Dogs and cats have a third eyelid, called the nictitating membrane or nictitans. This shiny, pink membrane is tucked behind the lower eyelid and pops up when a pet is sedated or sick, has a mass behind or under the eye, or has a neurological condition. The nictitans contains a gland that is responsible for tear production. Cherry eye is a condition where the gland within the third eyelid protrudes from its normal position, resulting in a red, swollen mass near the inner eyelid that kind of looks like a little red cherry. It is believed to be caused by weak tissue fibers failing to hold the gland in place. One or both eyes can be affected, and improper treatment of this condition can result in dry eye.
Keratoconjunctivitis sicca (KCS), also known as dry eye, is a common eye problem in dogs. It is typically the result of inadequate tear production or a deficiency in the quality of tears produced. Two tear glands, the lacrimal gland and nictitans gland (also called the gland of the third eyelid) are responsible for tear production and play a huge role in maintaining the health of your dog’s eyes. Tears supply nutrition to the cornea, keep the surface of the eye lubricated, and wash away debris from the eye. Inadequate tear production can lead to painful, red eyes and thick ocular discharge. KCS can affect one or both eyes. Some dogs may even develop corneal ulcers and a bacterial infection of the white of the eye secondary to KCS.
A dog’s eye with the third eyelid exposed
Native to the Andes Mountains of South America, Guinea pigs are rodents that are common pets in the United States. Also called cavies, there are several common breeds including the Abyssinian (rough, short coat with cowlicks), the American/ English (classic shorthair) and the Peruvian (longhair). Guinea pigs are herbivores and need to feed continuously, therefore they produce fecal pellets continuously. Like rabbits, guinea pigs will form softer stools called cecotropes that they will ingest throughout the day. Guinea pigs typically live 5-8 years and are very social animals that do well in pairs or trios. It is important to note that guinea pigs and rabbits should not be housed together as rabbits can carry bacteria called Bordetella Bronchiseptica which, while usually harmless to rabbits, can be fatal to guinea pigs.
Pet rabbits are descended from the European wild rabbit, Oryctolagus cuniculus. There are well over 50 breeds, including giant, medium, and dwarf breeds. Rabbits are classified as lagomorphs, not rodents, because of the presence of an extra set of upper incisors called “peg” teeth. Both the incisors and molars continue to grow throughout a rabbit’s life. Rabbits are herbivores and feed continuously. In the wild, rabbits primarily eat grasses. Digestion in rabbits occurs mainly in the hindgut (cecum), and this high fiber grass maintains normal gastrointestinal activity and fermentation. It is normal for rabbits to eat their “soft” stools (cecotropes) during the night. These re-ingested fecal pellets provide important proteins and vitamins.
Since your pet’s eyes are front and center every time you look at them, abnormalities of the eyes are easy to notice. Below are descriptions of some of the more common eye disorders in dogs and cats.
Older dogs commonly have a visible cloudiness to their eyes. The cloudiness is normal aging of the lens, called nuclear sclerosis. Nuclear sclerosis does not compromise vision, and is often mistaken for cataracts. Cataracts are an abnormal cloudiness of the lens caused by a buildup of protein or pigment in the lens which interferes with normal vision. In dogs, genetics and diabetes play a role in cataract development. Canine cataracts can be removed surgically, followed by placement of an artificial lens. Cataracts are uncommon in cats.
Dry eye is a decrease in tear production and occurs in dogs, especially those with bulgy eyes, like pugs. Treatment requires lifetime eye medications to stimulate tear production.
Under the third eyelid of dogs and cats is a small tear gland. In certain breeds, such as bulldogs, cocker spaniels and Burmese cats, the gland pops up and forms a red mass in the eye, colloquially known as “cherry eye.” This abnormality typically occurs in young dogs and cats. Treatment involves tacking the gland back in place with a suture.
One of the most common eye abnormalities pet families recognize is a red eye. Glaucoma is one cause of a red eye. The redness results from a painful increase in pressure inside the eye. Management of glaucoma can be challenging and involves drops, ointments and even surgery.
Another cause of a red eye is a corneal ulcer, a sore on the clear part of the eye. Corneal ulcers are common in dogs with dry eyes, as a sequela to feline viral respiratory infections, or trauma. A dog or cat with a corneal ulcer will squint or rub their eye because ulcers are painful. Typically, application of antibiotic ointment and oral pain medication correct this condition.
Conjunctivitis is probably the most common eye problem on the list, since allergies are common in dogs. Allergic conjunctivitis is yet another condition resulting in red, weepy eyes. Distinguishing it from red eyes due to glaucoma or a corneal ulcer requires testing the pressure inside the eye and measuring tear production. Making the correct diagnosis is critical, since the treatment for each is different. Management of allergies with antihistamines or immunotherapy, plus anti-inflammatory eye ointment usually resolves allergic conjunctivitis.