Age related macular degeneration
Age-related macular degeneration is a common, chronic, progressive degenerative disorder of the macula that affects older individuals and features loss of central vision as a result of abnormalities in the photoreceptor/retinal pigment epithelium/Bruch’s membrane/choroidal complex often resulting in geographic atrophy and/or neovascularization.
In this article:
- What is age related macular degeneration(AMD)?
- Types of AMD
- Dry
- What is Drusen?
- Wet
- Stages of AMD
- Early AMD
- Intermediate AMD
- Late AMD
- Symptoms
- What is metamorphopsia?
- Risk Factors
- Am I at risk for AMD?
- How can I lower my risk for AMD?
- Diagnosis
- Optical coherence tomography
- Fundus autofluorescence
- Fluorescein angiography
- Preferential hyperacuity perimetry (PHP) test
- Are there home devices for macular degeneration monitoring?
- Prevention
- References
What is age related macular degeneration(AMD)?
What does that mean in simple terms – macular degeneration? The most important part of the eye where the images are captured is the retina – a mesh of the nervous cells with receptive elements for light and color. These receptors transmit signals into the layers of nervous fibers and nucleus, which then come together into the optic nerve. Macula is the most dense and sensitive reception area of the retina. Without a correct reception the images cannot reach the brain.
With time, or age rather, the cells of the macula deteriorate. At first this process may not be noticeable, but then it will progress to blurry vision and could eventually lead to complete vision loss. Macular degeneration is the leading cause of vision loss in the world.
Aging brings many unfortunate problems to the eyes. This happens because the cells of retina do not regenerate during our life, and do wear off. Do all of us develop degenerative disease of the retina and optic nerve? Probably yes, while some are affected more and earlier than others.
The risk of macular degeneration increases with age and is most likely to occur with those age 55, and is very common after 75.
Types of AMD
The age-related changes of the retina can be different. Advanced macular degeneration is divided by ophthalmologists into dry type, which is the most often, and wet type, which is more rare but more severe. Both of the types affect vision and eventually may lead to blindness.
Dry
“Dry” macular degeneration refers to the Atrophic type of the condition, which account for the majority of all AMD. This will occur when the blood vessels in the eye do not leak. This is a progressive condition and often affect both eyes.
What is Drusen?
Drusen are one of the earliest signs in AMD. Clinically, typical drusen appear as focal, whitish yellow excrescences deep to the retina. Typical drusen deposits are located beneath the retinal pigment epithelium and Bruch’s membrane and vary widely in number, shape size, and distribution. Most drusen are 20-100 µm and are characterized as hard or soft.
Hard drusen, which appear as round, discrete yellow-white spots are commonly identified in many populations. They are not age-related and do not carry an increased risk for the development of neovascularization.
In contrast, soft drusen are ill defined, with non-discrete borders, measuring 63 µm or greater. Different studies and trials have indicated that large, soft, confluent drusen are age-related and associated with a higher risk for the development of advanced AMD with neovascularization.
Wet
Wet macular degeneration is also called Neovascular, which means new blood vessels are growing and retinal pigment may detach.
The “wet” type of macular degeneration refers to the exudate type, in which accounts for only 10-15% of AMD. This is a more advanced form of the disease, where abnormal blood vessels grow in the eye and can lead to permanent vision loss. AMD occurs when the blood vessels leak into the macula. Wet and dry AMD can both occur, typically with a dry type occurring initially that progresses to the wet type.
Wet AMD is divided by ophthalmologists (based on microscope image analysis) into:
– Choroidal neovascularization (CNV) is an ingrowth of new vessels from the choriocapillaris through a break in the outer aspect of Bruch’s membrane into the sub-pigment epithelial space.
The clinical manifestations of neovascular AMD can include the following: subretinal fluid, intraretinal fluid, retinal, subretinal, or sub-RPE hemorrhage, lipid exudates, gray or yellow-green discoloration or plaque-like membrane, RPE detachment, RPE tear.
–Â Pigment epithelial detachment – a retinal pigment detachment (PED) may be caused by serous fluid, fibrovascular tissue, hemorrhage, or the coalescence of drusen beneath the RPE. Serous PED manifests as a dome shaped detachment of the RPE, exhibiting bright, diffuse hyper- fluorescence with progressive pooling in a fixed space. Hemorrhagic PED manifests as a dark elevation of the RPE due to underlying blood, showing blocked fluorescence throughout all phases of angiography.
Stages of AMD
Early AMD
Early on, you may not have any signs or symptoms of AMD. A doctor may see a sign on it on your eyes during an eye exam. For example, an early sign is call drusen – which is a tiny yellow spot seen under the retina. Although these changes may be seen during an eye exam, you may still not have any visual symptoms at this early stage of the disease.
Intermediate AMD
Large drusen spots noted on an eye exam can indicate intermediate AMD. In addition, there may be vision loss or visual impairment at this stage. Vision loss will depend on the size of the deposits that are present.
Late AMD
Dry or wet macular degeneration that had advanced to a stage where vision loss is present and permanent. Most people with late, or advanced, AMD tend to have the wet form. In late stages you may lose the ability to read or recognize faces. Although it is uncommon to have complete and total vision loss of the visual field, late stages include visual impairment significant enough to be considered “legally blind.”
Symptoms
Although you may have no symptoms in early stages of AMD, eventually objects will appear blurry, distorted, and/or you may no longer be able to see objects. You may notice this visual disturbance particularly when you look at objects straight on.
 In a person aged >55 years with good visual acuity (VA), alarming signs include the following:
1)Â Â Progressive or sudden decreased vision not improved with optic correction
2)Â Â Central field defect (whether absolute or relative)
3)Â Â Metamorphopsia, micropsias, or macropsias; or
4)Â Â Difficulties in daily life activities (eg, watching television, going down stairs, recognizing people, and going around a corner)
What is metamorphopsia?
Metamorphopsia is a key symptom in the assessment of a patient with AMD. Metamorphopsias is a hallmark sign in patients with macular diseases and can be easily recognized using the Amsler grid or M-charts.
Metamorphopsia is an important symptom in retinal disease and may occur through a variety of mechanisms. Although the human visual system is exquisitely sensitive to metamorphopsia, commonly used tests of this symptom may be unreliable in real-life conditions. Newer tests of metamorphopsia such as preferential hyperacuity perimetry may improve early detection rates of exudative age-related macular degeneration in at-risk populations.
Risk Factors
While it is not known for sure who and when will develop macular degeneration, there are many factors which are related to the earlier signs of AMD that were already identified by scientists.
Risk factors for AMD may be broadly classified into personal or environmental factors (e.g., smoking, sunlight exposure, and nutritional factors including micronutrients, dietary fish intake, and alcohol consumption).
Am I at risk for AMD?
The risk of AMD is higher in those who have close relatives who also have the condition. The risks increase the older you get. You are also at an increased risk if you smoke cigarettes. Smokers tend to get AMD at a younger age as well. There has been indication to support the idea that frequent, direct sunlight may increase your risk of AMD although more evidence is needed at this time to confirm this conclusion.
Personal factors leading to macular degenerations are:
- Sociodemographic (e.g., age, sex, race/ ethnicity, heredity, and socioeconomic status)
- Ocular (e.g. iris color, macular pigment optical density, cataract and its surgery, refractive error, and cup/ disc ratio)
- Systemic factors (e.g., cardiovascular disease and its risk factors, reproductive and related factors, dermal elastotic degeneration, and antioxidant enzymes)
Risk factors for progression to choroidal neovascularization:
- Presence of five or more drusen
- Hyperpigmentation
- Systemic hypertension
- One or more large drusen (> 63 µm in greatest linear dimension)
- White race
- Smoking
How can I lower my risk for AMD?
You can lower your risk by quitting smoking and/or using eye protection with UV protection in direct sunlight. Dark, leafy greens may help due to their antioxidant benefits. Maintain a healthy weight and good blood pressure control so ensure adequate blood flow to the vessels of the eyes.
Diagnosis
AMD can be diagnosed through a standard eye exam. A doctor can detect drusen spots when looking inside your eyes. In addition, you may be asked to look at a Amsler gird – a pattern of straight lines which should look like a checkerboard. If any of the lines appear wavy or missing to you this is an indication of AMD.
While any ophthalmologist can notice AMD on a regular exam, modern microscopy and computer-generated imaging gives huge advantages in management of the patients with AMD.
Optical coherence tomography
Optical coherence tomography may be a useful ancillary test in any stage of AMD. In patients with dry AMD, the high definition B-scans are useful to assess the ultra-structure of drusen and to examine adjacent retinal layers that can be compromised by the disease process.
The progression of early AMD to severe forms, such as geographic atrophy, can be monitored by OCT. The high definition B-scans can be used to identify some of the wet AMD features, such as the presence of intraretinal or subretinal fluid, presence of retinal PEDs, which can be classified in serous, fibrovascular, and hemorrhagic PEDs.
Fundus autofluorescence
Fluorescence is the capability of absorbing light at a specific wavelength and releasing it at a longer, less energetic wavelength. This phenomenon raises an especial interest when the released radiation is found within the spectrum of visible light permitting its visualization, recording and measurement. Autofluorescence is the spontaneous fluorescence that some substances present naturally. Fluorophore is the part of a molecule that makes it fluoresce.
The human eye contains auto fluorescent substances in the retina, especially within the retinal pigment epithelium (RPE). The main auto fluorescent component of the RPE is lipofuscin (LF), containing at least ten different fluorophores presenting discrete emission spectra within the green, golden-yellow, yellow-green, and orange-red emitting range. The RPE plays an important role in the physiopathology of age-related macular degeneration (AMD)
This diagnostic method represents an imaging modality capable of reflecting the morphological changes associated with the metabolism of lipofuscin. Areas of geographic atrophy exhibit very low to extinguished fluorescence signals (dark) due to loss of RPE and lipofuscin, which leads to a region with a high contrast transition between the area of atrophy and perilesional retina.
Fluorescein angiography
This is an amazing method that is usually performed to confirm the presence of neovascularization and identifies the characteristics of the lesion, including the location and composition of the neovascularization.
Based on the angiographic patterns of fluorescence, the neovascular lesion may be categorized as either classic or occult. Classic CNV is characterized by bright, uniform, early hyper-fluorescence exhibiting leakage in the late phase and obscuration of the lesion’s boundaries.
Occult CNV is angiographically recognized by one of two patterns: fibrovascular PED or late leakage from an undetermined source. Fibrovascular PED is characterized by an area of irregular elevation of the RPE (which is neither as bright nor as discrete as in classic CNV), often with stippled hyper-fluorescence present in the mid phase of the angiogram and leakage or staining by the late phase.
Preferential hyperacuity perimetry (PHP) test
Modern anti-VEGF treatment protocols for macular diseases such as a treat-and-extend regimen would ideally be supplemented by a self-monitoring tool as intuitive as the Amsler grid test, but with the ability to quantify even subtle changes of hyperacuity in corresponding retinal regions.
Are there home devices for macular degeneration monitoring?
In recent years, the preferential hyperacuity perimetry (PHP, Notal Vision Inc.) has gained popularity in patient self-testing for AMD. A clinical study showed a smaller decline in visual acuity compared to standard care when using the PHP test. In the NIH-led unmasked, controlled, randomized clinical trial, the scientists determined that home monitoring with the ForeseeHome device (Notal Vision Ltd, Tel Aviv, Israel), using macular visual field testing with hyperacuity techniques and telemonitoring, results in earlier detection of age-related macular degeneration-associated choroidal neovascularization (CNV), reflected in better visual acuity, when compared with standard care.
Alleye
A novel device was created by Alleye, Oculocare medical Inc. It is now cleared by CE (European Conformity) and FDA (Food and Drug Administration). The test is highly accurate to detect wet AMD and reasonably accurate to classify dry vs. wet AMD. A dot patient self-monitoring test (for the detection and characterization of metamorphopsia in age-related macular degeneration (AMD) can be used at home.
Prevention
There has been research indicating that certain vitamins can improve your vision and your overall eye health. Vitamins such as vitamin C, E, beta-carotene, zinc and copper have all been shown to reduce vision loss in AMD.