Last partial update: June 2019 - Please read disclaimer before proceeding
An overview of visual loss in Australia
There have been two studies of the causes of visual loss in Australia, one based in The Blue Mountains west of Sydney and the other in Melbourne. They predict that there are about half a million Australians suffering from low vision and about 50,000 with blindness and interestingly the causes are quite different. There are five diseases that cause about 80% of all visual loss and their ability to be successfully treated varies;
- Age-related macula degeneration. In most cases treatment is not very successful, although treatment of the more severe form slows progression. This is the most common cause, affecting 14% of adults over 50 years of age.
- Refractive error and cataracts are treatable in almost all cases. Unfortunately, many people just live with them and suffer unnecessarily.
- Diabetes related eye disease; good diabetic control and treatment of eye complications can slow disease progression.
- Chronic (or open-angle) Glaucoma. Early diagnosis allows successful treatment in most cases
Low vision
Low vision is defined as a visual acuity of worse that 6/12 in the better eye. People require 6/12 or better in one eye to drive.)
Low vision is mainly due to correctable illnesses, the two principle ones being uncorrected refractive error (62 per cent) and cataract (14 per cent). Most cases of uncorrected refractive error can be cured with new / better glasses and surgery can significantly improve sight in people with cataracts. Thus, there may well be an easy cure for those having problems with their vision. Age-related macular degeneration causes about 10 per cent of low vision but this is much more difficult to treat.
Severe loss of vision
Severe loss of vision is defined as visual acuity less than 6/60 in the better eye. The three commonest causes of severe loss of vision in Australia are macular degeneration (48 per cent), chronic glaucoma (14 per cent) and diabetic retinal disease (12 per cent). Age-related macular degeneration is unfortunately difficult to treat once present, although not smoking can significantly reduce the risk of developing the disease. Loss of vision from the other two main causes of blindness however is significantly preventable.
Principal causes of visual loss
Damage to the retina from diabetes (Diabetic Retinopathy)
About 25% of people with diabetes will develop diabetic retinopathy and eye checks should be done at least every two years in people with diabetes to identify these affected individuals. The first eye check should be done when diabetes is diagnosed as eye damage may already be occuring. Early diagnosis, prompt treatment and good diabetic control can help reduce the progression of diabetic retinal (eye) disease and prevent most loss of vision. (People with existing diabetic eye disease need eye checks more often that every two years.)
It is important to realise that the diagnosis of diabetes is often delayed and about 50 per cent of people with the disease remain undiagnosed. Unfortunately a lack of visual symptoms does not mean damage is not being done to the eyes and many people already have evidence of diabetic retinopathy when their diabetes is diagnosed. For this reason, it is important those who are at increased risk of diabetes or over 55 years of age to be checked regularly for the disease. These checks should occur at least every three years. See section on Diabetes.
Chronic glaucoma - A silent cause of blindness
Chronic glaucoma (also known as primary open-angle glaucoma) is a condition where the pressure in the eyes gradually increases. This increased pressure causes damage to the nerves at the back of the eyes, leading to irreversible loss of vision and in the end blindness. In most people it does not start to be a problem until the age of 60.
It is estimated that 300,000 people in Australia have this problem, including about one per cent of people over the age of 60 years. However, only about 50 per cent of these people know they have the disease because the gradual nature of the visual loss means that it is not noticed until significant loss of vision has occurred. It unfortunately usually involves both eyes.
Luckily, the condition is easily treatable and is also easily diagnosed by performing a couple of easy tests.
- The most important test is the measurement of the pressure in the eyes.
- An assessment of the person’s visual fields
- Measuring the cup-to-disc ratio in the retina as some people with have nerve fibre damage with pressure readings in the normal range.
All the above tests are necessary because about 30% of people with this condition do not have raised pressure in their eyes. Also, some that do have raised pressure do not develop any visual symptoms. (Measuring the thickness of the optic disc nerve fibre layer can also assist in diagnosis. Such testing is usually done by an opthalmologist or an optometrist.)
Screening for chronic glaucoma
If people have no risk factors for chronic glaucoma (see below), then they should consider having screening eye pressure checks at about the age of 60 (some recommend 50) and these checks should continue every second year until 70 years of age. After 70 it should be done yearly. The frequency of this testing will also depend on the pressure level found in the first test. Consultations for glasses prescription renewal are ideal times to have eye pressures checked. (Not all health authorities suggest that screening for this condition is necessary in normal risk individuals. However, pressure checks are so easily done with glasses renewal consultations that it would be silly to miss this opportunity at least; and most people need reading glasses after the age of 50.)
Risk factors for chronic glaucoma
There are three risk factors for chronic glaucoma;
- a history of increased pressure in either eye
- increasing age
- a family history of glaucoma. People with a first-degree relative that has chronic glaucoma have a 16 per cent chance of developing the disease. People with such a family history should be tested second yearly from 40 years of age until 70 years of age and then yearly.
This disease should not be confused with acute glaucoma. While both diseases cause an increase in eye pressure, in acute glaucoma the pressure build up is fairly sudden. This causes acute severe pain that hopefully leads to quick diagnosis and treatment. Chronic glaucoma causes no such pain.
Age-related macula degeneration
The retina is the tissue lining the back of the eye that is responsible for detecting the light rays entering the eye. It is thus a very important part of the visual system. The macula is the central part of the retina and, while it is small in size (about 4% of the retina), it is the area responsible for visual activities that require high definition, such as reading, and for colour appreciation. People with advanced age-related macular degeration (AMD) lose their central vision and have difficulty with reading, watching TV and recognising faces; and consequently are increased risk of depressin. Thus, the macula is the most important part of the retina and needs to be looked after very well.
Age-related degeneration of the macula (AMD) is a common disease and, as the name suggests, is one that increases with age. It occurs in about 14% of people over the age of 50 years and accounts for 48% of severe visual loss in Australia. The visual loss that occurs is in the centre of the vision. It is usually gradual in nature and thus easy to miss. (It can very occasionally cause a sudden loss of vision; see below.) Only about 5% to 15% of people with early AMD progress to severe late-stage disease (roughly 1% to 2% of people over 50 years) and this process generally takes about 15 years. in 50% of cases it develops in both eyes; usually to the same extent.
Here is a link to a 'Youtube' video explaining the disease. https://youtu.be/Q71n209PxlU
Risk factors for AMD include:
- Increasing age
- Race: AMD is more common in Caucasians than in Africa, Hispanic/Latino or Asian races.
- Smoking (Current smokers have three to four times the risk of people who have never smoked and it occurs earlier in smokers. The cause is probably related to tissue oxidation caused by oxidant chemicals inhaled in cigarette smoke.)
- Family history (four times the risk ) - People with a first degree relative with macular degenration have 50% chance of developing the disease. They should be regularly assessed for evidence of the disease by a medical practitioner or optometrist. An Amsler Grid is commonly used for this purpose.
- Lesser risk factors: These include vascular disease, high levels of sunlight exposure, and a diet low in fruit and vegetables, especially green leafy vegetables (i.e. low in vitamins and anti-oxidants). A diet low in fish.
Cause of AMD
AMD occurs due to long-term exposure to ‘oxidant substances’ that are produced by the processing of incoming light by the retina. It can be influenced negatively by additional sources of oxidants, such as smoking, and can perhaps be improved by the increased intake of antioxidants in the diet. Other areas of the retina are much less affected and peripheral vision is almost always spared.
This excess exposure to ‘oxidant stress’ causes numerous small yellowish deposits to form under the retina which are called drusen. They can be seen when the retina is examined with an opthalmoscope. (This is usually done by a doctor or optometrist.) Early AMD changes in the retina are present in seven per cent of people over 50 years of age and 28 per cent of people over 85 years. There is unfortunately no treatment for visual loss caused by the more advanced forms of the disease and thus prevention is very important.
There has been considerable debate in the media regarding the possible involvement of vegetable oils in causing AMD. At present the general consensus view is that the role if any of different types of fat is unclear as there has been insufficient study of this topic to date. Certainly substituting butter for vegetable oils in the diet as is advocated by some is not advised and could be dangerous as it may lead to an increased risk of cardiovascular disease.
There are over 34 known genetic links to AMD but at present there is no generally recommended genetic test for the disease.
Disease Progression
More advanced AMD can progress in either or both of the following two forms.
Atrophic or ‘Dry' AMD
Dry AMD acoounts for about 33% of cases and in people of Europeandn ancestry it increases in incidence from 1.5% at age 70 to 20% at age 90.
As these lesions gradually enlarge, the overlying retinal cells slowly cease to function and the vision in this patch of retina is lost. This slow process is called ‘dry AMD’ and it is present in 1.9 per cent of people over 50 and 18.5 per cent of people over 85. There is no real treatment and management includes the following.
- Monitoring vision in both eyes regularly so that any sign of the development of the more dangerous form of the disease, ‘wet AMD’, can be detected and treated early. (The frequency of monitoring will depend on the severity of the disease.) This monitoring includes the immediate assessment by an ophthalmologist of any change in vision noticed by the patient and routine vision testing using the Amsler grid test. (Any change in the test needs to be assessed by an ophthalmologist within a few days.)
- Avoiding risk factors, especially smoking.
- Ensuring visual damage from other diseases is minimised. Diabetes is the other important disease that can affect the macula and any person with diabetes should have eye checks by an ophthalmologist (eye specialist) at least once a year and more often if needed.
- Diet. There is some evidence that carotenoids found in dark green and yellow vegetables may help in preventing AMD and a diet high in such vegetables and low in fat is advocated. Margarine has been put forward by some as a cause of AMD and it has been suggested that substituting butter for margarine may be of benefit. There is no good evidence that any of this is true and increasing butter intake may cause harm by increasing vascular disease.
- High dose vitamin therapy: High dose vitamin therapy is perhaps an option in people with significant dry AMD, although there is significant controversy regarding evidence of benefit, especially once late stage diseasse is present. There are many different vitamin regimens offered as treatment with clear evidence that any particular regimen is optimal. This should be discussed with an ophthalmologist. Supplements are more commonly used in the USA than in Australia. (Smokers should not take beta-carotene supplements as it further increases their already high risk of lung cancer.)
- Exercise: Maintain recommended levels of physical activity for your age and health.
Important symptoms that need immediate medical assesment
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Neovascular or 'Wet' AMD
In this form of the disease (66% of cases), new abnormal blood vessels form under macula part of the retina. These can leak fluid and bleed and these fluids act to lift up the macula. This process distorts the vision in the affected area. (This distortion can be picked up by the Amsler Grid test.) Eventually this process causes a scar to form that permanently disrupts vision in the affected area. This process generally evolves over weeks to months and the earlier it is picked up and treated, the better the chance of minimising visual loss. Occasionally, a larger bleed from one of these vessels can occur and this can cause a sudden significant loss of vision. (Any sudden loss of vision, even if it only occurs temporarily for as little as a few minutes, needs to be assessed urgently by a doctor.)
Important: A very important factor in determining the outcome of people with 'wet AMD is the amount of visual loss they have at presentation to the Opthalmologist. Seek help soon.
The treatment of choice is injections into the the macular part of the eye of compounds that inhibits the action of vascular endothelial growth factor - A. (This factor promotes the growth of new blood vessels in the retina and thus inhibiting it slows the progression of the disease.) This is done in outpatients and is usually required monthly. Trials of these medications have demonstrated some improvement in vision. While results in normal practice have generally not produced long term improvement in vision, they have stopped disease progression in a significant number of patients (about one third) and slowed progression in most of the others. While this is a very worthy achievement, it is important to realise that treatment should not be expected to reverse existing visual loss and thus, as stated above, early detection and treatment is critical.
Previously used treatments such as laser therapy or photodynamic therapy are now second line therapies.
Diagnosis of AMD
The principle symptom caused by AMD is loss of vision and, as this is mostly gradual, doctors and patients need to be vigilant in looking for it, especially if risk factors for the disease are present. Early symptoms include:
- Distortion or loss of central vision. The early signs of this process are difficulty in reading or watching TV.
- Slow adaptation to different lighting conditions
It is important not to delay seeking advice regarding the cause of these symptoms as delay can greatly increase the risk of permanent visual loss. Doctors can help assess suspected cases by inspecting the retina and by checking the sight in both eyes. Early assessment by an ophthalmologist (eye specialist) is needed as treatment is easier at this stage and there will be less permanent visual loss.
Almost all elderly people have reading glasses and it is worthwhile asking about the presence of any drusen lesions when being examined for each new prescription. This is especially important in people with a family history of AMD or in smokers.
Amsler GridA diagram called an Amsler Grid can be used by people to help diagnose AMD; and in those with the disease, weekly assessment with the grid can be used to help monitor progess / indentify worsening of the condition. (This can be downloaded with instructions for use from here). You should discuss your results with your medical practitioner and obviously if you are using the chart because you have visual symptoms you should see your medical practitioner about these anyway whether or not using the chart identifies any abnormality. ) |
Further information
Macular Disease Foundation Australia: https://www.mdfoundation.com.au
Short-sightedness (Myopia)
In recent years there has been a large increase in the incidence of myopia or short-sightedness. (This means being able to see close objects well but having difficulty in seeing objects at a distance.) This trend has been occurring since the 1980s but it is accelerating.
While there is a complicated multi-gene genetic component to this illness, it is also related to the amount of time spent looking at close objects / 'near work' behavious, especially when young and this is what ischanging and causing the problem. It is thought that if current trends regarding urbanisation / indoor living and the use of mobile phones, tablets, computers and TVs (that all require near vision) continue, then up to 50% of the population will become near sighted. (In China at present it is thought that the problem is present in 90% of university students.) The rate in Australia in 2000 was about 20%.
While in most people the problem is mild and is reversed by wearing glasses, myopia is also associated with an increased risk of macula degeneration, glaucoma and retinal detachment, all of which can result in a very significant loss of vision.
All that is needed to reverse this trend is for children to spend more time outdoors and reduce time doing close-range activities, especially those related to screen viewing. Parents should aim for children to be outdoors for a couple of hours per day.
Screen time for children should be limited to:
- Under two years of age - No screen time (Use for communication with relatives and friends is ok.)
- Two to five years of age - Maximum of one hour per day
- Over 5 to 17 years of age - Two hours of recreational screen time per day.
Additional benefits of reducing screen time and spending more time outdoors include increasing physical activity and improving sleep and mental health outcomes.