What is Refractive Error?

By Laurel Quinn, MD | June 29, 2018, 4:43 p.m. (ET)

Triathletes love gear and crunching numbers, but there are some numbers most don’t enjoy: the refraction exam that determines the power of your eyeglasses.

“Better one? Or better two?” Frustrating.

The National Eye Institute estimates that 60 percent of Americans have refractive error. This means that in addition to the long list of gear and wardrobe changes all triathletes have to consider, those with refractive error also need a training and race plan for clear vision. 

The Basics

Refractive error is a mismatch between the power of your eye and the length of your eye. If the light ray-bending power of your eye exactly matches the length of your eyeball, the light rays entering your eye will all come together in focus at your retina (the back wall of your eye) and you will see clearly without any help.

If your eye is too powerful compared to its length, the light rays will come together in front of your retina and you will need a lens with a negative optical power to shift the focal point of the light rays further back so it lands on your retina.

If your eyeball power is not strong enough to bend the light rays into focus by the time they hit your retina, you need additional positive lens power to bend the light rays more and get them to come together sooner to get them to hit your retina in focus.

The power of your eye for bending light rays is determined by several factors, an important one being the amount of curvature of your cornea (the front surface of your eye).

Astigmatism is another common type of refractive error, where light rays coming into the eye on different axes are bent different amounts due to the surface of the eye not being perfectly round (being more curved on one axis and flatter on another). A lens of a special shape is then needed to compensate and get all of the light rays into focus together.

What does this mean for triathletes?

Almost everybody will have some degree of refractive error at some time in their life because the physical factors that dictate eyeball power change as a person grows and ages. If you need some optical assistance to get your incoming light rays in focus for clear vision, what are your options for dealing with that during workouts or on race day?

One option is to have refractive correction built into sunglasses which are great for cycling and running to keep sun, wind and bugs out of your eyes. 

But what about the swim? 

Adults have several options that work well in the water. Many of us have been fortunate enough to have successful refractive surgery. I had LASIK (laser in-situ keratomileusis) and my husband had PRK (photo-refractive keratectomy). These two procedures, which involve changing eyeball power by reshaping the curvature of the cornea with a laser, remain the two most popular procedures done in the United States to get out of wearing glasses. They differ in that LASIK involves lifting a flap of corneal tissue, treating with laser and then repositioning the flap back down, whereas PRK does not use a flap so the laser treatment is placed more superficially. These technologies continue to advance and have good safety track records — but they can be expensive and are not covered by health insurance. Refractive surgery is not an option for youth triathletes as ongoing eyeball growth continues to change eye power.

Contact lenses may be an option for adults and some youth triathletes. Infection is the main risk of contact lenses and swimming in contact lenses may increase that risk. A contact lens is a piece of plastic that can become contaminated with microbes and hold them right next to your eye. Corneal ulcers from contact lens infections can result in permanent vision loss of various degrees. I think there is a significant difference between wearing contact lenses in a chlorinated pool and swimming in many of the open water venues that make triathlon so appealing.

Pseudomonas is a notorious contact lens bacteria found in hot tubs and elsewhere. Acanthamoeba is a particularly durable microbe that infects patients who often report recent contact lens exposure to river or lake water. Fungal infections are more common in tropical climates. If you are going to take the occasional risk of swimming in open water while wearing contact lenses, my recommendation is to remove and dispose of the pair you swam in right after the race and resume use with a new pair. 

Swim goggles with optical correction are an excellent (and safe) option for triathlon training and racing for all ages. Sporting goods stores likely don’t stock them and opticians are often poorly informed about them, but they are now available from several trusted swim brands and can be found online easily. Corrective optical swim goggles are made with optical-grade polycarbonate and get great reviews from users. They are available with the same lens power in front of each eye in an impressively wide range of powers, from +8 diopters to -12 diopters, which would cover almost all athletes. The most amazing part is that these goggles are available for prices in the $20 to $35 ballpark — which is hard to beat for a good pair of regular swim goggles! 

Now that refractive error has been made clear, set your sights on your next triathlon!


Laurel Quinn, MD, is an American Board of Ophthalmology certified eye surgeon and USAT member practicing in Winona, Minn. She and her six children enjoy youth triathlon, their hometown Trinona event and family vacations to her husband’s IRONMAN races.