• Neuro-Ophthalmology/Orbit

    Review of: Red desaturation prevalence and severity in healthy patients

    Mikolajczyk B, Ritter A, Larson C, et al. Neurology Clinical Practice, February 2022

    Red desaturation is common after optic neuropathies, and therefore testing for relative red desaturation between eyes is often used in clinical practice to provide evidence of a prior unilateral optic neuropathy, especially optic neuritis. However, the prevalence of red desaturation has not been examined in a normal population. In this study, the investigators sought to determine the percentage of healthy adults who respond asymmetrically to the red desaturation test, to estimate the degree of red desaturation in the healthy population, and to determine whether there is a correlation between demographic variables (eg, race/ethnicity) and red desaturation prevalence and severity.

    Study design

    Investigators at a US institution recruited 101 adults with a normal eye exam who were asked if they perceived a difference in the redness of a red tropicamide bottle cap; participants were also asked to estimate the interocular percentage difference if present.


    The mean age of the study participants was 41.5 years, 68% were female, and 77% were White. Some degree of red desaturation was reported by 24% of participants, with an average interocular difference of 9% (range: 2%–25%). There was no statistical relationship between red desaturation and the demographic variables of race/ethnicity, age, or gender.


    Limitations include the sample size of 101 patients, which may be too small to detect differences related to demographic variables. Furthermore, this study did not evaluate the percent difference of red desaturation in patients with optic nerve pathology; therefore, the degree of red desaturation may still be a helpful clinical test.

    Clinical significance

    This study is important because it shows that nearly 25% of healthy individuals have some degree of red desaturation. This means that the specificity of the red desaturation test for asymmetric optic neuropathy may not be as high as clinicians once thought. Future studies will be helpful to determine whether there is a threshold that is helpful for separating physiologic from pathologic red desaturation.