Blue or Red Light
Red or blue target for comparing colour saturation between eyes.
For educational purposes only. A teaching and screening aid, not a medical device; it does not replace a standard clinical examination.
How to use
- Turn the screen brightness up and keep room lighting the same for both eyes. Show the target in full screen.
- Cover the eye you expect to be normal and show the target to the other eye, then swap. Ask: Does the colour look the same with each eye? Is it dimmer, darker, or more washed out with one eye?
- If it differs, ask the patient to rate the weaker eye: if the better eye sees the colour as 100 %, how much does the other eye see? Record it for that eye.
- For a hemifield comparison, use the split target: with one eye covered and the patient looking at the central dot, ask whether the two halves look the same. A duller temporal half in each eye is the pattern of a chiasmal lesion.
How it is scored
- The tool records what the patient reports — a relative percentage for each eye and, on the split target, which half looked duller — and shows them side by side. It computes nothing beyond that.
- A reduced, asymmetric saturation of red is a sign of optic nerve dysfunction; it is subjective and is interpreted alongside acuity, the pupils and the fields.
Limitations
- Screen colour is not standardised. The red and blue a display produces depend on its panel, brightness, colour calibration and any night or blue-light filter, and room lighting changes how saturated they look. Compare the two eyes on the same screen, at the same brightness, in the same light.
- The responses are subjective and the percentage is the patient’s estimate, not a measurement.
- This does not replace pupil testing, colour vision testing or perimetry.
References
- Danesh-Meyer HV, Papchenko TL, Savino PJ, Gamble GD. Brightness sensitivity and color perception as predictors of relative afferent pupillary defect. Invest Ophthalmol Vis Sci 2007;48:3616-3621.
- Miller NR, Newman NJ, Biousse V, Kerrison JB, eds. Walsh and Hoyt’s Clinical Neuro-Ophthalmology: The Essentials — examination of the afferent visual system.
- IEC 61966-2-1:1999. Multimedia systems and equipment — colour measurement and management — default RGB colour space (sRGB).
For educational purposes only. The Clinical Exam tools are part of an educational platform. They are screening and teaching aids, not certified medical devices: a result depends on the screen (letter sizes are estimated for the type of device), the lighting and the testing distance. They are not a diagnosis, and any abnormal or doubtful result should be confirmed with a standard clinical test.