Health Physics: Light and Sight

the bending of light as it passes from one material into another

• When light passes from air into glass it bends towards the normal
• when light passes from glass into air it bends away from the normal

causes rays of light to be brought to a focus

causes rays of light to spread apart

by the cornea and lens

the distance between a lens and the point where parallel rays of light are brought to a focus

• by placing the lens in front of a screen and moving the lens until a sharp image of a distant object is obtained on the screen
• then measuring the distance from the lens to the screen

dioptres, D

• upside-down
• back-to-front
• smaller than the object

+ positive

- negative

• unable to focus on distant objects clearly
• corrected by using a concave lens

• unable to focus on close objects clearly
• corrected by using a convex lens

rays of light from a distant object are brought to a focus in front of the retina

rays of light from a nearby object are brought to a focus behind the retina

• only light
• not heat

• to view the insides of a patient without the need for surgery
• optical fibres carry the light down into the patient
• a second bundle of fibres is then used to send the image back to the surgeons eye
• the fibres are flexible, so they can be moved around inside the patient