TL;DR: Dark crust in the corners of a cat's eyes is usually just dried tears and dust, but you should consult a vet if it is accompanied by yellow discharge, redness, or squinting.
What causes dry, dark crust to form in my cat's eyes?
Dry, dark-colored crust in the corners of a cat's eyes is very common and is often just dried tear film, dust, and natural debris. In healthy cats, tears are produced constantly to lubricate the eye; when these tears evaporate or drain toward the corner of the eye, they leave behind a residue that hardens into a reddish-brown or black crust. This is usually more noticeable in cats with light-colored fur or flatter faces.
When is eye crusting in cats considered an emergency?
Urgency Level: Low. Generally, a small amount of dry crusting is not an emergency and can be managed with routine cleaning. However, you should schedule a non-emergency appointment with your veterinarian if you notice:
- Yellow or green discharge
- Squinting or holding the eye shut
- Rubbing or pawing at the face
- Significant redness of the white part of the eye
- Signs of pain or corneal cloudiness
How does sharing a photo of my cat's eyes help with veterinary triage?
Providing a high-quality, close-up photo of your cat's eyes is one of the best tools for veterinary triage. A photo helps a professional in the following ways:
- Identifies the exact color and texture of any discharge.
- Assesses whether the eye itself looks clear, cloudy, or irritated.
- Determines if the issue is a normal part of aging and grooming.
- Confirms if the condition requires an immediate clinical examination.
Clinical Context (Merck Veterinary Manual)
In cats, crusting in the eye corners can be associated with several conditions. Common infectious causes include feline herpesvirus-1, Chlamydia, and Mycoplasma, frequently presenting as acute and recurrent conjunctivitis. Systemic diseases, such as feline infectious peritonitis, toxoplasmosis, feline immunodeficiency virus, and feline leukemia virus, can also manifest with ocular signs. Eyelid inflammation (blepharitis) may result from extension of generalized dermatitis, conjunctivitis, local glandular infections, or irritants. Nasolacrimal duct obstruction can lead to mucopurulent discharge; dacryocystorhinography may be needed to establish the cause.
Chapter: Ophthalmology, Infectious Disease, Dermatology, Immunology
Source: The Merck Veterinary Manual, 11th Edition (Page 505)