Progressive cortical visual failure associated with occipital calcification and coeliac disease with relative preservation of the dorsal ‘action’ pathway

We describe the first reported case of a patient with coeliac disease and cerebral occipital calcification who shows a progressive and seemingly selective failure to recognize visual stimuli. This decline was tracked over a study period of 22 years and occurred in the absence of primary sensory or widespread intellectual impairment. Subsequent tests revealed that although the patient was unable to use shape and contour information to visually identify objects, she was nevertheless able to use this information to reach, grasp and manipulate objects under central, immediate vision. This preservation of visuo-motor control was echoed in her day-to-day ability to navigate and live at home independently. We conclude that occipital calcification following coeliac disease can lead to prominent higher visual failure that, under prescribed viewing conditions, is consistent with separable mechanisms for visual perception and action control

Form completion across a hemianopic boundary: behindsight?

Patients with homonymous hemianopia may report the completion of forms that overlap the vertical meridian of their field defects. While previous investigations of “hemianopic completion” have variously attributed to the disorder to inattention, residual vision or unstable fixation, we believe that our investigation has controlled for such potentially confounding factors. We report patient P.O.V. who experienced hemianopic completion in everyday life following a surgical lesion of his left occipital lobe. He showed normal spatial attention and normal spatial orienting: hemianopic completion can therefore occur in the absence of inattention. His completion was retinotopic and affected partial as well as complete forms: his hemianopic completion cannot be attributed to residual visual input or poor fixation. P.O.V.'s completion was also systematically affected by varying stimulus contrast and pattern masking. We argue that while other explanations may be appropriate for different cases, P.O.V.'s hemianopic completion reflects normal “constructive” visual processes and can be attributed to the unconstrained operation of visual routines that are normally involved in the perception of partially occluded forms. As such, this disorder has the potential to shed light on some of the most basic aspects of visual perception