Function of the Eye

• 80% of what we perceive is based on sight

3 types of neurons• 1) Sensory Neurons

– Captures the information coming from the senses (from the sensory organs to the cerebrum)

• 2) Motor Neurons– Transmits to the muscles the command given by the brain (from

the cerebrum to the muscle)

• 3) Inter neurons– Ensures the transmission of the influx to all neurons

• Reflexes – travel at a speed of 100m/s or 360km/h

• Improve intelligences– use all sense – Vitamine B (eggs milk, meat) – strengthen

neurons– Exercise – brings needed 20% of Oxygen– Rest

• Central Nervous system– Brain: consists of the cerebrum, the cerebellum and

the brain stem

• The brain is protected by many various layers– Skin– Skull bone– Fluids

• *** Interestingly enough, your brain does not have any nerves in it and therefore cannot feel pain.

Anatomy of the Eye

• Sclera: – 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

Eye Anatomy

• Cornea: – 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

• Rods: – work in dim light sees shape and size

• Cones: – work in bright light to see colors and specifics

• Optic nerve: – carries impulses from the neurons to the brain

• Blind spot:– area on the retina where there are no neurons.

Where the optic nerve and retina meet

• Aqueous humour: – transparent liquid between the cornea and lens– Function: nourishes and maintains shape of the eye

• Vitreous humour: – transparent liquid between the lens and the retina– Function : nourishes and maintains the shape of the

eye

• Lens: – Hard disc of the eye– Function : changes size forces to focus

Vision – close up

Vision – A natural Reflex

• Accommodation reflex:– The lens can modify its shape based on the

distance you are trying to focus with– For close elements

• short and fat • the lens curves and thickens

– For far elements• long and thin• the lens moves so light lands properly on the retina

Vision – Snellen Chart

• 20/20 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)

Vision – Eye Problems

• Astigmatism: – lens and cornea are not symmetrical and light does not land on

the right area of the retina

• Glaucoma: – Increase of level of aqueous – This build up should be expelled by the eye ducts but dusts gets

blocked so there is a blockage– Worst case: The eye duct do not drain so the pressure

increases. If left untreated the pressure becomes so high that the eye explodes

• Rods and cones don’t get O2 and die = blind• Cataract:

– the lens becomes opaque so light does not go through anymore

Vision – Other common ailments

• Near sightedness (myopia):– A person can see things from close clearly but not

from far. 2 reasons why people are myopic• a) 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 blurry• Accomodation 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 glasses

– Solution:• Concave lenses. They work because they give the extra

layers light needs to reach the retina

• Farsightedness:– person can see from far and not from close :

Prebyopic– 2 reasons

• a) congenital malformation: Eye is too short. Born with this problem. The light ays fall behind the retina so you see bleurry

• Lens 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 clear

– Solution: convex lenses. The shape of the lens that is missing. Image begins to be refracted earlier so image lands on retina.

Vision – Care of the eye

• read at 25-30 cm away

• Look away to curve the lens to focus at different positions

• Vitamin A promotes good vision (vegtables, meat)

• Daily eye care

How do we see?

The knowledge behind the light

Electromagnetic 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.

Electromagnetic spectrum

• All electromagnetic waves have energy– The higher the frequency (waves/sec) the

more energy it has and the more potentially damaging it can be.

The visible Spectrum

• Wavelengths found between 400 -700 nm

Red Orange Yellow Green Blue Violet

**White light is the combination of all the visible wavelengths

Light

• How does light react?

• Is it a particle or a wave?

Light

• Light always travels in straight lines

• Light diffuses in a homogeneous medium

• Light can be deviated by – Refraction– Reflection

Reflection

• Some 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.

Reflection

• Definition:– When light “bounces” off an object

How 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.

Normal

Incident RayReflected Ray

θi θr

Laws of Reflection

1. The angle of incidence (θi) and the angle of refraction (θr) are equal

2. Both angles are on the same plane

Reflection in a “flat” mirror

• Creation of a “virtual” image

To trace a virtual image…1. Prolong the mirror if

necessary2. Draw lines

perpendicular to the mirror

3. Measure the distance from the object to the mirror

4. Measure the same distance on the other side

5. Draw the lines from the virtual image to the observer

6. Draw lines from the object to the mirror

Refraction

• When 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

How 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.

NormalIncident Ray

Refracted Ray

θi

θr

• ** 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.

• *** At a specific incidence angle, the light rays are reflected instead of refraction (i.e. internal reflection)

• E.g. fiber optics

Light 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

If the prism’s 2 sides are not parallel, the sides will increase the separation of the outgoing rays

Mirages

• Mirages also work by refraction. The heat changes the water content in the air and modifies the refraction index, causing the light to bend

Refraction 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.