On some photos your pupils may turn red, because incoming light was reflected from the film of your eyes, the retinae, when the photos were taken. Taking pictures of your retinae through the pupil might show something like these sketchy drawings:
The yellow and red curves mark the nerve fibres, all converging to the head of the optic nerve. The black lines are drawn by pencil.
Notice that the nerve fibres are split by a horizontal line. The centre of the circles are right at the centres of the retinae. These locations are named maculae.
The macula of the retina is the producer of sharp vision!
Usually we look at objects at varying distances. In order to see them sharply, the images must be focused to the macula. Therefore, the lens has to change its refractive power continuously, a process called accommodation of the eye. The lens is supported in a system of fine threads (zonulae) attached to the accommodation muscles (ciliary muscles). When these are brought into action, the thickness and the refractive power of the lens increases.