MYOPIA
To enable us to see clearly, light rays need to be focused by the transparent cornea at the front of the eye and by the eye’s lens so that they form a sharp image on the retina, the light-sensitive membrane at the back of the eye. In people with myopia (nearsightedness), the eyeball is long relative to the combined focusing power of the cornea and the lens. Light rays from distant objects are therefore bent too much and are focused in front of the retina, resulting in blurry vision. Myopia is a very common condition that sometimes runs in families and can usually be corrected.
WHAT ARE THE SYMPTOMS?
The symptoms of myopia often become apparent around puberty, but the condition may begin to develop a few years before. The earlier myopia starts, the more severe it is likely to become. However, the condition usually stabilizes in early adulthood when growth stops. The main symptoms are:
□ Increasing difficulty in seeing objects clearly from a distance.
□ Deteriorating school work in children as a result of not seeing clearly.
If you are seriously myopic, you are more susceptible to eye disorders such as retinal detachment, chronic glaucoma, and macular degeneration. All of these disorders can badly damage eyesight. If you have problems seeing distant objects clearly, you should visit your ophthalmologist.
WHAT MIGHT BE DONE?
The ophthalmologist will do vision tests to check for myopia. Myopia can be corrected with concave lensed glasses or, for older children and adults, contact lenses. In mild cases, the cornea’s shape can be altered by surgery to correct the vision.
HYPEROPIA
The transparent cornea and the lens act together to focus light rays and create a clear image on the light-sensitive retina at the back of the eye. Hyperopis (farsightedness) occurs if the eyeball is short relative to the combined focus power of the cornea and lens. When the image falls behind the retina, it causes blurry vision that is often worse when looking at near objects. Young people with hyperopia can often see distant objects clearly because the lens is flexible and can change focus easily, but with age, the ability to focus lessens and distant vision is also affected.
WHAT ARE THE SYMPTOMS?
Mild or moderate hyperopia will probably not cause any vision difficulties in young people, but, the more severe the condition, the earlier in life its symptoms are likely to appear. Symptoms of severe hyperopia, which may be apparent from infancy, may include:
□ Lack of interest in small objects, toys, and similar items.
□ Difficulty with reading or following picture stories.
If the eyes are not equally affected by hyperopia, they may be unable to focus together on the same object. Without early treatment, young children may develop crossed eyes and may eventually lose vision in one eye. You should take your child to the doctor immediately if you notice any of the symptoms described here.
If you are having trouble seeing near objects clearly or you have difficulties in reading or doing other close work, you should visit your ophthalmologist for vision tests. These problems may indicate that you have presbyopia, which develops earlier in people with hyperopia than most people.
WHAT MIGHT BE DONE?
Your ophthalmologist will check your visual acuity and the level of detail you can see, and then assess the severity of hyperopia. Although the condition is sometimes detected in children during routine vision testing at school, all children with a family history of severe hyperopia should be tested before age 3 because early treatment is important.
Hyperopia can be corrected with contact lenses or glasses that have convex lenses. The focusing power octal lense decreases gradually with age and your prescription may need to be updated regularly. Some people who have hyperopia may be helped by laser treatment, which reshapes the surface of the cornia by laser beam to increase its focusing power.
Hyperopia does not cause complications, but people who have it are more prone to acute glaucoma, a serious condition that must be treated promptly.
ASTIGMATISM
In people with Astigmatism, the transparent cornea at the front of the eye is unevenly curved and refracts (bends) the light rays striking different parts of it to differing degrees. The lense is than unable to bring all the rays into focus on the light sensitive retina at the back of the eye, and vision becomes blurry. Astigmatism can run in families and often occurs in combination with myopia.
WHAT ARE THE CAUSES?
The most common form of astigmatism is present from birth and is due to a slight buckling of the cornia in both eyes. Instead of being round like a basketball, the cornea is shaped like a football, with a steep curvature in one direction and a shallow curvature in the other. This type may worsen slowly with age. Less often, astigmatism is due to eye disorder or an eye injury that causes a corneal ulcer.
WHAT ARE THE SYMPTOMS?
The majority of people have a slight degree of astigmatism. If you are only slightly affected, you probably will not notice much wrong with your vision. More severe astigmatism, however, may lead to significant visual problems.
Astigmatism can affect vision in a number of different ways. Symptoms may include the following:
□ Blurring of small print, causing difficulty in reading.
□ Inabillity to see both near and distant clearly.
If you are experiencing difficulty in seeing obects clearly at any distance, it is important to visit your ophthalmologist to have a vision test.
WHAT IS THE TREATMENT?
In people with astigmatism, vision can usually be corrected by glasses that have special lenses that compensate for the unevenly shaped cornea. Rigid contact lens are also effective because they smooth out the surface of the cornea. Conventional soft contact lenses mold to the shape of the cornea and can normally correct only mild astigmatism. However soft contact lenses (known as toric lenses), which are designed to correct the condition, are also available.
In some people, astigmatism may be corrected by surgical treatment that reshapes the cornea. One of the most widely used and least intrusive forms of surgical treatment for this condition is laser surgery, which tends in cause only minimal scarring.
PRESBYOPIA
After about age 40, almost everyone starts to notice increased difficulty in reading small print because of the development of presbyopia. A person with normal vision is able to see close objects clearly because the elastic lens of the eye changes shape, becoming thicker and more curved when focusing on near objects. The thicker lens brings light rays from close objects into sharp focus on the light-sensitive retina at the back of the eye in a process called accommodation. As we age, the lens becomes less elastic and the power of accommodation is reduced. Eventually, light rays from near objects can no longer be focused on the retina and the objects we see appear blurry.
WHAT ARE THE SYMPTOMS?
Since presbyopia develops very slowly, most people are unaware of the initial stages of this condition. However, the symptoms usually become noticeable between the ages of 40 and 50. Farsighted people may have noticeable symptoms from an earlier age. Common symptoms of presbyopia include:
□ The need to hold newspapers and books at arm’s length so that you can read them.
□ Increased difficulty focusing on near objects in poor light.
□ If you are nearsighted, the need to take off your glasses to see near objects clearly.
If you develop any of these problems, consult your ophthalmologist.
WHAT IS THE TREATMENT?
Presbyopia can be corrected by wearing glasses with convex (outward-curved) lenses, which bring light rays from near objects into focus on the retina. If you are also farsighted, nearsighted, or have astigmatism, you maybe prescribed glasses with a different power in different parts of the lens. For example, bifocals have an upper lens to correct distance vision and a lower lens to correct presbyopia. Progressive lenses that gradually alter the focusing power from top to bottom are also available. Presbyopia can sometimes be corrected with contact lenses, but glasses may still be necessary for reading.
Presbyopia tends to worsen with age, and you will probably need to have your lens prescription updated every few years. You should therefore see your ophthalmologist regularly in order to have vision tests. The condition eventually stabilizes at about age 60 by which time little natural focusing power is left.
By this stage most of the focusing work is done by glasses instead of the eye.