Online Photo Diagnosis

By William Townsend, OD, FAAO

Noninfectious Staphylococcal Marginal Keratitis
This 74-year-old patient presented to the VA Medical Center Eye Clinic complaining of bilateral mild-to-moderate ocular discomfort, which was more severe in the left eye. He had been treated previously with topical antibiotics for a "bacterial corneal ulcer." Visual acuities were 20/40– OD and OS. Biomicroscopy revealed severe bilateral blepharoconjunctivitis and meibomian gland dysfunction. Superficial corneal neovascularization extended 4mm to 5mm into both corneas, and corneal clarity was reduced on the visual axis OD and OS. In the left cornea, inferior to the visual axis was a 2mm by 3mm area of epithelial loss extending down to Bowman's layer.

We diagnosed this patient with staphylococcal marginal keratitis (SMK). This condition, once referred to as "catarrhal ulcer," is frequently associated with chronic blepharitis. The initial presentation is typically one or more focal, noninfectious subepithelial infiltrate(s) located in the 2 o'clock, 4 o'clock, 8 o'clock, and 10 o'clock positions of the peripheral cornea. Over time they often progress to a full-thickness sterile ulcer. A unique feature of SMK that is useful in differentiating it from corneal conditions that have a similar appearance is a clear zone of unaffected tissue separating the lesion(s) from the limbus.

This condition may be erroneously diagnosed as early herpes simplex keratitis; however, the latter typically presents initially as epithelial changes followed by the subsequent appearance of underlying infiltrates. In SMK, infiltrates precede the development of ulceration. Evaluating corneal sensitivity is useful in differentiating between these two conditions.

SMK may also be mistaken for phlyctenules, which present as focal, sterile infiltrates located on the bulbar conjunctiva, the limbus, or the cornea. Infiltrates associated with phlyctenulosis may break down overlying epithelium. These infiltrates stain with fluorescein. Phlyctenulosis was initially associated with type IV hypersensitivity to tuberculosis, but since has been linked to hypersensitivity to Staphylococci toxins, certain fungi, and to viruses.

In managing SMK, it is important to remember that this condition is not an infection but rather an inflammatory response to the presence of bacteria and their toxins on the lids and ocular surface. Therapy is directed toward two goals: initially reducing the levels of bacteria (and their byproducts) and moderating the immune response.

Lindsley et al (2012) reviewed 34 studies (2,169 participants) targeting blepharitis and found that topical antibiotics provided symptomatic relief and reduced the bacteria load on the eyelid margins. Topical steroids also provided some symptomatic relief. The authors reported that lid hygiene, including warm compresses and lid scrubs, provides symptomatic relief in blepharitis, but they concluded that none of the treatments cured chronic blepharitis. In treating SMK and accompanying blepharitis, it is important to advise patients that the condition is chronic and will probably require ongoing therapy. It is also important to monitor intraocular pressure, taper the steroids as soon as possible, and otherwise minimize the risk of steroid-associated side effects.

Lindsley et al (2012) reviewed 34 studies (2,169 participants) targeting blepharitis and found that topical antibiotics provided symptomatic relief and reduced the bacteria load on the eyelid margins. Topical steroids also provided some symptomatic relief. The authors reported that lid hygiene, including warm compresses and lid scrubs, provides symptomatic relief in blepharitis, but they concluded that none of the treatments cured chronic blepharitis. In treating SMK and accompanying blepharitis, it is important to advise patients that the condition is chronic and will probably require ongoing therapy. It is also important to monitor intraocular pressure, taper the steroids as soon as possible, and otherwise minimize the risk of steroid-associated side effects.

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