In this text, I will touch on a few select ocular emergencies that are deemed dire if vision or the globe is to be saved.
In this text, I will touch on a few select ocular emergencies that are deemed dire if vision or the globe is to be saved. The information provided herein provides the primary clinician with tools for immediate triage and thus is not all encompassing. The points made are few, with the hopes of them being salient, thus assisting the primary clinician with an ocular emergency treatment plan.
It should be noted that glaucoma is also considered a dire ocular emergency but is not covered in this text. I have covered glaucoma in another presentation. Thus, I refer you to "Glaucoma: The 5 O'Clock Emergency" for a discussion of the physiology, medical treatment and surgical advancements in the treatment of glaucoma.
Protrusion of the eye, called proptosis, results from sudden, forward displacement of the globe from the orbit and simultaneous entrapment of the eyelids behind the globe, causing venous congestion. This leads to swelling and inflammation of the retrobulbar contents and can frequently lead to blindness.
Trauma, including dog fights or being struck by a car, is the most common reason for proptosis of the globe. Proptosis in brachycephalic breeds occurs more readily due to their shallow orbits, prominent globes and their abnormal eyelid conformation, and thus even mild trauma, such as excessive restraint, can cause proptosis in these breeds. Proptosis occurring in dolichocephalic dogs and cats is typically caused by severe trauma and thus yields a guarded prognosis.
On initial presentation, the proptosed globe should be lathered with sterile lubricating ointments to prevent dessication of the cornea while other systemic body systems are assessed. Prior to replacing the globe into its correct anatomic location and restoring the protective function of the eyelids, it should be determined whether or not the globe is salvageable.
Avulsion of three or more extraocular muscles or an avulsed optic nerve certainly yields an unfavorable prognosis for saving the globe as does severe corneal trauma. Typically, the medial rectus muscle and the ventral and ventral oblique extraocular muscles are the first to be avulsed, causing a prominent dorsolateral strabismus. Less favorable prognostic indicators for vision include a fixed and dilated pupil, which could mean that there is severe damage to either the ocular motor or optic nerves or the ciliary ganglion, and hyphema, which could indicate severe damage to the ciliary body.
Miosis is typically a good prognostic indicator, as this is a natural ocular response to trauma. That said, sometimes the prognostic indicators for vision are not as immediately reliable, due to the sympathetic response that ensues after trauma. Therefore, the indicators for return to vision are best determined one to two weeks after the incident.
Prior to globe replacement, the conjunctiva and conjunctival sac should be flushed thoroughly with diluted betadine solution to remove any debris. Also, copious amounts of sterile gels or ointments should be used to lather the globe to facilitate its replacement. A lateral canthotomy can be performed to provide exposure as well as release tension on the eyelids, and thus simplify globe replacement. Three or four temporary sutures should be preplaced in the upper and lower eyelid margins rostral to the meibomian gland openings (the white line). These temporary tarsorrhaphy sutures using 5-0 non-absorbable monofilament should be placed through or approximately1mm anterior to the meibomian gland openings at the eyelid margins using a simple interrupted or horizontal mattress suture pattern. The simple interrupted pattern is preferred as it provides more apposition than the horizontal mattress pattern, which is more likely to cause eversion of the tissue.
Once these are placed, a No. 11 Beaver blade handle is placed horizontally under the preplaced sutures, and with gentle upward motion and simultaneous downward pressure on the globe, the eyelids are pulled over the globe and the temporary tarsorrhaphy sutures are secured, ensuring that tight apposition of the eyelid margins is achieved to decrease iatrogenic trauma to the cornea.
Post-operatively, an oral steroidal anti-inflammatory is imperative to reduce the possibility of exophthalmos from retrobulbar swelling as well as periorbital, intraocular and optic nerve swelling. Additionally, topical and oral antibiotics are warranted if open wounds or ulcers are present. An Elizabethan collar and analgesics are also warranted in most cases. Removing the temporary tarsorrhaphy sutures is staged over the next four to six weeks.
Sequela to proptosis include lagophthalmos, which leads to exposure keratitis, keratoconjunctivitis sicca and corneal ulcerations. Other long-term sequela include blindness, strabismus, optic nerve degeneration, retinal detachment, retinal degeneration, uveitis/glaucoma and phthisis bulbi.
Corneal emergencies include full-thickness corneal lacerations, Descemetocoeles, and melting corneal ulcerations.
Full-thickness corneal lacerations are secondary to foreign bodies, cat scratches or other severe trauma. Corneal lacerations may seal themselves initially with the iris as a result of an iris prolapse or from a fibrin clot from within the eye. These initial seals are temporary in nature and, if not provided the appropriate surgical treatment, they tend to re-rupture.
The prognosis for return to vision following a corneal laceration is typically good with appropriate and timely treatment. Corneolimbal and especially scleral ruptures, however, have a poorer prognosis for a good visual outcome than do other corneal lacerations.
During initial examination, full thickness corneal foreign bodies may be shortened if necessary but not removed, as removal will cause the anterior chamber to deflate. Not only is uncontrolled deflation extremely painful, but it can also damage other intraocular structures. Additionally, it is very important to determine whether there is lens involvement during the initial exam of a corneal laceration, particularly when the laceration is the result of a full thickness foreign body or other trauma, usually a cat scratch.
Prompt medical attention is indicated for all corneal lacerations and particularly those involving lens capsule tears greater than 1.5mm. Such tears require lens extraction via phacoemulsification to prevent extensive phacoclastic uveitis that leads to painful glaucoma. Other concerns in these cases include bacterial translocation, which can lead to endophthalmitis, which may necessitate removal of the globe. Additional potential complications associated with corneal lacerations include cataract formation, chronic uveitis (the sequela of which could be anterior/posterior synechiation), blindness and phthisis bulbi.
Full-thickness corneal lacerations (sealed or not) should receive immediate aggressive medical treatment until they can be evaluated by a veterinary ophthalmologist. This treatment should consist of a topical mydriatic/cycloplegic (e.g., Atropine, to decrease the chance for posterior synechiation and help stabilize the blood ocular barrier while providing a cycloplegic effect); both topical and systemic antibiotics (with solutions being preferred over ointments for the topical antibiotics); an aggressive oral anti-inflammatory; an analgesic; and an Elizabethan collar.
Corneal lacerations of less than 2mm in diameter are able to be surgically repaired via direct suturing. Lacerations that exceed 2mm in diameter typically need to be grafted.
A Descemetocoele is a deep corneal ulceration that extends to the level of Descemet's membrane and should be considered a pending perforation. Descemet's membrane is hydrophobic, unlike the surrounding hydrophilic stroma. Thus, a Descemetocoele will present with a fluorescein positive rim and a clear, sometimes darkened center. In some cases, Descemet's membrane will bulge anteriorly due to the intraocular pressure and lack of supportive tissue to that area of the cornea.
A fibrin clot or iris will temporarily provide a seal in the event of a corneal perforation. However, these seals are fragile and thus care needs to be taken on examination. Seidel positive perforations with a collapsed anterior chamber need to be surgically treated as soon as possible. In these cases, a third eyelid flap is indicated to provide support until the patient can receive appropriate surgical treatment from a veterinary ophthalmologist.
Examining the unaffected eye might provide a clue as to the reason behind the corneal pathology in the affected eye.
On initial assessment, a culture and sensitivity of the affected region should be obtained and, if possible, a Gram stain assessed right away to ensure the appropriate antibiotic treatment, both topical and systemic. Atropine solution should be considered as a mydriatic, due to its cycloplegic effect. Systemic anti-inflammatories should also be considered to control secondary uveitis. This medical treatment should be administered promptly and aggressively until surgery can be performed. Thus, prompt referral to an ophthalmologist is indicated to ensure the best possible visual outcome for the patient.
Typically, grafting procedures are needed for corneal ruptures or Descemetocoeles. These grafts, either synthetic or autogenous, provide tectonic support to the cornea, and the materials that are used will integrate into the cornea, typically with minimal scarring (some less than others). For instance, a corneal conjunctival transposition transposes normal cornea into the defect and allows visual rehabilitation of the patient versus a conjunctival pedical graft that, although it will thin over time, will always have a level of prominent scarring. The advantage of autogenous grafting procedures over synthetic grafts is that they not only provide tectonic support but also angiogenic factors, which increase the healing rate and decrease further progression of the ulcer, due to their anti-collagenolytic properties.
Melting ulcers typically present as localized areas of gellatenous cornea and are extremely progressive and rupture can occur within the day. Pseudomonas aeroginosa and Beta-hemolytic Streptococcus species are the primary bacteria that will cause melting corneal ulcerations. That said, andogenous upregulation of lysozymes and other endogenous factors of the tear film can also precipitate corneal melting. Thus, in these cases, it is imperative to employ the use of anti-collagenolytic agents, serum being the most readily available, together with the aforementioned medical regime (as discussed above in relation to Descemetocoeles). The anti-collagenolytic agents can be combined for greater affect, for instance using serum every hour along with the prescribed systemic dose of Doxycycline.
Tectonic grafting should be considered in cases where the ulcers exceed 50% of the depth of the corneal stroma.
Anterior lens luxations are considered true emergencies and prompt removal of the anteriorly luxated lens is imperative if vision is to be saved.
Anterior lens luxations result from zonular dysplasia, buphthalmos due to chronic glaucoma, or from a chronic resorbing cataract, chronic uveitis (as in cats), or rarely, trauma.
Zonular dysplasia is an inherited defect of the suspensory apparatus or ciliary zonules of the lens. This defect most commonly occurs in dogs 3 to 6 years of age with a mean age of 4. The breeds most commonly associated with inherited zonular dysplasia include most Terriers and Terrier crosses (e.g., Jack Russell, Wirehair Fox, Sealyham), Healer breeds and Shar Pei.
At presentation, dogs with acute lens luxations will exhibit significant blepharospasm as a result of pain, and the cornea often will be significantly edematous, thus precluding adequate examination of the intraocular contents. Also, the intraocular pressure is typically extremely elevated, frequently greater than 80mmHg, due to the anteriorly displaced lens abutting the cornea. The anteriorly luxated lens is often not readily apparent. Therefore, understanding the breeds and signalment of these patients that are predisposed to anterior lens luxations is extremely important.
If it is unclear at initial examination whether an anterior lens luxation is present, it is critical that prostaglandin analogs, such as Latanoprost, not be used on the affected eye. Latanoprost is a very potent anti-glaucoma medication that is often used for emergency glaucoma treatment; however, Latanoprost causes miosis, which can incarcerate the lens in the anterior chamber, further exacerbating the pupillary block glaucoma that has occurred. Topical beta blockers, although often used with carbonic anhydrase inhibitors, can also cause miosis, albeit mild. Thus, they can be used initially, but should be used with caution.
It is more useful to administer intravenous Mannitol as the initial anti-glaucoma treatment. IV Mannitol dehydrates the vitreous, thus facilitating posterior displacement of the anterior uvea. Often, after administering IV Mannitol, the extent of the corneal edema will decrease with decreasing pressure, thus allowing better visualization of the anterior chamber and, therefore, a more accurate assessment of whether or not there is indeed an anterior lens luxation. Also, topical (Dorzolamide) and systemic (Methazolamide) carbonic anhydrase inhibitors can help control the intraocular pressure in these dogs. Alpha adrenergic agonists should be considered when a lens luxation is suspected or known because they can be effective in lowering pressure and also cause dilation, thus sometimes alleviating the effects of the pupillary block.
It is imperative for an anterior luxated lens to be removed as soon as possible if vision is to be saved. Prior to referral, systemic and topical anti-inflammatory medications are also indicated to decrease the uveitis that always accompanies these conditions.
Posteriorly luxated lenses, on the other hand, can be treated with a miotic, which sometimes facilitates retention of the luxated lens in the posterior segment. That said, evaluation by an ophthalmologist is indicated, and removal of the posterior luxated lens should be considered if intraocular pressure is elevated or if there is forward displacement of the anterior uvea.
With luxations, both anterior and posterior, in these breeds that are considered predisposed, evaluation of the fellow eye should also occur and cautioning the owners on limiting their dog's jumping is sound advice.
Regarding anterior lens luxations in cats, although prompt action is indicated, the condition often does not constitute a dire emergency, as it does in dogs, given that the anterior chamber in cats is far deeper and the iridocorneal angle in cats much wider. Also given the shape of the pupil, ellipsoid versus circular, a pupillary block is less apt to occur. For cats with anterior lens luxations, systemic blood work should be considered as should testing for infectious diseases, especially Feline Immunodeficiency Virus (FIV). FIV should be considered a rule out, given that it can cause a pars planitis, weakening the lenticular zonules and compromising lens stability.
Regarding ocular emergencies, your local or nearest veterinary ophthalmologist should be considered part of the emergency team to best help triage and treat patients with these ocular conditions. Consulting with a veterinary ophthalmologist will ensure and facilitate progressive veterinary care across the disciplines.