How is astigmatism diagnosed?

People usually complain of blurred vision or children may fail an eye test before they are diagnosed with astigmatism.

One or more of these four tests may be used to diagnose astigmatism and measure the severity.

Visual acuity test. It's the simplest yet most important part of an eye test. Using a standardised chart, patients read the letters they can see from six metres away. If your vision is 6/6, this means you can see at six metres what a normal eye can see from six metres. If your vision is 6/18, this means you can only see at six metres what a normal eye should be able to see from 18 metres away.

Refraction. The optometrist uses loose lenses or a lens machine (phoropter) to hold corrective lenses in front of your eye. He or she looks at the light reflex from your eye through a handheld device called a retinoscope to determine if any refractive error is present. You will then be offered different choices of lenses through the phoropter to refine the correction until you can see the vision chart clearly. After both eyes are measured, the optometrist will write a prescription for glasses based on which corrective lenses worked for you.

Keratometry. This machine measures the curvature of your central cornea. Corneas that have no astigmatism exhibit uniform or symmetrical curvature. Corneas with astigmatism do not have uniform curvature. The keratometer determines the steepest and the flattest curves. These measurements tell the optometrist about the shape of your cornea and its focusing power. The keratometer is also used to fit contact lenses and to monitor corneal curvature after eye surgery.

Corneal topography. This advanced technology provides the most detailed information about the shape of a cornea. The patient looks at a visual target while the device collects thousands of tiny measurements. A computer then constructs a colour map on the computer from the data. This corneal map allows the doctor to see a three-dimensional picture of your cornea. Such sophisticated measurements are important when planning refractive surgery and occasionally for fitting contact lenses.

What are the treatments for astigmatism?

Astigmatism can be corrected with glasses, contact lenses or surgery.

Glasses (spectacle) lenses are shaped to counteract the shape of the cornea that's causing blurred vision. Glasses work well when the person looks straight ahead, but depending on the specific correction, the glasses can make the floor appear to tilt. Some eye specialists argue that people with very small amounts of astigmatism are best left untreated. Patients with significant astigmatism usually adjust to their first pair of glasses within a week or so. If things remain unclear ask your eye specialist to recheck the prescription and verify the correction in your new glasses.