What test uses a screen that is half red and half green and is used during refinement?

The test that utilizes a screen that is half red and half green during refinement is designed to assess visual acuity and refractive errors more accurately, particularly for the determination of proper corrective lenses. This method is known as the Duochrome test. It takes advantage of the chromatic aberration of the eye, as red light focuses slightly behind green light on the retina.

In practice, when a patient looks at the dual-colored screen, they'll often be asked to determine which color appears clearer. This can help the examiner refine the patient's prescription, especially when dealing with astigmatism, as it provides insight into how the lenses are correcting the visual perception of different wavelengths of light.

The other tests mentioned, such as the Snellen chart, primarily measure visual acuity without color differentiation, while the cover test evaluates ocular alignment and motion, and the astigmatic fan assesses astigmatism through a pattern of lines but does not involve the dual-color aspect crucial to the Duochrome methodology.