Ophthalmic Diseases

Canine Diseases

• Cataracts
  

  Though many people mistakenly believe cataracts are a cloudy film on the surface of the eye, cataracts are actually opacities within the lens, located inside the eye. Most cataracts are genetic, and the condition is prevalent in breeds such as Cocker Spaniels, Poodles, Siberian Huskies, Schnauzers, Golden and Labrador Retrievers, and Terriers. Cataracts can also be caused by Diabetes mellitus, trauma, and inflammation, and can occur at any stage of life. However, some genetic cataracts can develop predictably at a young age. Many cataracts will worsen to the point of blindness, but certain types, especially in the Retriever breeds, can remain small for the entire life of the pet.

  Even if cataracts are just beginning to form, it’s important to identify and monitor them early. Developing cataracts leak proteins into the eye, causing an inflammatory reaction. Untreated inflammation can result in many complications, including scar formation, glaucoma, and permanent blindness. Cataracts can change from small opacities to complete cloudiness of the lens rapidly (over a few days) or slowly (over several months or years).

  Cataracts may be treated either medically or surgically. Tests can be performed to determine if the surgical removal of the cataracts will improve his or her vision. In certain cases, cataract surgery is not recommended or the owner decides not to pursue surgery. In these cases, medical treatment of the cataracts is recommended. Because of the possible complications associated with cataracts, it is important to treat cataracts whether or not surgery is performed. These treatments usually include a topical anti-inflammatory once or twice daily. Sometimes, a drop that dilates the pupil and allows more light into the eye is used to help your pet see better around the cataracts.

  View Image: Image 1
  Download our detailed Cataract Information (PDF)
  Video: Cataracts, You, and Your Pet

• Glaucoma
  

  Glaucoma is the elevation of pressure inside the eye (intraocular pressure) beyond a specific point at which vision is being lost. Glaucoma is a frequent cause of blindness in humans and in our pets. Glaucoma can be genetic, involve both eyes, and is seen in many purebred breeds.

  To understand glaucoma, it is necessary to understand how the fluid inside the eye normally flows and maintains normal intraocular pressure. Fluid inside the eye (aqueous humor) is produced behind the the iris in a portion of the eye called the ciliary body. The aqueous humor flows through the pupil and drains from the eye at the junction of the clear cornea and the iris. This junction is called the drainage angle and is similar to a sieve. Aqueous humor should be produced and drained from the eye at the same rate, resulting in a stable intraocular pressure of 15-25 mm of Hg.

  Glaucoma is the consequence of a blockage of the outflow of aqueous humor and a subsequent build-up of pressure inside the eye. The resulting high pressure compresses the optic nerve fibers and results in progressive loss of vision. Once the optic nerve has been permanently damaged, there can be no restoration of vision. Initially, there may be no discomfort associated with high pressure, which can go undetected. However, uncontrolled high pressure will eventually lead to enlargement of the eye and pain.

  Many of us are familiar with glaucoma because it is a common eye problem in people. It is usually detected early and treated aggressively in humans, which often results in comfort and maintenance of pressure for life. In animals, the disease can develop rapidly without detection, and may be in advanced stages before it is recognized and able to be treated. At this stage, the disease is often more difficult to treat and may require more aggressive medical and surgical treatments.

  Monitoring intraocular pressure in animals should be an important part of annual examinations, especially in predisposed purebred breeds or animals with a family history of glaucoma. With early medical and occasionally surgical therapy, your pet’s vision and comfort can be maintained.

  View Image: Image 1
  Download our detailed Glaucoma Information (PDF)

• KCS (Keratoconjunctivitis Sicca)

  Keratoconjunctivitis sicca, commonly known as “dry eye,” describes the changes in the eye which result from lack of tear production.

  The tear film that covers the surface of the eye is comprised of 3 layers (oily, aqueous/watery, and mucous) that protect and provide nutrients to the cornea (the clear portion in front of the iris). A breakdown in any component of the tear film and a loss of the aqueous layer causes dry eye. This loss results in dryness to areas of the corneal surface or, in more advanced cases, drying of the entire corneal surface. When the cornea is deprived of oxygen and nutrients through the tear film, it rapidly undergoes destructive changes. These changes result in brown pigmentation, scar tissue growth, ulcer development, and blood vessel growth across the cornea leading to partial vision loss.

  The eyes of a patient with KCS sting constantly, just as ours do on a very windy day. The stinging we feel is due to the wind drying our eyes quicker than tears can be provided. Therefore, the patient with dry eye is uncomfortable almost all of the time.

  When a patient has “dry eye” where there is a lack of the watery layer of the tears, the oil and mucus layers are increased. This leads to a thick, mucoid, greenish discharge that sticks to the hairs around the eye. Often this is the main reason that a patient is presented to the veterinarian. The discharge will clear up whenever any medication is used but will return when the medication is stopped. When this occurs, the patient is often referred to a veterinary ophthalmologist for further examination and treatment.

  Untreated KCS can result in blindness. Most patients with dry eye will do well if medications are administered on a timely basis. In general, with good owner compliance, no patient needs to lose eyesight due to KCS.

  Download our detailed KCS Information (PDF)

• Corneal Ulcers

  The cornea is the clear front part of the eye. It is less than 1mm thick and consists of several complex layers. A corneal ulcer is a break in one or more of these layers. The ulcer may be very shallow, involving the outermost layers of the cornea (similar to a scrape or an abrasion), or it may be very deep, penetrating nearly all of the corneal layers.

  Corneal ulcers have many different causes, including trauma, keratoconjunctivitis sicca (KCS or “dry eye”), entropion (rolling in of the eyelids), exposure, distichiasis (extra eyelashes), foreign bodies, and chemical burns. Symptoms of a corneal ulcer include squinting, sensitivity to light, ocular discharge, and a hazy or blue cornea.

  If recognized early, most superficial ulcers will heal quickly with proper treatment. Deep or infected ulcers may not heal without surgical treatments. Medications are prescribed to control infection, inflammation, and pain. Your pet will also need to wear an Elizabethan collar (“lamp shade”) to prevent self-trauma (rubbing). Several types of surgical techniques may be recommended, including conjunctival graft or corneal conjunctival transposition.

  Download our detailed Corneal Ulcer Information (PDF)

• Third Eyelid Gland Prolapse (a.k.a. “cherry eye”)

  The third eyelid lies between the eyelids and the eye at the inside corner and contains an accessory lacrimal (tear) gland. When the gland prolapses, it protrudes above the free border of the third eyelid and becomes inflamed, red, and enlarged, hence the name “cherry eye.”

  The third eyelid gland may prolapse following trauma to the lids or eye. Some breeds of dogs and cats are born with a lack of connective tissue to anchor the gland in place, which results in prolapse of the gland without trauma.

  The gland can occasionally be repositioned with topical anesthesia and sedation, but surgical correction is often recommended. (Removing the gland is not recommended as it contributes 30% of the tear film that keeps the eye moist and the cornea healthy.) If the condition is not surgically corrected, the pet is predisposed to chronic conjunctivitis, irritation, and discomfort.

• Eyelid Abnormalities
  

  If diseases of the eyelids are allowed to persist, their constant irritation can cause serious damage to the cornea (corneal ulcerations, ocular infections, corneal scarring, and/or corneal vascularization) and can affect vision.

  Entropion is an inward rolling of the eyelids that may involve the upper lids, lower lids, or both. This is often an inherited disorder in many breeds. It can result in eyelashes rubbing against the front of the cornea and is often very uncomfortable or painful. Symptoms commonly seen with entropion are excessive tearing, a prominent third eyelid, conjunctivitis, and corneal changes.

  The treatment for entropion is determined by species, age, severity, and the presence of corneal ulcers. If an ulcer is present, surgery may be recommended. Young dogs may be treated by temporary “tacking,” as some of these dogs may outgrow their entropion.

  Ectropion is an outward rolling of the eyelids. It can lead to chronic irritation and discharge. Surgical correction may be necessary or medical management may be advised.

  Eyelid Masses. The eyelid is a common site for mass formation. The presence of a mass is not only of cosmetic concern, but can cause ocular irritation, discomfort, and permanent corneal scarring. Most eyelid masses in dogs are benign and cured by surgical removal, but some eyelid tumors are serious and require aggressive therapy. Tumors that are malignant tend to be locally invasive, but rarely metastasize (spread to the rest of the body). Eyelid masses in cats are more frequently malignant. Surgical removal is generally the treatment of choice.

  View Image: Image 1

Feline Diseases

• Corneal Sequestrum
  

  The cornea is the clear front part of the eye less than 1mm thick that consists of several complex layers. Corneal sequestrum occurs most frequently in cats and is characterized by the degeneration of corneal collagen and the accumulation of brown pigment in the cornea. This disease can occur in all breeds of cats, but Persian, Himalayan, and Burmese breeds appear to be predisposed.

  These lesions may be fairly superficial at first (involving only the surface layers of the cornea), but can progress to the deepest layers of the cornea. Possible causes include entropion, hereditary corneal degeneration, abnormalities in the tear film, feline herpes virus, and immune-mediated disease. Any corneal ulcer in a cat that does not heal quickly can develop into a corneal sequestrum.

  The recommended treatment for corneal sequestrum is a surgery called a superficial keratectomy. There is a possibility of recurrence after surgical excision, but this is unlikely if all of the affected tissue is able to be removed.

  View Image: Image 1

• Feline Uveitis

  Uveitis (inflammation within the eye) is one of the most frequent and significant ophthalmic disorders in cats. Both the direct and secondary effects may be destructive to the eye and maintenance of vision. Cats with serious systemic diseases may first be presented to the veterinarian for ocular signs of uveitis. Possible clinical signs include decreased vision, squinting, redness, elevated third eyelid, cloudy cornea, iris color change and small pupil. Long term sequela include cataract development, lens dislocation and secondary glaucoma.

  Potential causes:

  • Traumatic (blunt or penetrating wound)
  • Infectious (feline leukemia virus, feline infectious peritonitis, feline immunodefieciency virus, fungal diseases, yeast and protozoal diseases)
  • Neoplastic (cancer)
  • Lens-induced (cataract or lens dislocation)

  Because the list of potential underlying causes is so diverse, additional diagnostic testing including a complete history, vaccination status, complete blood count, serum biochemical profile, urinalysis and specific testing for the infectious diseases is performed.

• Herpetic Keratitis

  Feline herpesvirus-1 (FHV-1) is a major cause of conjunctivitis and corneal ulceration in both kittens and adult cats. Infection with FHV-1 is common, and the virus is widespread among cat populations. Primary (or first exposure) to FHV-1 can result in fever, sneezing, coughing, upper respiratory conditions, nasal discharge and conjunctivitis. The virus is spread from cat to cat either by direct contact or by aerosolization of the virus. Vaccination against FHV-1 provides temporary immunity. Once cats become infected, they become carriers.

  The virus becomes latent (inactive) within nerves that supply the eye. Stressful events such as illness, surgery, environmental changes, pregnancy and lactation, vaccination and administration of steroid medications may occur before an outbreak; however, in other cats, no apparent stressor can be identified as a trigger. Establishing an accurate diagnosis has been problematic; therefore, diagnosis may be based on clinical signs and response to treatment.

  Treatment should include topical antiviral medications. Cidofovir has been recently studied and has been shown to be highly effective at reducing FHV-1 replication. Systemic antiviral medications include Lysine and topical antibiotic if ulcerated.

Equine Diseases

• ERU (Equine Recurrent Uveitis)

  ERU is synonymous with “moon blindness.” This equine recurrent uveitis can affect any age, type, or sex of horse (though Appaloosa horses are predisposed) and is a potential cause of blindness in affected animals. Both eyes can be affected, although not necessarily at the same time.

• Fungal Keratitis

  Fungi are normal inhabitants of the equine eye, but they can become problematic following a corneal injury. Exposure to hay, grasses, shavings, straw, and dust in the environment may influence exposure to fungi, and horses may be more susceptible because of their large, prominent eye. Fungal ulcerations in horses are a serious, sight-threatening disease. Diagnosis is made on the basis of visualizing the fungal hyphae during cytologic examination, culture of the organism, or histoapthology. Treatment is directed against the fungi as well as against the corneal and intraocular inflammatory responses that occur following fungal replication and death. Combined medical and surgical therapy is generally indicated.

• Squamous Cell Carcinoma

  Squamous cell carcinoma is the most common tumor of the eye and surrounding tissues in horses. The cause may be related to ultraviolet (UV) exposure, lack of pigment on the eyelids or tissues surrounding the eye, and increased susceptibility to cancer development. The occurrence rate increases with age. Many areas, including the eyelids, third eyelid, conjunctiva, and limbus (where the white sclera meets the clear cornea), are commonly affected. Definitive diagnosis is made based on obtaining a small piece of affected tissue and submitting the tissue for histopathologic examination.

  Treatment depends on tumor location, size, extent of invasion, vision status, the horse’s purpose, and available equipment. If left untreated, it can spread to local tissues, the brain, regional lymph nodes, salivary gland, and the lungs. Surgery alone does not provide a cure. Additional therapy (radiation therapy, cryotherapy, hyperthermia or chemotherapy) is also required.

Systemic Diseases Affecting the Eye

• Diabetes

  Diabetes is a dysregulation of blood glucose that has been increasingly seen in dogs as well as humans.  Aside from the primary effects of diabetes on a patient, diabetes can create a variety of secondary conditions in other organ systems in the body, including the eyes.  The most common ophthalmic problem associated with diabetes in dogs are diabetic cataracts.  The majority of diabetic dogs develop cataracts and vision loss within a year of being diagnosed.  (While felines can get diabetes, their metabolic processes are different than canines, so they do not develop diabetic cataracts.)   Diabetic cataracts can develop slowly over months or rapidly overnight. If left untreated, they can lead to inflammation inside the eye (lens-induced uveitis) or glaucoma, which is both painful and can cause permanent vision loss. Once a diabetic dog’s eyes are in this condition, surgery to remove the cataracts may not be possible. However, diabetic dogs also tend to have a better success rate following cataract surgery than “normal” dogs with cataracts. Early surgical intervention to prevent complications and restore vision is often recommended following diagnostic testing.  Diabetic patients are also at a higher risk of  keratoconjunctivitis sicca (dry eye) and reduced corneal sensitivity, both of which can lead to painful ulceration.  Diabetic patients should routinely have their eyes examined for any changes.

• Systemic Hypertension

  Systemic hypertension (elevated blood pressure) is a common abnormality in humans and is being recognized more frequently in pets. Hypertension can cause acute blindness as a result of hemorrhage and detachment of the retina (the nerve layer at the back of the eye that senses light). Retinal detachment occurs because of bleeding between the layers of the retina. This can be commonly seen in older cats. Hypertension may occur as a primary disease or may result from other systemic diseases such as renal disease or metabolic diseases. Early diagnosis and treatment is important for restoration and maintenance of vision.

• Systemic Neoplasia

  Certain systemic neoplasms (cancers) can have ocular manifestations. Lymphosarcoma (lymphoma) is the most common secondary neoplasia in dogs and may result in uveitis (intraocular inflammation), retinal hemorrhages, and eyelid diseases.

• Blastomycosis

  Blastomycosis is a systemic fungal infection caused by the organism Blastomyces dermatitidis. This fungus can be found in various river valleys in the United States and is commonly found here in middle Tennessee. Blastomyces is inhaled into the lungs, but up to half of dogs infected can have ocular symptoms as their only sign of infection. Retinal detachment, secondary glaucoma, and vision loss can occur with Blastomyces infection. Blastomycosis is treatable with oral antifungal medications and can be diagnosed with urine or blood tests.

• Rickettsial Infections

  Rickettsial infections are transmitted by ticks. They can cause inflammation and/or bleeding in the eyes. Retinal bleeding, retinal detachments, and optic neuritis, all of which can cause vision loss, can also be the result of rickettsial infections. The rickettsial titers commonly tested for include Ehrlichia canis, Rickettsia rickettsia (causative agent of Rocky Mountain Spotted Fever), and Borrelia burgdorferi (causative agent of Lyme disease). In addition to ocular disease, rickettsial infections can cause low platelet counts and bleeding in other areas of the body.