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FELINE CORNEAL SEQUESTRUM: CAUSES, TYPES AND TREATMENT.

In this article we are going to delve into the causes and treatment of corneal ulcers in cats. A most common types of corneal ulcer is defined as a loss of epithelium or stroma that may be severe enough to perforate the cornea. In felines, a superficial corneal ulcer should always be considered as it may have a herpetic origin (Feline Herpesvirus-1). The pathognomonic appearance of the corneal ulcer caused by the feline Herpesvirus is that defect in which dendritic ulcers are seen (tree-like appearance, see photo).

CORNEAL ULCERS IN CATS: DIAGNOSIS AND TREATMENT

Sometimes these herpetic ulcers can also manifest as flaking or geographic ulcers. It is important to keep in mind that herpetic ulcers primarily affect the epithelium, since the virus is epitheliotropic.

When there is a progression of the corneal ulcer in cats towards the corneal stroma, we must consider the possible colonization by bacteria or perhaps the persistence of the inciting cause (such as the presence of a foreign body).

Another cause of corneal ulcers in cats is due to collagenase (keratomalacia): caused by an imbalance in the production and destruction of metalloproteinases in the cornea.

There are other causes of corneal ulcer: such as those caused by tear problems (both quantitative and qualitative), entropion, foreign bodies and neurological problems that involve a loss of corneal sensitivity or a loss of blinking. A good examination of the eyelids, the tear film and the conjunctival sac should always be carried out in case there is any foreign body. 

PDA L-R diagnosis of corneal ulcers caused by feline Herpesvirus-1 can become complicated when no dendritic ulcers are present. It is possible to take samples from the ulcerated area to perform a PCR, but many of these results can give false negatives.

Treatment of corneal ulcers

Regarding the treatment of these herpetic ulcers, we have the option of giving both topical (for example, ganciclovir) and systemic (for example, famciclovir) antivirals in combination with antibiotic treatment.

We aim corneal cytology and culture they are of great help for choosing the antibiotic and avoiding the appearance/increase of resistance. Although it has been suggested in the literature that topical anesthesia can affect bacterial growth in culture, recent articles suggest that a cytological sample can be taken after instilling topical anesthesia, since an effect on bacterial growth results has not been demonstrated. . ATTENTION!: Sampling a fragile cornea should be done with extreme care as there is a risk of perforation.

Both Gram + bacteria (Sthaphylococcus spp, Streptococcus spp) like Gram – (Pseudomonas spp) have been cultured in cases of septic keratitis in the recent literature. The role of Mycoplasma in corneal ulcers has also been reported in one study.

Antibiotic treatment

Initial antibiotic treatment should be based on the cytological result and then adapted to the culture result. The presence of cocci should lead us to choose a chloramphenicol or a triple antibiotic (polymyxin B, neomycin, gramicidin) and the presence of bacilli, to a fluoroquinolone or an aminoglycoside. The use of autologous or heterologous serum would also be indicated when keratomalacia is present. Relatively recent studies also report the use of the cross-linking technique to strengthen the bridges between collagen fibers and reduce the bacterial/fungal load in these cases of keratomalacia. We should also include the use of a topical cyclopegic treatment (for example, atropine or cyclopentolate) to control reflex uveitis.

An untreated corneal ulcer can lead to perforation and require surgical treatment.

From Panacea Vet we always recommend remembering that, as a general rule, an uncomplicated ulcer should heal in about 3-5 days. When the ulcer persists over time, it is necessary to ask whether the inciting cause is still present (for example, a foreign body or an entropion) or that there is a bacterial/fungal infection that current treatment does not cover. Performing routine cytology and corneal culture, but especially in ulcers that do not heal as expected, can provide us with invaluable information at the level of establishing the appropriate treatment, thus trying to avoid the creation of resistance. When we suspect the presence of a herpetic ulcer but do not have pathognomonic evidence of dendritic ulcers, we can start treatment with antivirals without taking samples for PCR, due to possible false negatives. In these cases, the response to treatment itself can be our diagnostic test.

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BIBLIOGRAPHY

  1. Edwards SG, Maggs DJ, Byrne BA, et al. Effect of topical application of 0.5% proparacaine on corneal culture results from 33 dogs, 12 cats, and 19 horses with spontaneously arising ulcerative keratitis. Veterinary Ophthalmology; 2019: 415-422
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