All about the accommodation of the eye

Every day, the eye makes use of the ability to accommodate, which is also known as the “autofocus function” of the human eye. In this article, you can find out exactly what accommodation is, how the process works and everything else about the ability to accommodate.

What is accommodation of the eye?

Accommodation allows the eye to change the total refractive power (refraction) of the crystalline lens by curving the lens in such a way that objects at different distances can be perceived sharply.

Why is accommodation important?

Importance of accommodation for vision

Accommodation ensures that a functional near and far adjustment of the eye is possible within just one second. People do not usually notice this process in everyday life. However, the eye is constantly accommodating. This function makes it possible to see clearly at both near and far distances.

The process of accommodation in the eye

The lens of the eye can be curved due to its flexibility. This is done by a ring-shaped muscle that is located behind the iris and is fixed by zonular fibers: The ciliary muscle. The ciliary muscle surrounds the lens of the eye. When the muscle contracts, the lens is pulled together in a spherical shape. This increases the refractive power of the eye. This is important for sharp vision at close range – known as near accommodation.

With distance vision, less refractive power is required for sharp vision. This is because the rays of light fall almost parallel into the eye when objects are far away. The ciliary muscle does not need to be strained. The lens of the eye becomes flat again and therefore larger – distant objects are then clearly visible. This process is known as distance accommodation.

What is the accommodation width?

The range between the maximum flat and maximum spherical lens is called the accommodation width. Young people with healthy eyes have an accommodation width of 15 diopters . A deviation of three diopters already noticeably restricts vision.

Role of the eye lens system

The accommodation of the eyes is so important because the lens of the eye focuses the light. Clear vision is only possible if the radius of curvature of the crystalline lens is adjusted so that the light rays are projected onto the retina in a focused manner. If the light rays do not fall on the retina, vision is blurred. Depending on the distance of the targeted object, the eye lens must always be readjusted.

Consequences and causes of impaired accommodation

Possible effects of impaired accommodation

If the process of accommodation is disturbed, there are disturbances when switching from near to far vision. It is also possible that vision is only impaired at certain distances.

Diseases or conditions that can affect accommodation

A disorder of accommodation can be caused by diseases. These include, in particular, spasm and paralysis. The spasm can extend to the ciliary muscle. This involves a permanent tensing of the ciliary muscle, known as spasm. Accommodation spasm. Patients then report eye pain and blurred distance vision. This can be caused by the following:

• Medication
• Psychogenic causes
• Organically caused

The paralysis can affect the nerve of the ciliary muscle (parasympathetic nerve). As a result, the ability to accommodate is lost – sharp vision at close range is then no longer possible. The paralysis is triggered by medication or damage to the components of the eye involved in accommodation.

The role of accommodation in defective vision

Myopia and hyperopia: effects on accommodation

Despite long-sightedness (hyperopia), most people affected can often still see well up to the age of 30, so that the defective vision is not noticed. This is because the eye is constantly accommodating and can compensate for farsightedness by adjusting the refractive power. However, the eye muscles are strained more frequently, so that symptoms such as headaches can still occur. If the curvature ability decreases with age, the accommodation ability is limited and the defective vision can no longer be compensated for.

With short-sightedness (myopia), the eyeball is too long or the refractive power of the eye is too high. As a result, the accommodation range is shifted closer. As a result, objects within the accommodation range can be perceived sharply. Objects in the distance, however, cannot – a visual aid is required for this.

Astigmatism and accommodation

Those affected by astigmatism can suffer from distorted or blurred vision at both near and far distances. Here too, the eye muscles are particularly strained as the eye tries to correct the visual defect. This leads to symptoms such as headaches and burning eyes.

Whether the defective vision is noticed depends on the degree of astigmatism. A slight astigmatism can often be compensated for by accommodation. If the astigmatism is particularly severe, vision problems will be noticed.

Accommodation and presbyopia

What is presbyopia and how does it develop?

Presbyopia is one of the most common consequences of an accommodation disorder. Presbyopia is an age-related decrease in the curvature of the lens of the eye. The lens becomes stiffer and stiffer, which means that it is no longer possible to adjust the curvature and therefore the refractive power. The near vision of those affected is restricted. The first symptoms are often noticed by people without other visual defects around the age of 45.

Treatment options for presbyopia

Presbyopia can be easily corrected with the help of visual aids. The strength of the visual impairment is determined by an optician. Suitable reading glasses or varifocals can then be used. Another option is refractive surgery. Multifocal lenses can be inserted. The natural lens of the eye is removed and replaced with an artificial lens. The multifocal lens has several focal points, which is why it can provide sharp vision at different distances. However, laser eye surgery, e.g. with PresbyMAX, is also possible.