OverviewThe nasolacrimal duct (n-g duct) is a tube that runs through the skull starting at the inside corner of the eye and ends just inside the nostril.
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Every eye (yours and the horse) produce tears which lubricates the eye. Without tears, dry eye occurs which is at best irritating and at worse causes blindness and loss of the eye. The tears are produced constantly and cover the entire eyeball. Evaporation removes most of the used tears but any excess is removed by gravity through the n-g tube and blown out the nostrils.
Of course when we cry, tears overflow down the cheek.
In the horse, sometimes the tube’s ability to drain becomes limited either through debris or inflammation. The result is a flow of tears from the affected eye down the cheek of the horse. Usually, but not always, both eyes are affected equally.
The treatment varies by veterinarian. What I did was place a 14 ga catheter (used and cleaned) into the opening of the n-g duct at the nostrils. Most horses did not like this and this was the rare time I would use a twitch. With a syringe attached to the catheter and my finger pressing and sealing the catheter within the n-g duct opening, I would back flush the duct forcing my mix of saline and steroid (dexamethasone) through the duct. Often, a plug of dry mucus would be ejected from the corner of the eye.
One of my secrets to success would be to start the horse on a treatment of 3 applications of an eye ointment containing antibiotics and steroid. The treatments would be every 8 hours, in other words, 1 day of treatment. This would help decrease the inflammation. However, in horses prone to this blockage, the condition would return if the cause was not removed.
Causes included the seasonal allergies, excessive dust, types of bedding, flies, etc. Changing seasons, environment, or adding a fly mask were effective in preventing further blockage.