Initial 7C questions Why can’t we see in the dark? Why can we see in the dark? How do we cry? How do our eyes form the color in them? How do your eyes work? What is the purpose off the Iris? Why do people have different eye colors? Does the color of your eye affect your seeing? How do we see different colors? Why do we see upside down and our brain flips it right side up?

The Cow and Human Eye

What do the parts do?

Eye Parts and Functions Aqueous humor – a clear fluid that helps the cornea (the front of the eye) keep it’s rounded shape. Blind spot (disc) or beginning of the optic nerve. The place where all nerves from the retina join to form the optic nerve, there are no light-sensitive (photoreceptor) cells here. (see picture) Cones- photoreceptor (light sensitive cells) that detect color. Cornea- The front clear covering of the eye. It helps protect the eye and bends the light some.

The Human Retina

Eye Parts and Functions (cont) Iris – the colored muscle that controls how much light enters the eye. It is suspended between the cornea and lens. (cow’s are all brown) Lens- A clear, flexible structure that makes an image on the eye’s retina. It can change shape to focus on objects nearby and close. (see pict) Optic nerve – the bundle of nerve fibers that carry a signal from the retina to the brain. (you will place your dissecting needle tool through this) Pupil – The pupil is the dark circle in the center of your eye. It’s a hole that lets light into the eye. Humans are round and a cow’s is oval.

Last eye parts and functions  Tapetum – layer found behind the retina in animals with good night vision. It is colorful and shiny and reflects light back through the retina. Vitreous humor- the thick, clear (in a chemically untreated eye) jelly that is behind the lens and helps give the back of the eyeball its shape.

Dissection Tools – Demo Kit Blunt probe Dissecting scissors Dissecting needle Scapel – Very important to handle carefully and to not use too much force as the blade can break. Forcepts (fancy tweezers)

Eye Parts and functions Retina – the layer of light-sensitive cells at the back of the eye. It detects images focused by the cornea and lens. It is made up primarily of rods and cones. Sclera – the thick tough white outer covering of the eyeball.

Rods and Cones Rods – a photoreceptor (light sensitive) type off cell that can’t detect color, only dim light. Best for motion. Cones- photoreceptor (light sensitive cells) that detect color and detail. Photoreceptor – cells that detect light and send signals. They are a type of neuron. Neuron- a nerve cell (they can send signals)

Is it yellow? https://www.youtube.com/watch?v=R3unPcJDbCc (only watch the first 2:15 min, can cut at electricity)

Front of eye near lens (almost all rods) Sides of retina middle of eye (more rods than cones) Back/Center of retina (Macula/fovea/dark spot) only cones Optic disk (no photoreceptors – it is a blind spot)

Two spots on the retina 1 spot is the dark red macula (fovea in center) This is where the detailed reading image of your vision straight ahead (0 to 5 degrees) is projected on your retina. 1 spot is the optic disk (blind spot) This is the spot which looks bright in the picture. It is where the optic nerve that goes to the brain attaches. Many blood vessels come from here. There are no photoreceptors (rods or cones) here.

The cones are fewer (only about 5% of the photoreceptors in the eye! ) 3 types of cones, each detects one color Red Blue Green 125 million rods – only 6 million cones Cones need light to function Cones are not at the front of the eye, only middle and back.

Sharpest eyesight – Birds of prey                                                                     © law_keven – flickr Sharpest eyesight – Birds of prey The eyesight of birds such as eagles, hawks and buzzards is 3-4 times sharper than ours. Eagles can spot rabbits from several miles away while hawks and buzzards often scan the earth from a height of 10-15,000 feet looking for tasty rodents! And when they spot one, these birds can dive at over 100mph and still keep their target in complete focus. Share  

Best bird night vision – Owls                                                       © Floridapfe – flickr Best bird night vision – Owls Despite their smaller size, owls have eyes almost as big as ours and their huge pupils capture lots of light. In fact, an owl could probably spot a mouse on a football pitch lit by a single candle. Secondly, like other birds, their brains can capture an ‘at a glance’ picture that a human eye would have to scan back and forth to understand. However because their forward-facing eyes are so big, they can’t move them. Which is why, like eagles, they can swivel their heads 270 degrees - allowing them a wide field of vision.

© law_keven – flickr Best mammal night vision – Cats Cats have awesome night vision. This is because their pupils widen until they are large circles letting far more light into their eyes - nearly doubling their ability to see (and hunt) in darkness. Which is very bad news if you’re a mouse.

Cow eye dissection https://www.exploratorium.edu/video/cows-eye-dissection?autoplay=true

< 2 min video on human eye model https://www.youtube.com/watch?v=TXFt1Ikl__I

Retina structure The retina is an extension of the brain! The retina is made of 2 types of photoreceptors (neurons). Rods for detecting (motion) dim light (no color) Cones for detecting color and detail

Retina Function To detect movement To detect color To detect detail.

Why don’t we see the blind spot? Our left eye sees the part that is “blind” or missing from the right eye (and vice versa). Blind spot structure Contains the beginning of the optic nerve going out. Contains the blood vessels flowing in and out of the eye. Contains no photoreceptors.

Blind Spot Function To send the signal from all of the photoreceptor cells to the optic nerve (which carries the signal to the brain). To allow blood to flow into the retina bringing nutrients such as oxygen and sugar, and getting rid of waste such as carbon dioxide) It doesn’t “see” or detect images however.

Our Retina Macula /fovea – Structure Function the macula is a circular concentration of cone cells The fovea is a pit in the retina, it has more cones than the rest of the eye. Few blood vessels to interfere with sight. Function The greatest detail is seen here The color is most intense We use this spot for reading and seeing details

Retinal imaging Retinal imaging is the shape a pattern created by the blood vessels on the retina. Each individuals retinal pattern is unique like a fingerprint. Therefore some high-security fields use retinal scans to identify people.

Regions of Vision Peripheral vision (180°) outer most edges of vision mostly motion is detected very little color seen – almost all rods Intermediate zone – (90° to 120°) between peripheral and straight ahead Details are not defined Color if light is intense Mix of rods and cones Straight ahead – (10°) Only cones (object falls on the macula/fovea) Good detail Subtle color differences detected here.

color blindness testenchroma.com