Name That Prescription! Hyperopic, Myopic, or Both

Prescriptions may at first seem like just a bunch of numbers and letters, however, as learned in article Have An Eyewear Prescription?  Learn To Read It!, there is much more to them than that…especially to the healthcare professional.

When eyewear prescriptions are written, they can then be classified into different areas depending on the power or refractive error.

For instance, if a person is prescribed a -2.50 sph, then the refractive error is called simple myopia, or just myopia because the prescription is written in (-), or minus, for someone who is near sighted, or myopic.  The (-) prescription allows the person to see better with distance.

There are seven categories to which prescriptions can fall and they are listed below.  It is pretty self explanatory, and will assist any Optician or apprenticing certified Optician fairly well as it is quite easy to memorize and use daily.

IF A PERSON SUFFERS FROM:    

Simple Hyperopia, the Rx is (+) sphere

Simple Myopia, the  Rx is (-) sphere

Simple Myopic Astigmatism, the Rx is  plano sphere  (-) cylinder

Simple Hyperopic Astigmatism, the Rx is  plano sphere    (+) cylinder

Compound Hyperopic Astigmatism, the Rx is (+) sphere  (+) cylinder

Compound Myopic Astigmatism,the Rx is  (-) sphere   (-) cylinder

Mixed Astigmatism, signs in sph and cyl must be opposite

Every single prescription that an optician runs across will fall in one of these sections.  Myopic eyes have minus Rx’s and hyperopic eyes have plus Rx’s.  Mixed Astigmatism is exactly what it says…both signs, minus and plus are in the prescription.

An example of mixed astigmatism would be +3.00 – 4.00 x 90.

The power is +3.00 at 90 degrees, and the power is -1.00 at 180 degrees.  Therefore, the refractive error is mixed astigmatism.

No, the -1.00  is not a mistake.  It is a calculation that must be done in order to correctly identify the type of refractive error.  At 90 degrees, the sphere power remains the same, thus +3.00.  At 180 degrees, 90 away from 90 degrees, one must algebraically add the two sphere and cylinder together which gives  the power of -1.00 at 180.

The signs are opposite and therefore prescription is written for mixed astigmatism.