Astigmatism

 

Astigmatism is simply a type of refractive error or vision condition, which causes blurry, fuzzy or distorted vision.  

Cause

Astigmatism is a condition caused by subtle flaws in the way your eye bends light (a process called refraction) that passes to the retina, the light-sensitive area at the back of the eyeball. The optic nerve transmits nerve impulses from the retina to the brain, which translates them into eyesight.

If your vision works properly, your cornea and the lens behind it refract light into the retina. Alas, imperfections in the curvature of the cornea or the lens (or both) can prevent images from properly focusing on the retina. The brain perceives these ocular foul-ups as unclear or distorted images.

Astigmatism is one of the three most common kinds of refractive error. You’ve most likely heard of the other two: myopia (nearsightedness) and hyperopia (farsightedness).

Your cornea is a transparent dome covering the front surface of the eye. It’s curved like the lens on a telescope or camera. A perfectly curved cornea and natural lens focus light signals on the retina to produce crisp, clear vision in the brain.

Unfortunately, corneas and lenses may have imperfect curves that interfere with refraction, generating the fuzzy or distorted vision that we call astigmatism. Defects in other structures within the eye may also contribute to astigmatism. 

Symptoms

Common signs and symptoms of astigmatism include:

• Squinting
• Blurred or distorted vision at all distances
• Poor night vision
• Double vision in one or both eyes
• Eyestrain
• Headaches

Diagnosis

During a vision test, your eye doctor will scan your eyeball to measure its entire surface in three dimensions. Sections of the eye called meridians help your eye doctor identify high and low spots on the cornea that generate astigmatism. A measurement called a diopter estimates how much refraction happens in each meridian.

The meridians of the eye look like the face of a traditional clock. One meridian, for example, is the line connecting the 6 (bottom) to the 12 (top). Another meridian is the line from 9 (left) to 3 (right).

Eye doctors assess the differences between the meridians of the eye to determine the proper prescription to produce clear vision. Tests such as a retinoscopy involve shining a light in your eye while you look through different lenses until your doctor finds one that best clarifies your eyesight. 

Astigmatism in children

Babies are often born with astigmatism, though it generally clears up within the first year. Few children show signs of astigmatism by the time they’re 5 to 9 years old.

However, some children do not outgrow their astigmatism, and uncorrected astigmatism can negatively impact learning and development.

Thus, it is important to schedule regular eye exams for children in order to detect astigmatism and/or other uncorrected refractive errors.

Types of astigmatism

Astigmatism has three primary classifications, defined by the principal meridians (the steepest and flattest meridians of the eye).

• Myopic astigmatism: Principal meridians of the eye are nearsighted (myopia + astigmatism).
• Hyperopic astigmatism: Principal meridians are farsighted (hyperopia + astigmatism).
• Mixed astigmatism: Principal meridians are both near and farsighted (astigmatism is the primary refractive error).

You may also see astigmatism described as:

• Corneal: Defects in the cornea.
• Lenticular: Defects in the lens of the eye. 
• Regular: Principal meridians are perpendicular (90 degrees apart).
• Irregular: Principal meridians are not perpendicular (sometimes caused by injuries and scarring of the cornea). Keratoconus, a long-term thinning of the cornea, and some forms of eye surgery also can cause irregular astigmatism.

CONTACT US AT PREMIUM OPTICALS AND EYECLINIC FOR MORE INFORMATION.