Cornea infections

Hobden, J.A., et al. 1989. Tobramycin iontophoresis into corneas infected with drug-resistant... 

Plate 1 Inflammation of the cornea caused by severe bacterial infection, in this case, Pseudomonas. 

The five layers of the cornea contain no blood vessels but are nourished by tears, oxygen, and aqueous humor. Minor corneal abrasions heal quickly. Moderate abrasions take 24 to 72 hours to heal. Deep scratches may scar the cornea and require corneal transplant if vision is impaired. Do not use eye patches to treat corneal abrasion, as they decrease oxygen delivery, increase pain, and increase the chance of infection.3... 

Bacterial keratitis is a broad term for a bacterial infection of the cornea. This includes corneal ulcers and corneal abscesses. The cornea in a healthy eye has natural resistance to infection, making bacterial keratitis rare. However, many factors predispose a patient to bacterial infection by compromising the defense mechanisms of the eye (Table 60-5).19... 

M. D. Trousdale, R. Nobrega, D. Stevenson, T. Nakamura, P. M. dos Santos, L. LaBree, and P. J. McDonnell. Role of adenovirus type 5 early region 3 in the pathogenesis of ocular disease and cell culture infection. Cornea 14 280-289... 

Inflammatory conditions Treatment of steroid-responsive inflammatory conditions of the palpebral and bulbar conjunctiva, lid, sclera, cornea, and anterior segment of the globe, such as Allergic conjunctivitis acne rosacea superficial punctate keratitis herpes zoster keratitis iritis cyclitis and selected infective conjunctivitis (when the inherent hazard of steroid use is accepted to obtain an advisable diminution in edema and inflammation [prednisolone]) vernal conjunctivitis episcleritis epinephrine sensitivity and anterior uveitis. 

Acute epithelial herpes simplex keratitis (dendritic keratitis) fungal diseases of ocular structures vaccinia, varicella and most other viral diseases of the cornea and conjunctiva ocular tuberculosis hypersensitivity after uncomplicated removal of a superficial corneal foreign body mycobacterial eye infection acute, purulent, untreated eye infections that may be masked or enhanced by the presence of steroids. 

Infections Treatment of superficial ocular infections involving the conjunctiva or cornea (eg, conjunctivitis, keratitis, keratoconjunctivitis, corneal ulcers, blepharitis, blepharoconjunctivitis, acute meibomianitis, dacryocystitis) caused by strains of microorganisms susceptible to antibiotics. 

The topical ophthalmic antiviral preparations appear to interfere with viral reproduction by altering DNA synthesis. Trifluridine is effective treatment for herpes simplex infections of the conjunctiva and cornea. Ganciclovir is indicated for use in immunocompromised patients with cytomegalovirus (CMV) retinitis and for prevention of CMV retinitis in transplant patients. Foscarnet is indicated for use only in AIDS patients with CMV retinitis. 

Efficacy In other conditions The clinical efficacy in the treatment of stromal keratitis and uveitis caused by herpes simplex or ophthalmic infections caused by vaccinia virus and adenovirus, or in the prophylaxis of herpes simplex virus keratoconjunctivitis and epithelial keratitis has not been established by well-controlled clinical trials. Not effective against bacterial, fungal, or chlamydial infections of the cornea or trophic lesions. 

Infections of the external eye (the eyelids and conjunctiva or cornea) conjunctivitis, keratitis, corneal ulcer are distinguished from intra-ocular infections. The latter include infection of the vitreous (endoph-talmitis), uveitis and retinitis. Orbital and periorbital infections are often due to complications of sinusitis. 

Only solutions of lipophilic antibiotics are able to cross the external barrier of the cornea (drops) and the internal blood-retina barrier (systemic administration) to yield sufficient concentrations in the internal eye (vitreous). Keratitis and ulceration of the cornea can be treated by frequent administration of highly concentrated (fortified) antibiotic drops. In endophtalmitis, emergency vitreous aspirate and in-travitreal and subconjunctival injection of antibiotic solutions with a long half-life is the cornerstone of treatment. These solutions should be prepared by the hospital pharmacy. Empiric topical treatment of minor external eye infections consists of antibiotic containing gels or ointments. 

Herpes simplex virus ocular infections-. Ophthalmic 1 drop onto cornea q2h while awake. Maximum 9 drops/day. Continue until corneal ulcer has completely reepithe-lialized then, 1 drop q4h while awake (minimum 5 drops/day) for an additional 7 days. 

It is used systemically in enteric infections caused by gram negative organisms and topically for pseudomonal infections of conjunctiva and cornea, bums and skin. 

A 47-year-old woman undergoing face peeling with 35% trichloroacetic acid developed left eye burning sensation, excessive tearing, marked conjunctival injection, conjunctival infection, and mild inferior superficial punctuate keratitis involving 25% of the cornea [32],... 

The third patient developed the infection after 1 month the keratitis cleared on withdrawal of latanoprost and antiviral therapy reinstitution of latanoprost with prophylactic antiviral medication (valaciclovir) kept the cornea clear, but as soon as the antiviral drug was discontinued, //. simplex virus keratitis reappeared. 

Fujihara, T. and Hayashi, K. 1995. Lactoferrin inhibits herpes simplex virus type-1 (HSV-1) infection to mouse cornea. Arch. Virol. 140, 1469-1472. 

The toxicity associated with SM is quite profound. The Army s Chemical Defense Equipment Process Action Team estimated in 1994 that a 900 mg-min/m SM vapor exposure would be lethal in 2-10 min, based on animal studies (National Research Council Review, 1997). Fortunately, in the battlefield, lethality has been limited. Only 1-3% of exposed soldiers died from SM exposure after WWI, and mortality mostly was not a direct consequence of SM, but rather the indirect effect of secondary respiratory infections. The 1999 Material Safety Data Sheet, put out by the US Army Soldier and Biological Chemical Command, USA Edgewood Chemical Biological Center, has estimated the LD50 of a skin exposure to sullur mustard as lOOmg/kg. This roughly translates into as little as 7 ml of neat SM (i.e. 8.9 g) spread over the skin resulting in the death of a 80 kg adult (Department of the Army, MSDS, 1999). The cornea, of course, is more sensitive than the skin. Below we review three chief toxic effects of severe SM exposure to the cornea. 

Gram-negative cocci that cause infections include Neisseria gonorrhoeae, which causes gonorrhea. Aetoena gonorrhoeae initially causes hyperpurulent conjunctivitis but can quickly invade the cornea and the rest of the eye. 

Ocular polymyxin B is commercially available in combination with other antibiotics (see Table 11-6) or with steroids (seeTable 11-7) to treat infections of the lids and conjunctiva. It is also used to prevent infection when the conjunctiva or cornea is compromised or when a steroid is used. 

Itraconazole Topical 1% suspension 1 drop qlh Oral 200 mg PO qd-bid Topical not effective for severe infections, penetrates cornea poorly not commercially available must be compounded Penetrates all eye tissues poorly with oral administration Side effects include hepatotoxicity, gastrointestinal problems, hypokalemia, elevated Uver enzymes, rash, vasculitis, headache, fever, HTN, hypertriglyceridemia Many drug interactions exist including CYP3A4 substrates. Coadministration of itraconazole is contraindicated with multiple antiretrovirals (refer to Table 11-12) Pregnancy category C lactation safety unknown... 

Sotozono C, Inagaki K, Fujita A, et al. Methicillin-resistant Staphylococcus aureus and methicillin-resistant Staphylococcus epidermidis infections in the cornea. Cornea 2002 21 S94-S101. 

Microbiologic culture studies are useful fc>r bacterial identification, especially when an ocular infection foils to respond to treatment. Cultures are often obtained from the eyelids, the conjimctiva, expressed material from the lacrimal sac, and the cornea. Because preserved ophthalmic anesthetics have a bacteriostatic effect, cultures should be obtained if possible before anesthetic instillation. In the case of corneal sampling, it is necessary to provide topical anesthesia for patient comfort. The anesthetic of choice is 0.5% proparacaine because it causes the least bacterial growth inhibition. To enhance the bacterial yield, sterile preservative-free anesthetic may be used. Samples obtained may be inoculated directly onto soUd media plates (e.g., blood agar). Amies without charcoal transport medium (e g., BBL CultureSwab Plus) appears to be an acceptable alternative to direct plating and has the added benefit of convenience. 

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