Lecture 5 - Functional Eye Anatomy: Optics Flashcards by andrea shelton

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.

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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..

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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)

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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

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mammals have what kind of retina?

inverted!

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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

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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)

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vitreous humor

liquid that fills the inner eye

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where transduction takes place

back of the retina

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

dilate - to get more sensory or light information

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Focusing light (onto the back of the retina)

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

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cornea

is a transparent

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

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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?

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far point

eye not changing the size of the lens

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

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near point

The closest you can bring an

object and keep it in focus

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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

1. 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