Lecture 5 - Functional Eye Anatomy: Optics

Question 1

Using Marr’s first level of analysis (computational), how would we describe the eye’s function?

Answer 1

The human eye is sensitive to a narrow portion of
the electromagnetic spectrum. Our visual spectrum
ranges from 400 to 700 nanometers.

Question 2

what is the eye as this compound camera, really doing in its simplest terms? what problems is it solving?

Answer 2

the eye is a light detector sensitive to a narrow spectrum

forget about images, objects, etc..

Question 3

how does light get to the receptors in the eye - the path that light has to go through

Answer 3

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)

Question 4

as the light comes through, before it gets to the rods and cons (photo-reactive elements) it has to go through…

Answer 4

tissue and cell bodies

Question 5

mammals have what kind of retina?

Answer 5

inverted!

Question 6

Iris

Answer 6

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

Question 7

pupillary light reflex

Answer 7

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)

Question 8

vitreous humor

Answer 8

liquid that fills the inner eye

Question 9

where transduction takes place

Answer 9

back of the retina

Question 10

sympathetic nervous system, fight or flight response will cause pupils to

Answer 10

dilate - to get more sensory or light information

Question 11

Focusing light (onto the back of the retina)

Answer 11

first we have to go through the fixed lens of the cornea

Question 12

cornea

Answer 12

is a transparent

structure that provides about 80% of the eye’s focal power.

Question 13

lens

Answer 13

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?

Question 14

far point

Answer 14

eye not changing the size of the lens

The closest point at which a
RELAXED eye makes an object
appear CLEAR

Question 15

near point

Answer 15

The closest you can bring an

object and keep it in focus

Question 16

accommodation

Answer 16

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.

Question 17

ciliary muscle relaxed

Answer 17

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.

Question 18

ciliary muscle constricts and the lens

Answer 18

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.

Question 19

Age related changes in the lens

Answer 19

• 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.

Question 20

presbyopia

Answer 20

The distance of the near point will then increase.

(“old eye”).

Question 21

Detail Vision

Answer 21

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.

Question 22

macula

Answer 22

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

Question 23

fovea

Answer 23

only has cones!

is in the center of the
macula. It has the densest
concentration of cones that
provides fine detail vision.

Question 24

Optimal vision occurs when

Answer 24

cornea and lens focus light
directly into the center of the
fovea’s surface.

Question 25

one of the ways that the mammalian eye has overcome

Answer 25

is to “shunt” cell bodies off to the side: clear path so the light can come through

Question 26

Myopia (nearsightedness)

cause?

Answer 26

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

Question 27

Two types of myopia

Answer 27

1. Refractive myopia

2. Axial myopia

Question 28

treatment for myopia

Answer 28

The treatments are to use a corrective lens or to reshape (flatten) the cornea.

Question 29

Refractive myopia

Answer 29

the cornea or lens converges (focuses) light too much.

Question 30

Axial myopia

Answer 30

the eye is too long. Eyes aren’t perfect circles, and for some people its a little longer on the axial side

Question 31

Focusing light

• what’s the goal?

Answer 31

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.

Question 32

Hyperopia (farsightedness)

cause?

Answer 32

• 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).

Question 33

treatment for Hyperopia

Answer 33

usually a corrective

lens or surgery.

Question 34

Vitreous humor

Answer 34

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

•

Question 35

Floaters

Answer 35

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

Question 36

If your cornea refracts (bends) light too much, you are most
likely to have which of the following vision problems?

Answer 36

Myopia (nearsightedness)

Question 37

Cones aid in what sort of detection?

Answer 37

detailed vision, like color

located in the fovea (middle of the retina)

Question 38

Rods helpful for what sort of detection?

Answer 38

motion detection!

they are located in the periphery, which means you detect motion before you detect color