Macular degeneration
Macular degeneration is wear and tear of the macula - the part of the retina responsible for central vision. It usually affects both eyes but may produce symptoms in one eye long before affecting the other eye. Visual loss is restricted to the central part of the vision and will not affect peripheral vision if there are no other diseases.
Causes
The most common cause of macular degeneration is increasing age. Age-related macular degeneration (ARMD) typically occurs in people who are over 50 years.
About 15 in every 100 people over this age have early signs of ARMD. Over the age of 75, about 30 people in 100 have early signs and several become severely affected. Other significant risk factors include smoking and a family history of macular degeneration. Hypertension, hyperlipidaemia (high cholesterol) and a diet poor in antioxidant vitamins may also increase the risk for ARMD.
Types
Dry Macular Degeneration develops very slowly. Central vision slowly deteriorates as small patches of photoreceptors in the macular die. 90% of people with macular degeneration suffer from this.
Wet Macular Degeneration is characterised by the presence of large soft drusen (yellow deposits) and a risk of developing new blood vessels under the retinal that can leak and bleed, resulting in rapid deterioration of vision.
Symptoms
Distortion of straight lines
Blurry or fuzzy vision
Difficulty recognising faces
A blurred or blind spot in the centre of vision
Investigations
Amsler Grid
The most common
cause of macular degeneration is increasing age. Age-related macular degeneration (ARMD) typically occurs in people who are over 50 years. About 15 in every 100
people over this age have early signs of ARMD. Over the age of 75, about 30 people in 100 have early signs and several become severely affected.
The Amsler Grid consists of evenly spaced horizontal and vertical lines printed on black or white paper. A small dot is located in the centre of the grid for fixation. While staring at the dot, the patient looks for wavy lines and missing areas of the grid.
It is a diagnostic tool that aids in the detection of visual disturbances caused by changes in the retina, particularly the macula (e.g. macular degeneration), as well as the optic nerve and the visual pathway to the brain.
Fluorescein Angiography (FFA)
This is a dye test that involves injecting a fluorescent dye into a vein. This dye travels through the vascular system whereby the blood flow through the retina can be charted. This can show up abnormalities of the blood vessels such as leakage, occlusion and new growth.
Indocyanide Green Angiography (ICG)
This is another dye test used to evaluate the circulatory system of the choroids (the layer just behind the retina). ICG reacts to light with a longer wavelength than fluorescein dye, allowing the doctor to pinpoint the location of leaking vessels deeper within the eye that may not be apparent with fluorescein angiography.
Optical Coherence Tomography (OCT)
Optical backscattering of light is used to rapidly scan the eye and obtain a cross-sectional image of the retina. Each layer of the retina and its thickness can be distinguished, allowing diagnosis and evaluation of a variety of retinal diseases.
Treatment of Wet ARMD
Laser Photocoagulation
The abnormal blood vessels (subfoveal neovascular membrane) are cauterised to seal them from leakage to prevent further vision loss. The type of laser can only be
performed if the membrane is not under the very centre of the
macula.
Photodynamic Therapy (PDT)
A light sensitive chemical is injected into an arm vein where it will travel to the abnormal vessels in the retina to clot the abnormal blood vessels under the application of cold laser.
Transpupillary Thermotherapy (TIT)
This is similar to PDT but is suitable for cases where the membrane is not well defined or partially hidden by blood. The laser elevates the temperature of the retina by 10 degrees C and clots form to close the abnormal vessels.
VEGF Inhibitors
A number of drugs are now available for the treatment of vascular membranes associated with macular degeneration. The drug is injected into the eye and works by blocking the action of growth factor on the abnormal vessels.
Antioxidant Vitamin Supplements For Macular Degeneration
Evidence from a large study (Age-related eye disease study - ARE OS) shows that a combination of antioxidant vitamins help reduces the risk of severe visual loss in those with moderate to advanced ARMD.
Source: Eye Centre- Raffles Hospital Singapore
