The Mystery of Zero Ishihara Plates with 20/20 Vision

Herein we present a case of 71-year-old retired teacher who presented with difficulty reading over the past year. On examination, the patient had difficulty identifying even the control plate on Ishihara testing in both eyes (OU), despite intact color recognition. Humphrey visual field testing revealed reproducible right sided visual field deficits OU at presentation. MRI of the brain had been done before we saw her and was initially read as unremarkable. However, upon review high signal intensity involving the subcortical white matter in the occipital lobe on the left, as well as encephalomalacia with increased CSF spaces were noted. The differential diagnosis included posterior cortical atrophy, a neurodegenerative condition. Her visual difficulty preceded the diagnosis of depression; the latter was actually believed to be due to having seen several eye doctors and not being given an explanation for the worsening vision. It is important to remember that inability to identify Ishihara color plates is sometimes the earliest sign of simultanagnosia. This case emphasizes the importance of performing a thorough history and examination, including interpretation of all exam findings, in order to timely diagnose and manage the underlying disorder.