Lenses come in a vast array of materials and colours that pass the above standards but they are not all equal. Choose lenses that cut 100% UV (ultra-violet light), that means UVA, UVB and UVC. Please check because lenses that pass the above standards dont have to cut 100% UV and babies require total protection as they have no chromophores in their eyes (like adults) that protectively absorbs UV rays. Also 10% of boys and 1% of girls are colour blind so lens colour is critical at an early age and the lens colour that is best suited for clarity, no colour distortion and maximum glare reduction is "G-15", meaning a neutral green lens with 15% visible light transmission which is a category #3 lens. Please dont buy bright coloured lenses (pink, blue, yellow etc.) also no categories #0, #1 or #2 lenses as they are to light and provide limited glare reduction. Also avoid category #4 lenses as they are too *dark for general purpose baby sunglasses and are designed for special purpose only, mountaineering / skiing. *Note: cat. #4 lens only allow 3 to 8% of light through so your toddler will not be able to see properly.
Polycarbonate (PC) lenses - Are 10 times more impact-resistant than plastic or glass lenses, light weight (comfortable) and scratch resistant. Buy only virgin (PC) lenses as recycled (PC) lenses just don't last.
Trivex lenses - similar to PC lenses but not as widely available.
Polycarbonate (PC) Polarized lenses, - Are up to 10 times more impact-resistant than plastic or glass lenses and being polarized totally eliminate all white reflected light, giving the best, ultimate crisp clear vision. Lenses should be approximately 2 mm thick to avoid distortion and breakage.
Lenses to Avoid
Acrylic lenses - are very soft and break or scratch easy. Once scratched they should not be worn as they distort vision and wear out the babies eye muscle (ciliary muscle) trying to focus through the scratches leading to early wearing of prescription glasses.
TAC lenses Tri Acetate Cellulose) - usually used in conjunction with a polarizing filter. Note, these lenses are very thin and distort out of shape and scratch easy.
Glass lenses - can make great sunglass lenses just not for babies or toddlers due to breakage.