Verteporfin photodynamic therapy for neovascular age-related ...

66 Discussion of resultsStrengths and weaknesses of the verteporfin photodynamictherapy cohort studyDespite its observational nature, the VPDT cohort study has many strengths. These includeits size, pragmatic nature, and systematic collection of standardised data on acuity and lesioncharacteristics. This was the largest study of its kind to date, giving new insights into the HRQoLof people with nAMD and new data that will be pivotal to future studies of effectiveness inthis population. Many aspects of the data collected in this study were robust. Protocol-basedBCVA and CS were measured and HRQoL instruments administered at multiple time points,which allowed us to investigate in detail the relationships between clinical measures of visionand HRQoL. The large sample gave us reasonable power to test secondary hypotheses about theshape of the relationships and adaptation to vision loss over a 2-year period, even though theproportion of patients with data for more than three visits was small.The VPDT cohort study was the first with concurrent concurrent collection of data on HRQoLand patient-level data on HSS resource use, and, hence, first to have undertaken a systematicCEA using data acquired during treatment rather than data stipulated by a trial protocol. OurCEA also tackled three major methodological concerns not previously addressed in CEAs ofinterventions for nAMD. Thus, our work extends the literature on the costs and cost-effectivenessof interventions for nAMD, and its findings will assist future CEA.Set against these strengths, there were a number of limitations. These include the observationalnature of the study, the loss to follow-up of large proportions of the original sample, missingdata and the lack of a BSC comparison group of current relevance. There were major logisticalchallenges in establishing the study, which were discussed at a project review meeting about18 months after the contract for the study started; key observations and recommendations fromthis meeting are set out in Appendix 3.Unlike the pivotal trials, in which almost all patients were followed up for 24 months, 3,4,30 abouthalf of the patients included in our analyses did not have 1-year follow-up. Because poor dataquality is a well-recognised limitation of observational studies, we undertook computeriseddata validation checks on an on-going basis and when compiling the final data set. We checkedwhether or not data were missing for some visits by (a) matching records from paper andelectronic systems for collecting BCVA and (b) requesting that centres should check explicitlywhether or not additional visits had taken place for selected patients. The results from thesechecks implied that data had been submitted for > 95% of completed visits.The exact reasons for loss to follow-up are not known. We attempted to collect informationabout reasons for completing a treatment episode early or for patients being lost to follow-up,but participating centres did not report reasons reliably. Anecdotally, we became aware thatsome hospitals had a policy of not rebooking appointments for patients who missed a visit,and some ophthalmologists were put under pressure to discharge patients who did not requireactive treatment rather than to continue to review them. The context for these policies was theextremely overstretched nature of macular clinics. It should be remembered that providingVPDT required hospitals to make regular appointments (up to four per year) to review a largenumber of patients who had previously had fewer than one; reviewing a patient required FA and,if treatment was required, administration of VPDT. Irrespective of whether or not funding wasavailable to pay for these resources, the expert workforce needed to provide VPDT could not beexpanded rapidly.