The conjunctiva of horses is a mucous membrane that is formed by the palpebral conjunctiva (covers the inner face of the eyelids), the bulbar conjunctiva (covers the sclera, that is, the surface of the eyeball) and the conjunctiva of the nictitating membrane (covers the inner and outer face of the nictitating membrane or third eyelid). When an inflammation of one or several of these parts of the conjunctiva occurs, it is called conjunctivitis. Although conjunctivitis in horses can be a primary process, it generally appears secondary to other ocular or systemic pathologies, which must be taken into account both in its diagnosis and treatment.
Causes of conjunctivitis in horses
When we talk about conjunctivitis in horses, we have to make a distinction between primary conjunctivitis and secondary conjunctivitis. The causes of primary conjunctivitis in horses can be:
- Foreign bodies: such as hay, straw, shavings, dust, spikes, etc.
- Injuries: Eye injuries are common in horses due to the large size of the eyes and their lateral location on the head. If you want to know more about the Anatomy of the horse, do not hesitate to take a look at this other article that we recommend.
- Infectious agents: including bacteria (Moraxella spp., Chlamydophila spp, Mycoplasma spp, Streptococcus equi), viruses (Equine Herpesvirus 1 and 2, Equine Viral Arteritis virus and Adenovirus), fungi (Aspergillus spp, Histoplasmosis, Blastomycosis, Rhinosporidium seeberi) and parasites (Habronema spp, Thelazia lacrymalis, Onchocerca cervicalis, Trypanosoma evansi, Babesia spp). Conjunctivitis caused by flies is also common. We leave you this other post on our site so you can find out the Natural Remedies for flies in horses.
- Neoplasms: squamous cell carcinoma, lymphoma, papilloma, hemangioma, hemangiosarcoma, mast cell tumors, melanoma and multiple myeloma.
- Allergic reactions: to dust, sand, hay, ammonia, ashes or pollen, among others.
However, not all conjunctivitis are primary, but in most cases they appear secondary due to:
- Other ocular pathologies: affecting the eyelids, cornea, sclera, uvea, nasolacrimal system and orbit. Conjunctivitis is often associated with keratitis, corneal abscesses, uveitis, and nasolacrimal duct obstruction.
- Systemic pathologies: in foals, conjunctivitis frequently appears secondarily as placentitis, Neonatal Maladjustment Syndrome (INS), sepsis, pneumonia, or subconjunctival or episcleral hemorrhages caused by birth trauma. In adults, conjunctivitis can be associated with polyneuritis, Vestibular syndrome, equine protozoal myeloencephalitis, African horse sickness, and epizootic lymphangitis.
To learn more about common diseases of horses, consult this article that we recommend.
Symptoms of conjunctivitis in horses
The clinical signs that can be observed in horses with conjunctivitis are the following:
- Conjunctival hyperemia: redness of the conjunctiva.
- Chemosis: edema at the level of the conjunctiva. As a consequence, swollen eyes and thickened conjunctiva are observed.
- Epiphora: continuous tearing.
- Ocular discharge: from serous discharge (in viral or allergic conjunctivitis) to purulent (in bacterial conjunctivitis).
- Formation of lymphoid follicles: by accumulation of lymphoid cells such as lymphocytes, plasma cells and histiocytes.
- Ocular and periocular granulomas: in conjunctivitis caused by Habronema spp and Onchocerca cervicalis.
Diagnosis of conjunctivitis in horses
As we have explained, not all conjunctivitis are primary, but sometimes appear associated with other ocular or systemic pathologies. Therefore, the diagnosis of conjunctivitis in horses must be accompanied by a deeper investigation to determine what is the true cause of the inflammation and if it is accompanied by any other concomitant pathology.
To differentiate between primary and secondary conjunctivitis, it is necessary to perform and carry out one:
- Good general examination of the horse: to detect signs that may indicate the presence of a systemic disease.
- Complete eye exam: to detect ocular alterations that may be causing inflammation of the conjunctiva.
When no other signs of associated ocular or systemic disease are found, it will be a primary conjunctivitis. In this case, it is important to investigate the origin of the inflammation in order to establish the most appropriate treatment. To do this, one or more of the following additional tests must be performed:
- Microbiological culture: bacterial, viral and/or fungal. The normal microflora of the ocular surface consists mainly of gram-positive bacteria and fungi. Usually, these microorganisms remain in balance, but sometimes they can act as opportunistic pathogens and cause conjunctivitis. Therefore, for the diagnosis it is important to make a correct interpretation of the microbial culture and the conjunctival cytology.
- Antibiogram: to determine the sensitivity of the infectious agent to different antibiotic groups. This test will allow the establishment of a specific antibiotic therapy and will prevent the appearance of antibiotic resistance.
- Cytology: from conjunctival scrapings.
- Histopathological diagnosis: from a conjunctival biopsy.
Treatment of conjunctivitis in horses
At this point, we must consider how to cure conjunctivitis in horses. To do this, the first thing to consider is whether it is primary or secondary conjunctivitis.
Treatment for primary conjunctivitis in horses
In primary conjunctivitis, treatment may focus solely on resolving the conjunctival inflammation. To do this, it is necessary to know what the specific cause is that caused the conjunctivitis in order to establish a specific treatment.
- Foreign Body Conjunctivitis: Foreign bodies should be removed under local anesthesia. Next, the conjunctival sac should be washed to remove any remaining dirt.
- Infectious conjunctivitis: they are treated with antimicrobial drugs, including antibacterial, antiviral, antifungal or antiparasitic depending on the causal agent. Bacterial and fungal conjunctivitis can be treated initially with broad-spectrum antibiotics and, once the results of the antibiogram are obtained, switch to the antibiotic of choice. In conjunctivitis caused by Habronema spp and Onchocerca cervicalis, in addition to antiparasitic treatment, an ophthalmic corticosteroid should be administered (provided there are no corneal ulcers) and debridement of nodular lesions should be performed.
- Conjunctival tumors: tumor resection combined with cryotherapy, radiotherapy or intralesional chemotherapy.
- Allergic conjunctivitis: treated with ophthalmic corticosteroids. In addition, it is important to avoid exposure to the triggering cause of the hypersensitivity reaction.
Treatment for secondary conjunctivitis in horses
In the case of secondary conjunctivitis, it will also be necessary to treat the primary cause in order to resolve the conjunctival inflammation. In this way, a physical and ophthalmological examination will be carried out, in addition to eye secretion tests.
Prognosis of conjunctivitis in horses
The prognosis of conjunctivitis varies depending on the cause that originates it. In this case, we can find ourselves in situations such as the following where:
- Infectious conjunctivitis usually responds well to antibiotic treatment within 5-7 days: lack of response or recurrence (recurrence) suggests the existence of an unidentified underlying cause (for example, a foreign body hidden in the conjunctival sac).
- Conjunctival neoplasms have a variable course and prognosis: depending on the specific type of neoplasm and the degree of tissue invasion surrounding.
- Allergic conjunctivitis can be difficult to eliminate when it is not possible to completely avoid exposure to the triggering cause of the allergy.
- Conjunctivitis secondary to serious systemic diseases can have a poor prognosis.
