Rats (Rattus spp.) have eyelids very similar to humans, with an outer covering that closes during certain parts of the day. There are some differences, however, and while rats are not known for having trouble with their eyelids, you should watch your pet for signs of pain or discomfort that might indicate an eye or eyelid is infected or functioning improperly.
Rat eyelids function much the same as human eyelids do. When rats close their eyes, they are actually using muscles to pull the upper eyelid and lower eyelid toward each other and seal off the eyeball. Rats close their eyelids when they sleep, and are born with their eyes closed. They don't open their eyelids for about 10 to 12 days after birth. Rats also have a third or inner eyelid known as the nictitating membrane.
The nictitating membrane is present in many animals, excluding humans and including rats. This is a thin film that normally hides in the medial canthus, or upper edge of the lower eyelid, when it isn’t being used. It's used to form a protective covering to guard the cornea when necessary, and is also used as a cleaning device to remove debris or other particles from the surface of the eye. This should not be confused with the tear film, which is an ever-present layer of mucous and tears that protects the eyes.
Normal Eyelid Function
Most of the time, eyelids function normally. They close when rats are at rest or asleep, and the nictitating membrane is usually absent from the visible part of the rat’s eye. Rat owners are sometimes alarmed to see a red or brownish-red discharge coming from the eyes (or sometimes the nose, though this is less common) of their rats, but this is actually normal as well. Rat tears are red in color, and are likely being produced to lubricate the eye or deal with illness or allergies.
Tears may be an indicator of a more serious problem, however, such as an eye lesion or tumor. The rat may also have a plugged duct. If the discharge does not abate after a few days, you should take your rat to the vet to determine whether it needs medicine. If eyes are red, squinted, swollen or you see a thick mucous layer covering the eye or eyelid, you should also take your rat to see a professional. Finally, if rats show any sign of pain or consistent itchiness in the eye area, do the same.
- Johns Hopkins University Animal Care and Use Committe: The Rat
- Investigative Ophthalmalogy and Visual Science: Eyelid Opening Induces Expression of a Glycocaly x Glycoprotein of Rat Ocular Surface Epithelium
- Arkansas State University Beebe: The classification of the Rat (Rattus Norvegicus)
- American Fancy Rat and Mouse Association: Medical -- Eye and Nose
- Rat Health Guide: Eye Infections
- Penn State University: Nictitating Membrane
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