MLK 2005-2006 How the Eye Works How the Eye Works Observations
Mar 27, 2015
MLK 2005-2006 How the Eye Works
How the Eye Works
Observations
MLK 2005-2006 How the Eye Works
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.
MLK 2005-2006 How the Eye Works
HumansLevels of Organization
Highest-
•Organisms
•Organs (eye)
•Tissue (eg. lens, pupil, cornea, etc.)
•Cellular (eg. Rod and cone cells)
•Atoms - Lowest
MLK 2005-2006 How the Eye Works
Eye Anatomy
MLK 2005-2006 How the Eye Works
The Eye Diagram
MLK 2005-2006 How the Eye Works
Frontal View of the Eye
MLK 2005-2006 How the Eye Works
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
MLK 2005-2006 How the Eye Works
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
MLK 2005-2006 How the Eye Works
Electromagnetic Spectrum
• Long wavelength – Radio waves
•Visible Light – range of wavelengths that humans can see
• Short wavelength – Gamma rays
Decreasing wavelengthIncreasing frequency
MLK 2005-2006 How the Eye Works
MLK 2005-2006 How the Eye Works
Law of Reflection
MLK 2005-2006 How the Eye Works
Prism Refraction
MLK 2005-2006 How the Eye Works
Overview of Image Processing
MLK 2005-2006 How the Eye Works
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
MLK 2005-2006 How the Eye Works
Fixation Point to Focus Point
MLK 2005-2006 How the Eye Works
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.
MLK 2005-2006 How the Eye Works
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
MLK 2005-2006 How the Eye Works
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)
MLK 2005-2006 How the Eye Works
Convex or Concave?
Convex
Concave
MLK 2005-2006 How the Eye Works
Refractive errors
Long- or far-sighted
Short- or near-sightedCorrective lenses
MLK 2005-2006 How the Eye Works
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
MLK 2005-2006 How the Eye Works
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.
MLK 2005-2006 How the Eye Works
Retina stimulationThe
photosensitive cells of the retina contain the rods and cone which convert the light stimulus to electrical stimulus.
MLK 2005-2006 How the Eye Works
Rods and Cones
MLK 2005-2006 How the Eye Works
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.
MLK 2005-2006 How the Eye Works
Rods and Cones
MLK 2005-2006 How the Eye Works
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
MLK 2005-2006 How the Eye Works
Rods• Rods provide for
vision in dim light– Most dense at the
on the sides of the retina
– Contain the pigment rhodopsin
MLK 2005-2006 How the Eye Works
Neuron – Neervvve Cellllls
MLK 2005-2006 How the Eye Works
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
MLK 2005-2006 How the Eye Works
Optic Nerve
MLK 2005-2006 How the Eye Works
Cortical processing
…or how do we fill in the gaps?
MLK 2005-2006 How the Eye Works
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.
MLK 2005-2006 How the Eye Works
Challenge QuestionExplain why the top of the rainbow
appears red, while the bottom appears violet and not other way around?
MLK 2005-2006 How the Eye Works
THANK YOU