The main determining factor to select the best lens material for your baby or toddler eyeglasses is the prescription. Most prescriptions for babies in the US are plus (+) power lenses for the correction of hypermetropia, commonly called farsightedness. In a hypermetropic eye, the light does not bend sufficiently so that it focuses at a point behind the retina. It is caused by an imperfection in the eye, usually when the eyeball is too small or the crystalline lens in the eye cannot become bi-convex (round) enough, resulting in difficulty to focus on near objects.
Polycarbonate lenses are a typical choice for babies, toddlers or children eyeglasses because they are the safest, being 10 times more impact resistant than traditional plastic lenses. Using these lenses will considerably reduce the number of eye injuries. Polycarbonate lenses are 10 – 25% lighter and thinner than lenses made of other plastic lens materials with specific gravity of 1.2 g/cm^3. The only exception is Trivex lens material with specific gravity of 1.11 g/cm^3, however, when your baby eyeglasses require prismatic correction, Polycarbonate lenses are not recommended due to a high coefficient of chromatic aberration, ABBE Value 30! When Polycarbonate lenses are used with prescribed prism correction the materials’ low ABBE will results in signicant and substantial longtitudinal aberration, which manifests itself as a “fuzzy focus” and blurred vision. Trivex, 44 ABBE Value, or 1.6 lens index (MR 8 or MR 20), 41 & 42 ABBE respectively, are the recommended lens choice.
Please note that Polycarbonate lenses, refractive index if 1.586, and 1.6 index lenses have high reflectance factor. Therefore, good Anti Reflection coating with Oleophobic treatment is a must in order to utilize your toddler’s or baby’s eyeglasses to it’s maximum visual performance.
Do not forget: your child’s emotional development and 80% of learning is based on vision. Your child should have it’s first vision examination as early as at 6 months old.
It is recommended to watch out for the following symptoms:
- Sitting close to the television
- Rubbing their eyes frequently
- Complaining of headaches
- Holding books unusually close or far away
- Excessive blinking
- Unusual head posturing, or tilting the head cockeye
Your child’s well being is totally dependent on you! Give him/her all your love and care they deserve.
Michael Walach is also the President of Quest Vision Care Specialty Lab in Largo, Florida, specializing in eyeglasses prescription lenses with strong powers or special prescription requirements.