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Photophobia is a medical symptom of abnormal intolerance to visual perception of light. [1] As a medical symptom, photophobia is not a morbid fear or phobia, but an experience of discomfort or pain to the eyes due to light exposure or by presence of actual physical sensitivity of the eyes, [2] though the term is sometimes additionally applied to abnormal or irrational fear of light, such as ...
Light sensitivity or photosensitivity refers to a notable or increased reactivity to light. Apart from vision , human beings have many physiological and psychological responses to light. In rare individuals an atypical response may result in serious discomfort, disease, or injury.
Sensitivity of the skin to a light source can take various forms. People with particular skin types are more sensitive to sunburn . Particular medications make the skin more sensitive to sunlight; these include most of the tetracycline antibiotics , heart drugs amiodarone , and sulfonamides .
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It is a light-sensitive receptor protein that triggers visual phototransduction in rods. Rhodopsin mediates dim light vision and thus is extremely sensitive to light. [6] When rhodopsin is exposed to light, it immediately photobleaches. In humans, it is regenerated fully in about 30 minutes, after which the rods are more sensitive. [7]
At moderate to bright light levels where the cones function, the eye is more sensitive to yellowish-green light than other colors because this stimulates the two most common (M and L) of the three kinds of cones almost equally. At lower light levels, where only the rod cells function, the sensitivity is greatest at a blueish-green wavelength.
A rod cell is sensitive enough to respond to a single photon of light [11] and is about 100 times more sensitive to a single photon than cones. Since rods require less light to function than cones, they are the primary source of visual information at night (scotopic vision). Cone cells, on the other hand, require tens to hundreds of photons to ...
The pupillary light reflex (PLR) or photopupillary reflex is a reflex that controls the diameter of the pupil, in response to the intensity of light that falls on the retinal ganglion cells of the retina in the back of the eye, thereby assisting in adaptation of vision to various levels of lightness/darkness.