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a circular structure, such as a luminous circle seen surrounding an object or light.
Fick's halo a colored circle appearing around a light, experienced by wearers of contact lenses.
halo glaucomato´sus (glaucomatous halo) a narrow light zone surrounding the optic disk in glaucoma.
senile halo a zone of variable width around the optic disk, due to exposure of various elements of the choroid as a result of senile atrophy of the pigmented epithelium.
circumpapillary halo seen in choroidal atrophy of the aged.