What is the difference between stromal keratitis and epithelial keratitis?

Difference Between Stromal and Epithelial Keratitis

Epithelial keratitis affects the outermost corneal layer with superficial involvement, while stromal keratitis involves deeper corneal tissue with inflammatory infiltration and edema that can lead to scarring and vision loss.

Anatomic Location and Depth

• Epithelial keratitis is confined to the corneal epithelium (the outermost layer), presenting as punctate defects, dendritic ulcers, or geographic epithelial erosions 1
• Stromal keratitis involves the deeper corneal stroma beneath the epithelium, characterized by infiltrates, edema, and white cell infiltration in the stromal tissue 1
• Confocal microscopy can image both layers distinctly, showing epithelial versus stromal bullae to help determine depth of involvement 1

Clinical Appearance and Characteristics

Epithelial Keratitis Features:

• Superficial punctate keratopathy or dendritic/geographic ulcerations 1
• Epithelial defects visible with fluorescein staining 1
• Generally less dense infiltration compared to stromal disease 2
• May present with pleomorphic or excavated patterns in HSV epithelial disease 1

Stromal Keratitis Features:

• Suppurative stromal infiltrates with indistinct edges, particularly those >1mm in size 1
• Dense white cell infiltration in surrounding stroma with edema 1
• May present as disciform keratitis, ring infiltrates, or diffuse stromal inflammation 3
• Stromal thinning, neovascularization, and scarring can occur 1
• Endothelial involvement with keratic precipitates or endothelial plaque may be present 1

Pathophysiology

• Epithelial keratitis typically results from direct viral cytopathic effects (HSV, VZV, adenovirus) or superficial bacterial/parasitic infection 1, 2
• Stromal keratitis is often immunologically mediated, representing a hypersensitivity response to viral antigens or active deep infection 4, 5
• Stromal disease can be infectious (bacterial, fungal, Acanthamoeba) or noninfectious (immune-mediated from prior viral infection, autoimmune disease) 1

Sequelae and Complications

Epithelial Keratitis:

• Generally self-limited if treated appropriately 1
• Can progress to stromal involvement if untreated 6
• Risk of bacterial superinfection with larger epithelial defects 1

Stromal Keratitis:

• More severe visual consequences including permanent corneal scarring, neovascularization, thinning, and perforation 1
• Progressive vision impairment with recurrent episodes 5
• May require penetrating keratoplasty in severe cases 7
• Anterior chamber inflammation with hypopyon in bacterial stromal keratitis 1

Treatment Implications

• Epithelial keratitis from HSV is treated primarily with topical or oral antivirals 1
• Stromal keratitis often requires topical corticosteroids in addition to antimicrobial therapy (except in fungal, Acanthamoeba, or Nocardia infections where steroids are contraindicated) 7, 4, 5
• Bacterial stromal keratitis requires aggressive broad-spectrum antibiotics with cultures obtained for central, large, or treatment-resistant cases 1

Critical Pitfall

The most important clinical distinction is recognizing that stromal involvement requires different management than purely epithelial disease—particularly the judicious use of corticosteroids in immune-mediated stromal keratitis versus their absolute contraindication in fungal stromal disease 7, 4. Misdiagnosis can lead to devastating complications including corneal perforation and vision loss 1, 6.