Accommodation is the process by which the human eye changes optical power to maintain a clear focus on an object
- This is mediated by ciliary muscles, which contract to change the aperture of the lens (and thus adjust focal distance)
Normally, the light from an object will be focused on the centre of the retina (at the fovea) in a healthy person
- However some individuals may be short / near-sighted (myopic) or long / far-sighted (hyperopic)
Short Sightedness
- Light is focused in front of the retina, causing distant objects to appear blurry (close objects still appear focused)
- Commonly develops with age (the ciliary muscles start to lose tensile strength, resulting in the widening of the lens)
- Most common corrective measure is the use of concave lenses to refocus the incoming light
Long Sightedness
- Light is focused on a point behind the retina, causing nearby objects to appear blurry (distant objects still appear focused)
- It is a type of refractive error caused by imperfections in the eye (e.g. the eyeball may be too short)
- Most common corrective measure is the use of convex lenses to refocus the incoming light
Short-Sightedness versus Long-Sightedness
Type of Refraction:
Unassisted accommodation
With corrective lenses