Colour perception deficits in posterior stroke: Not so rare after all?

Cerebral achromatopsia is an acquired colour perception impairment caused by brain injury. Although we lack precise knowledge about prevalence, acquired colour perception deficits are considered to be rare. While both hemispheres contribute to colour perception, most published cases have had bilateral or right hemisphere lesions. In contrast to congenital colour blindness that affects the discrimination between specific hues, cerebral achromatopsia is often described as affecting perception across all colours. Most of the knowledge on cerebral achromatopsia comes from single case studies or case series of patients with colour perception deficits. Here, we explore colour perception deficits in an unbiased sample of patients with stroke affecting the posterior cerebral artery (N=63). Patients were selected based on lesion location only, and not based on the presence of a given symptom. All patients were tested formally with the Farnsworth D-15 Dichotomous Colour Blindness Test and their performance was compared to matched controls (N=44) using single case statistics. In patients with abnormal performance, a qualitative analysis of the patterns of colour difficulties was performed and lesion lateralization was examined. The study is part of the Back of the Brain project (BoB).27% of the patients in the sample showed significant problems with colour discrimination. Within the lesion subgroups, 44% of patients with bilateral lesions, 34% with left hemisphere lesions and 10% with right hemisphere lesions had significant colour impairments. This suggests that colour perception impairments are more common following left hemisphere lesion than right hemisphere lesion. While some patients only had mild deficits, colour perception impairments were in many cases severe. Many patients had selective deficits only affecting the perception of some hues. The results suggest that colour perception difficulties after a PCA stroke are common, and that they vary in severity and expression. In addition, the results point towards a left hemispheric domination in colour processing, contradicting previous reports.