Herpes simplex virus (HSV) is a DNA virus commonly affecting the mouth, genitals and eyes in humans. HSV keratitis is a leading cause of corneal blindness in the developed countries.[1]. Clinically the commonest form encountered is ‘Epithelial Keratitis’ which may present as simple superficial punctate erosion (SPE’s), dendritic ulcer, or larger geographic ulcer [2]. Diagnosis is often clinical and treatment is simple. The virus however, is notorious to establish latency and recur even after successful treatment with antiviral agents. [3,4]. Also in some cases the presentation may be atypical, delaying the diagnosis and appropriate treatment, and may lead to visual morbidity. In this case we present a peculiar, brown-pigmented subepithelial corneal plaque, in an otherwise quiet eye, which developed a superimposed dendritic ulcer within the pigmented plaque, following uneventful cataract surgery.

A 54-year-old housewife presented to our Cornea Clinic with chief complaints of diminution of vision in the right eye for 2 years. The best-corrected Visual acuity (VA) was Finger Counting at 2 metres. There was no history of trauma, previous ocular surgery, or systemic disorders.

The slit-lamp examination revealed an unusual, brown coloured, band-shaped plaque in the interpalpebral cornea, extending horizontally from limbus to limbus, measuring 12mm x 5 mm, with well-defined margins and a smooth surface. [figure 1a] The plaque was subepithelial, with an intact overlying epithelium, as was noted after the initial scraping.

A grade 3 nuclear sclerosis cataract was also noted in the right eye.

The remaining anterior and posterior segment evaluation was within normal limits.

The lesion was scraped with a 15 no. blade for microbiological assessment. KOH mount, Gram stain, and Giemsa stain came back negative for fungus and bacteria. Blood agar and Sabouraud dextrose agar showed no growth at end of 2 weeks. PCR could not be done due to financial constraints.

As the eye was unremarkable except for the pigmented plaque, the patient was advised cataract surgery for that eye. The surgery was uneventful.

In this particular case, a literature review done to find an etiology for the peculiar pigmented plaque did not yield any tangible results. A working hypothesis of iron/ferritin pigment deposition due to the accumulation of tear-film over an irregular ocular surface was made.

Iron is present extracellularly in the tear film on the surface of the cornea. It is carried by lactoferrin which is secreted by acinar epithelial cells in the lacrimal gland. In the tears, more than 90% of lactoferrin is not bound to iron and is available as a chelator and performs anti-oxidative and anti-microbial functions. [5,6].

Excess iron deposition leading to brownish corneal iron lines is observed in many conditions such as Fleischer's Ring in keratoconus, Stocker's Line in a pterygium, Ferry's Line anterior to a filtering trabeculectomy bleb, and the Hudson Stahli line seen as an age-related iron deposition.

Various hypotheses have been put forth to explain the pathophysiology of iron deposition.[7]. These include; Tear Pooling Hypothesis (Gass 1964), Basal-Cell-Migration theory (Rose and Lavin 1987), Tear Desiccation hypothesis (Assil 1993), Senescent basal cell hypothesis (Assil in 1993).

Assil proposed that iron deposition occurs in the areas of tear desiccation, rather than in areas of pooling, and evaporation of the tears increases the relative concentration of iron.[8]. Iron lines typically exist in the basal epithelial cells of the cornea (similar in location to the pigmented plaque seen in our case), and electron microscopy of these lines, demonstrates abundant ferritin.[9].

Figure 1: (a) Brown pigmented corneal subepithelial plaque with intact overlying epithelium noted in the interpalpebral area, in a phakic eye at first visit. (b) Dendritiform ulcer developed 2 weeks after an uneventful cataract surgery that responded to topical antivirals.

Figure 2: Dendritic ulcer staining with 2% fluorescein and rose Bengal dye