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The human eye can function from very dark to very bright levels of light; its sensing capabilities reach across nine orders of magnitude.This means that the brightest and the darkest light signal that the eye can sense are a factor of roughly 1,000,000,000 apart.
Light from a single point of a distant object and light from a single point of a near object being brought to a focus. The accommodation reflex (or accommodation-convergence reflex) is a reflex action of the eye, in response to focusing on a near object, then looking at a distant object (and vice versa), comprising coordinated changes in vergence, lens shape (accommodation) and pupil size.
The size of the pupil, which controls the amount of light entering the eye, is adjusted by the iris' dilator and sphincter muscles. Light energy enters the eye through the cornea, through the pupil and then through the lens. The lens shape is changed for near focus (accommodation) and is controlled by the ciliary muscle.
There are many types of accommodation anomalies. It can be broadly classified into two, decreased accommodation and increased accommodation. [50] Decreased accommodation may occur due to physiological (presbyopia), pharmacological (cycloplegia) or pathological. [50] Excessive accommodation and spasm of accommodation are types of increased ...
Visual phototransduction is the sensory transduction process of the visual system by which light is detected by photoreceptor cells (rods and cones) in the vertebrate retina.A photon is absorbed by a retinal chromophore (each bound to an opsin), which initiates a signal cascade through several intermediate cells, then through the retinal ganglion cells (RGCs) comprising the optic nerve.
The visual system is the physiological basis of visual perception (the ability to detect and process light).The system detects, transduces and interprets information concerning light within the visible range to construct an image and build a mental model of the surrounding environment.
The parasympathetic tone is dominant when a higher degree of accommodation of the lens is required, such as reading a book. [6] The ciliary body is also known to receive sympathetic innervation via long ciliary nerves. [7] When test subjects are startled, their eyes automatically adjust for distance vision. [8]
Normally, as part of the pupillary light reflex, the pupil dilates in the dark and constricts in the light to respectively improve vividity at night and to protect the retina from sunlight damage during the day. A mydriatic pupil will remain excessively large even in a bright environment. The excitation of the radial fibres of the iris which ...