Astigmatism causes blurry vision that an eye doctor can correct with the proper eyeglass prescription. During an examination, the doctor will have the patient look through a phoropter, a flat machine that sits against the patients face. The doctor will show the patient various choices in order to determine the proper prescription to correct the astigmatism. However, the doctor may have a difficult time correcting some types of astigmatism, and this depends heavily on the cause.
Natural Shape
Many people are born with an astigmatism, which is not a disease, but refers most often to the shape of the cornea, the front window of the eye. In an eye without astigmatism, the cornea will have a rounded shape, much like a basketball. An eye with astigmatism has a cornea in a more oblong, or football shape.
Good vision begins with the light entering the eye. It passes through the cornea, then through the natural lens inside the eye, landing on the retina. Once the retina passes the light information to the optic nerve and onto the brain, the initial light that passed through the cornea becomes a visual image. Astigmatism may disrupt the image. People can have varying amounts of astigmatism, and higher amounts will cause more distortion in vision, says the American Optometric Association. Eyeglass prescriptions will often correct natural astigmatism.
Disease
Some people may have astigmatism caused by a corneal condition called keratoconus. This condition causes the cornea to thin and bulge out away from the eye, gradually forming a cone shape, states the National Eye Institute. The condition often occurs in both eyes, and in the beginning, doctors can resolve the astigmatism with an eyeglass prescription. As keratoconus continues to disrupt the shape of the cornea, an eye doctor will recommend using special contact lenses to help with vision and reduce distortion. Some people experience corneal scarring from the condition, and in such cases, a doctor may recommend a corneal transplant.
Surgery
Eye surgeons perform corneal transplants to restore lost vision from corneal scarring. The procedure, however, often results in significant astigmatism. Corneal healing after a transplant may take a year, or even longer, explains Indiana University's School of Optometry. In that time, the astigmatism and overall eye glass prescription may change multiple times. Some corneal transplant patients will require special contact lenses to reduce visual distortion, though most doctors recommend waiting three or more months before fitting the special lenses. This allows the corneal graft to take hold and begin the healing process.
