Subjective refraction

Subjective Refraction is a technique to determine the combination of lenses that will provide the best corrected visual acuity (BCVA).

[1] It is a clinical examination used by orthoptists, optometrists and ophthalmologists to determine a patient's need for refractive correction, in the form of glasses or contact lenses.

The red-green duochrome test is performed monocularly, and is used to refine the spherical component of the refraction.

The examiner asks the patient: "Do the black letters stand out more on the red or green background?

Neutrality is achieved when the patient subjectively reports that the letters on both backgrounds appear equally as prominent.

(Top) 0.50 confirmation set; (Middle) trial lens box, including pinhole and occluder; (Bottom) Snellen chart
Trial frames fitted comfortably on the patient and occluder over left eye.
Step 1: Using the +/-0.50DS on the confirmation set to determine the initial best sphere correction.
Step 2: Presenting the 0.50JCC initially @ 90deg to determine any presence of astigmatism on that axis.
Step 3: The axis of the JCC must straddle the axis of the correcting cylinder in the trial frames, in both flip positions.
Step 4: The axis of the JCC must superimpose the axis of the correcting cylinder lens in the trial frames.
Step 5: Spherical lens power is altered and refined, if required.
"Do the letters stand out more on the red or green background?"
Duochrome is based on chromatic aberration of the eye.
The patient's subjective response to the duochrome test is a perfect indicator as to whether you have under-corrected, over-corrected, or adequately corrected their refractive error during the subjective refraction process.