VISION BLIND SPOTS

What Cause Vision Blind Spots?

Blind spots are also referred to as scotoma. They are typically caused by the lack of vision receptors (rods or cones) where the optic nerve and blood vessels leave the eye.

Vision blind spots or an absence of seeing, can be either a blackness, or as a lack of visual sensation. Most often these blind spots relate to a condition called Macular degeneration.

Age-Related Macular Degeneration (AMD) is a common, painless eye condition in which the central portion of the retina deteriorates leading to a loss of central detailed vision.

AMD is the leading cause of legal blindness and severe vision loss in Australia.

Who is at Risk of Age-Related Macular Degeneration?

The strongest risk factor for AMD is increasing age but it is not a normal or inevitable consequence of ageing. A positive family history and smoking are other strong risk factors.

Impact of Age-Related Macular Degeneration

Age-Related Macular Degeneration damages the macula, which is responsible for detailed vision such as reading and the ability to recognise faces. The peripheral vision is usually unaffected.

Types of Macular Degeneration

In the early and intermediate stages of AMD there is a build up of debris (drusen) under the retina. While the visual clarity is usually minimally affected during these stages, patients often notice that they require brighter light to be able to read.

The late stage is divided into two forms: Dry and Wet AMD

Dry AMD
The dry form of AMD is a gradual process where the retinal cells die resulting in a slow progressive loss of central vision. Although there is currently no treatment or prevention, this is an area of active research.

Wet AMD
The wet form of AMD is characterised by a more rapid loss of central vision. This is the result of small blood vessels growing underneath the retina. This process is termed Choroidal Neovascularisation and the abnormal blood vessel may bleed or leak and scar tissue can form.

What are the Symptoms of Macular Degeneration?

In the early stages there may be no symptoms. One of the earliest manifestations is a need for brighter light when reading. In the late stage blurred or distorted vision is commonly reported. Near (reading) vision is commonly affected to a greater degree than distance vision.

Diagnosis and Prevention of Macular Degeneration

The early detection of AMD is important as steps can be undertaken to help slow its progression. In its early stages, macular degeneration may not result in noticeable visual symptoms but it can be detected with a detailed eye examination in conjunction with Optical Coherence Tomography (OCT) scanning of the macula.

In the later stages, patients may be aware of blurred vision or distortion.

A patient suffering blurred vision or difficulty vision focus should never be dismissed as just a part of getting older.

Macular Degeneration Prevention

Preventive measures can be taken for slowing down the progression of macular degeneration.

Smoking is the most important modifiable risk factor for AMD development and progression. Smokers have a three-fold increased risk of developing AMD compared with people who have never smoked. Stopping smoking can halve this risk.

Dietary measures may also reduce the risk.

Some dietary guidelines include:

Limit the intake of fats and oils
Eat a healthy, well-balanced diet
Eat dark green leafy vegetables and fresh fruit daily
Eat fish two to three times a week
Choose low glycemic index (low GI) carbohydrates instead of high GI
Eat a handful of nuts a week

Vitamin Supplements & the Age-Related Eye Disease Study (AREDS)

Supplements may be of value in patients with Intermediate AMD where there is a substantial collection of debris (drusen) at the macula or in patients who already have late AMD in one eye. In patients with Early AMD the risk of progression to late AMD is lower and the role of supplementation is less clear.

The Age-Related Eye Disease (AREDS) study showed that supplementation reduced the risk of progression to wet AMD by 25% in high risk individuals, but does not prevent progression of dry AMD.

The original daily AREDS Supplement formula included:

Vitamin C 500mg,
Vitamin E 400IU,
Zinc (as zinc oxide) 80mg,
Copper (as cupric oxide) 2mg,
Beta-carotene 15mg (excluded from commercial formulations as this may increase the risk of lung cancer in smokers)

In the AREDS 2 study, a lower dose of zinc (25mg) was studied. The addition of Lutein 10mg and Zeaxanthin 2mg (naturally found in foods such as fruit and vegetables), was shown to be beneficial in those with poor diets. The addition of fish oil was shown to be of no additional benefit.

There are a number of commercially available AREDS supplements on the market in Australia.

Wet Macular Degeneration Treatment

First-line therapy since 2007 has been with intravitreal injections of anti-vascular endothelial growth factor (anti-VEGF) drugs. These drugs do not cure the disease but aim to suppress the growth and leakage of the abnormally leaking and bleeding blood vessels. They stabilise vision in most cases, and up to a third of patients experience a significant improvement in vision. Treatment should be started with as little delay as possible as these agents cannot reverse scarring or retinal thinning which occurs in many untreated cases.

The two most commonly used agents are Lucentis (Ranibizumab) and Eylea (Aflibercept). In some cases off-label Avastin (Bevacizumab) is used. Numerous new drugs are in development.

Photodynamic Therapy (PDT)

Photodynamic Therapy (PDT) is treatment combining injection of a photosensitive drug called Verteporfin into the bloodstream followed by laser treatment. this was a popular treatment between 2000 and 2007 but has now largely been superceded by antiVEGF injection therapy. Some patients with a subtype of wet AMD known as Polypoidal Choroidal Vasculopathy (PCV) may still benefit from this treatment, usually in conjunction with antiVEGF injections.

Direct Photocoagulation Laser

Ablation of the abnormal blood vessels (choroidal neovascularisation) used to be the only treatment modality for wet AMD. It can lead to blind spots in the vision and recurrences occur in a significant proportion of cases, despite this treatment. For these reasons, direct laser treatment has largely fallen out of favour but may be appropriate in select cases where the centre of the macula is uninvolved.

What if Macular Degeneration is Untreated?

If Wet Age-Related Macular Degeneration goes untreated, central vision loss can develop rapidly. The longer it is left untreated, the greater the risk of permanent visual deficit.