Macular Degeneration

The macula is found at the center of the retina where the incoming rays of light are focused.  The macula is responsible for what we see straight in front of us, for the detailed vision needed in activities such as reading and writing, for recognizing faces, and our ability to appreciate color.

Macular Degeneration is a condition in which the delicate cells of the macula become damaged and stop working.  Vision loss usually occurs gradually and typically affects both eyes at different rates.

Causes and Development; Contributing Risk Factors

The root cause of macular degeneration is unknown, but it tends to happen as people get older.  There are two forms of age-related macular degeneration, namely "dry" and "wet".

The "dry" form makes up around 70% of cases: the visual cells simply cease to function, like the colors fading in an old photograph.  The process involves thinning of the macular tissues and disturbances in its pigmentation.

The "wet" form makes up the remaining 30% of cases and can involve bleeding within and beneath the retina, opaque deposits, and eventually scar tissue.  The "wet" form accounts for 90% of all cases of legal blindness amongst macular degeneration patients.

During the early stages of macular degeneration, central vision becomes blurred and/or distorted

The dry form will often begin to convert to wet, with the formation of abnormal choroidal blood vessels – angiogenesis.  The reason why angiogenesis occurs is unknown but it is believed that this additional blood vessel development is somehow caused by deposits being left in the back of the eye.  These deposits are similar to age spots on the skin.  These new blood vessels are fragile and have a propensity to leak and bleed, eventually forming scar tissue and resulting in irreversible vision loss.

Different forms of macular degeneration may occur in younger patients.  These non-age-related cases may be linked to heredity, diabetes, nutritional deficits, head injury, infection, or other factors.

Studies of twins indicate that both genetic and non-genetic factors play important roles in age-related macular degeneration.  If several members of a family are sufferers then it is very important that other members have their eyes checked regularly.  Inherited macular degeneration is known as macular dystrophy.

Any type of smoking or exposure to tobacco smoke can accelerate the development of the "wet" type of macular degeneration.

Signs and Symptoms

The formation of new blood vessels and yellow deposits ("drusen") in and under the macula is often the first physical sign that macular degeneration may develop.

In advanced macular degeneration, a blank or dark area develops in the center of vision, leaving only peripheral vision

In the early stages, central vision becomes blurred or distorted, with objects having an unusual size or shape.  This may happen quickly or develop over several months.  The patient may be very sensitive to light or actually see lights that are not there.

Those with the advanced condition will often notice a blank patch or dark spot in the center of their sight.  This makes activities like reading, writing, driving and recognizing small objects or faces very difficult.

The following are NOT known to be linked to macular degeneration: floaters (moving spots caused by debris floating in the vitreous fluid between the lens and the retina); dry eye syndromes; cataracts and cataract surgery.

Peripheral vision (side vision) isn't affected by macular degeneration.

Diagnosis and Tests

Some cases of age-related macular degeneration are detected early during a routine eye test.  It will often be suspected in those aged over 60 who are experiencing changes in their central vision.

Amsler grid eye test: Cover one eye and look at the dot in the center. Note any blurry, distorted, broken or missing lines.

The following tests may be performed:

• Visual acuity test – how well the patient can see at various distances
• Dilated eye exam – eye drops are used to widen the pupils before looking for signs of macular degeneration
• Tonometry – to measure the pressure inside the eye
• The Amsler Grid – viewing a simple black-and-white grid with a dot at the center to see if areas on the grid are distorted, blurry, or discolored.

Early detection is important because a patient destined to develop macular degeneration can sometimes be treated before symptoms appear and this may delay or reduce the severity of the disease.  Furthermore, as we develop better treatments for macular degeneration, whether they are medicinal, surgical, or low vision aids, those patients diagnosed with macular degeneration can sooner benefit from them.

Treatment and Prevention

At this time there is no known cure for macular degeneration.  There are ways to slow macular degeneration, depending on the type and the degree of the condition.  Current treatments fall into three main categories:

• Nutritional Intervention

• Surgery. Laser surgery to remove the scar produced by macular degeneration has been successful in about 10% of people with disciform degeneration, mainly the younger patients.  If the degeneration is associated with leaking blood vessels in the center of the macula and vision is worse than ²⁰⁄₇₀ then laser surgery called photocoagulation is recommended.  This will not improve vision but generally reduces further vision loss.  Unfortunately for most people, the area of degeneration is in the middle of the macula, at its focal point.  This means that treatment cannot be given because the scars produced by the laser would make central vision worse rather than better.  'Dry' degeneration cannot be treated by laser.

  Retinal transplantation is a new experimental approach to macular degeneration, but will require research to determine its safety and effectiveness.

• Making the most of remaining vision. Low vision aids (such as brighter reading lights, magnifying glasses and more sophisticated devices) and techniques for maximizing the use of peripheral vision are used to help patients adapt better to their loss of central vision.

Special sunglasses that block out the blue end of the spectrum may decrease the progress of the disease.  It has been demonstrated that the blue rays of the light spectrum seem to accelerate macular degeneration more than the others.  This means that very bright light, such as sunlight or its reflection in the ocean and desert, may worsen macular degeneration.

Although the medications used to treat hypertension have not been shown to have any direct effect on macular degeneration, they may slow progression of the disease by reducing hypertension.  Hypertension tends to make some forms of macular degeneration worse, particularly in the "wet" form where the retinal tissues are invaded by new blood vessels.

Prognosis; Seek medical attention if...

There is some good news: macular degeneration is not painful, and never leads to total blindness.  It is the most common cause of poor sight in people over 60 but never leads to complete sight loss because it is only the central vision that is affected.  Macular degeneration never affects vision at the outer edges of the eye, so most sufferers will have enough side vision to get around and keep their independence.

The bad news is that if you have macular degeneration in one eye then it will usually develop in the other also.  In the early stages, only one eye may be affected, but as the disease progresses, both eyes are usually affected.  Even with a loss of central vision, however, color vision and peripheral vision may remain clear.

In some cases, macular degeneration may be active and then slow down considerably, or even stop progressing for many years.

The following signs may be indicative of macular problems and anyone experiencing these symptoms should consult an ophthalmologist immediately:

• The major risk factors: aging, atherosclerosis and hypertension
• Straight lines appear distorted and, in some cases, the center of vision appears more distorted than the rest of the scene
• A dark, blurry area or "white-out" appears in the center of vision
• Color perception changes or diminishes