PubMed · 14459307
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W KRAMER, G R MARTENS. 1962-08-18. [Posttraumatic bitemporal hemianopsia].. https://pubmed.ncbi.nlm.nih.gov/14459307/
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This article comprises a historical review of the literature pertaining to the representation of the visual field in human primary visual cortex. A brief survey of the anatomy of the visual system is followed by a critical evaluation of the key studies that have informed both the issue of the disproportionate representation of central vision within primary visual cortex, and the anatomical basis underlying the phenomena of macular sparing and macular splitting hemianopia.
PURPOSE OF REVIEW: This review of the more recent literature and testing strategies in patients with chiasmal syndromes focuses on the clinical evaluation and management of these patients. Visual loss is often the initial manifestation of disorders involving the optic chiasm. Hemianopic defects and preferential involvement of the temporal visual field are the earliest and most common visual deficits. Progression of the lesion may cause compression of adjacent structures, including the optic nerves and cavernous sinuses, and may result in more profound visual loss, ocular motor deficits, and hypopituitarism. RECENT FINDINGS: Although a number of modalities have been used to assess visual function in patients with chiasmal disorders, perimetry remains the most effective means of detecting and following the visual deficit. SUMMARY: Most chiasmal syndromes can be categorized as intrinsic (thickening of the chiasm itself) or extrinsic (compression of the chiasm from an adjacent structure). Magnetic resonance imaging is the best mode of neuroimaging for most chiasmal lesions and may also provide clues to the etiology of an isolated chiasmal syndrome.
OBJECTIVE: To investigate the role right foveal/parafoveal sparing plays in reading single words, word arrays, and eye movement patterns in a single case with an incongruous hemianopia. METHODS: The patient, a 48-year-old right handed male with a macular sparing hemianopia in his left eye and a macular splitting hemianopia in his right eye, performed various reading tasks. Single word reading speeds were monitored using a "voice-trigger" system. Eye movements were recorded while reading three passages of text, and PET data were gathered while the subject performed a variety of reading tasks in the camera. RESULTS: The patient was faster at reading single words and text with his left eye compared with his right. A small word length effect was present in his right eye but not his left. His eye movement patterns were more orderly when reading text with his left eye, making fewer saccades. The PET data provided evidence of "top-down" processes involved in reading. Binocular single word reading produced activity in the representation of foveal V1 bilaterally; however, text reading with the left eye only was associated with activation in left but not right parafoveal V1, despite there being visual stimuli in both visual fields. CONCLUSIONS: The presence of a word length effect (typically associated with pure alexia) can be caused by a macular splitting hemianopia. Right parafoveal vision is not critically involved in single word identification, but is when planning left to right reading saccades. The influence of top-down attentional processes during text reading can be visualised in parafoveal V1 using PET.