Bacterial colonization of disposable soft contact lenses is greater duringcorneal infiltrative events than during asymptomatic extended lens wear

Microorganisms, especially gram-negative bacteria, are considered to play a role in the etiology of certain corneal infiltrative events (CIEs) observe d during soft contact lens wear. This study explored the possibility of mic robial colonization of soft contact lenses as a risk factor leading to CIEs , In a clinical trial conducted from March 1993 to January 1996, 330 subjec ts wore disposable soft contact lenses on a 6-night extended-wear and dispo sal schedule. During this period, 4,321 lenses (118 during CIEs; 4,203 duri ng asymptomatic lens wear) were recovered aseptically and analyzed for micr obial colonization. A greater percentage of lenses were free from microbial colonization during asymptomatic wear than during CIEs (42 versus 23%; P < 0.0001), The incidence of gram-positive bacteria, gram-negative bacteria a nd fungi was greater during CIEs than during asymptomatic lens wear (P < 0. 05), During asymptomatic lens wear, gram-positive bacteria were isolated mo st frequently and were usually normal external ocular microbiota, Of the gr am-positive bacteria, the incidence of Streptococcus pneumoniae was greater during CIE than during asymptomatic wear (7.6 versus 0.6%; P < 0.0001), Wh ile gram-negative bacteria were seen in few cases during asymptomatic wear, their incidence during CIE in comparison to asymptomatic wear was substant ial and significant (23.7 versus 3.8%; P < 0.0001), Also, the level of colo nization was high. Of CIEs, events of microbial keratitis, contact lens acu te red eye, and asymptomatic infiltrative keratitis were associated with le ns colonization with gram-negative bacteria or S, pneumoniae. Colonization of soft contact lenses with pathogenic bacteria, especially gram-negative b acteria and S, pneumoniae, appears to be a significant risk factor leading to CIE.