Dr. Thomas Clark of Colchester poses with his patented measuring prototype at his office, Williston Optometry, on September 23. The device allows optometrists to more accurately measure prescriptions for bifocal contact lenses. He’s currently in talks to have it manufactured in China. (Photo by Kaylee Sullivan)

Colchester resident Dr. Thomas Clark is improving people’s vision by looking at optometry with a different perspective, or through a different lens.

Clark, the optometrist at Williston Optometry, has two patents. Patented in 2009, the first is a measuring device for bifocals, and the second is a verification device. Together, they make what he coined as the “Clark Visual Axis Measuring System.”

The system is meant to make wearing bifocal lenses more comfortable for patients. It uses a different axis in the eye than the industry standard to measure a patient’s prescription to a more exact number, changing the process from subjective to objective.

A patient lifts the patented prototype machine to his or her eyes and slides two panels to shift a circle into the middle of their line of vision, Clark demonstrated. The measurement it produces is used to calculate the prescription.

Clark investigated this new system because he saw a high number of patients who were unhappy with bifocals. Most patients didn’t know there was a better way to fix discomfort with their lenses.

“You don’t know what you don’t know,” he said. “If you’re wearing the same pair of shoes for 10 years, you don’t know that there’s shoes that are three times more comfortable.”

Clark said the same thing goes for glasses. When patients take advantage of his system, 90 percent of them are satisfied, showed a study he conducted with 57 of his patients.

The number of people who come back for a second bifocal fitting also decreases with Clark’s system, as 65 percent of the patients studied adapted to their new bifocals in one day.

After thorough research, Clark focused on a common biometric difference people have in their eyes called angle kappa, or the angle between two axes in the eye.

Most people are unaware this issue exists, he said, so they have trouble with their bifocal prescriptions because other optometrists don’t take the angle kappa into account.

Once a patient is fitted using the measuring device prototype, the system’s second product is used: The verification device patented in August 2015.   

While looking at a measurement card, the device is used – a pair of glasses with a laser that marks a line on the card – to verify the measurement. If the patient does not have to shift his or head to get the laser to mark a line on the correct focal point, then the prescription is correct.

If a head shift does occur, then a segment placement error exists, and he re-does the measurement from step number one, he explained.


Kelly Quinlan, optician at Williston Optometry, demonstrates the first installation of the “Clark Visual Axis Measuring System,” which helps better patient’s bifocal lenses. (Photo by Kaylee Sullivan)

Three eye doctors – two in the United States and one in Canada- are using Clark’s method. Clark is also in negotiation with individuals in China about manufacturing his system, he said.

Clark said he is the only one who has focused on the biometric issue because people assume the followed norm is correct.

“There’s disconnect between what the optical lens people do and what the medical optometrist people do,” he said, noting that some people don’t understand the optics of how a lens is placed.

Clark usually places bifocals on people over age 40 who need a reading component to their glasses.

Kelly Quinlan, optician at Williston Optometry, attested that effectiveness and patient satisfaction has increased with the patents. She said many people have bad experiences with bifocal lenses and are surprised when Clark can correct their lenses.

“You’re investing in a very expensive pair of lens, and if it’s not measured properly, you’re not going to get the benefits of it,” she said.