Refractive Errors and Treatment Options
The eye is essentially an optical instrument that works much like a camera. Light rays from the outside world pass through the cornea (the transparent outermost layer) and the lens, both of which refract the rays so that they focus on the macula — the area of the retina responsible for sharp vision. When the rays focus elsewhere, the result is a refractive error. Refractive errors are usually classified into three main groups: myopia, hyperopia and astigmatism.
In addition, after the age of 40 the lens of the eye gradually loses its ability to focus on near objects, leading to a reduction in near vision known as presbyopia. Presbyopia is not a disease — it is a natural part of the ageing process.
MYOPIA (NEAR-SIGHTEDNESS): Myopia is the inability to see distant objects clearly. It occurs when the rays of light entering the eye focus in front of the retina, most often because the eye’s anterior–posterior axis is longer than normal. It is a structural feature of the eye and is frequently inherited. It usually appears at school age and tends to progress while the eye continues to grow. In later life, cataract formation can also induce myopia by altering the refractive power of the lens.
HYPEROPIA (FAR-SIGHTEDNESS): Hyperopia is, in general terms, the inability to see near objects clearly. It occurs when the rays of light entering the eye focus behind the retina. In contrast to myopia, the eye in hyperopia is smaller than average. Structural and genetic factors are the most common cause. Untreated hyperopia in children increases the risk of amblyopia (lazy eye), which is why every child should undergo an eye examination before starting school.
ASTIGMATISM: Astigmatism arises when the cornea refracts light differently in different meridians. It causes blurred vision at every distance. As well as being structural, astigmatism may result from degenerative corneal conditions, infections or trauma.
PRESBYOPIA: Presbyopia is the loss of near vision typically seen after the age of 40. The lens inside our eye is a flexible structure: thanks to this special ability, when an object comes close to the eye the lens swells and increases its refractive power, allowing us to see the near object sharply. From around age 40 the eye gradually loses this ability, and the difficulty in near vision known as presbyopia begins.
What Causes Presbyopia?
Presbyopia is the loss of near vision seen in patients over the age of 40. The lens inside our eye is a flexible structure: thanks to this ability, when an object comes close to the eye the lens swells and increases its refractive power, allowing us to see near objects clearly. From around age 40 the eye gradually loses this ability and the difficulty in near vision known as presbyopia begins.
Prepared by the Editorial Board of Eye Foundation Hospitals.
