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Representation of Thevisual Field in the Occipital

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Representation of Thevisual Field in the Occipital BritishJournal ofOphthalmology 1994; 78: 185-190 185 Representation of the visual field in the occipital striate cortex Br J Ophthalmol: first published as 10.1136/bjo.78.3.185 on 1 March 1994. Downloaded from Robert McFadzean, Donal Brosnahan, Donald Hadley, Erkan Mutlukan Abstract pole,2 although Inouye included a small repre- The representation of the field of vision in the sentation of the ipsilateral macula in each human striate cortex is based on the Holmes occipital lobe following the discovery of macular map in which about 25% of the surface area of sparing in some clinical cases.' Such bilateral the striate cortex is allocated to the centrallS representation of the macula has subsequently degrees of vision. Foliowing the introduction been invoked by a number of authors in primate of computed tomography of the brain, he animal experimental studies to explain the accuracy of the Holmes map was apparently clinial phenomenon of macular sparing,""-15 confirmed by clinical/radiological correlation, although in other studies bilateral representation but a revision has been proposed by Horton of the macula in the striate cortex did not and Hoyt based on a magnetic resonance occur.'6-18 Clinically, owing to fixational eye imaging study ofthree patients with visual field movements of one to two degrees during peri- defects due to striate lesions. They propose metry, there must be at least three degrees of that the central cortical representation of macular sparing to make the finding reliable vision occupies a much larger area. This study using currently available perimetric tech- reviews the perimetric and imagingfindings in a niques."" However, the bilateral representa- larger series of patients with striate cortical tion theory proposed in the above experimental disease and provides support for the revised studies is dependent on a nasotemporal overlap representation. The clinical phenomenon of across the vertical meridian which is only 0-6 to macular sparing and its relation to representa- 2 degrees wide."-" tion of the macula at the occipital pole is also Recently the traditional Holmes hypothesis discussed. was challenged in a magnetic resonance scanning (BrJ Ophthalmol 1994; 78: 185-190) study5 ofthree patients with striate disease and a revised map of the representation of the visual field in the human striate cortex was produced The representation of the visual field in the in which the area serving central vision was occipital striate cortex was initially delineated expanded and the area devoted to peripheral by Inouye' and subsequently by Holmes and vision reduced. Similarities to data from closely http://bjo.bmj.com/ Lister2 in studies of wounded soldiers in the related non-human primate species were noted, Russo-Japanese war (1904-1905) and the first in particular to electrophysiological studies of world war (1914-1918).2 Thereafter Holmes Old World primate genera, in which central devised his original 'schema' which gained wide- vision occupied a large proportion of the striate spread acceptance.4 In this diagrammatic outline cortex.'6172324 Indeed, in macaque monkeys the ofthe striate cortex Holmes demonstrated repre- central 15 degrees ofvision occupy about 70% of sentation of the contralateral hemifield of vision the total surface area ofthe striate cortex.2324 on September 29, 2021 by guest. Protected copyright. in each cerebral hemisphere, with the horizontal Horton and Hoyt's revision of the classical meridian occupying the base of the calcarine Holmes 'schema' requires confirmation in fissure and the vertical meridian demarcating a larger series of patients and the clinical the outer perimeter of the striate cortex. The phenomenon ofmacular sparing further elucida- macular region was represented posteriorly at tion. This paper attempts to address these two the occipital pole, while the peripheral visual issues. field occupied the anterior striate cortex in the region ofthe junction ofthe parieto-occipital and calcarine fissures. It was appreciated that the Materials and methods Departments of Neuro- macular region extended over a relatively large Patients suspected of suffering from occipital ophthalmology and part ofthe striate cortex and, using a planimeter, cortical disease had a full neuro-ophthalmic Neuro-radiology, Institute ofNeurological it has been calculated that 25% ofthe surface area examination including detailed perimetry. Sciences, Southern of the striate cortex was attributed to the central Goldmann dynamic and/or Humphrey's static General Hospital, 15 degrees ofvision.' Following the development threshold perimetry were used in the majority of Glasgow R McFadzean of computed tomography (CT) of the brain, cases, but if there was any doubt about the D Brosnahan several authors confirmed this original concept findings these were confirmed on the Bjerrum D Hadley when they found a good correspondence screen in a few cases. Imaging of the visual E Mudukan between visual field defects and the location of pathways, to confirm the presence of striate Correspondence to: Mr R McFadzean, striate lesions on CT according to the Holmes cortical disease and exclude any other lesion, was Department ofNeuro- 'schema'.`-9 An activation study of the visual carried out using a CT tomoscan and/or 0-15 ophthalmology, Institute of Neurological Sciences, cortex using positron emission tomography Tesla magnetic resonance (MR) scan. In some Southern General Hospital, (PET) scanning also supported the Holmes patients an initial planning scan was carried out 1345 Govan Road, Glasgow G51 4TF. 'schema'.'0 in the sagittal plane to identify the oblique course Accepted for publication Furthermore Holmes believed that the macula of the calcarine fissure, which does not of course 22 September 1993 was unilaterally represented at the occipital run in a straight line. Its oblique plane was 186 McFadzean, Brosnahan, Hadley, Mutlukan Table I Pathological lesions (n=26) No ofcases Br J Ophthalmol: first published as 10.1136/bjo.78.3.185 on 1 March 1994. Downloaded from Infarction 15 Neoplasm 5 Haematoma 3 Cerebromalacia 2 Arteriovenous malformation I Table 2 Visualfield defects (n=26) No ofcases Complete homonymous hemianopia 17 Incomplete homonymous hemianopia 5 Discrete homonymous scotomas 2 Bilateral altitudinal 2 Figure 3 Ti weighted (IR 16001401400) parasagittal Table 3 Macular Table 4 Occipitalpole/operculum sparing (n= 17) magnetic resonance sectwn shows a left occipital infarct involvement (n= 17) involving the superior bank ofthe striate cortex (arrowhead), No ofcases* but sparing the posterior striate cortex. No ofcases Macular sparing 9/11 Sparing 10 Macular splitting 0/7 determined by drawing a straight line on the Splitting 6 Sparing/splitting 1 *One case demonstrated both macular sparing and splitting sagittal scan joining its anterior (at the junction (case 5). with the parieto-occipital fissure) and posterior (at the occipital pole) limits. Subsequent scans were performed axially in the plane of the calcarine fissure or coronally at right angles to it. The imaging changes were then compared with the patient's visual fields and the expected visual fields according to the Holmes 'schema' and Horton and Hoyt's map. Results Occipital striate cortical disease was identified in 26 patients with an age range of 21-82 years (average 50 years) and a male to female ratio of 11:15. The majority of patients suffered from were a occipital infarction but there also number http://bjo.bmj.com/ of other pathologies (Table 1). The visual field defects were recorded (Table 2) in which a complete homonymous hemianopia is defined as one which extends to within 10 degrees ofcentral fixation, while an incomplete homonymous hemianopia lies beyond 10 degrees from central a fixation. A blind patient presented with on September 29, 2021 by guest. Protected copyright. macular sparing homonymous hemianopia and then lost the residual field a few days later due to FigureI T2 weighted (SE presumed bilateral occipital infarctions. 2000180) axial magnetic Macular involvement - that is, within 10 resonance section shows a left central occurred in 17 occipital infarct involving degrees of fixation, the anteromedial striate patients, unilaterally in 16 patients, and bilater- cortex, but sparing the ally in one patient (see below). These were posterior striate cortex. Figure 2 Goldmann dynamic visualfield shows a right homonymous hemianopia to within 10 degrees ofcentralfixation usingI2e and I4e targets. RE Representation ofthe visualfield in the occipital striate cortex 187 infarct following a head injury (Fig 1). Accord- ing to Holmes this infarct should have produced a right homonymous hemianopia extending to Br J Ophthalmol: first published as 10.1136/bjo.78.3.185 on 1 March 1994. Downloaded from within 60 degrees of fixation, while Horton and Hoyt predict a perimetric defect extending to within 20 degrees of fixation. In fact Goldmann 300 dynamic perimetry showed a right homonymous hemianopia extending to within 10 degrees of central fixation (Fig 2). Case 2 A 35-year-old woman developed a left occipital infarct (Fig 3). According to Holmes such a LE RE lesion would produce a right homonymous Figure 4 Humphrey's hemianopia extending to within 30 degrees of static threshold central visual fixation, while Horton and Hoyt predict a field field (30-2 program) shows a right homonymous defect extending to within 12 degrees offixation. hemianopia to within 10 Humphrey's static threshold perimetry showed a degrees ofcentralfixation. right homonymous
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