Measuring Contact Lens Discomfort

The measurement of contact lens discomfort is complex; the sensation experienced is inherently variable, and existing measurement scales may not be optimal. This manuscript aims to review and describe instruments commonly used to measure contact lens discomfort. Appropriately designed questionnaires undergo a rigorous process of item development and validation. Interval scales (e.g. numerical rating scale and visual analogue scale) are frequently used to measure temporal characteristics of contact lens discomfort and remain useful in assessing qualities such as duration, onset and chronicity. The majority of studies of contact lens discomfort have used questionnaires designed and validated for use in dry eye patients, most commonly the ocular surface disease index. This practice is questionable as the characteristics, epidemiology and underlying mechanisms of the sensations of discomfort experienced by contact lens wearers differ from those reported by dry eye patients. There is a clear need for context specific validation of these instruments to occur. Improved instruments urgently need to be developed. Until then, interval scales and the CLDEQ-8, a short version of the contact lens dry eye questionnaire, represent the best-validated instruments currently available for measuring the temporal characteristics and the frequency and intensity of contact lens discomfort, respectively.