pupilless, adj.
/pyooh"peuhl/, n.
1. a person, usually young, who is learning under the close supervision of a teacher at school, a private tutor, or the like; student.
2. Civil Law. an orphaned or emancipated minor under the care of a guardian.
3. Roman Law. a person under the age of puberty orphaned or emancipated, and under the care of a guardian.
[1350-1400; ME pupille < MF < L pupillus (masc.), pupilla (fem.) orphan, ward, diminutives of pupus boy, pupa girl]
Syn. 1. apprentice, novice. PUPIL, DISCIPLE, SCHOLAR, STUDENT refer to a person who is studying, usually in a school. A PUPIL is one under the close supervision of a teacher, either because of youth or of specialization in some branch of study: a grade-school pupil; the pupil of a famous musician. A DISCIPLE is one who follows the teachings or doctrines of a person whom he or she considers to be a master or authority: a disciple of Swedenborg.
SCHOLAR, once meaning the same as PUPIL, is today usually applied to one who has acquired wide erudition in some field of learning: a great Latin scholar. A STUDENT is a person attending an educational institution or someone who has devoted much attention to a particular problem: a college student; a student of politics.
pupilless, adj.
/pyooh"peuhl/, n. Anat.
the expanding and contracting opening in the iris of the eye, through which light passes to the retina. See diag. under eye.
[1350-1400; ME < L pupilla lit., little doll; for sense cf. Gk kóre girl, doll, pupil of the eye, alluding to the tiny reflections visible in the pupils. See PUPA]

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      in the anatomy of the eye (eye, human), the opening within the iris through which light passes before reaching the lens and being focused onto the retina. The size of the opening is governed by the muscles (muscle) of the iris, which rapidly constrict the pupil when exposed to bright light and expand (dilate) the pupil in dim light. Parasympathetic nerve fibres from the third (oculomotor) cranial nerve innervate the muscle that causes constriction of the pupil, whereas sympathetic nerve fibres control dilation. The pupillary aperture also narrows when focusing on close objects and dilates for more distant viewing. At its maximum contraction, the adult pupil may be less than 1 mm (0.04 inch) in diameter, and it may increase up to 10 times to its maximum diameter. The size of the human pupil may also vary as a result of age, disease, trauma, or other abnormalities within the visual system, including dysfunction of the pathways controlling pupillary movement. Thus, careful evaluation of the pupils is an important part of both eye and neurologic exams.

Daniel M. Albert David M. Gamm

 in optical (optics) systems, the virtual image of an aperture associated with mirrors, prisms, and lenses and their combinations. The Figure—> shows the case of an optical system composed of two lenses with a stop between them. The virtual image of the aperture for lens I (as seen from the object point) is called the entrance pupil. The amount of light leaving the object and traversing the system is limited, in effect, by the entrance pupil, just as it is actually by the stop aperture. The image of the aperture for lens II is the exit pupil. In general, an optical system has one effective aperture, and the entrance pupil is formed by all lenses preceding the stop, whereas the exit pupil is formed by all lenses following it.

      In visual instruments, the exit pupil falls at the eye position. In the microscope and telescope the objective acts as the aperture, its image is the exit pupil, and all light reaching the objective passes through the exit pupil. Thus, it is important for the exit pupil to be no larger than the pupillary diameter of the eye to take advantage of the light-gathering power of the instrument.

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Universalium. 2010.