Eyes 2 Flashcards
what has the most refracting power in the eye
cornea
how refraction works
Light that strikes cornea is refracted (bent) going from air to solid cornea to fluid aqueous humor in the anterior chamber of the eye because of a change in speed of light rays as they pass through different media.
As light hits fluid in eye, it slows and bends toward the normal or line perpendicular to air-fluid interface.
Eye collects refracted light and focuses it on the retina to form images.
focal distance
the distance from the cornea (refractive surface) to the point where light rays converge at one point (focal point).
more curved on the fovea
less curved on the fovea
the shorter the focal distance
the longer the focal distance
vision under water
When under water, the speed of light rays is the same as in the fluid of the eye. Therefore without the refraction of light by the cornea, it is only bent by the lens and the image is focused behind the retina. Images appear blurry.
Wearing a scuba mask restores the refraction at the air-cornea interface and therefore images are clear.
why can some animals see in and out of water
Relatively flat corneas and spherical lenses but mediocre vision in both air and water – Penguins, Puffins, seals
Strongly curved corneas but also very deformable lenses – Cormorants, Mergansers
Four-eyed fish have eyes divided horizontally, hourglass shaped pupils and two halves of retina are sensitive to slightly different wavelengths of light.
lens accommodation
Changing shape of lens allows extra focusing power (changes focal distance)
The more curved your lens is,
the greater the refracting power (light will bend more with curve)
Far away objects =
Closer objects =
light rays parallel, don’t need as much bending
Light rays coming in from all angles or diverge, need to be bent to hit fovea
When Ciliary muscles contract =
muscles pull toward center of circle, forming a smaller space, less tension on zonule fibers, lens becomes rounder (more curvature, shorter focal length, see close up).
When Ciliary muscles relax =
muscles move toward outside of circle, increasing the open area, pulling on zonule fibers, lens becomes flatter (less curvature, longer focal length, see far away).
pupillary light reflex
Shine light into eyes and pupils constrict due to the contraction of circular muscles in the iris.
Continuously adjusting to different ambient light levels (like aperture on a camera).
direct light reflex
pupil constriction in the eye with light
consensual light reflex
pupil constriction in the eye with no light
If you shine a light in the right eye and there is no reflex in either eye, then what does this mean?
Lesion in optic nerve
If you shine a light in the right eye and there is no direct light reflex but the consensual light reflex is normal, then what does this mean?
Lesion in the right oculomotor nerve
What would happen if there were a lesion at the midbrain?
No reflex in both eyes
visual field
the whole area that can be viewed by one eye
binocular vision
depth perception due to overlapping visual fields.
image projected on retina is
Images are upside down and flipped from right to left
snellen eye chart
measures visual acuity. 20/20 vision means that you can discriminate letters/numbers at a distance of 20 feet. (20/40 would mean that a person would need to move to 20 feet to see the letters that a normal person could see at 40 feet and has half the normal acuity.)
pathway for visual field information to brain
Brain organizes visual information by combining what is seen from both eyes into visual fields.
Each half of the retina sends information via the optic nerve to the optic chiasma.
At the optic chiasma, right visual field data from both eyes goes to the left side of the brain and vice versa.
visual field test
Maps central and peripheral vision to detect areas of vision loss by having patient stare at a light directly ahead while other lights are flashed in the periphery. Patient pushes a button when light is detected and the visual field result is mapped for each eye, dark areas representing visual loss.
Detects blind spots caused by brain tumor, stroke, glaucoma, diabetes, hypertension, or head trauma.
