Astigmatism refers to an imperfect curvature of the eye that results in a defocused or blurred image. Astigmatism is not a disease; it is a type of refractive error that can be present along with other refractive errors, such as nearsightedness (myopia) or farsightedness (hyperopia). Refractive error occurs when the eye is unable to focus light into a single point. The focusing power of the eye is determined by a combined interaction of the cornea, the clear front surface of the eye, and the lens inside the eye. Astigmatism typically occurs in the cornea but can also occur in the lens as well.
Individuals without astigmatism have a smooth spherical cornea shaped like a round basketball. Alternatively, individuals with astigmatism have an oblong-shaped cornea – more like a football – with images focused to 2 different points resulting in distorted vision. Symptoms of astigmatism can vary from distorted or blurred vision to eyestrain, squinting, and headaches. Anyone experiencing these symptoms should see an eye care provider, such as an optometrist or ophthalmologist, for a complete eye examination. During an eye exam, astigmatism can be easily determined by refraction, or an individual’s prescription. A corneal topography, which displays the overall corneal shape and power, may be performed. Large amounts of worsening astigmatism can rarely occur due to a condition called keratoconus.
For individuals with astigmatism, correction can be achieved with prescription glasses, contact lenses, or refractive surgery. Prescription glasses and soft contact lenses for astigmatism, or Toric lenses, have an additional cylinder component in the refraction. This cylinder specifies an axis in which greater bending of light is required to achieve optimal focus for good vision. For individuals with high astigmatism or keratoconus, rigid gas permeable lenses are an excellent option. Refractive surgery, such as LASIK or PRK, is also a safe option for those who have stable astigmatism and meet the criteria for the procedure.
Older individuals with cataracts have other options to surgically correct astigmatism at the time of cataract surgery. An accurate measurement of the magnitude and location of astigmatism is critical in achieving the optimal outcome after surgery. For low amounts of astigmatism, “limbal relaxing incisions” can be made into the peripheral cornea. These incisions have traditionally been performed with a diamond knife, but more recently, a laser has come into favor due to improved precision. For moderate to higher amounts of astigmatism, specially designed lens implants called Toric intraocular lens implants can be inserted into the eye to obtain excellent vision.
Astigmatism may slowly increase with age, and this is why it is important to have regular eye exams done to ensure and maintain good vision.