Keratoconus is a progressive, degenerative disorder of the cornea that significantly impairs visual function and reduces the quality of life for affected individuals.1 The characteristic corneal irregularities associated with this condition lead to refractive errors, decreased visual acuity, heightened light sensitivity, and other visual disturbances, which profoundly affect patients’ daily activities and psychological well-being.2

Conventional clinical parameters such as Kmax, corneal thickness, or astigmatism do not always reflect patients’ subjective visual experience. Therefore, increasing attention has been given to assessing visual quality from the patient’s perspective using standardized questionnaires that quantify the impact of keratoconus on everyday visual functioning. One of the instruments designed for this purpose is the Keratoconus Outcomes Research Questionnaire (KORQ). This tool validated instrument developed by Khadka et al.3 to assess the impact of keratoconus on patients' vision-related quality of life. It specifically addresses activity limitations and symptom severity, considering the unique visual impairments associated with the condition. The original version consists of 29 items, divided into two subscales: the Activity Limitation subscale (18 items) and the Symptom subscale (11 items). Responses are recorded using a four-point Likert scale, with an additional "not applicable" option. The questionnaire is being progressively validated across an increasing number of countries worldwide.4–7,35 It functions as a standardized instrument for assessing visual quality and monitoring changes, particularly following interventions such as corneal crosslinking.8–9 The KORQ was successfully validated for the Polish context.10This study aimed to evaluate the impact of keratoconus on visual quality by integrating clinical measurements with subjective patient-reported outcomes, utilizing the Keratoconus Outcomes Research Questionnaire (KORQ).Previous studies on this topic, including those by Tan et al,11 Gothwal et al,12 Pinto et al,13 consistently show that poorer best-corrected visual acuity (BCVA) and greater disease severity are associated with worse quality-of-life scores. However, these studies primarily focused on visual acuity and corneal topography, with little or no attention to higher-order aberrations (HOA). Gothwal et al.12 reported only a weak correlation between total HOA RMS and KORQ outcomes, without examining individual aberration components. Similarly, Schümmer et al.14 demonstrated that increased coma and total HOA were associated with poorer visual-functioning scores, but their study used a general visual-functioning questionnaire rather than the keratoconus-specific KORQ.

Despite the growing number of studies assessing quality of life in keratoconus, several important gaps remain. Previous KORQ-based research has primarily focused on visual acuity and corneal topography, whereas only one study included aberrometric data, and even then, only total HOA RMS was analyzed without examining individual aberration components. Moreover, most studies averaged results between both eyes, overlooking the functional asymmetry characteristic of keratoconus, where the better-seeing eye often dominates visual performance. No research to date has investigated the relationship between specific higher-order aberrations and KORQ outcomes, particularly in a Central European population. Finally, prior analyses relied mainly on simple correlation methods, without considering the complex, potentially non-linear relationships between optical parameters and self-reported visual functioning. Despite extensive research on the vision-related quality of life in keratoconus patients, there is a noticeable lack of such studies within the Polish population, underscoring the need for localized research in this area. Upon further exploration, we identified a notable limitation in the availability of validated instruments for evaluating visual quality in this patient population.15

Combining objective clinical measurements such as higher-order aberrations (HOA), corneal topographic parameters (e.g., Kmax, pachymetry), and visual acuity with subjective patient-reported outcomes from the KORQ questionnaire, this study identifies key predictors of visual disability and symptom burden in keratoconus. The findings provide a comprehensive evaluation of how corneal irregularities, optical distortions, and loss of visual acuity contribute to functional impairment, underscoring the importance of advanced optical corrections and personalized treatment strategies to improve the quality of life for keratoconus patients. The analysis distinguished between the better- and worse-seeing eye and used advanced multivariable and non-linear statistical models to capture the complex relationships between visual function and quality-of-life outcomes. This comprehensive approach offers new insight into how optical irregularities and visual acuity contribute to perceived visual disability and may support more individualized strategies for improving patients’ visual quality and well-being.

This cross-sectional study with prospective data was conducted between July 2023 and November 2024 in the Department of Ophthalmology of the District Railway Hospital in Katowice, Poland. The Polish KORQ questionnaire was administered to 100 patients. The inclusion criteria for participation were as follows: adult men and women with a confirmed diagnosis of keratoconus at any stage and no other significant ophthalmic diseases. Patients who had undergone corneal transplantation in one eye were also included, if keratoconus had been diagnosed in the other eye as well. Each participant underwent a comprehensive ophthalmologic evaluation, accompanied by a detailed medical history interview. Information on the type of visual correction was collected for all participants. Patients who reported alternating between glasses and contact lenses were instructed to complete the KORQ based on their most frequently used form of correction.

Uncorrected visual acuity (UVA) and best-corrected visual acuity (BCVA) for each eye was measured monocularly using the Early Treatment Diabetic Retinopathy Study (ETDRS) chart (Precision Vision, La Salle, IL, USA) under standardized photopic conditions. The results were recorded in decimal notation. All measurements were performed by the same experienced examiner to ensure consistency. The stage of keratoconus was determined using the Amsler–Krumeich classification. Topographic (Kmax, astigmatism), pachymetric (CCT, MCT). and Higher-order aberrations (HOA) were derived from Scheimpflug-based corneal topography using the Pentacam HR system (Oculus, Germany). All measurements were performed under standard mesopic conditions with proper fixation, and image quality was verified according to the manufacturer’s guidelines. Aberrometric parameters were analyzed for a standardized 6.0-mm pupil diameter. Additionally, an effort was made to identify other factors influencing vision quality by incorporating a range of clinical parameters such as Total uncorrected visual acuity (Total UVA) was defined as the sum of uncorrected visual acuity values for the better- and worse-seeing eyes, and Total best-corrected visual acuity (Total BCVA) as the sum of best-corrected visual acuity in both eyes. BCVA asymmetry was calculated as the difference between BCVA in the better- and worse-seeing eyes, reflecting interocular disparity in visual performance. The thickness gradient (TG) represented the absolute difference between central corneal thickness (CCT) and minimum corneal thickness (MCT), providing an estimate of corneal thinning severity. The better-seeing eye was defined as the eye with higher BCVA

For statistical analysis, data were stratified by the better-seeing and worse-seeing eye. This division was necessary due to the high asymmetry of keratoconus, where one eye often exhibits significantly more advanced disease than the other. The better-seeing eye predominantly determines overall visual function and practical performance in daily life, while the worse-seeing eye plays a key role in binocular vision, contrast sensitivity, and visual discomfort due to aberrations. Analyzing both eyes together could obscure these distinct functional contributions and lead to misleading conclusions about the impact of keratoconus on quality of life. By evaluating them separately, it was possible to more accurately determine which clinical parameters best predict functional limitations versus symptom severity, allowing for a more precise understanding of the disease’s real-world consequences.

Statistical analyses were performed with a significance level set at α = 0.05. The normality of continuous variables’ distributions was evaluated using the Shapiro-Wilk test.16 The method of data presentation (mean ± SD for normally distributed variables and median with interquartile range for non-normally distributed variables) was already specified in the footnotes below the relevant tables. Continuous variables that did not conform to a normal distribution were summarized using medians and interquartile ranges (IQRs), defined as the difference between the first and third quartiles. For ordinal variables, such as questionnaire scores from the Keratoconus Outcomes Research Questionnaire (KORQ), means and standard deviations were reported as measures of central tendency and variability, respectively. Categorical variables were described using absolute frequencies (n) and corresponding percentages (%).

Differences in numerical variables between two independent groups were assessed using the Wilcoxon rank-sum test for non-normally distributed data.17 To explore relationships between the total domain scales of the KORQ and numeric clinical parameters, biweight mid correlation coefficients – a robust alternative to traditional similarity metrics were computed.18 For the analysis of the effects of numeric clinical parameters on the total domain scales of the KORQ, robust linear regression (RLM) was employed to estimate regression coefficients, with adjustments for age and gender as covariates.

The study investigated the impact of keratoconus on patients’ quality of life by combining objective clinical data with subjective self-assessment using the Polish version of the Keratoconus Outcomes Research Questionnaire (KORQ).

Regarding gender distribution, males represented approximately 80% of participants in our sample. Although keratoconus is generally considered to affect both sexes with similar frequency, some epidemiological studies have reported a modest male predominance, possibly related to environmental or behavioral factors.33–34 In our cohort, the male predominance was likely incidental and may reflect local referral patterns or lower participation rates among women in examinations requiring full aberrometric assessment and completion of questionnaires. Nevertheless, this imbalance should be considered when interpreting and generalizing the results to the broader keratoconus population.

No significant differences in KORQ scores were observed between patients who had undergone surgical interventions (corneal cross-linking or keratoplasty) and those who had not. This finding is consistent with Pomberger et al5, who reported similar outcomes in a German cohort, where surgical procedures did not significantly alter subjective visual function. However, Pinto et al.13 found that patients who had undergone cross-linking reported worse functional scores, possibly due to post-procedural discomfort or incomplete visual recovery.

Patients reported the greatest difficulties in daily functioning during tasks requiring distance vision, in low-light conditions, and while driving at night. Visual symptoms such as distorted vision, dry eyes, fatigue, and discomfort in dusty or smoky environments significantly affected their quality of life. These results are consistent with previously published papers. The average score for the Activity Limitation subscale was 51.53 (SD = 17.19) and for the Symptom subscale 55.60 (SD = 16.14), indicating a moderate but meaningful impact of keratoconus on everyday functioning. Results were closely aligned with those found in studies by Alatawi36 in Saudi Arabia and Kandel et al. in Australia.37 Slightly higher scores, particularly in the Activity Limitation (AL) subscale, were reported by Pinto et al.7 in Portugal. These results suggest a consistent pattern of patient-reported outcomes across diverse populations.

The study demonstrated a clear and statistically significant difference in Activity Limitation and symptoms between male and female patients, suggesting a potential influence of sex-related factors on the perceived impact of keratoconus. Women reported greater functional impairments and more severe visual symptoms than men. These findings are consistent with those of Al Bdour et al.38 and Gothwal et al.12 also identified gender-based disparities in keratoconus-related quality of life. Potential explanations for this difference may include differences in the perception of discomfort, as women may be more sensitive to irritation, dryness, or photophobia, a greater tendency to report symptoms, and possible hormonal differences affecting the tear film and ocular surface stability. However, the influence of gender on vision-related quality of life in patients with keratoconus remains inconclusive, as previous studies have reported conflicting results. Notably, in the univariate analysis conducted by Pinto et al13, male patients exhibited worse KORQ scores in the functional domain. In the study by Danish researchers Bak-Nielsen et al6, no significant differences were found between women and men. This may be related to a different clinical profile, a limited number of female participants in other cohorts, or cultural factors influencing symptom reporting. Such exceptions should be considered when interpreting and generalizing the results.

Robust linear regression models, adjusted for age and gender and biweight correlation analyses identified several variables that were significantly associated with scores on both the Activity Limitation and Symptoms subscales of KORQ Questionnaie. These variables are discussed in detail below.

Best-corrected visual acuity (BCVA) in the better-seeing eye emerged as one of the strongest and most consistent predictors of both activity limitation and symptom severity Regression analysis show strong and statistically significant associations between best-corrected visual acuity (BCVA) and both the Activity Limitation and Symptoms subscale scores of the KORQ.

Previous studies have consistently demonstrated that BCVA, particularly in the better-seeing eye, is more strongly associated with patient-reported KORQ scores. For instance, Gothwal et al12, Kandel et al.37 and Tan et al.11 identified BCVA as a key predictor of reduced visual functioning scores across diverse international cohorts. These findings are further supported by Pinto et al.13 who reported moderate to strong correlations between BCVA and both KORQ subscale scores. Similarly, Ferrini et al.4 observed a statistically significant relationship between BCVA in the better-seeing eye and both KORQ subscale scores in an Italian population.

Although BCVA did not show statistically significant associations in biweight correlation analyses, it emerged as an independent predictor in multivariate regression models. The lack of statistically significant associations between BCVA and KORQ scores in correlation analyses suggests that the relationship between visual acuity and patient-reported outcomes is not purely linear and may be influenced by other coexisting clinical factors. In particular, the effect of BCVA appears to be modulated by variables such as higher-order aberrations, which may obscure its contribution in univariate correlation analyses. When these factors are accounted for in multivariate regression models, the independent role of BCVA—especially in the better-seeing eye—becomes evident. This finding highlights the importance of multivariable analytical approaches when assessing determinants of vision-related quality of life in keratoconus.

It was demonstrated that there were no statistically significant correlations between KORQ scores and classic tomographic parameters, corneal thickness (CCT/MCT), astigmatism, or thickness gradient. Studies by Al Bdour et al38, Pomberger et al5, and Bak-Nielsen et al.6 similarly reported weak or non-significant associations between topographic measures and QoL outcomes, questioning the clinical relevance of these parameters in isolation. However, a weak but statistically significant correlation was observed for Kmax in the worse-seeing eye in Activity Limitation Scale, although this relationship lost significance in the regression model. Despite the fact, Kmax in the worst-seeing (Activity Limitation subscale) showed a weak but statistically significant correlation (rbicor = 0.21; p = 0.035), which might suggest that greater corneal protrusion is associated with increased functional limitations. However, in regression models that included BCVA and HOA, Kmax lost its significance, confirming that its importance is secondary to more direct factors such as visual acuity and aberrations. A similar pattern was observed in the validation study of the German version of the KORQ questionnaire5, where, although significant correlations between Kmax and K2 with KORQ scores were found, BCVA emerged as a stronger and more independent predictor of quality of life. These findings reinforce the conclusion that while Kmax may appear important in univariate analyses, in multivariate models it is outweighed by more influential factors.Importantly, several higher-order aberration (HOA) parameters were also identified as significant contributors to reduced quality of life in patients with keratoconus. Our results confirm and reinforce existing evidence that optical and functional parameters (HOAs and BCVA) better predict subjective visual outcomes than corneal curvature metrics alone

Specifically, RMS HOA in the worse-seeing eye was significantly associated with higher KORQ scores in both the Activity Limitation and Symptoms subscales . Moreover, horizontal coma, vertical coma for Activity Limitation and Symptoms subscales, and trefoil aberration at 180° for the Symptoms subscale were all statistically significant predictors.

The results obtained in the Activity Limitations subscale indicate that certain higher-order aberrations have a significant impact on the subjectively perceived functional difficulties in patients with keratoconus.

Both the biweight correlation analysis and regression models consistently demonstrated significant associations for aberrations located in the worse-seeing eye, such as: RMS HOA, horizontal coma, vertical coma., RMS HOA, horizontal coma, vertical coma. Additionally, trefoil aberration at 180° in the better-seeing eye was significant in both the correlation and the regression analyses, (making it one of the few functionally relevant predictors derived from the better eye.

It is worth noting that other aberrations, such as trefoil (30°) or horizontal coma in the better-seeing eye, reached significance only in the correlation analyses but were not significant in regression (although sometimes close to the significance threshold). The reverse situation, significance in regression without a significant correlation, was not observed.

This partial concordance between correlation and regression models suggests that while the impact of HOA on daily functioning is evident, it may be modulated by other clinical factors, such as visual acuity.

In the Visual Symptoms subscale, correlation analyses and regression models showed consistent results, indicating clear and reproducible relationships. Particularly evident was the impact of aberrations originating from the worse-seeing eye, confirming their dominant role in subjective visual discomfort. The following variables were statistically significant in both biweight correlations and regression RMS HOA, vertical coma, horizontal coma, trefoil (180°), RMS Error.Other variables that were significant in correlation but not in regression included: astigmatism (0°), which did not reach significance in the regression model and spherical aberration, which also lost significance when other variables were accounted for.

Aberrations from the better-seeing eye, in turn, did not show significant associations in any of the analyses, further supporting the notion that the image quality in the worse (possibly more distorted) eye dominates the subjective perception of visual symptoms such as halos, blurring, or shape distortions.

The overall agreement between correlation and regression results in this subscale enhances the reliability of the observed associations and emphasizes the importance of selected aberrations. The consistency of findings across analytical approaches underscores the particular relevance of aberrations in the worse-seeing eye, especially coma (horizontal and vertical) and trefoil 180°.

In summary, higher-order aberrations (HOA), particularly those present in the worse-seeing eye, significantly affect the subjectively perceived quality of vision. In the Activity Limitations subscale, their impact was noticeable, though partially modulated by other factors such as BCVA. In the Visual Symptoms subscale, the relationship between HOA and symptom severity was strong and unequivocal, with high consistency between correlation and regression results. The most significant contributors were the coma components, trefoil, and total RMS HOA. These findings suggest that the assessment of visual quality in keratoconus patients should consider not only visual acuity but also the optical image quality, especially in the worse-seeing eye.

Similar relationships were described in the study by Gothwal et al12, in which total HOA RMS in the worse eye showed a significant association with KORQ outcomes. Unlike Gothwal’s study, the present research conducted a detailed analysis of individual aberration components, demonstrating a significant impact of horizontal and vertical coma as well as trefoil aberrations. Importantly, their influence on visual quality remained statistically significant in regression models even after accounting for BCVA, indicating a partially independent effect of HOA.

Previous studies have explored the relationship between visual function and patient-reported outcomes in keratoconus, either through disease-specific tools such as the KORQ, Tan et al.11 Gothwal et al12, Pinto et al.13 or through general visual function questionnaires such as the VFQ Schümmer et al.14 However, no published KORQ-based study has incorporated detailed aberrometric analysis, and no HOA-based study has assessed quality of life using the KORQ. The present work is, to our knowledge, the first to integrate both approaches by combining a culturally KORQ with component-level HOA data.

Moreover, unlike previous studies that used only total HOA RMS, we analyzed individual aberration components (coma, trefoil, spherical aberration) and their independent and non-linear relationships with KORQ outcomes, separately for the better and worse eye. This multidimensional approach provides a more complete understanding of how optical distortions affect vision-related quality of life and represents the first such analysis in a Central European population.

We would like to discuss several limitations of the present study. One limitation is the relatively small subset of participants (approximately 40 eyes) with complete higher-order aberration data. This limited sample size may have reduced the statistical power to detect weaker associations, particularly in multivariate models including several covariates. Although key relationships between specific aberration components and KORQ outcomes reached statistical significance and were consistent across both subscales, these results should be interpreted with caution. At the same time, the replication of similar effect patterns in both eyes and in sensitivity analyses supports the robustness of the main findings.

Another limitation of this study is that the study population was recruited from a university-affiliated ophthalmology center providing specialized care, which may be associated with a higher proportion of patients with more advanced keratoconus. Although the cohort covered the full spectrum of disease severity, the findings may therefore not be fully representative of keratoconus patients managed exclusively in non-referral or community-based clinical settings. In addition, the limited availability of publicly funded interventions aimed at slowing keratoconus progression prior to 2023 in Poland may have contributed to later referral and more advanced disease at presentation.

Additional limitations related to measurements and methodology should also be considered. Some participants reported alternating between spectacles and contact lenses and were asked to respond based on their most frequently used form of correction. Although this approach was intended to standardize responses, it may have introduced recall bias and recall-related variability in questionnaire responses.

Aberrometry was performed using the Pentacam HR (Oculus), and all HOA values were analyzed for a standardized 6.0-mm pupil, following the device’s default settings. Therefore, the observed associations between HOA and KORQ outcomes should be interpreted with caution and verified in larger samples.

Another potential limitation of the study is that visual assessment was primarily based on monocular measurements, whereas visual quality under everyday conditions is inherently binocular. Attempting to relate parameters obtained monocularly to those that may better represent binocular vision is a challenging task and could, to some extent, limit the interpretation of the results. Future research could consider further exploration of binocular vision and the potentially insufficient suppression mechanisms in the more affected eye, which may contribute to discrepancies between optical image quality and subjectively perceived visual performance. Including binocular measurements in future analyses may provide additional insights into the perceptual mechanisms underlying vision in keratoconus.

No statistically significant differences in KORQ scores were observed concerning the stage of disease severity. This result is not surprising, considering that none of the corneal parameters proved to be significant predictors of questionnaire outcomes. Perhaps the use of a classification system that incorporates visual acuity, such as the ABCD grading system39, would have been a better choice, which represents a potential limitation of our study.

Overall, this study demonstrates that vision-related quality of life in patients with keratoconus is influenced by multiple interacting factors, with optical quality and visual acuity playing a more significant role than corneal structural parameters alone. Both correlation and regression analyses revealed that higher-order aberrations (HOA), particularly in the worse-seeing eye, are strongly associated with the severity of subjective visual symptoms. Moreover, best-corrected visual acuity (BCVA) in the better-seeing eye emerged as an independent and consistent predictor of both functional limitations and symptom burden, as measured by the KORQ questionnaire.

These findings carry important clinical implications. They challenge the conventional structure-based model of assessment and highlight the need for a more comprehensive understanding of visual function. Recognizing the role of the worse-seeing eye, often overlooked in routine evaluation, may be crucial for accurately assessing a patient’s difficulties. Moreover, the results support the integration of subjective assessment tools, such as patient-reported outcome measures like the KORQ, into routine clinical care to better capture the real-world impact of the disease.

Ultimately, the goal of keratoconus management should not be limited to improving clinical metrics alone. A more holistic and individualized approach, incorporating both objective data and the patient’s perspective, may lead to more effective and meaningful therapeutic decisions.

Best-corrected visual acuity (BCVA) is a key determinant of vision-related quality of life in patients with keratoconus, playing a more important role than corneal structural parameters. Higher-order aberrations (HOAs), particularly in the worse-seeing eye, are significantly associated with greater symptom severity and functional limitations. The results show that improving best-corrected visual acuity (BCVA) and reducing higher-order aberrations should be the main goals of treatment to enhance patients' vision and everyday functioning.

The study was approved by the Bioethics Committee of the Medical University of Silesia, Katowice, Poland (protocol code: BNW/NWN/0052/KBI/70/23, date of approval: 11 July 2023).

Informed consent was obtained from all individual participants included in the study. The privacy rights of patients were always observed.

During the preparation of this work, the author(s) used ChatGPT (OpenAI) in order to improve language and grammar. After using this tool, the author(s) reviewed and edited the content as needed and take(s) full responsibility for the content of the publication.

Conceptualization, M.N. and E.W.; methodology, M.N. and A.W.; formal analysis, E.W., A.W. and M.N.; investigation, D.S., M.K., M.N. and B.M.; data curation A.W. and M.N.; writing—original draft preparation, M.N., J.P; writing—review and editing, E.W., A.W., M.K., D.S. and B.M.; supervision, E.W. and A.W.; project administration, E.W. All authors have read and agreed to the published version of the manuscript.

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.