Function of the eye Flashcards
How does the lens focus?
The lens changes shape; the distance between the lens and the object remains unchanged
Emmetropia
The normal resting condition of the eye when the lens is flattened so that parallel rays from a distant object are focused
What is the far point of vision?
It is where the lens doesn’t have to thicken to focus
It’s about 20ft from the eye
Focal point
Where light rays cross and converge and cause focusing
What are the 3 events required to bring an image closer than 7 feet to focus called?
1) Accommodation
2) Pupil constriction
3) Convergence
Accommodation
The lens shape changes and becomes more spherical so it’s easier to see close up
Near point of vision
Where the lens can no longer become more convex and close up objects become blurry
Presbyopia
Increase in near point of vision as one ages. It’s why old people need reading glasses
Pupil construction
Responsible for depth of focus
Depth of focus
The greatest distance an object can move and still be focused
Covnergence
Medial rotation of the eye (cross-eyed)
2 Layer of the retina
Pigmented (anterior) and Nueronal (posterior)
Rods
Photoreceptor cells for noncolor vision
Rhodopsin
Purple pigment located in the discs of rods
Opsin
A protein in Rhodopsin
Renital (Vitamin A)
Yellow photosensitive pifment that bonds with opsin
Where are rod cells unstiumlated?
In the dark
Where are rod cells stimulated/ hyperpolarized
In the light
How does rod cell hyperpolarization work
Na+ channels close, less Na+ enters the cells, thus glutamate released decreases and the cell is hyper polarized
Light and dark adaptation
Adjustment of the eye changes in the amount of light.
It is achieved by changes in amount of available rhodopsin
Cones
Responsible for color vision and visual acuity
Require bright light to work well
Iodopsin
A visual pigment in cone cells
Why can we see all the colors?
Even thought there are only Red, green, and blue photo pigments, their wavelengths overlap which allows us to perceive multiple colors
Where are cones most numerous?
In areas of the retina associated with visual acuity, like the macula and fovea
Where are rods?
The are in the remainder of the retina
Myopia
Nearsightedness
Correct with a concave lens
Hyperopia
Farsightedness
Correct with a convex lens
Astigmatism
Cornea / lens is not uniformly curved
Dichromatism
Red/green colorblindness
2 cell types in the inner layer of the retina
Bipolar cells and ganglion cells
Optic disk
Where teh cells of the retina converge
Optic nerve
The cranial nerve leaving the eye and taking information to the visual cortex of the brain.
Optic chiasm
The place in the brain, behind the pituitary cavity, where the optic nerves meet and divide into two optic tracts
The optic tracts do what?
Take the information to the back of the brain to the optic radiations
Optic radiations
Take visual information to the visual cortex, where the brain interperates it.
Tunnel vision
Inability to detect objects in temporal half of visual field
Often a sign of a pituitary tumor
Binocular vision
Where the field of vision between both eyes overlap and gives us depth perception
