Looking after your eyes. All you need to know for free.

Your eyes are your most important organs after your brain, heart and the essential metabolic organs like the liver, pancreas and kidneys. Good eyesight is essential to maintaining good quality of life. Globally, in 2002 more than 161 million people were visually impaired, of whom 124 million people had low vision and 37 million were blind. However, refractive error as a cause of visual impairment was not included, which implies that the actual global magnitude of visual impairment is greater. These figures are from those compiled by the World Health Organization. Prevention of blindness and visual impairment should be sufficient reason to care for your eyes. If well cared for they will help you keep an eye on the world and give you added years of safe and quality living.

Before I start talking about what to do to keep your eyes healthy I will illustrate the parts of a normal eye. Each of these parts is represented in the diagram and I have described the parts in more detail below. If you intend to look after your eyes, it is essential that you know the important parts.

Picture 1.External Parts of the eye.

Lens

The lens are the transparent bodies located just behind the iris. The iris is a collection of longitudinal and circular muscles which control the amount of light which enters the eyes. The lens bends light rays so that they form a clear image at the back of the eye where the rods and cones are found. The lens are elastic, they can change their shapes, getting fatter (more convex) to focus close objects and thinner for distant objects.

Cornea

The cornea is the transparent membrane which forms the outer coating at the front of the eyeball and covers the iris and pupil. It also focuses light on the retina. There are no blood vessels in the cornea. Oxygenation takes place by diffusion.

Diagram 1 Parts of the Eye. (figure from allaboutvision.com)

Pupil

The pupil is the dark circular hole in the centre of the iris. The pupil adjusts to ambient light situations. When there is more light, the pupil is constricted, when there is less light the pupils become dilated.

Iris

The iris is the colored circle surrounding the pupil. It changes the size of the pupil and allows different amounts of light to enter the eye.

Retina

The retina is the light-sensitive inner lining of the back of the eye. Imagine that the eye is like a camera, and the retina is the film. Rays of light enter the eye and are focused on the retina by the cornea and lens. The retina produces an image which is sent along the optic nerve for the brain to interpret, rather like developing a camera film.

Macula

The macula is the small area at the centre of the retina responsible for what we see straight in front of us, at the centre of our field of vision. The macula is very important as it gives us the vision needed for detailed activities such as reading and writing, and the ability to appreciate colour.

Sclera

The sclera is the white of the eye and forms the outer coating of the eyeball. It is fibrous, is tough and has a protective function.

Conjunctiva

The conjunctiva is a transparent, mucous membrane that covers the exposed front portion of the sclera and lines the inside of the eyelids. It must be moist at all times.

Tear film

The tear film is the moist layer that covers and protects the outer surfaces at the front of the eye.

Vitreous Humour.

The vitreous is the clear, jelly-like substance that fills the inside of the eye from the lens to the retina. It gives shape to the eye.

Aqueous Humor

The aqueous is the thin, watery fluid that fills the space between the cornea and the iris (anterior chamber). It is continually produced by the ciliary body, the part of the eye that lies just behind the iris. This fluid nourishes the cornea and the lens and gives the front of the eye its form and shape. Alterations in pressure in this part of the eye can cause visual disturbances.

Common Problems and Management of the eye.

TRAUMA

The most common problem of the eye is damage to the cornes. Corneal Trauma is a major cause of impaired vision in developing countries. The cornea can be damaged from infection, injury or other disease. The whole cornea can become cloudy or parts can be damaged by scars. If light cannot pass through the cornea, vision will be affected. The result is similar to cataracts; visual acuity is reduced, good contrast is needed and the amount of light affects vision. Glasses are unlikely to improve vision damaged by corneal scars or clouding. The best method to prevent this is to prevent injury to any part of the. Children need to be supervised when playing and adults need to be aware of the fact that flying objects at work and in the home environment are the major causes of blindness. These are preventable by thinking about safety and having safe practices.

Neonatal Conjunctivitis. (conjunctivitis of the new born).

Severe neonatal conjunctivitis appears in the first week of life. Serious damage to vision occurs if it is not treated immediately. The eyes must be cleansed and drops or ointment given. In Canada, US , UK and Australia this is standard practice

Xerophthalmia (Also known as conjunctivitis arida).

This is vitamin deficiency disease, (Vitamin A deficiency). It starts with the drying of the conjunctiva and cornea. The retina is also affected causing poor vision in dull light and at night. Xerophthalmia is caused by poor diet – a lack of dark green leafy vegetables, yellow vegetables, tubers and fruits, eggs and milk. Treatment can be given by one or more doses of vitamin A. The condition can be present and then disappear during different seasons because of the fruits and vegetables that are available. If the condition is allowed to progress, the cornea becomes cloudy and is eventually destroyed. A child with xerophthalmia may have poor general health.

The treatment depends on the cause. Artificial tears, which lubricate the eye, are the principal symptomatic treatment for dry eye. They are available over-the-counter as eye drops. Using humidifiers, wearing wrap-around glasses when outside, and avoiding outside windy and dry conditions may bring relief. For people with severe cases of dry eye, temporary or permanent closure of the tear drain (small openings at the inner corner of the eyelids where tears drain from the eye) may be helpful.

Measles and xeropthalmia.

Cause corneal ulceration (keratomalacia) and blindness very rapidly. The use of harmful eye medicines to treat conjunctivitis during measles can damage the cornea and lead to low vision or blindness. Easily preventable by using professionally approved medications which are clean.

Trachoma

Caused by an infection of the conjunctiva. If not treated, scars form on the cornea and eventually blindness can result. Poor hygiene and lack of treatment affect the seriousness of trachoma. Regular washing of the face to keep eyes clean can prevent eye damage from trachoma and the spread to other people.

Cataract.

Cataract is clouding of all or part of the lens. Usually, visual acuity is reduced and vision is blurred and depth perception can be affected. The effect on vision depends on the area and cloudiness of the cataract.

A cataract can be present at birth. It can develop later in life from injury, illness, a lifetime of sunlight exposure or in old age. Some cataracts don’t change but others become worse. Blindness can result.

The treatment for cataract is the surgical removal of the lens. This needs a specially trained person to do the operation. Glasses or special lenses are needed to take the place of the lens that has been removed.

Near or distance vision or both may be affected. Materials and objects of good contrast are better for a person with cataracts. Large print or increase in size of materials may not be necessary. The most important needs are for good lighting without glare and good contrast.

Refraction disorders are covered as a separate topic.

Picture 2. Cataract of the eye. Note the complete opacity of the eye.

Glaucoma

Glaucoma is a disease of the nerves (retina/optic nerve) that can occur with either ‘normal’ or high pressure in the eye. Peripheral visual fields become reduced and visual acuity is affected. Vision is affected in dull light and at night so good lighting is needed. Sometimes drops or an operation are needed to help control the pressure in the eyes. If drops are prescribed they should be used regularly. Blindness can result if it is not treated.

Many eye diseases such as glaucoma run in families.

Rubella

Congenial Rubella Syndrome occurs in babies whose mothers have been infected by rubella (German measles) during pregnancy. Congenital Rubella Syndrome results in multiple disabilities including cataracts, glaucoma, deafness and heart disease.

Retinal Dystrophies.

There are a large number of conditions where the retina and especially the macula never develop properly or are destroyed (degeneration). Age-related macular degeneration (AMD) can have onset in childhood but more commonly occurs in older people. Both near and distance vision are affected when the central area of the retina is involved. Making objects or print larger will help make things easier to see. Low vision devices are often helpful.

Albinism

People with albinism have pale or white skin and hair, and vision is poor. Near vision is usually better than distance vision. They can have nystagmus, refractive errors and poor visual acuity. Spectacles usually improve vision but do not give normal vision. Albinos usually prefer dark or tinted spectacles. The skin should be protected from the sun. Low vision devices can be useful for distance and are sometimes needed for near activities.

Retinitis pigmentosa

This usually affects young adults. There is a slow worsening of vision. The peripheral (side) vision is the first area affected. Visual acuity may remain normal or become poor. In good light the person may be able to do many activities that require good vision. Vision is often poor in dull light or at night. It can be difficult to move around safely and avoid objects.

Diabetic Retinopathy

There are increasing numbers of people with vision impairment caused by diabetes in the developed and developing world. Growth of new blood vessels in the retina and vitreous can occur which causes the blood vessels to become weak and leak and can lead to vision loss. Laser treatment can help prevent blindness provided it is given before vision loss occurs. Vision loss depends on the amount and the area of the retina affected. Tight medical control of diabetes and regular eye examinations are important to prevent vision loss from diabetic eye disease.

Optic Atrophy

This is a degeneration of the optic nerves caused by injury to the eye, glaucoma, poisons, congenital (present at birth) defects and difficulties at birth. Visual acuity is affected and sometimes parts of the visual field are missing. Good lighting is usually needed for better visual functioning. Low vision devices and large print may be helpful.

Nystagmus

Nystagmus is a movement of the eyes which cannot be controlled or stopped. Usually the movements are small and from side to side but movements in other directions also occur. Nystagmus usually occurs when an eye condition has been present from birth. Vision may be blurred but the person does not see the world as moving. Near vision is usually better than distance vision. Nystagmus cannot be treated. There may also be an unusual head posture or shaking or nodding of the head.

Onchocerciasis (River Blindness)

Onchoceriasis is an insect-borne, disease caused by a parasite Onchocerca volvulus and transmitted by blackflies of the species Simulium damnosum. Onchocerciasis is often called “river blindness” because the blackfly which transmits the disease abounds in fertile riverside areas, that frequently remain uninhabited for fear of infection. O. volvulus is almost exclusively a parasite of man.

Adult worms live in nodules in a human body where the female worms produce high numbers of first-stage larvae known as microfilariae. They migrate from the nodules to the sub-epidermal layer of the skin where they can be ingested by blackflies. They further develop in the body of the insect from which more people can be infected. Eye lesions in humans are caused by microfilariae. They can be found in all internal tissues of the eye — except the lens — where they cause eye inflammation, bleeding, and other complications that ultimately lead to blindness.

Onchocerciasis is a major cause of blindness in many African countries. As a public health problem, the disease is most closely associated with West and Central Africa, but it is also prevalent in Yemen and six countries in Latin America. Onchocerciasis has in the past greatly reduced the economic productivity in infected areas and left vast tracts of arable land abandoned. It is estimated that there are about half a million blind people due to river blindness.

Much progress has been made in fighting the disease in several countries through control of the blackfly, however, the disease can now also be treated with an annual dose of the drug ivermectine, Mectizan, which also relieves the severe skin itching caused by the disease.

Trauma

Accidents to the eye. Often vision is impaired in only one eye in accidents but sometimes both eyes can be affected. Injuries to the surface of the eye (conjunctiva or cornea) are common. Immediate treatment of an eye injury is essential to prevent blindness. Vision loss can also occur after an injury to the head. Immediate treatment facilitates healing and prevents infection.

Harmful Eye Practices

Untrained eye doctors and traditional healers often use practices which are unsafe. Some of these practices include the use of hot objects, fluids and solids (such as extracts from plants, human or animal body fluids) applied to the eye can cause serious damage to the eye. The damage caused, is often irreversible.

Conclusion

It is true that many eye conditions and diseases are both treatable and manageable. It is equally true that many are preventable and others are the products of mismanagement by untrained practitioners. I hope that each individual will take eye care seriously and professionally. Blindness cannot be reversed.