Development and Validation of the “Keratoconus End-Points Assessment Questionnaire” (KEPAQ), a Disease-Specific Instrument for Evaluating Subjective Emotional Distress and Visual Function Through Rasch Analysis
Received 23 March 2020
Accepted for publication 27 April 2020
Published 12 May 2020 Volume 2020:14 Pages 1287—1296
Checked for plagiarism Yes
Review by Single-blind
Peer reviewer comments 3
Editor who approved publication: Dr Scott Fraser
Kepa Balparda,1,2 Tatiana Herrera-Chalarca,3 Laura Andrea Silva-Quintero,4 Sneider Alexander Torres-Soto,4 Claudia Marcela Vanegas-Ramírez5
1Department of Cornea and Refractive Surgery, Black Mammoth Surgical, Medellín, Colombia; 2Universidad de Valladolid, Valladolid, Spain; 3Department of Clinical Research, Black Mammoth Surgical, Medellín, Colombia; 4General Physician, Medicarte, Medellín, Colombia; 5Department of Ophthalmology, Universidad Pontificia Bolivariana, Medellín, Colombia
Correspondence: Kepa Balparda
Clínica de Oftalmología Sandiego, Carrera 43 #29– 35, Consultorio 712, Medellín, Colombia
Background: Keratoconus is a disease characterized by progressive distortion of the corneal anatomy, coupled with a decrease in vision. Assessing quality of life (QoL) in keratoconus is essential. So far, no instrument in the world has been designed to evaluate both visual function and emotional distress in this population. The purpose of the following study is to develop and validate the “Keratoconus End-Points Assessment Questionnaire” (KEPAQ) in a population of ectatic patients, the very first disease-specific scale to measure emotional latent traits in keratoconus.
Methods: A last generation, Rasch analysis method was used for scale validation. First, a number of focus groups were carried out to create a pool of potential items. Then, a series of processes (such as “Content Validity Index”) was carried out to develop a prior, 20-question version of the KEPAQ. Then, a study including 150 keratoconus patients was performed, followed by a careful Rasch analysis to validate and optimize both sub-scales (Emotional Compromise, KEPAQ-E, and Functional Compromise, KEPAQ-F).
Results: Initially, 86 items were considered as potential elements. After test optimization, 20 items were retained. A total of 150 patients with a confirmed diagnosis of keratoconus were included for the Rasch analysis. The mean age was 29.84 ± 9.96 years. In 150 patients, 12.6% had a history of keratoplasty, 46.0% had corneal rings, and 31.3% had crosslinking. For both sub-scales, misfitting items were removed until no misfitting was determined by repetitive Rasch runs. For the final version of the KEPAQ-E sub-scale, variance explained by the model was 62.4% with a dimensional scale. Person Separation Index and Person Number of Strata were 2.43 and 3.57, respectively. For the final version of the KEPAQ-F sub-scale, variance explained by the model was 61.3% with a unidimensional scale. Person Separation Index and Person Number of Strata were 3.19 and 4.59, respectively. Both sub-scales showed excellent Person Reliability.
Conclusion: The KEPAQ is a robust scale, developed and validated through the latest theoretical models. It shows excellent psychometric properties, which render it extremely useful for both clinical and research use. To date, the KEPAQ is the only disease-specific scale worldwide to evaluate both functional and emotional compromise in keratoconus patients.
Keywords: keratoconus, quality of life, vision ocular
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