PS262 Chapter Notes - Chapter 3: Retinitis Pigmentosa, Macular Degeneration, Ciliary Muscle

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Published on 28 Sep 2012
School
WLU
Department
Psychology
Course
PS262
focusing light onto the retina
o light - the stimulus for vision
vision based on visible light
band of energies within electromagnetic spectrum
electromagnetic spectrum
continuum of electromagnetic energy produced by electric charges
and radiated as waves
can be described by wavelength
distance between peaks of the electromagnetic waves
measured in nanometers
visible light to humans is between 400 to 700 nanometers
also associated by the colours in a wavelength
o the eye
light refracted from objects enter through the pupil and focused on
cornea and lens to form sharp images on retina
retina has two receptors for vision
rods and cones
contain light-sensitive chemicals called visual pigments
reactive to light and triggers electrical signals
signals go through optic nerve and sends it to the brain
o light is focused by the eye
cornea accounts for 80% of the eye's focusing power
fixed in place and can't adjust focusing power
lens provides the remaining 20% of focusing power
can change shape to adjust focus for stimuli's distance
accommodation occurs to help the ciliary muscles increase or
decrease curvature to create sharp image on retina
o demonstration
near point
distance where your lens can't adjust to bring close objects into
focus
distance of near point increases as age increases
presbyopia
myopia / near-sightedness
inability to see distant objects clearly
can be caused by two factors
refractive myopia
cornea and/or lens bends light too much
axial myopia
eyeball is too long
faraway objects are not focused clearly so they
look blurred
far point
distance which spot of light becomes focused on retina
hyperopia / far sightedness
can see distant objects clearly, but not nearby objects
clearly
LASIK (laser-assisted in situkeratomileusis)
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surgery that involves sculpting cornea with excimer laser
if surgery is successful, it will result in good vision
transforming light into electricity
o visual receptors and transduction
transduction carried out by receptors
neurons specialized for receiving external stimuli
rods
key part is outer segment
light acts to create electricity on this
contains stacks of discs
discs contain thousands of visual pigment
molecules
molecules are long strands of protein
(opsin)
each molecule only contains one molecule
called retinal
retinal - crucial for transduction
since it's the only part that's
sensitive to light
when retinal is hit by a photon of light, it changes shape
process known as isomerization
triggers transformation of light into
electricity in receptors
o how does transduction work?
isomerization of visual pigment is a chemical process
can be studied by looking at the chemistry of visual pigments
can also measure it by doing psychophyiscal experiments
physiology of transduction
only one photon needed to activate a rod receptor
process known as enzyme cascade
sequence of reactions triggered by activated visual
pigment molecule
pigments and perception
o distribution of rods and cones
rods and cones interspersed in retina, not evenly
ratio of rods and cones depends on location on retina
fovea only contains 1% of all cones in retina (about 50,000)
fovea is all cones, when we look directly at object, image falls on
fovea
peripheral retina (rest of the retina outside fovea) contains rods and
cones
about 120 million rods, 6 million cones
most of retina's receptors are located here
two degenerative eye diseases that affect that retina
macular degeneration
common in older people
destroys cone-rich fovea, leaving a blind spot
retinitis pigmentosa
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Document Summary

Focusing light onto the retina light - the stimulus for vision. Electromagnetic spectrum continuum of electromagnetic energy produced by electric charges and radiated as waves can be described by wavelength. Distance between peaks of the electromagnetic waves. Visible light to humans is between 400 to 700 nanometers. Accommodation occurs to help the ciliary muscles increase or decrease curvature to create sharp image on retina: demonstration. Distance where your lens can"t adjust to bring close objects into focus. Distance of near point increases as age increases. Myopia / near-sightedness inability to see distant objects clearly can be caused by two factors refractive myopia cornea and/or lens bends light too much. Eyeball is too long faraway objects are not focused clearly so they look blurred far point. Distance which spot of light becomes focused on retina. Hyperopia / far sightedness can see distant objects clearly, but not nearby objects clearly.

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