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Some skates and rays have crescent shaped pupils, [17] gecko pupils range from circular, to a slit, to a series of pinholes, [18] and the cuttlefish pupil is a smoothly curving W shape. Although human pupils are normally circular, abnormalities like colobomas can result in unusual pupil shapes, such as teardrop, keyhole or oval pupil shapes.
A slit pupil can indicate the common multifocal system, while a circular pupil usually specifies a monofocal system. When using a circular form, the pupil will constrict under bright light, increasing the f-number, and will dilate when dark in order to decrease the depth of focus. [49] Note that a focusing method is not a requirement.
The extraneous pupil is c. 2.5mm away from the principal pupil. In cases of true polycoria there is an intact sphincter muscle , which contracts and dilates the pupils. [ 7 ] In an eye without polycoria, the sphincter muscle is a part of the iris that functions to constrict and dilate the pupil.
Few people have spent time gazing into a sheep’s eyes, but if you have, you may have noticed something very strange about their pupils. Instead of being round, as is the case with humans, they ...
Pupils equal, round, reactive to light and accommodation PH Pinhole see Pinhole occluder and Visual_acuity#Legal_definitions: PHNI Pinhole No Improvement see Pinhole occluder and Visual_acuity#Legal_definitions: PHVA Pinhole Visual Acuity: PL Perception of light POH / PrOH Previous ocular history PPA Peri-papillary atrophy Pt Patient RAPD
One explanation for the evolution of slit pupils is that they exclude light more effectively than a circular pupil, helping to protect the eyes during daylight. [48] On the rear wall of the eye is a tapetum lucidum , which reflects incoming light back onto the retina, thus utilizing the small amount of light available at night to best advantage.
The pupil function of an ideal optical system with a circular aperture is a disk of unit radius. The optical transfer function of such a system can thus be calculated geometrically from the intersecting area between two identical disks at a distance of 2 ν {\\displaystyle 2\\nu } , where ν {\\displaystyle \\nu } is the spatial frequency ...
Several species of Felidae (cats) and snakes have vertically elongated (slit) pupils, advantageous for nocturnal ambush predators as it helps them to estimate the distance to prey in dim light; diurnal and pursuit predators in contrast have round pupils. [30]