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by Dr. Daniel Sim
Blindness can take various forms. Some are blind from congenital conditions at birth, whilst others lose their sight later in lift. Blindness from acquired conditions such as cataracts can be completely reversed with surgery. Other conditions such as glaucoma lead to blindness that is irreversible. Glaucoma blindness is largely preventable, yet many have tragically lost their sight from this condition.
It is estimated that there are 60 million people with glaucoma worldwide with 6 million blind in both eyes as a result. Glaucoma is prevalent in both developing and developed nations, and is among the major causes of blindness in Singapore and the United States. A recent Singaporean population study also indicates that glaucoma is the most common cause of blindness amongst adult Chinese Singaporeans, accounting for 60% of blindness in the community.
Glaucoma blindness is also expected to increase because of the growing ageing population. In fact, glaucoma affects up to 10% of some segments of the elderly population in Singapore. While much effort has gone into educating the public about diabetes and blindness occurring from diabetic eye conditions, awareness about glaucoma is still lacking.
Visual impairment by glaucoma amongst the elderly is not always recognized because the elderly are not part of the active workforce. The elderly also tend to be more reclusive, depressed and resigned to their condition and are therefore easily marginalized. They are also more difficult to rehabilitate and they often have to contend with other age-related conditions. A visual handicapped also places the elderly at greater risk for falls and accidents because they may not see an obstacle or an oncoming car.
A major reason for the relatively high rates of glaucoma blindness is the fact that many are diagnosed late in the advanced stages. Again, the elderly are more likely to suffer from glaucoma because of a lack of awareness and a tendency to delay seeking treatment.
Glaucoma is also unique in the way which it leads to blindness. Most people only suspect they have an eye problem when there is blurred vision or when there is something blocking their vision. Few are aware of the fact that a person can become blind and progressively lose most of their vision and yet not be aware of it. This is how glaucoma silently leads to blindness and the reason it is also known as the "sneak thief of sight". The lack of awareness of the loss of vision is not due to ignorance or poor observation, but the unique nature of glaucoma.
There are many misconceptions about glaucoma because some articles and descriptions about glaucoma are seemingly contradictory and misleading. This is because glaucoma is a complex condition with many different forms that may vary in some ways. Five common misconceptions about glaucoma are
1. My vision will be blurred if I have glaucoma
2. I will see dark patches in my field of vision if I have glaucoma.
3. I will experience eye pain if I have glaucoma
4. The pressure in my eyes will be high is I have glaucoma.
5. Glaucoma treatment will help me see clearer.
All that we see of our surroundings with one eye is known as the field of vision. Our field of vision is made up of the peripheral and central vision. Glaucoma leads to a loss of peripheral vision first before central vision is affected. Central vision is important for sharp vision and side vision is important for navigating (i.e. walking and driving) as well as for alerting us to potential danger (e.g. an oncoming car). A patient with glaucoma can lose up to 90% of the side vision before the central vision is affected and vision is blurred. Blurring of vision is therefore a very late indicator of glaucoma.
The areas where peripheral vision is damaged or lost are not seen as dark patches as commonly depicted in posters or patient literature. This is not a symptom of glaucoma but can be caused by other eye conditions. The areas of peripheral field loss are typically not apparent at all to the patient because of compensation by the brain. The brain "fills in" the areas that are not seen so they do not appear as "dark" or "missing" areas. Only when the glaucoma damage is severe and the patient is already blind or on the verge of blindness does the patient notice that the vision is dark. The loss of vision from glaucoma is unique in that it is often not interpreted as an eye disorder even when it results in functional disability. The loss of peripheral vision may lead to repeated trips, falls and knocks because obstacles were not seen but these may be attributed to carelessness or slow reflexes with aging. There may be greater difficulty with stairs or locating small dropped objects. Vision at night may be poorer. Drivers may experience greater difficulty, particularly with reversing and may get involved in more minor accidents or near-miss situations. People or vehicles may seem to appear suddenly as they were not seen approaching from the side. These functional disabilities are only experienced if there is advanced loss of peripheral vision and are therefore not indicators of early glaucoma. Nevertheless, the individual typically does not attribute these difficulties to a problem with their vision because their vision seems normal.
An ache around the eye or a one-sided headache is a very important warning sign of possible glaucoma but this is only experienced with some forms of glaucoma. The majority of glaucomas are silent with no symptoms at all. The angle closure glaucomas are the form of glaucoma that can give rise to a sudden, severe pain or milder intermittent aches around the eye that may be accompanied by coloured haloes around lights.
Centuries ago, glaucoma was first described when it was found that a high pressure in the eye could lead to blindness. Today, we know that a raised eye pressure is very important in glaucoma. However, we also know that checking the eye pressure alone is not an ideal way to detect glaucoma because up to 50% of glaucoma patients do not have a raised eye pressure at the time of examination. There are many reasons for this. One reason is that the standard guidelines used for the eye pressure do not apply to all individuals. A normal pressure for one individual may be relatively high for another. Another reason for the limited role of eye pressure measurements is that glaucoma does occur at normal eye pressure and this form of glaucoma is known as normal tension glaucoma. It is the predominant form of glaucoma amongst the elderly.
The visual damage from glaucoma is permanent. The aim of treatment is to prevent further irreversible damage. Unfortunately, many patients have failed to see the importance of this and have even gone blind because they were not compliant with treatment and follow-up monitoring. Glaucoma poses a special challenge in the prevention of blindness. Like other silent conditions like hypertension and diabetes mellitus, increased awareness through public education is vital. A good public screening programme is a greater challenge. Support groups can play an important role in glaucoma blindness prevention through the sharing of information and experiences that can help prevent blindness in others.
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