What is Duochrome test and how to do Duochrome test.

                      DEUOCHROME TEST

PRINCIPLE:

A deuochrome test is a test commonly used to refine the final sphare in refraction. Which makes use of the transverse chromatic aberration of the eye. The shorter wavelengths green are focused in front of the longer red wavelength.

Dark Room Procedure

Firstly turn off the room light:-

Occlude one eye with the help of occluder.

Follow this formula also:- GAP or RAM

• GAP:- Green Add Plus

• RAM:- Red Add Minus

Remember:- Always put (+-0.25DS)

Testing Procedures 

The patient is asked to compare the clarity of the latter on the green and the red side. If the latters of the green side are clearer +0.25DS is added and if the latters on the red side are clearer -0.25DS is added.

Ask to the patient:- Are the latters clearer and blacker on the red or on the green, Or are they the same??

• If patient says green are more clearer compaire with both of them.

• Than acording to formula we put +0.25D sphare in front of patient eye.

Again ask to the patient:-

• If patient says red are more clearer compaire with both of them.

• Now than according to the formula we added -0.25D sphare in front of the eye.

Now we get the final power of the sphare

Point to be remember forever:-

• We know this test is besed on the chromatic aberration not on color discrimination.

• It is used even with people having color vision deficiency also.

• If the eye is over active accommodation may still require too much minus sphare to balance the red and green.

• Cycloplegia may be necessary.

• The Deuochrome test is not performed on those patients who have 20/30 and 6/9 visual acuity

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