The protocol was approved by the Vision CRC (Cooperative Research Centre) Human Ethics Committee and complied with the Declaration of Helsinki 1975, as revised in 1989. All subjects signed a record of informed consent.
Forty subjects took part in the study. As we were not interested in making comparisons between groups of subjects in terms of their responses, a traditional sample size calculation was not appropriate to the study design, and this number was chosen so that there would be a reasonable distribution of cases across the various possible judgment categories. All were in good health and were examined to ensure that they were free of ocular abnormality.
At the beginning of the study, a pair of apparently identical, new contact lenses of the same type was placed on the eyes of each subject. The eye into which the first lens was inserted was chosen at random, and subjects were masked to lens type and were not informed that the lenses were identical. Immediately after initial insertion, the lenses were manipulated by gentle lateral displacement to remove any debris from the postlens space. Subjects were then instructed to blink normally. After 15 minutes, subjective comfort was assessed for each eye, using a 1 to 100 numerical rating scale (NRS) with anchors at 100 (“perfect, I cannot feel the lens on my eye”) and 1 (“intolerable, lens must be removed immediately”). Subjects then indicated their preference between the two eyes using a five-point Likert scale (1 to 5: strongly prefer right, prefer right, no preference, prefer left, strongly prefer left, respectively). The specific question put was: “Of the two lenses in your eyes, which do you prefer in terms of comfort?”
After this, both lenses were removed and discarded.
The whole procedure was repeated three times: once using the same lens type and twice with a different lens type. This method increased generalizability and permitted the consistency of the outcome to be assessed. The two lens types used were:
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Lens A: 8.4/14.0/-3.0/ACUVUE OASYS (Johnson & Johnson Visioncare, Jacksonville, FL)
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Lens B: 8.6/14.2/-3.0/Air OPTIX (Ciba Vision, Duluth, GA)
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At least 15 minutes elapsed between the end of one trial and the start of another, and no more than two wearing events took place on any given day. All the trials took place in the same airconditioned, windowless, illumination-controlled clinic room.