Robert M. McFadzean

Pituitary apoplexy and its effect on vision.

A series of 15 patients with a clinical diagnosis of pituitary apoplexy is reviewed. Clinical features are highlighted, with stress on the defects of visual function and ocular motility, and the associated endocrine abnormalities are described. Potential diagnostic errors and their significance are considered. The incidence of this complication in a large series of pituitary adenoma patients is measured, and the radiological and pathological findings are recorded. The results of treatment by surgery and/or radiotherapy and/or bromocriptine are assessed, particularly in relation to visual consequences, and compared with previous reports in the literature, which are reviewed.

Habituation-like Effects Cause a Significant Decrease in Response in MRI Neuroactivation During Visual Stimulation

A wide range of rest/stimulus cycle durations (40-360 sec) is reported to have been used by various groups for MRI neuroactivation studies of the visual cortex. In this paper we demonstrate a clear habituation-like response for longer cycle durations which results in a halving of apparent activation between cycle durations of 138 and 276 sec. This has important implications, not only in terms of optimizing the technique, but also in providing an insight into the underlying physiological mechanisms.

Indirect injury to the optic nerves and optic chiasm

Abstract. Twenty-five cases of indirect injury to the optic nerve or chiasm following blunt trauma to the head were retrospectively reviewed. Falls onto the head and road traffic accidents together accounted for most (88%) of the head injuries. Bony skull fractures were identified in 23 cases (92%), although in only five of these (20%) was one of the optic canals or anterior clinoid processes involved in a fracture. Visual loss was bilateral in 11 patients (44%). In eight of these bilateral cases the visual field defects suggested a lesion at or near the optic chiasm. In one case optic nerve function deteriorated after the initial assessment. This deterioration was reversed by treatment, which consisted of surgical drainage of an orbital haematoma and systemic corticosteroids.

Nerve sheath tumors of the sellar region

Nerve sheath tumors, including schwannomas and neurofibromas, rarely affect the sellar region. The authors report two such cases that were mistaken for pituitary adenomas on the basis of clinical and imaging features.

Homonymous quadrantanopia respecting the horizontal meridian : A feature of striate and extrastriate cortical disease

It has been proposed that homonymous quadrantanopic visual field loss that respects the horizontal meridian is a pathognomonic sign of extrastriate cortical disease. However, two patients with this sign are reported-one with a rare striate and the other with an extrastriatal lesion of the visual cortex. It is therefore hypothesized that a homonymous quadrantanopia respecting the horizontal meridian may indicate striate and/or extrastriate cortical disease.

A diagnostic quartet in leptomeningeal infiltration of the optic nerve sheath.

A rare case of optic leptomeningeal carcinomatosis secondary to a rectal adenocarcinoma is recorded. The presentation of rectal disease with blindness is unique. A diagnostic quartet of symptoms and signs of leptomeningeal infiltration of the optic nerve sheath is proposed and its value emphasized by the inability of further investigation to confirm the clinical diagnosis. The investigation and treatment of leptomeningeal carcinomatosis is reviewed.

The representation of the visual field in the occipital striate cortex

The traditional Holmes’ view of the representation of the visual field in the occipital striate cortex was universally accepted for most of the last century.However, following the advent of detailed brain imaging, a reappraisal has taken place during the past decade. In particular, Horton and Hoyt have proposed a revised representation hypothesis with an increased representation of the central 10°. Nevertheless, controversies remain concerning firstly, the precise representation of the entire visual field throughout the occipital striate cortex, and secondly, the representation of macular or foveal vision (unilateral or bilateral). These issues have been addressed through experimental studies in non-human primates, clinical lesional studies in humans with correlation of perimetric deficits to brain-imaging abnormalities, and functional imaging studies in healthy volunteers. Recently, more sophisticated perimetric techniques with monitoring of fixational eye movements have allowed more detailed understanding of the macular/foveal representation in humans. An historical review will be contrasted with current concepts and compared with recent functional imaging studies.

Functional magnetic resonance imaging in the visual system.

Functional magnetic resonance imaging (fMRI) is a relatively new technique for measuring brain function during resting and activated conditions with good spatial and temporal resolution. Because of a robust and reproducible activation response to visual stimuli in the occipital cortex, many studies have been directed at visual function. The methodology has been refined progressively to allow more accurate detection of the small activation signal, and using computational mapping foci of cerebral activity have been displayed in a two-dimensional format. Several factors modifying the activation signal have been identified. fMRI has been used to define the retinotopic representation of areal boundaries and the localization of higher visual functions in the occipital cortex. Motion perception in area middle temporal (MT) is well-recognized, but eye movement studies are limited. The activated signal may have significant implications for our understanding of brain metabolism, but cerebral blood flow and oxygenation sensitive recordings after prolonged visual stimulation have given conflicting results. Clinically, fMRI can follow changes in cerebral activity during a progressive neurologic illness and measure responses to treatment. Neurosurgical planning in disorders such as epilepsy may be facilitated.

Positional acuity in amblyopia : does a perceptual consequence of neural recruitment exist?

Animal models of amblyopia have shown that visual deprivation for even brief periods can result in dramatic changes in cortical architecture. Active neural recruitment mechanisms present the possibility that the non‐deprived eye of amblyopes may show enhanced visual capacity. This idea was tested by measuring a form of positional acuity which we have termed alignment threshold. Three subject groups were examined, adults, visually normal children, and children with amblyopia in which the non‐deprived eye was tested. Alignment thresholds in adults were significantly better (∼0.3 log unit) than the thresholds for visually normal children. No significant difference was found in thresholds between the visually normal children and the non‐deprived eye of the amblyopic children. The results of this study suggest that subjects with unilateral amblyopia do not show enhanced visual alignment performance in their non‐deprived eye.

Local Expression of IL-18 in the Temporal Artery Does Not Correlate with Clinical Manifestations of Giant Cell Arteritis

Giant cell arteritis (GCA) is the commonest systemic vasculitis affecting patients older than 50 years and has been shown to be associated with up-regulation of the cytokine interferon (IFN)-gamma, whose activity is promoted by interleukin (IL)-18, a novel cytokine of the IL-1 family. Immunohistochemical staining was performed on 47 temporal artery biopsies (TAB) (38 positive and 9 negative). Positive staining was identified in 74% of positive temporal artery biopsies. All negative TABs showed no staining. The presence of positive staining showed no correlation with clinical manifestations or hematological parameters in these patients suggesting that factors other than IL-18 control the systemic effects of IFN-gamma in GCA.