problem 1 - the eye Flashcards
The pupil
- controls intensity of the light entering the eye
- controlled by the contraction of the iris
the cornea
- focuses the light that enters the eye
- accounts for 80% of the eye’s focusing power - but its fixed in place, so can’t adjust its focus (like a glasses lense)
- transparent membrane
the lens
- works with cornea to adjust the light
- supplies the remaining 20% of the eyes focusing power - can adjust (ciliary muscles and zonule fibers) its shape to focus on stimuli located in different distances
diff between iris and lens:
iris is responsible for the amount of light and is adjusted to the light in the room, whereas the lens is focused on the objects and their shapes
the iris
- colored part, a small donut-shaped muscle with an opening in the middle (light enters)
Intense light = contraction (constricts) = pupil smaller
Dim light = relaxation (dilates) = pupil larger
the lens: accomodation
ciliary muscles at the front of the eye tighten and increase the curvature of the lens so that it gets thicker
→ the curvature bends the light rays, which pull the focus point back to retina (image becomes sharp)
the lens: near point
limit of accommodation → distance at which your lens can no longer adjust to bring close objects into focus
the 3 membranes: sclera/fibrous tunic
tough, protective covering (the white of our eye) with transparent cornea
the 3 membranes: choroid/vascular tunic
- lines the interior of sclera
- contains most of the blood vessels (supply the eye with oxygen and nutrients)
the 3 membranes: retina
made up of neurons including the receptors that convert the light entering the eye into neural signals
the 3 chambers: anterior chamber
- between cornea and iris, filled with clear thin fluid called aqueous humor
- contains nutrients for the eye & helps to keep pressure
the 3 chambers: posterior chamber
between iris and lens, filled with clear thin fluid called aqueous humor
the 3 chambers: vitreous chamber
- main interior portion of the eye
- filled with vitreous humor: a clear more gel-like fluid - helps maintain shape of the eye
intraocular pressure
the pressure of fluids in the chambers must be > than air pressure (to prevent collapsing of the eyes)
optic nerve
brings the light info to the brain from the eye through electrical impulses
photoreceptors in the retina: rods
- provide black and white vision in dim light
- rods are more sensitive to light than cones
- there are many more rods than cones in the retina (120m rods and 6m cones)
photoreceptors in the retina: cones
provide high-acuity color vision in bright light
* S-cones: most sensitive to short wavelengths of light
* M-cones: most sensitive to medium wavelengths of light
* L-cones: most sensitive to longer wavelengths of light
* Cones are more responsible for detailed vision - responsible for color perception
horizontal cells (retina)
- transfer info to other horizontal cells + to the cones and rods
- determine how much other cells around them will be activated or not activated (related to lateral inhibition)
bipolar cells (retina)
receive signals from the rods and the cones to transfer it to the other cells, the amacrine and the ganglion cells
amacrine & ganglion cells (retina)
send action potential to the optic nerves which goes further to the brain
myopia / near-sightedness
inability to see distant objects clearly
* myopic eye brings the rays of light into focus in front of the retina = image reaching the retina is blurry
refractive myopia: cornea and/or lens bends the light too much
axial myopia: eyeball is too long
hyperopia / farsightedness
trouble seeing nearby objects
* light into focus behind the retina = image reaching the retina is blurry
* can be caused by eye being too small
astigmatism
blurred distance and near vision
* caused by cornea having an irregular shape - it is more oblong than round
presbyopia
the distance of the near point increases as a person gets older
* lens gets harder & muscles get weaker = cannot accommodate as easily
retinitis pigmentosa
degeneration of the retina (hereditary) - first attacks the peripheral rod receptors = poor vision of the peripheral field
In severe cases, foveal cone receptors also attacked = complete blindness
macular degeneration
fovea and area around it destroyed = blind spot in central vision
* when the person looks at something, they lose sight of it (most common in elderly)
* peripheral vision is still intact
the blind spot
place where the optic nerve leaves the eye = no receptors
* everyone has one
* Is located off to the side of our visual field, where objects are not in sharp focus
* We don’t see the blind spot because the brain “fills it in”
detached retina
- Usually caused by accidents
- Vision is disturbed because you cannot process the light anymore
- No connection between photoreceptors and the brain
glaucoma
a group of eye diseases that can cause vision loss and blindness by damaging the optic nerve due to a lot of pressure
* The pressure comes from a build up of fluid in the anterior chamber
lateral inhibition
inhibition transmitted across the retina - the phenomenon in which a neuron’s response to a stimulus is inhibited by the excitation of a neighboring neuron
* Influences how one perceives light and dark - causes you to be less sensitive to light
simultaneous contrast
occurs when our perception of the brightness or color of one area is affected by the presence of an adjacent or surrounding area
hypothesis of belongingness (white’s illusion)
area’s appearance is influenced by the part of the surroundings to which the area appears to belong
* explains white’s illusion where lateral inhibition cannot
