Vision

Kristen, Erin, Jyra, Michelle, Andrew, and Kayla

Essential Questions

• How does the eye transduce images into neural impulses?

• What are the structures of the eye and their functions?

• How does the visual system create color and brightness?

• What are some common sensory disorders in relation to seeing?

Transduction of Vision

• The eye is unique because it can take info from light waves and turn it into neural signals that the brain can process

• This transduction occurs in the retina

• Retina: thin, light sensitive layer at the back of the eyeball that contains photoreceptors

• The two types of photoreceptors are rods and cones

Photoreceptors• Rods and cones absorb light energy and

respond by creating neural impulses• Rods: photoreceptors in the retina that

detect low intensities of light and help you see in the dark

• Cones: photoreceptors in the retina that help you see colors

- The cones focus in on the very center of the retina in a small region called the fovea

- The fovea is where our sharpest vision lies

- Acuity: the capacity of the eye to see fine detail

Other Important Structures of the Eye

• Bipolar cells: collects impulses from rods and cones and transfers them to ganglion cells

• Ganglion cells: makes up the optic nerve shuttles impulses to other destinations

• Optic Nerve: transports visual information to the brain

• Blind Spot: small area in the retina of each eye where everyone is blind because there are no photoreceptors

The Brain’s Role in Vision• Optic Chiasm: X-shaped structure formed by the

crossing of optic nerves from each eye in the brain. This is necessary for our brain to process information from the right eye with the left hemisphere and vice versa.

• The impulses are sent through the thalamus which direct them to the visual cortex in the occipital lobe

• The optic chiasm leads to the visual cortex where the brain begins to transform incoming neural impulses into visual sensations of color, form, boundary, and movement.

• The information from the occipital lobe is then sent to the forebrain for higher processing.

Other Visual Characteristics• Accommodation: when the eye changes optical power to

focus on an object as its distance changes• Dark Adaptation: the adjustment of a human eye to a dark

environment. Leaving a bright room to a dark one takes longer for the eye to adjust than vice versa

• Retinal Disparity: the slight difference in the image from two different angles of each eye

• Parallel Processing: when images combine from each eye• TRY IT!

– Hold one finger up an arm length from your face– Alternate closing one eye and then the other– What happens?

Processing light and color

• Wave length: distance light travels in making one wave cycle as it vibrates in space

• Color (hue): sensation the brain creates based on the wave length of light striking our eyes

• Sensations of brightness come from the intensity, or amplitude, of light

• Amplitude: how much light reaches the retina• Saturation: determined by a combination of light

intensity and how much it is distributed across the spectrum of different wave lengths

Light and Color Continued…

• Radiant light: light that comes directly from the source

• Reflected light: a light ray that bounces off of a reflective surface at the exact angle at which it contacted the surface

• The only light we can see on the electromagnetic spectrum is in the visible spectrum because we don’t have biological receptors for other parts of the spectrum

• Longer waves: red, orange• Medium waves: yellow, green• Short waves: blue, purple

Theories Related to Vision• There are two ways of sensing color:- Trichromatic theory: there are three different types of

cones that sense different parts of the visible spectrum – red, blue, and green

- Young Helmholtz Theory: the eye has 3 separate elements each of which are stimulated by a different primary color

- Opponent-process theory: beyond the bipolar cells, the visual system processes colors complementary pairs (ex. Red or green or as yellow or blue)

- Helps us understand color blindness and negative afterimages (sensations that linger after the stimulus is removed; appears in reverse color)

DEMOMO

Vision Perception

• Monocular Cues: part of depth perception is the ability to perceive the distance of an object; some of these cues can be processed by one eye which is why they’re called monocular

• Binocular Cues: - the different view of the world provided by having two

eyes is referred to as steropsis- binocular vision allows us to see the world in three

dimensions- occurs when two eyes look at the same thing at a slightly

different angle resulting in slightly different images

Vision DisordersHyperopia (Far Sightedness)

Myopia (Short Sightedness)

Presbyopia(Age Related)

Astigmatism

People with far sightedness have trouble seeing objects up close. Sewing, reading or using the computer may become difficult causing eye strain and headaches.

Hyperopia or far sightedness occurs as a result of an imperfection in the eye. When light enters the eye it focuses behind the retina instead of directly on it resulting in blurring of the image.

People with short sightedness have trouble seeing objects at a distance. Driving a car may be difficult as the road signs can’t be seen clearly and children at the back of the class may have trouble seeing the chalk board at school.

Myopia occurs when the shape of the eyeball is slightly longer than normal. Light entering the eye focuses in front of the retina instead of directly onto it causing a blurred image.

Presbyopia occurs in most people as a result of the aging process. The eyes gradually lose their capacity to see things at close range. This is why you may see people holding a book or newspaper at arms length as it becomes easier to read the further away it is.

Astigmatism occurs when the cornea of the eye is oval shaped instead of round or when the lens of the eye is an irregular shape. The result is blurred vision as the light entering the eye cannot focus correctly onto the retina.

Cure For Eye Disorders:1.Glasses or contact lenses2.Laser eye surgery3.Eye exercises4. Sunglasses with glasses

What Is Color Vision Deficiency ???????• the inability to distinguish certain shades of color or in more severe cases, see colors at all• color blindness is also used to describe this visual condition, but very few people are completely color

blind• Monochromat - you only see one shade• Dichromat - You use only two of the three visual pigments- red, green, or blue is missing

What causes vision deficiency??????????•diabetes

•glaucoma

•macular degeneration

•Alzheimer's disease

•Parkinson's disease

•multiple sclerosis

•chronic alcoholism

•leukemia

•sickle cell anemia

TREATMENTS:• Organizing and labeling clothing, furniture or other colored objects (with the help of friends or family) for ease of

recognition.• Remembering the order of things rather than their color can also increase the chances of correctly identifying colors.

For example a traffic light has red on top, yellow in the middle and green on the bottom.

Color Vision deficiency (2006). In Color Vision Deficiency/ American Optometric Association. Retrieved November 28, 2011,

Color deficiency can be diagnosed

through a comprehensive

eye examination.