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The patient with 20/20 vision who can’t read UBC Clinical Neuroophthalmology Day Jason Barton What do you need to read? • 1. Low-level visual processes - intact central 5 degrees • 2. Eye movements - steady fixation and accurate saccades • 3. Attention • 4. Higher level visual processes - to decode form into letters and words • 5. Linguistic analysis - generating meaning and pronunciation from word forms that are seen Conclusion: reading can be derailed by a wide variety of problems. A systematic approach to acquired reading disorders is useful. 1. Visual fields and reading A. hemianopic dyslexia - central 5 degrees. Left hemianopia: trouble finding the beginning of lines, since the left margin disappears into the field defect as they scan rightwards. • Marking their place with an L-shaped ruler helps. Right hemianopia: prolongs reading times, with increased numbers of fixations and reduced amplitude of reading saccades to the right. • Smaller type and learning to read obliquely with the page turned nearly 90 degrees may help. • Reading performance can improve with time as both types of patients learn adaptive strategies Hemianopic dyslexia- eye movements: Trauzettel-Klosinski S, Brendler K. Eye movements in reading with hemianopic field defects: the significance of clinical parameters. Graefe’s Arch Clin Exp Ophthalmol 1998; 236: 91-102 Normal Left hemianopia Right hemianopia Case: Hemianopic dyslexia 37 year old man in MVA with brief LOC. Complains of difficulty reading. 20/20 ou. 1. Visual fields and reading B. hemifield slide, with bitemporal hemianopia absence of overlapping regions of binocular visual field leads to unstable binocular alignment with transient duplication or disappearance of words during reading. Case: Hemifield slide. 35 year old woman with 3 days of episodic diplopia: with reading, letters suddenly double, at other times they disappear. across the room vertical steps appear in windowsills and doorframes. She denied any visual loss. 20/20 OU. no RAPD. bilateral optic disc pallor. 2. Eye movements and reading. A. Inability to maintain steady fixation: (i) Nystagmus in primary position - congenital (usually with reduced acuity) - acquired - vestibular (usually too dizzy to read) - central (downbeat! - worse in downgaze) (ii) Saccadic intrusions - opsoclonus and ocular flutter - square wave jerks - PSP 2. Eye movements and reading. B. Inability to make accurate saccades: (i) Saccadic dysmetria (cerebellar lesions) (ii) Saccadic gaze palsy: - acquired ocular motor apraxia (bilateral frontal/parietal lesions) - supranuclear downgaze palsy (PSP, paramedian infarct) * Note: smooth pursuit is irrelevant to reading Case: Saccadic dysmetria and macrosaccadic oscillations 33 year-old woman with multiple sclerosis, presenting 12 years prior with optic QuickTime™ and a Cinepak decompressor are needed to see this picture. 3. Attention and reading. Neglect dyslexia. Left hemi-neglect, right parietal or frontal lesions • space-centered deficit: omit left side of lines or pages. • object-centered deficit: omit left side of words. - omissions ('bright' = 'right'), - additions ('right' = 'bright') - substitutions ('right' = 'light'). vertically printed text is not affected. *may occur without other signs of hemi-neglect 4. Higher level visual processes Pure alexia (alexia without agraphia) Spectrum of severity: • global alexia: cannot read numbers, letters and other abstract symbols (musical notation, road signs and map symbols) • letter-by-letter reading: slow reading with occasional errors, decipher words one letter at a time characteristic = word-length effect: reading time correlates with the number of letters in the word Associated signs (not invariable): • right hemianopia/superior quadrantanopia • anomia for colours and sometimes other visual objects. • impaired verbal memory, other visual agnosias, • optic ataxia: right hand has difficulty reaching to left visual field Left medial occipitotemporal lesion (PCA infarct) Two major explanations exist for pure alexia. 1. Disconnection alexia Most commonly, a) left occipital lesion = complete right hemianopia. Therefore no visual input to left language areas from the left brain. AND b) splenium/forceps major/periventricular white matter occipital horn, interrupt callosal fibers from the intact right occipital lobe. Therefore no visual input to left language areas from the right brain. Support: unusual cases with combination of a splenial lesion and right hemianopia from left non-occipital lesions, e.g. LGN. Two major explanations exist for pure alexia. 2. Word form agnosia visual agnosia from dysfunction of the left ventral extrastriate cortex fMRI shows activation of left “visual fusiform word area” by reading. associated with impaired processing of local texture, identification of complex objects in drawings Support: pathologic reports showing left fusiform and lingual gyral lesion but no splenial degeneration 5. Central (linguistic) dyslexia Most often associated with aphasia, dementia “Alexia with agraphia” - left angular gyrus lesion may be associated with other signs of Gerstmann’s syndrome (acalculia, right-left disorientation) Linguistic variants: • Phonological dyslexia - patients have lost the spelling rules but not their dictionary. problems only emerge when they have to spell novel words or pseudo-words (‘grickle’, ‘centus’). • Surface dyslexia - patients have lost the dictionary but not the rules patients can only read if they can sound it out. Hence they have trouble with irregular words (‘yacht’, ‘colonel’) • Deep dyslexia - patients have lost spelling rules and also make semantic errors (reading ‘cat’ for ‘dog’) Alexia with agraphia 55 year-old right-handed man with several weeks of daily headaches. Subtotal resection of left angular gyrus mass: glioblastoma. Exam: fluent speech, normal comprehension, mild anomia. trouble with calculations, right/left orientation. 20/30 od, 20/20 os. macular-splitting right hemianopia. Fundi normal. Difficulty reading- made semantic errors: (beautiful = ‘pretty’, but = ‘and’) Difficulty writing - spider = ‘sitre’, kite = ‘kibe’, hammer = ‘harer’ SUMMARY: When reading doesn’t work: • Low-level visual processes: hemianopic dyslexia (central 5 degrees) hemifield slide • Eye movements: fixation - nystagmus, saccadic intrusions saccades - dysmetria or palsy • Attention: hemineglect dyslexia • Higher level visual processes: pure alexia (disconnection, word-form agnosia) • Linguistic analysis alexia with agraphia, central dyslexias