Neural correlates of hemianopic completion across the vertical meridian.

Hemianopic completion refers to the perceptual completion of figures located across the vertical meridian in the context of hemianopia, such that one half of the figure falls within the blind hemifield. It can occur whether the figure is itself complete (veridical completion) or incomplete (paracompletion). Psychophysical evidence suggests that this phenomenon may be a constructive one, and may share features with completion phenomena in normal vision. The neural structures mediating hemianopic completion are unknown. Here we studied the neural activity evoked by hemianopic completion using event-related fMRI in an individual (POV) with a large right visual field homonymous hemianopic scotoma due to left occipital damage. Either a large achromatic circular contour straddling the vertical meridian or a semicircular contour within the left hemifield just crossing the vertical meridian was presented to POV on each trial. POV indicated by button press whether he perceived a semicircular contour, a patchy circular contour or a complete circular contour. On trials where he reported perceiving a complete circular contour despite being presented with a semicircular contour (paracompletion), activity was increased in a region of ipsilateral extrastriate cortex (contralateral to the lesion, ipsilateral to the illusory edge of the circle). These results are discussed in the context of illusory contour completion in healthy subjects and more generally in the recovery of function after brain damage.

Assessing visual fields for driving in patients with paracentral scotomata.

BACKGROUND: The binocular Esterman visual field test (EVFT) is the current visual field test for driving in the UK. Merging of monocular field tests (Integrated Visual Field, IVF) has been proposed as an alternative for glaucoma patients. AIMS: To examine the level of agreement between the EVFT and IVF for patients with binocular paracentral scotomata, caused by either ophthalmological or neurological conditions, and to compare outcomes with useful field of view (UFOV) performance, a test of visual attention thought to be important in driving. METHODS: 60 patients with binocular paracentral scotomata but normal visual acuity (VA) were recruited prospectively. Subjects completed and were classified as "pass" or "fail" for the EVFT, IVF and UFOV. RESULTS: Good agreement occurred between the EVFT and IVF in classifying subjects as "pass" or "fail" (kappa = 0.84). Classifications disagreed for four subjects with paracentral scotomata of neurological origin (three "passed" IVF yet "failed" EVFT). Mean UFOV scores did not differ between those who "passed" and those who "failed" both visual field tests (p = 0.11). Agreement between the visual field tests and UFOV was limited (EVFT kappa = 0.22, IVF kappa 0.32). CONCLUSIONS: Although the IVF and EVFT agree well in classifying visual fields with regard to legal fitness to drive in the UK, the IVF "passes" some individuals currently classed as unfit to drive due to paracentral scotomata of non-glaucomatous origin. The suitability of the UFOV for assessing crash risk in those with visual field loss is questionable.

Familial British dementia with amyloid angiopathy: early clinical, neuropsychological and imaging findings.

Familial British dementia with amyloid angiopathy (FBD) is an autosomal dominant condition characterized by a dementia, progressive spastic tetraparesis and cerebellar ataxia with onset in the sixth decade. A point mutation in the BRI gene has been shown to be the genetic abnormality. Genealogical work with the large family originally reported by Worster-Drought and updated by Plant has identified nine generations dating back to the late eighteenth century. The pedigree now includes six living affected patients, 35 historical cases, and 52 descendants at risk of having inherited the disease. A common ancestor has been identified between the large pedigree and a case report of 'familial cerebellar ataxia with amyloid angiopathy'. An autopsy case from a separate family with an identical condition is described but no common ancestor with the large pedigree has been found. Case histories have been researched and updated in each pedigree. Eleven individuals at risk of FBD, aged between 44 and 56 years, agreed to undergo a clinical and neuropsychological assessment along with MRI brain imaging in order to clarify early diagnostic features. Five of the eleven were thought to show early clinical signs of the disease. Neurological examination was abnormal in three, with limb and gait ataxia and mild spastic paraparesis. Three had impaired recognition and recall memory and another had mild impairment of delayed visual recall. All affected individuals had an abnormal MRI of the brain, consisting of deep white-matter hyperintensity (T(2)-weighted scans) and lacunar infarcts, but no intracerebral haemorrhage. The corpus callosum was affected particularly, and in one patient it was severely atrophic.

Cerebral achromatopsia as a presentation of Trousseau's syndrome.

A 67-year-old man developed a sudden onset of achromatopsia. Magnetic resonance imaging showed occipital lobe infarction. Repeated episodes of neurological deficit referable to the posterior circulation initially suggested an embolic source, but subsequently proved to be due to a coagulopathy related to a carcinoma of the bladder. This has implications for the management of patients presenting with achromatopsia, and progressive or recurrent neurological episodes, and in particular the use of anticoagulation in this situation.