Thickness/Thinnes of Eyeglasses Lenses
By Michael Walach
“How thick are my baby eyeglasses lenses going to be?” is probably the most often asked question the mother asks the eye care professional.
There is no simple answer because the question of your baby or toddler lens thickness is a complex topic.
On minus power lenses there is a minimum center thickness requirement.
Minimum center thickness of lenses is further affected by the stability of the material and its impact resistance in its final form i.e., with any hard and AR coatings applied.
In the US the prescription lenses for your baby, toddler or child will have plus power. The primary factor in determining the lens thickness on plus power lenses is the minimum edge thickness. The minimum edge thickness is measured on edged lens at the point where the lens edge is the thinnest. Just like in minus lenses, there is no simple, plain answer.
In the table below see general guidelines for minimum edge thickness on low power plus lenses. As the plus power of the lenses gets stronger, over +2.00 D, the minimum edge thickness required gets smaller and various methodologies can be applied in order to determine that minimum edge thickness requirement.
The minimum edge thickness is also altered when frame styles requested require things like grooving or drilling as there is a minimum edge thickness required for durability in these types of frames. Too thin an edge wall on either side of a groove for semi-rimless will often flake unless a less notch sensitive like material poly, trivex, high index is chosen.
In conclusion, whenever the lens thickness is of concern, keep in mind the following:
- Frame size – a smaller frame will give you a thinner lens. I strongly recommend looking into eyeglass frames that are designed specially for babies, toddlers or small children like Miraflex, Solo Bambini, Banz, Tomato, Hello Kitty, Liberty Sport, etc. Those frames are safe, durable, come in small sizes and many attractive styles.
- Frame shape – the larger the lens’ diagonal measurement the thicker the lens
- Frame type – rimless or semi-rimless frames will increase the lens thickness on plus power lenses; not the best choice for your baby or child eyeglasses.
- Pupil distance – for babies and children this usually ranges from 41 to 55 mm, for adults 54-68 mm. The larger the pupil distance the thicker the lens unless smaller frame size is selected.
- Lens material – the higher the lens index the thinner the lens.
Get advice from an optical professional; a frame might look great on baby when just a plano lens/filler is in the eyewire, with strong power lens it will be a different story. Be wise with the frame selection. Yes, your child can see well, feel comfortable, look great, improve learning skills and have a better quality of life