Refractive Errors: Myopia, Hyperopia, and Astigmatism
What is a Refractive Error?
A refractive error is a problem with the shape of the eye that prevents it from accurately focusing light on the retina. It is not a disease but a physical condition of the eye. The three main components that determine an eye's focusing power are the length of the eyeball, the curvature of the cornea, and the flexibility of the lens. When any of these are not in a precise balance, a refractive error occurs.
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Myopia (Nearsightedness)
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Myopia occurs when the eyeball is too long or the cornea is too curved. This causes light to focus in front of the retina instead of directly on it. As a result, distant objects appear blurry, while near objects remain clear. Myopia is a very common condition, often developing during childhood and stabilizing in early adulthood.
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Hyperopia (Farsightedness)
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Hyperopia occurs when the eyeball is too short or the cornea is not curved enough. This causes light to focus behind the retina. Individuals with hyperopia can often see distant objects clearly, but near objects appear blurry. Young people with mild hyperopia may not experience symptoms, as their eyes can compensate through a process called accommodation.
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Astigmatism
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Astigmatism is caused by an irregularly shaped cornea or lens, which is shaped more like a football than a basketball. This irregular shape causes light to scatter and focus on multiple points on the retina instead of a single point. As a result, vision is blurred or distorted at all distances. Astigmatism often occurs in combination with myopia or hyperopia.
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Refractive Errors Symptoms
The most common symptom of a refractive error is blurred vision. Other symptoms can include:
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Difficulty reading or seeing fine details
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Eye strain or fatigue
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Headaches
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Squinting to see clearly
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Haloes around lights, especially at night
Causes of Refractive Errors
The exact causes are not fully understood, but genetics and environmental factors play a significant role. Refractive errors often run in families, suggesting a strong hereditary component. Additionally, certain environmental factors, such as prolonged near-focus activities (reading, screen time), may contribute to the development of myopia.
Diagnosis of Refractive Errors
Refractive errors are diagnosed during a standard comprehensive eye examination by an ophthalmologist. The process typically involves:
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Visual Acuity Test: Measures how well you see at various distances.
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Autorefractor: An automated test that measures how light changes as it enters your eye to provide an objective estimate of your refractive error.
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Keratometry: Measures the curvature of your cornea to detect astigmatism.
Management and Treatments
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Glasses or Contact Lenses Correction
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This is the most common and accessible method of vision correction. Glasses and contact lenses work by using corrective lenses to redirect light onto the retina, compensating for the eye's refractive error.
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Myopia Prevention
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While there is no definitive way to prevent myopia, some strategies are being explored to slow its progression in children. These include:
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Spending time outdoors: Increased time spent outdoors may help to reduce the risk of myopia progression.
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Limiting screen time: Reducing prolonged near-focus activities, especially on digital devices.
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Specialty contact lenses: Certain types of contact lenses or spectacles are designed to slow the progression of myopia in children.
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Eye drops: Atropine eye drops, in low concentrations, may be prescribed to slow myopia progression.
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Refractive Surgery
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For those who wish to reduce or eliminate their dependence on glasses or contacts, refractive surgery offers a permanent solution. Procedures like LASIK and ICL surgery precisely correct the eye's focusing ability, providing a clear vision. It is important to note that a thorough examination is required to determine eligibility for these procedures.
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Kobe iClinic
Dr. Daiki Sakai, MD