26 - Corneal Infiltrative Events

Abstract

Keratitis refers to inflammation of the cornea. From the perspective of the aetiology and pathology of contact lens–associated keratitis, it is possible to characterise a condition as being either sterile (non-infectious) or microbial (infectious). However, the difficulty with this approach is that from a clinical perspective, it is virtually impossible to distinguish between the two in the early stages of the disease. To complicate matters further, it has been suggested that sterile keratitis can be classified into four sub-groups – the so-called contact lens peripheral ulcer, contact lens–associated red eye, infiltrative keratitis and asymptomatic infiltrative keratitis. Subsequent research has shown that these entities cannot be readily differentiated. This approach has now been largely abandoned, in favour of considering all corneal infiltrative events – from the mildest symptomatic infiltrate to severe microbial keratitis – as a potential disease continuum, and to treat less severe events with caution, as possible precursors to microbial keratitis. From an aetiological perspective, contact lens–associated corneal infiltrative events can result from a variety of mechanisms, such as solution toxicity, bacterial endotoxicity (as distinct from infectivity), immunological reaction, trauma, hypoxia and metabolic disturbance. Other aetiological factors include breakdown of trapped post-lens tear film debris, lens deposits and poor patient hygiene. The condition may be ulcerative or non-ulcerative. Histopathological analysis of human tissue from patients suffering from corneal infiltrative events reveals focal areas of epithelial loss, attenuated epithelium and stromal infiltration with polymorphonuclear leucocytes. Bowman’s layer is unaffected.