Refraction and muscular imbalance, as simplified through the use of the ski-optometer

by Daniel Woolf

Why Concave Cylinders Are Used Exclusively

The Ski-optometer contains only concave cylinders, as it is universally admitted that convex cylinders are not essential for testing purposes.

In fact, concave cylinders should alone be used in making an examination, even where a complete trial-case is employed. To repeat one of the first rules of refraction: “As much plus or as little minus spherical power as patients will accept, combined with weakest minus cylinder, simplifies the work of refraction and insures accuracy without time-waste.”

After an examination with the Ski-optometer is completed, the total result of plus sphere and minus cylinder may be transposed if desired, though in most instances it is preferable to prescribe the exact findings indicated by the instrument. This will also avoid every possibility of error, eliminating responsibility where one is not familiar with transposition—since, after all, it is the duty of the optician to thoroughly understand that part of the work.