Accessory visual structures

Accessory visual structures are the components of the visual system that are not directly involved in the process of vision, but play a crucial role in supporting and enhancing visual perception. These structures include the eyelid, conjunctiva, lacrimal apparatus, and extraocular muscles.

Eyelid

The eyelid is a thin fold of skin that covers and protects the human eye. It has the primary function of spreading tears and other secretions on the eye surface to keep it moist, since a dry eye can lead to discomfort and blurred vision. The eyelid also helps to shield the eye from dust and other foreign bodies.

Conjunctiva

The conjunctiva is a thin, clear, moist membrane that covers the inner surface of the eyelids and the white part of the eyeball (the sclera). It helps to lubricate the eye by producing mucus and tears, although a larger volume of tears comes from the lacrimal glands. The conjunctiva also contributes to immune surveillance and helps to prevent the entrance of microbes into the eye.

Lacrimal Apparatus

The lacrimal apparatus is the physiological system containing the orbital structures responsible for the production and drainage of tears. It consists of the lacrimal gland, which secretes the tears, and the lacrimal ducts, which convey the tears to the surface of the human eye. Tears serve to keep the surface of the eye moist, help defend against microbial invasion, and provide nutrients to the cornea.

Extraocular Muscles

The extraocular muscles are a group of six muscles that control the movements of the eye. These muscles work in coordination to allow the eye to move smoothly in various directions, enabling the visual field to be changed without moving the head.

See Also

• Visual system
• Human eye
• Vision