0749-0739/92 $0.00 + .20
OPHTHALMOLOGY
OCULAR MANIFESTATIONS OF SYSTEMIC DISEASES J.
D. Lavach, DVM, MS
This article describes some of the ocular findings associated with systemic diseases. Veterinary literature contains very few detailed descriptions of the ocular findings associated with systemic diseases,18 yet most systemic diseases can and do affect the ocular tissues to some extent. Unfortunately, the eyes are not always examined and ocular abnormalities are not detected unless an ophthalmic examination is performed. Ocular findings can provide the examiner with more information about the particular illness and its prognosis. In addition, early recognition and treatment of the ocular components of any systemic disease can minimize ocular damage and might aid in preservation of vision.
NEONATAL ONSET SYSTEMIC DISEASES Neonatal Hypogammaglobulinemia
Foals acquire passive immunity during their first 24 hours of life by absorption of colostral antibodies. Complete or partial failures of passive immune transfer are diagnosed by measuring serum IgG concentrations. Several screening techniques have been used in the diagnosis of equine neonatal hypogammaglobulinemia. 6 Foals low in serum IgG concentration are at greatly increased risk for neonatal septicemic infections and death. 16, 22 Ocular manifestations of septicemic diseases are nonspecific, but include anterior uveitis, hyphema, chorioretinitis, From the Eye Clinic for Animals, Garden Grove, California
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retinal detachments, and blindness from severe intraocular diseases or central nervous system involvement. Neonatal Septicemia
Neonatal foals affected with septicemia often acquire ocular involvement. The inflammatory reaction can be a sterile immunologic consequence, or it can be an infectious process. Panuveitis with vitreous abscess formation occurs in severe infections. The causative agents reported include Streptococcus sp. and Rhodococcus equi, but any bacterium can overwhelm a neonatal foal. 1, 10 One study found gram-negative bacteria in all of 47 foals examined in addition to various gram-positive bacteria and anaerobic bacteria. 33 Predisposing conditions, including stressful environments and delayed colostrum intake, contribute to the foal's susceptibility.lO Bacillus piliformis
Bacillus piliformis infection, Tyzzer's disease, is an acute fatal disease of neonatal foals. Most affected foals are found dead, although depressed and recumbent foals are occasionally encountered. The clinical ophthalmic features of the disease are nonspecific, but positional nystagmus was mentioned in one affected foal just before its death. 14 Intraocular hemorrhages or accumulations of fibrin can be found in foals that go into seizure. Neonatal Maladjustment Syndrome
Neonatal maladjustment syndrome is a complex and poorly understood disorder. Possible causes include cerebral hemorrhage, fetal hypoxia, and cardiopulmonary aberrations. 7 Birth trauma can contribute to this syndrome. It is characterized by gross behavioral disturbances, respiratory distress, convulsions, coma or semicoma, and, occasionally, death. Complete or partial blindness can occur. Specific ocular findings include anisocoria, scleral hemorrhage, papilledema, and retinal hemorrhage. Secondary ocular findings in foals with severe central nervous system disturbances include keratoconjunctivitis, corneal ulcers, and entropion. Entropion is often due to spasm from corneal pain. Immunologic Deficiencies
Immunologic deficiencies occurring in older foals or adult horses can be transient or permanent. 9, 13 Affected horses are predisposed to infectious diseases. The ocular signs are variable but usually consist of
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uveal involvement. Intraocular inflammatory exudates can accumulate, and retinal detachments are common. Keratoconjunctivitis with corneal ulcerations are commonly encountered in recumbent horses. Corneal epithelialization is delayed, and chronic infections with progressive corneal destruction occur in debilitated patients.
Immune-mediated Hemolytic Anemia
Immune-mediated hemolytic anemia and thrombocytopenia were reported in a 2-week-old foa1. 29 The foal developed hyphema and petechial hemorrhages of the conjunctivae and other mucous membranes. Both eyes developed uveitis characterized by corneal edema, clotted blood and fibrin in the anterior chambers, miosis, and swollen irides. Small focal posterior synechiae were transient. Neonatal isoerythrolysis occurs when the dam produces antibodies against the foal's erythrocytes. The antibodies are absorbed with colostrum and clinical signs become apparent 12 to 96 hours after birth. Conjunctival, episcleral, and intraocular hemorrhage can occur. All mucous membranes, including the conjunctivae, become icteric.
ADULT-ONSET SYSTEMIC DISORDERS Systemic Lupus Erythematosus
Systemic lupus erythematosus was described in a 2-year-old Standardbred filly.ll Clinical features included small punctate ulcers at the mucocutaneous junctions of the lips, external nares, and rostral portion of the tongue. The diffuse lesion pattern was typical of what has been reported in other animal species. Specific ocular lesions were not mentioned, but mucocutaneous ulceration along the eyelid margins should alert the veterinarian to consider this disease as a differential diagnosis.
Lymphosarcoma
Malignant lymphoma can affect the eyes and cause blindness. The primary ocular site is the uveal tract, which becomes invaded by neoplastic cells. Affected eyes can have severe anterior uveitis, characterized by corneal edema, diffuse thickening of the irides, and intraocular hemorrhage. The eyes are usually hypotonic, but secondary glaucoma can occur in one or both eyes. The posterior segment is involved less commonly, but neoplastic cells in the choroid, retina, vitreous, and optic nerve have been found. Vitreous hemorrhage and retinal detachments can be consequences of posterior segment disease. Conjunctival
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infiltration can lead to conjunctival exposure and desiccation with conjunctival ulceration. Malignant lymphoma can involve the periocular tissues, causing mass lesions to develop in the orbit, third eyelid, or eyelids. Focal mass lesions can displace the globe in any direction, or the eye can become exophthalmic. The eye can be completely normal and free from invasion by neoplastic cells during orbit involvement. Diagnosis is usually accomplished by aspiration and examination of cytology specimens, or through biopsy of orbit tissues. One affected horse had a monoclonal aggregating immunoglobulin class and cryoglobulinemia associated with lymphoma. 31 Another report described an affected horse with a monoclonal gammopathy and hyperviscosity, but without a cryoglobulin. IS Multiple Myeloma
Multiple myeloma is a fatal neoplastic disorder of plasma cells. It can cause a variety of ocular signs, including episcleral hemorrhage, uveitis, intraocular hemorrhage, retinal detachments, and blindness. 12, 19 Both eyes are affected simultaneously. Streptococcus equi
Streptococcal infections are characterized by systemic illness in young horses. Generalized lymphadenopathy and respiratory tract signs are common. 23 The ocular surfaces are affected with a mild inflammatory reaction. Dacryocystitis can develop secondary to chronic inflammation. Transient keratoconjunctivitis sicca can occur during active septicemic episodes. More severe manifestations affecting the eye and visual system are associated with abscess formation in lymph nodes, lungs, central nervous system, and other organs. 30 Intraocular manifestations include anterior uveitis, panuveitis, chorioretinitis, retinal detachment, vitreous abscess, and optic neuritis. Leptospirosis
Several species and serologic subtypes of leptospira have been implicated as causative agents for equine recurrent uveitis, peripapillary chorioretinitis, and optic neuropathies. 28 The ocular manifestations can be caused directly by the organism entering the ocular tissues, or they can be latent manifestations related to immunologic reactions. See the article by Schwink for more information. Equine Herpesvirus type 1
Equine herpesvirus agents have been classified into type 1 with two subtypes-equine rhinopneumonitis (EHV-4) and equine abortion
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virus (EHV-l). The EHV-l subtype of equine herpesvirus type 1 causes abortion and neurologic disease; less commonly, it is associated with a respiratory tract infection. The neurologic disease is the result of an immune reaction occurring with the vasculature of the central nervous system. The EHV-4 subtype of equine herpesvirus type 1 usually causes a respiratory infection but it occasionally causes abortion. The viral-mediated respiratory disease is characterized as an acute rhinopharyngitis and tracheobronchitis. 20 It is highly contagious, although some adult horses may have subclinical infections. The respiratory infection is accompanied by conjunctivitis that begins with an increased serous lacrimal discharge. A purulent conjunctivitis can develop in more severely affected horses. Ocular signs are usually minimal and self-limiting, but treatment with topical antibiotics is recommended to control opportunistic bacterial organisms. EHV-l encephalomyelitis can cause a variety of clinical signs and ocular abnormalities are not necessarily present. Ocular lesions are the result of central nervous system involvement and might include nystagmus, blindness, facial paralysis with secondary exposure keratitis, and keratoconjunctivitis sicca. Adenovirus Infection
Adenovirus infections primarily affect the respiratory tract of horses. They are usually self-limiting, with low mortality. Foals with normal passive immunity or competent immune systems are more resistant to infections. Arabian foals with combined immunodeficiency disease, on the other hand, are highly susceptible to equine adenovirus infection. Other immunodeficient foals infected with adenovirus are at risk for developing a fatal suppurative bronchopneumonia. Common clinical findings include mucopurulent nasal and ocular discharges that accumulate on the muzzle and eyelids. Chemosis is evident as the conjunctivae become inflamed and scleral congestion is obvious. Intranuclear inclusion bodies can be found in the conjunctival epithelium. 21 Equine Infectious Anemia
Equine infectious anemia is caused by a retrovirus, and is transmitted by blood-feeding arthropods. Ocular findings associated with equine infectious anemia are nonspecific, but include hemorrhages on the conjunctival surfaces and within the fundus. Equine Viral Arteritis
Equine viral arteritis is caused by a nonarthropod-borne togavirus. Infection is characterized by panvasculitis, especially affecting small
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arteries. 32 Clinical signs are variable, but ocular findings include a serous to mucoid ocular discharge, low-grade conjunctivitis, and periorbital edema and can be similar to those caused by EHV-l, EHV-4, and influenza. Intraocular abnormalities have not been reported in horses infected with equine viral arteritis. Influenza Type A2
Influenza infections in horses produce upper respiratory disease. Associated ocular involvement is usually limited to a mild conjunctivitis or keratoconjunctivitis. Ocular discharge can be serous to mucoid. Topical treatments are indicated in patients with signs of severe inflammation or secondary infections. The clinical features of influenza are difficult to differentiate from EHV-l, EHV-2, and equine viral arteritis. Potomac Horse Fever (Ehrlichiosis)
Ehrlichia equi and Ehrlichia risticii lead to rickettsial infections in horses. The method of transmission probably involves ticks and other blood-sucking arthropods, but oral transmission is possible. Either infection can result in severe systemic illness, with severe endotoxemia. 24 The eyes can be affected by the organism or indirectly as a result of septicemic complications. 34 Hemorrhages can occur on the ocular surfaces. Hyphema is associated with uveitis as a result of ocular infection. Borrelia burgdorferi (Lyme Disease)
Borrelia burgdorferi is a tick-borne infection that can develop into a profound spirochetemia. Ocular involvement can manifest as severe panuveitis with hyphema. Chronic inflammation leads to rubeosis irides, proliferation of uveal pigment, synechiae, cataract formation, retinal atrophy and detachment, and blindness. Glaucoma or ocular hypotony can be present, depending on the status of the ciliary epithelium and the iridocorneal outflow systems. Organisms have been found in the anterior chamber of an affected horse. 4 Equine Encephalitis
Three different encephalitides are encountered in the United States: eastern, western, and Venezuelan equine encephalitis. They are transmitted by blood-feeding insects. The clinical features of infection are nonspecific and vary depending on which portions of the central nervous system are most affected. Ocular signs are secondary to central
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nervous system dysfunction and include blindness, facial muscle paralysis, and exposure keratopathy. The intraocular tissues are not affected. Polyneuritis Equi
Polyneuritis equi is probably an immune-mediated inflammatory process that can affect the cranial nerves. Blindness results from central nervous system involvement. Facial paralysis and decreased tear production contribute to ocular surface abnormalities. The intraocular tissues are not directly affected. Equine Protozoal Myeloencephalitis
Equine protozoal myeloencephalitis is caused by Sarcocystis neurona. Affected horses can develop a wide range of clinical signs, depending on which portion of the nervous system is infected. 2 Brain stem or cerebral infections can cause head tilt, facial paralysis, visual impairment, and secondary keratoconjunctivitis from exposure and decreased tear production. No specific ocular disorders have been described with this parasitic disease. Vestibular Disease
Vestibular disease is a complex syndrome with a variety of causes, including head trauma, otitis media/interna, neoplasia, polyneuritis equi, hypothyroidism, septicemias, autoimmune disorders, migrating parasites, and ingestion of toxic substances. Ocular findings often include head tilt, nystagmus, Horner's syndrome, facial neuropathy, keratoconjunctivitis sicca, and lagophthalmos. The intraocular tissues are not directly affected by this disorder. Brain Abscess
The eye is not directly affected by brain abscess formation. Unilateral or bilateral blindness or impaired vision can be caused by lesions of the central nervous system. Nystagmus, pupillary reflex abnormalities, and facial muscle abnormalities can be caused by focal brain lesions. 3, 25 The most common cause of brain abscesses is Streptococcus sp. infection. Tetanus
The typical clinical findings in a horse affected with tetanus include a rigid posture. The facial muscles are taut, causing the eyelids to be
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opened widely and the nostrils flared. The ears are pulled erect. Both third eyelids are prominent. Loud noises or sudden movements around the horse cause exaggerated responses; the facial muscles and third eyelids often twitch.
Malignant Edema
Malignant edema is a potentially fatal myositis caused by Clostridium spp. Infection occurs following intramuscular injections or puncture wounds. Ocular manifestations are related to severe local tissue swelling and necrosis when the head and neck are involved. 26 Passive congestion occurs in recumbent horses; this can prevent normal eyelid function and result in exposure keratoconjunctivitis. No specific intraocular abnormalities have been reported.
African Horse Sickness·'
African horse sickness is a fatal disease caused by a viscerotropic virus of the family Reoviridae. It is transmitted by arthropods, especially Culicoides sp. One form of the disease causes an acute pulmonary edema and death. A subacute cardiac form causes localized hemorrhages and edema. 3 The supraorbital fossa is often distended with hemorrhagic edema. 5 The conjunctivae and eyelids can be swollen and edematous, with ecchymotic hemorrhages observed in the skin and subcutaneous tissues. Intraocular abnormalities have not been reported in horses affected with African horse sickness. Differential diagnoses include anthrax, equine infectious anemia, and equine viral arteritis.
Borna Disease
Borna disease is a viral infection that causes encephalomyelitis in horses. Visual impairment or blindness can accompany the central nervous system signs, but clinical ocular findings have not been described in affected horses. Nevertheless, microscopic examination of the eyes reveals perivascular infiltrates occurring in the choroid, and this could cause grossly visible changes in the fundus. I7
Epizootic Lymphangitis
Epizootic lymphangitis is a chronic infection of the lymphatic system. It is caused by Histoplasma organisms. The principal ocular lesion is chronic conjunctivitis, but nonhealing ulcerative lesions of the conjunctiva and eyelid can occur. 27
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SUMMARY
The diseases included in this article constitute a wide range of maladies that affect the horse. Certainly, the diseases that are known today to produce ocular lesions are just a few of what will be discovered if attending veterinarians always examine the eyes of patients with systemic diseases.
References 1. Blogg JR, Barton MD, Graydon R, et al: Blindness caused by Rhodococcus equi infection in a foal. Equine Vet J (suppl)2:25, 1983 2. Boy MG, Galligan DT, Divers TJ: Protozoal encephalomyelitis in horses: 82 cases (1972-1986). J Am Vet Med Assoc 196:632, 1990 3. Brown CC, Dardiri AH: African horse sickness: A continuing menace. J Am Vet Med Assoc 196:2019, 1990 4. Burgess EC, Gillette 0, Pickett JP: Arthritis and panuveitis as manifestations of Borrelia burgdorferi infection in a Wisconsin pony. J Am Vet Med Assoc 189:1340, 1986 5. Callis H, Dardiri AH, Ferris DH, et al: Illustrated Manual for the Recognition and Diagnosis of Certain Animal Diseases. Plum Island Animal Disease Center, MexicoUnited States Commission for the Prevention of Foot-and-Mouth Disease, 1982 6. Clabough DL, Conboy HS, Roberts MC: Comparison of four screening techniques for the diagnosis of equine neonatal hypogammaglobulinemia. J Am Vet Med Assoc 194:1717, 1989 7. Clabough DL, Martens RJ: Equine neonatal maladjustment syndrome. Compend Contin Educ Pract Vet 7:497, 1985 8. de Lahunta A, Cummings JF: Neuro-ophthalmologic lesions as a cause of visual deficit in dogs and horses. J Am Vet Med Assoc 150:994, 1967 9. Deem DA, Traver OS, Thacker HL, et al: Agammaglobulinemia in a horse. J Am Vet Med Assoc 175:469, 1979 10. Dubielzig RR: Streptococcal septicemia in the neonatal foal. Equine Med Surg 2:28, 1978 11. Geor RJ, Clark EG, Haines OM, et al: Systemic lupus erythematosus in a filly. J Am Vet Med Assoc 197:1489, 1990 12. Henry M, Prasse K, White S: Hemorrhagic diathesis caused by multiple myeloma in a three-month-old foal. J Am Vet Med Assoc 194:392, 1989 13. Hovda LR: Neonatal septicemia. In Robinson NE (ed): Current Therapy in Equine Medicine. Philadelphia, WB Saunders, 1992, p 435 14. Humber KA, Sweeney RW, Saik JE, et al: Clinical and clinicopathologic findings in two foals infected with Bacillus piliformis. J Am Vet Med Assoc 193:1425, 1981 15. Jacobs RM, Kociba GJ, Ruoff WW: Monoclonal gammopathy in a horse with defective hemostasis. Vet Pathol 20:643, 1983 16. Koterba AM, Brewer BD, Tarplee FA: Clinical and clinicopathological characteristics of the septicaemic neonatal foal: review of 38 cases. Equine Vet J 16:376, 1984 17. Krey H, Ludwig H, Rott R: Spread of infectious virus along the optic nerve into the retina in Borna Disease virus-infected rabbits. Arch Virol 61:283, 1979 18. Lavach JD: Systemic disease. In Large Animal Ophthalmology. St Louis, CV Mosby, 1990, P 240 19. MacAllister C, Qualls C Jr, Tyler R, et al: Multiple myeloma in a horse. J Am Vet Med Assoc 191:337, 1987 20. Martens JG, Martens RJ: Equine herpesvirus type 1: Its classifications, pathogenesis, and prevention. Vet Med 86:936, 1991 21. McChesney AE, England H, Rich LJ: Adenoviral infection in foals. J Am Vet Med Assoc 162:545, 1973 22. McQuire TC, Crawford TB, Halliwell AL, et al: Failure of colostral immunoglobulin
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23. 24. 25. 26. 27. 28. 29. 30.
31. 32.
33. 34.
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transfer as an explanation for most infections and death of neonatal foals. J Am Vet Med Assoc 170:1302, 1977 Nara PL, Krakowka S, Powers TE, et al: Experimental Streptococcus equi infection in the horse: Correlation with in vivo and in vitro immune responses. Am J Vet Res 44:529, 1983 Palmer JE: Potomac Horse Fever. In Murray MJ (ed): Current Therapy in Equine Medicine, ed 3. Philadelphia, WB Saunders, 1992, p 250 Raphel CF: Brain abscess in three horses. J Am Vet Med Assoc 180:874, 1982 Rebhun WC, Shin SJ, King JM, et al: Malignant edema in horses. J Am Vet Med Assoc 187:732, 1985 Singh J: Studies on epizootic lymphangitis. Study of clinical cases and experimental transmission. Indian J Vet Sci 36:45, 1966 Sillerud CL, Bey RF, Ball M, et al: Serologic correlation of suspected Leptospira interrogans serovar pomona-induced uveitis in a group of horses. J Am Vet Med Assoc 191:1576, 1987 Sockett DC, Traub-Dargatz JL, Weiser MG: Immune-mediated hemolytic anemia and thrombocytopenia in a foal. J Am Vet Med Assoc 190:308, 1987 Sweeney CR, Whitlock RH, Meirs DA, et al: Complications associated with Streptococcus equi infection on a horse farm. J Am Vet Med Assoc 191:1446, 1987 Traub-Dargatz JL, Bertone A, Bennett 0, et al: Monoclonal aggregating immunoglobulin cryoglobulinaemia in a horse with malignant lymphoma. Equine Vet J 17:470, 1985 Traub-Dargatz JL, Ralston SL, Collins JK, et al: Equine viral arteritis. Compend Contin Educ Pract Vet 7:490, 1985 Wilson WD, Madigan JE: Comparison of bacteriologic culture of blood and necropsy specimens for determining the cause of foal septicemia: 47 cases (1978-1987). J Am Vet Med Assoc 195:1759, 1989 Ziemer EL, Keenan DP, Madigan JE: Ehrlichia equi infection in a foal. J Am Vet Med Assoc 190:199, 1987
Address reprint requests to J.D. Lavach, DVM, MS Eye Clinic for Animals 13132 Garden Grove Boulevard Garden Grove, CA 92643
OPHTHALMOLOGY
OCULAR MANIFESTATIONS OF SYSTEMIC DISEASES J.
D. Lavach, DVM, MS
This article describes some of the ocular findings associated with systemic diseases. Veterinary literature contains very few detailed descriptions of the ocular findings associated with systemic diseases,18 yet most systemic diseases can and do affect the ocular tissues to some extent. Unfortunately, the eyes are not always examined and ocular abnormalities are not detected unless an ophthalmic examination is performed. Ocular findings can provide the examiner with more information about the particular illness and its prognosis. In addition, early recognition and treatment of the ocular components of any systemic disease can minimize ocular damage and might aid in preservation of vision.
NEONATAL ONSET SYSTEMIC DISEASES Neonatal Hypogammaglobulinemia
Foals acquire passive immunity during their first 24 hours of life by absorption of colostral antibodies. Complete or partial failures of passive immune transfer are diagnosed by measuring serum IgG concentrations. Several screening techniques have been used in the diagnosis of equine neonatal hypogammaglobulinemia. 6 Foals low in serum IgG concentration are at greatly increased risk for neonatal septicemic infections and death. 16, 22 Ocular manifestations of septicemic diseases are nonspecific, but include anterior uveitis, hyphema, chorioretinitis, From the Eye Clinic for Animals, Garden Grove, California
VETERINARY CLINICS OF NORTH AMERICA: EQUINE PRACTICE VOLUME 8 • NUMBER 3 • DECEMBER 1992
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retinal detachments, and blindness from severe intraocular diseases or central nervous system involvement. Neonatal Septicemia
Neonatal foals affected with septicemia often acquire ocular involvement. The inflammatory reaction can be a sterile immunologic consequence, or it can be an infectious process. Panuveitis with vitreous abscess formation occurs in severe infections. The causative agents reported include Streptococcus sp. and Rhodococcus equi, but any bacterium can overwhelm a neonatal foal. 1, 10 One study found gram-negative bacteria in all of 47 foals examined in addition to various gram-positive bacteria and anaerobic bacteria. 33 Predisposing conditions, including stressful environments and delayed colostrum intake, contribute to the foal's susceptibility.lO Bacillus piliformis
Bacillus piliformis infection, Tyzzer's disease, is an acute fatal disease of neonatal foals. Most affected foals are found dead, although depressed and recumbent foals are occasionally encountered. The clinical ophthalmic features of the disease are nonspecific, but positional nystagmus was mentioned in one affected foal just before its death. 14 Intraocular hemorrhages or accumulations of fibrin can be found in foals that go into seizure. Neonatal Maladjustment Syndrome
Neonatal maladjustment syndrome is a complex and poorly understood disorder. Possible causes include cerebral hemorrhage, fetal hypoxia, and cardiopulmonary aberrations. 7 Birth trauma can contribute to this syndrome. It is characterized by gross behavioral disturbances, respiratory distress, convulsions, coma or semicoma, and, occasionally, death. Complete or partial blindness can occur. Specific ocular findings include anisocoria, scleral hemorrhage, papilledema, and retinal hemorrhage. Secondary ocular findings in foals with severe central nervous system disturbances include keratoconjunctivitis, corneal ulcers, and entropion. Entropion is often due to spasm from corneal pain. Immunologic Deficiencies
Immunologic deficiencies occurring in older foals or adult horses can be transient or permanent. 9, 13 Affected horses are predisposed to infectious diseases. The ocular signs are variable but usually consist of
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uveal involvement. Intraocular inflammatory exudates can accumulate, and retinal detachments are common. Keratoconjunctivitis with corneal ulcerations are commonly encountered in recumbent horses. Corneal epithelialization is delayed, and chronic infections with progressive corneal destruction occur in debilitated patients.
Immune-mediated Hemolytic Anemia
Immune-mediated hemolytic anemia and thrombocytopenia were reported in a 2-week-old foa1. 29 The foal developed hyphema and petechial hemorrhages of the conjunctivae and other mucous membranes. Both eyes developed uveitis characterized by corneal edema, clotted blood and fibrin in the anterior chambers, miosis, and swollen irides. Small focal posterior synechiae were transient. Neonatal isoerythrolysis occurs when the dam produces antibodies against the foal's erythrocytes. The antibodies are absorbed with colostrum and clinical signs become apparent 12 to 96 hours after birth. Conjunctival, episcleral, and intraocular hemorrhage can occur. All mucous membranes, including the conjunctivae, become icteric.
ADULT-ONSET SYSTEMIC DISORDERS Systemic Lupus Erythematosus
Systemic lupus erythematosus was described in a 2-year-old Standardbred filly.ll Clinical features included small punctate ulcers at the mucocutaneous junctions of the lips, external nares, and rostral portion of the tongue. The diffuse lesion pattern was typical of what has been reported in other animal species. Specific ocular lesions were not mentioned, but mucocutaneous ulceration along the eyelid margins should alert the veterinarian to consider this disease as a differential diagnosis.
Lymphosarcoma
Malignant lymphoma can affect the eyes and cause blindness. The primary ocular site is the uveal tract, which becomes invaded by neoplastic cells. Affected eyes can have severe anterior uveitis, characterized by corneal edema, diffuse thickening of the irides, and intraocular hemorrhage. The eyes are usually hypotonic, but secondary glaucoma can occur in one or both eyes. The posterior segment is involved less commonly, but neoplastic cells in the choroid, retina, vitreous, and optic nerve have been found. Vitreous hemorrhage and retinal detachments can be consequences of posterior segment disease. Conjunctival
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infiltration can lead to conjunctival exposure and desiccation with conjunctival ulceration. Malignant lymphoma can involve the periocular tissues, causing mass lesions to develop in the orbit, third eyelid, or eyelids. Focal mass lesions can displace the globe in any direction, or the eye can become exophthalmic. The eye can be completely normal and free from invasion by neoplastic cells during orbit involvement. Diagnosis is usually accomplished by aspiration and examination of cytology specimens, or through biopsy of orbit tissues. One affected horse had a monoclonal aggregating immunoglobulin class and cryoglobulinemia associated with lymphoma. 31 Another report described an affected horse with a monoclonal gammopathy and hyperviscosity, but without a cryoglobulin. IS Multiple Myeloma
Multiple myeloma is a fatal neoplastic disorder of plasma cells. It can cause a variety of ocular signs, including episcleral hemorrhage, uveitis, intraocular hemorrhage, retinal detachments, and blindness. 12, 19 Both eyes are affected simultaneously. Streptococcus equi
Streptococcal infections are characterized by systemic illness in young horses. Generalized lymphadenopathy and respiratory tract signs are common. 23 The ocular surfaces are affected with a mild inflammatory reaction. Dacryocystitis can develop secondary to chronic inflammation. Transient keratoconjunctivitis sicca can occur during active septicemic episodes. More severe manifestations affecting the eye and visual system are associated with abscess formation in lymph nodes, lungs, central nervous system, and other organs. 30 Intraocular manifestations include anterior uveitis, panuveitis, chorioretinitis, retinal detachment, vitreous abscess, and optic neuritis. Leptospirosis
Several species and serologic subtypes of leptospira have been implicated as causative agents for equine recurrent uveitis, peripapillary chorioretinitis, and optic neuropathies. 28 The ocular manifestations can be caused directly by the organism entering the ocular tissues, or they can be latent manifestations related to immunologic reactions. See the article by Schwink for more information. Equine Herpesvirus type 1
Equine herpesvirus agents have been classified into type 1 with two subtypes-equine rhinopneumonitis (EHV-4) and equine abortion
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virus (EHV-l). The EHV-l subtype of equine herpesvirus type 1 causes abortion and neurologic disease; less commonly, it is associated with a respiratory tract infection. The neurologic disease is the result of an immune reaction occurring with the vasculature of the central nervous system. The EHV-4 subtype of equine herpesvirus type 1 usually causes a respiratory infection but it occasionally causes abortion. The viral-mediated respiratory disease is characterized as an acute rhinopharyngitis and tracheobronchitis. 20 It is highly contagious, although some adult horses may have subclinical infections. The respiratory infection is accompanied by conjunctivitis that begins with an increased serous lacrimal discharge. A purulent conjunctivitis can develop in more severely affected horses. Ocular signs are usually minimal and self-limiting, but treatment with topical antibiotics is recommended to control opportunistic bacterial organisms. EHV-l encephalomyelitis can cause a variety of clinical signs and ocular abnormalities are not necessarily present. Ocular lesions are the result of central nervous system involvement and might include nystagmus, blindness, facial paralysis with secondary exposure keratitis, and keratoconjunctivitis sicca. Adenovirus Infection
Adenovirus infections primarily affect the respiratory tract of horses. They are usually self-limiting, with low mortality. Foals with normal passive immunity or competent immune systems are more resistant to infections. Arabian foals with combined immunodeficiency disease, on the other hand, are highly susceptible to equine adenovirus infection. Other immunodeficient foals infected with adenovirus are at risk for developing a fatal suppurative bronchopneumonia. Common clinical findings include mucopurulent nasal and ocular discharges that accumulate on the muzzle and eyelids. Chemosis is evident as the conjunctivae become inflamed and scleral congestion is obvious. Intranuclear inclusion bodies can be found in the conjunctival epithelium. 21 Equine Infectious Anemia
Equine infectious anemia is caused by a retrovirus, and is transmitted by blood-feeding arthropods. Ocular findings associated with equine infectious anemia are nonspecific, but include hemorrhages on the conjunctival surfaces and within the fundus. Equine Viral Arteritis
Equine viral arteritis is caused by a nonarthropod-borne togavirus. Infection is characterized by panvasculitis, especially affecting small
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arteries. 32 Clinical signs are variable, but ocular findings include a serous to mucoid ocular discharge, low-grade conjunctivitis, and periorbital edema and can be similar to those caused by EHV-l, EHV-4, and influenza. Intraocular abnormalities have not been reported in horses infected with equine viral arteritis. Influenza Type A2
Influenza infections in horses produce upper respiratory disease. Associated ocular involvement is usually limited to a mild conjunctivitis or keratoconjunctivitis. Ocular discharge can be serous to mucoid. Topical treatments are indicated in patients with signs of severe inflammation or secondary infections. The clinical features of influenza are difficult to differentiate from EHV-l, EHV-2, and equine viral arteritis. Potomac Horse Fever (Ehrlichiosis)
Ehrlichia equi and Ehrlichia risticii lead to rickettsial infections in horses. The method of transmission probably involves ticks and other blood-sucking arthropods, but oral transmission is possible. Either infection can result in severe systemic illness, with severe endotoxemia. 24 The eyes can be affected by the organism or indirectly as a result of septicemic complications. 34 Hemorrhages can occur on the ocular surfaces. Hyphema is associated with uveitis as a result of ocular infection. Borrelia burgdorferi (Lyme Disease)
Borrelia burgdorferi is a tick-borne infection that can develop into a profound spirochetemia. Ocular involvement can manifest as severe panuveitis with hyphema. Chronic inflammation leads to rubeosis irides, proliferation of uveal pigment, synechiae, cataract formation, retinal atrophy and detachment, and blindness. Glaucoma or ocular hypotony can be present, depending on the status of the ciliary epithelium and the iridocorneal outflow systems. Organisms have been found in the anterior chamber of an affected horse. 4 Equine Encephalitis
Three different encephalitides are encountered in the United States: eastern, western, and Venezuelan equine encephalitis. They are transmitted by blood-feeding insects. The clinical features of infection are nonspecific and vary depending on which portions of the central nervous system are most affected. Ocular signs are secondary to central
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nervous system dysfunction and include blindness, facial muscle paralysis, and exposure keratopathy. The intraocular tissues are not affected. Polyneuritis Equi
Polyneuritis equi is probably an immune-mediated inflammatory process that can affect the cranial nerves. Blindness results from central nervous system involvement. Facial paralysis and decreased tear production contribute to ocular surface abnormalities. The intraocular tissues are not directly affected. Equine Protozoal Myeloencephalitis
Equine protozoal myeloencephalitis is caused by Sarcocystis neurona. Affected horses can develop a wide range of clinical signs, depending on which portion of the nervous system is infected. 2 Brain stem or cerebral infections can cause head tilt, facial paralysis, visual impairment, and secondary keratoconjunctivitis from exposure and decreased tear production. No specific ocular disorders have been described with this parasitic disease. Vestibular Disease
Vestibular disease is a complex syndrome with a variety of causes, including head trauma, otitis media/interna, neoplasia, polyneuritis equi, hypothyroidism, septicemias, autoimmune disorders, migrating parasites, and ingestion of toxic substances. Ocular findings often include head tilt, nystagmus, Horner's syndrome, facial neuropathy, keratoconjunctivitis sicca, and lagophthalmos. The intraocular tissues are not directly affected by this disorder. Brain Abscess
The eye is not directly affected by brain abscess formation. Unilateral or bilateral blindness or impaired vision can be caused by lesions of the central nervous system. Nystagmus, pupillary reflex abnormalities, and facial muscle abnormalities can be caused by focal brain lesions. 3, 25 The most common cause of brain abscesses is Streptococcus sp. infection. Tetanus
The typical clinical findings in a horse affected with tetanus include a rigid posture. The facial muscles are taut, causing the eyelids to be
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opened widely and the nostrils flared. The ears are pulled erect. Both third eyelids are prominent. Loud noises or sudden movements around the horse cause exaggerated responses; the facial muscles and third eyelids often twitch.
Malignant Edema
Malignant edema is a potentially fatal myositis caused by Clostridium spp. Infection occurs following intramuscular injections or puncture wounds. Ocular manifestations are related to severe local tissue swelling and necrosis when the head and neck are involved. 26 Passive congestion occurs in recumbent horses; this can prevent normal eyelid function and result in exposure keratoconjunctivitis. No specific intraocular abnormalities have been reported.
African Horse Sickness·'
African horse sickness is a fatal disease caused by a viscerotropic virus of the family Reoviridae. It is transmitted by arthropods, especially Culicoides sp. One form of the disease causes an acute pulmonary edema and death. A subacute cardiac form causes localized hemorrhages and edema. 3 The supraorbital fossa is often distended with hemorrhagic edema. 5 The conjunctivae and eyelids can be swollen and edematous, with ecchymotic hemorrhages observed in the skin and subcutaneous tissues. Intraocular abnormalities have not been reported in horses affected with African horse sickness. Differential diagnoses include anthrax, equine infectious anemia, and equine viral arteritis.
Borna Disease
Borna disease is a viral infection that causes encephalomyelitis in horses. Visual impairment or blindness can accompany the central nervous system signs, but clinical ocular findings have not been described in affected horses. Nevertheless, microscopic examination of the eyes reveals perivascular infiltrates occurring in the choroid, and this could cause grossly visible changes in the fundus. I7
Epizootic Lymphangitis
Epizootic lymphangitis is a chronic infection of the lymphatic system. It is caused by Histoplasma organisms. The principal ocular lesion is chronic conjunctivitis, but nonhealing ulcerative lesions of the conjunctiva and eyelid can occur. 27
OCULAR MANIFESTATIONS OF SYSTEMIC DISEASES
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SUMMARY
The diseases included in this article constitute a wide range of maladies that affect the horse. Certainly, the diseases that are known today to produce ocular lesions are just a few of what will be discovered if attending veterinarians always examine the eyes of patients with systemic diseases.
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Address reprint requests to J.D. Lavach, DVM, MS Eye Clinic for Animals 13132 Garden Grove Boulevard Garden Grove, CA 92643
