<p>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</p>

Abstract

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, 20question 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.

Standardizing the measurement and classification of quality of life using the Keratoconus End-Points Assessment Questionnaire (KEPAQ): the ABCDEF keratoconus classification

“…B.) and who had previously undergone application of the final version of the KEPAQ [ 1 ]. If the same patient had undergone application of the KEPAQ more than once, all applications were taken into account as far as more than 2 months had passed between such applications.…”

“…Measuring quality of life in ophthalmology is of utmost importance for both the researchers and clinicians alike, as it provides important information that cannot be completely obtained by measuring other variables, such as visual acuity and corneal distortion [ 1 ]. Whenever available, the researchers and clinicians should use disease-specific scales, as these will report more accurately than general-purpose scales in the specific studied population.…”

“…Whenever available, the researchers and clinicians should use disease-specific scales, as these will report more accurately than general-purpose scales in the specific studied population. So far, only two keratoconus-specific scales have been developed and validated through Rasch modeling: the Keratoconus Outcomes Research Questionnaire (KORQ) developed by Khadka et al [ 2 ] and the Keratoconus End-Points Assessment Questionnaire (KEPAQ) developed by our group [ 1 ].…”

“…Although we have demonstrated that the KEPAQ complies with the stringent expectations of the Rasch model [ 1 ], and correlates well with corneal distortion [ 3 ], there is still some uncertainty regarding the best way to calculate, report and interpret results from the scale, especially for non-Rasch experienced researchers. Prior published papers have suggested calculating KEPAQ score by a raw-score-to-Rasch-measure table [ 1 ], but it is clear that this is not optimal as it does not allow for calculation when there are missing items. Moreover, it does not consider the relative weights of different questions while calculating the final score, which is one of the main hallmarks of Rasch modeling [ 4 ].…”

<p>Both Subjective Emotional Distress and Visual Handicap Correlate with Belin ABCD Classification in the Worse Eye as Measured with the “Keratoconus End-Points Assessment Questionnaire” (KEPAQ)</p>

“…This paper studies whether corneal distortion as measured with the Belin ABCD classification correlates with QoL scores as measured with the Keratoconus End-Points Assessment Questionnaire (KEPAQ), a previously validated disease-specific scale. 4 This is important not only because it will demonstrate construct validity for the scale but also because it will give good insight as to how different stages of the disease cause greater affections in visual and emotional distress from the patient's point of view.…”