Biology Today’s Lesson: The Eye Ms. Pretty Ms. Roy.
-
Upload
clifford-stokes -
Category
Documents
-
view
219 -
download
2
Transcript of Biology Today’s Lesson: The Eye Ms. Pretty Ms. Roy.
Introductory Activity
Instructions: Close your right eye and stare at the cross below. Slowly move towards the image, staring at the cross all the time. Where it is about 20cm or 8in away, the dot will suddenly vanish.
What happened to the circle??
. +
The EyeReview: Parts and Functions
Part Function
Aqueous Humor
Clear watery fluid found in the anterior chamber of the eye; maintains pressure and nourishes the cornea and lens
Vitreous Humor
Clear, jelly-like fluid found in the back portion of the eye; maintains shape of the eye and attaches to the retina
Cornea Transparent tissue covering the front of the eye; does not have blood vessels; does have nerves
Iris Circular band of muscles that controls the size of the pupil. The pigmentation of the iris gives color to the eye. Blue eyes have the least amount of pigment and brown have the most
Lens Transparent tissue that bends light passing through the eye; to focus light, the lens can change shape
Review: Parts and Functions(Cont’d)Part Function
Optic Nerve Bundle of over one million axons from ganglion cells that carry visual signals from the eye to the brain
Pupil Hole in the center of the eye where light passes through
Choroid Thin tissue layer containing blood vessels, sandwiched between the sclera and retina; because of the high melanocyte content, the choroid acts as a light absorbing layer
Retina Layer of tissue on the back portion of the eye that contains cells responsive to light (photoreceptors)
Sclera Tough, white outer covering of the eyeball; extraocular muscles attach here to move the eye
Today: Important Parts and FunctionsPart Function
Retina Layer of tissue on the back portion of the eye that contains cells responsive to light (photoreceptors)
Macula Small central area of the retina that provides vision for fine work and reading
Fovea Central part of the macula that provides sharpest vision; contains only cones
Optic Disc (‘Blind Spot’)
Small area of the retina where the optic nerve leaves the eye; any image falling here will not be seen; there are no rods or cones present here
Cones Photoreceptors responsive to color and in bright light conditions; used for fine detail
Rods Photoreceptors responsive in low light conditions; not useful for fine detail
Retina: PhotoreceptorsRods: Cones:
125 million rod cells
Photoreceptors responsive in LOW LIGHT conditions
NOT useful for fine detail
Best suited for NIGHT and PERIPHERAL vision
Absorbs all wavelengths of visible light but their inputs are perceived in GRAY TONES
Have HIGH sensitivity
6 million cone cells
Photoreceptors responsive to COLOUR and BRIGHT LIGHT conditions
Used for FINE DETAIL
Need bright light for activation
Have LOW sensitivity
Light Adaptation and Dark AdaptationLight Adaptation (time to adjust: seconds or minutes)
Dark Adaptation (time to adjust: up to hours)
Occurs when going from darkness into bright light (ex: movie matinee or waking in the morning)
Initially, we all see in white light because the sensitivity level of the retina is still set for dim light
Both Rods and Cones are stimulated strongly and therefore causes an influx of information
Compensations occur in this situation:
1. the sensitivity of the retina decreases dramatically
2. the retinal neurons adapt rapidly, switching from the Rod to the Cone System
Retinal sensitivity (rod function) is lost, but visual acuity is gained
Occurs when we go from a well-lit area to a dark area (ex. Walk indoors on a sunny day)
Initially we see blackness because our Cones stop functioning in low light our Rod pigments have been bleached out by the bright light
Compensations occur in this situation:
1. The sensitivity of the retina increases
2. The Rods adjust over time, thus switching from a Cone to a Rod system
Rod function is essential here as they are best for night and peripheral vision