The Internet is enticing a rapidly growing number of shoppers to make a very personal purchase, prescription eyeglasses, online. Deep discounts and greater variety are prompting many to try something new.

Customers can't pluck a pair of glasses from their smartphone screen to learn how they feel, but shoppers can try on frames virtually or have them delivered for a free test. They also can quickly scroll through hundreds of choices and send pictures to friends for a second-opinion.

Technology, however, hasn't erased all the advantages of buying glasses in a store. Here are some issues to consider before clicking on a pair of glasses and adding them to your virtual shopping cart.

1. What are some options for buying eyeglasses online?

A mix of websites sells eyewear in men's and women's styles, with some featuring well-known brands such as Oakley and Gucci. They include established vendors like Framesdirect.com and 39dollarglasses.com and more recent entrants like Warby Parker.

These sites let customers scroll through hundreds of options and styles in different colors. Some, like Framesdirect.com, allow visitors to upload pictures so they can see how a pair of glasses would look on their face.

Retailer 1-800-Contacts will offer a three-dimensional version of this concept next month, when it launches a free app that enables users to virtually try on glasses after taking a picture of their face with a smartphone or tablet.

The app will produce an image that is scaled so the glasses appear more like they would if the customer picked them off a store shelf. It will enable visitors to turn the image and slide the glasses up and down the nose. 1-800-Contacts runs the website Glasses.com.

2. What are the advantages of shopping online?

Virtual vendors can offer page after page of variety. Framesdirect.com, which dates back to 1996, says on its website that it carries more than 100,000 products and 500 brands.

Bargains also can be found online. The website 39dollarglasses.com features glasses that sell for — wait on it — $39. That price includes single-vision lenses and the frame.

Warby Parker advertises prescription glasses starting at $95. The company developed its own styles for men's and women's glasses, plus a monocle it sells for $50, in part because its founders thought prescription eyewear shouldn't cost $300 or more.

Of course, bargains are not limited to online vendors. Some Walmart stores offer prescription, single-vision lenses that start at $29.

Convenience can be another benefit. Warby Parker will send up to five pairs of glasses to a customer to try on at home for five days and then return with a pre-paid shipping label. 1-800-Contacts will send five frames and give customers seven days to try them.

"I think a lot of people feel that they need to touch and hold the frame before buying," said Neil Blumenthal, a Warby Parker co-founder.

3. What are the limitations?

Store visits connect customers with eyewear experts who can walk them through a purchase.

For instance, if customers wants rimless glasses, a store employee might point out that the lenses may be thicker than they anticipate to support the frame and could be uncomfortable to wear, said Sam Pierce, a trustee with the American Optometric Association. The employee also could tell a customer whether his or her prescription would fit properly in the style they want or whether the frame may be too big or too small.

The initial cost for glasses advertised on a website may be a bargain, but extra fees for a strong prescription or tinted lenses can add to the bill. Traditional eyewear stores also can bump up the amount a customer spends by pushing features like ant-smudge protection.

Some online companies also may charge shipping fees. Know the extra costs that come with a pair of glasses before buying.

Online shoppers also may want to do a little research on their vendor before buying glasses, since the customer can't simply drive to the store to talk to someone if a problem arises. Find out how the vendor handles adjustments to a prescription or returns. Some sites offer money-back guarantees on returns if the glasses are sent back within a certain time frame.

4. Will eyewear stores become obsolete?

Online sales eyewear sales jumped 31 percent from 2010 to last year, when they totaled $1.1 billion, according to The Vision Council, a trade group representing industry manufacturers and suppliers.

That's a big growth spurt, but online sales won't take over the industry soon. Last year, they represented just 4 percent of the roughly $27.5 billion eyewear product market.

In contrast, online sales for apparel and accessories totaled $36.3 billion, or 12 percent of that total market of $303.8 billion, according to Forrester Research Inc.

1-800-Contacts CEO Jonathan Coon said he thinks online eyewear sales can eventually reach and surpass the same percentage of its total market.

But Warby Parker's Blumenthal still sees a need for physical store locations that customers can visit. His company operates showrooms in New York, Chicago and Los Angeles, among other cities.

"We think there is always going to be some sort of balance there because humans are social creatures, and shopping is a form of entertainment, and it's not just about convenience," Blumenthal said.