Report by WHO
Fact Sheet N°282 – Updated October 2013
- 285 million people are estimated to be visually impaired worldwide: 39 million are blind and 246 have low vision.
- About 90% of the world’s visually impaired live in developing countries.
- 82% of people living with blindness are aged 50 and above.
- Globally, uncorrected refractive errors are the main cause of visual impairment; cataracts remain the leading cause of blindness in middle- and low-income countries.
Global Data of Visually Impairment for 2010
Estimates of prevalence
The prevalence of visual impairment and blindness were determined for the 6 WHO regions for three age groups: 0 to 14 years, 15 to 49 years and 50 years and older, non disaggregated by gender.
A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light. Early in the development of age-related cataract the power of the lens may be increased, causing near-sightedness (myopia), and the gradual yellowing and opacification of the lens may reduce the perception of blue colours. Cataracts typically progress slowly to cause vision loss and are potentially blinding if untreated. The condition usually affects both eyes, but almost always one eye is affected earlier than the other.
A senile cataract, occurring in the elderly, is characterized by an initial opacity in the lens, subsequent swelling of the lens and final shrinkage with complete loss of transparency. Moreover, with time the cataract cortex liquefies to form a milky white fluid in a Morgagnian cataract, which can cause severe inflammation if the lens capsule ruptures and leaks. Untreated, the cataract can cause phacomorphic glaucoma. Very advanced cataracts with weak zonules are liable to dislocation anteriorly or posteriorly. Such spontaneous posterior dislocations (akin to the historical surgical procedure of couching) in ancient times were regarded as a blessing from the heavens, because some perception of light was restored in the cataractous patients.
As a cataract becomes more opaque, clear vision is compromised. A loss of visual acuity is noted. Contrast sensitivity is also lost, so that contours, shadows and color vision are less vivid. Veiling glare can be a problem as light is scattered by the cataract into the eye. The affected eye will have an absent red reflex. A contrast sensitivity test should be performed and if a loss in contrast sensitivity is demonstrated an eye specialist consultation is recommended.
In the developed world, particularly in high-risk groups such as diabetics, it may be advisable to seek medical opinion if a ‘halo’ is observed around street lights at night, especially if this phenomenon appears to be confined to one eye only.
CAUSES AND RISK FACTORS
Cataracts develop for a variety of reasons, including long-term exposure to ultraviolet light, exposure to radiation, secondary effects of diseases such as diabetes, hypertension and advanced age, or trauma (possibly much earlier); they are usually a result of denaturation of lens protein. Genetic factors are often a cause of congenital cataracts and positive family history may also play a role in predisposing someone to cataracts at an earlier age, a phenomenon of “anticipation” in pre-senile cataracts. Cataracts may also be produced by eye injury or physical trauma. A study among Icelandair pilots showed commercial airline pilots are three times more likely to develop cataracts than people with non-flying jobs. This is thought to be caused by excessive exposure to radiation coming from outer space. Cataracts are also unusually common in persons exposed to infrared radiation, such as glassblowers who suffer from “exfoliation syndrome”. Exposure to microwave radiation can cause cataracts. Atopic or allergic conditions are also known to quicken the progression of cataracts, especially in children. Cataracts can also be caused by iodine deficiency.
Cataracts may be partial or complete, stationary or progressive, hard or soft. Some drugs can induce cataract development, such as corticosteroids and Seroquel.
Although cataracts have no scientifically proven prevention, it is sometimes said that wearing ultraviolet-protecting sunglasses may slow the development of cataracts. Regular intake of antioxidants (such as vitamin A, C and E) is theoretically helpful, but taking them as a supplement has been shown to have no benefit. The less well known antioxidant N-acetylcarnosine has been shown in randomized controlled clinical trials to treat cataracts, and can be expected to prevent their formation by similar mechanisms. N-acetylcarnosine is a proposed treatment for other ocular disorders that are instigated, or exacerbated by oxidative stress including glaucoma, retinal degeneration, corneal disorders, and ocular inflammation.
TREATMENT & SURGERY
When a cataract is sufficiently developed to be removed by surgery, the most effective and common treatment is to make an incision (capsulotomy) into the capsule of the cloudy lens in order to surgically remove the lens. There are two types of eye surgery that can be used to remove cataracts: extra-capsular (extracapsular cataract extraction, or ECCE) and intra-capsular (intracapsular cataract extraction, or ICCE).
Extra-capsular (ECCE) surgery consists of removing the lens but leaving the majority of the lens capsule intact. High frequency sound waves (phacoemulsification) are sometimes used to break up the lens before extraction.
Intra-capsular (ICCE) surgery involves removing the entire lens of the eye, including the lens capsule, but it is rarely performed in modern practice.
In either extra-capsular surgery or intra-capsular surgery, the cataractous lens is removed and replaced with a plastic lens (an intraocular lens implant) which stays in the eye permanently.
Glaucoma is a disease of the optic nerve. Optic nerve is the part of the eye that carries images we see from the eye to the brain. The optic nerve is made up of many nerve fibres (like an electric cable containing numerous wires). Glaucoma damages nerve fibres, which can cause blind spots in our vision and vision loss will develop.
WHAT ARE THE CAUSES?
There are many causes of optic nerve head failure, just like there are many causes of heart failure. The unique feature of this condition is there are absolutely no symptoms in majority of the cases in early stages. By the time vision is affected, it is too late to reverse the blindness caused by it. This is how the disease is known as the sneak thief of sight! You just do not realize you have this condition until it is too late.
One major risk factor has to do with the pressure inside the eye or intraocular pressure (IOP). When the clear liquid called the aqueous humor which normally flows in and out of the eye cannot drain properly, pressure builds up in the eye. The resulting increase in IOP can damage the optic nerve.
Other risk factors are: being in the older age-group
- Family History
- Extreme Refractive Errors (Long-Sightedness/ Short-Sightedness)
- History of Steroid Use
- Eye injury
This list is not exhaustive. If you are above 40 and have the risk factors mentioned above, you are:
PRIMARY OPEN-ANGLE GLAUCOMA
The most common form of glaucoma is primary open-angle glaucoma, where the aqueous fluid that normally circulates in the front portion of the eye is blocked from flowing out of the eye through a tiny drainage system. This causes the pressure inside your eye to increase, which can damage the optic nerve and lead to vision loss. Most people who develop primary open-angle glaucoma do not notice any symptoms until their vision is impaired.
In angle-closure glaucoma, the iris (coloured part of the eye) may drop over and completely close off the drainage angle, abruptly blocking the flow of aqueous fluid. This can lead to increased IOP or optic nerve damage. In acute angle-closure glaucoma, there is a sudden increase in IOP due to the build-up of aqueous fluid. This condition is considered an emergency because optic nerve damage and vision loss can occur within hours of the problem. Symptoms can include headache, nausea, vomiting, seeing haloes or colours around lights, and eye pain. If you fit any of the criteria – female or in the older age-group or have hyperopia (longsightedness), you are at higher risk of this type of glaucoma.
NORMAL TENSION GLAUCOMA
Even people with “normal” IOP can experience vision loss from glaucoma. This condition is called normal tension glaucoma. With this type of glaucoma, the optic nerve is damaged even though the IOP is considered normal. Normal tension glaucoma is not well understood but we do know lowering the IOP has been shown to slow down progression of this form of glaucoma.
PAEDIATRIC OR CHILDHOOD GLAUCOMA
Childhood glaucoma is rare and can start in infancy, childhood or adolescence. Like primary open-angle glaucoma, there are few, if any, symptoms in the early stage. Blindness can result if left untreated. Like most types of glaucoma, this type of glaucoma may be hereditary.
TREATMENT & SURGERY
Regular examinations with your ophthalmologist are important if you are at risk for this condition. If you are diagnosed to have glaucoma, the normal treatment is to use eye drops to lower your intraocular pressure. There are many types of effective eye drops available nowadays and are usually administered once or twice daily. However if you are diagnosed to have angle closure then the definitive treatment is to perform a laser to open up the angles.
Treatment and follow-up checks for glaucoma require life-long effort. It is similar to having high blood pressure or diabetes. If you control your blood pressure or diabetes, then you are unlikely to get complications. If you are a glaucoma patient who control your intraocular pressure, then blindness can be prevented. If you stop using eye drops or stop going for follow-up eye checks, then the disease can still progress and lead to blindness.
Surgery can be done if your eye pressure cannot be controlled despite being treated with eye drops or laser. If your disease has not worsened, surgery can prevent further visual field loss. Surgery, however, cannot recover any lost vision. There are a number of operations that can be done to lower the intraocular pressure and your eye specialist will be able to advise you on the most suitable treatment.
Diabetes mellitus, a condition where the blood sugar concentration is persistently elevated, is a major health affliction in our population. A recent national health survey estimated that 9% of our population, or about 1.9 million Malaysians, suffer from this malady. Generally, diabetes mellitus (DM) can be divided into two main types. Type 1 DM refers to the disease in which the age of onset is 30 years or younger, whereas Type 2 DM refers to adult onset disease, usually above the age of 30 years. By far, the most common type of DM is the Type 2 DM, accounting for more than 95% of all diabetic patients.
Of the many body system that can be affected by uncontrolled diabetes, the eye is an important organ that often takes the brunt of the disease, and literally, with ‘visible’ effect. Essentially, the structure and the function of the blood vessels in the diabetic person are altered, making the blood vessel walls prone to hardening, narrowing, leaky and eventually, poor blood flow. Such changes when occur in the eye, usually affects the light-sensing layer at the rear of the eye.
This layer, the retina, is analogous to the film in the camera. For the eye to see well, the retina must be of good health. However, in the early stages of the abnormal changes in the retina, or diabetic retinopathy, the patient may not notice any symptoms. With progression of retinopathy, the patient will experience blurriness in vision. This blurriness is usually caused by fluid and fats leakages from abnormal blood vessels in the retina layer, making the nerve layer swollen.
With deterioration in retinopathy, the altered blood vessels may soon be blocked, and the retina will be starved of oxygen and nutrients that are normally delivered with the blood flow. The vision may decrease further and often abnormal growth of ‘new’ vessels on the retina will ensue. These new vessels formation is the result of an attempted compensatory mechanism by the eye in response to the oxygen-starvation state. These ‘new’ vessels bring about devastating results as they are highly fragile and often grow hand-in-hand with abnormal scar tissues on the retina surface.
The fragile, abnormal ‘new’ vessels can cause massive sudden bleeding inside the eye, obscuring vision. In addition, the scar tissues on the retina surface often contracts, the effect of which crumple and distort the retina layer. Moreover, the pull by these contracting scars on the retina detaches the retina from its usual place, i.e., lining the rear part of the eye, This leads to further permanent damage to the eye and vision.
There had been highly effective treatment for retinopathy, primarily the use of laser, for some 20 years now. Prior to the introduction of laser in treatment of diabetes retinopathy, about 10% of patients with severe retinopathy will go blind with each passing year. With appropriate and timely laser treatment, the risk of blindness is reduced by more than 95%. The aim of the laser treatment is the prevention of deterioration in retinopathy. Appropriate laser treatment works by preventing the growth of abnormal ‘new’ vessels and the scar tissues, and minimizes their attendant catastrophic visual effects in the diabetic eye. Therefore, it is important for the patient to realize that laser treatment in diabetes is not meant to improve but to maintain vision, and the reason behind the recommendation for treatment by their eye doctors even though the patient may not had experienced any visual disturbances yet.
In more severe cases, where abnormal blood vessels and scar tissues had resulted in serious retinal damage, laser treatment alone is no longer effective in restoring sight. The patient will require retinal surgery to remove the abnormal vessels, blood, and scar tissues on the retina in order to salvage vision and the eye. Although such sophisticated surgery is technically challenging, it is currently available and offered by selected retinal surgeons in our country.
AMD, ARMD is condition that can occur in individuals above the age of 50 years. It tends to occur bilaterally but can affect only one eye initially. It is the leading cause of irreversible blindness in the industrialized world and in Asia; it is fast becoming a major problem.
One of the reasons for this is due to the lack of understanding about the condition amongst the public. Only 2% of adults know that ARMD is the leading cause of vision loss in people over 50 years of age and almost 75% of people do not know of a treatment for ARMD. Although it is a cause of irreversible blindness, early detection and intervention will be able to arrest its development.
ARMD occurs when the central portion of the retina, called macula, is damage (pic 1). The macula is the part of the retina that allows us to see fine details. If it is damaged, the central vision would blur or darken. Untreated, simple essential tasks like reading and driving will be severely affected.
There are two types of ARMD;
The Dry type occurs in about 90% of patients with ARMD. There is a gradual thinning of the macula area with deposition of yellowish materials called Drusens (pic 2). Generally vision is well maintained in the Dry type but regular ophthalmological assessment is crucial since about 15-20% will progress to the Wet type.
The Wet type is caused by leaking abnormal blood vessels (choroidal neovascular membranes) located beneath the macula area. Although it constitutes only about 10% of ARMD, it is the cause of more than 90% of blindness associated with ARMD. Untreated this leakage will lead to the formation of scar tissues beneath the macula. This will lead to irreversible loss of sight. (pic 3).
The symptoms associated with ARMD are mainly due to the Wet type and these include:
- Loss of the ability to see objects clearly.
- Straight lines appear to be wavy and distorted.
- Loss of clear and correct color vision.
- Print looks washed out while reading.
- A dark area blocks the vision in the center of your eye
CAUSES AND RISK FACTORS
The greatest risk factor for ARMD is age. Studies show that people over age 60 are clearly at greater risk than other age groups. For instance, a large study found that people in middle-age have about a 2 percent risk of getting ARMD, but this risk increased to nearly 30 percent in those over age 75.
Other risk factors include:
- Smoking. Smoking may increase the risk of ARMD.
- Obesity. Research studies suggest a link between obesity and the progression of early and intermediate stage ARMD to advanced ARMD.
- Race. Whites are much more likely to lose vision from ARMD than African Americans.
- Family history. Those with immediate family members who have ARMD are at a higher risk of developing the disease.
- Gender. Women appear to be at greater risk than men.
There is as yet no outright cure for macular degeneration, but some treatments may delay its progression or even improve vision. These include:
Thermal Laser Photocoagulation
The benefit of this treatment is that it can prevent further degeneration of the macula. However, the laser treatment can damage healthy macula cells meaning that you might lose a little sight to save a lot.
Photodynamic Therapy (PDT)
PDT utilizes a light-sensitive dye which is injected into the bloodstream and transported to macula which will highlight the abnormal blood vessels. A low energy or ‘cold’ laser beam is then applied to induce a chemical reaction and destroy the leaking blood vessels without damaging the surrounding healthy tissue
Anti Vascular Endothelial Growth Factor (VEGF)
The most recent development in the treatment of ARMD is the availability of anti VEGF’s. These drugs inhibit the role of VEGF in the formation of new vessels. It is injected directly into the eye with a small needle and is done in the clinic under topical anesthesia. It is however, necessary to have repeated 4-6 weekly injections for about 3-4 month.
Congenital Eye Disease
A congenital eye disease is a disease of the eye that is present at birth. There are several conditions that can cause congenital eye diseases, including Down syndrome, dysplasia syndrome and chondrodysplasia syndrome. In some cases, patients may develop an illness during pregnancy that passes to the fetus, and birth defects may be expected. However, some congenital eye diseases do not stem from an underlying illness and may not be suspected until after the baby is born.
A cataract is a clouding of the lens of the eye. Many conditions can cause congenital cataracts, including ectodermal dysplasia syndrome, trisomy 13 and Pierre-Robin syndrome. The most common characteristic of congenital cataracts is a cloudiness or white spot in the pupil that is present at birth and easily seen without special equipment, according to the National Institutes of Health. Other symptoms include failure of an infant to show awareness and unusual or rapid eye movement.
Nystagmus is the term for rapid, repetitive involuntary eye movements. Eye movement may be side to side, up and down or rotational. The National Institutes of Health explains that congenital nystagmus is usually mild and not associated with other disorders. People with nystagmus are often not aware of the eye movements. A diagnosis of nystagmus commonly includes a computed tomography scan or a magnetic resonance imaging scan of the head, an electro-oculograph to measure eye movements and vestibular testing to record eye movements and response to stimulation. In most cases, there is no treatment for congenital nystagmus.
Congenital glaucoma is a group of eye conditions present at birth that lead to optic nerve damage. Pressure is the most common cause of damage to the optic nerve. Congenital glaucoma often runs in families and results from abnormal development of the fetus’ fluid outflow channels of the eye. Symptoms of congenital glaucoma are commonly observed when the child is just a few months old and often include cloudiness of the front of the eye, tearing, sensitivity to light and enlargement of one or both eyes. Physicians diagnose congenital glaucoma with a complete eye exam that includes examining intraocular pressure, the outflow channels of the eye, pupillary reflex response, visual acuity and visual field measurements.
Amblyopia is a condition that occurs in children when vision has not developed properly in each eye. If amblyopia is left untreated, a child’s vision will not develop correctly. The child’s brain, as it matures, will start “ignoring” the image coming from the bad eye. This causes vision in the affected eye to become poor. Because amblyopia can result in permanent vision loss in one eye, it is important to have a child with amblyopia regularly tested by an eye doctor.
WHAT ARE THE CAUSES?
Amblyopia usually starts when one eye has much better focus than the other eye. For example, one eye might be very nearsighted or have a lot of astigmatism, while the other does not. When the child’s brain is confronted with both a blurry image and a clear image, it will begin to ignore the blurry image. If this goes on for months or years, the vision in the eye that sees the blurry image will deteriorate.
Another cause of amblyopia is strabismus. Strabismus is an ocular misalignment, meaning that one eye turns inward or outward. This prevents the eyes from focusing together on an image and can cause double vision. In order to combat this, the child’s brain generally chooses to ignore the image from the deviated eye, causing the vision in that eye to deteriorate. Because one of the eyes is misaligned, some people refer to this as a “lazy eye.”
Family history of amblyopia is a risk factor for amblyopia. Parents cannot tell just by looking at their child if they have amblyopia. Early diagnosis and treatment are the keys to the best visual outcome.
TREATMENT & SURGERY
The most common treatment for amblyopia is to force the brain to start using the “bad” eye by putting a patch over the “good” eye. At first, the child will have a hard time seeing with just the weaker eye. However, it is very important that your child wear the patch diligently because this will eventually improve vision. It can take weeks or months for an eye patch to improve vision.
Corneal opacity is a disorder of the cornea, the transparent structure on the front of the eyeball, which can cause serious vision problems. Corneal opacity occurs when the cornea becomes scarred. This stops light from passing through the cornea to the retina and may cause the cornea to appear white or clouded over.
If you experience any of these symptoms, do not assume it is due to corneal opacity. These symptoms may be caused by other health conditions as well. If you experience any one of the following, see your eye doctor immediately:
- Vision decrease or loss.
- Pain in the eye or feeling like there is something in your eyes.
- Eye redness or light sensitivity.
- Area on the eye that appears cloudy, milky, or is not completely transparent.
There are many causes of corneal opacity. In some cases, your doctor can recommend a treatment that will reverse the opacity and lessen your chance of needing additional treatment, such as surgery.
Infection, injury, or inflammations of the eye are the most common causes of corneal opacity.
The following factors increase your chance of developing corneal opacity. If you have any of these risk factors, tell your doctor:
- Vitamin A deficiency.
- Measles (when measles result in scarring/infection of the eye).
- Foreign bodies striking the eye.
- Eye injury, whether from a force, such as a poke in the eye, or from a chemical agent.
- Herpes simplex virus (which can be transmitted to the eyes).
- Other infections, including conjunctivitis or “pink eye”.
To help reduce your chance of developing corneal opacity, take the following steps:
Take care to avoid injuring the eye. Wear eye protection during any potentially dangerous activity. Make sure the safety goggles are worn tight against the face, otherwise a foreign body can fly up under the goggles and injure the eye.
Take proper care of contact lenses, and follow your doctor’s recommendations regarding wear and cleaning. See your doctor immediately if you suspect you have an eye infection, including conjunctivitis (pink eye), if you injured your eye, or if you develop any pain or change in vision.
Talk with your doctor about the best treatment plan for you. Treatments vary depending on the most likely cause of the scarring and how severe the scarring is. Treatments may include:
Eye drops containing antibiotics, steroids, or both Oral medications
In some cases, scar tissue may be removed surgically. The surgery may be performed using a laser, called phototherapeutic keratectomy (PTK), if the scarring is close to the corneal surface. In more severe cases, a cornea transplant may be necessary.