Macular degeneration 

Age related macular degeneration (AMD, sometimes abbreviated ARMD) is a condition which typically affects older people, usually over the age of 60 years. It’s the most common cause of blindness for this age group.

It causes a loss of central vision and possible distortion, making straight lines look bent and letters or numbers may appear jumbled when reading. Peripheral vision usually remains unaffected.

How it develops

The earliest changes occur at the level of the Bruch’s membrane, which is like a waterproof membrane between the retina and the underlying choroid, followed by retinal pigment epithelium (RPE) and the photoreceptors of the eye.

The retina functions like a busy photochemical processing plant which generates chemical residue waste products. In the early stages, the Bruch’s membrane starts to thicken in patches or mounds called drusen. They can vary in different people in size, amount, age of onset and can differ in the type of fat (liquid) that forms around them (this is not related to obesity issues). This is the beginnings of age-related maculopathy (ARM).

The larger drusen, especially those that grow larger and merge, can progress to become a more severe AMD.

Types of AMD

There are two types of AMD – wet and dry. Currently it’s not possible to know which eye will be affected, or which type may develop.

1. Wet AMD. This is defined by the development of abnormal new blood vessels growing from the choroid through Bruch’s membrane. This abnormal vessel growth causes vision loss. Ultimately, it leads to blood and protein leakage into the central macular area of the retina – hence the name ‘wet’ AMD, which can be likened to a ‘wet rot’ of the delicate macular tissue. The leaked fluid (oedema), together with the distortion of the macula, cause the symptoms. These can range from mild distortion to loss of central vision. The condition can develop quite suddenly, or over days or weeks. However the symptoms develop, it’s essential to seek urgent treatment within 1-2 weeks.
2. Dry AMD. This is a degenerative change which causes a withering away (atrophy), or loss of photoreceptors, retinal pigment epithelium and the underlying blood vessels (capillaries) of the choroid. This geographic decline tends to develop more slowly, sometimes over months and even years.

Symptoms

Depending on the specific form of AMD, symptoms will vary with the most obvious being blurred vision, shadows or missing areas of vision and distorted vision (straight lines appearing wavy, for example).

Also, discerning colours can be difficult, particularly detecting darks from other darks, or light from other lights. Slower adaptation to dark conditions after being exposed to bright lights may also be noticeable. For instance entering a darkened room after being out in bright sunlight.

Macular degeneration won’t lead to absolute overall blindness, but the loss of central vision represents the loss of the most important vision for reading text or numbers, recognising faces, driving and independent living. Therefore, it’s important to seek attention urgently if you believe you may be suffering from AMD.

Causes

There are three primary causes of age related macular degeneration: age, family history of AMD and smoking. There are other possible factors such as exposure to ultra violet light and genetic predispositions.

Diagnosis and treatment

The maintain public health measures for management of AMD involve prevention and early detection.

1. Prevention. A diet full of antioxidants can decrease the risk and rate of progression of AMD. If your diet is insufficient in antioxidants –e.g. green leafy vegetables, coloured fruits and vegetables, fish (omega 3) and nuts –  you can consider antioxidant tablets with your doctor’s advice. Ceasing smoking will have an even greater positive benefit.
2. Early detection. Early detection of Wet AMD is so important because we now live in an era where treatment gives excellent visual results if instituted early in development. Sadly, it offers very little vision if treatment is instituted too late in the wet AMD process. Self-monitoring of your central vision is the best method, which will avoid discovering you have a problem until it’s too late – a common issue with macular degeneration.

The simple way to check for yourself is to look at an Amsler chart (sometimes called an Amsler Grid), which is readily available free from Vision Eye Institute clinics.

It’s important to test each eye separately, making sure you wear your glasses. Cover the other eye when checking.

For wet AMD, the mainstay of treatment – intravitreal injections of drugs that shrink abnormal blood vessels and dry up the abnormal macular fluid (oedema) – represents one of the truly significant advances in medical history.

Wet AMD used to be a fast track to legal blindness until as recently as 5-10 years ago, but with intravitreal injections,  it is now possible to prevent further vision loss in 95% of AMD patients and improve vision significantly by up to 40%, thanks to the use of repeated intravitreal injections of drugs. This requires early detection and early intervention as well as the use of repreated intravitreal injections of drugs. 

Some patients’ macula don’t dry up with intravitreal injections, and such eyes may require photodynamic therapy (PDT) in addition to injection treatments.

For wet AMD, it has been an exciting new era. Although there are no cures available, treatment does suppress the problem for a period of time. So, at present, any wet AMD patient will require ongoing treatment.

For dry AMD, although there is no specific treatment, the aim for the future is to re-grow the worn out macula and repopulate it with new macular tissue. Ongoing research is attempting to solve this, but in the meantime, low vision aids are helpful in aiding the atrophic ‘dry’ AMD macula to see as much as possible.