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Photopsia is the presence of perceived flashes of light in the field of vision. It is most commonly associated with: [4] posterior vitreous detachment; migraine aura (ocular migraine / retinal migraine) migraine aura without headache; scintillating scotoma; retinal break or detachment; occipital lobe infarction (similar to occipital stroke)
This can occur in low-light conditions, in the dark, or when the visual system amplifies light perception. In these cases, visual snow is a normal reaction of the body, related to the way photoreceptors (rods) and neurons respond to weak or insufficient stimuli. [citation needed]
In medicine, proton therapy, or proton radiotherapy, is a type of particle therapy that uses a beam of protons to irradiate diseased tissue, most often to treat cancer.The chief advantage of proton therapy over other types of external beam radiotherapy is that the dose of protons is deposited over a narrow range of depth; hence in minimal entry, exit, or scattered radiation dose to healthy ...
Vertical beams of light focus in front to horizontal beams of light, in the eye. This problem may be corrected using spectacles which have a "minus" cylinder placed on this horizontal axis. The effect of this will be that when a vertical beam of light in the distance travels towards the eye, the "minus" cylinder (which is placed with its axis ...
Myopia, also known as near-sightedness and short-sightedness, [5] is an eye disease [6] [7] [8] where light from distant objects focuses in front of, instead of on, the retina. [1] [2] [7] As a result, distant objects appear blurry while close objects appear normal. [1] Other symptoms may include headaches and eye strain.
Signs and symptoms are also applied to physiological states outside the context of disease, as for example when referring to the signs and symptoms of pregnancy, or the symptoms of dehydration. Sometimes a disease may be present without showing any signs or symptoms when it is known as being asymptomatic . [ 13 ]
Retinoblastoma (Rb) is a rare form of cancer that rapidly develops from the immature cells of a retina, [2] the light-detecting tissue of the eye. [3] It is the most common primary malignant intraocular cancer in children, and 80% of retinoblastoma cases are first detected in those under 3 years old.
The slotted optical switch, sometimes known as opto switch or optical switch but not to be confused with the optical component, is a device comprising a photoemitter (e.g. LED) and a photodetector (e.g. photodiode) mounted in a single package so that the photoemitter normally illuminates the photodetector, but an opaque object can be inserted in a slot between them so as to break the beam.