Accommodation is the process by which the vertebrate eye changes optical power to maintain a clear image or focus on an object as its distance varies). It is the natural response of the vision system to trying to examine something nearby. The process is achieved primarily by the lens changing its shape when focusing shifts from distant to near objects and vice versa. The key features of accommodation include:

• Pupil: The pupil is located in the middle of the eyes, it is black in color and constricts to prevent light rays that have diverged from touching the retina and causing blurred vision.

• Lens: This transparent, elastic disc provides fine adjustments to focus, especially for near objects and reading. For clear vision, the lens usually remains stretched tight across most distances, but this changes during accommodation.

• Cornea: This clear half-dome on the front of the eyeball bends rays of light that pass into it.

The accommodation reflex is the visual response for focusing on near objects. The mechanism of accommodation reflex involves three responses: convergence, accommodation, and miosis. Convergence is the inward movement of the eyes to maintain binocular vision, accommodation is the change in the optical power of the lens to focus on the object, and miosis is the constriction of the pupil to increase the depth of field.

Accommodation typically weakens with age, forcing most people to get corrective lenses after age 40. Dysfunction of the accommodation reflex can be physiological like in aging and presbyopia, pathological or pharmacological. Accommodation deficits can occur in neurological conditions like supranuclear lesions, encephalitis, pineal tumors, or in neuromuscular disorders like myasthenia gravis.