2Function of the Eye 80% of what we perceive is based on sight 3 types of neurons1) Sensory NeuronsCaptures the information coming from the senses (from the sensory organs to the cerebrum)2) Motor NeuronsTransmits to the muscles the command given by the brain (from the cerebrum to the muscle)3) Inter neuronsEnsures the transmission of the influx to all neurons
3Reflexes – travel at a speed of 100m/s or 360km/h Improve intelligencesuse all senseVitamine B (eggs milk, meat) – strengthen neuronsExercise – brings needed 20% of OxygenRest
4Central Nervous system Brain: consists of the cerebrum, the cerebellum and the brain stemThe brain is protected by many various layersSkinSkull boneFluids*** Interestingly enough, your brain does not have any nerves in it and therefore cannot feel pain.
5Anatomy of the Eye Sclera: Choroids: Retina: Outer membrane of the eye (white part of the eye) that protects the eye and gives it its shape.Choroids:Middle back layer of the eye (black) that has blood vessels that supplies the eye with nutrients and O2.Retina:Back of the eye that responds to the light due to its rods and cones (neurons, nerves) that respond to light and send messages to the brain via the optical nerve
6Eye Anatomy Cornea: Iris: Pupil: Transparent part at the front of the eye (what you would touch when you touch your eye) that protects the eye. It is sensitive to cold, wind or smoke.Iris:Color of the eye. Its function is to control the amount of light going into the eye. (changes sizes to make the pupil look bigger or smaller)Pupil:black hole of the eye where light enters
7Rods: Cones: Optic nerve: Blind spot: work in dim light sees shape and sizeCones:work in bright light to see colors and specificsOptic nerve:carries impulses from the neurons to the brainBlind spot:area on the retina where there are no neurons. Where the optic nerve and retina meet
8Aqueous humour: Vitreous humour: Lens: transparent liquid between the cornea and lensFunction: nourishes and maintains shape of the eyeVitreous humour:transparent liquid between the lens and the retinaFunction : nourishes and maintains the shape of the eyeLens:Hard disc of the eyeFunction : changes size forces to focus
10Vision – A natural Reflex Accommodation reflex:The lens can modify its shape based on the distance you are trying to focus withFor close elementsshort and fatthe lens curves and thickensFor far elementslong and thinthe lens moves so light lands properly on the retina
11Vision – Snellen Chart20/20 what you should see is located at the bottom what you do see is at the top. Go forward by 1 foot until line number seven becomes clear (13/20)Some people have above normal vision (25/20)
12Vision – Eye Problems Astigmatism: Glaucoma: lens and cornea are not symmetrical and light does not land on the right area of the retinaGlaucoma:Increase of level of aqueousThis build up should be expelled by the eye ducts but dusts gets blocked so there is a blockageWorst case: The eye duct do not drain so the pressure increases. If left untreated the pressure becomes so high that the eye explodesRods and cones don’t get O2 and die = blindCataract:the lens becomes opaque so light does not go through anymore
13Vision – Other common ailments Near sightedness (myopia):A person can see things from close clearly but not from far. 2 reasons why people are myopica) congenital malformation (you are born with it, it didn’t form properly as a fetus)problem: The eye is too long so the image does not reach the retina properly so the images are blurryAccomodation reflex does not work properly. The muscles of the lens are weak and the leans stays in the short and fat position. So you see clearly from close but not from far. It can get better if you always wear your glassesSolution:Concave lenses. They work because they give the extra layers light needs to reach the retina
14Farsightedness: person can see from far and not from close : Prebyopic 2 reasonsa) congenital malformation: Eye is too short. Born with this problem. The light ays fall behind the retina so you see bleurryLens always stays in the long and thin position. Often happes as a person gets older. When looking at something close it is bleurry but from far is is clearSolution: convex lenses. The shape of the lens that is missing. Image begins to be refracted earlier so image lands on retina.
15Vision – Care of the eye read at 25-30 cm away Look away to curve the lens to focus at different positionsVitamin A promotes good vision (vegtables, meat)Daily eye care
16The knowledge behind the light How do we see?The knowledge behind the light
17Electromagnetic spectrum Definition:The EM is the range of all possible electromagnetic radiation.The "electromagnetic spectrum" (usually just spectrum) of an object is the characteristic distribution of electromagnetic radiation from that object.
18Electromagnetic spectrum All electromagnetic waves have energyThe higher the frequency (waves/sec) the more energy it has and the more potentially damaging it can be.
19The visible Spectrum Wavelengths found between 400 -700 nm Red Orange Yellow Green Blue Violet**White light is the combination of all the visible wavelengths
20LightHow does light react?Is it a particle or a wave?
21Light Light always travels in straight lines Light diffuses in a homogeneous mediumLight can be deviated byRefractionReflection
22ReflectionSome objects are visible because they emit their own light, however most objects do not.These objects can be seen because light hits the object and is reflected.
23ReflectionDefinition:When light “bounces” off an object
24How do we see colour?The white light hits the object. The visible wavelengths are absorbed except the wavelength that corresponds to the object’s colour, this wavelength is reflected.
26Laws of ReflectionThe angle of incidence (θi) and the angle of refraction (θr) are equalBoth angles are on the same plane
27Reflection in a “flat” mirror Creation of a “virtual” image
28To trace a virtual image… Prolong the mirror if necessaryDraw lines perpendicular to the mirrorMeasure the distance from the object to the mirrorMeasure the same distance on the other sideDraw the lines from the virtual image to the observerDraw lines from the object to the mirror
29RefractionWhen light is deviated by passing from one translucent medium to another that does not possess the same mass/volume ratio.Examples of mediums that refract light:Glass, plastic, water, diamonds, oil
30How does refraction work? The light changes direction because, depending on the medium, light travels at different speeds.The higher the mass/volume ratio the slower the light will travel.
32** A ray going from an area of low m/v ratio to an area with a higher m/v ratio will have an θr smaller (will be closer to the normal) than the θi.** A ray going from an area high m/v ratio to an area with a lower m/v ratio will have an θr larger (will be farther to the normal) than the θi.
33*** At a specific incidence angle, the light rays are reflected instead of refraction (i.e. internal reflection)E.g. fiber optics
34Light and prisms The refraction angle depends on the wavelengths The greater the wavelength the smaller the refraction angleIf the prism’s 2 sides are parallel, the outgoing rays are parallel to the incoming ray
35If the prism’s 2 sides are not parallel, the sides will increase the separation of the outgoing rays
36MiragesMirages also work by refraction. The heat changes the water content in the air and modifies the refraction index, causing the light to bend
37Refraction and Sight Emmetropia (Perfect vision) Hyperopia (farsightedness) Difficulty to see near objects. The image focuses behind the retina. Either the cornea or the shape of the eye is incorrect.Myopia. Images focus before the retina. Either the cornea or the shape of the eye is incorrect.