What is the retina?
The retina is the back surface inside the eyeball, opposite the lens. It contains millions of light sensitive cells, called rods and cones. An image projected by thelens onto the retina is sensed by the rods and cones as different intensities of light and different colors. When light hits rods or cones, a biochemical reaction occurs, which initiates the transmission of signals along nerve cells to the brain, with information about light, color and position in the retina. In the brain, the signals from throughout the retina are assembled into the experience of seeing what is before us.
What is the macula?
The central portion of the retina directly opposite the lens, is called the macula. It is rich in cones, the cells which enable us to see fine detail and color. There are three classes of cones, each most sensitive to a different color: red, green or blue.
What is the fovea?
At the center of the macula is very small area called the fovea. Cones are most concentrated in the fovea. Despite its small size, relative to the rest of the retina, the fovea is very important for our ability to see fine detail and color
What is macular degeneration?
In macular degeneration, the light-sensing cells of the macula mysteriously malfunction and may over time cease to work. Macular degeneration occurs most often in people over 60 years old, in which case it is called Age Related Macular Degeneration (ARMD). Much less common are several hereditary forms of macular degeneration, which usually affect children or teen-agers. Collectively, they are called Juvenile Macular Degeneration. They include Best's Disease, Stargardt's Disease, Sorsby's Disease and some others.
How is macular degeneration diagnosed?
The major symptoms of macular degeneration are:
1) When viewing an Amsler grid, some straight lines appear wavy, and some patches of the grid appear blank.
2) When visual acuity is measured with a Snellen chart, visual acuity has typically declined by at least 2 lines (e.g. 20/20 -> 20/80) if macular degeneration has occurred.
3) In dry macular degeneration, drusen spots are evident in fundus photographs (i.e. photographs of the retina).
4) In wet macular degeneration, when angiography is performed, leakage of the indicator dye into the bloodstream is seen from blood vessels behind the macula.
5) When an electroretinogram is performed, the electrical signal obtained when a point in the macula is illuminated, is weaker or absent compared to a normal eye.
6) Visual acuity and color sensitivity are similar for the three primary colors, red, green and blue.
What are dry and wet macular degeneration?
About 85 - 90% of ARMD cases are the dry, or atrophic, form, in which yellowish spots of fatty deposits called drusen appear on the macula. The rest of ARMD cases are the wet form, so called because of leakage into the retina from newly forming blood vessels in the choroid, a part of the eye behind the retina. Normally, blood vessels in the choroid bring nutrients to, and carry waste products away from, the retina. Sometimes the fine blood vessels in the choroid underlying the macula begin to proliferate, a process called choroidal neovascularization, or CNV. The cause is unknown. When those blood vessels proliferate, they leak, and cells in the macula are damaged and killed. The principal symptom of macular degeneration is reduction or loss of central vision, with retention of peripheral vision.
What is laser photocoagulation?
Laser photocoagulation is a technique used by ophthalmic surgeons to treat a number of conditions, including leakage from submacular neovascularizations. At present, it is the only treatment which has been proven effective for any form of macular degeneration. The laser beam essentially "cooks" the tissue which is exposed to it. The beam has a very small cross section, which is aimed at a leakage point revealed by angiography. With luck, the cooking, or coagulation, of the cells at the leakage point will stop or slow leakage, hence the progress of macular degeneration caused by the leakage. Only about half of patients with wet ARMD are candidates for laser photocoagulation, because those with occult or subfoveal leakage are not candidates. Also, laser photocoagulation is only effective about half the time it is done as a treatment for wet macular degeneration. When effective, the benefit lasts on the average about one year.
What are occult leakages from neovascularizations?
When angiography is performed, if specific, well-demarcated points of leakage are not revealed by the indicator dye entering the macula, the leakage is said to be occult, meaning hidden. Laser photocoagulation should not be done if the leakage points are occult, because the surgeon will not have well-defined aiming points for the laser.
What are subfoveal leakages from neovascularizations?
When angiography is performed, if the points of leakage are either in or at the edge of the fovea, then the leakage is said to be subfoveal. Laser photocoagulation should not be performed on subfoveal leakage points because the laser destroys the portion of the fovea which is exposed to the laser beam. That does more severe damage to the patient's vision than can be justified by the possible temporary stopping or slowing of macular degeneration.
What is hereditary disease?
Each of us is the result of genes inherited from our parents, and the influence of our environment on the functioning of the genes and body components encoded in our genes. Sometimes an error occurs during replication of genes as part of the reproductive process. Most of the errors are analogous to typos in printed text - a single wrong character appears in an instruction in a gene. The defective gene results in the production of a faulty component for the body. Because the defect in the gene is accurately copied in subsequent reproductive cycles, the defect in the body component is inheritable. The defect is called a hereditary, or genetic, disease. Because so-called genetic diseases are not caused by an infectious agent, genetic diseases are not transmitted through contact.
What is hereditary macular degeneration?
Hereditary macular degeneration, better known as juvenile macular degneration (JMD) is suspected when MD occurs in more than one relatively young member of a family, and in more than one generation of that family, where the genetic relationships of the affected members is consistent with the rules of inheritance of genes. Hereditary forms of macular degeneration, which affect children and young adults, are much less common than age-related macular degeneration.
What is retinitis pigmentosa?
Retinitis pigmentosa is a hereditary disease which results in reduction or loss of night vision and peripheral vision. The peripheral region of the retina, which is rich in the light-sensing rod cells, becomes damaged. The rods detect light by means of their light-sensitive pigment protein, rhodopsin. In some families exhibiting retinitis pigmentosa, various mutations have been found in the gene encoding rhodopsin.
What is the relationship between blindness and age-related macular degeneration?
Macular degeneration can result in central vision blindness. Macular degeneration among people over 65 is the leading cause of blindess in the U.S. and U.K.
What are maculopathy and macular dystrophy?
The appearance of drusen spots on the macula, possibly drusen accompanied by some scarring of the macula, is referred to by ophthalmologists as maculopathy or macular dystrophy. These are general terms meaning "something is not quite right about the macula". There is evidence that people with drusen spots, especially large drusen spots, have an increased likelihood of developing macular degeneration, which is usually diagnosed when central vision has begun to deteriorate.
What is cone dystrophy?
Cone dystrophy is a genetic disorder which typically affects one of the three classes of cones rather than generally affecting rods and cones in the macula, as macular degeneration does. Cone dystrophy is often misdiagnosed as macular degeneration.
What is central serous retinopathy?
Central serous retinopathy is sometimes misdiagnosed as macular degeneration. Central serous retinopathy is a disorder in which blood vessels underlying the retina leak, and there is secondary detachment of the retinal pigment epithelium. These leakages are usually stopped by laser photocoagulation. The condition has also sometimes been treated with anti-inflammmatory corticosteroids, but there are indications that they sometimes worsen the condition.