^Human eye

Eyes ball: 1 inch diameter

Cornea: Front bulged transparent, causes most of the refraction.

Eye lens: Crystalline lens hard at the middle but becomes soft towards the corners & has a average refractive index of about 1.4

Pupil: Adjustable aperture that control the amount of light entering the eye. Its size is adjusted by the iris. In ordinary light the diameter of the pupil is about 2 mm; in dim light it is about 8 mm.

Retina: It is a translucent layer at the curved back surface of the eye composed of about 125 milllion sensitive cells (optical fibers) called rods (sensitive to light) & cones (sensitive to colour) covering the curved back surface the eye & send the information of this image to brain for further processing.

Ciliary muscles:  Holding eye lens & adjust the convexity of eye lens so that the near and the far objects are distinctly visible to the eye is called power of accommodation.