What is the lacrimal duct?
The lacrimal duct is part of the nasolacrimal system. The nasolacrimal system consists of a series of narrow tubes that allow tears to drain from the eye. The nasolacrimal duct begins with two small openings in the eyelids near the nose; one of these openings is located on the upper eyelid and one is on the lower eyelid. These two small ducts meet in a single, larger nasolacrimal duct, which extends down to the nasal passages.
This system allows excess tears to drain from the eye to the nose and mouth. While not as common in cats as in dogs, this nasolacrimal duct can become obstructed or blocked. Obstruction may result in tears overflowing and running out of the eye. This overflow of tears can lead to moisture and tear staining below the eye.
What are the possible causes of lacrimal duct obstruction?
In some cases, the obstruction is related to the shape and size of the cat’s head and muzzle. Obstruction may also be caused by a hereditary defect in the formation of the nasolacrimal duct. This defect results in the lack of an opening where the nasolacrimal duct meets the conjunctiva (pink tissue surrounding the eye). This is referred to as imperforate puncta.
In other cases, lacrimal duct obstruction develops after birth. Inflammation or infection, within the eye or lacrimal duct, may lead to swelling that blocks the duct. Obstruction may also be caused by tumors that develop along the duct, or by foreign material lodged within the lacrimal duct.
What are the clinical signs of lacrimal duct obstruction?
The signs of nasolacrimal duct obstruction are largely cosmetic in nature. Most affected cats have excessive watering of the eyes or reddish-colored tear staining of the face. In chronic or severe cases, however, bacteria may begin to grow in the moist hair around the eyes. You may notice that your cat’s face develops a foul odor, due to the presence of these bacteria. Cats may also develop a skin infection below the eyes, resulting in redness, itching, swelling, and/or hair loss.
How is a lacrimal duct obstruction diagnosed?
Nasolacrimal duct obstruction is often diagnosed using a dye known as fluorescein. This dye fluoresces (glows) under a black light, allowing your veterinarian to visualize even small amounts of dye. Several drops of this dye are placed in the eyes and from there, the dye should travel down the nasolacrimal duct and be visible in the mouth and nose. If the dye does not appear in the nasal cavity within 5-10 minutes of administration, a nasolacrimal duct obstruction is likely.
In a sedated patient, the veterinarian may examine the eye with magnification to ensure that there is a duct opening visible at the eye. If this opening is visualized, a cannula (thin tube) can be inserted into the opening and used to flush saline into the nasolacrimal duct. This may be enough to alleviate mild obstructions but can also assist the veterinarian in the diagnosis of more severe obstructions.
In some cases, further diagnostic tests may be recommended. These tests might include imaging, such as X-ray, CT scan, or MRI, to rule out tumors that could cause obstruction. Your veterinarian may also recommend bacterial culture to identify infection, or other tests depending on your pet's condition.
How is a lacrimal duct obstruction treated?
"Surgery may be used to enlarge the opening to the duct, remove tumors that are compressing the duct, or remove foreign bodies from the duct."
Many cases of nasolacrimal duct obstruction are caused by inflammation. In these cases, anti-inflammatory medications and antibiotics may alleviate the obstruction. In other cases, surgery may be required for treatment. Surgery may be used to enlarge the opening to the duct, remove tumors that are compressing the duct, or remove foreign bodies from the duct. In more severe cases, a stent may be placed to allow flow through the lacrimal duct.
What happens if the lacrimal duct obstruction is not treated?
Without treatment, the lacrimal duct obstruction will cause continued issues with tear staining. Untreated cats also have an increased likelihood of skin infection around the eyes due to excessive moisture.