Q. A Sticky Wicket
With the higher indices of refraction in the marketplace now, we are more confused than ever about which to recommend. Can you define which index is best for various prescriptions?

A.
The answer can depend on whom you ask. A manufacturer of 1.60 index may claim that any minus correction can use 1.60, with some justification. Other doctors and dispensers tend to choose a favorite index and use it for everyone (not to the patient's advantage, in our opinion). Here are some rough guidelines, partially taken from VCA's video, "Recommending From the Chair."

• When the correction is plus, order aspheric, preferably poly or high index.

• When the correction is between -3.00 and -5.00, order 1.60.n When the correction is over -5.00, order 1.66 or higher.

• When the correction is between plano and -3.00, order polycarbonate.

• Order AR coating for everyone.

Other factors cloud the issue: Some mid-index lenses are produced in aspheric form, producing thinning similar to a higher index. Some materials, like poly, can be surfaced thinner, adding another variable to the mix. Lastly, cost can be a factor. Except for poly, high index lenses generally increase in cost as the index rises.

Q. Poly Over Poly? 
We were told recently that using polycarbonate clip-ons over glasses having poly prescription lenses create undesirable visual problems. Have you heard of this problem?

A.
None of our sources could conceive of any valid reason why poly clip-ons shouldn't be worn over poly Rx lenses. Darryl Meister, Sola's technical marketing director, says there would be slightly more loss of light transmission due to four lens surfaces reflecting light, but this is typical of all clip-ons. Poly's 90 percent light transmission is slightly less than CR 39's 92 percent, but this isn't an issue with sunwear.

The overall Abbe value effect would be no different than if the Rx lens was surfaced thicker. Poly industrial safety lenses are two to three times thicker than normal and present no visual problems. This appears to be another urban myth that can be ignored.

-Patricia J. Brenner, LDO, Pearle Vision, Knoxville, Tenn.

Q. A Legal Question

A.
Content of a prescription for spectacles or contact lenses is determined by each individual state's law. Some states do not specify the content of a prescription, leaving it up to the prescriber's discretion. Other states list out mandatory components for a prescription which may include: Date of issuance, date of expiration, signature of prescriber, name of patient, specifications for spectacles or contacts which may include various elements, etc. We are unaware of any state law that references what location on a prescription pad this information must be placed. If you have questions regarding possible prescription content requirements in your state, contact the optometry board for further information.

-Sherry Cooper, staff, AOA Licensure & Regulation Committee EB

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