When the ciliary muscle contracts in response to parasympathetic stimulation, this reduces tension on the suspensory ligaments, and the capsule of the lens is relaxed. The lens then becomes shorter and fatter and accommodates for viewing near objects.

What happens when ciliary muscle contracts?

When the ciliary muscle is contracted, the lens becomes more spherical – and has increased focussing power – due to a lessening of tension on the zonular fibres (a). When the ciliary muscles relax, these fibres become taut – pulling the lens out into a flatter shape, which has less focussing power (b).

Do the ciliary muscles contract to thicken the lens?

When the ciliary muscle is relaxed, the choroid acts like a spring pulling on the lens via the zonule fibers causing the lens to become flat. When the ciliary muscle contracts, it stretches the choroid, releasing the tension on the lens and the lens becomes thicker.