Astigmatism

Defining Astigmatism

When a part or all of what you see is blurred, you are suffering from astigmatism. Rooted in the Greek “a” for without and “stigma” for point, the word literally means “without a point” which signifies that the focusing of light through the eye’s curved surface has no point of convergence on the retina to make an object register as sharp and detailed as it should. The loss of focus happens on objects seen at any distance and they all appear blurred. It’s a common visual impairment and it can be said that almost every adult has astigmatism in varying degrees. Some are so slight as to cause no vision problem.

Causes

Light entering an astigmatic eye can’t be focused uniformly on the retina. Rays going through the curved surface of the cornea get focused correctly while those going through a flattened or less curved part of the cornea will fail to focus. Astigmatism, is therefore, an error in refraction caused primarily by an irregularity in the curvature of the corneal surface so that light gets focused clearly on one plane but not so focused on another.  The net result is blurred vision at all distances and only one part could be clearly focused in as astigmatic eye.  It can be accompanied by other refraction problems such as farsightedness and nearsightedness. A severe or untreated chalazion condition on the eyelid that pushes against the corneal surface over a long period of time can also cause a temporary deformation of the corneal curve to cause astigmatism.

Symptoms and Diagnosis

Mild astigmatism generally do not have symptoms but the more severe ones cause blurry vision, easy fatigue, headache, squinting and asthenopia. Some studies even point to a link between the condition and a high incidence of migraine headaches. A severe degenerative eye disorder called keratoconus where the corneal curvature becomes more conical result in a substantial astigmatism complicated by distorted vision, multiple images and hypersensitivity to light.

The condition can easily be verified with vision tests carried out by optometrist and ophthalmologists. For starters, the standard Snellen chart will reveal diminished visual acuity.  A keratometer may be used to check the curvature for the flattest and steepest meridians in a cornea’s surface.  It can estimate the degree of astigmatism by getting the difference in power between these two meridians.  For a more objective estimate, a retinoscope or autorefractor can gauge the eye’s refractive error.  Using a trial frame or the Jackson cross cylinders in a phoropter can refine these measurements.

Dealing with Astigmatism

The condition was not identified until the 19th century. The first spectacles to correct astigmatism were presumably hand made and worn by Benjamin Franklin in 1784.  Indeed, the condition can be corrected with the use of eyeglasses and contacts.  A more invasive refractive surgery provides a more lasting solution. The choice is often dictated by one’s health condition, severity in refractive error and lifestyles.

The lens used to correct astigmatism takes on a slightly cylindrical form that is meant to compensate for the irregular corneal curvature. In doing so, the lens exhibit a higher light bending power in one direction than in the other. It tends to elongate images in one direction and truncate them in the other.

In astigmatic patients with mild keratoconus, toric contact lenses can achieve superior visual acuities than regular eyeglasses. They were once available online in rigid gas permeable form, but toric contacts now come as soft lenses.

In some cases, there’s an underlying cause in the deformation of the corneal surface, such as chalazion which can grow large enough to push against the eyeball’s surface and cause blurry vision.  Treat the chalazion and the astigmatism could well go away.

For some people with severe astigmatism or are bothered with a dependency on contacts or eyeglasses, the only lasting solution would be to undergo refractive eye surgery. There are various surgical methods for remodeling the cornea but the most widely used method today is excimer laser ablation.  The method reshapes the corneal curvature. These are outpatient procedures requiring only a local anesthetic eye drop. For instance, the Photorefractive Keratectomy (PRK) surgery reshapes the cornea by taking out microscopic tissues from the corneal stroma using computer assisted excimer laser. Another is the Laser Assisted Sub-Epithelium Keratomileusis (LASEK) that ablates the corneal stroma tissue under the corneal epithelium, a bit more painful in the healing process. According to the American Society of Cataract and Refractive Surgery, there have been close to a million refractive surgeries in the 2005.