F220
Eye Diseases and Problems


anatomy and terms | eyelids | entropion | ectropion | glaucoma | conjunctivitis | abrasions, lacerations | ulcerative keratitis | pinkeye | cataract | uveitis | eye medications


Introduction: It is important to examine an animalís eyes on a routine basis. Repeated examination allows one to become familiar with the normal appearance of the eye, so any abnormalities will be noticed immediately. Signs of an eye problem vary tremendously and may include cloudiness, tearing, squinting, discharge, redness, blinking, swelling, an increase in blood vessels, or changes in the size or shape of the pupil. Some animals may rub the eye in an attempt to relieve irritation and itching. Any change in the eye or surrounding tissue may signal a problem and should be a cause for concern.

Many different problems can result in the same set of disease signs, so diagnosis cannot be made by clinical signs alone. Physical examination and special tests are needed to properly identify the cause of most problems. Tests may include a fluorescein dye test, a Schirmer tear test (testing for tear production), tests to measure pressure within the eyeball, and ocular examination with different types of lenses. The eye may be dilated to allow for proper visualization of the back of the eye.

Eye problems should be brought to the attention of a veterinarian immediately. Prompt diagnosis and treatment can prevent further eye problems that can lead to loss of sight. In addition, changes in the eyes may be a sign of whole body disease. By immediately identifying and reporting any changes, diseases can be diagnosed early and treatment can begin.

Although all eye problems should be reported to a veterinarian, it is important for the sheep or goat owner to identify and recognize common eye ailments. The eye is composed of several parts, all of which can be injured or become diseased. Eye problems and diseases can affect one portion of the eye or simultaneously be found in several areas of the eye.

Basic Anatomy and Terms: The eye is protected by upper and lower lids, as well as a third eyelid, called the nictitating membrane. Glands which produce tears are located under the lids. The front portion of the eye itself is covered with a thin, clear covering called the cornea. The remainder of the eye is covered with dense white tissue, the sclera. The margin of the cornea and the sclera is called the limbus. The episclera is the outside surface of the sclera. The conjunctiva is the tissue which reflects from the inside of the eyelids onto the globe. Glands which produce tears are also located in the conjunctiva.

The iris is the colored portion of the eye; the black open space in the iris is the pupil. Behind the pupil is the lens. The lens is attached to the ciliary body. The back of the eye is covered with a layer of tissue called the retina. The inside of the globe is filled with a clear fluid called aqueous humor. This fluid is produced by the ciliary body and nourishes the eye while helping to maintain its shape. This fluid is continually produced and drained from the eye. Drainage occurs at the iridocorneal angle, also called the drainage or filtration angle.

Glossary of Eye Terms:

  1. Anterior chamber - The space in the eye bounded in front by the cornea and behind by the iris. It is filled with aqueous humor.
  2. Anterior uvea - The front portion of the uvea, made up of the iris and ciliary body.
  3. Anterior uveitis - Inflammation of the iris and ciliary body.
  4. Anti-inflammatory - A medication that reduces inflammation.
  5. Aqueous humor - The clear, watery fluid which fills the eye.
  6. Blepharitis - Inflammation of the eyelids.
  7. Blepharospasm - Spasm of the muscles that control the eyelids.
  8. Cataract - An opacity of the lens or its capsule, or both.
  9. Choroid - The part of the vascular layer of the eye (uvea) located at the back of the eye. It helps to nourish the retina. It is the posterior uvea.
  10. Ciliary body - The part of the vascular layer of the eye (uvea) located between the iris and the choroid.
  11. Conjunctiva - The mucous membrane lining the back of the eyelids and the front of the eye, except for the cornea.
  12. Conjunctivitis - Inflammation of the conjunctiva.
  13. Cornea - The transparent portion of the outer layer of the eye, which allows light to enter the eye. It attaches to the sclera.
  14. Corneal ulceration - An open lesion or sore on the surface of the cornea.
  15. Enucleation - Removal of the eye.
  16. Epiphora - The abnormal flow of tears over the face.
  17. Fibrous - Composed of cells that form tough, connective tissue.
  18. Fluorescein dye - A special dye that is applied to the cornea that will not penetrate intact cornea or conjunctiva, but will adhere to and outline areas of ulceration.
  19. Glaucoma - Increased ocular pressure resulting from altered flow of aqueous humor.
  20. Globe - The eyeball.
  21. Intraocular - Within the eyeball.
  22. Iris - The colored, circular portion of the eye located behind the cornea. It is part of the uvea.
  23. Keratitis - Inflammation of the cornea.
  24. Keratoconjunctivitis - Inflammation of the cornea and conjunctiva.
  25. Lacrimal apparatus - The structures in the eye responsible for tear production.
  26. Lens - A transparent structure suspended in the front portion of the eye. It refracts light that passes through the cornea on its way to the retina.
  27. Lens luxation - Displacement of the lens.
  28. Miosis - Contraction of the pupil so that the pupil becomes small.
  29. Miotic - A medication that causes the pupil to become small.
  30. Mucoid - This is a general term for types of secretions that are made up of mucous materials.
  31. Mucopurulent - A secretion or exudate that is made up of pus and mucous.
  32. Mydriatic - A medication that causes the pupil to become large.
  33. Mydriasis - A dilated pupil.
  34. Nasolacrimal - The system of the eye responsible for proper drainage of tears out of the eye and into the inside of the nose.
  35. Nictitans (nictitating membrane) - The third eyelid.
  36. Ophthalmoscope - A device for studying the interior of the eyeball.
  37. Optic nerve - The nerve that originates from the retina and carries light signals to the brain.
  38. Posterior uvea - The portion of the uvea made up of the choroid.
  39. Posterior uveitis - Inflammation of the choroid.
  40. Pupil - The circular opening in the center of the iris through which light passes into the eye.
  41. Primary - The first, or foremost. Used in this case to describe problems that occur first and may be followed by other, secondary problems.
  42. Proptosis - Prolapse of the eye.
  43. Retina - The innermost coat of the eye, formed of cells sensitive to light.
  44. Retinal degeneration - A progressive, pathological change that interferes with the function of the retina.
  45. Schirmer tear test - A method of measuring tear production using small strips of absorbent paper placed into the lower corner of the eye.
  46. Sclera - A layer of dense connective tissue that supports the eye. It is the white portion of the eye that connects to the cornea. The cornea and sclera make up the fibrous tunic of the eye.
  47. Secondary - A problem or disease which occurs after the first or primary disease or problem.
  48. Tonometry - The measurement of intraocular pressure.
  49. Topical - Medication that is applied locally on an external portion of the eye.
  50. Uvea - The portion of the eye which contains many blood vessels. It is comprised of the iris, ciliary body, and choroid. It is called the vascular tunic.
  51. Uveitis - Inflammation of the uvea.

 

Figure #1: Vertical cross-section of the eye  .
  1. Anterior chamber
  2. Cornea
  3. Suspensory ligament
  4. Ciliary body
  5. Sclera
  6. Choroid
  7. Vitreous chamber
  8. Optic disc
  9. Retina
  10. Lacrimal gland
  11. Eyelid
  12. Pupil
  13. Iris
  14. Lens


Copyrighted graphic used by permission from Anatomy of Domestic Animals, Sudz Publishing (email: sudzpub@mac.com)

 

Eyelids

Introduction: Sheep and goats have three eyelids. The upper and lower lids help to protect the eye from the environment, distribute tears over the entire eye surface, and control the amount of light that enters the eye. The third eyelid is located in the inner corner of the eye and sweeps across the eye as it closes. It functions to protect and lubricate the eye. It has its own set of tear glands that produce lubricating tears for the entire eye.

Problems with the lids can result in pain, swelling, redness, excessive tearing, and drainage from the eye. Animals with lid pain may attempt to rub their eyes, squint, and show other signs of pain. Problems with the lids can lead to additional problems with closely associated structures such as the cornea, conjunctiva, and nasolacrimal drainage system of the eye.

  1. Entropion: This is a condition of the lids characterized by an inward turning of the lids. The inward turning is called inversion. The turned-in lids can result in irritation and abrasion of the cornea caused by contact with either the eyelid itself or hairs on the eyelid. This can lead to corneal ulceration, which will interfere with vision. Severe, untreated entropion can lead to perforation of the cornea. The condition can be seen in any animal, but is most often seen in lambs in the first days to weeks of life. Additional details about entropion can be found on page C202 of this manual.
     
  2. Ectropion: This is a rolling out of the eyelids. The outward turning, which is called eversion, results in exposure of the conjunctiva. Exposure of the conjunctiva can result in inflammation and disease of the conjunctiva and cornea. Chronic changes in the cornea caused by ectropion can lead to loss of vision. This problem is relatively rare in sheep and goats.

    Signs of ectropion include the visible outward rolling of the eyelid with exposure of the conjunctiva. Associated conditions include drainage from the eye, recurrent infections of the eye, and irritation and inflammation of the conjunctiva. Drainage may be mucoid (looks like mucus) or mucopurulent (looks like mucus and pus) and is accompanied by staining of the face.

    Treatment includes applying lubricants and protectants to the eye and conjunctiva and treating infections with appropriate antibiotics. Daily cleaning of the eyes and face are part of this therapy. If conservative therapy does not control the irritation and infection, definitive therapy includes corrective surgery to reduce or lift the eyelid.
     
  3. Blepharitis: Blepharitis is inflammation of the eyelids. It can be caused by any condition that results in inflammation. In sheep and goats, the most common causes of blepharitis are viral, bacterial, or fungal infections. Conditions such as trauma, parasites, and neoplasia can also cause blepharitis. Parasitic diseases that potentially cause blepharitis include Psoroptes, Psorergates, and Chorioptes mites infestations. Elaeophoriasis (sorehead) caused by Elaeophora schneideri can also cause problems. Blepharitis may occur alone, but is often accompanied by inflammation and infection of surrounding tissues leading to conjunctivitis and keratitis.

    All animals can suffer from blepharitis. It may involve one or more lids, and be localized to one spot or involve large areas of the involved lids. Signs may include eyelid spasm, squinting, pain, ocular discharge, discoloration of the lids, hair loss surrounding the lids, redness, crusting, abscesses, pustules, and swelling. There may be concurrent irritation and scarring of the cornea, and redness and swelling of the conjunctiva.

    Diagnosis is based on physical examination and specialized tests. Cultures and sensitivities, cytology, skin scrapings, and biopsies may be performed to help in the diagnosis. Underlying conditions such as fungal infections, parasitic skin infections, and bacterial skin infections must be diagnosed and eliminated. Once a diagnosis is reached, treatment is designed to eliminate the underlying cause and remove the inflammation from the eyelid. Treatment may involve medications such as antibiotics, antifungals, and anti-inflammatories, along with topical medications that are instilled into the eye and on the lids. Topical therapies may include appropriate antibiotics, corticosteroids, and combination antibiotic/anti-inflammatory medications.
     
  4. Tumors of the Eyelid: Growths can occur on the eyelids. Many of the masses and growths that occur on the eyelids are benign. Those that are malignant tend to invade immediate tissues, but do not typically spread (metastasize) to other places. Common growths include squamous cell carcinomas, fibromas, fibrosarcomas, and melanomas. Papilloma virus infection can cause warts on the eyelids.

    Animals with eyelid masses will show various signs depending on the location of the mass. Blepharitis is common. If the mass contacts the conjunctiva, irritation and conjunctivitis will result, leading to signs that include epiphora, ocular discharge, and squinting. If the mass contacts the cornea, corneal irritation and infection may result. This may cause squinting, epiphora, photosensitivity, and other signs of keratitis.

    Diagnosis is based upon physical examination. Treatment involves removal of the mass by appropriate surgical techniques, which will vary depending on the size and location of the mass. Reconstructive eyelid surgery may be needed. Prognosis is typically good, but depends on the size and type of the mass. Completely removing a benign a mass will usually cure the problem. If removal is not complete, many masses will return. Most malignant masses are also controlled by surgical removal.

     

Nasolacrimal Duct System and Lacrimal System

Introduction: The lacrimal and nasolacrimal duct system function together to ensure that the eye is continuously bathed in protective tears and that the tears are removed from the eye. The lacrimal system is responsible for the production of tears. Glands in the eye produce tears that act to lubricate the eye and cornea, protect the eye from environmental debris, supply nutrients to the eye, and wash away irritants. Both the lacrimal glands and the gland of the third eyelid contribute to tear production. After the tears protect and bath the eye, they are drained via the nasolacrimal system. This duct system is responsible for drainage of tears from the inner corner of the eye into the inside of the nose. Health of the cornea and conjunctiva depends on the continuous production of tears and their uninterrupted removal from the eye.

If there is a problem with any part of the system, drainage of tears from the eye may be impeded. If the tears do not drain into the duct system, they will spill over onto the face, creating a condition called epiphora. Signs include wet facial hair and skin.

Problems Associated with the Nasolacrimal System

Obstruction of the Puncta or Ducts: One of the most common causes of nasolacrimal duct problems in sheep is caused by nasal bot larvae. Nasal bot larvae normally reside in the sinuses of the sheep. Occasionally, one of these larvae will migrate up the nasolacrimal duct and cause a blockage. Animals with a blockage of the duct will have tears that spill over onto the face (epiphora) and they may experience conjunctivitis. General nasal bot infections cause the animal to sneeze and have a nasal discharge. Treatment for this problem includes removal of the bot larvae from the duct, along with flushing of the duct. Oral ivermectin is also necessary.

Other causes of obstructions may include inflammation that closes down any part of the duct system. This obstruction can be caused by conjunctivitis or by physical irritants such as sand, plant stems, and other foreign objects. Diagnosis is based on ocular examination and appropriate testing. Treatment would include antibiotic and anti-inflammatory medical therapy, removal of any foreign objects, and flushing of the duct system.

 

Problems with the Eye and Associated Structures:

Globe or Eyeball

  1. Glaucoma: Glaucoma is defined as an abnormal increase in pressure inside the eyeball (intraocular). It is caused by impairment to the drainage of aqueous humor. Aqueous humor, the fluid that nourishes the eye, is continually produced and drained from the eye. It is drained at an area called the iridocorneal or filtration angle. This area is bounded in the front at the location where the cornea meets the sclera and behind at the location where the lens meets the musculature of the ciliary body. If this area is blocked, drainage is impeded. If drainage is impeded, fluid and pressure build in the eye, damaging internal structures. Damage to the retina and optic nerve can result in permanent loss of vision.

    Most glaucoma cases in sheep and goats occur secondarily to other diseases that cause inflammation. Conditions such as corneal ulcers, keratoconjunctivitis, eye trauma, luxation of the lens, and neoplasia can all lead to glaucoma. The condition may be acute or chronic. Acute glaucoma has a rapid onset. The rapid increase in intraocular pressure results in an extremely painful eye. The pain can cause eyelid spasm and epiphora.

    Diagnosis is based upon examination of the eye and measurement of the pressure in the globe. Upon examination, the glaucomatous eye may have cloudiness, corneal edema, redness, and engorgement of the blood vessels in the episclera. The pupil may be dilated and unmovable. The globe may be enlarged and firm to the touch. Accompanying problems such as uveitis, a luxated lens, or neoplasia may be noted. Specific eye examination may show a closure of the normal drainage area of the eye. The blood vessels in the retina may be compressed by the increase in pressure. Measurement of the intraocular pressure will show it to be elevated. Definitive diagnosis is based on measurement of an elevated intraocular pressure. Acute glaucoma can rapidly lead to blindness in as little as 24-48 hours.

    Treatment of acute glaucoma is considered an emergency. Rapid treatment may prevent permanent blindness. If the glaucoma is secondary to an underlying cause, treatment of the primary cause may result in resolution of the glaucoma. Medical treatment may include diuretics, such as mannitol, and topical medications to reduce aqueous production. If medications are insufficient to lower the intraocular pressure, surgical treatment is needed. Surgery may be performed to reduce the production of aqueous humor and to create drainage. Laser treatment may be used. A combination of medical and surgical therapies may be needed for long-term control of the problem. It is important to note that if only one eye is involved, both eyes should be medicated. If treatment is not successful and blindness results, removal of the eye may be recommended to eliminate any pain.

    Chronic glaucoma
    occurs if the signs of acute glaucoma go unnoticed, or if acute glaucoma therapy is not effective. The signs may include all of those noticed with acute glaucoma, although to a lesser degree. The most obvious sign is the enlarged globe. In addition, corneal ulceration, lens luxation, cataracts, and keratitis may occur. Ocular examination will show degeneration of the retina and the head of the optic nerve. The animal is typically blind in the affected eye. Diagnosis is based on the physical and ocular examination.

    Treatment is aimed at reducing the pain of chronic glaucoma. The blindness is not reversible. The medical and surgical treatments described for the control of acute glaucoma may be used. Removal of the eye may be needed to control pain. If only one eye is affected, the normal eye should be examined and monitored for any signs of glaucoma. Preventative (prophylactic) treatment of the unaffected eye should be started if indicated by ocular examination.

    Prognosis for treatment of glaucoma depends on the underlying cause and the time between onset of disease and treatment. Treatment to maintain or restore vision will be unsuccessful in acute glaucoma cases unless initiated within hours of onset. Chronic glaucoma patients may be blind before treatment begins. Secondary glaucoma cases can resolve following successful treatment of the primary cause.
     
  2. Exopthalmos - The term exopthalmos refers to a condition where the eye is pushed out away from the face in an abnormal fashion. This condition can be caused by abscesses that from behind the eye or cancerous tumors (lymphoma and squamous cell carcinoma) that physically force the eyeball outward. Treatment for this condition may involve removing the eye and as much of the tumor as possible. Abscesses should be lanced and drained.
     
  3. Cyclopia - Cyclopia is a developmental defect that occurs in lambs where the head only has one orbit or eye socket. The eye itself may or may not be present. This condition is associated with ewes consuming the toxic plant Veratrum californicum (skunk cabbage, false hellebore) on the 14th day of gestation. In addition to the cyclopia, these lambs often have abnormally shaped heads and faces.

     

Conjunctiva

Introduction: The conjunctiva is the membrane that lines the inside of the eyelids and the third eyelid, and covers the outside of the sclera. The conjunctiva is a mucous membrane with an excellent blood supply. It connects the lids to the globe and contains specialized glands. These glands produce the inner layer of the tear film.

Problems affecting the conjunctiva may be limited to only the conjunctiva or may involve other portions of the eye. Conjunctival inflammation or disease may also signal illness that affects the entire body. It is important to recognize whether disease processes are limited to the conjunctiva, extend to other parts of the eye, or signal whole body (systemic) disease.

  1. Conjunctivitis: Inflammation of the conjunctiva is termed conjunctivitis. Any animal can suffer from conjunctivitis. Conjunctivitis may be primary or secondary to other problems. Primary conjunctivitis can be caused by trauma (feeding coarse forage in a deep manger or over-head feeder), foreign objects in the conjunctiva, or environmental irritants (wind, dust, chemicals). Bacterial infections commonly cause conjunctivitis in sheep and goats. Bacterial organisms such as Branhamella ovis, Mycoplasma, Chlamydia psittaci, and Listeria monocytogenes can cause the infection and conjunctivitis. Problems in the eye can also be caused by eye worms (Thelazia rhodesii). These eye worms are spread by face flies and other flies of the Musca family when they feed on eye secretions. On rare occasions, conjunctivitis can also be caused by viral and fungal infections of the eye. Conjunctivitis can also be secondary to other eye problems such lid malformations or nasolacrimal diseases. Other cases of conjunctivitis occur following glaucoma, cancer, uveitis, or corneal inflammation.

    Signs of conjunctivitis may include spasm of the eyelids, swelling and redness of the conjunctiva, and discharge from the eyes. The discharge may be clear, mucoid, or mucopurulent. Animals with conjunctivitis may be sensitive to and avoid the light (photophobia). They may respond to the conjunctival irritation by rubbing the face and eyes.

    Conjunctivitis is diagnosed on physical examination. Additional specific tests are performed to identify other eye problems and to rule out other eye diseases that can lead to conjunctivitis. These include a Schirmer tear test, fluorescein dye, intraocular pressure test, bacterial culture and sensitivity, and if indicated, conjunctival cytology. Steps are taken to identify any underlying or accompanying disease situations that contribute to the conjunctival inflammation.

    Treatment involves both medicating the conjunctiva and treating any underlying or secondary problems. Depending on the cause of the conjunctivitis, treatment may include topical medications to control inflammation and infection, eye washes to remove discharge, lubricants to add moisture to the eye, and systemic medications to control infection and inflammation. Topical therapy may include antibiotic agents, corticosteroids, or combination medications. All discharge should be flushed from the eye before treatment is attempted to allow the medications to contact the surface of the eye and the conjunctiva.

    Most bacterial infections in sheep and goats can be treated with topical tetracycline and long-acting injectable products given in the muscle. Because of their ability to remain in the eye, ointments are the preferred topical treatments. The ointment should be applied to the eye 3-4 times a day until the conjunctivitis is corrected. If eye worms are suspected as the cause for the problem, the worms can often be removed with forceps after topical anesthesia has been applied to the eye. In cattle, reports indicate that systemic ivermectin and levamisole are effective at controlling eye worms. Fly repellants and sprays are also important in the prevention of eye worms.

    Prognosis depends on the underlying cause and severity of the condition. Simple bacterial conjunctivitis is typically very responsive to treatment with the appropriate antibacterial medications. Secondary conjunctivitis may not respond until the underlying cause is identified and treated. Some secondary conjunctivitis problems may be controlled, but not totally eliminated.

     

Cornea

Introduction: The cornea is the outer, transparent layer of the front of the eye. It protects the eye while still allowing light to pass through. The cornea is protected by a layer of tears and by continuously replacing its superficial cells. It lacks blood vessels (which helps make it transparent), and so does not heal easily. Any disease process or insult to the cornea can result in cloudiness, swelling, or pigmentation, which in turn may lead to loss of vision. Corneal irritation or inflammation is extremely painful. It is critical to treat any corneal problem as rapidly as possible.

  1. Abrasions, Lacerations: Any animal can suffer from a traumatic corneal abrasion, scratch, or laceration. Mild injuries can result in a superficial abrasion. Deeper wounds are identified as penetrating or perforating. A penetrating laceration involves the cornea, but does not pass through it. A perforation goes entirely through the cornea. If wounds are caused by a penetrating or perforating object, the object may still be in the cornea. Wounds can be caused by any object that can contact the eye. The same things that can cause conjunctivitis (feeding on coarse hays, bacterial infections, etc.) can also lead to corneal lesions.

    Signs of a corneal wound include pain and inflammation of the eye. The eyelids may be kept closed and the animal may resist examination. The wound may be visible on the cornea, along with swelling, cloudiness, and hemorrhage. Diagnosis is made by history and physical examination. An immediate diagnosis can be made if the object that caused the wound is still in the eye. Additional testing is done to determine the severity and extent of the wound, assess vision, and identify trauma to other portions of the eye and face. Bacterial culture and sensitivity may be necessary. A specific test called a fluorescein dye test is performed using special stain to ascertain if the cornea is intact or if it has been perforated.
     
    Figure #2: The arrows identify a corneal abrasion that has caused anterior uveitis in this sheep eye.

    Treatment depends on the severity, depth, and age of the wound. Care should be taken to apply only minimal pressure to the face and eye to prevent rupture of the eyeball. Any foreign body should be flushed out, removed with a dampened cotton-tipped applicator, removed with forceps, or surgically removed from the eye. Superficial wounds can be treated with topical medications to prevent infections and calm the eye. Topical eye medications include antibiotics and atropine.

    Extensive corneal lacerations and corneal penetrations require surgical repair. Surgical repair will also be needed for those injuries that contain a foreign body that is not easily removed. All corneal wounds should be rechecked at specific intervals to monitor healing. Superficial wounds can be checked at 3 day intervals; deep wounds should be checked daily for the first several days.

    Prognosis depends on the extent of the wound and the time elapsed between injury and veterinary treatment. The deeper the wound, the poorer the prognosis. Most superficial corneal abrasions and wounds heal quickly and satisfactorily. Deeper wounds or those created by blunt trauma may result in permanent loss of vision, inflammation, and pain. The full extent of the damage caused by the wound may not be apparent for days to weeks following the injury, so re-examination is necessary.
     

  2. Keratitis: Keratitis refers to inflammation of the cornea. Signs may include swelling (edema), cloudiness, and pigmentation.

    Ulcerative Keratitis: This refers to inflammation of the cornea accompanied by ulceration of the surface of the cornea (a corneal ulcer). This is a very common condition in all animals.

    Ulcerative keratitis can be caused by any condition that disrupts the layers of the cornea, including trauma, entropion, ectropion, trichiasis, keratoconjunctivitis, damage to the nerves of the face, and burns caused by chemicals and cleaners. Infection by bacterial or fungal organisms may occur secondary to other irritations and injuries.

    Ulcerative keratitis is a very painful condition. Signs of disease include tearing (lacrimation), spasms of the lids, squinting, spilling of tears onto the face (epiphora), avoidance of sunlight (photophobia), redness, and discharge from the eye. One or more defects in the cornea may be visible and are referred to as corneal ulcers. Some ulcerative keratitis cases have a mushy, gelatinous appearance as the cornea breaks down due to excessive enzyme production; this is sometimes called a "melting" ulcer. Chronic ulcers may show vascularization, scarring, pigmentation, and swelling. Healing ulcers may have a hazy, white appearance. Fluorescein dye testing helps to determine the depth, severity, and number of ulcers.
     
    Figure #3: A Pseudomonas infection has caused an ulcer to form in the corner of this eye.

    Diagnosis is based on ocular examination and fluorescein dye testing. If needed, specific examination of the interior of the eye and cytology can also aid in the diagnosis. Other tests, such as a Schirmer tear test, are performed to rule out additional or contributory eye diseases.

    Treatment involves elimination of the cause, along with specific treatment for the ulceration and inflammation. Underlying eye problems, such as keratoconjunctivitis, entropion, or ectropion, should be treated appropriately. Treatment of the ulcer may include topical antibiotics to prevent infection, topical atropine to control pain, specific medications to control fungal or viral infections, and if indicated, specific medications to prevent collagen breakdown. Animals may be placed on systemic non-steroidal anti-inflammatory (NSAIDs) medications such as aspirin or banamine.

    Some ulcers are treated with protective contact lenses. Others may require surgery to trim (debride) the ulcer edges. Additional surgical procedures include punctuate keratotomy, conjunctival flaps, and flaps created from the nictitans. Eyes should be rechecked at approximately 3-day intervals; those with deep ulcers should be rechecked daily until satisfactory healing is observed.

    The prognosis for ulcerative keratitis depends on the underlying cause, the severity of the ulceration, the type of treatment employed, and response to therapy. Simple, superficial ulcers often heal nicely in approximately 1-2 weeks. Deeper ulcers treated with surgical techniques may require 4-6 weeks to heal; those treated without surgery may take longer, or never heal satisfactorily. Refractory ulcers may remain unhealed for months unless treated with surgical techniques. After surgery, healing may occur in 2 weeks, and conjunctival flaps may be left in place for a month or longer. Untreated or incorrectly treated corneal ulcers can progress, resulting in rupture of the cornea and loss of vision. This often results in removal of the globe.
     

  3. Infectious Keratoconjunctivitis (pinkeye): The term keratoconjunctivitis refers to inflammation of the cornea and conjunctiva. A very common problem found in sheep and goats is a condition often referred to as pinkeye. Pinkeye is usually a bacterial infection that leads to keratoconjunctivitis. Pinkeye is not the only cause of keratoconjunctivitis in ruminants. Additional causes of keratoconjunctivitis in ruminants include Branhamella ovis, Listeria monocytogenes, and infectious bovine rhinotracheitis (IBR) in goats. For additional information on pinkeye, refer to page F635 of this manual.
Figure #4: This is an example of keratoconjunctivitis (pinkeye) in a sheep.

 

Lens

Introduction: The lens focuses light waves that come through the pupil. It is held in place by small suspensory ligaments called lens zonules that attach the lens to the ciliary body. The ciliary body can contract and relax, thereby changing the shape of the lens. The changing shape of the lens allows it to properly focus light waves from different distances onto the retina.

Cataract: Cataracts are the most common lens problem in sheep and goats. Cataracts refer to either opacities within a lens or an entire lens that is opaque. The term cataract means "to break down," referring to the loss of normal architecture of the fibers in the lens or its capsule, resulting in an increase of fluid in the lens and loss of transparency. Cataracts are hereditary in many breeds of sheep and goats, and are often present at birth.

Although most cataracts are hereditary, other factors can contribute to the formation of cataracts. These can include metabolic diseases, trauma to the globe, exposure to toxins, and inflammatory diseases such as uveitis. Diagnosis is made by examination of the eyes. Cataracts can be classified by location in the lens and degree of development. Examination of the retina should accompany any examination for cataracts.

Treatment is reserved for cataracts that cause blindness. There is no effective medical therapy. Treatment involves surgical removal of the lens. Because of the complicated and expensive nature of this surgery, it is not commonly done in large animals. Although several techniques can be used, phacoemulsification is commonly used today. This technique involves the use of a small ultrasonic probe that is placed into the eye. It shatters the cataract and then removes the broken-down debris by suction.

 

Uvea

Introduction: The uvea is a very vascular structure that is critical for the maintenance of a healthy eye. It is a pigmented, vascular tunic that sits between the outer fibrous layer of the eye (cornea and sclera) and the inner nervous layer (retina). It is comprised of 3 connected portions - the iris, the ciliary body, and the choroid. The anterior uvea is made up of the iris and the ciliary body. The posterior uvea, located towards the back of the eye, is comprised of the choroid. The iris controls the amount of light that enters the eye. The ciliary body controls the focus of the lens, produces aqueous humor, and helps regulate intraocular pressure. The anterior uvea acts as a blood-aqueous barrier and prevents unwanted particles from the bloodstream from entering the aqueous humor. The choroid provides nourishment to the retina, and most diseases of the choroid are linked to disease of the retina.

Because the uvea is highly vascular, it is very reactive to changes in the body and is easily inflamed. Inflammation of the uvea is called uveitis. Specifically, inflammation of the iris and ciliary body is termed anterior uveitis. Posterior uveitis refers to inflammation of the choroid. Inflammation may be limited to only the anterior or posterior uvea, or involve both portions. Inflammation of the uvea allows particles to cross the blood-aqueous barrier and enter the aqueous humor. This causes an inflammatory response in the aqueous which can lead to a reduction or total loss of vision.

Uveitis: Inflammation of the uvea may occur with several disease conditions seen in the eye. The cause may be external to the eye and include trauma. In addition, uveitis may follow corneal injuries and corneal ulceration. Uveitis in sheep and goats is most often caused by infectious agents such as Mycoplasma, Listeria monocytogenes, Chlamydia psittaci, and Toxoplasma gondii. These infections can be limited to the eye or cause disease throughout the body.

Signs of uveitis may include pain, redness of the conjunctiva, corneal edema, red blood cells or white cells in the anterior chamber, epiphora, spasm of the eyelids, and aversion to light. Other ocular changes are specific to anterior uveitis. These include constriction of the pupil, a change in the color of the iris (often darker), swelling of the iris, and enlargement and engorgement of deep blood vessels located in the ciliary body. In addition, inflammatory cells and pigment may clump together and adhere to the cornea, forming small, visible masses called "keratic precipitates." As particles form or flood into the inflamed area, the aqueous humor becomes turbid. This condition is referred to as "aqueous flare." In chronic cases, the iris may actually adhere to the lens, "fixing" the pupil in an unmovable position. This results in a distorted and immobile pupil. Finally, uveitis can be associated with other serious eye problems, including cataracts, ulcerative keratitis, and secondary glaucoma.

Figure #5: This eye has uveitis caused by an abrasion and a Chlamydia infection.

 

Figure #6: This is another example of uveitis.

Diagnosis is based upon complete physical and ocular examination. A thorough eye examination includes measurement of the intraocular pressure. The pressure is typically decreased with uveitis. Additional testing may include blood testing and urinalysis to search for the underlying cause of the disease.

Treatment is aimed at reducing the inflammation of the uvea while determining and eliminating the underlying cause. Anti-inflammatory agents including corticosteroids (1% prednisolone acetate, 0.1% dexamethasone) and non-steroidal anti-inflammatories can be applied topically. Topical medications that dilate the pupil are also used (atropine). In some cases, corticosteroids can be injected under the conjunctiva or administered systemically. Treatment may be altered depending on the cause of the uveitis and the systemic illnesses that are present. Treated animals should be re-examined within one week following the initial treatment and re-evaluated every few weeks.

Prognosis depends on the severity of the uveitis at the time of treatment and the underlying cause of the uveitis. Early, aggressive treatment of the uveitis and the initiating cause is necessary to prevent secondary problems. Prognosis is good if the underlying cause is identified and eliminated, and appropriate eye therapy is instituted. If uveitis is left untreated, glaucoma, lens luxation, and blindness can result. Successful treatment can involve several months of continual medication and follow-up examinations.

 

Retina

Introduction: The retina is the back portion of the eye. It is considered the "film" that records the visual images that come through the cornea and are focused by the lens. The cells of the retina receive the light images. These cells are of two main types, rods and cones. The rods are sensitive to dim light and the cones are sensitive to bright light. The rods are useful at dusk, while the cones perceive images in the day and help distinguish colors.

The rods and cones translate the light images into chemical messages which affect adjacent nerve fibers. The retinal nerve fibers converge together at an area called the optic disc to form the optic nerve. The messages travel as nerve impulses along the optic nerve to the brain where they are again converted into visual images. Any type of damage to the retina will result in interruption of this process and cause loss of vision.

Degeneration of the Retina: If the retina degenerates or atrophies, messages from the eye will no longer reach the brain and blindness will result. Conditions such as trauma, infection, neoplasia, retinal detachment, malnutrition, glaucoma, and inflammation can lead to degeneration of the retina. In many cases, retinal degeneration is a primary condition that is inherited in certain breeds of sheep and goats (South Hampshire sheep and Toggenburg goats).

Infections of Listeria monocytogenes, Toxoplasma gondii, Elaeophora schneideri, scrapie, and the bluetongue virus can all cause inflammation and problems in the retina. Vaccinating ewes with a modified live bluetongue vaccine during the first half of gestation can also cause retinal damage to their lambs. Animals that continually graze bracken fern (causing "bright blindness") or locoweed can develop retina problems. Deficiencies in vitamin A can also cause the retina to degenerate.

No matter the exact cause of retinal degeneration, the signs of retinal degeneration are often the same. In the early stages of retinal disease, the animal may not show many signs. As the retinaís cells degenerate, the animal loses vision. For animals that consume toxic plants such as bracken fern, the loss of vision may not appear until several months after starting to consume the toxic plant on a regular basis. Similarly, animals that are being fed a diet that is deficient in vitamin A will not usually show any signs for at least 3 to 7 months. Affected animals typically lose night vision first ("night blindness"). These animals may have difficulty seeing in poorly lit areas or at night. Eventually, the retinal atrophy will progress, and total blindness will result. An owner may be aware of dilated pupils or a shine from the back of the dilated eye, or may notice nothing until the animal has totally lost vision. Some animals may develop other eye changes, such as cataracts. Many animals will not eat and begin to lose weight and condition.

Diagnosis is based upon ocular examination. Pupils will be dilated and non responsive to light. The retinal area will be hyperreflective and retinal examination will show degeneration of the retina and optic nerve, along with changes in the retinal blood vessels and pigmentation.

In many of these cases, if the animal is completely blind, there is no treatment. Once damage has been done to the retina and surrounding structures, it cannot be reversed. However, for cases of vitamin A deficiency, where the animal only experiences "night blindness," placing the animal on vitamin A supplements and allowing the animal access to plenty of green forage can reverse the problems. Vitamin A can be given as an injection or as an oral supplement. Non-lactating animals should receive 45-50 international units (IU) of vitamin A per kg of body weight per day. Lactating or pregnant animals may require up to 85 IU per kg per day. Animals that are grazing bracken fern or locoweed should be denied access to the plants. This may not reverse any damage already in place, but it will help prevent continued injury. Animals that have a hereditary form of retinal disease should not be used for breeding purposes.



Eye Medications:
Eye medications can be delivered by several methods. Topical medications are applied directly to the eye surface. The topical medications may be available as eye drops and ointments. This method of administration is appropriate for both hospital and home treatment of eye diseases in sheep/goats. In addition, veterinarians may administer medications via injection into the eye. Common sites for these injections are subconjunctival (beneath the conjunctiva), retrobulbar (behind the eye), or intraocular (into the eyeball).

In addition, diseases of the eye may be treated with medications that are given directly to the animal, either by mouth or by injection. Finally, eye diseases may not be limited to the eyes; they may be a sign of disease that is affecting the entire body. In this case, the veterinarian will prescribe medication to treat the primary illness, as well as to control the problems in the eyes.

The following tables list commonly used eye medications. Depending on the combination of related eye problems present at one time, a specific medication may need to be combined with other medications or may be inappropriate for its original, intended use. All eye medications should be used under the guidance of a veterinarian. Page C220 of this manual has information on how to properly clean the eye and administer products.

CLASSIFICATION/USE/INDICATION MEDICATION SPECIFIC USE NOTES CONTRA-INDICATION (IF ANY)
EYE RINSES

USE: Clean, rinse, flush

INDICATIONS: Clear mucus before instilling medications, remove debris from eye

Sterile, buffered isotonic solutions containing sodium chloride, sodium citrate, sodium phosphate    
Combinations of water, boric acid, zinc sulfate    
       
EYE LUBRICANTS

 USE: Lubricate, prevent eye irritation, relieve dryness

INDICATIONS: Whenever general anesthesia is used, keratitis, ectropion

Pilocarpine Irritating, can cause conjunctivitis and worsen uveitis, not commonly used Can affect respiration and cardiac function
Polyvinylpyrrolidone    
Polyvinyl alcohol    
Methylcellulose    
Ethylene glycol polymers    
Refined petrolatum    
Refined lanolin    
Refined peanut oil    
       
MUCOLYTICS

USE: Prevent collagen break-down, break up mucus

INDICATIONS: "Melting" corneal ulcers, chronic conjunctivitis, keratoconjunctivitis

Acetylcysteine   Very expensive
Autologous plasma   Sometimes used in place of acetylcysteine
       
ANESTHETICS

USE: Topical pain relief

INDICATIONS: Minor surgery, eye examination, diagnostic procedures, preoperative evaluation of entropion, removal of foreign bodies

Proparacaine 0.5%   Never use therapeutically. May cause corneal irritation.
Tetracaine HCl 0.5%*  
       
ANTIBIOTICS (SINGLE)

USES: Preparation for an intraocular procedure. 

Treatment of infection (if possible, select specific agent for microbe; if testing is not possible, broad spectrum or combination antibiotic is preferred.) 

Preventive pre and/or post-procedure.

INDICATIONS: Treat susceptible infections contributing to uveitis, conjunctivitis, blepharitis, keratitis. 

Control secondary bacterial infections in conditions such as proptosis of the globe, entropion, ectropion, corneal ulcer, corneal abrasion.

Gentamicin 0.3% solution and 0.3% ointment Susceptible bacteria may include Staphylococcus, Corynebacterium, Pseudomonas, Proteus spp, Escherichia coli, Hemophillis, Enterobacter, Moraxella  
Tetracycline 1% solution and 1% ointment Susceptible bacteria may include Staphylococcus, Corynebacterium spp,, Hemophillis spp, Moraxella, Chlamydia, Mycoplasma spp  
Tobramycin 0.3% solution and 0.3% ointment Susceptible bacteria may include Pseudomonas, Proteus spp, Escherichia coli, Hemophillis, Enterobacter, Moraxella, Staphylococcus  
Bacitracin 500 U/g ointment Susceptible bacteria may include Staphlococcus, Streptococcus, Corynebacterium spp  
Chlortetracycline 1% ointment    
Erythromycin 0.5% ointment    
Neomycin 0.35% ointment Susceptible bacteria may include Staphylococcus, Corynebacterium spp, Hemophillis spp, Moraxella, Enterobacter, Mycoplasma  
       
ANTIBIOTICS (COMBINATION)

USE: Same as single antibiotic 

When more than one type of microbe is present or when testing for specific identification is not possible.

INDICATIONS: Same as single antibiotic

Neomycin sulfate, Polymyxin B sulfate solution and ointments    
Neomycin sulfate, Polymyxin B sulfate, gramacidin solution Preferable drug for broad spectrum coverage without culture/sensitivity  
Neomycin sulfate, Polymyxin B sulfate, Bacitracin ointment Preferable drug for broad spectrum coverage without culture/sensitivity  
Oxytetracycline HCl, Polymyxin B ointment    
       
ANTIINFLAMMATORY - STEROIDAL

USES: All allergic ocular diseases. Nonpyogenic inflammations of any ocular tissue. Reduction of scar tissue. Certain ocular surgeries.

INDICATIONS: Blepharitis, conjunctivitis, proptosis of the globe, uveitis, entropion, chronic superficial keratitis

Prednisolone acetate suspension   Avoid when there is no specific indication for steroid use. 

Contraindicated in the treatment of corneal ulceration, viral infection, & keratomalacia. 

May promote fungal infections. 

Dexamethasone  
Triamcinolone 
(topical and injectable)
 
Betamethasone 
(topical and injectable)
 
Methylprednisolone acetate (injectable)  
       
ANTIBIOTIC/STEROID COMBINATIONS

USES: Control inflammation and bacterial infection, treat acute and chronic inflammatory processes of the eye

INDICATIONS: Acute or chronic conjunctivitis, inflammation of the anterior segment of the eye, blepharitis, conjunctivitis, proptosis of the globe, entropion, uveitis

Neomycin sulfate, Polymyxin B sulfate, Dexamethasone solution and ointment Commonly used Any condition in which corticosteroid use is contraindicated
Neomycin sulfate, Hydrocortisone acetate solution and ointment  
Neomycin sulfate, Zn bacitracin, Polymyxin B sulfate, Hydrocortisone ointment Commonly used
Neomycin sulfate, Polymyxin B sulfate, Hydrocortisone solution  
Neomycin sulfate, Prednisolone solution & ointment  
Neomycin sulfate, Dexamethasone phosphate solution  
Neomycin sulfate, Methylprednisolone ointment  
Gentamicin with Betamethasone Commonly used
       
TOPICAL NON-STEROIDAL ANTI-INFLAMMATORY

USE: Reduce inflammation and pain

INDICATIONS: Uveitis, cataract surgery, panophthalmitis, corneal ulcers

Flurbiprofen   May delay corneal healing
Suprofen  
Diclofenac  
       
MYDRIATICS

USE: Dilation of the pupil (mydriasis), control ciliary spasm and the accompanying pain which causes eyelid spasm, photophobia, and lacrimation

INDICATIONS: Non-surgical treatment axial cataracts.  Preoperative mydriasis for cataract surgery and other ocular surgery, corneal abrasions, corneal ulceration, keratitis, anterior uveitis, possibly proptosis of the globe.

Atropine sulfate Not for routine eye examination May compromise tear production.

May predispose to local irritation.

Contraindicated in glaucoma or in animals predisposed to glaucoma.
Tropicamide Short-acting - used for eye examinations
Phenylephrine HCL Combined with atropine
       
MIOTICS

USE: Cause contraction of the pupil, enhance aqueous outflow

INDICATIONS: Keep luxated lens in posterior chamber, treat glaucoma

Demecarium bromide   Cholinesterase inhibitor, do not use with organophosphate insecticides
Pilocarpine   May irritate the eye
Carbachol   All miotics are contraindicated in glaucoma secondary to anterior uveitis
       
ADRENERGICS

USE: Lower intraocular pressure. Control capillary bleeding during surgery

INDICATIONS: Control/treat glaucoma

Epinephrine Adrenergic agonist/increases outflow of aqueous humor  
Timolol maleate Beta blocker/ Reduces aqueous formation  
       
CARBONIC ANHYDRASE INHIBITORS

USE: Decrease aqueous humor production

INDICATIONS: Control/treat glaucoma

Acetazolamide 
(given orally)
  May cause metabolic acidosis and electrolyte imbalances
Methazolamide 
(given orally)
   
Dichlorphenamide 
(given orally)
  Use with caution in animals with sulfonamide sensitivity
Ethoxzolamide 
(given orally)
   
       

 

Summary: The eye is a complex structure that processes images for transfer to the brain. It is composed of several interrelated structures. A problem that affects any portion of the eye can result in loss of vision. A problem that affects one portion of the eye may also affect adjacent structures. Because different disease processes can cause the same signs in the eye, examination by a veterinarian is necessary for proper diagnosis and treatment. Prompt examination and treatment can prevent severe, progressive disease. Animals should be examined by a veterinarian at the first sign of any eye problem.

* All of the pictures were used with permission from Colorado State University Ophthalmology Service.