The Human Eye: A Remarkable Optical Device

The Human Eye: A remarkable optical device  In many ways, the human eye is similar to a camera. Light enters through an opening, is focused through a lens, passes through a light-reduced (dark) space, and forms a smaller, inverted, real image on a light-sensitive surface at the back. ...

The Human Eye: A remarkable optical device  In many ways, the human eye is similar to a camera. Light enters through an opening, is focused through a lens, passes through a light-reduced (dark) space, and forms a smaller, inverted, real image on a light-sensitive surface at the back.  Parts of the Human Eye Cornea (clear covering) Iris (coloured disc) Sclera Vitreous Humour Ciliary Pupil Sclera Muscle Cornea Optic Nerve Pupil Fovea Lens Retina Iris  Anatomy of the Eye - Pupil Pupil – The hole in the middle of the iris Where light enters the eye – Size changes depending on the amount of light present in the environment  Anatomy of the Eye - Iris Iris – The coloured part of the eye A muscle that opens and closes around a central hole to control the amount of light that enters.  Anatomy of the Eye - Lens Lens – Transparent structure behind the iris Helps focus light rays onto the retina Changes shape based on the distance of the object  Anatomy of the Eye - Retina Retina – Nerve layer at the back of the eye Senses light and creates nerve impulses Location of the: – Rods: detect black and white – Cones: detect red, blue, & green Rods and Cones  Anatomy of the Eye – Optic Nerve Optic Nerve – Carries nerve signals from the retina to the brain, where the image is interpreted  How Do Our Eyes Work? In order for use to see the light from the object that we are looking at must reach the retina. From there our brain can process the image and interpret it.  We see with our brains, not our eyes. The cornea and the lens act like a converging lens and focus the light onto the retina, creating a smaller, real and inverted The brain image. flips the inverted image so the image appears upright. Why do we squint to see more clearly? -To change the shape of the eye lens so that the light rays refract directly onto the retina.  Accommodation Is Not Always Perfect Hereditary or Age related factors can cause: ○ Myopia - near-sightedness – able to see close object but far objects are unclear ○ Hyperopia - far-sightedness – able to see far objects but close objects are unclear 13  Myopia Light refracts through the lens Image falls SHORT of the retina Vision is corrected using a diverging (concave) lens Light diverges before hitting the 14 Myopia  Corrective Lenses Near-sightedness – difficulties seeing far away Glasses with diverging lens Hyperopia - Light refracts through the lens - Image forms BEYOND the retina - Vision is corrected using a converging (convex) lens - Light converges before hitting the natural lens of the 17 Hyperopia  Corrective Lenses Far-sightedness – difficulties seeing objects nearby Glasses with converging lens  Applications (1) Laser Eye Surgery: Doctors can reshape the cornea of the eye using a laser to fix “misshaped” eyes. This prevents the need to use corrective lenses like glasses and contacts. (2) Cataracts Eye Disease: When the lens in your eye which is normally clear gets cloudy. This makes vision blurry. Most people will develop cataracts when they get older. Surgery can fix the cloudy lens.  Blind Spot Where the retina attaches to the optic nerve. There are NO rods or cones in the blind spot tic nerve carries info to the occipital lobe  Color blindness Color blindness occurs when one or more cones are defective Red-green color blindness is most common Caused by a genetic defect on the X chromosome What numbers do you see? Normal Vision Reduced sensitivity to blue Normal Vision Reduced sensitivity to red http://enchroma.com/test/instructions/