The Clinical Use of Retinotopy in Functional Hemianopia

Functional visual loss presents a challenge in clinical practice. Its classical diagnostic approach includes the use of bedside techniques, visual-evoked potentials (VEP), among other techniques that can be cumbersome and not always diagnostic. We investigated the use of population receptive field (pRF) mapping, a functional magnetic resonance imaging (fMRI) technique mostly used in research to study visual function in cortical visual areas, to support the diagnosis of functional hemianopia in the clinical setting. A 27-year-old female patient presenting with a 6-month history of blurred vision in both eyes, underwent clinical exam, computerized perimetry, optical coherence tomography (OCT), brain MRI, EEG, and VEP. Subsequently, she underwent fMRI stimulation. There were inconsistent responses in the left hemifields during confrontational visual field testing. Computerized perimetry showed a left homonymous and congruous hemianopia. Brain MRI, EEG, and VEP were unremarkable. fMRI stimulation showed similar pRF maps between hemispheres, indicating preservation of visual function. Follow-up OCT showed no signs of homonymous transsynaptic retrograde degeneration. The diagnosis of functional hemianopia was explained, and the patient was reassured. Cortical mapping of pRF might be a potential and helpful tool in the clinical assessment of functional visual loss.