However, the wearing regimen was not taken into account when comparing the two groups, which was a critical omission by the investigators, leading to a skewed result delineating lens type (disposable lenses). In a recent letter,2 Ederer and Ferris wrote, "The choice of controls in casecontrol studies is one of the most formidable problems in epidemiologic practice. The controls, except for the disease under study, should be as similar to the cases as possible. If the cases are drawn from a clinic population, then the controls should be chosen so as to duplicate the selective factors which brought the cases to the clinic." Thus, if the case patient has worn the lenses on a continuous basis without nightly removal, so should the controls regardless of lens type.
Considering the failure of the investigators to consider this aspect of lens wear in choosing controls, I do not believe that they
Levy B. Ulcerative Keratitis and Disposable Lenses. Arch Ophthalmol. 1993;111(4):431–432. doi:10.1001/archopht.1993.01090040021014
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