By: Elizabeth Obigwe. Datelinehealth Africa Volunteer Freelance Writer, with editorial support from The DLHA Team
Behind the visible coloured part of your eye (the iris), there is a clear, and small oval structure called the lens. This structure helps to focus light onto the retina at the back of your eye, which then sends images to your brain.
The lens is made up of proteins called crystallin. Proteins are large complex molecules (amino acids) that form the basis of body function.
Cataract occurs when the crystallin proteins of the lens lose their ordered structure and form clumps which start to cloud the lens. At first, the clouding may be small and not affect your vision much, but over time it can grow larger and denser. As the cataract progresses, it becomes harder for light to pass through the lens, resulting in blurry vision and other vision complications.
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Eye showing clouding of the lens beyond the dilated pupil in mature cataract.
A cataract is simply a clouding of the lens in your eye that can cause vision problems and eventually lead to blindness.
Cataract is the leading cause of reversible eye damage globally. According to the World Health Organization, about 94 million people in the world have moderate or severe vision impairment or blindness due to unaddressed cataracts. Similarly, an old study estimated that 1.2% of the entire African population is blind, and that cataract was responsible for 36% of the cases. Newer studies indicate that this estimate may be too high.
This condition can affect only one eye. However, it usually affects both eyes, but the severity and time of appearance might vary. Also, cataract is largely age-related. So, it is more common among older adults. It may first appear around age 40 - 50, but will typically not affect vision until about 60 years of age.
There are different types of cataracts, but three main types are discussed below.
Age-Related Cataract
Age-related cataract, also known as senile cataract, is caused by changes within the eyes as a person ages. This is the most common type of cataract and the number of cases increases with an increase in the age population. For example, a study revealed that in Kenya, 4.37% of cataract blindness occurs under age 40, 8.7% occurs between 40 and 59, and 87% occurs after age 60.
Childhood Cataract
Childhood cataracts can either be congenital or juvenile. People with congenital cataracts are born with it while juvenile cataracts develop during childhood. Childhood cataract is usually a result of genetic conditions, congenital disorders or intrauterine infections. This condition might not affect the vision of the child.
Secondary Cataract
This type of cataract is caused by a number of different factors like:
Aside from these three major types of cataracts, the condition is also divided into three categories based on their location on the eye lens (see figure 1).
Figure 1: Showing categories of cataract. Click on image to enlarge.
Nuclear Cataract
Nuclear cataracts are also known as age-related nuclear cataracts. It affects the centre of the lens and is responsible for 50% to 90% of cataracts in developing countries. During the initial stage, a nuclear cataract may cause nearsightedness or it may improve your reading sight, but only for a while. Eventually, the clouding of the lens which may later start to appear yellowish or brownish obstructs your view.
This type of cataract usually results in blurry vision, difficulty identifying colours, difficulty recognizing faces and even seeing things like golf balls and car number plates.
Cortical Cataract
This type of cataract is more common among the elderly and diabetic patients. It affects the edges of the lens and begins as a wedge-shaped or radial spoke opaque appearance in this area. Over time, the opacity extends to the centre of the lens and interferes with vision. It may cause glare, difficulty reading, and light sensitivity.
Subcapsular Cataract
Steroids or corticosteroids are associated with posterior subcapsular cataracts. This is the least common type of cataract and also the fastest to progress compared to others. It is located behind the lens and on the path through which light passes. Subcapsular cataract often causes a paradoxical effect where vision is poor in bright light and improved in dim light.
Note that it is possible for opacity to appear in more than one of the areas discussed above, causing an overlap in this classification.
The main cause of cataracts is age due to the alteration of the lens cells with age. However, there are other factors that may trigger the opacity of the eye at an earlier age. Some of them are:
What Are The Risk Factors for Cataracts?
Aside from the causes listed above, some factors increase a person’s risk of developing cataracts. They include:
1. Smoking
According to the World Health Organization, smokers and people living with smokers stand to develop cataracts as well as age-related macular degeneration earlier than non-smokers. The use of e-cigarettes is also detrimental to general and eye health.
2. UV-B Exposure
Studies have shown that excessive exposure to sunlight can increase a person’s chances of suffering from cataracts.
3. Diabetes
Diabetes accounts for up to 4% of all cataract cases. Although it is known to increase the risk of cataracts, scientists have not proven if optimal treatment of diabetes also reduces the risk of the condition.
4. Use of Steroids
Steroids are a type of medication that reduces inflammation in the body, but they can also cause damage to the lens. They generally alter the composition of the lens, causing the proteins to clump together and form cataracts.
5. Alcohol
Doctors say that excessive consumption of alcohol can also place a person at risk of developing this condition.
6. Family History
Cataracts can be inherited. If you have a parent or sibling who has suffered from cataracts, it increases your risk of suffering the same.
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Figure 2: Showing how cataract affects vision. Click on image to enlarge
These include:
If you notice any of the symptoms above, especially if you are at risk of developing the condition, see your doctor as soon as possible.
There are no studies that have shown conclusively that cataract is preventable. But some measures that doctors say may help to slow the onset and progression of the condition are:
When you visit the hospital, your general doctor or eye doctor (ophthalmologist) will take your full medical history, ask some questions and perform focused eye tests in order to determine if your complaints are due to the presence of cataracts. Your general health may also be checked to exclude the possibility of other conditions that may be the cause of your visual impairment.
Some of the eye tests that your ophthalmologist may perform on you, include:
1. External Examination
As the name implies, this is a visual inspection of the eyes and surrounding tissues. Your doctor will look for any signs of abnormalities, such as swelling or redness or whiteness in your pupils.
2. Visual Acuity Test
It is also called the "eye chart exam." This is a basic eye test that measures how well you can see. You'll be asked to read letters from an eye chart at a specific distance, one eye after another, to determine the sharpness of your vision.
3. Glare Testing
This test measures how well you see in bright light or glare. It can be especially important for people who drive at night. The doctor shines a bright light in your eyes and asks you to read.
4. Assessing Pupillary Function
Your pupil is the darker part in the centre of your iris (the coloured part of your eye). This process involves examining how your pupils respond to light. The doctor will shine a light into your eyes to check how your pupils react.
5. Examining Ocular Alignment
This test assesses how well your eyes work together. The doctor will ask you to look at a target that is moved briefly while your eye movements are observed.
6. Measuring Intraocular Pressure (IOP)
This test checks the pressure inside your eyes. High IOP can be a sign of glaucoma, a condition that can damage the optic nerve and lead to vision loss.
7. Slit-lamp Examination
This test uses a specialized microscope called a slit lamp to examine the front part of your eye, including the cornea, iris, lens, and the fluid inside the eye.
8. Ophthalmoscopy
This is an examination of the back part of your eye, which includes the retina, macula, and optic nerve. Your doctor will use a special instrument to look at the inside of your eye and check for any signs of damage or disease.
The only available treatment for cataracts at the moment is surgery. However, there are different types of surgeries used to treat the condition.
Every surgical operation for cataract treatment involves removing the damaged lens and replacing it with an artificial one known as Intraocular Lens (IOL). But the way of getting this done varies depending on the surgical procedure employed.
Cataract treatment surgeries do not take too much time and most times, the patient can go home after the surgery. Also, as many as 95% of patients who undergo surgery will have improved vision.
When a cataract starts to develop, there is no way to stop or reverse the damage. However, it can be managed. If the cataract is not affecting your ability to perform daily tasks like reading and driving, your doctor may recommend some management tips for the time being.
Some of the surgeries that can be performed to treat your cataract include:
1. Intracapsular Cataract Extraction (ICCE)
This is an early procedure that is no longer in use. It involves removing the entire lens and capsule through a single incision.
2. Extracapsular Cataract Extraction (ECCE)
During this procedure, the eye surgeon removes the clouded lens. The capsule surrounding the lens is left intact as a protective barrier between the front and back of the eye. This is also the area where a new lens will be implanted to replace the clouded one. The incision made for this process is often between 9mm to 13mm. ECCE is common in developing countries because it is relatively cheaper.
3. Manual Small-Incision Cataract Surgery (MSICS)
MSICS is similar to extracapsular extraction. But in this case, a much smaller external incision (6.5 mm to 7 mm) and a larger internal incision (9 mm to 11 mm) are made for extraction.
4. Phacoemulsification
This is the most modern procedure and it is practiced in developed countries because of its high cost of treatment. Developing countries may not be able to provide sufficient eye care with this method.
This procedure involves using sophisticated machinery to break down the lens into little parts. A smaller incision of 2mm to 3mm is then made to remove lens pieces.
Although it is a safe and effective process, cataract surgery does have direct complications. These may be immediate or delayed, but most of them can be managed.
Immediate complications include;
While the delayed complications which are likely to be more severe are;
Final Words
In 1999, the World Health Organization launched a “Vision 2020: The Right to Sight” initiative. The aim was to eliminate avoidable blindness by 2020. Cataract is the leading cause of avoidable blindness globally. In Africa, it is responsible for 36% of the cases of blindness with trachoma and glaucoma coming after it as the top leading causes of blindness as well. So far, the WHO has not been able to achieve the ambitious goal of eliminating avoidable blindness. However, this bold move has led to lots of improvement.
Unfortunately, Africa, among other developing regions still has significant cases of avoidable blindness and vision complications caused by different eye diseases including cataracts. Hence, there is a need to reassess the journey so far and create better plans on how to further treat and eliminate cataracts among other avoidable diseases.
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Related: Priority eye diseases in Africa.
Published: May 9, 2023
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