A1 The eye and sight

A. 1. 1 Describe the basic structure of the human eye A.1.1 Describe the basic structure of the human eye. The structure should be limited to those features affecting the physical operation of the eye.

Functions of the Parts of the Eye Need to know: Cornea Iris Pupil Ciliary muscles Lens Retina Optic Nerve Rod & Cone Cells

A.1.2 State and explain the process of depth of vision and accommodation. The near point and the far point of the eye for normal vision are also included. Depth of vision With two eye we are able to obtain two images of the same thing and the brain is then able to judge distanced and motion. The size of any image formed on the retina of the eye depends on the angle subtended by the object at the eye. The closer the object is to the eye the greater will be the angle and thus the angular magnification.

The near point is just what it sounds like- the position of the closest object that can be brought into focus by the unaided eye (~25 cm). The far point is the position of the furthest object that can be brought into focus by the unaided eye (normal, healthy eye ~infinity). Accommodation is the ability of the eye to focus over this range and is controlled by the ciliary muscles pulling and relaxing in order to change the lens and thus the focal length of the eye.

A.1.3 State that the retina contains rods and cones, and describe the variation in density across the surface of the retina.

Variation in density of rod and cone cells Rods have fast response rates, and are sensitive at low light levels but they are insensitive to color. ~120 million Cones have slow response rates and are insensitive at low light levels, and give us our color vision. ~6.5 million They are NOT evenly spread out across the retina.

Blind spot – no rod or cone cells are located were the optic nerve attaches to the retina. Peripheral vision – at night you will see things better if you do not look right at them. (very helpful in astronomy)

A.1.4 Describe the function of the rods and of the cones in photopic and scotopic vision. Students should be able to sketch and interpret spectral response graphs and give an explanation for colour blindness. Photopic Vision- refers to color vision under normal lighting and is the function of the cones. Scotopic Vision- refers to our ability to see in dim light, it is completely lacking in color and is the function of the rods. Spectral response curves for cones: each of the three types of cones responds to a different region of the visible spectrum associated with the primary colors of light (red, green, and blue).

Stare at the flag for one minute. Then look at a white piece of paper Stare at the flag for one minute. Then look at a white piece of paper. What do you see?

Color blindness Color blindness (color vision deficiency) is a condition in which certain colors cannot be distinguished, and is most commonly due to an inherited condition. Red/Green color blindness is by far the most common form, about 99%, and causes problems in distinguishing reds and greens. Another color deficiency Blue/Yellow also exists, but is rare and there is no commonly available test for it. Depending on just which figures you believe, color blindness seems to occur in about 8% - 12% of males of European origin and about one-half of 1% of females. I did not find any figures for frequency in other races. Total color blindness (seeing in only shades of gray) is extremely rare. There is no treatment for color blindness, nor is it usually the cause of any significant disability. However, it can be very frustrating for individuals affected by it. Those who are not color blind seem to have the misconception that color blindness means that a color blind person sees only in black and white or shades of gray. While this sort of condition is possible, it is extremely rare. Being color blind does keep one from performing certain jobs and makes others difficult.

Life's minor frustrations (and occasional dangers) for the color blind: Weather forecasts Bi-color and tri-color LEDs (Light Emitting Diodes): Is that glowing indicator light red, yellow, or green? Traffic lights Getting in the sun with your girlfriend: Am I getting red? Color observation by others: "Look at those lovely pink flowers on that shrub". Purchasing clothing: Kids and crayons: Test strips for hard water, pH, swimming pools, Cooking and foods: cannot tell whether their piece of meat is raw or well done. Inability to make the difference between a blue-eyed blonde and a green-eyed redhead.

Ishihara Test for Color Blindness 25

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This test is simpler. The individual with normal color vision will see a 5 revealed in the dot pattern. An individual with Red/Green (the most common) color blindness will see a 2 revealed in the dots.

Nearsightedness & Farsightedness

Nearsightedness = Myopia Nearsightedness is the ability to see things near you clearly (far away objects are blurry). Concave lenses are used to correct nearsightedness. They diverge the light so it comes to a focus on the retina.

Farsightedness = Hyperopia Farsightedness is the ability to see things far from you clearly (near objects are blurry). Convex lenses are used to correct farsightedness. They converge the light so it comes to a focus on the retina.

An Astigmatism An astigmatism occurs when the front surface of your eye, the cornea, is slightly irregular in shape. (rugby ball shaped instead of football shaped) Now, can be corrected with contacts that float with weights on the bottom.

A. 1. 5 Describe colour mixing of light by addition and subtraction A.1.5 Describe colour mixing of light by addition and subtraction. Students should be able to “identify” primary and secondary colours. Primary Colors of Light Color Addition Secondary Colors of Light Red + Green + Blue = White Light Red + Blue = Magenta Blue + Green = Cyan Red + Green = Yellow Primary Colors of Pigments Color Subtraction Secondary Colors of Pigments Magenta (absorbs green) Cyan (absorbs red) Yellow (absorbs blue) Red (absorbs blue and green) Green (absorbs red and blue) Blue (absorbs red and green)

A.1.6 Discuss the effect of light and dark, and colour, on the perception of objects.3 Students should consider architectural effects of light and shadow (for example, deep shadow gives the impression of massiveness). Glow can be used to give an impression of “warmth” (for example, blue tints are cold) or to change the perceived size of a room (for example, light-coloured ceilings heighten the room). TOK: This can contribute to a discussion on perception. Wave phenomena: (A2–A6 are identical to 11.1–11.5).

Work Cited http://upload.wikimedia.org/wikipedia/commons/9/96/N2_Human_eye.jpg http://media.photobucket.com/image/human%20eye/xiuhan23/anatomy_of_eye.jpg http://www.ecse.rpi.edu/~schubert/Light-Emitting-Diodes-dot-org/chap16/chap16.htm http://www.toledo-bend.com/colorblind/aboutcb.asp