MLK 2005-2006How the Eye Works Observations MLK 2005-2006How the Eye Works Parts to the Puzzle –Anatomy the study of the names of the structures in the

MLK 2005-2006 How the Eye Works

How the Eye Works

Observations


Parts to the Puzzle– Anatomy

• the study of the names of the structures in the human body

• When we learn the names of eye parts we are studying Anatomy.

– Physiology• the study of the functions of body parts• When we learn how the eye parts work we are

studying Physiology.


HumansLevels of Organization

Highest-

•Organisms

•Organs (eye)

•Tissue (eg. lens, pupil, cornea, etc.)

•Cellular (eg. Rod and cone cells)

•Atoms - Lowest


Eye Anatomy


The Eye Diagram


Frontal View of the Eye


Vision Summary

• Light rays enters through the pupil after crossing through the cornea

• Light rays cross in the lens• Retina receives reversed & upside

down image• Rods & cones are stimulated• Optic nerve carries impulse to the

brain


Observation:In your ScienceLog notes, copy and carefully label the transverse waves. In your own words, explain what you think wavelength and frequency mean.

You have two minutes (2 minutes) to do this activity. The clock is counting


Electromagnetic Spectrum

• Long wavelength – Radio waves

•Visible Light – range of wavelengths that humans can see

• Short wavelength – Gamma rays

Decreasing wavelengthIncreasing frequency



Law of Reflection


Prism Refraction


Overview of Image Processing


Images and Light• The image projected

onto the retina is inverted or upside down. Visual processing in the brain reverses the image

• The pupils regulate the amount of light entering the eye.

• In bright light they constrict to 1.5 mm.

• In the dark they dilate to 8 mm. • The increase in the depth of field

seen under bright light results from a narrower beam of light focussing on the retina.

The diameter of the pupils is controlled by the autonomic

nervous system


Fixation Point to Focus Point


Focusing Abilities• When an object is distant,

the light rays are essentially parallel and brought to a focus on the retina.

• If the object moves closer, the focal point then moves behind the retina.

• To bring the image into focus on the retina, the lens refractive power must be increased. This is the process of accommodation.


Optics & the focal point

Focal point falls on retina, image in

focus

Focal point falls on beyond retina,image not in focus

Lens accommodates to correct focal point, image becomes in focus


Refraction – How the light is bent• Most of us (~70%) have a refractive

error in which light rays come to a point focus either behind the retina (hyperopia) or in front of it (myopia).

Hyperopia Myopia (farsighted) (nearsighted)


Convex or Concave?

Convex

Concave


Refractive errors

Long- or far-sighted

Short- or near-sightedCorrective lenses


Converting Light Stimulus to Electrical Impulse

• Requires great coordination of parts• Also occurs with the other senses:

– Ears: sound waves

– Taste: chemical stimulus

– Touch: mechanical stimulation

– Scent: chemical stimulus


Cross-section of the eye

Choroid

Sclera

Eyelid

3 main layers

(connective tissue)(vascular)

Filled with aqueous humour at anintraocular pressure 15mmHg.Supplies nutrients & secretedfrom the ciliary body. Drains viamesh at junction of cornea & sclera into venous system viacanal of Schlemm.


Retina stimulationThe

photosensitive cells of the retina contain the rods and cone which convert the light stimulus to electrical stimulus.


Rods and Cones


Colour vision: Rods and Cones• Light sensitive visual pigments are bound to the

cell membranes of the disk-like photoreceptors found within the rods & cones.

• Rods have one visual pigment, rhodopsin which has an absorption max of 496nm

• Cones have one of 3 colour sensitive pigments related to rhodopsin.

• Cones are responsible for colour vision and a contain pigments that can be excited optimally for

a) blue (absorption max 419nm) b) green (absorption max 530nm) c) red (absorption max 560nm)

• White light is seen when all three types of cone are equally stimulated.


Rods and Cones


Cones• Cones allow for sharp color vision

in bright light– 3 types, each with a different pigment

– Cones are most concentrated towards the back of the eye


Rods• Rods provide for

vision in dim light– Most dense at the

on the sides of the retina

– Contain the pigment rhodopsin


Neuron – Neervvve Cellllls


Braineacts

• LGN – a part of the

thalamus that relays signals from the eye to the visual cortex.

– It also receives signals back from the cortex.

RetinaRetina

LGNLGN

Primary Primary Visual Visual CortexCortex

Primary Primary Visual Visual CortexCortex

Visual Visual FieldField

Rods&

Cones


Optic Nerve


Cortical processing

…or how do we fill in the gaps?


RAINBOWS In a rainbow, raindrops in the air act like

tiny prisms.

Light enters the drop at A, is reflected at the back of the drop at B and leaves the drop at C. In the process the sunlight is broken into a spectrum just like it is in a triangular glass prism.

The angle between the ray of sunlight coming in and the ray coming out of the drops is 42 degrees for red and 40 degrees for violet rays.

This small difference in angles between the returning rays causes us to see the bow.


Challenge QuestionExplain why the top of the rainbow

appears red, while the bottom appears violet and not other way around?


THANK YOU

Documents

MLK 2005-2006How the Eye Works Observations MLK 2005-2006How the Eye Works Parts to the Puzzle –Anatomy the study of the names of the structures in the