What is AMD?
AMD – Age-Related Macular Degeneration – is a common eye disease like cataract and glaucoma. It is the leading cause of severe vision loss in people aged 50 or more. In susceptible people, their macula, a delicate region in the retina, gets gradually damaged. The macular region is responsible for our central vision. In people with AMD, the central vision is blurred and over the time it develops as a blank spot known as central scotoma.
The macula is a region in the retina. It is made up of millions of cone cells which are responsible for the “day vision”. These cone cells are highly concentrated in this region. When we see something, the reflected light of that object falls on the macula which makes us see that object in fine details with vibrant colours. This is called central vision. When the macula is damaged, the central vision is blurred, distorted or dark.
The macula is the most sensitive part of the retina. The retina turns the light into an electrical signal and sends these signal to the brain through the optic nerve. The cortex in our brain converts these signal to visual image and thus we see 1)Grierson, Ian (2000). “Eyes and Eye problem explained”. (Liverpool University Press): p.75-79.
Symptoms of AMD
- Dark blurry area in the central vision
- Diminished or changed colour perception
Risk Factors of AMD
- Cardiovascular Disease
- Hypertension (HTN or HT)/ High Blood Pressure (HBP)
- Female Gender- Females tend to be slightly larger than the males
- Hypercholesterolemia- High cholesterol level in the blood
- Obesity- Having too much body fat
- Hyperopia (Farsightedness)- Shorter eyeball length
- Family History
- Light irides- Different coloured eye
- Environmental Factors- Radiation, Sunlight, etc
- And Subretinal drusenoid deposits
Modifiable Risk Factors?
We cannot stop or modify the factors that cause the AMD like the Ageing, Family history. But what we can actually do is minimise some risk factors like,
– Smoking: reduces 34X times the risk
– Obesity: reduces 20X
The Stages of AMD?
Drusen are yellowish deposits occurring under the retina, they are made up of lipids, a fatty protein2)Ying Gui-Shuang(2012). “Age-Related Macular degeneration – The Recent Advances In Basic Research and Clinical Care”. (InTechOpen.com): p.44. Drusen itself do not cause AMD. However, their presence increases the risk of developing AMD. Drusen are categorised by sizes as small(<63μm), medium (63-124 μm) and large (>124μm). They are also considered as hard or soft depending on the appearance of their margins on ophthalmological examination. While hard drusens have clearly defined margins, soft ones have less defined and fluid margins.
Classically the condition is divided into two main subtypes; dry/nonexudative and wet/exudative. The Age-related Eye Disease Study (AREDS) fundus photographic severity scale is one of the main classification systems used for this condition:
No AMD (AREDS category 1):
No or a few small (<63 micrometres in diameter) drusen.
Early AMD (AREDS category 2):
Many small drusen or a few intermediate-sized (63-124 micrometres in diameter) drusen, or macular pigmentary changes.
Intermediate AMD (AREDS category 3):
Extensive intermediate drusen or at least one large (≥125 micrometres) drusen, or geographic atrophy not involving the foveal centre.
Advanced/ Late AMD (AREDS category 4):
People with late AMD have vision loss from damage to the macula in the retina.
Late AMD is further classified as Dry AMD and Wet AMD.
It is characterised by the presence of yellow deposit, called drusen in the macula. A few small drusen may not lead to AMD. However, they grow larger in number and degenerate the macula leading to atrophy or tissue death in the slow withering process. Due to this the central vision slowly fades away. Currently, there is no medical or surgical treatment for dry-AMD.
This develops more rapidly than the dry type. The blood vessels called CNV (choroidal neovascularization) grows below Macula and leak liquid or blood. This causes blurred and distorted central vision. Vision loss progress more rapidly than in Dry AMD. A laser treatment is employed to arrest the leaking blood vessels.
How is AMD Diagnosed?
During a routine eye examination, the early and intermediate AMD are detected as they are symptomless. Whereas the late AMD presents with symptoms like blurry vision and difficulty in colour perception. If the eye care professional detects AMD, he would employ either one of the following diagnostic procedures for confirmation of AMD.
Visual acuity test: This chart test measures how well you see the details of the letter.
Dilated eye test: Your eye care professional places drops in your eyes to widen or dilate the pupils. This provides a better view of your eye. Once dilated, each eye is examined using a special magnifying lens that provides a clear view of important tissues at the back of the eye, including the retina, the macula, and the optic nerve.
Amsler grid: Your eye care professional also may ask you to look at an Amsler grid. Changes in your central vision may cause the lines in the grid to disappear or appear wavy, a sign of AMD.
Fundus Fluorescein angiography[FFA]: is a procedure in which fluorescein dye is injected into the bloodstream. The dye highlights the blood vessels in the back of eye so they can be photographed.
After dilating the eyes, the patient will be seated in front of the specialised camera and will rest his/her head on a support to keep it motionless. The eye care professional will take a series of pictures of the inner eye. After the first batch of pictures taken the fluorescein is injected into the vein in the arm. Then the second batch of pictures is taken as the fluorescein moves through the blood vessels of the retina.
Studying the pictures taken, the eye care professional arrives at a decision on whether the patient has AMD or not.
The patient will need to arrange for someone to pick up and drive him home since his pupils will be dilated for up to 12 hours after the procedure.
OCT – Optical coherence tomography: is a non-invasive imaging procedure that uses light waves to take cross-section pictures of the retina, the light-sensitive tissue lining the back of the eye.
With OCT, each of the retina’s distinctive layers can be seen, allowing your eye care professional to map and measure their thickness. These measurements help with diagnosis and provide treatment guidance for AMD
The patient will be seated in front of the OCT machine and will rest his/her head on a support to keep it motionless. The equipment will then scan his/her eye without touching it. Scanning takes about 5 to 10 minutes. If patient’s eyes were dilated, they may be sensitive to light for several hours after the exam.
Treatment for AMD?
Early AMD: There is no treatment exist for the early AMD. Regular exercise, eating green vegetable and fish can keep AMD at bay.
Intermediate and late AMD: Researchers at the National Eye Institute tested whether taking nutritional supplements could protect against AMD in the Age-Related Eye Disease Studies (AREDS and AREDS2). They found that daily intake of certain high-dose vitamins and minerals can slow progression of the disease in people who have intermediate AMD, and those who have late AMD in one eye.
The first AREDS trial showed that a combination of vitamin C, vitamin E, beta-carotene, zinc, and copper can reduce the risk of late AMD by 25 percent.
AREDS2 trial tested whether this formulation could be improved by adding lutein, zeaxanthin or omega-3 fatty acids.
Anti-angiogenesis drugs: The drugs like Avastin (VEGF-A), Eylea, Macugen can blocks the development of new blood vessel’s within the eye.
PDT – Photodynamic therapy: is a procedure that uses a drug, called a photosensitizer or photosensitizing agent, and a particular type of light. When photosensitizers are exposed to a specific wavelength of light, they produce a form of oxygen that kills nearby cells.
Laser Surgery: Eye care professional will dilate your pupil with eye drops. Then he or she puts drops in your eye to numb it. Sometimes your provider will give you a shot around or behind the eye to numb the eye more. Then your provider will aim the laser at the blood vessels. The laser seals the blood vessels so that they no longer leak fluid behind the retina.For cold laser treatment, a medicine that reacts to light is injected into your bloodstream. When the medicine reaches the retina, a cold laser (light) is used to activate the medicine and close the leaking blood vessels. This procedure may need to be repeated 3 or more months later. It may help stop or slow down more vision loss, but it does not improve vision in most cases.
Researchers are studying new treatments for macular degeneration. The following treatments are considered experimental:
– Submacular surgery: Surgical procedure to remove the abnormal blood vessels or blood.
– Retinal translocation: procedure to destroy abnormal vascular vessels that are located directly in the centre of the macula, where the laser beam cannot be placed safely.
References [ + ]
|1.||↑||Grierson, Ian (2000). “Eyes and Eye problem explained”. (Liverpool University Press): p.75-79|
|2.||↑||Ying Gui-Shuang(2012). “Age-Related Macular degeneration – The Recent Advances In Basic Research and Clinical Care”. (InTechOpen.com): p.44|