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Over 25% of the world’s population wears glasses to correct vision problems caused by a refractive error. Refraction is the bending of light rays as they pass through one object to another. In the eye, the cornea and lens bend light rays to focus them on the retina, the nerve layer at the back of the eye. The cornea in the front of the eye provides approximately 70% of the focusing power of the eye, the other 30% is from the lens inside the eye. The lens is flexible and changes shape to allow the focus to change depending on the distance of the objects we are looking at. Clear vision is achieved when the cornea and lens, in combination, focus light directly onto the retina. If the light does not land correctly on the retina, a refractive error occurs, resulting in unclear or blurred vision. TYPES OF REFRACTIVE ERRORS The four most common refractive errors are myopia (shortsightedness), hyperopia (farsightedness), astigmatism and presbyopia. Affecting about 22% of the global population, myopia is a common refractive error. The light entering the eye is focused before reaching the retina rather than on the retina itself. It occurs as a result of the eye being too long or the cornea and/or lens too curved for the length of the eye. People with myopia have difficulty seeing distant images clearly, but objects close up will be in focus. They may experience eye strain or headaches and may squint when trying to focus on far objects. |
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Hyperopia has a prevalence of about 10% in the world. Due to the eye being too short in length, a lens or cornea which is flatter than normal or the lens being in an unusual position in the eye, light entering the eye is focused on a point behind the retina. Images in the distance will be seen clearly, while near objects will appear blurred. Eye strain or headaches may occur after reading or doing close work. |
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The most common refractive error worldwide is astigmatism, which occurs when the cornea or lens has an irregular curvature — more like a rugby ball than a perfectly round soccer ball. Because of this uneven shape, light entering the eye cannot focus evenly on the retina, resulting in blurred or distorted vision at all distances. People with astigmatism may also experience eye strain, headaches, double vision, or difficulty seeing clearly at night. |
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As we age, the natural lens of the eye gradually loses its flexibility and ability to adjust focus. This condition, known as presbyopia, makes it harder to see objects clearly at close range. Many people notice the change when reading — especially in dim light — and often find themselves holding books, phones, or other material farther away to bring the words into focus. It is a completely normal part of aging and typically begins to affect people in their early to mid-40s. Thankfully, presbyopia can be easily managed with solutions such as reading glasses, multifocal lenses, or contact lenses. |
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CAUSES AND RISK FACTORS Refractive errors can be caused by several factors, including the shape of the cornea, the length of the eyeball, inability of the lens to adequately change focus, and changes in the lens, especially with age. Anyone can have a refractive error, but there is a higher risk if there are family members who wear glasses or contact lenses. Genetics has been found to play a significant role in the development of myopia and astigmatism. A number of additional factors are thought to contribute to the alarming increase in myopia in children over recent years, including extended periods of time spent looking at screens, too much time spent indoors and insufficient outdoor time. Hyperopia can develop as a result of congenital defects in the eye, injury, conditions such as diabetes and certain medications. |
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DIAGNOSIS AND TREATMENT Refractive errors are diagnosed as part of a comprehensive eye examination by your optometrist, who will measure the focusing ability of the eyes, as well as both close and distance vision. To check for other eye problems, the pupils may be dilated with eye drops, so that the optometrist can clearly observe the retina and the back of the eye. Accurately diagnosing astigmatism may involve specific tests to examine the curvature of the cornea. Once the prescription is determined, a decision will be made regarding management. Refractive errors are corrected with glasses, contact lenses or refractive surgery. For hyperopia, glasses may only be necessary for close work or reading. If presbyopia is accompanied by other refractive errors, reading glasses, bifocals or multifocals may be an option, depending on your specific needs. Presbyopia can also be treated with surgical insertion of intraocular lenses and corrective laser surgery. Refractive laser surgery can change the shape of the cornea and is an effective option for adults who would like to correct their myopia permanently and eliminate the need for glasses or contact lenses. It is usually only recommended for adults whose prescription has remained stable for over 2 years. High levels of myopia have been linked to the development of glaucoma, retinal detachment and cataracts later in life. A personalised programme of myopia management may be recommended to slow or prevent the progression of myopia. This may be accomplished through various methods, including ortho-k contact lenses, multifocal lenses or atropine eye drops. Treatment for astigmatism includes contact lenses and glasses that address the particular curvature of the cornea. Occasionally, custom-made contact lenses or RGP lenses might be necessary to provide clear and comfortable vision. |
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Some people may not notice the symptoms of refractive errors or be unaware that their vision is not the same as other people’s. It is important to have regular eye examinations, not only for the correction of refractive errors, but to detect other vision conditions for which symptoms are not yet noticeable. The earlier problems are diagnosed, the sooner they can be managed and the better the long-term outcome will be. Encourage family members to have their eyes examined, as many vision conditions can run in families. |
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