Elsevier

Controlled Clinical Trials

Volume 24, Issue 6, December 2003, Pages 711-718
Controlled Clinical Trials

Use of a run-in period to decrease loss to follow-up in the contact lens and myopia progression (CLAMP) study

https://doi.org/10.1016/S0197-2456(03)00097-7Get rights and content

Abstract

Rigid gas permeable (RGP) contact lenses are initially less comfortable to wear than spectacles. In previous studies evaluating the use of RGP contact lenses to control myopia, more subjects randomly assigned to wear RGP contact lenses have been lost to follow-up than spectacle wearers. Previous rigid contact lens myopia control studies have lost 44% and 47% of the rigid contact lens wearers. This unequal loss to follow-up may compromise the results of the study, so we conducted a run-in period prior to randomized treatment-group assignment to ensure that all participants could adapt to RGP contact lens wear. We enrolled 147 children ages 8–11 years with myopia in the run-in period. Of the 147 subjects, 116 (78.9%) were able to wear RGP contact lenses for at least 40 hours per week and reported that they were “usually comfortable” or “always comfortable.” After 3 years, no subjects were lost to follow-up. The run-in period greatly reduced the loss to follow-up suffered by previous RGP contact lens myopia progression studies and may help provide more definitive answers regarding myopia control with RGP contact lenses.

Introduction

A run-in period is a time of observation prior to randomization during which potential subjects can be screened for compliance with a treatment regimen. A run-in period may increase the proportion of compliers participating in a trial, decrease losses to follow-up, improve the statistical power of a study, and allow investigators to assess the outcome measures prior to randomization [1], [2], [3]. However, run-in periods may also limit generalizability, increase the length of the study, and reduce the sample of eligible subjects [4]. The advantages and disadvantages of a run-in period must be considered prior to implementation in a clinical trial.

The Contact Lens and Myopia Progression (CLAMP) study is a randomized clinical trial to examine the effects of rigid gas permeable (RGP) contact lenses on myopia progression in children. The CLAMP study utilized a run-in period to reduce the potential for unequal loss to follow-up suffered by previous RGP contact lens myopia control studies [5], [6]. This paper describes our experience conducting a run-in period with 147 children ages 8–11 years who desired to wear contact lenses during the CLAMP study.

RGP contact lenses provide clear vision with relatively few ocular health risks, and they are a standard management option for correcting myopia. While RGP contact lenses are used to correct myopic refractive error, they may also provide a therapeutic effect and retard the progression of myopia. However, RGP contact lenses are initially less comfortable than soft contact lenses, but the long-term comfort of RGP contact lenses is comparable to soft contact lens comfort [7], [8].

Two RGP contact lens myopia control studies showed that discomfort accounted for one-fifth to one-third of the loss to follow-up [5], [6]. The absence of data from subjects who drop out of a study may compromise the validity of the results [9]. For example, if the inability to adapt to rigid contact lens wear is associated with a higher rate of myopia progression, the result may be a false impression that rigid contact lenses slow the progression of myopia. In reality, the subjects assigned to wear rigid contact lenses whose myopia progresses faster may have simply been lost to follow-up, creating the illusion of slowing the progression of myopia.

In this report, we show the benefits of a run-in period to aid retention in an RGP contact lens myopia control clinical trial; we report the percentage of children who successfully adapted to RGP contact lens wear during the run-in period of the CLAMP study; and we show the ocular characteristics and children's contact lens-related reports that are associated with successful RGP contact lens adaptation.

Section snippets

Methods

We enrolled 147 eligible children in the CLAMP study. The children were between the ages of 8 and 11 years, had between −0.75 D and −4.00 D myopia, and had not worn contact lenses previously. Successful adaptation to rigid contact lens wear was defined by the subjects' report of at least 40 hours of wearing time per week and contact lenses that were “always comfortable” or “usually comfortable.” Subjects were examined for eligibility, and follow-up visits were scheduled according to the

Results

At both the 1-year visit and the 2-year visit, 114 out of the 116 subjects (98.3%) were examined. At the 3-year visit, all of the subjects were examined, so the 3-year retention rate was 100%. Subjects were examined at 98.9% of the potential follow-up visits.

Subjects who successfully completed the run-in period are called “adapters,” and subjects who did not successfully complete the run-in period are called “nonadapters.” Boys and girls were able to adapt to RGP contact lens wear equally, and

Discussion

A careful inspection of previous rigid contact lens myopia control studies helped determine the beneficial effects of a run-in period. Because significant proportions of subjects were lost to follow-up in previous RGP contact lens myopia control studies due to poor initial comfort [5], [6], we predicted a run-in period would increase the number of compliant subjects, decrease losses to follow-up, and improve the statistical power of the study. Without the run-in period, one of every five

Acknowledgements

This work was supported by NIH/NEI grants K23-EY00383, T35-EY07151, and R21-EY12273; NIH/NHLBI grant K30-HL04162, Menicon Ltd.; CIBA Vision Corporation; SOLA Optical, USA; and an American Optometric Foundation William C. Ezell Fellowship, sponsored by Essilor.

References (13)

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