Refractive Errors
- Feb 25
- 3 min read
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Refractive Errors: Understanding Common Prescriptive Issues
Refractive errors are among the most common causes of blurred vision. They occur when the shape of the cornea or length of the eyeball prevents light from focusing directly and sharply on the retina, or when the natural lens in the eye loses the ability to adjust focus, resulting in unclear images. The four main types are myopia, hyperopia, astigmatism, and presbyopia.
Myopia (Near-Sightedness)
Myopia, also known as short-sightedness or near-sightedness, causes distant objects to appear blurry while near objects remain clear. This typically happens because the eye ball is too long or the cornea is too curved, causing light to focus in front of the retina rather than directly on it. Myopia often begins in childhood and may gradually progress over time through to adulthood.
There have been much research into myopia causes and prevention. High myopia is a risk factor for sight-threatening eye conditions such as retinal detachment,
Hyperopia (Far-Sightedness)
Hyperopia, also known as long-sightedness or far-sightedness, can cause near objects to appear blurry, while distant vision may be clearer with effort. It occurs when the eye is too short or the cornea is too flat, causing light to focus behind the retina. Mild hyperopia may go unnoticed in younger individuals because the eye can compensate by adjusting its focus.
Astigmatism
Astigmatism results from an irregular curvature of the cornea or the lens inside the eye. Instead of being perfectly roundish or spherical, the surface is shaped more like a rugby ball, causing light to focus across multiple points in the eye. This leads to a mild double-vision feeling or distorted vision at all distances and may occur alongside myopia or hyperopia.
Presbyopia
Presbyopia is an age-related condition that typically begins after age 40. Over time, the natural lens inside the eye loses flexibility, making it difficult to focus on close objects. People with presbyopia often notice they need to hold theiir mobile phones or reading material further away to see more clearly, or use excessive amounts of effort to 'strain' to see near objects.
Sudden Changes in Vision: When to Seek Evaluation
Gradual changes in refractive error are common and usually not concerning. However, sudden or significant changes in vision should always be evaluated by an eye doctor (also known as an ophthalmologist).
Rapid shifts in prescription may signal underlying issues such as diabetes, cataracts, corneal problems, or other eye conditions. Sudden blurred vision, distortion, or vision loss requires prompt medical attention.
The Importance of Best Corrected Visual Acuity
While an optical store or optician may do a refraction (i.e. 'test your eye degree or eye power') in order to make spectacles or fit you with contact lenses, we often do the refraction in order to find how well you can see. We call this Best-Corrected Visual Acuity (BCVA).
Best corrected visual acuity (BCVA) refers to the sharpest vision a person can achieve with the appropriate glasses prescription.
If vision improves to normal levels with correction, the issue is likely due to refractive error alone. However, if vision does not fully improve even with the correct prescription, this may indicate an underlying eye condition affecting one of the eye structures - for instance a retinal issue, bleeding in the eye, or cataracts.
Therefore, measuring BCVA helps distinguish between simple refractive errors and potentially more serious eye health concerns.
Regular comprehensive eye examinations are essential for maintaining clear vision and detecting underlying eye disease early - so visit your ophthalmology clinic today!
