Age-Related Macular Degeneration (AMD)
By Bjarne Lühr Hansen PhD, MD and Philipp Skafte-Holm MD, Mentor Institute
The abbreviation AMD stands for age-related macular degeneration. Today, AMD is the common term for what was previously known as calcification of the retina. It is, however, not a case of calcified blood vessels as seen in e.g. heart and brain, which is why this term has been abandoned.
AMD is an illness in the macula of the retina or the ‘yellow spot’ (in Latin macula lutea and in short form macula). Inside the macula the retina has the greatest concentration of cone cells. It is particularly these specialised ‘cones’ that are responsible for the eye being able to perceive fine details, colours and see the world three dimensional. The illness is often two-sided meaning that it affects both eyes. However, there is often a difference between the degree of severity in right and left eye, respectively.
Today, AMD is the most frequent cause of reading blindness in the developed countries. The illness is often seen from the age of 55 and its frequency increases with age. 12% of the population over 60 years have symptomized AMD and others have an undiscovered eye disease since the nuisances are often quite modest, at the beginning.
The cause of AMD is not known in details. Age, heritage and tobacco are known causes of the development of AMD.
AMD is categorised in two main forms called ‘dry’ and ‘wet’ AMD.
The dry form, with waste of the cone cells in the yellow spot, is the most frequent form of AMD (makes out approximately 85% of the cases). In the early stages of dry AMD, there are rarely any symptoms.
However, some patients can tell how they see a dark spot in the ceiling of the bedroom for a few minutes after waking up. Shyness of light can be the first symptom of incipient illness of the retina. Subsequently, difficulties with reading arise because the text looks ‘moth-eaten’.
A sign of AMD can be difficulties with identifying people in the street. This is because when you direct your gaze towards a person the face often disappears because it is located within one of the blind areas of the yellow spot.
The ‘dry’ AMD progresses slowly, as the ability to see details deteriorates. You will have difficulty reading and driving and feel the need to move closer to the TV. It can be necessary with optical aids for reading and watching TV. However, you do not lose your orientation as a result of AMD.
The ’wet’ AMD is caused by the development of recently formed blood vessels outside the retina. The growth of these blood vessels is out of control and, therefore, they can grow into the retina itself where their continued growth will lead to haemorrhaging and destruction of cone cells. Unfortunately, this formation of blood vessels takes place in the central area of the retina (macula).
A haemorrhage cause acute symptoms with violent deterioration of sight and distortion of the visual image. This is called metamorphopsia where straight lines winds, letters break in half and faces are distorted.
Usually, the ‘wet’ AMD has a more acute progress than ‘dry’ AMD and the deterioration of sight is experienced over a few days. ‘Wet’ AMD usually leads to permanent reduction of sight.