- The Washington Times - Wednesday, May 21, 2003

Millions of Americans look through them every day, but many lack real insight into how eyeglasses are made and how they work. Eyeglass-wearing Bill White, however, knows the ins and outs of corrective lenses. As a lab manager of Homer Optical, a Silver Spring optical lens company, he says it’s his business to know.

“By surfacing the lens, we create a certain prescription,” Mr. White says.

Surfacing a lens refers to grinding the back side or back curve of a blank lens, one that is without a prescription. The front side of the lens, also referred to as the base curve, remains untouched, he says.

Grinding the lens so that the thickest part is the outer edge and the thinnest is the middle — making a concave shape — creates a minus lens designed for a nearsighted person.

If the outer edge is ground thinner than the middle of the lens — making a convex shape — the lens is a plus lens designed for a farsighted person.

When someone has a vision problem, whether it’s being nearsighted, farsighted or astigmatic, it means the eye is unable to focus an image, or light rays, onto the retina, says Dr. Mark Falls, an ophthalmologist with Inova Fairfax Hospital.

“The corrective lens changes, or bends, the light rays to focus on the retina,” Dr. Falls says.

In other words, the way the corrective lenses bend the light rays is what constitutes the prescription. The bending of the light is what neutralizes a person’s vision problem.

In nearsighted people, the eye focuses the light rays too soon, before they hit the retina. So the concave lens helps push the focus back to the retina by bending the light rays [or image], Dr. Falls says. The light will bend toward the thicker portion of the lens, and because the concave lens is thicker at its edge, this type of lens will spread the light from the center and move the focal point farther back.

When people are farsighted, the image generally falls behind the retina.

Astigmatism, which often accompanies farsightedness and nearsightedness, is also a condition in which the eye can’t focus the light rays onto the retina. Instead of focusing the light rays in one spot, an astigmatic eye focuses in two points.

Astigmatism occurs when the shape of the cornea has an irregular curvature, Dr. Falls says.

Corrective lenses for astigmatism also bend the light to land on the retina. These lenses are cut to have greater light-bending power in one direction in order to neutralize the astigmatism, creating only one focal point and pushing that point to the retina.

“The principle of all glasses is to focus the light ray on the retina,” Dr. Falls says.

Grinding, polishing, framing

Once an eye doctor has determined a patient’s prescription, that prescription is forwarded to a company such as Homer Optical, where the lens is ground.

First, Mr. White or one of his crew members feeds the prescription information, the material of the lens and the make of the blank lens into a computer program that determines exactly how the lens should be ground to achieve the prescription.

The material is important to take into consideration because different materials have different reflective indexes, meaning they bend the light rays to different degrees.

Most people nowadays choose lenses made out of some form of plastic because it’s lightweight, but glass is more durable, and Mr. White says some people still prefer glass.

Once the amount and angle of grinding needed have been determined, a piece of plastic sheeting is adhered to the front of the lens to protect it during the grinding process. The back part of the lens is ground in a machine called a cutter until the right shape of the back curve has been created.

The lens then goes through several stages of polishing and buffing to remove scratches and other irregularities created during the cutting.

“For smoothing out, we use a form of sandpaper,” Mr White says. “Later, for polishing, we use felt pads and polish to get a buffing action.”

Before the lens is sent to an optician for framing and other finishing work, its prescription is inspected using a lensometer, which shows if it has the right strength.

Blank lenses are about a quarter-inch thick and 2 inches in diameter. After the grinding and polishing, they still have the same diameter, but they are much thinner.

Generally, the stronger the prescription, the thicker the lens.

The ground lens then goes to an optician who does the framing, which includes cutting the lens to fit a patient’s desired frames.

“The size of the frames [and lenses] have to do with the patient’s preference,” says Kevin Beaver, an optician at Virginia Vision Associates in Arlington. Bigger frames and lenses don’t necessarily provide a better visual aide, Mr. Beaver says.

“Many people just want the thinnest and lightest frames,” he says.

Trees have leaves

The reason some people still prefer glasses over contact lenses is manifold, Dr. Falls says. “Some people like the way they look in glasses; others don’t like to stick their fingers in their eyes.”

Others have very dry eyes that will reject contact lenses or have inflammations in and around the eyes, he says.

“With the over-40 crowd that need reading glasses — they don’t like to switch back and forth — they find it easier just to wear bifocals,” he says. “If they had reading glasses, they would have to take them on and off.”

Some people also prefer glasses because they create a physical barrier, he says. Glasses protect the eyes better than contacts.

Vision changes over time, and sometimes a new prescription might be needed as often as once a year, Mr. Beaver says.

A person might not be aware of how much his or her vision has changed until he or she gets new glasses and thereby acquires 20/20 vision.

When someone has 20/20 vision, it means he or she can read the smallest letters on the eye chart from 20 feet away.

“Many people have an immediate response to their new glasses,” Mr. Beaver says. “They’ll say, ‘Wow, this is so much clearer.’”

Dr. Falls agrees. When he gets younger patients who have had a blurry view of the world for a long time and are trying their very first set of glasses, their responses can be pretty dramatic, he says.

“It’s a cliche, but some people say, ‘I didn’t know the trees had leaves on them.’”

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