Eye

Squinting or excessive blinking is the motion or position of the eyelid over the eye to protect against pain or irritation. In horses causes of pain or irritation to the eye include injuries, infections, and environmental irritants.

Red eyes occur in cats when there is a change of color in the white part of the eyeball. Typically, redness indicates that an underlying condition has stimulated the blood vessels to bring more blood to the eye.

Eye discharge in cats describes an abnormal amount or type of drainage of tears, mucus, blood, pus, or other fluid from the eye.

Swollen eyes, a symptom where the eye and/or eyelids appear abnormally enlarged, can be caused by a number of different underlying conditions, including allergies, insect bites or stings, injury, conjunctivitis, or glaucoma.

Enlarged eyes in horses can be caused by a number of different underlying conditions, including facial injury, glaucoma, infections, and cysts.

Swollen eyes occur when the eyelid, eyeball, or other structures of the eye increase in size due to irritation, injury, or inflammation. Often, swelling of the eyes and associated tissues results in voluntarily closing the eyes or in being swollen shut.

Sunken eyes (also known as enophthalmos) occur when the eyeball sinks back into the head. Sunken eyes are unusual in cats, and commonly are the result of changes to the size of the eyeball or to the structures that hold the eyeball in place.

Sunken eyes (enophthalmos) in dogs is a symptom in which the eyes appear to be recessed into the skull.

Bulging eyes occur when one or both eyeballs are larger than normal (called ‘buphthalmos’), or when they are the same size as usual but the eyeball is protruding from the eye socket (called ‘exophthalmos’).

A bulging eye in cats may be characterized as abnormal enlargement of the eyeball (referred to as buphthalmos) or as protrusion of the eye beyond the socket (referred to as exophthalmos).

Blindness in horses is uncommon, and often difficult to identify due to their ability to adjust to gradual vision loss.

Eye discharge in horses describes any fluid leaking from the eyes.

Eye redness is a common symptom in horses that is associated with ocular conditions.

Dilated pupils (also referred to as mydriasis) describes when the hole in the middle of the iris of the eye is very large. Pupils normally change size in reaction to light changes or a particular emotional state such as anxiety or excitement. 

The pupil is the dark circle located at the center of the iris (the colored portion) of dogs’ eyes. The size of dogs’ pupils varies depending on light levels. When one or both eyes dilate (when the pupil becomes larger), this is called mydriasis.

The pupil is the opening in the center of the eye. Dilated pupils in cats occur normally in response to decreased light levels and some physiologic conditions, such as during the natural fear response.

Blindness in cats can appear varies in severity and can include partial or full blindness. Cats are especially good at learning their environment and adapting to vision loss, so detection of vision loss can be difficult.

Blindness refers to loss of vision, either due to a problem within the eye itself, or within the nerves or brain affecting the processing of visual input from the eyes. Vision loss can affect one eye or both, and be partial or complete.

Equine Recurrent Uveitis (ERU), or moon blindness, is an uncommon condition affecting horses, characterized by inflammation within the eye that occurs repeatedly. ERU cycles through periods where it is active, aggressive, and painful, as well as mild phases which often show no symptoms.

Crossed eyes (strabismus) is a common symptom in cats where one or both eyes have abnormal, persistent positioning. Strabismus can be congenital and is most often seen in Siamese, Himalayan, and flame point Persian breeds.

Strabismus describes an uncommon disorder in dogs in which one or both eyes are not correctly aligned, giving the appearance of crossed eyes or eyes not pointing in the same direction together. 

Blepharospasm is a term that describes repeated, spasmodic movement of the eyelids, commonly referred to as squinting. Blepharospasm is a broad symptom that is seen as a feature of different underlying diseases in cats, including injury, infection, inflammation, and developmental abnormalities.

Squinting (blepharospasm) occurs when the eyelids are lowered so that there is only a small space for the eye to look out of. Squinting is considered a symptom in dogs if it continues for a prolonged period and is not related to protecting the eyes from bright light.

Cloudy eye, also called corneal edema, describes an opacification of the eye which makes the outer surface of the eyeball appear gray, white, or blueish instead of clear.

Tumors of the eye, defined as abnormal cell growth in or around the eyes, are uncommon in cats. Most eye tumors are malignant, aggressive, fast-growing, and likely to spread throughout the body where they have serious consequences.

Anisocoria is the term for unequal pupil size in dogs. One pupil is normal, while the other is either constricted or dilated. Anisocoria is common in dogs experiencing Horner’s syndrome, but it also results from a variety of conditions and injuries that either affect one eye directly or the parts of the nervous system that control pupil size.

Blepharitis describes inflammation of the eyelids affecting one or both eyes. Eyelid inflammation is a common presentation in dogs with a variety of underlying triggers.

Progressive retinal atrophy (PRA) is a disorder of the retina which eventually results in blindness in dogs. The retina is a layer of tissue at the back of the eye which translates signals from the eye into images in the brain.

A tumor is a proliferation of cells resulting in uncontrolled tissue growth. Primary eye tumors originate from within the eye, and secondary tumors spread to the eye from somewhere else in the body. Retroviruses, UV exposure, and genetics can predispose a dog to eye tumors.

Lead is a highly toxic heavy metal that can be found in paints, fishing tackle, ammunition, drapery weights, and old toys produced prior to the late 1970s. When lead is ingested or inhaled it damages blood cells and circulates throughout the body where it causes widespread damage.