General definition: unwanted effect(s) (i.e. physical and/or psychological symptoms and signs) resulting from treatment; any undesirable effect or problem that is present during the period of treatment.
In contact lens practice, common categories:
• Serious adverse reaction = symptomatic adverse reaction of sufficient clinical concern to warrant permanently discontinuing lens wear and that produces or has the potential to produce significant visual impairment.
• Significant adverse event = mostly symptomatic adverse reaction of sufficient clinical concern to warrant temporary or permanent discontinuation of lens wear.
• Non-significant adverse events = asymptomatic adverse event not of sufficient clinical concern; may not warrant discontinuation of the patient from lens wear.