The Morphology of Thygeson’s Superficial Punctate Keratitis Lesions
Thygeson’s Superficial Punctate Keratitis affects cells that lie within the intraepithelial region of the cornea. At an individual level, each entity is small, round, light reflecting cells around 10-15 μm in diameter). The disease can present itself as a single cell entity or cells clustered in small groups or they can aggregate into lesions that are conspicuous when viewed with a slit-lamp (in excess of 400 μm in diameter). The shapes of the lesions can appear as a mass collection or interlaced with other cellular debris. It is not clear if the disease represents invading inflammatory cells or damaged epithelial cells.
While superficially located, the abnormal cells appear rounded. The depth of the abnormal cells is difficult to estimate, but they do not have any stromal involvement, which suggests an intraepithelial location. In mild cases, subepithelial opacities develop as a haze lacking abnormal cells. As the disease develops, there can be round abnormal cells found between larger lesions and outside larger concentrations of cells. Where the tear film is stained with Fluorescein Sodium, dark areas are visible due to small groups of cells concentrated together creating elevated areas on the corneal surface caused either by swelling of the epithelial cells or the presence of other cell matter or from inflammatory cells.
Fluorescein shows up focal surface damage as bright green dots in the light reflecting areas of the eye’s surface. Damaged surface cells that reflect gray or white develop later within the lesions. There is no loss of surface epithelium by Thygeson’s SPK. Rose Bengal will stain damaged surface cells red or adherent Fluorescein will stain yellow. Outside the lesions, the epithelial surface is well preserved without any staining.
Epithelial cysts with some round cells occur occasionally among TSPK patients. Some atypical cases show the presence of abnormal rounded cells and could be a variant of TSPK where the pattern of lesions is not the same as typical Thygeson’s SPK patients, which can be confused with an HSV infection.
Typical features include chronic, recurring flaring up of the disease. It is often misdiagnosed as a form of Adenovirus infection, the effect of the keratitis being sensitive to topical steroids only to flare up after treatment, the presence of lesions without symptoms, and no permanent damage or sequelae affecting sight after twenty years of having the disease.
Many patients had corneal lesions even after treatment with a weak steroid solution.
Reference: Adenovirus Epithelial Keratitis and Thygeson’s Superficial Punctate Keratitis : In Vivo Morphology in the Human Cornea By Helena M. Tabery