Guide to Macular Degeneration: Short Answers to Complex Questions

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.

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)

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 1/16^th 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.

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.

Dr. Randolph Kinkade
Low Vision
Magnification Demonstration

Dr. Randolph Kinkade
Low Vision
Lighting Demonstration










Dr. Randolph Kinkade's Macular Dengeneration
Treatment Television Interview

 

                              http://www.youtube.com/watch?v=8M5evKk0L9Y&feature=plcp

 

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