefit from the
use of low-vision aids and, possibly, orientation and mobility training.
Juvenile retinoschisis is an inherited disease
diagnosed in childhood that causes progressive loss of central and
peripheral vision (side, upper and lower) due to degeneration of the
retina.
CLINICAL DESCRIPTION
Juvenile retinoschisis (also known as X-linked
retinoschisis) occurs almost exclusively in males. Although the
condition begins at birth, symptoms do not typically become apparent
until after the age of 10. About half of all patients diagnosed with
juvenile retinoschisis first experience a decline in vision. Other early
symptoms of the disease include an inability of both eyes to focus on an
object (strabismus) and roving, involuntary eye movements (nystagmus).
The splitting of the retina into two layers causes
vision loss associated with juvenile retinoschisis. This retinal
splitting most notably affects the macula, the central portion of the
retina responsible for fine visual detail and colour perception. On
examination, the fovea (the centre of the macula) has spoke-like
streaks. The spaces created by the separated layers are often filled
with blisters and ruptured blood vessels that can leak blood into the
vitreous body (the transparent, colourless mass of jelly-like material
filling the centre of the eye). The presence of blood in the vitreous
body causes further visual impairment. The vitreous body degenerates and
may eventually separate from the retina. The entire retina may also
separate from underlying tissue layers causing retinal detachments.
The extent and rate of vision loss vary greatly
among individuals with juvenile retinoschisis. Central vision is almost
always affected. Peripheral vision loss occurs in about half of all
cases. Some affected individuals retain useful vision well into
adulthood; with others experience a rapid decline during childhood.
RELATED DISEASES
Juvenile retinoschisis can resemble other retinal
degenerative diseases such as retinitis pigmentosa (RP), Goldman-Favre
viteoretinal dystrophy. Wagner's vitreoretinal dystrophy, and Stickler's
syndrome. A thorough eye examination, including diagnostic tests
measuring retinal function and visual field, combined with an accurate
documentation of family history, can distinguish between these disease.
INHERITANCE
Juvenile retinoschisis
is genetically passed through families by the X-linked pattern of
inheritance.
Sometimes, however, when carrier females are examined, the retina shows
minor signs of the disease.
(click
here for Inheritance Pattern)
TREATMENT
At this time, there is no treatment for juvenile
retinoschisis. However, in some cases, surgery can repair retinal
detachments. Ongoing scientific research is directed at identifying the
gene that causes juvenile retinoschisis as the first step in developing
means of treatment and prevention.
Individuals with juvenile retinoschisis may
benefit from the use of low-vision aids, including electronic,
computer-based and optical aids, as well as orientation and mobility
training.
Genetic Conditions Associated with Macular Degeneration
Inherited conditions include:
Which are caused by the accumulation of drusen, yellow-white
deposits, in the macular area. Drusen deposits usually appear in the
first three decades of life, and become larger as a person ages.
Decreased vision may not be noticed until the fourth decade, with vision
varying between 6/9 and 6/24. If the drusen causes other complications
in the retina, vision may decrease to 6/60.
Which is a rare disorder in which new blood vessels grow under the
fovea, resulting in fluid build-up in the macular, haemorrhage, and
general wasting of other layers of tissue in the eye. Usually symptoms
do not appear until after the age of 40. Drusen may also be present.
People with this disorder may experience a rapid decrease in vision. The
gene for this disorder has been identified as the TIMP3 gene, which is
located on the long arm of Chromosome 22.
Which describes a group of disorders that includes Butterfly shaped
Pigment Dystrophy of the fovea, North Carolina Macular Dystrophy, Macro
reticular (Spider) Dystrophy and Sjogren Reticular Pigment Epithelium
Dystrophy. The macular changes in these patients can occur at any age,
but usually first appear in childhood. Many patients do not experience
symptoms and may have visual acuities in the 6/6 to 6/24 range. Some of
the genes have gene identified for these disorders and are located on
chromosome 6.
|
