Do you have to maintain spherical equivalent (SE) during the subjective refraction?

• A. Yes
• B. No
• C. Sometimes
• D. Not necessary

Answer: (A)

Maintaining the spherical equivalent during subjective refraction is about isolating the cylinder’s effect on vision. The spherical equivalent is the eye’s overall power represented by the sphere plus half the cylinder. If you change the sphere while you’re testing different cylinder powers, you’re altering the total refractive power in addition to testing cylinder, which makes the patient’s responses harder to interpret. By keeping the SE constant and adjusting only the cylinder power and axis, you’re effectively testing how much cylinder correction the eye needs without confounding changes from the sphere. This leads to a clearer determination of the best cylinder correction first, and then you can fine-tune the spherical component afterward if needed.