[Appraisal of the formation of afterimages by means of a new computer application in patients with demyelinating optic neuropathies].

INTRODUCTION: The perception of colour is one of the visual functions affected by optic neuritis. Most of the tests currently available for evaluating dichromatism are based on assessing the hue, but no clinical studies have been conducted to investigate the formation of afterimages on the retina of these patients.

AIMS: To evaluate the dichromatism acquired in demyelinating optic neuritis by means of the formation of afterimages on the retina.

SUBJECTS AND METHODS: This is an observation-based, cross-sectional, case-control study. The cases are patients with at least one bout of optic neuritis and confirmed multiple sclerosis. A healthy age- and sex-paired control was selected for each case. The main variable is the capacity to see afterimages after saturation of the retinal photoreceptor cells. A specific computer application was developed to evaluate this phenomenon.

RESULTS: The sample consisted of 30 cases and 30 controls (63% females; mean age: 33 years; range: 18-48 years). The cases showed less probability of seeing the afterimage (36.6% of the cases, while none of the controls failed to see an afterimage) and, if it was seen, it remained for less time. The ROC curve shows a sensitivity of 86.3% and a specificity of 83.3%. The odds ratio was 5 (95% confidence interval: 2.21-11.3) for the probability of seeing the afterimage in controls versus cases.

CONCLUSIONS: Patients with at least one episode of optic neuritis presented a lower capacity to observe afterimages. The test is therefore useful in the assessment and follow-up of functional damage in demyelinating optic neuropathies.