The Neural Arc is comprised of the interaction between the corneal sensory nerves, the brain, and the three main tear producing glands in the eye. The corneal sensory nerves send signals to the brain, these signals are then processed, and in turn, sent to the various glands that participate in the production of tears. If the Neural Arc is dysfunctional or damaged, there is a resulting decrease in these signals.

Tear production
is facilitated by the response of the lacrimal, meibomiam and sebaceous glands. These three glands are the manufacturing network for healthy tear production. Each gland receives signals from the brain independently of the others. The dysfunction of any one of these glands can result in dry eye symptoms. In order to understand how these glands work together in tear production, we need to examine the three layers of the tear film.


Three layers of tear film on surface of cornea The sebaceous glands produces the lipid or oil film layer. This outer layer slows the evaporation, and prevents contamination of the tear layer.The lacrimal glands produce the fluid that is the aqueous or tear layer. This middle layer contains the water soluble contents of the tear film.The meibomiam glands located in your eye lid produce the mucin layer. The innermost mucin layer is semi-solid and functions much like two sided sticky tape or velcro, and acts as a bonding agent between the cornea and the aqueous layer. Tears contain at least three substances with antibacterial properties including lysozyme, beta-lysin, and lactoferrin. As you blink the tears are spread over the surface of the eye, removing exfoliated cells, debris, and foreign bodies. The tear film also acts as a lubricant between the surface of the cornea and the upper eye lid and helps to fill the uneven ridges on the surface of the cornea. A deficient tear film leads to increased friction between the cornea and the eye lid when blinking. This increased friction often results in surface inflammation. Dry eye symptoms which occur in relation to LASIK are directly as a result of the corneal nerves being cut during LASIK, and therefore, there is an expected decrease in sensory stimulation resulting in a decrease in tear production. The corneal nerves do not send appropriate messages to the brain, the brain does not send appropriate messages to the tear producing glands, and the glands do not produce a healthy tear film.Artificial lubricants and anti-inflammatory therapy have improved the signs and symptoms of dry-eye syndrome. Artificial tears compensate for reduced tear production and corticosteroids (anti-inflammatory agents) have been reported to the improve signs and symptoms of dry eye, improve tear clearance, and to normalize ocular surface mucous production. Patients often have a sustained benefit from just a 2-week treatment with topical corticosteroids.

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For more information contact:
Dr. Murray McFadden
(BSc, MD, FRCS(C), Diplomate of the
American Board of Ophthalmology)
© Copyright 1996-2005 Murray McFadden MD, Inc.

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This page last updated on September 14, 2001.
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