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

Rasch validation of the Keratoconus End-Points Assessment Questionnaire in a Spanish population with keratoconus

OBJECTIVE

To carry out a methodologically complete validation of the Spanish version of the Keratoconus End-Points Assessment Questionnaire (KEPAQ) in a Spanish population with keratoconus.

METHODS

Analytical, prospective study, including patients with keratoconus without previous surgical history, in which a measurement of quality of life was performed using the KEPAQ questionnaire, a complete exploration of the anterior pole and a corneal elevation topography with the Galilei G6 topographer. The evaluation of the psychometric characteristics of the scale in the studied population was carried out using Rasch modeling.

RESULTS

A total of 140 patients with keratoconus were included, with a median age of 26.0 years, the majority (57.6%) being men. For the KEPAQ-E subscale, the median score was 69.3, with a reliability of 0.85 and an eigenvalue of the first contrast of 2.34. For the KEPAQ-F, the median score was 56.4, with a reliability of 0.88 and an eigenvalue of 2.00. All infit and outfit parameters were within normal limits for both subscales. A significant evaluation was found between the evaluations of both subscales (rho = 0.696; p < 0.001). The evaluations of the subscales and various clinical and tomographic characteristics showed a significant classification between them (p value between 0.048 y 0.001).

CONCLUSION

The KEPAQ is a psychometrically robust and valid scale to evaluate quality of life in the Spanish population with keratoconus. This questionnaire can be easily used for both clinical and research aims.

Impacts of keratoconus on quality of life: a qualitative study

BACKGROUND/AIMS

To identify the domains of quality of life (QoL) in people with keratoconus.

METHODS

Semi structured in-depth in person and telephone interviews were conducted with participants diagnosed with keratoconus and recruited from the Sydney Eye Hospital, Sydney, Australia. Thematic analysis of interview content was conducted using inductive and deductive processes. Data was collected until thematic saturation was obtained.

RESULTS

33 patients with keratoconus with median age 37 (range 18 to 65) years and majority male (n = 25; 75.8%) were interviewed and a total of 2551 quotes coded. Thematic analysis resulted in 7 broad themes, Driving (199 references), Career (259 references), Symptoms (647 references), Enjoyment (149 references), Relationships (250 references), Financial (104 references) and Healthcare (881 references). Most references described a negative relationship between keratoconus and these 7 domains. The diverse QoL issues expressed included frustration with treatment effectiveness, fear of disease progression, inconvenience with contact lenses, forced career changes and job loss, cost of contact lenses, and feelings of isolation and discrimination. Themes and subthemes described a complex and varied relationship between keratoconus and QoL.

CONCLUSION

Severe quality of life impairment was experienced by keratoconus patients despite treatment. Keratoconus diminishes various aspects of individual's QoL. Therapies able to improve QoL are still needed for keratoconus.

Quality of life and tomography indices in patients with keratoconus

OBJECTIVE

Keratoconus is a corneal ectasia that leads to thinning and steepening of the corneal surface. We aimed to assess the relationship between quality of life and corneal tomography indices, irrespective of visual acuity.

METHODS

This was a cross-sectional study using a translated and validated Keratoconus Outcomes Research Questionnaire (KORQ) in Arabic language. We screened patients with keratoconus using the Belin/Ambrósio D-Index. We included the best-seeing eye in each patient with keratoconus, with a best corrected visual acuity better than 0.5. We collected variables including KORQ scores, flattest meridian keratometry, steepest meridian keratometry, mean keratometry front, maximum simulated keratometry, astigmatism front, Q value front, and thickness at the thinnest location. We performed linear regression analysis to identify predictors of the visual function score and symptom score.

RESULTS

Sixty-nine patients were included in this study, 43 (62.3%) male and 26 (37.7%) female patients, with a mean age 34.0 ± 11.50 years. The only predictor for visual function score was sex (β = 11.64, 95% confidence interval: 3.50-19.78). None of the topographic indices were related to quality of life.

CONCLUSION

In this study, quality of life in patients with keratoconus was not related to specific tomography indices and might be related to visual acuity itself.

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

Background

Measuring quality of life is of importance in keratoconus. So far, the Keratoconus End-Points Assessment Questionnaire (KEPAQ) is the only keratoconus-specific scale to measure emotional well-being along with functional compromise in this population. Nevertheless, there is still a lack of clarity and standardization as to how KEPAQ scores should be computed and reported. There are also no guidelines for interpretation of classification of quality of life when using this instrument. The purpose of this study is to provide a specific framework on how to grade and classify keratoconus by using the KEPAQ and propose an extension of current classification to encompass subjective compromise.

Methods

A group of patients with a confirmed diagnosis of keratoconus underwent application of the KEPAQ. First, a Rasch modeling was performed to evaluate the psychometric characteristics of both sub-scales of the instrument. Then, a linear transformation was performed to turn data into a more relatable scale ranging from 0 to 100. Finally, by using Tukey’s Hinges, scores of the KEPAQ were divided in a 1-to-4 scale, allowing for an easy E&F classification system.

Results

A total of 386 applications of the KEPAQ were included. Analysis provided evidence of the KEPAQ being unidimensional, well-fitted to the Rasch Model, and provided adequate interval-level scores. Linear transformation resulted in a user-friendly final score ranging from 0 to 100, where a higher score translates to having a better quality of life. Two methods of easily computing final score, one by hand and the other one by an Excel file, were constructed. An E&F 1-to-4 classification was proposed, which may work well with the current ABCD classification of keratoconus.

Conclusions

The KEPAQ is a psychometrically robust scale, which confidently measures both emotional-related and functional-related quality of life in patients with keratoconus. It can be easily computed, and the results are interpretable and classified in a manner similar to that used in the ABCD keratoconus classification, by adding letters ‘E’ for emotional and ‘F’ for functional compromise.

Both subscales of the Keratoconus End-Points Assessment Questionnaire have excellent test-retest reliability

Purpose:

The keratoconus end-points assessment questionnaire (KEPAQ) is a disease-specific scale designed to evaluate the quality of life in keratoconus patients and provides the measurement of both functional and emotional compromise in keratoconus. It was previously developed, tested, and validated and now we want to evaluate the test-retest reliability of the KEPAQ, in an effort to contribute evidence on its internal consistency and capability of measuring clinical state with minimal inference of random chance.

Methods:

This is a prospective analytical study, designed to evaluate the test-retest reliability of the KEPAQ through the repeated application of the questionnaire to a group of clinically stable individuals. A number of patients with a confirmed diagnosis of keratoconus underwent double application of the KEPAQ, seven days apart. Mean KEPAQ score was obtained through Rasch analysis, while test-retest reliability was evaluated through Spearman rank-order correlation and intraclass correlation coefficient. Rasch analysis was performed in JMetrik version 4.1.1 (Psychomeasurement Systems LLC; Charlottesville, VA, USA) in a MacBook Air computer running macOS Catalina version 10.15.2 (Apple Inc.; Cupertino, CA, USA).

Results:

A total of 100 patients were included. For KEPAQ-E, Spearman correlation was R = 0.963 while ICC was 0.981 (95% confidence interval 0.972–0.987). For KEPAQ-F, Spearman correlation was R = 0.921 while ICC was 0.952 (95% confidence interval 0.929–0.968).

Conclusion:

The KEPAQ is a robust, well-developed, extremely reliable scale which can be confidently used for clinical and research endeavors.

Rasch development and validation of a new faces scale for measuring pain, and its comparison with a gold standard: the Balparda-Herrera Pain Scale

Aim: Faces pain scales are widely used to measure pain. So far, no faces pain scale has ever been constructed by Rasch modeling. Hence the authors aimed to construct a new scale by this method. Methods: Rasch modeling was used to provide an initial calibration and development of the 'Balparda-Herrera Pain Scale' (BHPS) and this scale was compared with the existing Faces Pain Scale - Revised. The scale was later refined. Results: Both the existing scale and the initial version of the BHPS required category collapsing. Statistical tests demonstrated an excellent concordance between both scales. The final version of the BHPS was found to behave excellently and to be capable of adequately measuring pain. Conclusion: The BHPS provides an excellent instrument for measuring pain in the adult population.

Translation and validation of the "Questionnaire for research on keratoconus results" (KORQ) in the Colombian population

OBJECTIVE

It is proposed to carry out a process of translation and adaptation of the "Questionnaire for Research on Keratoconus Results" (KORQ) into Spanish and its validation in a Spanish-speaking population, such as Colombia. This is intended to provide a tool for measuring and monitoring the commitment to quality of life of patients with this corneal ectasia.

MATERIAL AND METHODS

A prospective analytical study was carried out, in which 200 subjects diagnosed with keratoconus completed a translated version of the KORQ questionnaire. The internal validity of the questionnaire was evaluated using Cronbach's Alpha, while its construction was evaluated by an Exploratory Factor Analysis, including a Parallel Horn Analysis for the selection of the number of underlying factors. Subsequently, 50 patients were re-selected to complete the questionnaire one week later. The repeatability of the questionnaire was measured by the Spearman test.

RESULTS

The KORQ questionnaire in its Spanish version showed some internal validity in both sections. Both sections of the questionnaire showed an essentially unidimensional behaviour. The test-retest repeatability of the test was excellent (Spearman rho> 0.95).

CONCLUSIONS

The translated version of the KORQ is valid in Colombian population.

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)

BACKGROUND

Keratoconus is a disease characterized by progressive corneal distortion and quality of vision. So far, no study using disease-specific scales has evaluated whether different stages of the disease correlate with higher quality of life (QoL) compromise.

METHODS

A total of 114 patients with a confirmed diagnosis of Keratoconus were included in this retrospective study. All patients underwent a clinical and a Pentacam evaluation. They were also administered the "Keratoconus End-Points Assessment Questionnaire" (KEPAQ). Belin ABCD criteria were used for Keratoconus classification. "Better eye" was defined as the eye with the lowest maximum keratometry value. Spearman Rank Order Correlation was used to determine the correlation between the different Belin criteria and the KEPAQ scores in both subscales.

RESULTS

Mean age was 28.13 ± 11.57 years, with 39.47% of patients being male. Mean score for the KEPAQ-E was 2.33 ± 3.40 Logit, while for the KEPAQ-F, it was 1.85 ± 3.61 Logit. Criteria A (anterior elevation), B (posterior elevation) and D (visual acuity) in the worse eye correlated significantly with a greater decrease in QoL (p < 0.05 for all correlations). No correlation could be found regarding the better eye.

CONCLUSION

A greater corneal distortion in the worse eye, as determined by Belin ABCD, is associated with a greater decrease in patient's QoL. Surgical improvement of the worse eye should probably be performed before surgery of the better eye, as it may provide a better response regarding the quality of life improvement.

Both sub-scales of the "Keratoconus End-Points Assessment Questionnaire" (KEPAQ) are unidimensional and reliable

BACKGROUND

Measuring quality of life in keratoconus is important and demands for well-constructed instruments and scales. To date, the Keratoconus End-Points Assessment Questionnaire (KEPAQ) is the only disease-specific scale to measure both functional and emotional compromise due to disease. Nevertheless, not much information exists regarding whether both sub-scales of the test show unidimensionality, a necessary condition in well-functioning instruments.

METHODS

A sample of patients with a confirmed diagnosis of keratoconus were administered the full version of the KEPAQ. A Rasch analysis and principal component analysis were performed.

RESULTS

A total of 249 patients with keratoconus were included. Their average age was 29.19 ± 10.91 years, and 51.40% were male. Mean score for the KEPAQ-E was 2.51 ± 3.29 logit while it was 2.26 ± 3.70 logit for the KEPAQ-F. For both sub-scales, Kaiser Criterion, Scree Plot Criterion, and Variability Criterion demonstrated unidimensionality. Reliability as measured by Cronbach's alpha was 0.85 for the KEPAQ-E and 0.87 for the KEPAQ-F.

CONCLUSIONS

The KEPAQ is a robust, well-designed disease-specific questionnaire that shows unidimensionality. It can be reliably used to measure quality of life in keratoconus patients.