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S P E C I A L E D I T I O N 2 0 1 5 • O P T O M E T R I C M A N A G E M E N T . C O M 17 FE ATURE lens, if one is being worn). Te energy expended to overcome friction is called frictional energy. Te frictional energy between surfaces is a function of two things: (1) whatever lubricant exists between the sur- faces and (2) the state of the surfaces themselves. For example, it is much easier — and, therefore, demands less energy — to push a large box over a shiny polished foor than over a rough concrete sidewalk. Although there are factors in addition to roughness that determine frictional energy, it is clear that surfaces with difering degrees of roughness will require diferent levels of force to obtain the same degree of motion. FRICTIONAL ENERGY AND THE EYE Our eyes do "work" during the blink process because energy is required to overcome the frictional forces resist- ing eyelid movement. Fortunately, the tear flm lubricates the lid and ocular surface. But what happens if friction be- tween the lids and ocular surface increases as the day wears on? Tis could be the case, for example, with a contact lens whose surface becomes less lubricious and less smooth as drying and deposits take their toll throughout the course of a day. In this situation, the repeated movement of the eye- lid over an increasingly resistive surface thousands of times throughout the day can create a signifcant a mount of additional "work" for the eye. Tis correlates with the common observation that many patients who are comfortable in their contact lenses in the morning start to experience ocular symptoms of fatigue as the day progresses. 1 L IFE IS diferent today. It's faster. Many of us have internalized an ethic that pushes us to work and play as hard as possible. In this driven environment, we charge from activity to activity. Our eyes jump from computer screens to smartphones to the person talking to us as we text; or we watch our child's soccer game while jotting notes for work and simultaneously emailing on a tablet. Working as hard as we do, it is no wonder that we're ofen worn out at the end of such a demanding day. OUR EYES CAN FEEL FATIGUED Our eyes experience demanding days, too. Te myriad activities we pursue — and the changing environments we experience as we go from home to car to work to sports to the movies and back home again — all afect our eyes. And millions of us do all this while wearing contact lenses. While we are going about our demanding days, our eyes and eyelids are hard at work, maintaining clear vision and a healthy ocular surface by blinking approximately 14,000 times per day. Blinking requires energy, and while the en- ergy required for a single blink is insignifcant, the energy required for 14,000 blinks every day may be considerable. Just how much efort we put into blinking can be calcu- lated. From high school physics we know that "work" is the product of Force × Distance. In this case, the distance is the 10 or so millimeters the lid travels during the blink cycle, and the force is the efort required to overcome resistance to the blink, which comes largely from friction between lid and the cornea (or a contact IN THE MOST LITERAL AND SCIENTIFIC SENSE OF THE WORD, YOUR EYES "WORK" AS HARD AS YOU DO. INNOVATIVE CONTACT LENSES MAY EASE THEIR WORKLOAD HOW HARD ARE YOUR PATIENTS' EYES WORKING? Charles Scales, Ph.D., and Brian Pall, O.D, M.S., F.A.A.O. Spotlight on Science OPTOME TRIC MANAGEMENT