duochrome test
Subjective refraction technique using red and green backgrounds to fine-tune spherical correction in cooperative children.
Full Definition
The duochrome test, also known as the red-green test or bichrome test, is a subjective refraction method that utilizes chromatic aberration to determine the optimal spherical lens power. The test presents identical optotypes on red and green backgrounds simultaneously. Due to chromatic aberration, red light focuses slightly behind the retina while green light focuses slightly in front when properly corrected. Patients report clearer vision on the green background when under-corrected and clearer on red when over-corrected. Equal clarity indicates proper spherical correction. This test is particularly useful in pediatric patients who can communicate but may have difficulty with more complex subjective techniques.
Usage
Usage note: Also written as 'duo-chrome' in some texts, but 'duochrome' is the preferred single-word form.
In Context
- "The duochrome test confirmed that the child's prescription was slightly over-minused and required +0.25D adjustment." — refraction examination note
- "Children as young as 4 years can often participate reliably in duochrome testing when properly instructed." — clinical technique guide