What to expect from your macular degeneration test
Age-related macular degeneration (AMD) is a common eye condition caused by the deterioration of the macula. The macula is a small, central area of the retina that is responsible for making sure our central vision — objects straight ahead of us, as opposed to in our periphery — is clear and sharp. The health of our macula directly affects our ability to perform everyday activities that require us to see fine detail, such as reading, recognising faces, driving, watching television, and using a computer.
How is macular degeneration diagnosed?
Macular degeneration is diagnosed as either dry (non-neovascular) or wet (neovascular). The dry form of macular degeneration is usually characterised by the presence of yellow deposits on the retina (drusen), which cause vision to worsen, while the wet form is characterised by the growth of abnormal blood vessels in the choroid; a layer of blood vessels beneath the retina.
It’s these blood vessels that can leak blood and fluid into the retina and potentially affect your vision. For example, wet AMD can make straight lines look wavy, cause blind spots, and even bring on a loss of central vision.
Macular degeneration symptoms usually develop gradually and may include visual distortions, reduced central vision in one or both eyes, dim vision, difficulty in adapting to low light levels, increased blurriness, and decreased intensity or brightness of colours. If you start to experience these symptoms, it’s essential you get a diagnosis from a qualified eyecare professional. If your doctor thinks that you have age-related macular degeneration, they may want you to undergo one or more of these exams:
Visual acuity and Amsler grid test
Standard screening tests for AMD include the visual acuity exam (reading letters from the letter chart) which measures how well you see at various distances, and the Amsler grid, which looks like graph paper. Your doctor will investigate whether the lines on the grid look wavy or distorted to you, or whether there are any blind spots in your visual field. If you experience any of these sensations, it may be an indication of AMD.
Dilated eye exam
In this exam, your doctor will dilate your pupils with eye drops in order to obtain a better view of the back of your retina. They will examine your macula through a magnifying lens, and check for signs of disease and optic nerve damage. A mottled appearance caused by pigmentary changes in the macula and presence of drusen underneath the retina may indicate presence of AMD.
Fundus fluorescein angiography (FFA)
Fluorescein angiography (FFA) allows your doctor to study the circulation within the retina and choroid in detail. In FFA, a yellow dye called sodium fluorescein is injected into a vein in the arm or hand, which enters the blood circulation in the eye via the ophthalmic artery soon afterwards. How fast it gets there depends on the rate of injection, your age, and your cardiovascular health. After about a minute, sequential photographs of the eye are taken using a special camera. If the image shows fluorescein dye leaking out of retinal capillaries into the retina, this may indicate blood flow and possible leakage (wet AMD) within the retina and choroid. This method of imaging takes about 20 minutes altogether and requires dilation drops1.
Indocyanine green angiography (ICG)
ICG is a diagnostic procedure that uses ICG dye to examine the blood flow in the choroid. Although similar to fluorescein angiography, ICG uses indocyanine green dye that is injected intravenously, which glows and is visible in infrared (non-visible) light. This makes the circulation in the eye’s deeper layers, as well as the distinct outlines of the vessels within the choroid, visible when photographed with an infrared sensitive camera.
The most common application of ICG is to detect the creation of new blood vessels in the choroid (choroidal neovascularisation), which is a common manifestation of AMD. ICG is sometimes used to complement fluorescein angiography (FA). FA is often referred to as retinal angiography, while ICG is referred to as choroidal angiography. The procedure takes about 20 minutes and requires your pupils to be dilated. ICG was first used in 1969 but was brought into practical clinical settings in 1992, and has since been a standard method for diagnosing AMD2.
Optical coherence tomography (OCT)
OCT is a commonly-used, non-invasive imaging method used to generate a 3D image of the retina. In this method, infrared light waves are used to make cross-section photographs of the retina and choroid layer.
OCT provides extremely useful information about drusen, retinal structure, new blood vessels, and haemorrhaging, because it allows experts to measure the many layers of the retina itself, giving the optometrist or ophthalmologist a comprehensive look into the health of your eye. While undergoing OCT, you will rest your chin on a machine and look into a lens for a few minutes per eye.
Because OCT is an optical method, which means that it uses light as its means of investigation, it allows your doctor to examine various properties of the eye, which interact with light, that can identify tissue structure and composition. High-resolution imaging of retinal structure by OCT is currently used extensively for the diagnosis of a variety of conditions such as glaucoma, macular degeneration, and macular oedema3.
Fundus autofluorescence (FAF)
Even without the use of special dyes, parts of the fundus — the interior surface of the eye, opposite the lens and including the retina — can become fluorescent in certain conditions.
This has recently been found to have potential as both a diagnostic indicator and a tool for monitoring the progress of AMD. FAF imaging can provide information about the health and function of the central retina as well as side vision (periphery). It is now considered an important tool for evaluating AMD, macular dystrophies, retinitis pigmentosa, white dot syndromes, retinal drug toxicities, and various other retinal disorders. FAF may detect abnormalities beyond those detected on other tests, including in a fundoscopic exam, fluorescein angiography, or optical coherence tomography4.
AMD and vision loss can profoundly affect your life. This is especially true if you lose your vision rapidly. Even if you experience gradual vision loss, you may not be able to live your life the way that you used to. Therefore, it is essential that everyone above the age of 40 undergo a comprehensive eye exam regularly to help detect AMD early and manage it correctly.
1. Hayreh, Sohan Singh. "Anterior ischaemic optic
neuropathy. II. Fundus on ophthalmoscopy and fluorescein
angiography." The British journal of ophthalmology 58.12
2. Slakter, J.S., Yannuzzi, L.A., Guyer, D.R., Sorenson, J.A. and Orlock, D.A., 1995. Indocyanine-green angiography. Current opinion in ophthalmology, 6(3), pp.25-32.
3. Huang, D., Swanson, E.A., Lin, C.P., Schuman, J.S., Stinson, W.G., Chang, W., Hee, M.R., Flotte, T., Gregory, K. and Puliafito, C.A., 1991. Optical coherence tomography. science, 254(5035), pp.1178-1181.
4. Sepah, Y. J., Akhtar, A., Sadiq, M. A., Hafeez, Y., Nasir, H., Perez, B., … Nguyen, Q. D. (2014). Fundus autofluorescence imaging: Fundamentals and clinical relevance. Saudi journal of ophthalmology : official journal of the Saudi Ophthalmological Society, 28(2), 111–116. doi:10.1016/j.sjopt.2014.03.008