On average, completion rates were higher for the 48-h recall interviews than for the prospective diaries. For example, 87 % of caregivers completed the first diary 2 months after surgery; while a month later the completion rate for the 48-h interview was 10 % higher (97 %). The completion rates of both interviews and diaries declined over time (see Table 14.1). Even so, nearly 5 years after surgery, telephone interviews were completed by almost three-quarters of caregivers. Half of the caregivers returned the diary when the children were 4 years of age. Forty-three (38 %) of the caregivers completed all five diaries and an additional 24 (21 %) completed four of the five diaries. Eight (7.0 %) caregivers did not complete any of the diaries. All of the caregivers completed at least four of the 48-h recall interviews and nearly two-thirds (n = 71, 62.2 %) completed 17 or more interviews. All participants had adherence data available for the first year following surgery with three-quarters (n = 89, 78.1 %) completing all five possible assessments in this first year. Although there was some tendency for caregivers who did not provide adherence data at subsequent time points to report less adherence with occlusion than parents who did provide data, these differences were neither consistent nor did they approach statistical significance (data not shown).

Table 14.1 also documents the effort required to collect these data. Half of all interviews were completed within two phone calls, regardless of the time since surgery. However, numerous attempts were required to successfully collect data on some participants. For example, at nearly all time points, more than ten contact attempts were required in order to collect data on one or more participants.

Overall, caregivers report patching consistently. For example, the number of hours of patching reported in one interview was strongly correlated with patching reported 3 months later. Further, reports of adherence to patching show excellent reliability, particularly after the first year (see Table 14.2). Further, although caregivers reported slightly more patching on the prospective diaries than on telephone interviews, the amount of patching reported on the diaries correlates well with the amount of patching reported in interviews (see Table 14.3).

A number of investigators have reported that adherence to patching is more accurately estimated using Occlusion Dose Monitors (ODM) than using parental report [24] although others have found good correspondence between adherence reported on diaries and ODM’s [21]. They further suggest that parental reports overestimate adherence to occlusion, are not free from bias and require observation of entire treatment period [20]. However, IATS data suggest that caregivers can report adherence to prescribed occlusion. Further, our methods can be used in situations in which ODMs might not be appropriate or acceptable. In IATS, for example, ODMs were not deemed acceptable for use with infants and other young children because of parental and IRB concerns about risks associated with the devices. Additionally, we monitored adherence over a nearly 5 year period. It may be difficult to use ODMs over this extended time. Finally, using parental reports, we were able to successfully monitor adherence on both occlusion and use of contact lenses and spectacles. Although methods to separately monitor adherence to spectacle use and occlusion are under development [25], as currently configured, ODMs are only able to monitor adherence to the use of eye patches for occlusion.

In summary, we believe that our findings show that adherence to patching and visual occlusion can be successfully reported by caregivers of infants and young children over an extended period of time. We further conclude that, although either prospective diaries or retrospective telephone interviews may be used to gather data on adherence to patching, obtaining data via quarterly telephone interview may be preferred given the higher completion rates obtained. Additionally, the frequent telephone contact may have an added benefit of enhancing retention in clinical research.

There was substantial inter- and intra-subject variation in the amount of patching reported. For example, in the first twelve months after surgery, caregivers reported patching their children from 0.37 to 7.63 h/day with an interquartile range from 2.7 to 4.7 h/day. Half of all caregivers reported patching their children less than 3.7 h/day in the first year of life (see Fig. 14.2). Between 12 and 48 months of life, caregivers reported patching their children an average of 3.39 h/day, with 75 % of caregivers reporting patching their children 1.86–4.91 h/day (see Fig. 14.3).