MACULAR DEGENERATION


Macula

It is the point on the retina where light rays meet when focused to see an object. It is a small point about 0.5mm and is responsible for 90% of vision. Damage to it may cause loss of central vision and makes difficult for person to read and do fine work. The eye still sees from the side (Peripheral Vision) and so there in no total blindness.

Macular degeneration

Macular degeneration is damage or breakdown of the macula.

Causes


The causes of macular degeneration, and the process(es) by which it develops are not yet fully understood. Some proposed causes for Age Related Macular Degeneration are:

Poor circulation in the blood vessels of the retina, particularly the macula.

Decline in the body's antioxidant systems with age, which serve to destroy harmful free radicals produced in normal     metabolism. Deterioration of the antioxidant systems are thought to be a key part of the aging process.

Consequence of environmental insults to the body, which affect some sensitive people by causing macular degeneration.

Hereditary. 

Age Related Macular Degeneration

Aging is the most common cause for macular degeneration. In 90% of these cases vision loss is not much.

In 10% of these cases called exudative type there is marked visual loss. A thin membrane separates the macula from the very fine blood vessels nourishing the back of eye. In this case blood vessels break or leak through this layer and form a scar tissue. New fragile blood vessels also grow in it. These leak easily and further increase the scarring. Vision gets blurred and dense scar blocks the central vision similar to looking at a clock and seeing all the numbers, but not seeing the clock hands.

Symptoms

If in one eye it may remain unnoticed.
Symptons are:

  Loss of central vision making reading and close work difficult.
  In early stages distortion of vision.
  Color vision may be affected 

Diagnosis

Ophthalmoscopic examination.

Grid test (amsler chart): wherein with one eye closed one looks at a dot in the centre of grid. Any distortion of lines  around the dot suggests macular problem. Patients prone to the disease are asked to look at the grid daily and report  Doctor immediately if such distortion is seen.

Normal Amsler Chart Distortion seen in cases of ARMD Picture seen in case of ARMD

Fluorescein angiography : wherein a fluorescein dye is injected in vein and retinal photographs are taken. It detects  the defects in the blood vessel.

Indocyanine Green (ICG) Angiography: It shows mainly choroidal vasculature and so identify the subretinal new vessels in a better way.

Treatment

No medical cure is available. Antioxidants are said to reduce the progress of the disease. However following treatment modules are available:

Argon / Diode Laser: This causes destruction of new vessels and surrounding retina causing immediate deterioration of vision but when compared with untreated eyes the visual loss is less in laser treated eye. It is cheapest treatment available. If there is recurrence the laser may have to be repeated. However if the membrane is not under the center of fovea, this is the best choice.

Vitreo Retinal surgeries: These are difficult with high complication rates but may lead to visual improvement.

  1. Submacular surgery: In this the subretinal scar tissue is removed by surgery. Has a limited role in ARMD. It can be done in case with scars. 

  2. Retinal Translocation: In this procedure the retina is moved away from diseased choroid and retinal pigment epithelium to healthy area.

Transpupillary thermotherapy: Diode laser is used in lower intensity. It causes improvement in vision. in some cases.

Photodynamic/ Visudyne therapy: In this a dye is injected intravenously which sensitises the new vessels. The minimal laser application then blocks the new vessels and so stops deterioration of vision. This causes reduction of size of diseased complex and leakage and so causes minimal improvement in vision in about 10% of cases. The laser amount used is too less to cause damage to surrounding retina as seen by argon / diode laser and so no loss of vision is directly associated with treatment.
Disadvantages: Needs repeated treatment and is expensive.

Feeder vessel treatment: In this the feeder blood vessel is identified by ICG angiography and focal laser treatment is done to it.

Radiation treatment.

The results of all the above treatments are limited and not very good. However transpupillary thermo therapy and photodynamic therapy appears to give promising results.

Rehabilitation

Does not cause total blindness. As side vision remains one can take care of oneself.
The main problem of these old patients is difficulty in reading. They can be helped by low visual aids. 


Low visual aids

These are devices, which magnify the image making the reading easier for the patients. Low visual aids are:

  High plus powered specks.
  Hand and stand magnifiers.
  Telescopes.
  Closed circuit TV


Subretinal neovacular membrane

It is same as exudative type of age related macular degeneration. Other causes for it are:

  Myopia.
  Blunt trauma.
  Angioid streaks.
  Low grade uveitis.
  Presumed Ocular Histoplasmosis Syndrome.
  Laser Therapy.
  Etc.


Related Site

http://www.ahaf.org/macular/about/maabout.htm
http://www.maculardegenerationinfo.com/Macular-Degeneration.html


 



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