The ciliary muscle is a muscle in the ciliary body, an area of the eye which helps people focus. With the assistance of the ciliary muscle, the lens of the eye can be flattened or rounded to allow people to focus on distant and near objects. This muscle is also responsible for controlling part of the drainage system of the eye to maintain the proper fluid pressure in the eye. Damage to this muscle can lead to vision problems.
This smooth muscle is circular, surrounding the lens of the eye. It is attached to the lens with small fibers known as zonules or suspensory ligaments. When the ciliary muscle is relaxed, the ligaments are pulled taught, which flattens the lens of the eye. With a flattened lens, someone can see more distant objects. When the ciliary muscle is contracted, the ring becomes smaller, and the lens is pushed into a rounded and bulged shape which allows it to focus on near objects. The shape of the lens can be minutely adjusted for fine tuning when it comes to focus.
Incredibly rapid changes in focus are possible with the ciliary muscle. This structure in the eye also allows for very precise focusing at a wide variety of distances, which allows people to move their center of focus quickly when examining various objects in the visual field. The muscle is innervated by the third cranial nerve, also known as the oculomotor nerve, one of several nerves which plays a role in the control of eye movements.
In addition to being involved in focusing, the ciliary muscle also regulates the flow of fluid into Schlemm’s canal, allowing the eye to drain aqueous humour. This fluid is constantly in production and must be drained so that the pressure in the eye remains consistent. If the eye cannot drain aqueous humour, it can build up in the eye and cause health problems. Glaucoma is an example of eye conditions characterized by elevated intraocular pressure.
This tiny muscle is best viewed under magnification so that people can see the details of the muscle structure and its point of attachment. On very high magnification, the suspensory ligaments can be seen clinging to the ciliary muscle like wisps of cotton. The apparent fragility of these structures belies the fact that they are used thousands of times a day to adjust the focus of the eye in order to meet the needs of its owner.