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During the examination, a laser beam passes through the pupil opening onto the back of the eye and scans the optic nerve head and the retina. A three-dimensional image is generated from several tens of thousands of measuring points, which allows a quantitative assessment of all relevant anatomical structures: [5] disc cup (shape, asymmetry),
The use of optic nerve sheath diameter (ONSD) for the assessment of ICP dates back to 1987 when Cennamo and colleagues [31] demonstrated a linear relationship between ICP and the sheath diameter measured with a trans-orbital ultrasound probe in an A-scan mode (principally equivalent to the time-of-the-flight measurements of the cranium diameter).
Normal retinal correspondence NV Near vision NWT Normal wearing time o symptoms Zero symptoms ϕ Horizontal orthophoria θ Vertical orthophoria ⊕ Horizontal and vertical orthophoria OC's Optical centres Occ. Occupation OD oculus dexter (right eye) OH Ocular history OMB Oculo motor balance ONH Optic nerve head Oph Ophthalmoscopy OS
In IIH these scans typically appear to be normal, although small or slit-like ventricles, dilatation and buckling [18] of the optic nerve sheaths and "empty sella sign" (flattening of the pituitary gland due to increased pressure) and enlargement of Meckel's caves may be seen.
In megalopapilla the optic disc diameter exceeds 2.1 mm (or surface area more than 2.5 mm 2 [1]) with an increased cup-to-disc ratio. [2] Although the optic disc is looks abnormal, the disc colour, sharpness of disc margin, rim volume, configuration of blood vessels and intraocular pressure will be normal.
Further evaluation with a CT scan or MRI of the brain and/or spine is usually done. Recent research has shown that point-of-care ultrasound can be used to measure optic nerve sheath diameter for detection of increased intracranial pressure and shows good diagnostic test accuracy compared to CT. [3]
The fibers from the retina run along the optic nerve to nine primary visual nuclei in the brain, from which a major relay inputs into the primary visual cortex. A fundus photograph showing the back of the retina. The white circle is the beginning of the optic nerve. The optic nerve is composed of retinal ganglion cell axons and glia.
In-flight ultrasound shows proximal kinking and increased optic nerve sheath diameter (ONSD) of approximately 12 mm that is consistent with raised ICPs. Optic nerve shown in purple and the ONSD in green. Figure 10: MRI (R+30 days) of the fourth case of visual changes from long-duration spaceflight. There is prominence of central T2 ...