Refractive errors are the main reason for blurry vision and forcing the affected individuals to seek out an ophthalmologist. Since human vision is perceived when the light is refracted within the eye, the refractive errors emerge when there is an optical imperfection preventing the light to fall properly on the retina.
Formation of Image in the Human Eye
Light has a bending property when traveling through a lens medium. When light travels through eye, it crosses the cornea, a curved frontal area of the eye. The cornea along with the eye lens, tear film, vitreous and aqueous humor bends the light to a precise direction needed for sharp vision.
If the vision is perfect, then the light focuses on the retina, a tissue consisting of photo-receptors, located at the back of the eye that captures light and transmits it to brain via optic nerve for image creation. Any improper refraction can make the vision blurry.
Why Refractive Errors Occur?
There are three major anatomical features of the eye that determine the ability of sharpness or refraction of the light traveling through the eye:
1. Overall Length of the Eye
The focusing of light is inter-dependent on the eye length, as too long a length can cause nearsightedness while too short a length can cause farsightedness. Due to abnormal length of the eye, the light either focuses on a point before the retina or after, respectively.
2. Curvature of the Cornea
Image can be refracted irregularly if the curvature of the cornea is not completely round, causing astigmatism.
3. Curvature of the Lens
The steepness of the curvature of the lens with respect to the length of the eye can cause refractive errors as well making vision blurry. Too steep a lens curvature causes nearsightedness while too flat a lens curvature causes farsightedness.
Types of Refractive Errors
There are three major types of refractive errors that can occur in the eye due to reasons discussed above:
1. Nearsightedness (Myopia)
In this refractive error, the length of the eye is too long and thus the light focuses in front of the retina instead of on the retina. This causes objects located far away to appear blurry while the objects nearby can be perceived clearly. In myopic eyes, the optical power exceeds the normal range and has to be reduced with the help of eyeglasses or contacts.
2. Farsightedness (Hyperopia)
In this type of refractive error, the length of the eye is too short and thus the light focuses behind the retina instead of on the retina. This causes objects located far away to be perceived clearly while the objects nearby appear blurry. In hyperopic eyes, the optical power is quite less than the normal range and reading glasses are prescribed at an early age. Farsighted people also suffer from myopia in the later age
In this type of refractive error, the curvature of the cornea varies from normality and is more curved in one direction than the other. This causes the eye to not focus the light equally leading to astigmatism. Astigmatism can either occur individually or with nearsightedness/farsightedness creating perfect vision blurry.
Treatment of Refractive Errors
The refractive errors can either be treated by eyeglasses or by contact lenses. The glasses are the simplest way for correction of refractive errors, while the contact lenses are a more popular option. Also another trend for treatment of refractive errors is the LASEK or LASIK surgery.