What is the use of these green and red lines on Snellen/Eye chart? - Medical Sciences Stack Exchange

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I read that in eye tests red and green colors are used. For example: But in Snellen/Eye chart, these are not background colors. These are lines only. What is the purpose of it?

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Why do eye doctors ask us which colour between red and green appears closer to us, and what does it mean if they appear the same to me? - Quora

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Snellen Plastic Eye Chart

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Distance Snellen eye chart for vision testing at 20 Feet Visual acuity range 20/100 to 20/16. Includes red and green bars for color vision test. Eye

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Snellen Chart with Red Green Lines 20 Feet