Why have you got a cataract?
The lens of the eye consists of transparent protein fibres and water.
Protein fibres are arranged in precise fashion and layers which enables your lens to be clear and also flexible when you are young so that it can focus on near and distance targets. The primary function of the lens is to focus light properly onto the retina.
With ageing, which is the most common cause of a cataract, the protein fibres in the lens appear to alter and form clumps, which are areas of cloudiness. The disorderly arrangement of the protein fibres causes opaqueness and interferes with visual function.
These cloudy opaque areas are the cataract. Parts of the lens can be involved, either to the centre of the lens which is the pip of a peach called the nucleus, or the softer cortex around it, or even the outer fibres near the capsule where you can get a posterior subcapsular cataract.
What are the causes of cataract?
At first, the cloudiness in your vision caused by a cataract may only affect a very tiny part of the eye lens, and you can be completely unaware of any visual loss. However, as the cataract grows in size and the lens fibres become more disordered, it will cloud up more of your lens and distort the light passing through the lens. The most common cause is an age-related cataract, but cataracts can be drug-induced, for instance, with long-term use of steroid medications.
Cataract can be caused by medical conditions such as diabetes or by prior eye surgery, for instance, on the retina where surgical instruments have had to enter the eye. Cataract can also be traumatic either as a result of a blunt injury or as a result of a penetrating injury.
Smoking and ultraviolet (UV) radiation are believed to cause free radicals which contribute to stress on the lens fibres and oxidation. Certainly, smoking and exposure to ultraviolet light such as sunlight are associated with you having a greater risk of cataract development. Because ultraviolet exposure increases the risk of cataract, occupations that involve working outdoors such as sailors, farmers and even airline pilots are more at risk. Just as you would protect your skin from UV light, you should wear sunglasses to protect your eyes in similar circumstances.
Cataracts can be congenital, i.e. present at birth, but not all congenital cataracts are troublesome, sometimes it can just be a very small dot cataract or some speckles within the lens that are not particularly noticed, and you will only have that picked by an incidental eye examination with your optometrist or ophthalmologist.
Do we all have the same probability of developing a cataract?
Around the world, over 20 million people are blind because of cataract, and even though cataract is treatable with surgery we should be thinking more about the causes and whether we can prevent cataract. Unfortunately, the most common form of cataract that is related to age remains an enigma and may not be able to be easily prevented at this stage of our scientific knowledge.
The fact that patients with diabetes under the age 60 have much high prevalence of cataract (three to four times higher) than the rest of the population and that patients who have galactosaemia have a much higher rate of cataracts has provided evidence that glucose metabolism is important in cataract formation, probably causing increased pigmentation and protein aggregation (clumping) in the lens.
Ultraviolet radiation such as sunlight is partly filtered out by the cornea, but still, some wavelengths such as those higher than 295 nm can pass through the cornea. The lens does absorb most of the ultraviolet light between 295 to 400 nm. Therefore this does help to explain why there is a higher prevalence of cataracts in those countries with hot sunny climates and those persons with greater exposure to sunlight. The discolouration of the lens which occurs with sunshine is a common nuclear sclerotic cataract which is yellow, then brown and then white.
Fortunately, in the western world, we rarely see the advanced white cataracts that cause reversible blindness, but this is still prevalent in developing countries such as India, Africa and the countries in the Himalayas.
You may be interested in a study that was done on watermen working in the Chesapeake Bay which showed there was a high correlation between cataract and prolonged exposure to sunlight particularly UVB radiation 295 to 320 nm and that they thought that ultraviolet radiation (302 to 400 nm) was less critical. They found that in that particular study group that UVB was causing a cortical rather than nuclear cataract.
Thinning of the ozone layer has also increased the exposure of our eyes to ultraviolet light and although wearing dark glasses that are both UVA and UVB were resistant can help, we may also benefit from wearing a hat and taking antioxidants and vitamin C in the hope that this can help slow and prevent our cataract.