Vision Flashcards
Refraction
Is the bending of light waves. At an angulated surface of a transparent material
Light does not bend when it strikes a perpendicular surface
What does the degree of refraction depend on?
The ratio of the two refractive indices of the two transparent media
The degree of angulation between the interface and the entering wave front of the light waves
Refractive index
In the ratio of the velocity of light in air to the velocity of light traveling in the substance
Refractive power
In a measure of how much a lens bends light waves, measures in diopters
1 diopter = 1 meter/focal length of lens
Focal point
The point through which all parallel rays of light will pass after passing through each part of the lens
Focal length
The distance from the center of the lens to the focal point
What is the funtion of the iris?
It controls the amount of light entering the eye, according to how much light is available
What’s the relationship between the pupillary diameter and the focus of the lens?
Depth of focus of the lens increased as the pupillary diameter decreased
Emmetropia
Normal with regard to depth of focus
Parallel light rays from distanct objects are in sharp focus on the retina when the ciliary mescle is completely relased
All distant objects are seen clearly
Hyperopia
Farsightedness
Usually due to an eyeball that is too short or weak lense
Distant objects are clear
Myopia
Nearsighted ness
When cillary muscle is completely relaxed, light rays from distant objects are focused in front of the retina
Eyeball long
What is visual acuity and resolving power? What is the max visual acuity for the human eye for two-point sources?
Visual acuity is the measure of the resolving power of the eye
Average diameter of a cone is 1.5µm
The max for two point source of light is 1.5 to 2µm
What are the cellular layer’s of the retina?
Photoreceptors - rods and cones
Horizontal cell
Bipolar cells
Amacrine cells
Ganglion cells
Rods and cones use which neurotransmitter?
Glutamate
They synapse with bipolar and horozontal cells
Amacrine cells use which type of neurotransmitters?
Inhibitory: GABA, Glycine, dopamine, Acetylcholine, indolamine
Horixontal cells
Recieve info from the rods and cones and transfer it to you bipolar cells - outer plexiform layer
the output in always inhibitory - lateral inhibition
Bipolar cells
Info from rods, cones and horozontal celss to inner plexiform later and synapse with amacrine and ganglion cells
Amacirne cells
Connetor between bipolar and ganglion cells
Interneurons that help analyze visual signals before they leave the retina
Ganglion cells
signals from retina to brain and make up optic nerves
Only retina cells that transmit AP
Which cells make up the pathway for cones (direct) pathway and the pure rod vision?
Direct pathway: cones, bipolar cells and ganglion cells
Pure rod vision: rods, bipolar cell, amacrine cells and ganglion cells
Rod vision pathway includes amacrine cells
Pathways in the fovea - fine vision
What are the functions of amacrine cells?
Part of the direct pathway for rod conductio n
Response to continuouing visual signals but fades quickly
Some respond with or without light
Response to movement across retine
Gen func: analyzing visual signals before they leave the retina
Ganglion cells
Make up optic fibers
In the fovea (visual acuity) less cones and rods converge on one ganglion cell
In the peripheral retina which are more sensitive to weak light, many rods converge on one ganglion cell
Three types: W, X and Y
W ganglion cells
Small, transmit signals in 8 m/sec
Mostly signals are from rods through bipolar or amacirne cells
Feilds in peripheral retine
40%
X ganglion cells
Medium size, signals transmit 14m/sec and the visual feild is small - represent discrete locations in the retina
Ever X ganglion has at least one cone cell. -> color vision?
55%
Y ganglion cell
Large, 50m/sec
Rapid changes in visual image
Fast CNS response/perception with lower accuracy
5%
How does fluid flow in the eye?
Flows from the anterior chamber into the canal of Schlemm and then into aqueous veins in the sclera
how is ion flow in the eye different in the light and the dark?
In the dark membrane is leaky to Na+ and the EN is reduced -> easier firing
In the light rhodopsin is damaged and transducin is released. Transducin causes sodium channels to close by cGMP and the cell is hyperpolarized.
What is the dorsal lateral geniculate nucleus? What is it’s purpose?
It relays information from the optic tract to the visual cortex by optic radiation. It serves as a transmission gate in that is controls how much of the signal is allowed to pass to the cortex
- by corticofugal fibers in primary visual cortex
- reticular formation from mesencephalon
Layers of the Primary Visual Cortex
Signals from macular area end in the macula
(Fovea)
The cortex extends along the calcarine fissure
What are color blobs and where are they?
Column areas intermixed in the columns of the secondary visual area, activated by color signals
What is accomadation?
Increasing the refractive power of the the lens. Children can have an accommodation of about 14 diotpers
