Kathryn Harris, a legal secretary in the District, wore hard contact lenses in high school even though she admits they hurt her eyes. "I would take them out at every opportunity," she said. "But I wore them because of vanity."

After another unsatisfactory attempt with hard lenses several years later, she walked into a shopping mall in 1979 and bought a pair of soft contacts from an optical store.

"I was immediately pleased," Harris said. "I didn't have an eye doctor at the time, and I wanted to get them quickly without the fuss and extra expense" of going to an ophthalmologist. Soft lenses, she said, are "one of the greatest inventions in the world, right up there with the birth control pill."

As Harris' experience indicates, the contact lens business has been transformed. Today contacts come in all varieties -- hard, semi-hard, soft, extended wear -- are more accessible and are just plain cheaper.

Since the mid-1970s, prices have been slashed in half as a result of vigorous competition among dispensers and manufacturers of lenses, according to a recent report by the Congressional Office of Technology Assessment. This competition is likely to continue, and prices will probably drop even more, OTA predicts.

According to industry figures, about 120 million Americans -- about half the population -- wear glasses. Sixteen million to 18 million use contact lenses, either exclusively or interchangeably with glasses.

While the percentage of the total population wearing glasses remained steady from 1966 to 1977 (about 47 percent), the percentage of people wearing contacts more than tripled during those years -- from 1 percent to 3.5 percent, according to OTA. Since 1977, the percentage of contact wearers has approximately doubled again, according to industry figures.

The introduction in 1971 of soft lenses, made from water-absorbing material, and in 1981 of extended-wear lenses, which can be worn for several weeks, made contacts more comfortable and convenient.

Adaption to hard lenses can be difficult, and as many as half the people fitted with them do not become long-term wearers. But soft lenses allow oxygen to reach the cornea -- the transparent covering over the eye's iris and pupil -- making them considerably more comfortable.

In 1978, about 50 percent of the lens-wearing population wore hard contacts. But by 1982, only 15 percent wore hard lenses, 75 percent wore soft lenses, and 10 percent wore a newer type, gas-permeable lenses, which are rigid like hard lenses but oxygen permeable like soft ones.

Alex Russell, director of product marketing for Bausch & Lomb, the largest manufacturer of soft lenses, said several factors have changed the lens industry.

One is that the cost of producing lenses has come down significantly in recent years. But a more important factor in price is the competition between eye care professionals who fit the lenses, Russell said.

"The biggest influence on the contact lens industry was the Federal Trade Commission ruling which allowed professionals to advertise their services," he said. "The cost of the contact lens is a relatively small part of the fee. It always has been."

According to the OTA, the wholesale cost of Bausch & Lomb's Soflens is $36 a pair; the extended-wear lenses are $40. The cost to the consumer, however, ranges from $100 to $300 a pair.

The actual amount a customer pays depends on where, and from whom, he purchases the contacts.

Diana Vega, who dispenses glasses and contact lenses at Sterling Optical on 10th Street NW, said her company is able to sell contacts at a discount -- $98 for extended-wear lenses and $78 for daily wear contact lenses -- because of the large volume they sell.

"We buy contacts in bulk and get a discount from the manufacturer, which we pass on to the consumer," she said. Sterling also advertises extensively in newspapers and on television. Last year the price for extended-wear lenses was $128, but a $98 sale price brought in so many customers that Sterling decided to keep the lower price, Vega said.

And $98 covers the cost of the eye exam by an optometrist, who is licensed to measure and fit corrective lenses, a year of follow-up care and the kit needed to carry the lenses.

The cost of getting contacts from an ophthalmologist, a medical doctor specializing in eye care, is as much as three to four times higher.

Dr. Neil F. Martin, a Silver Spring ophthalmologist, said the patient is paying for the care of a trained doctor. "You're not just buying the lenses, you're buying eye care," he said. "I've seen lots of problems caused by improperly fit or ill-selected lenses."

Vega said if a patient seems to have a serious problem or there is a question about an eye condition, he is referred to an opthalmologist or a consultation is made over the phone.

Prices have dropped for two other reasons: The increased number of lens wearers has helped lower distribution costs, and competion among lens manufacturers has forced prices down.

"There was a time when only one or two companies sold extended-wear lenses," said Robert V. Mahoney, vice president and treasurer of CooperVision, a company that helped popularize the extended-wear lens. "Now five or six big ones sell them as well as several small companies. I'm sure competition has helped decrease prices."

Lens marketing also has changed. Unlike glasses, contact lenses have traditionally been a product sold to young women age 18 to 34. Now marketers target men and older people, too.

"Ten to 15 years ago maybe it wasn't considered appropriate for men to be as publicly conscious of their appearance as it is today," said Russell. "Our advertising has been targeted at men in the past, and we expect that to continue."

Some sports-minded people use contacts to improve their performance.

Victor Marton, head of information for the Library of Congress' copyright office, said he got soft contacts about year ago just so he could jog.

"I couldn't stand my glasses fogging up when I ran," he said.

Marton, who runs an average of 50 miles a week, said he took 17 minutes off his time the first time he wore his contacts in a marathon "because I didn't have to stop and clean my glasses so I could see where I was going."

The introduction of bifocal contacts for older people and tinted, daily-wear lenses to enhance eye color has opened up other markets.

Later this year CooperVision plans to introduce extended-wear contacts in different colors, allowing people to change the color of their eyes for longer periods of time.

"If you let your imagination run wild, why not introduce tinted, extended-wear lenses for people who don't need vision correction at all," Mahoney said. "Maybe you'd like to have blue eyes, or purple eyes like Elizabeth Taylor. That possibility is much more a reality with an extended-wear product.

"We see our market not just as the 16 million to 18 million people who wear contacts, nor the 120 million who have vision problems," he said. "We see our market as everyone in the country."