Is your vision better in red, green or yellow?

The C.A.S.A VISION SCREENER is a self-testing vision chart, which has one size snellen letter 20/40, which corresponds to the minimum requirement for driving. The background colors employed on this chart are green, red and yellow, which are the diagnostic colors involved in chromatic aberration of the eye. The chart has a surface of specified reflectivity so as to best manifest chromatic aberration.

The test is based on the chromatic aberration of the eye, whereby green, red and yellow light are refracted differently in the eye.

The relative clarity in one color with respect to the others relays information as to the visual state of the observer, hence, lending diagnostic value to the test; better vision in the red = myopic tendency, with or without astigmatism; better vision in the green = hyperopic tendency, with or without astigmatism; better vision in the yellow can indicate uncorrected simple hyperopic or myopic astigmatism, mixed astigmatism as well as some uncorrected ammetropia.

UNCORRECTED MYOPIA AND ASTIGMATISM ARE MANIFESTED USING THIS TEST.

How to use Distance Vision Test

1. Use your distance prescription when using the chart
2. Open the chart to full size by clicking on the chart
3. Stand 10 feet (3 meters) from the sign
(The test distance can vary by 10% – that is test at 9 or 11 feet)
4. Test vision differences in one eye at a time and with both eyes
5. Note whether there are differences in your ability to see in the 3 sections of colour

Instructions for the Distance Vision Test (English)

Instructions for the Distance Vision Test (French)

DISTANCE VISION TEST

The C.A.S.A VISION SCREENER serves to detect changes in vision due to physiological
(ie. Age related) or pathological (ie. Hyperglycemia) reasons. Color vision deficiency
does not affect the results of this test.

How to use Near Vision Test

1. Use your near prescription when using the chart.
2. Open the chart to full size by clicking on the chart.
3. Place yourself 16″ (40cm) from the sign.
4. Test vision differences in one eye at a time and with both eyes.
5. Note whether there are differences in your ability to see in the 3 sections of colour. For example, if letters are clearer in the green colour or blurry in the red colour – this is an important indicator of a potential shift in form of macular degeneration if you have already been diagnosed with dry macular degeneration in the past.

Instructions for the Near Vision Test

NEAR VISION TEST

I. An observer would report better vision in the red, as a result of any of the following conditions:

A. Normal physiological progression of myopia.
B. Cataract formation.
C. Rise in blood sugar level with diabetes.

II. An observer would report better vision in the green, as a result of any of the following conditions:

A. Normal physiological development of hyperopia
B. Presence of central serous retinopathy
C. “Wet” form of macular degeneration

III. An observer would report best vision in the yellow… mixed astigmatism:

A pure astigmat, who develops hyperopia, would result in seeing better
in the yellow than the red or the green.

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If you are diabetic and the letters (words) are clearer in red color, your blood glucose level may be high. Report to your doctor

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If you are taking medication for diabetes, and the letters (words) are clearer in the green color, your blood glucose level may be low. Report to your doctor.

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If you are diabetic and the letters (words) are clearer in different colors on different days, your blood glucose level may be unstable.