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A mydriatic pupil will remain excessively large even in a bright environment. The excitation of the radial fibres of the iris which increases the pupillary aperture is referred to as a mydriasis. More generally, mydriasis also refers to the natural dilation of pupils, for instance in low light conditions or under sympathetic stimulation.
The pupil is a hole located in the center of the iris of the eye that allows light to strike the retina. [1] It appears black because light rays entering the pupil are either absorbed by the tissues inside the eye directly, or absorbed after diffuse reflections within the eye that mostly miss exiting the narrow pupil.
The iris controls the size of the pupil by means of contracting the iris sphincter muscle and/or the iris dilator muscle. The size of the pupils is dependent on many factors (including light, emotional state, cognitive load, arousal, stimulation), and can range from less than 2 mm in diameter, to as large as 9 mm in diameter.
When viewed at large angles from the side, the iris and pupil may still be visible by the viewer, indicating the person has peripheral vision possible at that angle. [14] [15] [16] About 15° temporal and 1.5° below the horizontal is the blind spot created by the optic nerve nasally, which is roughly 7.5° high and 5.5° wide. [17]
Anisocoria is a common condition, defined by a difference of 0.4 mm or more between the sizes of the pupils of the eyes. [2]Anisocoria has various causes: [3] ...
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]
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Doubling pupil diameter increases the spherical aberration component by a factor of 16. [7] Thus, a small change in pupil size can cause a significant change in spherical aberration. This possibility should be considered in patients who have fluctuating vision despite well-healed corneas following keratorefractive surgery.