Thursday, December 23, 2010

Bacterial Conjunctivitis

Patients with bacterial conjunctival infections present with injection of the bulbar conjunctiva, episcleral vessels and perhaps papillae of the palpebral conjunctiva. The infection often starts in one eye, then soon spreads to the other. There will be thick mucopurulent discharge, and patients usually say that their eyelids and eyelashes are matted shut upon awakening. There may be mild photophobia and discomfort, but usually no pain. Visual function is normal in most cases.

The eye has a battery of defenses to prevent bacterial invasion. These include bacteriostatic lysozymes and immunoglobulins in the tear film, the shearing force of the blink, the immune system in general, and non-pathogenic bacteria that colonize the eye and compete against external organisms that try to enter. When any of these defense mechanisms break down, pathogenic bacterial infection is possible.

Invading bacteria, and the exotoxins they produce, are considered foreign antigens. This induces an antigen-antibody immune reaction and subsequently causes inflammation. In a normal, healthy person the eye will fight to return to homeostasis, and the bacteria will eventually be eradicated. However, an extra heavy load of external organisms can be too difficult to fight off, causing a conjunctival infection and setting the eye up for potential corneal infection.

The most commonly encountered organisms are Staphylococcus aureus, Haemophilus influenzae, Streptococcus pneumoniae and Pseudomonas aeruginosa. In cases of hyperacute bacterial conjunctivitis, the patient will present with similar signs and symptoms, albeit much more severe. The most common infectious organisms in hyperacute conjunctivitis are Neisseria gonorrhoeae and Corynebacterium diptheroides. There is more danger in hyperacute bacterial conjunctivitis as these organisms can penetrate an intact cornea.

Ordering cultures and sensitivity tests is ideal for diagnosis but usually impractical and expensive. Most clinicians immediately begin treatment with a broad spectrum antibiotic and reserve culturing for hyperacute conditions or those that fail to respond to the initial therapy.

There are many antibacterial options. Excellent initial broad spectrum antibiotics include Polytrim (polymixin B sulfate and trimethoprim sulfate), gentamicin 0.3%, and tobramycin 0.3%. These will give good coverage of gram-positive and gram-negative organisms, though the aminoglycosides (gentamicin and tobramycin) have weak activity against Staphylococcal species; there are also resistant strains of Pseudomonas. Fluoroquinolones such as Ciloxan, Ocuflox and Chibroxin are also excellent options. Therapy should be aggressive, with administration from QID to Q1H for the first few days.

Although antibiotics will eradicate the bacteria, they will do nothing to suppress the concurrent inflammation. If there is no significant corneal disruption, prescribe a steroid such as Pred Forte, Vexol or Flarex along with your antibiotic of choice, or a steroid-antibiotic combination such as Maxitrol (neomycin, polymyxin B, dexamethasone 0.1%), Pred-G (gentamicin 0.3%, prednisolone acetate 0.1%), or Tobradex (tobramycin 0.3%, dexamethasone 0.1%).


Like patients with bacterial conjunctivitis, those suffering from viral and allergic conjunctivitis will often report that their lids are matted shut in the morning with mucopurulent material. However, these patients actually have crusting of the lashes due to drying of tears and serous secretions, not the wet, sticky, mucopurulent matting characteristic of bacterial conjunctivitis. Too often, clinicians will consider the crusting of the lashes to be the same as the mucopurulent matting and misdiagnose the condition.
Remember, due to the excellent defense systems of the eye, acute bacterial conjunctivitis is uncommon.

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