Chapter 5 Cornea
The cornea is a vital part of the eye. Lesions of the cornea are often readily obvious to pet owners, because these lesions may be easily observed and frequently manifest as painful conditions for the animal. The transmission and refraction of light in the eye require that the cornea be transparent; any pathologic problem that affects corneal transparency can significantly reduce vision. Some corneal lesions (notably ulceration) can affect the integrity of the entire eye. For these reasons corneal diseases are a very important part of veterinary ophthalmology. Corneal ulcers, from superficial to deep, are illustrated in this chapter. Other conditions that affect the cornea, such as eosinophilic keratitis and sequestra in cats, pannus and corneal dystrophies in dogs, and mass lesions in the cornea, are also illustrated here.
Figure 5-32 Descemetocele in a dog. The base of the ulcer looks black because the image appears against the dark iris. If the photograph had been taken against the tapetal reflex, the image would have resembled Figure 5-33. Corneal neovascularization is present.
Figure 5-37 Chronic keratoconjunctivitis sicca (KCS) with healing deep corneal ulcer (see staining pattern in Figure 5-38).
Figure 5-1 Superficial corneal opacification in the interpalpebral fissure region in a puppy. This finding is normal in young puppies after the eyelids have opened. The cornea becomes normal as the dog ages.
Figure 5-2 Normal superficial corneal opacification in the interpalpebral fissure region in a 5-week-old golden retriever. The opacity clears as a dog ages.
Figure 5-5 Yorkshire terrier with bilateral superficial ulcers stained with fluorescein dye 24 hours after cataract surgery. The eyes dried after surgery, which resulted in the ulceration.
Figure 5-6 Superficial corneal ulcer in a cat. The ulcer resulted from corneal drying while the cat was under general anesthesia without corneal lubrication or moistening.
Figure 5-7 Lower eyelid entropion in a domestic shorthair cat, which resulted in a chronic corneal ulcer and neovascularization.
Figure 5-9 Nonhealing (refractory, indolent) corneal ulcer with neovascularization. Note tag of epithelium in ulcerated area. Nonhealing corneal ulcers are seen in eyes with basement membrane defects. Superficial corneal ulcers do not heal because migrating epithelium does not adhere to the basement membrane.
(Courtesy Dr. Robert Playter.)
Figure 5-10 Superficial nonhealing corneal ulcer in a cat. Note the loose edges of epithelium (arrows).
Figure 5-11 Nonhealing superficial ulcer stained with flourescein dye. Note the tags of epithelium across the ulcer and the stain beyond the edges of the ulcer.
(Courtesy Dr. Robert Playter.)
Figure 5-12 Nonhealing superficial corneal ulcer that had been present for several weeks in this boxer. The ulcer is stained with fluorescein dye. Note the lack of corneal vascularization and the lip of epithelium at the edge of the ulcer, which is underrun by fluorescein.
Figure 5-13 Nonhealing corneal ulcer stained with fluorescein and photographed under a blue light. Note the stain that is migrating beyond the edges of the ulcer.
Figure 5-14 Nonhealing superficial ulcer. Note the loose tags of epithelium at the edge of the ulcer.
Figure 5-17 Dendritic ulcer (a thin, meandering, often arborizing epithelial defect) in the cornea of a cat with herpesvirus infection.
Figure 5-20 Feline herpesvirus keratitis. Corneal ulceration, edema, and vascularization are present.
Figure 5-21 Nonhealing corneal ulcer in a cat that tested positive for herpesvirus. Iris atrophy and increased pigmentation are present.
Figure 5-22 Herpesvirus keratitis stained with rose bengal in a cat. Faint, linear, red-stained lesions can be seen.
Figure 5-24 Corneal scarring in a cat undergoing treatment with trifluridine and oral lysine for herpesvirus infection.
Figure 5-25 Bilateral eosinophilic and herpesvirus keratoconjunctivitis in a cat. Cellular infiltration is present in the cornea with mixed inflammatory cell populations with high eosinophil numbers.
Figure 5-26 Neovascularization and cellular infiltrate in the cornea and nictitans of a cat with eosinophilic keratitis.
Figure 5-28 Herpesvirus keratitis and eosinophilic keratitis. This cat was being treated with topical trifluridine and corticosteroids.
Figure 5-29 Eosinophilic keratitis and blepharitis in a cat with a positive result on polymerase chain reaction testing for herpesvirus infection. Lesions responded to topical trifluridine and dexamethasone.
Figure 5-30 Deep corneal ulcer resulting from Candida species infection. “Red eye,” corneal edema, hypopyon, and anterior synechiae at the 6- to 8-o’clock position are present.
Figure 5-31 Melting corneal ulcer secondary to a bite from a copperhead snake to the upper eyelid, which penetrated, but did not perforate, the cornea.