Communication: Refraction Of Light In The Eye Flashcards
identify the cornea, aqueous humor, lens and vitreous humor as refractive media
In the eye, refraction occurs when light passes from the air to the cornea, from the cornea to the aqueous humor, from the aqueous humor to the lens and from the lens to the vitreous humor. Light spreading out from one point on an object can therefore be focused on a particular point on the retina.
identify accommodation as the focusing of objects at different distances, describe its achievement through the change in strength of the lens and explain its importance
Light rays reflected from an object six metres or more away are almost parallel to each other. The lens refracts these rays so that they fall on the fovea, the part of the retina where vision is sharpest. If an object is closer than six metres the light rays reflected from it will be diverging rather than parallel. To bend these light rays so that they fall on the fovea the lens must become more rounded.
Accommodation is the ability of the lens to change shape and focus light from objects at a range of distances. If the lens becomes more rounded (greater curvature) it refracts light to a greater extent and close objects can be focused. If the lens becomes less rounded (less curvature) it refracts light less and distant objects can be focused.
The ciliary muscles are responsible for adjusting the shape of the lens. When they relax, the lens is less rounded. When they contract, the lens becomes more rounded.
Accommodation is important because it allows the eye to form focused images on the retina from objects at a range of distances from the eye.
Accommodation
Accommodation
As a person ages the lens gradually loses its elasticity and can no longer accommodate for viewing close objects. Corrective spectacles are required.
compare the change in the refractive power of the lens from rest to maximum accommodation
When the eye is accommodated it focuses on close objects.
In the eye at rest (unaccommodated) the lens is flattened because it is subjected to tension by the suspensory ligaments. The focal length of the lens is long and so distant objects are in focus.
When accommodation occurs the ring of ciliary muscles contract, the tension in the suspensory ligaments is reduced and the lens bulges due to its natural elasticity. The refractive power of the lens increases therefore shortening the focal length.
distinguish between myopia and hyperopia and outline how technologies can be used to correct these conditions
Myopia is short-sightedness. A person with myopia sees objects that are close clearly but objects in the distance are out of focus. Rays from distant objects are focused in front of the retina rather than on the retina. The usual cause of myopia is that the eyeball is too long. Some forms of myopia improve with age.
Hyperopia is long-sightedness. A person with hyperopia sees objects that are in the distance clearly but close objects are out of focus. Rays from distant objects are focused behind the retina rather than on the retina. The usual cause of hyperopia is that the eyeball is too short or that the lens gradually hardens with age, reducing its power of accommodation.
Technologies used to correct these conditions include eyeglasses or spectacles, contact lenses or surgery. Myopia can be corrected with concave lenses worn for distance viewing. These lenses cause parallel rays to diverge slightly before they enter the eye so that the lens can focus them on the retina.
Hyperopia can be corrected with convex lenses worn for viewing close objects. These lenses cause parallel light rays to converge slightly before entering the eye so that the lens can then converge the rays to a point on the retina.
Examples of myopia and hyperopia
Refractive surgery may also be used to treat both myopia and hyperopia. A thin flap of the cornea is cut and folded back. A laser is used to reshape the cornea to a more suitable shape. The fold of skin is then folded back into place.
explain how the production of two different images of a view can result in depth perception
Some animals have forward facing eyes. This means that there is considerable overlap between the views on the left and the right. Because the two eyes are a few centimetres apart, each eye sees a slightly different view of an object.
The images formed by each eye are superimposed by the brain, and because each view is slightly different, objects appear to have depth as well as height and breadth, that is we see in three dimensions. This is known as stereoscopic or binocular vision.
This type of vision also makes it possible to judge distances of near objects.
Climbing animals such as monkeys and predators such as cats have forward facing eyes, but grazing animals such as horses have eyes on the side of the head so they have a wider field of view.
Focal length experiment.
This activity requires you to select glass or perspex lenses of different focal lengths and compare how they refract light. One possible method is to use a ray box and observe how the lenses refract light. Make sure that you compare how lenses of different focal lengths can focus objects at different distances away from the lens. As the curvature of the lens increases the focal length deceases. Remember that the same lens in the eye can vary its focal length by accommodation.
What is cataracts?
A cataract is a clouding of the clear lens in the eye and is one of the leading causes of vision impairment. While cataracts most commonly occur in those who are older, they can develop in younger people as well. Some people are born with a cataract.
identify the conditions under which refraction of light occurs
Light rays travel in straight lines. However, if a light ray passes from one medium to another at an angle other than 90 º, the ray is bent. This bending, as light passes from one medium to another, is called refraction.
Refraction of light occurs when light passes from one substance to another.
