Part 1 of 2: Why sunglasses are more than a fashion accessory.

It’s undeniable, isn’t it? Rock a great pair of sunglasses and look like a celebrity. Or at least look pretty hip. Ever since fighter pilots and movie stars started wearing them almost 80 years ago, sunglasses are our most visible fashion accessory and synonymous with cool.

But there are much more compelling reasons to wear sunglasses. In this two-part series, we’ll not only show you why you need a good pair of sunglasses for preventative eye care, but also how to find the perfect pair.

Let’s start with the medical side and why you need sunglasses for health reasons. We asked Christina Delany-Richardson, MD, an ophthalmologist at Davis Duehr Dean, for her thoughts. “When you’re outside, especially in summer months, sunglasses should be as mandatory as sunscreen. Aside from bringing bright outdoor light down to an acceptable level, good sunglasses provide true protection for your eyes and the delicate skin of your eyelids.”

If you don’t mind sunny days, maybe you’re asking, “What’s the big deal?” Two words should answer your question: Skin cancer. According to the Duke University Eye Center, instances of skin cancer of the eyelid are on the rise, and it’s not pretty. The condition may start with painless elevations, nodules or lesions. Sometimes they bleed, become irritated or crusted, and can distort the normal skin structure. In fact, people often think they have a sore that won’t heal when they actually have eyelid cancer. Yes, it’s treatable, but the complexities can be considerable.

So for the benefit of your eyelids and your eyes themselves, let’s go down a road called “An ounce of prevention is worth a pound of cure.” The main culprit here is UV radiation, and that’s what needs to be blocked.

UV is an invisible wavelength of light and causes all sorts of problems. Aside from contributing to skin cancer and cancers of the eye, UV is also thought to play a role in cataract formation.

There are two types: UVA and UVB.

• UVA (ultraviolet-A) has a longer wavelength and penetrates the skin and eyes more deeply. It’s considered the chief cause of long-term wrinkling, leathering and other aspects of photo-aging, and contributes to skin and eye cancers.

• UVB (ultraviolet-B) has a shorter wavelength and is more potent than UVA in causing sunburn and more obvious, immediate damage. These rays can be a significant cause of melanoma and eye damage.

In addition to invisible UV light, it’s important to block visible light, too. High-energy visible light (HEV light) is thought to play a role in macular degeneration, a disease that can lead to significant vision loss in some cases.

“You obviously notice the sun on a bright sunny day,” says Dr. Delany-Richardson. “But don’t forget bright reflective surfaces like water, sand and snow can be quite damaging, too. In some cases, a corneal burn is possible, and that’s something you definitely don’t want. That’s why you need sunglasses and a wide-brimmed hat or a baseball cap. Light conditions can change throughout the day, so always be prepared.”

What about overcast or mostly cloudy days? According to Dr. Delany-Richardson, “It’s just as important to wear them on those days, too. You might feel like you don’t need sunglasses, but remember, your perceptions are based on visible light alone. UV is invisible, and even on cloudy days, it’s still there. If sunglasses seem too dark, remember that you can also specify UV protection in your everyday glasses.”

Now get a load of this twist in the plot: “Your sunglasses should block 99 to 100 percent of UVA and UVB rays,” says Dr. Delany-Richardson. “If they don’t, they can actually do more harm than not wearing any sunglasses at all.”

Really? Why?

She explains: “While some sunglasses do restrict visible light, they might not block UV rays. Therefore, your pupils will be more dilated (opened up) because of the sunglasses, and if they allow UV rays to pass through, more of that damaging radiation will enter your eyes.”

OK, we’re convinced. From a medical standpoint, you need to wear sunglasses and they must block bright light and virtually all UV rays, period. Anything less is a compromise to the safety of your eyes and eyelids.

Next week, we’ll show you what to look for when you shop for your next pair.