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 Eye: Review from Last Class

The Eye Review: Parts and Functions PartFunction 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 LensTransparent tissue that bends light passing through the eye; to focus light, the lens can change shape

Review: Parts and Functions(Cont’d) PartFunction 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) ScleraTough, white outer covering of the eyeball; extraocular muscles attach here to move the eye

Today: Important Parts and Functions PartFunction 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 RodsPhotoreceptors responsive in low light conditions; not useful for fine detail

Retina: Photoreceptors Rods: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

Reading: Fun Cat Facts Please read the following handout

How did your eyes react?

Light Adaptation and Dark Adaptation Light 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

Are You Colour Blind??

Are You Colour Blind?? (Cont’d)

Are you Colour Blind?? Ishihara Test: Normal Color VisionRed-Green Color Blind Slide: 125Slide 1:25 Slide: 229Slide 2:Spots Slide: 345Slide 3:Spots Slide: 456Slide 4:56 Slide: 56Slide 5:Spots Slide: 68Slide 6:Spots