Kids don't see through segs the same way adults do...so they shouldn't be fitted the same as adults. Although the majority of prescriptions for children call for single-vision lenses, some youngsters do need to wear bifocals for visual correction. Unlike adults, who find that their arms "get shorter" because of presbyopia as they head toward their 40th birthdays, pediatric bifocal prescriptions are generally given to help correct any one of a variety of -phorias, -tropias, strabismus or other accommodative or convergence difficulties.

Doctors frequently include a specific bifocal type as part of the Rx. But sometimes dispensers are called upon to make that choice. Whether you are faced with the challenge of deciding upon the appropriate lens style for a child or you simply need to provide the best glasses possible to help the tyke, following are some areas that require particular attention when fitting children with bifocals.

OPTICAL CENTERS
To help pediatric bifocal wearers get the maximum benefit out of their eyewear, proper placement of optical centers (OCs) and segs is crucial. Make sure the lab has the most accurate measurements possible before fabrication by taking monocular PDs every time.

Monocular PDs. Use a pupilometer to measure precise mono PDs if the child is old enough to cooperate. If there is an obstacle to the use of the machine, use a PD ruler to take monocular near and far PDs.

Canthus-to-canthus. In cases in which the child is unable to sit still or is too young to focus for a PD measurement, use the canthus-to-canthus method to arrive at a PD. This technique calls for a measurement from the outermost corner of the right eye to inner corner of the left eye, or from the innermost corner of the right eye to the outermost corner of the left corner.

SEG PLACEMENT 
Unlike adults, kids won't recognize the importance of looking through the near portion of the bifocal when focusing on close-up activities such as coloring and doing homework. To ensure that they receive the maximum benefit from their glasses, the bifocal line must be placed so that it bisects the pupil--higher than the normal height for an adult's eyewear. Each height must be measured monocularly for proper line and OC placement.

Monocular seg heights. When fitting adults with a lined bifocal, most dispensers will place the bifocals at the same height for an attractive appearance, even if one eye is slightly lower than the other. Adults can accommodate for seg heights that are a millimeter or two away from the ideal position, but children need to be forced to use the bifocal. Avoid an O.U. height unless the child's eyes are perfectly even on a horizontal plane.

SPECTACLE FIT
To ensure that the child utilizes the bifocal area of the lens for all close work, proper frame fit is crucial. If the frame slides down the kid's nose, she will look right over the bifocal--or the entire lens. There are enough combinations of temples and bridges to make finding an attractive, well-fitting frame in each patient's price range a simple task.

Bridge fit. Children generally have almost no bridge until they enter their teen years, so pay close attention to bridge styles, especially for younger kids. If a saddle bridge (or a non-adjustable unifit bridge) does not provide a snug fit, look for a frame with nose-pads. Many children's plastic and metal frames are made with a one-piece silicone or soft adjustable unifit bridge just to solve this fitting dilemma. Consider the age and activity level of the child before recommending a frame with individual nosepads, as they can bend or break if subjected to too much roughhousing. Silicone nosepads or unifit bridges are a good choice because the material will absorb a little perspiration and help to prevent the frame from sliding.

When evaluating the bridge fit, remember that the frame will slide down a little once the weight of the lenses is added. Gently press down on the top of the bridge and see how far it slides down the child's nose. A bridge that fits will hug the nose and slide very little.

Temples. Cable temples are a good choice for keeping the glasses in place if the tyke is supposed to keep them on his face all the time. Very little kids might benefit from a frame with a built-in strap that fits around the back of the head. But for those who wear their glasses only part-time, putting them on and taking them off several times a day for different activities, regular paddle temples make the most sense.

Frame shape. To ensure that the glasses stay where they should, pay attention to the depth of the lens area. If a child has very chubby cheeks, a frame with a deep B measurement may move up and down as the tot smiles or talks, taking the bifocals on a ride with it. If the pantoscopic tilt can't be adjusted so that the bottom of the eyewire is off the cheeks, it's best to steer the child toward a frame with a shallower vertical area. One rule of thumb is that if the seg placement is more than 3mm above the geometric vertical center of the face, the wrong frame has been selected, explains Kathy Schramm, pediatric optician, owner of A Child's View in Mission Viego, Calif., and author of an upcoming book on kids and vision care.

LENS STYLE
Since kids will avoid using the bifocal if it's not placed right in their near field of vision, the choice of lens style is an important factor to help them maximize the use of their glasses. The wider the bifocal area, the more chance there is that the child will use it.

Straight-tops. The FT 35 is a good choice because it is a wide seg. In fact, in smaller kids' glasses, the 35-mm segment will extend across the entire bottom width of the lens area, providing a large near portion of the lens for the child to look through.

Executives. No longer made in poly, the glass exec is a one-piece construction, and thus has several drawbacks to its use for children.

Blended segs. A blended round seg looks less like a bifocal and more like a SV lens--an attractive prospect to many parents and kids. However, the round seg may be too narrow for your kids, for several reasons, and is not generally reccomended for children, young or old.

The choices are there. It's up to you to apply your own expertise to solving the visula problems of kids--your youngest but also potentially longest term customers. EB