Definition and Overview
Refractive errors refer to vision problems that occur when the eye’s ability to bend light correctly is compromised. This can develop if the shape of the cornea or length of the eyeball is abnormal. Refractive errors prevent people from focusing their sight properly.
The following are the most common types of refractive errors:
Myopia - Characterised by having clear vision up close but blurred vision when the object is far away. It is also called nearsightedness.
Hyperopia - Characterised by having clear vision at far distances but blurred vision when the object is up close. It is also called farsightedness.
Presbyopia - This condition affects the elderly. It is defined as farsightedness caused by loss of elasticity of the eye lens.
Astigmatism - A condition wherein the eye does not focus evenly, resulting in blurred or stretched images regardless of the distance. It is caused by problems with the cornea.
Causes of Condition
Refractive errors are generally caused by hereditary factors. Contrary to popular belief, they are not acquired due to overuse of the eyes. The exact causative factors differ depending on the type of refractive problem.
Myopia or nearsightedness is an inherited condition that usually begins early in childhood and continues to progress until teenage years. It develops when the eyeball is longer than normal.
Hereditary factors are also responsible for the development of hyperopia. The opposite of myopia, hyperopia develops when the eyeball is shorter than normal. This condition tends to lessen in severity as the patient enters adulthood.
Astigmatism is also hereditary. It usually develops in patients whose cornea is asymmetrically curved or has an incorrect shape. In a normal person, the cornea is curved equally in all directions. However, in some patients, the cornea curves abnormally toward one direction, causing distortion in the patient’s vision.
Of the four most common refractive errors, presbyopia is the most unique, as it is partially caused by ageing. As a person ages, the lens of the eye loses its ability to modify its shape to allow the eye to focus clearly.
Patients who suffer from refractive errors tend to experience the following symptoms:
Blurred or double vision
Who to See and Types of Treatments Available
Patients who notice any of the above symptoms or find that their eyesight is no longer as clear as before should consult an eye specialist.
Ophthalmologist - Ophthalmologists are highly qualified eye doctors with at least eight years of medical training. They can diagnose and treat all eye diseases and are licensed to perform eye surgery.
Optometrist - Optometrists can diagnose, treat, and manage vision changes, but they are not medical doctors. Their scope of responsibility is limited to performing eye exams and vision tests, prescribing corrective eyeglasses or lenses, and prescribing medications for some eye diseases. However, they do not treat all eye diseases and have to refer certain patients to an ophthalmologist when necessary.
Optician - An optician is responsible for designing and fitting eyeglasses and contact lenses for patients who need them. They rely on prescriptions provided by ophthalmologists and optometrists. They are not allowed to diagnose, treat, or make prescriptions on their own.
Since refractive errors can be corrected using eyeglasses and contact lenses, patients who suffer from such problems can go to either an ophthalmologist or optometrist for treatment. These eye care providers use a comprehensive eye examination to diagnose refractive errors. This is performed by asking patients to read a special vision chart. In most cases, this is sufficient to make a diagnosis.
After consultation, patients are referred to an optician for the preparation of corrective lenses. The first line of treatment is the use of eyeglasses, which provide the safest and simplest way to give patients optimal vision despite their refractive errors.
The second best option is to use contact lenses, which serve as the first refractive surface for the eyes. These lenses compensate for the irregularities in the shape or length of the eyeballs, allowing light to bend more precisely. They are highly effective in providing better focus for patients with refractive errors. They also hold several key benefits over eyeglasses, providing not only clearer vision but also a wider field of vision and unhindered peripheral vision. Many patients also find them more comfortable to use, as long as they are fitted properly. Contact lenses, however, are more sensitive. They should be used and handled with care. Patients need to be instructed carefully on how to use them to reduce any risks, such as the risk of infection. People who use contact lenses need to wash and dry their hands thoroughly before wearing the lenses. They also need to clean the lenses with a sterile solution prior to putting them on.
The last resort for the treatment of refractive errors is refractive surgery. This refers to surgical procedures designed to change the shape of the cornea for good, allowing light rays to bend properly as they hit the retina. This can restore the eye’s ability to see and focus clearly.
McCarty CA. “Uncorrected refractive error.” Br J Ophthalmol. 2006 May; 90(5): 521-522. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1857030/
Sewunet SA, Aredo KK, Gedefew M. “Uncorrected refractive error and associated factors among primary school children in Debre Markos District, Northwest Ethiopia. BMC Opthalmol. 2014; 14:95. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4120723/
Cochrane GM, Le Mesurier RT. “Management of refractive errors.” BMJ. 2010; 340:c1711. http://www.bmj .com/content/340/bmj.c1711