Ophthalmology & Optometry/lens thickness
My 8-year-old child is far sighted and was wearing a lens prescription at about 4.25 with a bifocal. The new ophthalmologist we saw today prescribed a 5.0 with no bifocal. Last year when we got her new lenses in the 4.25, they originally made them with what they called a base 5 lens, which made them a lot thicker than she had worn before, so they remade them with a base 4. My question is whether this new prescription will necessitate a base 5 lens... or does the absence of a bifocal help in keeping the lenses down in thickness? I would think that having a bifocal would require thicker lenses than would be necessary otherwise. I hope I've stated my question clearly. Thank you for your time.
The 1 diopter base curve difference is very little, and your child will adapt to whatever. These lens thickness/curve issues are best directed to the optical lab that produces the lenses for your optician that cuts and puts the leneses into the frame. Usually the optician you work with can call the lab and find out what options are available. Generally a high index lens will be flatter, with a lower base curve number, and thinner yielding less magnification effect.
The important point is to make sure the eyes aren't straining or tending to cross. Sometimes this is possible without a bifocal, but sometimes the doctor and/or parent wants to stop the bifocal though doing so may cause over-convergence. Make sure the eye alignment is tested with the new glasses at near and far to make sure they aren't requiring over compensation by your child to avoid crossed eyes, double vision, or eye strain.
Mitch Axelrod, OD