Main

Sir,

Epithelial basement membrane dystrophy (EBMD) is an important cause of intermittent epithelial breakdown leading to blurred vision, foreign body sensation, recurrent erosions or contact lens intolerance.1,2 The lesions, best seen in retroillumination, may be missed.3 Corneal valance, a sign described by Shahinian,3 can alert the examiner to the presence of EBMD and may occur even when other signs of the dystrophy are barely visible. Shahinian's sign is a ‘scalloped line of tear film thinning’ that typically runs horizontally across the top third of the cornea.3

Case report

A 64-year-old man presented with a 10-day history of blurred vision and glare in the right eye. There was no pain. He had no previous ocular history, was in good health and took no medications. Visual acuity was 6/6 OU. Slit-lamp examination revealed subtle dot and map-like patterns in the right superior cornea and similar, but less distinct, changes on the left (Figure 1). With topical fluorescein, corneal valance was seen on the right side (Figure 2). Nonpreserved lubricants were prescribed. After 1 month, the patient's right vision remained blurred and the corneal findings, including Shahinian's sign, remained unchanged.

Figure 1
figure 1

Dot and map-like lines in the right superior cornea.

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Figure 2
figure 2

Shahinian's sign in the top third of the right cornea seen with fluorescein and cobalt blue light.

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Comment

EBMD, also known as map–dot–fingerprint or Cogan's dystrophy, is characterised by map-like, geographic, and/or dot patterns and fingerprint lines in the corneal epithelium that can change in appearance, location and number over time.2,4 It is the most prevalent corneal dystrophy,5 and responsible for over one-fifth of the cases of recurrent erosion.6 Sometimes, such as our case, there is visual disturbance without pain.7

On histological examination, small intraepithelial cysts containing PAS-positive cytoplasmic debri and pycnotic nuclei1,2,4 along with abnormal quantities of multilaminar basement membrane are seen.2,8 The hemidesmosomes, between the basement membrane and basal epithelial cells, may be reduced or absent.9

Corneal valance (Shahinian's sign), a scalloped horizontal line of tear film thinning,3 is seen on slit-lamp examination with topical fluorescein and cobalt blue light typically in the top third of the cornea (Figure 2). The tear film thinning is accentuated by fluorescein pooling at its margins. The sign was termed ‘corneal valance’ by Shahinian as it resembled a valanced drapery.3 It occurs in areas of the map and fingerprint lines of EBMD. In recurrent erosion, it is particularly useful as it can alert the examiner to EBMD and thus allow more accurate prognostic counselling and better treatment.3

Tear film thinning seen as corneal valance in EBMD is thought to be because of minute epithelial irregularities, produced by the cysts and excess basement membrane material, increasing the rate of lipid contamination of the tear film's mucin layer.2,3,10 Other tear film abnormalities described in EBMD include a reduced tear film, rapid tear breakup, dry areas over fingerprint lines, negative fluorescein staining outlining the areas of dot and map patterns, and increased tear film debris.2,4,8,11,12 Tear film irregularities produce visual disturbance as a smooth optical surface is lost.1

In our case, painless visual disturbance, map and dot changes, and corneal valance were present (Figures 1 and 2) and a diagnosis of EBMD was made. In patients where the signs of EBMD are subtle or those presenting with painless visual disturbance corneal valance (Shahinian's sign) may be a useful sign, as it can alert the examiner to the presence of EBMD.3