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Eye Structure and Function Guided Notes Name: ________________________ Do Now Which ‘fact’ is false? 1) Your eye muscles are the most active muscles in your body. 2) Newborns don’t produce tears 3) Corneal scratches heal in about 48 hours. 4) If you sit too close to a TV , computer, or tablet, you will damage your eyes. External Eye and Accessory Structures __________________________refers to tears. Tears __________ and _________________ the eyes, and also __________________________. The lacrimal ducts empty into the nasal cavity This is why nose and eye irritation is often linked. • you get the sniffles if cry and • you get watery eyes if congested ___________________ are the membranes the line the eyelid and eyeball. __________________ inflammation of these membranes, caused by irritants, allergies, or infection (e.g. “pink eye”). Extrinsic Eye Muscles Control movement of the eyes. Remember: rectus = straight, oblique = slanting Eye muscle names and actions Name Action Lateral rectus Medial rectus Superior rectus Inferior rectus Inferior oblique Superior oblique Eyeball The eye has three ______________________, or coats. • _______________________ – “whites of the eye” , outermost, thick connective tissue. • _______________________ – has blood vessels, middle layer • _______________________ – contains the photoreceptors (rods & cones), inner layer The eye is divided into two fluid-filled chambers: • The anterior chamber is filled with ________________________________________ • The posterior chamber is filled with ______________________________________ • Both fluids ________________________________, and the aqueous humor _________________________________________. _______________________________ occurs when the aqueous humor doesn’t drain properly, resulting in increased eye pressure and blindness Pathway of Light 1. Light enters the eye at the ________________________ – a clear, hard part of the sclera. Functions: protects eye and focuses light Fun fact: the cornea is responsible for ~70% of the eye’s focusing ability 2. Light passes through the ______________________ which is the opening in front of the lens. • • The size of the pupil is controlled by the muscles of the __________ (the the eye). colored part of The pupil dilates or contracts to vary the amount of light hitting the retina. 3. The light passes through the ______________which focuses the light onto the retina. • 4. The __________________________ are muscles which change the shape of the lens to focus on nearby items, a process called __________________________. The light passes through the _________________________ to land on the retina, which contains the photoreceptors. There are no photoreceptors on the _____________________________, which is where the optic nerve exits the eye – this causes a small blind spot. Photoreceptors Rods Responsible for night and peripheral vision – • more abundant that’s why colors seem to be lost in the dark. • sensitive to ______________________________ • do not discriminate _______________________________________________ Cones - ________________________________________ • 3 types, _______________________________________________________________________ • triggering of more than one cone is interpreted by brain as different colors e.g. if both red and green are activated, the brain will interpret the light as yellow or orange • ________________ than cones • mostly found in ___________________________________ Responsible for color and fine detail vision – including reading Color blindness is usually caused by the absence of one or more cones. • Occurs in ~5% of population • X-linked trait … much more common in men Refraction and Accomodation Light is bent – or __________________________– by nearly every eye structure that it passes through on the way to the retina. However the lens is the only structure that can vary how much the light is bent in order to allow us to focus on different objects – a process called __________________________. • At rest, our eyes naturally focus on far-away objects. • However, by contracting the ________________ ____________________, we can make the lens bulge so that it has greater refractive ability – allowing us to focus on close items. As we get older, our lens loses elasticity – making it harder to focus on nearby items. This condition is called _____________________________(old eyes) Refraction flips and reverses the light rays, forming an upside down and reversed image on the retina … but the brain learns to interpret visual information correctly.