Chapter 9: The Eye Flashcards
Light
electromagnetic radiation that is visible to our eyes
Properties of light
energy is proportional to frequency, gamma radiation and cool colors = high energy. Radio waves and hot colors = low energy.
Optics
study of light rays and their interactions
reflection
bouncing of light rays off a surface
absorption
transfer of light energy to a particle or surface
refraction
bending of light rays from one medium to another
pupil
opening in the center of the iris where light enters the eye
lens
transparent, changes shape to focus light on retina. responsible for 20% of focusing.
retina
what the light is projected onto, part of eye responsible for actual vision.
cornea
clear covering of the center of eye, protects and bends light to focus on lens. Accounts for 80% of focusing
visual receptors
line the retina
sclera
white part of the eye
iris
colored part of the eye
choroid
brown layer with blood vessels
optic nerve
bundle of axons from the retina
aqueous humor
fluid behind cornea
Zonule fibers
ligaments that suspend the lens
ciliary muscle
forms a ring inside the eye
vitreous humor
viscous, jelly-like substance lies between lens and the retina, keeps eyeball spherical.
blind spot
where the optic nerve exits the eye to the brain.
macula
the part of the retina for central vision.
optic disk
where retinal vessels originate from, where optic nerve fibers exit the retina.
fovea
a dark spot, retina is thinner in fovea, consists solely of cones.
nasal retina
part of the retina that lies closer to the nose than the fovea
temporal retina
part of the retina that lies near the temple.
accomodation
additional focusing power provided by changing that shape of the lens. To focus on distant objects - Ciliary muscles relax, stretching the zonule fibers and flattening the lens. To focus on near objects - requires greater refraction, contracting ciliary muscle so there’s less tension in zolune fibers.
Pupillary light reflex
pupil continuously adjusts to different ambient light levels, connections between retina and brain stem neurons control muscles around pupil, consensual.
the visual field
amount of space viewed by retina when eye is fixated straight ahead, inverted image.
visual acuity
ability to distinguish two nearby points
visual angle
distance across the retina described in degrees.
Anatomy of the retina
information of light flows from photoreceptors to bipolar cells to ganglion cells which projects axons out of the eye in the optic nerve.
Horizontal cells
receive input from photoreceptors and project to other photoreceptors and bipolar cells.
amacrine cells
receive input from bipolar cells and project to ganglion cells, bipolar cells, and other amacrine cells.
Laminar organization of retina
cells are organized in layers
pigmented epithelium
light passes through ganglion cells and bipolar cells before reaching photoreceptors.
tapetum lucidum
a reflective layer beneath photoreceptors
ganglion cell layer
innermost retinal layer, contains the cell bodies of the ganglion cells.
inner nuclear layer
contains the cell bodies of the bipolar cells, horizontal cells, and amacrine cells.
outer nuclear layer
contains the cell bodies of the photoreceptors.
inner plexiform layer
between ganglion and inner nuclear layer, contains the synaptic contacts between bipolar cells, amacrine cells, and ganglion cells.
outer plexiform layer
between outer and inner nuclear layers, where the photoreceptors make contact with the bipolar and horizontal cells.
layer of photoreceptor outer segments
contains the light-sensitive elements of the retina.
pigmented epithelium
where the outer segments are embedded in.
cross section of fovea
pit in retina where outer layers are pushed aside, maximizes visual acuity.
central fovea
all cones, area of highest visual acuity.
rods
long, cylindrical outer segment with many disks, low spatial resolution, achromatic, all contain same photopigment, over 1000 times more sensitive to light than cones. Most abundant in periphery of the eye and respond to faint light.
cones
shorter, tapering outer segment with fewer disks, high resolution, chromatic, three types all containing different photopigments. Most abundant in and around fovea, essential for color vision and useful in bright light.
differences in rods and cones
duplex retina - two complementary systems in one eye.
young Helmholtz trichromatic theory
color perception occurs through the relative rates of response by three kinds of cones, each one maximally sensitive to a different set of wavelengths.
color vision deficiency
inability to perceive color differences, results when people with certain genes fail to develop one type of cone or develop an abnormal type of cone.
dark adaptation
getting used to the dark, sensitivity to light increases a millionfold or more during this period.
light adaptation
reversing the changes in the retina that accompanied dark adaptation.
receptive field
area of the retina where light changes neuron’s firing rate.
