Pediatric Eyeglasses: 
Opening Up a New World for Children

Vision is the sense that children rely on the most to discover the world around them.  It is reported that approximately 80% of learning occurs through the visual system. If something occurs early in a child’s life to upset the working of the visual system, learning and visual functions can be permanently impaired.

Luckily, early detection of problems and proper vision care can correct a situation before it progresses. The first person that a parent or teacher comes to with questions about a child’s visual health is the ECP. Therefore it is important to know the signs of visual discomfort and the most common reasons for them. The most frequent signs of vision problems are headaches, squinting, frequent blinking or winking, and closing one eye, especially in bright sunlight. When these symptoms occur, it is important to refer the parent and child for an eye examination.

Common vision problems seen in children are:

• Refractive Errors – these occur when the light entering the eye doesn’t bend properly and a blurred image results on the retina. Hyperopia, or far sightedness, occurs when the light entering the eye focuses behind the retina. The result is blurred images when viewing things up close. Myopia is near sightedness and occurs when the light entering the eye focuses in front of the retina. With this error, far images are blurry. Astigmatism is when the light entering the eye comes into focus at two separate points in the eye. Usually caused by an unevenly shaped cornea, the different foci result in a blurred image at all distances if the error is significant.
  

• Strabismus – also called” crossed eyes” or “wall eyed” by layman. This condition occurs when the eyes do not align properly when under normal conditions. With this condition, one or both eyes may turn in (eso), out (exo), up (hyper), or down (hypo). If the turning happens on a consistent basis, it is called a tropia. If the eyes align normally most of the time, but has a tendency to turn during times of fatigue or stress, the turning is called a phoria. Therefore, someone whose eyes turn inward on occasion would be labeled as having esophoria. Someone whose eyes turn outward consistently would be labeled as having exotropia.
  

• Amblyopia – About 5% of children have Amblyopia. Also called “lazy eye” by laymen, it occurs when the visual pathway is shut down by the brain due to confusion in processing the images received by both eyes. This confusion can be caused by misaligned eyes or poor vision in one eye causing a distorted image. Since the visual pathways need to become strong at an early age, the amblyopia must be detected and treated early in order to preserve vision for the child. If the pathway remains closed until the age of seven, then the visual system is complete and the child will likely have poor vision for life.

It’s all in the Material

Correcting a child’s vision is crucial for the life-long well being of the child. The most common method of vision correction for children is eyeglasses. When designing lenses for children, safety is crucial. The safest materials to use for children’s eyewear are polycarbonate and Trivex.

Polycarbonate:

• Advantages

  • Very light weight; 10% lighter than CR-39

  • The most impact resistant lens

  • At least 10% thinner than CR-39

  • Excellent UV protection that blocks 99.99% of UV at 380 nm

  • Superior scratch resistance

• Disadvantages

  • A low ABBE value of 32 which increases chromatic aberrations if fit improperly

  • Lower light transmittance like all high N lenses without AR coating

Trivex

• Advantages

  • Extremely impact resistant

  • Superior scratch resistance

  • A high ABBE value of 43 to 45 so there are lower incidences of chromatic aberrations

  • Lightweight

  • Blocks UV transmittance

• Disadvantages

  • Slightly thicker and heavier than polycarbonate

  • Expense

It is imperative that measurements are taken properly when working with polycarbonate and Trivex so that incidences of aberrations are decreased. Both lens materials should be fit with monocular pupillary distances, vertical optical centers, and a very close vertex distance to give the child the best possible vision.

Taking the Proper Measurements

Pupillary Distance

Monocular PDs should always be taken when fitting a child. The preferred way to measure the PD is using a corneal reflection pupilometer. This is the preferred method because they help eliminate parallax errors; they work very well on very dark irises, and comparatively easy to develop expertise. The first step is to adjust the working distance dial to the distance setting which is infinity for a distance only prescription. Sitting across from the patient, place the pupilometer on the patient’s nose with the forehead bar centered against the forehead. Ask the patient to look into the light. Move the hairline to bisect the corneal reflex. Repeat with the other eye. The monocular PD is then displayed on the top of the pupilometer. If the patient has trouble fixating with either or both eyes, the ECP should use the paddle switch to occlude one eye at a time. Occluding one eye will force the other eye to take up fixation so that the ECP can get an accurate pupillary distance.

To verify that this measurement is accurate, the pupilometer should be calibrated at least once a week. In order to verify accuracy, you should set the PD to 32/32 and place a ruler against the hairlines. The measurement should be 64. If it is, then the calibration is complete. If it is incorrect, note the difference, measure again at 29/29 and 35/35. If the pupilometer is off the same amount in each case, remember to adjust the measurements taken to correct them until the pupilometer can be sent for calibration. If there is no consistency, stop using the pupilometer and send if off for repair.

Optical Center Height

Whereas the PD is taken to insure the correct horizontal placement of the MRP of the lens, the height is taken to insure accurate vertical placement of the MRP. The OC is the point where the light is not deviated when it passes through the lens. The MRP is the point on a lens that matches the amount of prism prescribed. If no prism is prescribed, the MRP and the OC are at the same location. The OC is usually placed along the optical axis. Contrary to popular belief, this is not in front of the pupil. The rule of thumb for OC height is to place the measurement 1mm below the pupil for every 2 degrees of pantoscopic tilt had by the frame. Since most frames are worn by the patient with 10 to 12 degrees of pantoscopic tilt, an average OC height would be 5 to 6mm below the pupil.

Lens manufacturers can usually provide a tool to help measure pantoscopic tilt. One such tool is the Zeiss Individual™ Panto and Vertex Tool. When taking the pantoscopic measurement using this tool, it should be taken vertically, parallel to the face and perpendicular to the patient’s forward facing gaze.

Lens Options for Kids

Anti-Reflective Coating

Anti-reflective coatings (AR) have come a long way from the easily scratched and smeared coatings of the past. Intended to ease eye fatigue, increase visual acuity and contrast, as well as make the lenses more cosmetically appealing, AR is less effective if dirty or scratched. Luckily, current coatings have technologically advanced to repel water, oil, dust particles as well as resist scratches.

AR coatings are applied to a lens using a multilayer process. Using the principle of destructive interference, alternating layers of high and low index layers eliminate surface reflections. Since each layer interferes with one color range, the more layers that are applied, the more reflections that are eliminated. Premium AR coatings have up to seven layers, one for each color in the spectrum. In addition, on top of the AR coating itself, premium AR coatings have the extra benefit of oleophobic, hydrophobic, and antistatic treatments. Oleophobic, or oil repellent treatments, allow the lens to be cleaned easier and minimize scratching. Hydrophobic treatments cause water to bead on the lens, allowing it to be patted dry without smudging. When the two treatments are combined on the same lens, it acts as a scratch resistant coating by sealing and protecting the AR layers. Anti-static treatments repel dust and dirt by eliminating static buildup and preventing more build up from occurring.

Photochromic Lenses

Photochromic lenses are lenses that change from a lighter state to a darker state when exposed to ultraviolet radiation. Designed as comfort lenses, photochromics help the eye care professional provide clear, comfortable vision indoors and out to his or her patients. Although not a replacement for sunwear, photochromics can provide an added benefit of simplicity for a patient with a busy lifestyle by having one pair that can meet multiple visual needs.

Polarized Lenses

Although a tinted lens is always an option, for superior glare protection, there is no comparison to polarized sunglass lenses. Polarized lenses:

• Enhance contrast

• Eliminate dangerous glare

• Reduce eyestrain

• Increase depth perception, particularly around water

• Enhance visual clarity

The easiest way to describe polarization is to compare the polarized filter to a micro venetian blind. Like the venetian blind on a window, a polarized filter blocks light coming in at a certain angle, while allowing light to be transmitted through the lens at an angle 90 degrees away. The filter in the lens is horizontally aligned so that the horizontally reflected light is absorbed. This can be demonstrated by viewing light reflected off of a flat surface through a polarized lens. Rotate the lens 90 degrees so that the changes in the intensity of the reflection can be observed. The horizontal alignment of a polarized lens is crucial. Misalignment during the fabrication process will cause the lens to be less effective.

Choosing an Appropriate Frame

Children’s frames are stylish, well made, and durable. However, there are some features that the ECP should recommend for young or especially active children.

• Spring temples – springs enable the temple to be spread 90 degrees or more allowing the frame to maintain adjustment and prevent some forms of breakage. However, spring hinges may be a poor choice for any athletic activities. Oblique blows to the frame/head of the child can cause the hinge to expand and be driven into the eye socket
  

• Flexible alloys – hypoallergenic, lightweight, and corrosive resistant material that can be twisted or bent without breaking or losing most of its adjustment. It is not unbreakable, but it can stand up to a lot of accidents
  

• Stainless steel – less expensive than titanium, it is corrosive resistant and has a very strong tensile strength
  

• Cable temples/riding bow temples – these temples wrap around the ear and provide a more secure fit than a skull temple
  

• Deep eye wires – Deep grooves along the eye wire allow for lenses to be inserted more securely in the frame to prevent lenses from popping out or slipping axis within the frame
  

• Titanium frames – strong, lightweight and hypoallergenic these frames tend to hold up well to rough use

Conclusion

Pediatric fitting and dispensing is a rewarding part of an ECP’s practice. How a child sees today affects his or her whole life. If the visual process is disrupted at an early age it can lead to a permanent loss of vision if not corrected in a timely manner. It is a blessing that ECPs can open a whole new world for a child who is not seeing correctly and preserve a lifetime of quality vision simultaneously.