A1: The Eye and Sight

A1 The eye and sightDescribe the basic structure of the human eye. The structure should be limited to those features affecting the physical operation of the eye.

Main focussing

Fine tuning of focus

Controls amount of light

Changes the shape of the lens

Ciliary muscle changes the lens

Sends the signal to the brain

Main concentration of cones

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.

Near point (25cm) - Closest distance without straining

Far point, Muscles relaxed (Infinity)

Accommodation is the process by which the eye increases its optical power to maintain a clear image (focus) on an object as it draws near the eye.

Hyperlink

Click HERE for an online simulation for accomodation.

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

Describe the function of the rods and of the cones in photopic (cones) and scotopic (rods) vision.

Students should be able to sketch and interpret spectral response graphs and give an explanation for colour blindness.

Photopic vision is the vision of the eye under well-lit conditions. In humans and many animals, photopic vision allows colour perception, mediated by the cone cells.

Scotopic vision is the monochromatic vision of the eye in low light. Since the cone cells are nonfunctional in low light, scotopic vision is produced exclusively through the rod cells so therefore there is no colour perception.

S,M,L = short, medium and long wavelengths of cones

R = rods

Scotopic and photopic vision

The sensitivity of the cones in your eye is known as the photopic response and refers to colour vision and the perception of fine detail.

The sensitivity of the rods in your eye is known as the scotopic response and refers to vision under conditions of low level light intensity – so called ‘night vision’.

Colour blindness

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Cones and ColourThere are "red," "blue," and "green" cones, which are sensitive to those colors and combinations of them. You need all three types to see colours properly. When your cones don't work properly, or you don't have the right combination, your brain doesn't get the right message about which colours you're seeing.

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Describe colour mixing of light byaddition and subtraction.

Students should be able to “identify” primary and secondary colours.

Hyperlinks

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Questions

E.g. Shining white light on a yellow book.

Discuss the effect of light and dark, and colour, on the perception of objects.

Students should consider architectural effects oflight and shadow (for example, deep shadow givesthe impression of massiveness). Glow can be used to give an impression of “warmth” (for example, blue tints are cold; red tints are warm) or to change the perceived size of a room (for example, light-coloured ceilings heighten the room).

TOK: This can contribute to a discussion onperception.

Questions

Tsokos page 478 Q’s 1-3,6-9, 12-19.