Parts of the Eye

Cornea: protects the inner eye whilst letting light in Aqueous Humour: clear and colorless liquid that supports the shape of the cornea and lets light into the eye Pupil: opening that lets light into the eye Iris: colored part of the eye, controls the size of the pupil /amount of light let in

cilliary muscle Soft Lens: refracts light so that an image is projected onto the retina Cilliary Muscle: controls shape/thickness / focal length of lens Suspensory Ligament: a ringlike fibrous membrane to hold the lens in place

Vitreous Humour: clear and colourless gelatinous substance that supports the shape of eye and lets light through Retina: screen with light sensitive cells Choroid: black layer that absorbs light so it doesn't reflect back into the eye cilliary muscle

Optic Nerve: sends image signal to the brain Sclera: white, tough wall of the eye cilliary muscle

Parts of the Eye

cilliary muscle

Normal Vision The image forms on the retina

Eye Accommodation Accommodation – process by which the eye can focus on different objects. Normal Ciliary muscle relaxed – lens ‘long and thin’ with a focus at infinity. Squinting Cliiary muscle contracted - lens is ‘short and fat’ shortening the focal point.

Focused Eye Terms Near point – the point nearest the eye at which an object can be placed and still produce a sharp image on the retina. Ciliary muscle fully tensed Typically, 25 cm and increases to 50 cm by age 40. Far point – the location of the farthest object on which the fully relaxed eye can focus Normally, considered to be near infinite. Cutnell & Johnson, Wiley Publishing, Physics 5 th Ed.

Hyperopia (far sightedness) The image forms behind the retina

Farsighted (Hyperopia) Farsighted eyes form images behind the retina. Their cornea does not bend the light rays enough as they pass through. The remedy for this is to increase the converging effect of the eye. Wearing contact lenses or glasses with converging lenses does this. Designed so eye perceives light coming from a virtual image located at the near point. Cutnell & Johnson, Wiley Publishing, Physics 5 th Ed.

Hyperopia (far sightedness) A convex lens Correction converges light rays before the lens the image forms on the retina.

Myopia (short sightedness) The image forms in front of the retina

Nearsighted (Myopia) A nearsighted person can see nearby objects clearly, but does not see distant objects clearly because they are focused too near the lens, in front of the retina. The remedy is to wear lenses that diverge the rays from distant objects so that they focus on the retina instead of in front of it. Lens designed to transform a very distant object into an image located at the far point. Cutnell & Johnson, Wiley Publishing, Physics 5 th Ed. Eye Defects

Myopia (short sightedness) A concave lens Correction diverges light rays before the lens the image forms on the retina.

Common eye conditions and appropriate remedies ConditionCauseEffectCorrectionEffect Myopia (Near sightedness) Eye too long Cornea too strong (curved) Image formed in front of retina Concave lens diverge rays entering eye Hyperopia (far sightedness) Eye to short Cornea too weak (‘flat’) Image formed behind retina Convex lens Converge rays before entering eye, adding to the cornea’s power Presbyopia (old age vision) Ciliary muscle too weak Lens too rigid Lens does not change shape sufficiently when eye focuses on near objects Convex lens (reading glasses) As with hyperopia, but aiding the lens, not the cornea Albinism Lack of pigment in iris, making it transparent Too much light entering eye Sun glasses Decrease amount of light entering eye Cataract Protein crystalizes in lens Lens become cloudy Silicon lens implant Blindness

Cutnell & Johnson, Wiley Publishing, Physics 5 th Ed. Human Eye Retina – light sensitive part of the eye where the image forms. –Covered with light sensitive cells that record the arrival of light. 2 types of light sensitive cells – Rods & Cones –Rods – found primarily at the edges of the retina Large number are connected to the same nerve fiber. Sensitive to light of low intensity but produces images of less detail. –Cones – are concentrated near the principal axis of the eye. Distinguishes colors as three types each sensitive to a different color. Fewer are connected to the same nerve fiber produces more detailed images. However, only sensitive to high intensity light. Eye Diagram

Scotopic vs Photopic Vision Scotopic Vision Rods are used Used at night and in low light conditions Distinguishes shapes not colors Distinguishes little detail Photopic Vision Cones are mainly used Used during the day and high intensity light Distinguishes shapes and colors Distinguishes a lot of detail Rods and Cones

Seeing Color Possible by three types of cone cells which are sensitive to either red, green or blue light. Color Blindness – deficiency in the perception of color. (More prevalent in men) –affects ~8% of men ~ 1 / 2 % of women hereditary and sex-linked (in X chromosome) women can be unaffected carriers, men are 20 times more likely than women to be color-blind

Color blindness Most common involves the red and green cone cells. Unable distinguish between red and green. one of the 3 types of color detectors (cone cell) is missing, gaps are filled by cones of the other two types –If two types of cone cell are not functioning then one is unable to perceive color. eye_asu_380x300.gif

Presentations and Color-blindness

color-blindness example -- sea surface temperature no color-blindnessprotanope (red/green) deuteranope (red/green)trianope (blue/yellow - rare)