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AMD Diagnosis
Diagnosis
AMD is a painless condition and people with the early and intermediate stages of the condition do not usually experience any symptoms. Regular (annual/biennial) eye examinations are recommended in order to detect the early signs of AMD. These examinations also allow the detection of other eye diseases, many of which may also be painless and without obvious symptoms in their early stages (e.g. glaucoma).
Definitive diagnosis of AMD relies on a dilated eye examination using imaging techniques typically undertaken in specialist ophthalmology clinics. It is important to note that visual acuity tests alone are not sufficient for the detection of AMD. This is because sight measured by the visual acuity test can remain unaffected, even in the presence of nvAMD or GA, if the central part of the retina is not affected by the condition. Therefore, it is essential that any person suspected of having AMD is referred to a specialist clinic for accurate diagnosis and follow-up.
Several retinal imaging techniques may be used by the ophthalmologist to diagnose and monitor patients with AMD in clinical practice. These non-invasive imaging techniques include Colour Fundus Photography (CFP), Fundus Auto-Fluorescence (FAF), Fluorescein Angiography, Optical Coherence Tomography (OCT) and a very new technique called OCT angiography.
Stages of AMD
AMD pathology is characterized by degenerative changes in the outer portion of the retina, photoreceptors, retinal pigment epithelium (RPE), Bruch’s membrane, and the choriocapillaris, which ultimately lead to central vision loss in the later stages of the disease. The earliest visible sign of AMD during an eye exam is the appearance of yellowish deposits of an extracellular lipoprotein, called drusen, which accumulate underneath the retina, between the retinal pigment epithelium (RPE) and Bruch’s membrane.1
Progression and severity of AMD can be classified as ‘early’ or ‘intermediate’ or ‘late’ based on the size of drusen and the presence of pigmentary abnormalities in the retina of the affected eye.4
Early AMD is diagnosed based on the presence of medium-sized drusen (>63 and ≤125 μm), but is not usually associated with any loss of visual function or other symptoms. (Small drusen particles (≤63 μm) can appear in the retina as part of the normal aging process, and are not associated with an increased risk of progression to late-stage AMD.)
Intermediate AMD is characterised by the presence of large drusen (>125 μm), abnormalities in the retinal pigment, or both. Intermediate AMD also tends to be asymptomatic. People who develop intermediate AMD are at an increased risk of developing late-stage AMD.
Late-AMD, associated with central vision loss that occurs as a result of damage to the macula, can be classified into two types: 4
Geographic atrophy (GA) (also known as ‘dry’ or ‘non-exudative’ AMD) ) is characterised by the progressive, irreversible loss of the retinal pigment epithelium (RPE), photoreceptor cells, and underlying choriocapillaris layer of the macula, resulting in a decline in visual function.
Neovascular AMD (also known as ‘wet’ or ‘exudative’ AMD) is defined by growth and invasion of immature blood vessels from the underlying choroid into the retina. Leakage from these fragile blood vessels can cause build-up of blood and fluid under the retina leading to detachment of the RPE or retina and scarring.
Progression from early/intermediate- to late- AMD (GA and/or neovascular AMD) is a complex process. Some people progress quickly to late-stage AMD (either GA or neovascular AMD), whereas others may progress slowly over several years.5 The underlying mechanisms that cause an eye to develop GA versus neovascular AMD are not fully understood. No reliable genetic or environmental risk factors have been identified to predict whether a patient will develop one form or the other.6 Both types can occur simultaneously in the same eye, or simultaneously in different eyes; it has in fact been suggested that GA and neovascular AMD are not mutually exclusive diseases, but that they lie on the same disease continuum.7 Eyes developing both types may in fact be at a more advanced stage than either GA or neovascular AMD alone.