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A petechia (/ p ɪ ˈ t iː k i ə /; [1] pl.: petechiae) is a small red or purple spot (≤4 mm in diameter) that can appear on the skin, conjunctiva, retina, and mucous membranes which is caused by haemorrhage of capillaries. [2] [3] The word is derived from Italian petecchia 'freckle', of obscure origin. [1]
Blue–red contrast demonstrating depth perception effects 3 Layers of depths "Rivers, Valleys & Mountains". Chromostereopsis is a visual illusion whereby the impression of depth is conveyed in two-dimensional color images, usually of red–blue or red–green colors, but can also be perceived with red–grey or blue–grey images.
Similar effects, some related to red-eye effect, are of several kinds: In many flash photographs, even those without perceptible red-eye effect, the tapetum lucidum of many animals' pupils creates an "eyeshine" effect. Although eyeshine is an unrelated phenomenon, animals with blue eyes may display the red-eye effect in addition to it.
As an oculofacial plastic surgeon, I get all kinds of questions about the under-eye area, and I’m here to tell you that not all under-eye conditions are created equal. There are a few tricks to ...
Purpura (/ ˈ p ɜːr p jʊər ə / [1]) is a condition of red or purple discolored spots on the skin that do not blanch on applying pressure. The spots are caused by bleeding underneath the skin secondary to platelet disorders, vascular disorders, coagulation disorders, or other causes. [2]
White cells are larger than red blood cells and can be larger than the diameter of a capillary, so must deform to fit. As a large, deformed white blood cell goes through a capillary, a space opens up in front of it and red blood cells pile up behind. This makes the dots of light appear slightly elongated with dark tails.
Dark dots seem to appear and disappear rapidly at random intersections, hence the label "scintillating". When a person keeps their eyes directly on a single intersection, the dark dot does not appear. The dark dots disappear if one is too close to or too far from the image. Hering illusion
Subconjunctival bleeding, also known as subconjunctival hemorrhage or subconjunctival haemorrhage, is bleeding from a small blood vessel over the whites of the eye. It results in a red spot in the white of the eye. [1] There is generally little to no pain and vision is not affected. [2] [3] Generally only one eye is affected. [2]