Human eye - PPT slides

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The Human Eye

Anatomy of the eye

Light Regulation

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Layers of the Eye

▪ _{Sclera: outer white layer}

▪ _{Choroid: contains blood vessels}

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Sclera

▪ _{maintains shape of eye}

▪ _{muscles attached control eye movement}

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Fluids of Eye

Liquids (humour):

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Regulating Amount of Light

▪ _Iris

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contracted pupil

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Regulating amount of light

Parts Description Function Analogy

Iris coloured

ring

open and closes to control the amount of light entering eye

diaphragm in

microscope

Pupil black

centre

hole of iris where light enters eye

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Image Production

▪ _Retina

▪ _{Optic nerve}

▪ _{Optic disc}

▪ _{Macula lutea}

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Retina

▪ _{At the back of the eye}

▪ _{Consist of 2 types of}

light-sensitive cells:

▪ _{rods and cones}

▪ _{Converts light signal}

into an electrical signal that is

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Rods Cells

▪ _Composition:

▪ _{125 million rod cells}

▪ _{Absent in fovea centralis (centre of visual field)} ▪ _{Located in peripheral regions of the retina}

▪ _{Light sensitive}

▪ _{can functions in less intense light} ▪ _{responsible for night vision}

▪ _{used in peripheral vision}

▪ _{Doesn’t distinguish colour}

▪ _{detects black, white and shades of grey}

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Cone Cells

▪ _{Functions best in bright light}

▪ _{colour vision}

▪ _{perception of fine detail}

▪ _Composition:

▪ _{6 million cone cells}

▪ _{comprises less than 1% of retinal size but takes}

up over 50% of the visual cortex in the brain

▪ _{3 types that sense 3 primary colours of light:}

blue, green, red

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Macula Lutea

▪ _{Small yellowish area of the retina (yellow}

spot)

▪ _{The pit in the center is the fovea centralis}

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Fovea Centralis (Central Fovea)

▪ _{Contains no rod cells}

▪ _{Has high concentration of cone cells}

▪ _{No blood vessels to interfere with vision}

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Fovea Centralis: Centre of Visual Field

▪ _{The object, centre of lens and fovea centralis}

are in a straight line thus there is very little refraction

▪ _{Shortest distance light has to travel to reach}

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Fovea Centralis Summary

▪ _{Best visual acuity:}

▪ _{Sharp, detailed, clear vision}

▪ _{achieve the sharpest daylight vision by looking}

straight at the object of interest

▪ _{E.g. reading}

▪ _{Properties that contribute to acuity:}

▪ _{All cone cells, no rod cells} ▪ _{No blood vessels}

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Thought Question

▪ _{Explain why a dim star is best seen by}

looking at it from an angle rather than directly.

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Optic Disc

▪ _{Where the optic nerves converge and exit}

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Optic Nerve

▪ _{Nerve cells that transmit message from}

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Blind Spot

▪ _{No light-sensitive cells to detect light rays}

▪ _{Results in a break in the visual field, known}

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Activity: The reappearing dot

▪ _{Draw an X on a piece of paper. Then draw a}

dot 6 cm to the right of the X.

▪ _{Cover your left eye with your left hand.}

▪ _{Hold the paper with your right hand at arms}

length away.

▪ _{Focus your right eye on the X but keep the}

dot in your peripheral vision.

▪ _{Slowly move the paper towards your face}

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Right Eye

http://neil.fraser.name/news/2008/11/22/

Macula Lutea & Fovea Centralis

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Producing an Image

▪ _{The converging lens produces an inverted}

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Producing an Image

▪ _{Cells on retina trigger a nerve impulse}

▪ _{Nerve cells sends an electrical signal to the}

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Focusing Light Rays

▪ _Cornea

▪ _Lens

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Focusing Light Rays

▪ _{Which diagram shows light rays that require}

more refraction?

▪ _{Light rays from distant objects enter the eye}

parallel to one another

▪ _{Light rays from close objects diverge from each}

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Accommodations

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Vision Problems

▪ _{Myopia (near}

sightedness)

▪ _{Hyperopia (far}

sightedness)

▪ _Presbyopia

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Myopia (near-sightedness)

▪ _{inability of the eye to focus light from distant}

objects

▪ _{see close objects clearly}

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Myopia (near-sightedness)

▪ _{Develops in childhood and progressively}

worsens

▪ _{Tends to stabilize in adulthood}

▪ _{Has a genetic component}

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Cause of Myopia

▪ _{Distance between lens and retina is too long}

(long eyeball)

▪ _{Cornea & lens converge light too strongly}

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Corrected with a

diverging lens

Correcting Myopia

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Correcting Myopia

▪ _{Negative meniscus:}

▪ _{A modified diverging lens to make it more}

cosmetically appealing

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Hyperopia (far sightedness)

▪ _{Inability of the eye to focus light from near}

objects

▪ _{No difficulty seeing distant objects}

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Hyeropia (far sightedness)

▪ _{Babies are born slightly hyperopic. As eye}

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Cause of Hyperopia

▪ _{Distance between lens and retina is too small}

(short eyeball)

▪ _{Cornea & lens is too weak (}_doesn’t_converge

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Correcting Hyperopia

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Correcting Hyperopia

▪ _{Positive meniscus:}

▪ _{A modified converging lens to make it more}

cosmetically appealing

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Presbyopia

▪ _{A form of hyperopia}

(far sightedness) that occurs with age

▪ _{Cause: eye lens losing}

elasticity

▪ _{Not a result of eyeball}

being too short

▪ _{Correct with}

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Astigmatism

▪ _{Irregular shaped}

cornea “football”

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Astigmatism

▪ _{Astigmatism is a vision problem that results}

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Video: Laser Eye Surgery

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Lab: Cow Eye Dissection

Video: Exploratorium Cow Eye Dissection

▪ http://www.exploratorium.edu/learning_stud io/cow_eye/video_big_all.html

▪ http://www.teachersdomain.org/resource/lsp s07.sci.life.stru.coweye/

Video: Bill Nye