Accommodation for Near Vision During far vision, the ciliary bodies relax, the zonule stretch, and the lens flattens. During near accommodation, the ciliary bodies contract (i.e., shorten), which relaxes the zonule and rounds the lens (i.e., thickens it). This brings the near object into focus.

The young human eye can change focus from distance (infinity) to as near as 6.5 cm from the eye. This dramatic change in focal power of the eye of approximately 15 dioptres (the reciprocal of focal length in metres) occurs as a consequence of a reduction in zonular tension induced by ciliary muscle contraction.

The change in the shape of the lens is controlled by ciliary muscles inside the eye. Changes in contraction of the ciliary muscles alters the focal distance of the eye, causing nearer or farther images to come into focus on the retina; this process is known as accommodation.

The accommodation required for near vision results from contraction of the ciliary muscle. This reduces the tension in the anterior zonular fibers, while tension is placed on the posterior elastic tissues as the muscle moves forward and inward (Figure 2).

Testing for the accommodation reflex follows nicely on from eye movements. Ask the patient to keep focusing on the tip of your index finger and slowly move it towards them, aiming for the tip of their nose. You need to be watching their pupils to make sure you see them constrict as your finger gets closer.

The Near Point is the point in space conjugate to the retina when the eye is fully accommodated. The distance between the far point and the near point is the patient’s accommodative range. If this patient is a -2D myope, and has a maximal accommodation of 5D, what is her range of uncorrected clear vision?

The ability of the eye lens to adjust its focal length, to clearly focus rays coming from distant as well a near object on the retina, is called the power of accommodation of the eye.

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).

The innermost region of ciliary muscle, (Müller’s) annular muscle, is formed of circular muscle bundles with a sphincter type of action. These fibers are located near the major circle of the iris. Figure 3-14 shows the relationship between these regions of the ciliary muscle and surrounding structures.

iris sphincter muscle

The iris dilator muscle has fibers arranged radially from the sphincter to the ciliary border, receives sympathetic innervation, and functions to cause dilation of the pupil (mydriasis).

For starters, oxytocin and dopamine — the “love hormones” — have an effect on pupil size. Your brain gets a boost of these chemicals when you’re sexually or romantically attracted to someone. This surge in hormones appears to make your pupils dilate. Dilation may also be related to the biological need to reproduce.

How to make eye dilation go away faster

1. Having a loved one drive you home after your appointment.
2. Wearing sunglasses if you spend any time outside and on the ride home.
3. Limiting your time in the sun as much as possible.
4. Wearing blue-light protection glasses when looking at digital screens.

Most people can expect eye dilation to last somewhere between 4 and 24 hours. Generally, the effects last the longest in people with lighter colored eyes and in children who require stronger doses of eye dilation drops. People who are concerned about the effects of eye dilation should speak with their eye doctor.