THIRD EYELID GLAND PROLAPSE
The nictitating membrane (known as third eyelid) has been considered, for many years, an unnecessary structure of the mammalian eye. That statement deserves an expeditious burial.
In fact, it is an important protective mechanism of the eye, assisting in spreading of the precorneal film (possibly more important than the eyelids themselves in regard), covering, thus protecting the eye from injuries. The third eyelid gland produces 40% of the lacrimal fluid and participates in the immune protective system of the eye, providing an important barrier against entry of infectious agents.
The protrusion of the nictitans gland (or third eyelid gland prolapse, or cherry eye) is the most common primary disorder of the membrane nictitans. It occurs mainly in dogs.
The aetiology is unknown, but the most possible theory is that it results from weakness in the connective tissue attachment between the gland and the periorbital tissue. The gland flips up dorsally, it becomes enlarged and inflamed. Apparently, since no infectious agent is implicated in the aetiology, surgical repositioning of the gland is the only option.
It usually occurs in dogs younger than 2 years. In case it occurs in older animals, neoplasia should be considered in the differential diagnosis.
American Cocker Spaniel, Pekingese, Beagle, Lhasa Apso, English Bulldog, Mastiffs are the breeds predisposed to the prolapse.
Clinically, there is a reddened enlargement, like a mass, extending from the bulbar side of the third eyelid, in the medial canthal area. Mild irritation, and epiphora are usually present, while pain is absent. Self-trauma is possible, when the gland is hypertrophic.
Total excision is contraindicated. For several decades it was the treatment of choice, but ever since the gland’s contribution to tear production became apparent, surgical repositioning of the gland became widely recommended, and at least eight techniques have been published. Total excision usually results six months post-operatively, and especially in the predisposed breeds, in dry eyes (Kerato-Conjunctivitis Sicca), condition that requires life-long treatment.
Sadly, it is still recommended by some practitioners. It should be stressed that recurrence of the gland prolapse should serve at any case as an excuse for total excision. Removal of the entire gland and possibly the third eyelid is an option in case of neoplasia of the membrana nictitans.
KERATOCONUS POST-THIRD EYELID GLAND REMOVAL IN A NAPOLITAN MASTIFF DOG
CANINE IATROGENIC KERATO-CONJUNCTIVITIS SICCA
CANINE THIRD EYELID GLAND PROTRUSION
CANINE THIRD EYELID CARTILAGE EVERSION
FELINE THIRD EYELID CARTILAGE EVERSION
EURYBLEPHARON OR MACROBLEPHARON
Euryblepharon, also referred to as macroblepharon, is classified as macropalpebral fissure, meaning an abnormally long eyelid which results in an abnormally large palpebral fissure. In dogs with normal eyes, only a small proportion of sclera (the white part of the eye) is visible. Certain breeds, notably the bracycephalic (Boxer, Boston Terrier, Pug, Shih-Tzu, Lhasa-Apso, Pekingese) and breeds such as the Shar-Pei, English Cocker Spaniel, Bloodhound, St.Bernard, English Springer Spaniel, present an abnormally large palpebral fissure that exposes the cornea and the sclera.
In the bracycephalic breeds euryblepharon results from forward protrusion of the globe through the palpebral fissure.
The second type of euryblepharon results from an excess length of eyelid margin, thus the palpebral fissure is poorly supported by the globe.
Further more, the shape of the plapebral fissure can be deformed by lateral canthus instability, small globe size, enophthalmos and heavy facial skin folds, such as in breeds predisposed for «diamond eye», like the St.Bernard, Clumber Spaniel, Mastiffs and Bloodhound.
In bracycephalic breeds specifically, euryblepharon results in lagophthalmos, which means inability to complete the blink mechanism and thus, instability of the precorneal tear film and increased evaporation of the film. Pigmentary keratitis, corneal ulcers and exposure keratitis can result from drying and they can all compromise vision.
Prophylaxis, in terms of supporting the tear film either medically or surgically becomes essential. Artificial tear preparation can be helpful, but surgical shortening of the macropalpebral fissure offers a permanent solution.
The lateral canthal blepharoplasty also reduces the possibility of proptosis, which can be traumatic, mechanical or automatic, due to the eyelid conformation. In these cases, surgical repositioning of the globe is absolutely necessary, as soon as possible, and despite that the prognosis for vision might be poor. Also, there are really heavy cases where the globe has to be enucleated at the beginning.
All canthoplasty techniques (basically lateral canthoplasty) aim to reduce the size of the palpebral fissure by 30%.
Slatter D. Fundamentals of Veterinary Ophthalmology, Second Edition, W.B. Saunders, 1990
Maggs DJ, Miller PE, Ofri R. Slatter’s Fundamentals of Veterinary Ophthalmology, Edition 4, Saunders, 2008
Gelatt KN. Veterinary Ophthalmology. Second Edition. Lea & Febinger, 1991
Gelatt KN. Veterinary Ophthalmology. Fourth Edition, Blackwell Publishing, 2007
TWO YEARS POST-OP
CANINE EURYBLEPHARON AND CORNEAL PERFORATION
Corneal sequestration is a corneal disease unique to the cat. Synonyms include feline corneal necrosis, corneal mummification, and keratitis nigrum. Although any cat can be affected, Persian, Burmese, Himalayan, and maybe Siamese cats appear to be more susceptible. The cause of the disease is unknown, but it usually occurs after chronic ulceration. As such, Feline Herpesvirus (FHV-1) is frequently incriminated and can be detected in at least 50% of biopsy specimens from cats with this disease.
Occasionally corneal sequestration is seen in cats with no previous history of ulcerative corneal disease. The clinical signs are classic, with the appearance of a focal amber to black, usually central corneal plaque surrounded by a broader area of superficial or recurrent ulceration. These lesions tend to be painful, and blepharospasm and epiphora are expected. Depending on chronicity, sequestra are often accompanied by corneal vascularization, edema, and stromal white blood cell infiltration, due to a foreign body reaction stimulated by the necrotic tissue. The black material is not melanin, but pigmented and necrotic tissue.
The necrotic plaque sometimes sloughs without the need for surgical intervention. In such cases ongoing medical management of the ulcer and secondary uveitis with topical antibiotics and atropine, respectively, along with antiviral therapy, if FHV-1 is believed to be the initiating cause, should be provided until sloughing occurs. Corticosteroids are totally contra-indicated. However, most animals exhibit signs of marked ocular pain during this period, and removal of the plaque by keratectomy is preferred as it shortens this period of discomfort. Associated keratitis should be controlled before keratectomy is performed. Some sequestra extend to Descemet’s membrane and globe rupture is possible, therefore keratectomy has its limitations, as far as depth is concerned. Feline sequestra are painful and may take many months to slough. Surgical removal of the sequestrum is the treatment of choise, with the use of corneal graft or not. The results are usually excellent, because healing is faster, uncomplicated and relieves discomfort.
Recurrences after treatment may occur, but results are normally excellent.
Use of therapeutic contact lenses might be of great value, in case conservative treatment is chosen.
SEVERE CORNEAL SEQUESTRATION
WITH A CONTACT LENS APPLIED
These conditions are the most common cases that occur in the daily practice, presenting a real challenge, because early action is necessary. In any case it is also of utmost importance to diagnose the disorders before referral to a specialist, to prevent severe or permanent damage to the eye.
1. PROPTOSIS OF THE GLOBE
Forward displacement of the globe results in proptosis. It is a very common condition in bracycephalic breeds, due to facial conformation (exophthalmos and shallow orbit) and trauma. Immediate replacement of the globe within the orbit and temporary tarsorraphy should be done as soon as possible. Enucleation is the treatment of choice in case of irreversible damage to the optic nerve or severe damage to the eye.
Defined as increased intraocular pressure, but in fact consists mainly of pressure on the optic nerve head, causing degeneration and loss of vision. It is a painful disease, which requires urgent treatment, especially in case of acute congestion (pupillary block). Glaucoma presents a direct threat to vision for the affected eye and in time for the fellow eye. Definitive diagnosis and therapy should be immediate and targeted to the type of glaucoma, to restore and maintain vision.
3. CORNEAL LACERATION
Trauma, foreign bodies (plants, awns), contagious diseases (virus, bacteria, fungi), KCS, toxic substances, exposure keratopathy (lagophthalmos), facial nerve paralysis, and entropion are the most common causes of corneal laceration. Clinical signs involve blepharospasm, conjunctival congestion, ophthalmic discharge, corneal edema and miotic pupil. Diagnosis can be facilitated by fluorescein dye, whilst Elizabethan collar is absolutely necessary in all cases.
4. LID LACERATION
The important factors that determine treatment are: time of injury, which affects degree of bacterial contamination; involvement of lid margin and especially lacrimal puncti and canaliculi; and extent of lesion.
5. SEVERE OCULAR AND ADNEXAL CONTUSIONS AND CONCUSSION
The two important factors when treating contusions or concussions are: external trauma may cause severe intraocular injuries, even if the globe is not penetrated; post-traumatic uveitis is frequent and must be controlled.
6. PENETRATING INJURIES
These, full thickness lacerations in particular, are surgical emergencies which should be treated by a veterinary ophthalmologist immediately. In cases where definite surgical treatment cannot be performed, it is necessary to prevent self-trauma, minimize infection, and treat melting ulcers and complications.
7. DESCEMETOCELE AND IRIS PROLAPSE
This is the absolute ocular surgical emergency. Anticollagenase treatment and antibiotics should be immediately administered. Meanwhile, excess pressure to the globe or the jugular veins should be avoided.
The presence of blood into the anterior chamber may be the only clinical symptom in a red eye. Aetiology might be trauma, uveitis, bleeding disorders, neoplasia, congenital diseases, hypertension, chronic glaucoma and retinal detachment. A complete laboratory and clinical check-up is necessary. Treatment should be immediately initiated and cage rest is absolutely crucial.
9. ACUTE ANTERIOR UVEITIS
It is a fairly common ocular condition, which requires urgent treatment because it can be extremely painful and vision-threatening. Aetiology includes trauma, infectious diseases, sepsis, lens abnormalities, autoimmune disease, neoplasia, lymphosarcoma. Full ophthalmic and physical examination and laboratory studies are required to find the cause of uveitis, although the search might be fruitless. Topical treatment should be immediately initiated to relief from the ophthalmic symptoms and restore vision, whilst prognosis depends on the aetiology.
10. SUDDEN BLINDNESS
Complete history and ophthalmic examination is necessary to diagnose the cause of sudden loss of vision. Retinal detachment due to hypertension, acute inflammation-chorioiditis, granulomatous meningo-encephalitis, trauma, generalized retinitis, autoimmune disease, Sudden Acquired Retinal Degeneration, optic neuritis, Enrofloxacin toxicity can cause sudden blindness. In general, early retinal re-attachment is a better prognostic sign for vision.
1. Slatter D. Fundamentals of Veterinary Ophathlmology. Second Edition, 1990, W.B.Saunders
2. Mandell D.C, Holt E. Ophthalmic Emergencies. Vet Clin North Am Small An Pract, 35:2, 2005
CANINE OCULAR PROPTOSIS
CANINE MELTING ULCER
CANINE OCULAR FOREIGN BODY
CANINE OCULAR FOREIGN BODY
FELINE THIRD EYELID LACERATION
FELINE CORNEAL PERFORATION
CANINE IRIS PROLAPSE
CANINE ANTERIOR UVEITIS