Refractive errors such as blurred vision and difficulty focusing are optical imperfections that inhibit the eye from seeing properly. The predominant refractive errors are myopia (nearsightedness), hyperopia (farsightedness), and astigmatism.
Refractive errors are normally corrected with prescription glasses or contact lenses. For a permanent solution, refractive surgeries or LASIK can also be an option.
How Do the Eyes See?
Vision starts with reflecting light rays off an object and travels through the optical system of the eye where it is refracted and focused. To achieve a good vision, the point of focus must be on the retina. The retina is found on the back of the eye where light-sensitive cells (photoreceptors) are found. These photoreceptors capture images when exposed to light which is then transmitted to the optic nerve and to the brain for interpretation.
Similar to how the camera aperture adjusts the amount of light, the pupil of the eyes does the same as it constricts and dilates to adjust the amount of light that enters the retina. In dark conditions, the pupil dilates. In well-lit conditions, the pupil constricts.
Causes of Refractive Errors
The ability of the eye to properly refract or focus light on the retina relies on three anatomical features of the eye:
Eye length. If the eye is excessively long, light becomes focused even before it reaches the retina, leading to nearsightedness. Hence, if the eye is too short, light cannot be focused properly even by the time it reaches the retina, causing farsightedness.
Corneal curvature. If the cornea is not spherical, the image refracted or focused appears irregular, causing astigmatism.
Lens curvature. If the lens is sharply curved in relation to the eye length and corneal curvature, this causes nearsightedness. If the lens is extremely flat, the outcome is farsightedness.
More complex vision errors known as higher-order aberrations are also linked with how the light is refracted as it is transmitted in the optical system.
Diagnosis and Treatment of Refractive Errors
A refraction test may be done by your eye doctor to determine the type and degree of refractive error you may have. This may be done through a phoropter or automated refraction. The refraction results may help in discovering any other refractive errors you may have such as blurred vision caused by myopia and astigmatism.
These results may also be used to determine eyeglass prescription but not contact lens prescription which further requires a contact lens fitting.
Eyeglasses and contact lenses are built with precise curves to refract light to the appropriate degree required to compensate for refractive errors and deliver light to a crisp focus on the retina.
LASIK and other vision correction surgeries intend to correct refractive errors by altering the shape of the cornea to allow bending of light rays into a more accurate focus point on the retina.