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There are few things in life more heartwarming than meeting the steady gaze of your beloved dog or watching a young kitten eagerly explore their world, eyes wide with wonder, alert and aware of every movement in the room. We all realize how important our vision is, but how do we recognize problems with our pet’s eyes or vision?
Ocular emergencies, those that involve the eye or surrounding structures, can vary in scope from the obvious distress of a proptosed eyeball (an eyeball that has been displaced forward from the socket or “popped out”) to less obvious scratches or ulcers on the surface of the cornea. It is not difficult to convince pet owners that ocular emergencies are extremely important to manage as quickly as possible in order to prevent vision loss or permanent damage. The following article will describe how to identify some of the most common ocular injuries and provide basic information on treatment measures.
Normal Anatomy of the Eye
The basic structures of the eye that are most easily observed during routine interaction with your pet include the globe, cornea, lens, pupil, conjunctiva, vitreous, and eyelids.
What Should a Healthy Eye Look Like and What Signs Should Alert Me to a Problem?
- The globe is the actual eyeball. A normal globe rests behind the eyelids and is of a spherical shape. In most normal pets, each globe is similar in appearance in relation to size, shape, and position. A globe that has “popped out” or proptosed, an eye with a bulging appearance, or globe with a deflated appearance are all cause for alarm.
- The cornea is the outer clear surface of the eye. Light is transmitted through the cornea into the eye. A normal cornea is clear with a regular surface that does not bulge out or dip in. It is of uniform clarity and does not appear hazy or have holes, lines, or scratches on the surface. A normal cornea has a thin tear film overlying it.
- The lens rests inside the eye, just behind the pupil, and its job is to focus rays of light on the retina. The lens should appear clear in young pets, but can develop a hazy appearance as a pet ages and cataracts begin to form. The lens should appear to be suspended behind the pupil and not give the illusion of “tipping forward” out of the pupil, or falling to the bottom of the eye.
- The pupil is the hole, or aperture, within the iris that helps restrict or allow the entry of light into the eye. Both pupils should be symmetrically shaped. As previously noted, the lens should not appear to protrude through the pupil.
- The conjunctiva is a thin, semi-transparent mucous membrane that lines the inner surface of the eyelid and the white part of the eye (sclera). It should appear as a shiny, thin covering and should not be distinguishable from the actual surface of the sclera or eyelid. The conjunctiva should not appear thickened, red, inflamed, or “bloodshot.” Tear production should be just enough to keep the surface of the cornea clear and lubricated. Thick, yellow, or green discharge, or an excess amount of clear discharge is not normal. Alternatively, the absence of a normal tear film is abnormal. The vitreous (vitreous humour) is the gel-like, clear substance that is present between the cornea and the lens (anterior chamber) and the lens and the retina (posterior chamber) of the eye. This substance gives the globe its spherical shape and helps hold the retina in place. The vitreous should be clear. Hyphema (blood in the vitreous humour) or hypopyon (yellow pus in the vitreous humour) are not present in a healthy eye.
- The eyelids are the flaps of skin that surround and cover the eyeball when closed. The eyelid margin should be clear and free of defects or tears. The lids should open and close freely and should not appear swollen. Eyelids tightly pressed together (blepharospasm) is an indicator of eye pain and should be taken seriously.
How Can I Tell If My Pet Has Eye Pain?
Eye pain in pets is often subtle. In cases of mild discomfort your pet may appear to be “winking” at you through a half closed lid. Extreme pain is usually accompanied by an eye that is closed very tightly. Your pet may also rub the affected side of their face on the floor or attempt to rub their eye with a paw. If your pet is showing signs of eye pain, or you are concerned the appearance of your pet’s eye has changed, a visit to your veterinarian is always recommended. Waiting to see if an eye improves on its own can have severe consequences to your pet’s vision and well-being.
What Are Some Examples of Common Eye-Related Emergencies?
- Traumatic eye injuries occur as a result of serious events, such as being hit by a car or involved in a dog fight or attack. A common, and frightening, injury is proptosis of the globe. A proptosed globe is an eye that has been forced forward out of the orbit (eye socket) by blunt force trauma. The inflammation that results secondary to this event causes extreme swelling of all surrounding ocular tissue. This swelling forces the globe in front of the eyelids and it cannot be replaced without general anesthesia. Once an eye has been proptosed, the prognosis for retaining vision is very poor (20-30%). However, surgical removal (enucleation) of the eye is usually not necessary and most animals are comfortable after they recover from the initial trauma. Other traumatic injuries include penetration of the globe by foreign objects (such as sticks or metal), lacerations of the cornea or eyelids, and traumatic lens luxation. Foreign objects can easily lodge in the eye when playing with sticks or running and playing in the woods. Full thickness lacerations to the cornea or eyelid often result secondary to scratches from a cat claw or penetration of sticks or other foreign objects. These conditions often require general anesthesia and surgical exploration. Blunt force trauma to the head can result in lens luxation. The lens is normally suspended centrally in the eye, behind the iris. When forced forward into the anterior chamber of the eye, the lens can obstruct the normal flow of vitreous humour through the ocular chambers. This can lead to increased intraocular pressure (glaucoma) and resulting blindness. Referral for immediate surgical assessment of any traumatic injury to the eye is absolutely essential.
- Corneal ulceration occurs when the integrity of the corneal surface (epithelium) is disrupted. The deeper tissue of the cornea (corneal stroma) is also involved and may become infected. Superficial corneal ulcers usually heal uneventfully within a few days with application of topical broad spectrum antimicrobials and eye lubrication applied several times daily. However, some ulcers do not heal easily. These ulcers may become extremely large and deep, threatening to invade through the entire cornea, resulting in eye rupture. Deep ulcers that cause the cornea to thin to the point of near rupture are referred to as descemetoceles. Clinically, these ulcers appear as deep divots in the surface of the cornea. Dogs with corneal ulceration usually appear to have significant eye pain, even if the ulcer is superficial. They keep the affected eye closed, or partially closed, and there is often copious tearing associated with the affected eye. The surface of the cornea may appear irregular with a circular area that does not have the same shiny surface as the remainder of the cornea. A corneal ulcer is easily diagnosed using a fluorescein dye strip by your veterinarian. Treatment for especially deep ulcers may include surgical management. Any obvious abnormality associated with the surface of your pet’s eye should be seen immediately.
- Glaucoma refers to an increase in the intraocular pressure of the eye. Untreated, glaucoma will lead to blindness. Glaucoma is a painful condition that may be either acute or chronic in nature. Acute cases are associated with a cloudy appearance to the surface of the cornea (corneal edema) and extreme redness and prominent blood vessels (episcleral injection) within the white part of the eye (sclera). One may even appreciate a mild “bulging” appearance to the affected eye if pressure is significantly increased. Pets may even present to the veterinarian as already blind. Interestingly, there may be a hereditary component to glaucoma. Breeds including the Labrador Retriever, Chow Chow, Boston Terrier, American Cocker Spaniel, Basset Hound, Beagle, and Siberian Husky may be predisposed. A special device called a tonometer is used by your veterinarian to measure ocular pressure and diagnose glaucoma. Lifelong topical therapy is necessary for the management of glaucoma and the condition may prove difficult to treat.
- Sudden blindness is extremely disconcerting to owners and pets alike. Owners will note that a dog or cat suddenly walks into things, falls down, or seems disoriented. Depending upon the cause of acute blindness, the pet may not show any signs of pain. Sudden Acquired Retinal Degeneration (SARD) is a cause of total, irreversible blindness that is seen more frequently in Dachshunds and Miniature Schnauzers. There may be an immune component to the disease. An electroretinogram (ERG) is necessary for diagnosis and there is no known effective treatment. Another immune mediated disease, Immune Mediated Retinal Detachment Syndrome, also occurs in dogs, but, thankfully, it often responds to steroid therapy. Rapid onset blindness may also occur in diabetic dogs that suddenly develop mature cataracts. Strangely enough, diabetic dogs may develop mature cataracts resulting in complete loss of vision in as little as 48 hrs. Dogs with well-controlled diabetes are often good candidates for surgical cataract removal as a means of regaining vision. In cats, acute blindness often occurs due to retinal detachment secondary to uncontrolled hypertension in cats with renal disease.
It is impossible to provide an exhaustive list of all emergency conditions of the canine and feline eye in a single article. However, one simple rule of thumb will serve you well; when in doubt, it is always in your pet’s best interest to have your veterinarian examine them immediately if you have concerns about their ocular health. Preserving your pet’s eyesight will be as much a priority to your veterinarian as it is to you.