How is the spherical equivalent used in refractometry?
The refractometric technique involves presenting the patient with spherically equivalent choices (this does not involve the use of the cross cylinder). This technique is used after you have completed an initial refraction on the eye, including sphere power, cylinder axis, and cylinder power checks. Remember, you are trying to determine the lowest cylinder power that provides the best visual acuity. Let s look at some examples. The prescriptions are spherically equivalent. Example A: Consult the table below. You finish your refraction routine having found that the patient prefers #3. The patient is looking at the 20/30 line and you present a choice between #3 and #4. The patient prefers #3. You now present a choice between #3 and #2. The patient says the choices look about the same. You check the vision, and the best vision with #3 is 20/25. You check the vision with #2 and it is 20/20, so you prescribe #2 because it improves the vision. Minus cylinder 1.+1.50-3.50×90 2.+1.25-3.00×90 3.
