Illustration: Lu Ting/GT

According to the Youth Daily, a recent survey at one local middle school found that about 6o percent of the female students had worn contact lenses and about 22 percent of these respondents said they wore contact lenses three or four times each week. Moreover, many of the contact lenses were colored contact lenses - lenses that appear to change the color of one's eyes and come in a variety of colors including blue, green, hazel and purple.

Although the survey only focused on one particular school, I believe this is far from an isolated case. It is not unusual in Shanghai to encounter teenagers, both girls and boys, wearing colored contact lenses (some of them are not only colored but also patterned) that match their school uniforms - which means they are wearing these lenses while attending school.

This is not a recent trend. When I was a sophomore, all of a sudden colored contact lenses were all the rage and I started to see some of my Chinese schoolmates with lighter-colored eyes. The cutest guy at my school, for example, would occasionally wear green contact lenses to class.

I cannot help wondering why colored contact lenses are not strictly banned from schools. There are plenty of prohibitions banning hair dye and perms, colored nails, and makeup - all adornments that exist solely for cosmetic purposes. Colored contact lenses - unlike conventional, transparent contact lenses, which teenage wearers have reason to use (i.e. they make in-school physical exercise more convenient) - undoubtedly belong to this category as they offer no practical benefits to a student's school life at all, assuming of course that he or she attends school for education rather than for dating or beauty contests.

What's more, colored contact lenses can be highly risky. First, just like any contact lenses, they can lead to eye infections and corneal ulcers. According to opticians, these students are at greater danger as adolescents' immature eyes are more sensitive and vulnerable than an adult's.

Secondly, there has been endless media exposure of sub-standard colored contact lenses sold in Shanghai. According to a series of news reports, some vendors buy a large number of transparent contact lenses, dye them to colored ones at home and repackage them. Unsurprisingly, shoddy colored contact lenses far outnumber certified products at local markets. Opticians said some victims of shoddy lenses were found with "permanent tinted retinas" as the dyes in the lenses leached out and could not be washed away.

By banning colored contact lenses, schools can at least make sure that their students are not wearing them most of the time - opticians noted that regular wearers are at far greater risk.

Some might argue schools in which colored contact lenses are widely popular tend to be vocational or underperforming schools whose students are regarded as less observant of rules and guidelines, and therefore a ban might have little effect - teenage pregnancy is not uncommon in such schools even though sex education is implemented, they point out.

However, sex education does not ban unprotected sex, and even if schools were to officially ban this particular behavior, common knowledge tells us that generally, students hook up off campus where school rules cannot be enforced.

The case of colored contact lenses is different. Teachers not only have the responsibility, but also the ability, to identify rule-breakers and ask them to conform. Therefore, instead of doubting whether a ban will be effective, let's stop as many cases as possible.