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Microphthalmia is a congenital disorder in which the globe of the eye is unusually small and structurally disorganized. [ 2 ] [ 4 ] While the axis of an adult human eye has an average length of about 23.8 mm (0.94 in), a diagnosis of microphthalmia generally corresponds to an axial length below 21 mm (0.83 in) in adults.
The pupil is a hole located in the center of the iris of the eye that allows light to strike the ... from constriction to as small as 2 mm, ... In normal lighting ...
If there is a unilateral small pupil with normal reactivity to light, it is unlikely that a neuropathy is present. However, if accompanied by ptosis of the upper eyelid, this may indicate Horner's syndrome. If there is a small, irregular pupil that constricts poorly to light, but normally to accommodation, this is an Argyll Robertson pupil.
Anisocoria is a common condition, defined by a diameter difference of 0.4 mm or more between the sizes of the pupils of the eyes. [2] Anisocoria has various causes: [3] Physiological anisocoria: About 20% of the population has a slight
The entrance pupil is typically about 4 mm in diameter, although it can range from 2 mm (f /8.3) in a brightly lit place to 8 mm (f /2.1) in the dark. The latter value decreases slowly with age; older people's eyes sometimes dilate to not more than 5–6mm in the dark, and may be as small as 1mm in the light. [26] [27]
A normal population survey showed that during poor light or near dark conditions, differences of 1 mm on average between pupils was found. [3] The presence of physiologic anisocoria has been estimated at 20% of the normal population, so some degree of pupil difference may be expected in at least 1 in 5 clinic patients. [citation needed]
By analogy with a camera, the pupil is equivalent to aperture, whereas the iris is equivalent to the diaphragm. It may be helpful to consider the Pupillary reflex as an 'Iris' reflex, as the iris sphincter and dilator muscles are what can be seen responding to ambient light. [2] Whereas, the pupil is the passive opening formed by the active iris.
Distance PD is the separation between the visual axes of the eyes in their primary position, as the subject fixates on an infinitely distant object. [2] Near PD is the separation between the visual axes of the eyes, at the plane of the spectacle lenses, as the subject fixates on a near object at the intended working distance. [3]