Questions and Answers Concerning Vision and Macular Degeneration.
What is the miracle of sight?
Sight is something we use
almost every waking minute, and take for granted until it is diminished. Of our five major senses (taste, touch, sight,
smell, hearing), vision is primary as it best connects us to our world. Vision lets us be productive. Vision helps to protect us from danger. Vision brings us joy.
How does the eye work?
First, the eye focuses
light and images of our world onto the retina in the back of the eye. In “technical geek language” the eye is a
transducer. The retina cone and rod
photoreceptors instantly help convert the light energy all around us by a
biochemical reaction into electrical energy the brain can use. The electrical signal from each eye is transmitted
to the brain by its own optic nerve.
What are cone and rod cells?
Cones and rods are
light-sensing cells.
There are 120 million rod
cells and they are more sensitive to light than cone cells. Rods are located more in the peripheral
retina and are helpful for side and night vision. A rare condition, called retinitis pigmentosa,
affects these cells creating “tunnel vision”.
The 6-7 million cone cells
are critical for providing central detail vision. There are three types of cone cells, each
most sensitive to a different color:
blue, green or blue.
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| Rod and Cone Cell |
What are the similarities between the eye and a digital camera?
The cornea and the eye's lens, at
the front of the eye, are used to focus light similarly to a camera lens. Like a camera, the eye must capture and
process this light energy. This is done
by the retina in the back of the eye.
Instead of a retina,
digital cameras record images electronically on fingernail-sized silicon chips
that are image sensors having millions of photosensitive diodes. Each captures a single pixel in the
photograph.
Each optic nerve is a
bundle of over 1 million nerve fibers “cabling” the eye to the visual cortex at
the back of the brain. On route from the
retinal photoreceptors to the brain, the signal is starting to be
processed. The brain further processes
these signals.
What are the differences between the eye and a camera?
The eye is easily one
thousand times more complex than most advanced camera. The eye is essentially an extension of the
brain. Before birth, during embryological
development the eye, and brain develop from the same neural tube. That is why it is said “the eye is part of
the brain”.
You can easily replace
your camera, its components and batteries.
There are no whole eye transplants.
Only the cornea and lens can be replaced. There are no retina (macula) or optic nerve
transplants. There certainly are no
brain transplants.
What is the Retina?
The retina consists of
ten layers which make up the inside layer of the eyeball. It can be described as having the thickness
and consistency of a single sheet of wet tissue paper. The retina's rod and cone photoreptors change light energy into electrical energy.
What is the difference between central and peripheral
vision?
It is helpful to use the
analogy of two, but interrelated, bull’s eye targets to describe the
relationship between central and peripheral vision.
Clarity drops off
dramatically as one moves out from the center rings. By the fourth ring, acuity (sharpness)
approaches the level of legal blindness (20/200)
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The center red dot represents the macula.
Each consecutive ring from the center to the periphery represents another drop in acuity level. |
What is the Peripheral Retina?
Side vision, or peripheral
vision, is not affected by macular degeneration. Peripheral vision is very useful for walking
and general vision, but it provides low resolution (i.e., details are not
clear) vision.
With the use of
magnification and eccentric viewing techniques, the peripheral vision becomes
very beneficial for macular degeneration patients.
Where and what is the Macula?
The macula is a highly
pigmented spot near the center of the retina about 5 mm or ¼th inch in diameter.
It is about the size of the capital letter “O” Due to the density of cone
photoreceptors, the macula is responsible detail and color vision.
What is the Fovea?
The tiny fovea is the
sweet spot in the center of the macula where the highest resolution vision is
located. This is the “HD-high
definition” part of the macula and is only 1mm or less than 1/16th
of an inch in diameter. It contains over
100,000 densely packed cone cells and no rod cells.
The fovea comprises less
than 1% of the retina size or two degrees of visual field (twice the width of
your thumbnail arm’s length), but is vital for seeing fine detail and color.
Why is the Fovea so important to vision?
It is responsible for
providing the clearest and most distinct 20/20 vision. It is needed for reading, writing, driving
and any activity where visual detail is necessary.
Despite its small size, approximately
50% of the nerve fibers in the optic nerve carry information from the fovea, and
information from the fovea takes up over 50% of the visual cortex in the brain.
What is Macular Degeneration?
Macular degeneration is
the physical breakdown of the macula that causes problems with vision. Anything that affects the macula affects
one’s central high-resolution vision.
Anything that affects one’s central detail vision greatly affects one’s
quality of life.
Macular degeneration progresses
to a certain stage and then stabilizes.
What are the different types of macular degeneration?
Based on the age when the
condition manifests itself, there are early, middle, and late-onset macular
degenerations. The early and
middle-onset macular degenerations are hereditary and classified as a group of
macular dystrophies (juvenile macular degeneration). The late-onset macular degeneration is
usually age related, but may also have some hereditary influences.
What is Stargardt’s Disease?
Although rare, this
early-onset MD is the most common of the hereditary macular diseases
Stargardt’s is transmitted
recessively, meaning the gene had to come from both parents.
Other hereditary macular
diseases are:
1. Juvenile Best’s disease
2. Adult vitelliform
degeneration
3. Cone dystrophies (affects one of three classes of cones)
4. Leber’s congenital
amaurosis
What is Age-Related Macular Degeneration (AMD)?
For varied and not fully
understood reasons, the macula begins to break
down. AMD is disease associated with the
aging process of the macula. AMD
initially advances slowly with little change in vision. As the condition advances some vision-related
activities become more difficult than others (i.e., reading). Vision loss becomes debilitating when the
fovea in the better seeing eye is affected.
Thirty percent of adults
over age 75 have early signs of macular degeneration and over fifty percent by
age 80.
What are RPE cells?
The Retinal Pigmented
Epithelial cells (RPE) help support,
nourish and maintain the health of the photoreceptors. It is believed that it is the loss of the RPE
cells that causes the loss of the photoreceptors needed to see with.
What is Drusen?
Drusen are small yellow or
white deposits under the retina in the macula seen in the early stages of MD. They can be classified as “hard” or
“soft”. Soft drusen is more medically
significant. Drusen causes the RPE to
separate from the retina.
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| Drusen |
What are the levels of vision loss due to MD?
The severity of vision
loss depends on the stage of the disease.
In the early stages, only the doctor may notice changes in the macula
during an examination. In the
intermediate stages, optical aids are needed to help with reading and other
visual activities. At the advanced
stages of MD, low vision rehabilitation is required to help restore some visual
functioning.
How many people have Age-Related Macular Degeneration?
It is believed that about
10 million Americans or 3% of the population suffer from some degree of macular
degeneration. Based on current
demographics, approximately 200,000 people in Massachusetts, 100,000 people in Connecticut,
and 30,000 people in Rhode Island have this condition.
What is Dry Macular Degeneration?
Eighty-five to ninety
percent of people with macular degeneration have the dry form, which involves
thinning of macular tissue and disturbances in its pigmentation. It is usually the milder and more slowly
advancing form of the disease, but it still can lead to significant vision loss
(geographic atrophy).
What is Geographic Atrophy?
End-stage macular
degeneration due to loss of pigment
Vision Level: legal blindness
What is Wet Macular Degeneration?
Whereas Dry MD comes on
slowly over many years, the onset of Wet MD tends to appear suddenly
(overnight) and gets worse rapidly. In
reality, Wet MD also takes years to develop, but shows up quickly by its sudden
reduction in vision. There are
treatments to curtail the damage, but there is no cure.
What is Discaform Scarring?
End-stage macular degeneration
due to scar formation
Vision level: legal
blindness
Are there symptoms of MD?
a.
The most common
symptom is blurred vision
b.
A blind spot in
the center of vision
c.
Straight lines may
become distorted or crooked
d.
Reading mail or
newspapers becomes challenging
e.
Seeing road signs
and traffic lights become difficult
f.
Faces become more
difficult to recognize
g.
Considerable more
light is needed to read
h.
Side or
peripheral vision remains unaffected
i.
Glare sensitivity
increases
j.
Adjusting to
changes in lighting environments becomes problematic
What are the treatments for MD?
Presently there is no cure
for any form of macular degeneration. There
is only treatment for the wet from of age-related macular degeneration and
treatments are aimed at stabilizing and preventing severe vision loss. Current treatment consists of a series of
injections with the drugs Lucentis and Avastin (anti-angiogenesis drug) that
block the development of new blood vessels and damaging leakage.
Good nutrition, including
ocular vitamin supplements, appears to slow the progression of AMD.
For vitamin and nutritional therapy consult your doctor.
What is on the horizon for treatment of MD?
1.
Stem Cells:
growing replacement RPE cells for injection into the eye
2.
New drugs: in
clinical trials
3.
Gene Therapy: altering
hereditary factors
4.
Retinal Chips:
artificial retinas
What are the risk factors for AMD?
The risk for AMD increase
with age and age is the number one risk factor.
a.
Age (the number one risk factor, prevalence increase with age)
b.
Smoking
(increased risk 2-5 times)
c.
Race (blue eyed
Caucasians)
d.
Family history (25%-40% AMD patients have a family history)
e.
High fat diet or
one low in nutrients and antioxidants
f. Obesity
g.
High exposure to
ultraviolet light (UVA & UVB)
What is an Amsler Grid?
Self-monitoring of the
Amsler Grid can assist in monitoring the progression of the disease.
Any additional squiggly
lines or distortions require immediate medical attention.
Can you go totally blind with MD?
It is exceedingly rare to
go totally dark-blind with macular degeneration because peripheral vision
remains intact. Seeing well enough to
safely walk can become more challenging, but certainly not impossible.
Is there rehabilitation for macular degeneration?
Absolutely! Low Vision
Rehabilitation restores useful vision by eccentric view training and employing
magnification and lighting techniques. Low
vision rehabilitation serves a vital and necessary role in the treatment of
macular degeneration.
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Dr. Randolph Kinkade
Low Vision
Magnification Demonstration |
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Dr. Randolph Kinkade
Low Vision
Lighting Demonstration |
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Dr. Randolph Kinkade's Macular Dengeneration
Treatment Television Interview |
http://www.youtube.com/watch?v=8M5evKk0L9Y&feature=plcp
