What is Bichrome test?

The bichrome test is a subjective refraction procedure used to determine spherical correction. It is based on axial chromatic aberra- tion of the human eye in which refrative power increases with decreasing wavelength.

What is Duochrome eye test?

A duochrome test is a test commonly used to refine the final sphere in refraction, which makes use of the longitudinal chromatic aberration of the eye. Because of the chromatic aberration of the eye, the shorter wavelengths (green) are focused in front of the longer red wavelengths.

Why do we perform duochrome test?

The duochrome test examines the position of the focus of the green and red wavelengths with respect to the retina and theoretically enables precise determination of the spherical correction or of the Circle of Least Confusion (COLC).

Where is the best place to do the Bichrome test?

The bichrome test should be done in a completely darkened room. Starting with the results of your monocular subjective, +0.75 of spherical power is placed in front of each eye. Use the red-green filter along with the side-by-side letter chart.

What kind of eye chart do optometrists use?

Optometrists use eye charts as a basic vision check. Today many variations of the eye chart exist. The four most common eye charts used are: 1. Snellen The original eye chart designed in the 1860’s by the Dutch eye doctor Hermann Snellen. The first line on this chart is a giant letter E.

How is The duochrome test used in optometry?

This test is initially used for presbyopes who need near correction. When testing monocularly, one eye must be occluded. Ask the client to hold the test at 40 centimetres, wearing full correction for near. The client is asked to compare the two sides for their intensity, either the red/green colours or the letters.

How is the Bichrome test done in a darkened room?

The bichrome test should be done in a completely darkened room. Starting with the results of your monocular subjective, +0.75 of spherical power is placed in front of each eye. Use the red-green filter along with the side-by-side letter chart. Light rays from a green source are refracted to a greater extent than those from a red source.