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Firearms with a direct impingement design can, in principle, be constructed lighter than piston-operated designs. Because high-pressure gas acts directly upon the bolt and carrier in a direct impingement system, it does not need a separate gas cylinder, piston, and operating rod assembly of a conventional piston-operated system, only requiring a gas tube to channel gas from the barrel back ...
The accommodation reflex refers to the swelling of the lens of the eye that occurs when one looks at a near object (for example: when reading, the lens adjusts to near vision). [1] The eye's blind spot is a result of the absence of photoreceptors in the area of the retina where the optic nerve leaves the eye. [1]
Some humans have the ability to exert direct and voluntary control over their iris sphincter muscles and dilator muscles, granting them the ability to dilate and constrict their pupils on command, regardless of lighting condition and/or eye accommodation state. [15] However, this ability is very rare, and its potential use or advantages are ...
Oculomotor nerve palsy or oculomotor neuropathy [1] is an eye condition resulting from damage to the third cranial nerve or a branch thereof. As the name suggests, the oculomotor nerve supplies the majority of the muscles controlling eye movements (four of the six extraocular muscles, excluding only the lateral rectus and superior oblique).
There is a direct correspondence from an angular position in the visual field of the eye, all the way through the optic tract to a nerve position in V1 up to V4, i.e. the primary visual areas. After that, the visual pathway is roughly separated into a ventral and dorsal pathway .
Entoptic images have a physical basis in the image cast upon the retina. Hence, they are different from optical illusions, which are caused by the visual system and characterized by a visual percept that (loosely said) appears to differ from reality.
Distribution of rods and cones along a line passing through the fovea and the blind spot of a human eye [1]. A blind spot, scotoma, is an obscuration of the visual field.A particular blind spot known as the physiological blind spot, "blind point", or punctum caecum in medical literature, is the place in the visual field that corresponds to the lack of light-detecting photoreceptor cells on the ...
Accommodation is the process by which the vertebrate eye changes optical power to maintain a clear image or focus on an object as its distance varies. In this, distances vary for individuals from the far point—the maximum distance from the eye for which a clear image of an object can be seen, to the near point—the minimum distance for a ...