What is nummular epithelial keratitis?

Nummular Epithelial Keratitis: Definition and Clinical Significance

Nummular epithelial keratitis refers to a pattern of corneal inflammation characterized by round to oval, coin-shaped (nummular) lesions confined to the corneal epithelium, most commonly associated with viral infections (particularly adenovirus and herpes simplex virus), but also seen with microsporidial and occasionally fungal infections. 1

Anatomic and Clinical Characteristics

Epithelial keratitis is confined to the corneal epithelium, presenting as punctate defects, dendritic ulcers, or geographic epithelial erosions that are visible with fluorescein staining. 1 The nummular pattern specifically describes:

• Raised, coarse, punctate, multifocal, round to oval, greyish-white corneal epithelial lesions that typically evolve into nummular scars before resolution 2
• Multiple round stromal infiltrates that can appear bilaterally in some cases 3
• Subepithelial infiltrates that may develop as sequelae, particularly in adenoviral infections 4

Common Etiologies

The nummular pattern is NOT a single disease entity but rather a morphologic presentation of various corneal infections: 5

Viral Causes

• Adenoviral keratoconjunctivitis is the most common cause, presenting with nummular subepithelial corneal infiltrates and follicular conjunctivitis 4
• Herpes simplex virus (HSV) can produce nummular opacities representing resolved herpetic eye disease 6
• HSV epithelial keratitis is treated primarily with topical or oral antivirals 1

Parasitic Causes

• Microsporidial keratoconjunctivitis (MKC) characteristically presents with nummular epithelial lesions accompanied by mild-moderate non-purulent conjunctivitis with mixed papillary-follicular reaction 2
• Acanthamoeba can complicate adenoviral keratoconjunctivitis when epithelial breach allows inoculation 4

Fungal Causes (Rare)

• Candida keratitis can rarely present bilaterally in a nummular pattern, though this is uncommon and typically occurs with other risk factors 3

Critical Diagnostic Pitfall

The major clinical trap is assuming all nummular keratitis is viral and empirically treating with topical steroids, which can worsen fungal, Acanthamoeba, or bacterial infections. 3 When nummular keratitis fails to improve with standard therapy:

• Obtain corneal cultures for bacteria, fungi, Acanthamoeba, and viral testing 4
• Avoid topical steroids until infectious etiologies (particularly fungal and Acanthamoeba) are excluded 3
• Consider that epithelial keratitis can progress to stromal involvement if untreated 1

Documentation Requirements

When documenting nummular epithelial keratitis, the American Academy of Ophthalmology recommends: 7

• Location (central, peripheral, inferior, perineural)
• Size in millimeters (infiltrates ≥2 mm are considered large and clinically significant)
• Depth (superficial epithelial versus stromal involvement)
• Density and shape (light, moderate, or dense; distinctive patterns)
• Epithelial defect size and shape with fluorescein staining

Prognosis and Complications

Epithelial keratitis is generally self-limited if treated appropriately, but carries risk of progression. 1 Potential complications include:

• Progression to stromal keratitis with permanent corneal scarring, neovascularization, thinning, and perforation 1
• Reactivation of herpetic disease can occur with trauma or procedures 6
• Misdiagnosis leading to inappropriate steroid use can worsen fungal or parasitic infections 3