13. Perception of light, adaptation. Disorders of adaptation
Explains how the visual system turns light into neural signals, starting with the visible spectrum and the focusing role of the cornea and lens. Covers retinal layers, the photopigments of rods and cones, and the classes of colour vision deficiency. Closes with the changes during dark and light adaptation, including rhodopsin resynthesis and bleaching, pupil size, the Purkinje shift and the switch between rod and cone vision.
Topic 13 of 91 in the MU Sofia syllabus for Ophthalmology (Medicine, Year 4). The free AceMed note covers it in 1 section, about 474 words (3 min of reading), with 14 flashcards.
In this note
) Physiology of visual perception. Light perception. Adaptation
) Physiology of visual perception. Light perception. Adaptation
Visual perception
is the ability to interpret the surrounding environment
by using light in the visible spectrum, reflected by objects
visible spectrum of light: 390 – 700nm
the various physiologic components involved in vision ar referred to as
visual system
Visual system
part of the CNS
gives organism the ability to process visual detail
detects and interrets information from visual light
to build a representation of the surrounding environmen
carries out a number of complex tasks
reception of light
formation of mononuclear representations
idetification and categorization of visual objects
assessing distances to and between objects
guiding body movements related to the objects seen
act of seeing starts when
cornea and lens focuses light from its surroundings onto the retina
retina is actually a part of the brain
which is isolated to serve as a transducer
responsible for conversion of light into neuronal signals
based on feedback from the visual sstem the lens adjust its thickness
to focus the light on the photoreceptive cells of the retina
rods and cone detect photons of the light and respond by producing neural impulses
these signals are processed from the retina to central ganglia in the brain
the perception of objects is accomplished by the visual association cortex
combines all sensory information, received by the striate cortex
Transduction
the process in which enegry from an environmental stimuly is converted to neural activity
retina contains three different layers
photoreceptor layer
bipolar cell layer
ganglion cell layer
photoreceptor layer contains rods and cones
cones are responsible for color perception
three different cones (red, green and blue)
rods are responsible for objects in low light situation
protoreseptory contain a special photopigment composed of
opsin (protein)
retinal (lipid) → derivative of vitamin A
there are 3 specific photopigments, that respond to specific wavelength of light
when appropriate wavelength hits the receptor, the photopigment splits into two
this sends a message to the bipolar cell layer
which in turn sends a message to the ganglion cells
which then send information through the optic nerve to the brain
if the appropriate photopigment is not in the proper photoreceptor
result is color vision deficiency
trichromacy, bychromacy, monochromacy, achromacy
Rods
there are 120 million rods distributed over most of the retina
except near the retina
rod vision detects edges and motion very well
photochemical substance is rhodopsin
Cones
high concentration in fovea
photochemical substance is iodopsin
Adaption
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