Red desaturation testing is a simple assessment of optic nerve function that compares how bright or saturated a red object appears to each eye. It can reveal subtle differences in colour perception linked to optic nerve disease.
Method
A red target, such as a cap or light, is presented alternately to each eye while the other is covered. The person reports whether the colour looks equally bright and vivid in both eyes or appears washed out or darker in one.
- Quick and does not require specialised equipment
- Often used alongside other bedside tests for optic nerve function
- Best performed after correcting for obvious refractive error and lighting differences
- Can be repeated over time to monitor changes
Interpretation
Reduced red saturation in one eye suggests impaired conduction along the optic nerve or visual pathway on that side. Findings are interpreted with visual acuity, visual fields, and pupil responses.
- Commonly abnormal in optic neuritis and ischaemic optic neuropathy
- Not specific on its own and may be influenced by macular disease
- Useful as a quick screening tool in emergency or clinic settings
- Documenting baseline responses assists in follow-up evaluations
