Thyroid eye disease (TED) can be an incapacitating condition, with patients suffering a spectrum of clinical problems from mild dry eye symptoms to severe sight-threatening conditions, such as optic nerve compression and exposure keratopathy.
1 Facial disfigurement as a result of lid retraction, chemosis, squint, and proptosis often is a significant social embarrassment resulting in substantial psychologic burden.
2 Treatments include controlling and stabilizing the thyroid disease, followed by subsequent orbital decompression and then squint and eyelid surgery in those with moderate and severe disease. Patients often require multiple surgeries and must attend multiple follow-up appointments. Consequently, TED has been shown to have a substantial impact on patient quality of life (QoL), including reduced participation in activities of daily living and poorer emotional well-being.
4,5
Using QoL questionnaires has become the standard approach for assessing patient-centered outcomes in healthcare.
2,3,5,6 Similarly, patient reported outcomes (PROs) now are required by regulatory agencies, such as the Food and Drug Administration and National Institute of Clinical Excellence, both in the United States, in clinical trials to assess the effectiveness of novel treatments from the patients' perspective. QoL is a broad concept that assesses the impact of an illness on patients' physical, mental, social, and functional health.
7 Disease-specific factors, such as symptoms, treatment burden, inconvenience, and task-specific difficulty, have resulted in the development of several condition-specific QoL questionnaires in Ophthalmology,
8–10 including two for TED, namely the 15-item Graves' Ophthalmopathy-QOL (GO-QOL) and the 3-item TED-QOL.
6,11 However, as yet there is no TED-specific questionnaire to study the QoL impact of TED in adults in Asia. While translations of current TED-specific questionnaires have been used in several studies,
12,13 they may lack cultural specificity as they were not developed locally. This is important given that racial and ethnic differences in the use of eye care services and perception of eye-related care have been demonstrated in epidemiologic studies in Singapore.
14,15 Moreover, differences in living conditions and cultural and environmental habits between Asian and Western populations may mean that the QoL impact of TED also is different in Asian populations.
Furthermore, to our knowledge none of the current TED-specific QoL questionnaires has been validated using modern psychometric theory. While classical test theory (CTT) is useful in the early phases of instrument development, the benefits of item response theory, such as Rasch analysis, can provide a more robust and comprehensive psychometric evaluation than CTT.
16,17 The lack of a sophisticated TED-specific patient reported outcome measure restricts our understanding of the full impact of TED and related treatments on QoL.
We developed a TED-specific QoL questionnaire, the Singapore Thyroid Eye Disease Quality of Life questionnaire (STED-QoL), to assess the functional and psychosocial impact of TED from the patient's perspective. We described herein the content development phase of the STED-QoL and its psychometric evaluation using Rasch analysis.