EPIDEMIOLOGY OF CLD

The epidemiologic assessment of CLD faces many challenges, not least of which is the accurate assessment of the frequency of the condition. Since the first publication in 1960 linking hygienic contact lens care and comfortable lens wear, the issue of CLD remains a major reason for discontinuation of contact lens wear. It is estimated that there currently are more than 140 million contact lens wearers worldwide. It is much moredifficult to estimate the number of individuals who previously have worn contact lenses and then abandoned lens wear as a result of CLD. Studies report that between 12% and 51% of lens wearers ‘‘drop out’’ of contact lens wear, with CLD the primary reason for discontinuation.

While there have been tremendous developments in lens polymers, designs, replacement modalities, and care regimens over the last 50 years, the challenge of preventing or managing CLD still is a problem in clinical practice. A major deficiency in the literature is the lack of information derived from contact lenses that differ in only one parameter.

Our limited understanding of the etiology and correlation between signs and symptoms makes it all the more difficult to diagnose and manage CLD. The tools used to diagnose CLD and the expectations of contact lens wearers continually change, making it difficult to draw conclusions over time and to compare results from multiple studies. There are few validated instruments for assessing comfort in contact lens populations, and these tend to produce data that are highly variable, as most rely on a patient’s recall. In addition, the lack of postmarket surveillance studies, which would address many of the issues related to CLD in a longitudinal fashion, prevent drawing meaningful conclusions regarding the impact of technological advances on CLD. Future epidemiologic work designed to clarify the natural occurrence and evolution of CLD in rural and urban population settings, and in various countries and races are very much needed to enrich our understanding of CLD and associated risk factors.
As CLD is reported primarily by symptomatology as opposed to the observation of signs, and while the precise etiology of CLD is yet to be determined, the use of symptoms as an outcome measure is appropriate, because it relates directly to the patients’ experience with contact lenses, and the motivation to seek and use treatment, regardless of the presence of observable signs. The frequency and intensity with which these symptoms are reported can be assessed with the use of questionnaires. Further research and agreement of a universal adoption of a single measure of CLD is needed. The Contact Lens Dry Eye Questionnaire has been well received and, perhaps, is the most likely candidate for widespread CLD assessment.