Refractive Errors of the Eye
Definition
A refractive error is an error in the focusing of light by the eye and a frequent reason for reduced visual acuity.
Terms &Types
Emmetropia - no refractive error when viewing a distant object
Ametropia - refractive error when viewing a distant object
Myopia - the optics are too powerful for the length of the eyeball (this can arise from a cornea with too much curvature or an eyeball that is too long), images form a little in front of the retina
Hyperopia - the optics are too weak for the length of the eyeball (this can arise from a cornea with not enough curvature or an eyeball that is too short). images form a little beyond the retina
Refractive errors cause blurring of visioon.
Refractive errors are frequently categorized as spherical errors and cylindrical errors:
Spherical errors occur when the optical power of the eye is either too large or too small to focus light on the retina.
Cylindrical errors occur when the optical power of the eye is too powerful or too weak across one meridian of the optics - lens tends to become cylindrical along that meridian. The contours of a particular orientation are blurred, contours with orientations at right angles are clear.
Astigmatism : cylindrical error
Causes
Due to a combination of genetic and environmental factors, trauma or ocular disorders such as keratoconus
Correction
The refractive errors are treated or corrected by refraction ophthalmology : placing various types of lenses in front of the patient's eyes to determine which lens best improves the patient's vision
Cycloplegic agents are frequently used to more accurately determine the amount of refractive error, particularly in children.
Those who possess mild errors may elect to leave the condition uncorrected, particular if the patient is asymptomatic.
For those who are symptomatic, glasses, contact lenses, refractive surgery, or a combination of the three.
