# How Optometrists Use Math in their Careers

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Optometrists need more than good interpersonal skills and knowledge of eye anatomy to be successful in their field. You also need solid math abilities. You don’t have to be a genius who creates formulas to figure out how fast the universe is expanding. You do have to carry out calculations related to how light bends as it passes through substances, including the various materials used for eyeglasses and contact lenses, and the human cornea and lens.

## Calculating a Basic Prescription

When a person doesn’t have 20/20 -- or perfect -- vision, it’s because there is something less than perfect about the shape of his eyes. For example, his eyeball may be elongated or lack depth. These imperfections skew the focal point of light rays entering the eye -- just like when a projector is too close or too far from the screen. This is called a refractive error. Optometrists use a phoropter machine to measure refractive errors, and they calculate a lens prescription based on these readings. Because most exam rooms are not 20 feet long, optometrists also use math to program the phoropter or to manually adjust the readings to account for the distance between the patient and the screen when calculating a 20/20 correction.

## Correcting Astigmatism

Astigmatism, the most common vision problem, occurs when the cornea -- the clear covering over the eye -- is not perfectly spherical. This creates two images on the retina instead of one, which causes eye fatigue, headaches and blurred vision. Optometrists measure this corneal abnormality and use math to create a prescription that includes directions for a special curve in the corrective lens. The formula must include the steepness and the orientation of the curve on the lens, expressed in the degrees of a circle.

## Compensating for Presbyopia

The aging process causes the lens to lose its ability to bend, which makes it harder to see up close. So people beyond the age of 40 need a complex prescription that provides multiple levels of correction -- near, intermediate and distance -- to compensate for this decreased flexibility. For these patients, optometrists use math to first determine the distance prescription, then conduct additional tests to calculate an adjustment to this correction for close-range objects -- essentially adding the reading prescription to the distance correction.

## Prescribing Medication

Patients sometimes have eye injuries, infections or diseases, such as glaucoma, that require medication. The optometrist must calculate the proper dosage based on the patient’s age and weight, and take into account any medical conditions that would require a milder dosage, such as liver or kidney disease.

## Running a Private Practice

Many optometrists work in a private practice that they own, either alone or in partnership with other optometrists. They use math to calculate their profit-to-expense ratio and to make basic business decisions. For example, they must determine how much they can afford to pay employees or whether the price of a new piece of equipment will be offset by the increased efficiency and savings in other areas.

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A retired federal senior executive currently working as a management consultant and communications expert, Mary Bauer has written and edited for senior U.S. government audiences, including the White House, since 1984. She holds a Master of Arts in French from George Mason University and a Bachelor of Arts in English, French and international relations from Aquinas College.

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