Medicine and Radiology - Research Publications

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    Visual search efficiency and functional visual cortical size in children with and without dyslexia
    Nguyen, BN ; Kolbe, SC ; Verghese, A ; Nearchou, C ; McKendrick, AM ; Egan, GF ; Vidyasagar, TR (Elsevier, 2021-05-14)
    Dyslexia is characterised by poor reading ability. Its aetiology is probably multifactorial, with abnormal visual processing playing an important role. Among adults with normal reading ability, there is a larger representation of central visual field in the primary visual cortex (V1) in those with more efficient visuospatial attention. In this study, we tested the hypothesis that poor reading ability in school-aged children (17 children with dyslexia, 14 control children with normal reading ability) is associated with deficits in visuospatial attention using a visual search task. We corroborated the psychophysical findings with neuroimaging, by measuring the functional size of V1 in response to a central 12° visual stimulus. Consistent with other literature, visual search was impaired and less efficient in the dyslexic children, particularly with more distractor elements in the search array (p=0.04). We also found atypical interhemispheric asymmetry in functional V1 size in the dyslexia group (p=0.02). Reading impaired children showed poorer visual search efficiency (p=0.01), needing more time per unit distractor (higher ms/item). Reading ability was also correlated with V1 size asymmetry (p=0.03), such that poorer readers showed less left hemisphere bias relative to the right hemisphere. Our findings support the view that dyslexic children have abnormal visuospatial attention and interhemispheric V1 asymmetry, relative to chronological age-matched peers, and that these factors may contribute to inter-individual variation in reading performance in children.
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    MR-EYE: High-Resolution MRI of the Human Eye and Orbit at Ultrahigh Field (7T)
    Glarin, RK ; Nguyen, BN ; Cleary, JO ; Kolbe, SC ; Ordidge, RJ ; Bui, B ; McKendrick, AM ; Moffat, BA (Elsevier, 2021-02-01)
    Key points • Dedicated eye imaging can be implemented at 7T to acquire high-resolution, high contrast-to-noise, and high signal-to-noise images in a feasible imaging time suitable for clinical use. • Simple, reproducible participant preparation techniques can be adopted to reduce the motion of the eye leading to a reduction in subsequent artefacts. • Sequences available at ultrahigh field can be used in current 7T clinical applications to visualize ocular structures otherwise impossible with other ophthalmic imaging.
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    Ultra-High Field Magnetic Resonance Imaging of the Retrobulbar Optic Nerve, Subarachnoid Space, and Optic Nerve Sheath in Emmetropic and Myopic Eyes
    Nguyen, BN ; Cleary, JO ; Glarin, R ; Kolbe, SC ; Moffat, BA ; Ordidge, RJ ; Bui, BV ; McKendrick, AM (Association for Research in Vision and Ophthalmology (ARVO), 2021-02-09)
    Purpose: We aimed to image the optic nerve, subarachnoid space and optic nerve sheath in emmetropes and myopes ultra-high field (7-Tesla) magnetic resonance imaging (MRI). We targeted the retrobulbar distance of approximately 3 mm behind the eyeball, an area of clinical interest because of optic nerve sheath distensibility and pressure-related enlargement. Methods: Eleven emmetropes (+0.75 to −0.50D, aged 20–41 years) and 10 myopes (−4.5 to −12D, aged 21–37 years) participated. Cross-sectional area of the optic nerve, subarachnoid space and optic nerve sheath at approximately 3 mm behind the eye were measured from two-dimensional T2-weighted coronal oblique MRI images obtained through the left optic nerve. Axial length of the left eye was measured from T2-weighted axial MRI images. In nine emmetropes and seven myopes, the optic nerve head was imaged with optical coherence tomography to compare retrobulbar and intraocular measures. Results: Retrobulbar optic nerve, subarachnoid space and optic nerve sheath dimensions differed between myopes and emmetropes. Myopes tended to have smaller optic nerve and subarachnoid space. Longer MRI-derived axial length was associated with smaller optic nerve area (P = 0.03). Bruch's membrane opening area did not predict retrobulbar optic nerve area (P = 0.48). Conclusions: This study demonstrates the feasibility of using 7-Tesla MRI to measure optic nerve, subarachnoid space, and optic nerve sheath dimensions behind the eye. In healthy adults, the retrobulbar optic nerve and subarachnoid space size are influenced by the degree of myopia. Translational Relevance: ultra-high field MRI is a practical tool for assessing the morphometry of the optic nerve and surrounding anatomy behind the eye.