Lecture 5 - Functional Eye Anatomy: Optics Flashcards
Using Marr’s first level of analysis (computational), how would we describe the eye’s function?
The human eye is sensitive to a narrow portion of
the electromagnetic spectrum. Our visual spectrum
ranges from 400 to 700 nanometers.
what is the eye as this compound camera, really doing in its simplest terms? what problems is it solving?
the eye is a light detector sensitive to a narrow spectrum
forget about images, objects, etc..
how does light get to the receptors in the eye - the path that light has to go through
step 1: eyes open
step 2: go through the cornea: fixed lens that does a lot of the focusing for the eye,
then through some liquid behind the cornea - aqueous humor: feeding the inner tissue and outside of the iris
opening in the iris and then hits the lens (other focusing element of the eye)
after the lens, the inner eye (filled with vitreous humor) and finally projected on the back of the eye in the retina (contains the photoreceptive cells)
get the energy from the distal object back of the retina (where transduction takes place)
as the light comes through, before it gets to the rods and cons (photo-reactive elements) it has to go through…
tissue and cell bodies
mammals have what kind of retina?
inverted!
Iris
the colored bit
can constrict or expand to regulate light input to the eye
- reflex action that responds to other things as well, but mainly responds to the amount of light coming in
pupillary light reflex
Constriction in one eye, in
response to light, causes the other pupil to constrict, even without direct light (will dilate with darkness)= sympathetic response
if there is swelling in the brain then it can cut off that connectivity (doctors checking your eyes to check your brain function)
vitreous humor
liquid that fills the inner eye
where transduction takes place
back of the retina
sympathetic nervous system, fight or flight response will cause pupils to
dilate - to get more sensory or light information
Focusing light (onto the back of the retina)
first we have to go through the fixed lens of the cornea
cornea
is a transparent
structure that provides about 80% of the eye’s focal power.
lens
flexible lens, and has the remaining 20% of your focusing power = dynamic, lens can change to the amount of light = accommodation, how far away is the object to which you are trying to focus?
far point
eye not changing the size of the lens
The closest point at which a
RELAXED eye makes an object
appear CLEAR
near point
The closest you can bring an
object and keep it in focus
accommodation
The lens is flexible and its
curvature (thickness) can be
adjusted to focus light on the
retina.
accounts for 20% of focusing power
is just the process of changing the lens
shape in the eye.
ciliary muscle relaxed
surrounds the lens,
when it is relaxed then it will open
has little fibers pull the lens and flatten it, which doesn’t bend the light as much
A flattened lens (ciliary
muscle relaxed) will bend the
incoming light less, resulting in
a more distant focal point.
ciliary muscle constricts and the lens
gets fatter
when objects are close
A fatter, more convex lens (ciliary muscle constricted) will bend the light more. This brings the focal length closer to the lens.
Age related changes in the lens
- The lens gets harder and less flexible as you get older.
– The ciliary muscles controlling the lens can also weaken.
– presbyopia (“old eye”).
– Also a greater chance of cataracts – clouding of the
lens – as you get older.
presbyopia
The distance of the near point will then increase.
(“old eye”).
Detail Vision
cones!!!
Incoming light is focused on the macula, a cone-rich area that allows high-resolution vision. It has a yellow pigment that absorbs blue and ultraviolet light.
• The fovea is in the center of the macula. It has the densest
concentration of cones that
provides fine detail vision.
• It is also largely free of ganglion
cells and capillaries, allowing
more light through.
• Optimal vision occurs when
cornea and lens focus light
directly into the center of the
fovea’s surface.
macula
where incoming light is focused
a cone-rich area that
allows high-resolution vision. It
has a yellow pigment that
absorbs blue and ultraviolet light.
yellow pigment that absorbs blues and ultraviolet light so you don’t get as much interference
fovea
only has cones!
is in the center of the
macula. It has the densest
concentration of cones that
provides fine detail vision.
Optimal vision occurs when
cornea and lens focus light
directly into the center of the
fovea’s surface.
one of the ways that the mammalian eye has overcome
is to “shunt” cell bodies off to the side: clear path so the light can come through
Myopia (nearsightedness)
cause?
An inability to clearly see objects at a distance.
• Reason: Distant images are focused in front of the retina.
we want the focal point to be AT THE BACK OF THE RETINA
Two types of myopia
- Refractive myopia
2. Axial myopia
treatment for myopia
The treatments are to use a corrective lens or to reshape (flatten) the cornea.
Refractive myopia
the cornea or lens converges (focuses) light too much.
Axial myopia
the eye is too long. Eyes aren’t perfect circles, and for some people its a little longer on the axial side
Focusing light
- what’s the goal?
The goal is to focus light on
the back of the retina.
• A flattened lens (ciliary
muscle relaxed) will bend the
incoming light less, resulting in
a more distant focal point.
• A fatter, more convex lens (ciliary muscle constricted) will bend the light more. This brings the focal length closer to the lens.
• Accommodation is just the
process of changing the lens
shape in the eye.
Hyperopia (farsightedness)
cause?
- An inability to clearly see close objects.
- Distant images are focused beyond the retina - not enough focal power between the cornea and the lens working together
- cause can be due to cornea or lens shape, or length of eye (too short).
treatment for Hyperopia
usually a corrective
lens or surgery.
Vitreous humor
gelatenous, viscous material in the eye,
closed system: the stuff you had at birth you pretty much have now
After passing through the lens,
light must travel through the
vitreous humor, a gelatinous
substance that helps maintain the shape of the eye.
• Floaters
•
Floaters
cast a shadow on the back of the retina because the light has to go through it
gray fuzzy thing on the periphery
can sometimes be seen in the vitreous as debris (blood cells, clotted vitreous, etc.) casts a shadow on the retina.
sudden increase (car accident, sports) GET CHECKED BY A DOCTOR, could be a small tear in the retina that would let red blood cells in
•Most people experience floaters, though an abrupt increase can signal a detached retina, retinal
tear, or other injury
In the vitreous humor
If your cornea refracts (bends) light too much, you are most
likely to have which of the following vision problems?
Myopia (nearsightedness)
Cones aid in what sort of detection?
detailed vision, like color
located in the fovea (middle of the retina)
Rods helpful for what sort of detection?
motion detection!
they are located in the periphery, which means you detect motion before you detect color
