Vision Problems

Black-and-White Vision and Colour Vision The retina contains two types of light-sensitive cells called rods and cones. Rod cells are cylinder-shaped cells that allow us to see images in shades of light and dark when the light is dim. Cone cells are cone-shaped cells that allow us to see colour in bright light. rod cone Electron micrograph of the retina. See page 206 (c) McGraw Hill Ryerson 2007

Vision Problems

Near-sighted vision (Myopia) Can not clearly focus on distant objects. Occurs because the lens converges the light rays to form an image in front of the retina. Corrected with a concave lens See pages 208 - 209 (c) McGraw Hill Ryerson 2007

Far-sighted vision (Hyperopia) Can not clearly focus on nearby objects. Occurs because the lens converges the light rays to form an image behind the retina. A convex lens is used to correct far-sighted vision. hyperopia See pages 208 - 209 (c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007 Astigmatism Blurred vision due to an irregular shaped cornea. Causes the image to focus on more than one point on the retina. Corrected by using eyeglasses, contact lenses, or laser surgery. See pages 208 - 209 (c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007 Blindness Normal vision Blindness is any vision impairment that keeps people from carrying out important life functions. Most people who are legally blind can perceive some light. May be able to see a tiny part of the middle of the whole scene (tunnel vision). May be able to only see the edges but not directly ahead. May be able to see light and dark but not clearly, even with visual aids. Tunnel vision See page 209 (c) McGraw Hill Ryerson 2007

Other Types of Blindness Snow blindness is a temporary blindness caused by overexposure to the glare of sunlight. Night blindness is a condition in which it is difficult to see in dim light. A test for red-green colour vision deficiency. (c) McGraw Hill Ryerson 2007

Other Types of Blindness Colour blindness is the ability to see only in shades of grey. Colour vision deficiency is the inability to distinguish certain colours. The most common is the inability to distinguish between red and green. A test for red-green colour vision deficiency. (c) McGraw Hill Ryerson 2007

Macular Degeneration Someone with macular degeneration may see some of the lines as wavy or blurred, with some dark areas at the center.

(c) McGraw Hill Ryerson 2007 Cataracts A cataracts is a clouding of the lens. Usually occur after age of 40yr A surgeon can remove the cloudy lenses and insert artificial ones.  Artificial lenses cannot change shape like natural lenses so the eye can only focus on distant objects.  (c) McGraw Hill Ryerson 2007

Homework Read pages 206-210 Answer Reading Check Questions #1-7, p210 Hand in

Laser Eye Surgery During the LASIK procedure, a specially trained eye surgeon first creates a flap in the cornea. The surgeon then pulls back the flap to expose the underlying corneal tissue, and then a laser ablates (reshapes) the cornea in a unique pre-specified pattern for each patient. https://www.youtube.com/watch?v=LEewS9XhrWM

(c) McGraw Hill Ryerson 2007 Homework Read pages 206-210 Reading Check p210 #1-6 Rods and Cones p. Eye Dissection Video: https://www.youtube.com/watch?v=0rbCrJoTatE (c) McGraw Hill Ryerson 2007