Dry Eye Anatomy and Terminology

The more you know about your eyes and the specific diseases you have, the better able you will be to speak with your doctor and to manage your own treatment. Below are some common anatomical structures related to Dry Eye and terms you may encounter.

Blink Feedback Loop is the process that causes the lacrimal gland to produce tears. When tear film evaporates, the cornea senses this and sends a message to the lacrimal gland to produce aqueous tears, and at the same time triggers the lid to blink. During the blink, muscles in the eyelids squeeze the Meibomian glands, causing them to secrete oil. When all parts of the blink feedback loop are healthy and functioning properly, the process is imperceptible.

Caruncula, or caruncle, is the ball of pink tissue at the inner corner of the eye.

Co-morbidities, or co-morbid diseases, are diseases or pathological conditions that occur at the same time. The term is sometimes used without the hyphen, e.g.: comorbidity.

Conjunctiva is the clear tissue that covers the white of the eye and extends to the inside of the eye lid. The bulbar conjunctiva, or ocular conjunctiva, is the conjunctiva that covers the white part of the eye. The palpebral conjunctiva lines the inside of the eye lids.

Lacrimal Glands are the almond shaped glands above the outer corners of the eyes, just behind the eye brows, that are responsible for the production of aqueous tears.

Lid Margin is the narrow strip of tissue between the outer skin of the eye lid and the inner part of the eye lid. The orifices, or openings, of the meibomian glands are found here.

Lid Wiper refers to the upper lid that wipes the eye when it blinks.

Meibomian Glands, a type of sebaceous gland in the eye lids, produce the oil known as meibum. Each lid contains 20 – 30 of the long, finger-shaped glands, with openings along the lid margin. Meibum is produced when the cells, that lie along the inner lining of the gland, die off. When the cells break down, they turn into meibum and are naturally secreted. It is believed that blinking plays a role  in pumping meibum out of the Meibomian glands. Meibomian gland dysfunction (MGD) is considered the leading cause of evaporative dry eye.

Tear Ducts are the channels through which the tear film constantly drains, located at the inner corners of the eyes. Each eye has an upper and lower tear duct. Tear ducts are also called lacrimal ducts.

Tear Film is made up of three layers: the mucin layer, the aqueous layer, and the lipid, or oily, layer. The mucin layer, produced by goblet cells in the conjunctiva, helps the tear film bind to the eye, and makes up the layer closest to the eye surface. The aqueous layer is the middle layer produced by the lacrimal glands. The lipid layer is made up of meibum produced by the meibomian glands, and slows evaporation of the tear film.

Terms Related to Anatomical Location/Direction

Sometimes doctors use terms that help point to a specific location or part of the eye. We might say upper and lower or inner and outer, while doctors say:

Posterior = upper or toward the back
Inferior = lower
Anterior = toward the front
Nasal (toward the nose) = inner
Temporal (toward the temple) = outer