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.
