Halo

HALO, a term denoting various clinical pictures in which the color of the observed tissue depends on the visibility of deeper parts through more superficial ones, which mostly undergo atrophic changes. This includes the darkening of the lower eyelid with a bluish tint that appears with age due to the transparency of deeper vessels through the skin that is undergoing atrophy. An identical halo is also obtained in young subjects when the deeper vessels dilate due to changes in cardiac activity or vascular tone (strong tension, fatigue, exhaustion caused by diseases, nutritional deficiency, etc.). But most frequently, the name halo is given to the grayish-white ring tightly surrounding the optic nerve head in the glaucomatous eye (halo glaucomatosus). Here we are dealing with the transparency of the sclera through the almost completely vanished vascular membrane and partially atrophied retina, which in the area of the halo has lost the pigment epithelium and other layers and consists almost entirely of glial tissue. A similar peripapillary atrophy can be found in elderly people without glaucoma. But in these cases, proliferation of the pigment epithelius is usually observed at the peripheral edge of the halo, which is not characteristic of the glaucomatous halo.