The human eye and defects of vision
The normal, human eye forms a real, diminished, inverted image on the The light-sensitive area on the back of the eye. Light must be focused on the retina in order to see clearly..
Most of the Process by which a wave changes speed and sometimes direction upon entering a denser or less dense medium, eg a light ray changes direction when refracted by a lens. occurs at the air 鈥 cornea boundary.
Light then enters the lens after passing through the The area at the front of the eye where light enters..
The iris is the coloured part of the eye, surrounding the pupil.
The converging (convex) lens provides the rest of the Process by which a wave changes speed and sometimes direction upon entering a denser or less dense medium, eg a light ray changes direction when refracted by a lens. necessary to focus the rays of light sharply on the light sensitive cells of the retina at the back of the eye.
The ciliary muscles change the shape and hence the focal length of the lens, allowing the eye to focus on both near and far objects.
Near point
- The closest distance from the unaided eye at which an object can be seen clearly is called the near point.
- The near point is 25cm for a normal, adult eye.
Far point
- The furthest distance from the unaided eye at which an object can be seen clearly is called the far point.
- The far point is taken to be infinity for a normal, adult eye.
Range of vision
- The normal, adult, human, eye can see clearly objects at distances of 25cm from the eye to infinity.
- This range is more limited for the very young or as we get older.