The Eye

Facts about the Eye Receptor organ for light About 2.5 cm in diameter -Eye video (movie trailer)

ANATOMY

Ciliary muscles Zonular ligaments Macula

The 3 Layers of the Eye (from outside to inside) All 3 are opaque (not transparent) 1) Sclera White of the eye Gives the eye its shape Protects the eye Becomes transparent in front of the eye (cornea)

2) Choroid Dark brown Contains many blood vessels Becomes the the colour part of our eye (iris) in front of the eye -The iris is made up of 2 muscles and has an opening called the pupil -The iris controls how much light enters the eye through the pupil by contracting its muscles -The circular muscles close the opening of the pupil by contracting -The radial muscles open the opening of the pupil by contracting

3) The Retina -pinkish-beige membrane -the retina can sometimes detach due to violent shocks -composed of different types of the nerve cells, including the vision receptors -The two vision receptors (neurons) are rods and cones -there are 20 times more rods than cones

Cones: -the cones are concentrated in a small circular area called the macula in the middle of the retina -they can detect colour -three types of cones: red, green, and blue -certain colours stimulate one or more of the cones. -white light stimulates all 3 cones -cones provide the clearest image

Rods: -the rods are located around the macula and throughout the retina -detect contrasts not colours (ex. when you are in a dark room) -more sensitive to light

-the optic disc contains no rods or cones, it is where the optic nerve begins. -the optic disc is also called the blind spot

Ciliary muscles Zonular ligaments Macula

The Transparent Structures of the Eye How light travels through these structures Light -> cornea -> aqueous humour -> lens -> vitreous humor Cornea: -extension of the sclera -its spherical shape helps transmit and converge light rays 2) Aqueous humour -liquid, consisting mostly of water and a bit of glucose -this liquid is continually replenished -supplies glucose and oxygen to the lens and cornea

3) Lens -lies behind iris -flexible -biconvex in shape -normally completely transparent, but with aging or illness can be come opaque (cataracts) -focuses the image onto the retina 4) Vitreous humor -lies between lens and retina -gelatinous liquid, mostly made of water -exerts pressure on the membranes which gives the eye its shape

Structures near the Eye and Their Functions Eyebrows: stop sweat from running into eyes Eyelashes: trap dust Eyelids: spread tears over surface of eyes Conjunctiva: covers the surface of the eye Lacrimal glands: secrete tears Tears protect the eyes by cleaning them with a bacterial agent Excess tears run down your nose

PhysiologY

Lens Accomodation When light passes through transparent structures it refracts or bends Lenses also do this to light The lens of our eye changes in shape to accommodate what we are looking at

The lens becomes more curved when trying to focus an object that is closer in order to converge the more divergent rays

Even though the image we see is inverted on our retina, our brain interprets it as being upright

Eye Problems and how to Correct them Myopia or near-sighted Cannot see far -slightly elongated eyeball or overly curved lens -clear image is in front of retina -correction: diverging lens (concave)

Hypermetropia (far-sighted) -difficulty seeing close objects -slightly shortened eyeball or under curved lens -clear image is located behind the retina Correction: converging (convex) lens

Presbyopia is similar to hypermetropia except that it is caused by loss of elasticity of the lens (usually related to agin) Astigmatism is when your lens has an irregular curvature of cornea or lens There is no clear image You have difficulty seeing distant and nearby objects Correction: cylindrical lenses

Nerve Impulse Pathway

Role Pathway Light Receptor Eye Processor Rods and Cones Conductor Optic nerve Analyser Visual Area of the brain