Psychometric Properties of the Keratoconus Outcomes Research Questionnaire: A Save Sight Keratoconus Registry Study

Quality of life in patients with progressive keratoconus treated with corneal collagen crosslinking

PURPOSE

This study aims to analyze the vision-related quality of life (vr-QoL) in keratoconus (KC) patients after corneal crosslinking (CXL).

METHODS

A prospective clinical study was conducted, wherein 41 patients underwent assessment using the "National Eye Institute Visual Functioning Questionnaire" (NEI-25) and the "Keratoconus Outcomes Research Questionnaire" (KORQ) to evaluate vr-QoL, along with the examination of morphology and functional parameters before CXL, and at three and six months post-treatment. Rasch analyses were used to verify the measurement precision of the KORQ with our study population.

RESULTS

There were no statistically significant changes observed in corneal morphology and best corrected visual acuity after CXL. Analysis of the NEI-25 questionnaires and KORQ demonstrated no statistically significant changes throughout the follow-up period. Rasch analyses revealed a high measurement precision of the KORQ within our population.

CONCLUSION

The study indicates that patients with progressive KC maintain stable vr-QoL after undergoing CXL. Based on our findings, we suggest considering very early CXL treatment for KC patients that are at high risk of progression.

Intereye Asymmetry as a Predictor of Progression in Patients With Untreated Keratoconus: Findings From a Longitudinal Study

PURPOSE

The purpose of this study was to evaluate interocular predictors of progression in patients with untreated keratoconus.

METHODS

This is a multicenter longitudinal observational study with real-world data collected through the Save Sight Keratoconus Registry. Patients between the period of June 2000 and September 2022 were included in this study. Parameters such as patient age, sex, ocular history, visual acuity, K2, Max-K, and thinnest corneal thickness pachymetry (TCT) were analyzed.

RESULTS

There were 4342 untreated eyes from 2171 patients with keratoconus. A total of 333 patients showed progression of either Max-K, TCT, or both, whereas 1838 patients showed stable parameters. Factors associated with a higher incidence of progression in Max-K were younger baseline age (HR 0.96 per year older; 95% CI 0.95-0.98, P < 0.0001) and a higher baseline intereye asymmetry in Max-K (HR 1.02 per higher diopter; 95% CI 1.00-1.04, P = 0.04). A younger baseline age was the only predictor of progression in TCT (HR 0.97 per year older; 95% CI 0.95-0.99, P = 0.001).

CONCLUSIONS

Age is the most significant predictor of progression for both corneal thinning and progression of Max-K. Interocular asymmetry in Max-K at baseline could be used as part of an algorithm for determining the risk of keratoconus progression. It is recommended that patients with higher interocular asymmetry in Max-K have a closer follow-up of both eyes as they are at a higher risk of progression.

The impact of dry eye disease on patient-reported quality of life: A Save Sight Dry Eye Registry study

PURPOSE

The aim of this real-world registry study was to evaluate the quality-of-life (QoL) impact of dry eye disease (DED). The specific objectives were to determine factors affecting QoL in DED, and to evaluate the psychometric properties of the Ocular Surface Disease Index (OSDI), Ocular Comfort Index (OCI), and Patient Health Questionnaire (PHQ) in a real-world DED population using modern psychometric methods.

METHODS

This descriptive cross-sectional study included 368 DED patients (mean 54.7 ± 16.6 years; 80.2 % female) who completed one or more of the three questionnaires (OSDI, OCI and PHQ). Psychometric analysis of the QoL data was carried out with Andrich's Rating Scale Model of Rasch analysis.

RESULTS

The original OSDI and OCI had disordered categories. The Rasch-optimised final QoL scales (OSDI - Overall, OSDI - Symptoms [SY], OSDI - Activity limitation [AL], OSDI - Environmental trigger [EN], OCI Overall, OCI - Frequency [FR], OCI - Intensity [IN], and PHQ) had satisfactory psychometric properties. Patients diagnosed with a mixed aqueous/evaporative DED subtype had worse mean OSDI-Overall and OSDI-AL scores than individuals with evaporative DED (p = 0.012 and 0.001 respectively). Patients with corneal neuropathic pain had worse QoL scores (OSDI-Overall, OSDI-AL, OSDI-SY, OSDI-EN, OCI-Overall, OCI-FR, OCI-IN, and PHQ; all p < 0.05) than those without. Patients who reported undergoing prior treatment or procedure for DED had worse QoL scores than those who did not (all p < 0.05 except for PHQ). The associations between DED signs (tear breakup time and staining) and symptoms were weak or not significant.

CONCLUSIONS

In this real-world setting, diagnoses of mixed DED, corneal neuropathic pain, and history of DED treatment/procedures were associated with worse dry eye symptoms, activity limitation, and/or QoL.

Evaluation of the German Version of the Keratoconus Outcomes Research Questionnaire

PURPOSE

To translate, validate, and evaluate the psychometric properties of the German version of Keratoconus Outcomes Research Questionnaire (KORQ).

METHODS

This prospective study included 3 phases. In phase 1, the KORQ was translated in a standardized way; in phase 2, Rasch validation was performed; in phase 3, the validated questionnaire was evaluated in a separate patient cohort. All patients answered the German KORQ. Scheimpflug imaging (Pentacam) and optical coherence tomography scans (MS-39) were conducted. Corneal imaging measurements were correlated with patient-reported outcome measures.

RESULTS

After standardized translation, 100 patients self-administered the German KORQ. Rasch analysis was conducted for psychometric testing of the KORQ. Based on the results of the Rasch analysis, the original German version of the KORQ was modified and any items showing a misfit were excluded. This resulted in a new shortened version of the KORQ, which was evaluated in 30 patients. The revised German KORQ met the criteria of Rasch analysis and showed excellent internal consistency reliability and convergent validity. The correlation between the KORQ score and various clinical measurements was examined using Spearman correlation. A significant moderate correlation was observed between the D (r = 0.237; P = 0.006) and K max (r = 0.162; P = 0.065) values of Pentacam. Inverse correlations were observed for thinnest pachymetry measured with MS-39 (r = -0.167; P = 0.058) and best corrected visual acuity (r = -0.210; P = 0.016).

CONCLUSIONS

The shortened German KORQ met the assumptions of the Rasch model and displayed satisfactory psychometric properties. The German KORQ could be adopted as a powerful patient-reported outcome measures tool for German-speaking patients with keratoconus in the future.

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.

Linguistic and cultural validation of symptom questionnaire for visual dysfunctions (SQVD) for psychometric analysis in the Chinese context

The Spanish scale symptom questionnaire for visual dysfunctions (SQVD) was sinicized and tested for reliability and validity in the Chinese context, employing both classical measurement theory and item response theory. A meticulous translation was conducted using the modified Brislin translation model, with input from experts for cross-cultural debugging and in-depth review. Following a pre-survey study, the Chinese version of the SQVD was finalized. A convenience sampling method was used to select 270 patients from the target group and 252 valid questionnaires were successfully collected. The Rasch model was employed to assess response category functionality, fit statistics, unidimensionality, person and item reliability, separation, targeting, and differential item functioning. Classical test theory was applied to evaluate internal consistency and retest reliability, supplemented by correlation analysis. Job characteristic curves were also plotted to assess diagnostic accuracy. The Chinese SQVD conformed to a unidimensional structure with excellent reliability and validity. Person and item reliabilities were 0.85 and 0.99, respectively, indicating, high stability. Person and item separation indices were 2.37 and 11.54, respectively, signifying strong differentiation ability. Retest reliability was 0.917, further emphasizing the stability of the scale. The area under the receiver operating characteristic curve was 0.908 (95% CI: 0.854, 0.962), with a cutoff value of 7.5 and Youden index of 0.733, highlighting the scale's high diagnostic accuracy. The translated and culturally adapted Chinese SQVD demonstrated excellent psychometric properties. With streamlined items, short assessment time, and high efficiency, the scale is a stable and reliable clinical tool for detecting a variety of conditions related to refractive, regulatory, and binocular vision dysfunction.

Comparison of standard versus accelerated corneal collagen cross-linking for keratoconus: 5-year outcomes from the Save Sight Keratoconus Registry

OBJECTIVE

To compare long-term effectiveness of Standard (UV intensity: 3 mW/cm2, duration: 30 min) vs Accelerated (UV intensity: 9 mW/cm2, duration: 10 min) corneal cross-linking (CXL) for stabilising keratoconus.

METHODS

Data for this observational study were captured through a web-based registry system from the routine clinical practice (15 sites across Australia, New Zealand and Italy). The outcomes were compared using mixed-effects regression models. A total of 100 eyes (75 patients) who had standard CXL and 76 eyes (66 patients) who had accelerated CXL, with a follow-up visit at five-year post-CXL were included.

RESULTS

Both CXL protocols were effective and safe in stabilising keratoconus and improving outcomes. The adjusted mean changes (95% CI) in outcomes were better in standard CXL than in accelerated CXL [visual acuity gain, 10.2 (7.9-12.5) vs 4.9 (1.6-8.2) logMAR letters; pinhole visual acuity 5.7 (3.5-7.8) vs 0.2 (-2.2 to 2.5) logMAR letters; Kmax -1.8 (-4.3 to 0.6) vs 1.2 (-1.5 to 3.9)D; K2 -0.9 (-2.2 to 0.3) vs 0.1 (-1.3 to 1.6)D; MCT -3.0 (-13.7 to 7.7) vs -11.8 (-23.9 to 0.4) µm (p values for visual acuity, pinhole visual acuity, Kmax: <0.05; for K2 and MCT: >0.05)]. The frequency of adverse events at the 5-year follow-up visit was low in both groups [standard, 5 (5%; haze 3; scarring 1, epithelial defect 1) and accelerated 3 (3.9%; haze 2, scarring 1)].

CONCLUSIONS

Both standard and accelerated CXL were safe and effective procedures for stabilising keratoconus in the long term. The standard CXL resulted in greater improvements in visual acuity and keratometry.

Cross-Linking Improves the Quality of Life of People With Keratoconus: A Cross-Sectional and Longitudinal Study From the Save Sight Keratoconus Registry

PURPOSE

The purpose of this study was to comprehensively evaluate the patient-reported quality-of-life (QoL) outcomes after corneal cross-linking for keratoconus.

METHODS

This Save Sight Keratoconus Registry study used cross-sectional and longitudinal designs. For the cross-sectional study, 532 patients with keratoconus (mean age 30.9 ± 11.9 years; 31.6% female) completed the Keratoconus Outcomes Research Questionnaire (KORQ) and 343 patients with keratoconus (mean age 28.3 ± 10.7 years; 32.7% female) completed the Impact of Vision Impairment (IVI) questionnaires. Similarly, for the longitudinal study, 39 patients (mean age 24.2 ± 8.4 years; 23.1% female) completed the KORQ and 16 patients (mean age 27.9 ± 17.1 years; 50.0% female) completed the IVI questionnaire before and after 6 months of cross-linking. The QoL data were analyzed using the Andrich Rating Scale Model of Rasch analysis.

RESULTS

For both cross-sectional and longitudinal studies, the KORQ and IVI scales demonstrated satisfactory psychometric properties [ordered and well-spaced categories, variance explained by the measure 52%-73%, person separation index 2.4-3.9, and fit statistics <1.3 (most cases)]. The patients who had not undergone corneal cross-linking had worse mean activity limitation than those with cross-linking ( P = 0.008). However, the differences in symptoms and emotional scores between the groups were not statistically significant (both P > 0.05). The longitudinal study showed that cross-linking was associated with improved activity limitation, symptoms, and emotional scores.

CONCLUSIONS

The KORQ and IVI are psychometrically robust tools to evaluate the QoL outcomes of corneal cross-linking. Cross-linking is associated with improved activity limitation, symptoms, and emotional status.

Rasch analysis of the Chinese version of the clinically useful depression outcome scale in patients with major depressive disorder

OBJECTIVE

To examine the psychometric properties of the Chinese version of the Clinically Useful Depression Outcome Scale (CUDOS) in the Chinese patients with major depressive disorder (MDD) using Rasch analysis.

METHODS

The sample consisted of 283 patients with MDD (69% females). The Rasch model was applied to examine the overall fit of the Chinese version of CUDOS and the fit of the 18 items. Dimensionality, item-model fit, differential item functioning (DIF), reliability, ordering of response category and targeting were tested to examine the psychometric properties of the Chinese version of CUDOS.

RESULTS

Rasch analysis demonstrated the unidimensionality of the Chinese version of CUDOS. Of the 18 items, three items (item 4, item 5, item 6) showed misfit in the model. After merging item 4 into item 3 and item 6 into item 5, the overall model fit improved. The person separation index (PSI) was 3.0 and the person reliability coefficient was 0.90. No evidence of significant DIF was found when associated with gender and age. No disordered category and threshold of the rating response were observed, which meant the response category setting was reasonable. The mean ability of person was - 0.53.

CONCLUSION

The results suggested that the Chinese version of CUDOS has acceptable psychometric properties. In order to improve the quality and applicability of the Chinese version of CUDOS, the merging of item 4 into item 3 and item 6 into item 5 are suggested.

Patient-Reported Outcomes in Keratoconus: A Save Sight Keratoconus Registry Study

PURPOSE

The aim of this study was to evaluate the quality-of-life (QoL) status in keratoconus severity subgroups using the Keratoconus Outcomes Research Questionnaire (KORQ) and to determine the relationship between the QoL scores and the standard clinical variables.

METHODS

A cross-sectional study was conducted using prospective, web-based Save Sight Keratoconus Registry data. Rasch analysis was conducted on the KORQ data using the Andrich Rating Scale Model. Comparative analysis included Welch t test and 1-way ANOVA. Associations between visual acuity, corneal curvature, and minimum corneal thickness with KORQ scores were evaluated with Pearson correlation and multiple regression adjusted for age and sex.

RESULTS

The KORQ was completed by 542 patients with keratoconus (male, 67.7%; mean age, 31.6 years). Keratoconus severity, based on Kmax, was mild [<48 diopter (D)], moderate (48-55 D), and severe (>55 D) in 26.3%, 45.0%, and 28.7% of patients, respectively. Activity limitation (AL) and symptoms (SY) scales of the KORQ had robust psychometric properties including well-functioning response categories, unidimensionality, excellent measurement precision, and satisfactory fit statistics. In a group-wise analysis, the female patients had significantly lower AL and SY scores. Similarly, the severe keratoconus group had the worst AL and SY scores. Contact lens wearers had worse KORQ scores than the spectacles wearers. Overall, statistically significant but weak correlations between KORQ scores and visual acuity and corneal curvature (Kmax and K2) (Pearson r, 0.11-0.35) were observed. The correlations for SY were weaker than for AL scores.

CONCLUSIONS

Female sex, contact lens wear, reduced visual acuity, and higher disease severity were associated with worse AL and SY scores in keratoconus. Although the correlations between clinical and QoL scores were statistically significant, the low magnitudes suggested a complex relationship between clinical parameters and patient-reported outcomes.

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.

Impact of corneal collagen cross-linking on vision-related quality of life measured with the keratoconus outcomes research questionnaire (KORQ) in patients with keratoconus

PURPOSE

To assess the impact of corneal collagen cross-linking on self-reported vision-related quality of life (VR-QoL) in keratoconus patients by means of the Keratoconus Outcomes Research Questionnaire (KORQ), a new disease-specific patient reported outcomes measures (PROMs) tool.

METHODS

Patients with progressive keratoconus undergoing corneal collagen cross-linking were consecutively enrolled. Patients completed the KORQ before and after the treatment, at 1, 3 and 6 months. Data were collected regarding the visual acuity and the topographic, aberrometric and pachymetric parameters of both eyes. Patients were also asked to quantify their eye rubbing behavior on a Visual Analogue Scale (VAS) from 0 to 10, before and 6 months after treatment. The KORQ scores were associated with the visual acuity, topographic, aberrometric and pachymetric data by means of the Spearman correlation coefficient.

RESULTS

The Activity Limitation (AL) subscale score was higher after surgery. Preoperatively, negative correlations were observed between the KORQ AL score and Best Corrected Visual Acuity (logMAR), maximum keratometry, flattest keratometry, steepest keratometry, symmetry index front and higher order aberrations (HOA) of the treatment eye. Postoperatively, we observed a shift toward the fellow eye, with stronger correlation of the KORQ scores with the fellow eye parameters. The Symptoms subscale score correlated with the aberrometric parameters of both eyes at various time points. Statistically significant correlations were observed between the change in KORQ scores and the change in aberrometric parameters. A statistically significant reduction in the eye rubbing behavior was detected (p < 0,0001).

CONCLUSIONS

These results suggest that the corneal cross-linking treatment is effective both in improving the subjective perception of the disease by the patient and in stabilizing the objective indicators of disease progression. Keratometric, aberrometric and visual acuity values showed a significant impact on self-reported VR-QoL. Corneal cross-linking, by halting the worsening of these parameters, may bear a beneficial effect on VR-QoL.

Efficacy and Safety of Standard Corneal Cross-Linking Procedures Performed With Short Versus Standard Riboflavin Induction: A Save Sight Keratoconus Registry Study

PURPOSE

The objective of this study was to compare the effectiveness and safety of short versus standard riboflavin induction times in cross-linking (CXL) for keratoconus.

METHODS

A retrospective comparative study was conducted with data from the Save Sight Keratoconus Registry. Inclusion criteria were epithelium-off technique, standard UVA CXL protocol (3 mW/cm 2 for 30 minutes), riboflavin induction for 15 minutes (short) or 30 minutes (standard), and 1 year of follow-up data after CXL. Outcome measures included changes in best-corrected visual acuity (BCVA), keratometry in the steepest meridian (K2), maximum keratometry (Kmax), thinnest pachymetry (TCT), and adverse events. Analysis was conducted using mixed-effects regression models adjusted for age, sex, visual acuity, keratometry, pachymetry, practice, and eye laterality.

RESULTS

Two hundred eighty eyes (237 patients; mean, 27.3 ± 10.5 years old; 30% female) were included. The riboflavin induction time was short in 102 eyes (82 patients) and standard in 178 eyes (155 patients). The baseline characteristics (sex, mean age, BCVA, keratometry, and pachymetry [TCT]) were similar between the groups. At the 1-year follow-up visit, no statistically significant differences were observed in flattening in K2 and improvement in BCVA. Greater Kmax flattening [-1.5 diopters (D) vs. -0.5D, P = 0.031] and a greater proportion of >2% increase in TCT (23.5 vs. 11.3, P = 0.034) and haze (29 vs. 15, P = 0.005) were observed with short riboflavin induction.

CONCLUSIONS

Short and standard riboflavin induction times achieved similar degrees of flattening in K2 and improvement in vision. Greater improvements in Kmax and TCT were seen with short riboflavin times; however, this group had higher rates of haze.

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.

Oxygen in Corneal Collagen Crosslinking to Treat Keratoconus: A Systematic Review and Meta-Analysis

PURPOSE

Keratoconus is a disorder that results in visual loss from increased corneal high-order aberrations and irregular astigmatism and reduces quality of life. The primary treatment for progressive keratoconus is crosslinking (CXL). Recently, it has been suggested that oxygen enhances the type II photodynamic reaction of CXL that is oxygen dependent. Our study investigated the effect of increased oxygen availability in epithelium-on CXL on visual acuity and corneal curvature.

METHODS

We searched PubMed, EMBASE, Medline, Web of Science, and Scopus databases on November 3, 2021. We included studies that reported increased oxygen availability during CXL in patients with keratoconus published within the last 10 years. A meta-analysis on the primary outcomes, maximum keratometry, and corrected distance visual acuity, was conducted.

RESULTS

The search yielded 108 publications which were screened and assessed for eligibility. Six studies were included in the systematic review and 5 studies were included in our meta-analysis of the outcomes of increased oxygen availability in accelerated CXL. The meta-analysis on data after 6 months of follow-up found a significant decrease in mean maximum keratometry of 1.2 diopter (95% confidence interval: 0.2-2.3; P =0.02) and an improvement in mean corrected distance visual acuity by 0.08 logMAR (95% confidence interval, 0.02-0.13; P =0.01). There were no serious adverse events reported.

CONCLUSIONS

Increasing oxygen during epithelium-on CXL improved visual acuity and produced corneal flattening without any serious adverse events in patients with keratoconus. The demarcation line depth was significantly higher with oxygen compared to the control group. Further data are required with a control group and long-term follow-up across a range of CXL protocols for implementation into standard clinical practice.

Factors affecting quality of life in keratoconus

PURPOSE

To identify the factors affecting the quality of life (QoL) in adults with keratoconus, using the disease-specific Keratoconus Outcomes Research Questionnaire (KORQ).

METHODS

In this cross-sectional study, 574 patients with keratoconus completed the 29-item KORQ (18-item activity limitations and 11-item symptoms subscales) and demographic information. Based on mean corneal curvature to grade keratoconus severity, participants were categorised into four groups: mild <48 dioptres [D]; moderate: 48 to 53 D; advanced: 54 to 55 D and severe: >55D. Rasch analysis was used to assess the psychometric properties and to score the KORQ. Multivariable regression was performed to determine the independent impact of age, sex, laterality, severity and duration of keratoconus, education, employment status and mode of treatment for keratoconus on activity limitations and symptoms.

RESULTS

Mean (SD) age was 24.5 (5.1) years. 304 (53%), 160 (28%), 26 (4%) and 84 (15%) belonged to keratoconus groups 1, 2, 3 and 4, respectively. Rasch analysis demonstrated the 'activity limitations' and 'symptoms' KORQ subscales to possess good psychometric properties. Statistically significant associations were found between activity limitation score and the following measures: visual acuity (VA) in the better-seeing eye (r = -0.10, p = 0.01); VA in the worse-seeing eye (r = -0.09, p = 0.04) and ocular aberrations (r = -0.13, p = 0.008) in the worse-seeing eye. Statistically significant associations were also found between symptoms score and mean corneal curvature in the better-seeing eye (r = -0.10, p = 0.02). In regression models, female sex was associated with 21% worse symptom score than male (β = -0.33, 95% CI, -0.09, -0.59, p = 0.01) and working people experienced clinically and statistically significantly greater trouble from symptoms compared to those not working (β =0.44, 95% CI, 0.17, 0.70, p = 0.001).

CONCLUSIONS

People with keratoconus have poorer QoL in terms of activity limitations if they have poorer VA and greater wavefront aberrations, and in terms of symptoms if they are female and employed.

Quality of life impact of eye diseases: a Save Sight Registries study

BACKGROUND

The objectives of this study were to evaluate the quality-of-life (QoL) impact of eye diseases (keratoconus; neovascular age-related macular degeneration, AMD; retinal vein occlusion, RVO; and diabetic macular edema, DME) using the Impact of Vision Impairment (IVI) questionnaire, and to determine the relationship between the IVI scores and visual acuity.

METHODS

This cross-sectional, multicentre, real-world study utilised the prospective, web-based Save Sight Registries. The IVI was completed by 1557 patients: 307 with keratoconus, 1049 with AMD, 148 with RVO and 53 with DME. Statistical analysis included Rasch analysis, Welch t-test, one-way ANOVA, Tukey's test, Pearson correlation, and multiple regression.

RESULTS

The IVI scales (Overall; Visual Function, VF; Emotional, EM) had robust psychometric properties. The keratoconus patients had the worst Overall (adjusted mean: 48.2 vs. DME 58.8, RVO 64.6, AMD 67.6 units), VF (47.7 vs. DME 59.4, RVO 65.9, AMD 68.9 units) and EM (50.8 vs. DME 63.1, RVO 69.2, AMD 71.8 units) scores (all p < 0.05). The IVI scales scores weakly correlated with better and worse eye visual acuity (Pearson's r 0.24-0.39, all p < 0.05). The correlations were similar in the better eye (Overall 0.35, VF 0.39, EM 0.24) and the worse eye (Overall 0.31, VF 0.33, EM 0.25) visual acuity. Correlations with visual acuity were stronger for VF than for the EM scores.

CONCLUSIONS

The IVI was a psychometrically robust QoL questionnaire. Keratoconus patients had worse IVI scores than patients with retinal diseases. The low strength of correlations between visual acuity and QoL scores, although statistically significant, suggested that a complex relationship exists.

Validation of the Symptom Questionnaire for Visual Dysfunctions (SQVD): A Questionnaire to Evaluate Symptoms of any Type of Visual Dysfunctions

Purpose

To assess psychometric properties of the Symptom Questionnaire for Visual Dysfunctions (SQVD) questionnaire, including accuracy, validity, and reliability, in a clinical sample of patients having any type of visual dysfunction.

Methods

A clinical sample of 306 patients self-administered the SQVD. Rasch analysis was performed to analyze the functionality of the response categories, fit statistics, differential item functioning (DIF), person and item reliability, targeting, local dependency, unidimensionality, and transformation table. Accuracy was assessed by means of receiver operating characteristic (ROC) curves, using symptoms reported in each patient's clinical record as the gold standard for classifying patients with and without symptoms. The concurrent validity, known group validity, and test–retest reliability (repeatability, using the intraclass correlation coefficient [ICC]) were also examined.

Results

SQVD showed orderly category responses. The 14 items fit the Rasch model without significant DIF for gender, presbyopia, and dysfunctions. Person and item reliabilities were 0.81 and 0.85, respectively. Targeting was –1.49 logits. Yen's Q3 statistic showed no local dependency. SQVD was unidimensional (first contrast of the residual = 1.852 eigenvalue with a variance explained by measures of 52.23%). The area under the ROC curve was 0.836 (95% confidence interval [CI], 0.792–0.879) with a cutoff of ≥6 showing good accuracy (sensitivity = 0.759; specificity = 0.783). SQVD showed good concurrent and known group validity and high repeatability (ICC, 0.857; 95% CI, 0.710–0.933) when administered twice 1 week apart.

Conclusions

SQVD has shown good psychometric properties. It can be considered an accurate, valid, and reliable questionnaire to detect visual symptoms related to any type of refractive, accommodative, and binocular dysfunction.

Translational Relevance

SQVD may be used for diagnostic purposes, as it can accurately detect symptoms related to any sort of visual dysfunction. It may also be useful to monitor the treatment outcomes of these conditions.

Comparative Efficacy and Safety of Standard Versus Accelerated Corneal Crosslinking for Keratoconus: 1-Year Outcomes From the Save Sight Keratoconus Registry Study

PURPOSE

The aim of this study was to compare the efficacy and safety of standard [Ultraviolet (UV) light power: 3 mW/cm2, duration: 30 minutes] versus accelerated (UV power: 9 mW/cm2, duration: 10 minutes) corneal crosslinking (CXL) for stabilizing keratoconus.

METHODS

A total of 684 eyes (555 patients; mean age ± SD, 25.0 ± 7.9 years; women, 30.6%) from 24 international sites with epithelium-off CXL for keratoconus had follow-up data at 1-year and met the inclusion criteria. Two hundred sixty-six eyes (228 patients) had undergone standard CXL, and 418 eyes (327 patients) had undergone accelerated CXL. The outcome measures included changes in visual acuity, keratometry, minimum corneal thickness, and frequency of adverse events. The outcomes were compared using mixed-effects regression models adjusted for age, sex, visual acuity, keratometry, pachymetry, doctor, practice, and eye laterality.

RESULTS

The adjusted mean changes (95% confidence interval) in outcomes were similar in standard and accelerated CXL in visual acuity [6.5 (2.0, 11.1) versus 5.5 (0.4, 10.6) logMAR letters, respectively], Kmax [-0.9 (-1.4, -0.3) D versus -1.2 (-1.9, -0.4) D, respectively], K2 [-0.4 (-0.9, 0.2) D versus -0.4 (-1.1, 0.3), D respectively], or minimum corneal thickness [-13.3 (-20.3, -6.3) μm versus -16.6 (-24.5, -8.6) μm, respectively] (all P > 0.05). The frequency of adverse events at the 12-month visit was also similar between the CXL groups (standard, 8.3% vs. accelerated, 5.5%; P = 0.21).

CONCLUSIONS

This real-world observational study found that both standard and accelerated CXL were similarly safe and effective in stabilizing keratoconus at 1-year postsurgery in the real-world setting. The findings support the adoption of accelerated CXL for time and convenience.

Quality-of-life outcomes of long-term contact lens wear: A systematic review

PURPOSE

The aim of this review was to evaluate the evidence on quality-of-life outcomes of long-term contact lens wear.

METHODS

A search for original articles that used validated measures to evaluate patient-reported outcomes (PROs) in long-term (≥2 years) contact lens wearers was conducted in Medline Ovid, PubMed, Scopus, Web of Science, Cochrane, CINAHL, and PsycInfo databases. The information including PRO measure (name, type, content) and key quality-of-life outcomes findings were extracted.

RESULTS

Seven articles that used 4 PRO measures to evaluate quality of life outcomes of long-term contact lens wear met the inclusion criteria. The median (range) number of contact lens wearers in these studies was 116 (31-247). The studies were conducted in 4 countries: USA, Spain, China, and Russia. All studies were conducted in myopic populations. None of the studies provided information on psychometric properties, validity and reliability of the PRO measures used. Five studies were conducted in children of which 3 studies evaluated PROs of myopia control contact lens wear. The studies reported that contact lens wear, including myopia control lens wear, was an effective method of refractive correction in children and adults in the long term in PRO-perspective, and resulted in a better quality of life status than with glasses. However, long-term dry eye and discomfort related symptoms were reported.

CONCLUSION

Overall, contact lens use improved quality of life status in children and adults. More research is required to better understand the long-term quality-of-life outcomes of contact lens wear.

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 analysis for development and reduction of Symptom Questionnaire for Visual Dysfunctions (SQVD)

To develop the Symptom Questionnaire for Visual Dysfunctions (SQVD) and to perform a psychometric analysis using Rasch method to obtain an instrument which allows to detect the presence and frequency of visual symptoms related to any visual dysfunction. A pilot version of 33 items was carried out on a sample of 125 patients from an optometric clinic. Rasch model (using Andrich Rating Scale Model) was applied to investigate the category probability curves and Andrich thresholds, infit and outfit mean square, local dependency using Yen's Q3 statistic, Differential item functioning (DIF) for gender and presbyopia, person and item reliability, unidimensionality, targeting and ordinal to interval conversion table. Category probability curves suggested to collapse a response category. Rasch analysis reduced the questionnaire from 33 to 14 items. The final SQVD showed that 14 items fit to the model without local dependency and no significant DIF for gender and presbyopia. Person reliability was satisfactory (0.81). The first contrast of the residual was 1.908 eigenvalue, showing unidimensionality and targeting was - 1.59 logits. In general, the SQVD is a well-structured tool which shows that data adequately fit the Rasch model, with adequate psychometric properties, making it a reliable and valid instrument to measure visual symptoms.

The Italian version of the Keratoconus Outcomes Research Questionnaire (KORQ): Translation and validation of psychometric properties

PURPOSE

To develop and validate the Italian version of the Keratoconus Outcomes Research Questionnaire (KORQ).

METHODS

Cross-sectional validation study. Keratoconus patients with routine appointments at the outpatient clinic were consecutively enrolled in conjunction with a sample of non-keratoconus controls for comparison. The Italian translation from the original English version of the KORQ was administered to the patients together with the Italian version of the 25-item version of the National Eye Institute Visual Function Questionnaire (NEI VFQ-25). The reliability and validity of the Italian KORQ were assessed using standardized internationally accepted methods for cultural adaptation and validation of health-related quality of life measures.

RESULTS

One hundred patients were deemed eligible and completed the questionnaires. The Cronbach's alpha coefficient for internal consistency ranged from 0.71 to 0.956 across the subscales. Spearman correlation coefficient and intraclass correlation coefficient of 0.98 showed excellent test-retest reliability. The control group had better scores on every subscale. Statistically significant correlations were found between the KORQ and analogous domain of the NEI VFQ-25 and with disease severity indicators, such as visual acuity, maximum keratometry, and steepest keratometry, thus demonstrating good construct and concurrent validity.

CONCLUSION

The Italian version of the KORQ exhibited excellent internal consistency, test-retest reliability, validity, discriminatory power, and psychometric properties comparable with those of the original English version, and thus may be adopted as a powerful vision-targeted quality of life assessment tool for Italian keratoconus patients.

Quality of life in keratoconus: evaluation with Keratoconus Outcomes Research Questionnaire (KORQ)

To assess the quality of life of keratoconus patients using the Keratoconus Outcomes Research Questionnaire (KORQ), translated and validated in Portuguese language. The KORQ is the only validated keratoconus specific questionnaire and has a high rating for its psychometric properties. This cross-sectional study enrolled 100 keratoconus patients from a tertiary referral eye hospital between April 2018 and June 2019. Associations between age, sex, allergic conjunctivitis, keratoconus stage, best-corrected visual acuity (BCVA), maximum simulated keratometry (Kmax), steep keratometry (K2), pachymetry, treatments performed, hydrops, and KORQ scores were evaluated using univariate (Wilcoxon test and the Kruskal Wallis test) and multivariate linear regression with stepwise backward modeling. Lower KORQ scores are associated with better quality of life, whereas, higher scores are associated with greater impairment of functional activities and symptoms. Among the 100 patients, mild, moderate, and severe keratoconus were observed in 15%, 46% and 39% of participants, respectively. Univariate analysis showed lower function scores values, with male sex (p < 0.05) and both functional and symptom scores were significantly associated with BCVA < 0.3 (LogMAR) (p < 0.05). Multivariate analysis indicated significantly lower functional scores in individuals with BCVA < 0.3 (LogMAR) (p < 0.001) and those with a history of crosslinking treatment (p = 0.022), while symptom scores were only significantly associated with only BCVA < 0.3 (LogMAR) (p < 0.001). In patients with keratoconus, BCVA in the better eye and history of crosslinkig were factors associated with better quality of life scores using the KORQ.

The Save Sight Keratoconus Registry - Optometry Module: an opportunity to use real-world data to advance eye care

There is increasing focus on the value of real-world clinical registry data in multiple medical disciplines, including ophthalmology. However, disease-focused clinical registries that engage optometrists are rare. This paper introduces the Optometry Module of the Save Sight Keratoconus Registry (SSKR) and highlights the potential advantages it can offer to optometrists for improving their quality of patient care and for engaging in research. Optometrists are primary eye care providers and have a major role in providing clinical care to people with keratoconus. The SSKR system has been developed to collects high-quality information on essential clinical parameters including patient-reported outcomes (i.e., quality of life data). The real-world data from the Optometry Module of the SSKR can be analysed to obtain insights into contemporary optometry keratoconus practice, and be used to identify opportunities for improving clinical care. Optometrists' engagement with the registry supports reflective clinical practice through real-time benchmarking. Optometrists can use the registry system to track patient outcomes, and it provides a framework for educating patients about their keratoconus journey. The system also captures details relating to patient adverse events, with subsequent data analysis enabling risk factors for such events to be identified. In summary, the Optometry Module of the SSKR captures real-world clinical evidence that has the potential to inform practice improvement, facilitate safety surveillance and enable outcomes research in keratoconus, all with the ultimate intent of enhancing care for people living with keratoconus.

Predictors of progression in untreated keratoconus: a Save Sight Keratoconus Registry study

AIMS

We set out to identify risk factors for progression in untreated keratoconus patients from 34 centres across Australia, New Zealand, Spain and Italy.

METHODS

Patients were divided into 'progressors' and 'stable' patients for each clinical parameter: visual acuity (VA), steepest keratometry (maximum keratometry (Max-K)) and thinnest corneal thickness (TCT). Primary outcomes were the proportion of eyes with sustained progression in VA, Max-K or TCT within 3 years. Secondary outcomes included predictors of progression.

RESULTS

There were 3994 untreated eyes from 2283 patients. The proportion of eyes with VA, Max-K and TCT progression at 1 year were 3.2%, 6.6% and 3.1% respectively. Factors associated with VA loss were higher baseline VA (HR 1.15 per logMAR line increase in VA; p<0.001) and steeper baseline Max-K (HR 1.07 per 1D increase; p<0.001). Younger baseline age was associated with Max-K steepening (HR 0.96 per year older; p=0.001). Thicker baseline TCT, steeper baseline Max-K and younger baseline age were associated with TCT thinning: (HR 1.08 per 10 µm increase in TCT; p<0.001), (HR 1.03 per 1D increase; p=0.02) and (HR 0.98 per year younger; p=0.01), respectively.

CONCLUSIONS

Steeper Max-K and younger age were the most clinically useful baseline predictors of progression as they were associated with worsening of two clinical parameters. Every 1D steeper Max-K was associated with a 7% and 3% greater risk of worsening VA and thinning TCT, respectively. Each 1 year younger was associated with a 4% and 2% greater risk of steepening Max-K and thinning TCT, respectively.

Item banks for measurement of refractive error-specific quality of life

PURPOSE

To evaluate the psychometric properties of refractive error-specific quality of life (QoL) item banks and assess their performance using computerised adaptive testing (CAT) simulations.

METHODS

In this cross-sectional study a 392-item questionnaire, grouped under 11 QoL domains, was interviewer-administered to 305 people with refractive error [mean age ± S.D., 30.5 ± 14.1 (range (18 to 83) years; male, 50.5%; mean ± S.D. spherical equivalent refractive error -2.4 ± 2.9 (range: -15.0 to +11.0) Dioptres; spectacles (n = 257), contact lens (n = 37), refractive surgery (n = 25), uncorrected refractive error (n = 57)]. Rasch analysis was conducted on each QoL domain using the Andrich rating scale model to investigate parameters including response category functioning, person- and item-reliability, infit and outfit statistics, unidimensionality, targeting, differential item functioning and local item dependency. The resulting item banks underwent CAT simulations in 1,000 cases with 'high' and 'moderate' precision stopping rules.

RESULTS

Rasch analysis iterations resulted in 13 refractive error-specific item banks (Convenience, Health concerns, Economic, Activity limitation, Mobility, Emotional, Social, Visual symptoms frequency, Visual symptoms severity, Visual symptoms bothersome, Comfort symptoms frequency, Comfort symptoms severity and Comfort symptoms bothersome), containing a total of 366 items. The item banks had good psychometric properties including satisfactory measurement precision, infit and outfit statistics and unidimensionality. In CAT simulations, the mean number of items required to achieve high and moderate measurement precision was 9.4 and 4.7, respectively.

CONCLUSION

Overall, refractive error-specific QoL item banks show promise in their ability to comprehensively and precisely evaluate a range of quality of life parameters. These items banks when administered using a CAT system offer unique outcome tools for implementation in clinical trials, healthcare and research.

Quality of life in stable and progressive 'early-stage' keratoconus patients

PURPOSE

To analyse the vision-related quality of life (vr-QoL) in stable and progressive keratoconus (KC) patients with a still good visual acuity.

METHODS

Combined prospective/cross-sectional study design. The Refractive Status and Vision Profile (RSVP) and the National Eye Institute Visual Functioning - 25 (NEI-25) questionnaire were used in 16 emmetropic, 32 myopic and 56 KC patients, whereby KC patients with a stable (n = 26) and patients with a progressive stage (n = 30) and some of them before and after corneal cross-linking (CXL; n = 10) were included. All patients had a DCVA in at least one eye of ≥0.7 (decimal chart).

RESULTS

The analyses revealed a minor decline of the vr-QoL from emmetropes to myopes to early KC patients with a stable disease. Nonetheless, sociological subscales (i.e. 'social functioning', 'role difficulties' and 'dependency') did not display statistically significant differences comparing these groups. In progressive KC, we could demonstrate a statistically significant decline also of these sociological subscales, which did not improve after CXL.

CONCLUSION

Due to a still high and almost unaffected vr-QoL in early KC patients and the distinct decline after progression without rehabilitation after CXL, a reconsideration of current strategies to perform CXL only after a progression is diagnosed should be re-evaluated.

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.

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

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.