Contrast ways in which light rays are bent by concave and convex lenses.

Describe the relationship between the structure of the eye and sight

Identify types of corrective lenses used to correct different sight problems (Example: convex – farsightedness,

concave – nearsightedness)

VisionVision begins when light rays are reflectedreflected off an object and enter the eyes through the corneacornea, the transparent outer covering of the eye.

http://www.aoa.org/x6024.xml

http://www.tpub.com/neets/tm/106-3.htm

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The corneacornea bends or refracts the rays that pass through a round hole called the pupil.

CORNEACORNEA

The irisiris, or colored portion of the eye that surrounds the pupil, opens and closes.

IRISIRIS

The pupilpupil gets bigger or smaller to regulate the amount of light passing through.

PUPILPUPIL

The light rays then pass through the lenslens, which actually changes shape so it can further bend the rays and focus them on the retina at the back of the eye.

LENSLENS

Structure of the Eye: Cornea and LensCornea

EyelensRetina

There are two lenses in your eye, the cornea and the eyelens. The cornea, the front surface of the eye, does most of the

focusing in your eye The eyelens provides adjustable fine-tuning of the focus

The Eyelens: Accommodation

The eyelens changes its focal length by changing its shape. Ligaments pull on the lens to change the amount of “bulge”

Eyelens: Accommodation

Muscles contract, ligaments relax, more bulge, more bending power, shorter focal length

Muscles relax, ligaments contract, less bulge, less bending power, longer focal length

Eyelens Ligaments

The retinaretina is a thin layer of tissue at the back of the eye that contains millions of tiny light-sensing nerve cells. The images that we see are projected onto the retina upside down.  Our brain quite simply, flips the images over so that we see things upright.

RETINARETINA

Structure of the Eye: Retina The retina is the sensor or film of your eye.

Its layers do three thingsProvide blood and nutrients (choroid)Absorb light and convert to an electrical signal

(photoreceptors)Transfer the signal to the brain (nerve cells)

Plexiform layer (nerve cells)

Rods and Cones (photoreceptors)

Choroid (blood vessels)

Light

Structure of the Retina

← Nerve cells

← Photoreceptors

← Choroid

Light

Photoreceptors: Rods and Cones Light is detected and

converted to an electrical signal by the photoreceptors in the retina. There are two main kinds of receptors, rods and cones

This is a false color image, rods and cones are not actually different colors

rod

cone

Photoreceptors: Cones Cones are responsible for

our fine detailed and color vision

Cones are clustered near the center of your retina, called the fovea

There are 5 million cones in the average retina

Photoreceptors: Rods

Rods are responsible for low light and peripheral vision

They are present everywhere in the retina except the fovea

There are 125 million rods in the average retina

Rods and Cones Because of their different functions, rods and

cones are present in varying densities in the retina. The blind spot is due to the connection of the optic nerve

The optic nerve optic nerve transmits information to the brain.

OPTIC OPTIC NERVENERVE

The vitreous bodyvitreous body, or maculamacula, gives the eye its shape.

MACULAMACULA

Lenses bend light in useful ways. Most devices that control light have one or more lenses in them (some use only mirrors, which can do most of the same things that lenses can do).

There are TWO basic simple lens types: There are TWO basic simple lens types: Concave and Convex Concave and Convex

What are lenses?

CONVEXCONVEX or POSITIVE lenses will CONVERGE or FOCUS light and can form an IMAGE.

By wearing a convex (converging) spectacle lens, the rays of light from a near object are converged before entering the eye so that the cornea and eye lens can direct the focal point onto the retina.

http://www.passmyexams.co.uk/GCSE/physics/use-of-lenses-for-correcting-vision-eyesight.html

The correct name for farsightednessfarsightedness is HyperopiaHyperopia. The shape of your eye does not bend light correctly, resulting in a blurred image. A convex lens is usually used to correct this problem.

Convex lens

CONCAVECONCAVE or NEGATIVE lenses will DIVERGE (spread out) light rays.

By wearing a concave (diverging) spectacle lens, the rays of light from a near object are diverged before entering the eye so that the cornea and eye lens can direct the focal point onto the retina.

http://www.passmyexams.co.uk/GCSE/physics/use-of-lenses-for-correcting-vision-eyesight.html

The correct name of nearsightednessnearsightedness is MyopiaMyopia. Myopia occurs when the eyeball is slightly longer than usual from front to back. This causes light rays to focus at a point in front of the retina, rather than directly on its surface. A concave lens is usually used to correct this problem.

Concave lens

In simple magnificationmagnification, light from an object passes through a biconvex lens and is bent (refracted) towards your eye. It makes it appear to have come from a much bigger object.

http://www.sciencelearn.org.nz/Contexts/Exploring-with-Microscopes/Sci-Media/Images/How-lenses-magnify