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

doi:10.21203/rs.3.rs-3193649/v1

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Research Article

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

https://doi.org/10.21203/rs.3.rs-3193649/v1

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Purpose

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

Methods

In this prospective clinical study, next to comparing the morphology and functional parameters of KC patients, we applied the “National Eye Institute Visual Functioning Questionnaire” (NEI-25) and the “Keratoconus Outcomes Research Questionnaire” (KORQ) to analyze the vr-QoL in 41 patients before, three and six months after CXL. Rasch analyses was applied to verify the measurement precision of the KORQ in our study population.

Results

We did not find statistically significant changes of the corneal morphology and the best corrected visual acuity after CXL. The NEI-25 questionnaires did not show statistically significant changes throughout the follow-up period. Except from single items, the main scores of the KORQ also did not demonstrate statistically significant changes. Rasch analyses revealed a high measurement precision of the KORQ within our population.

Conclusion

We could demonstrate a stable (not-improving) vr-QoL after CXL in patients with progressive KC. Based on our findings we suggest very early CXL treatment in KC patients that are at high risk of progression.

keratoconus

vision-related quality of life

KORQ

NEI-25

corneal crosslinking

Keratoconus (KC) is a bilateral disease causing a decrease of visual acuity and -quality due to a progressive irregular ectasia of the cornea. The vision-related changes start during puberty and tend to stabilize during the 3rd and 4th decade of life [1]. A current metanalysis by Hashemi et al report a worldwide prevalence of 1.38/1000 [2].

Whereas the decrease of visual acuity (VA) during the early stages can be managed with glasses, the increasing irregularities of the cornea during more advanced stages require hard contact lenses and/ or surgical interventions up to corneal transplantation to ensure a VA at least suitable for daily life tasks. In case of a still adequate VA, corneal collagen crosslinking has been proven to be an effective therapy to stop further progression of the corneal ectasia and thereby stabilize the disease [3–5].

During recent years, numerous studies have been conducted improving not only our understanding of the Quality of Life of these patients, but also to improve our methods to measure the vision-related quality of life (vr-QoL) in keratoconus patients [6–10].

This study was designed to follow-up findings of our previous study whereby we demonstrated a decrease of the vr-QoL in patients with a progressive disease compared to patients with stable KC. A small-sample subgroup of the KC-patients who received CXL due to progression of their disease could be re-evaluated 3 months after the treatment, whereby the vr-QoL remained on the same (decreased) level [11]. With our current study, we want to verify the potential “not-improving” vr-QoL after CXL in progressive KC by including a higher number of CXL-treated patients and extended our follow up to 6 months after CXL. Above, we included a new KC-specific questionnaire to evaluate the vr-QoL.

This prospective study was performed as part of a cooperation between the Department of Ophthalmology, University Medical Center Hamburg- Eppendorf, and the Hamburg Vision Clinic, located at the university campus Hamburg-Eppendorf. Our study adhered to the Tenets of the Declaration of Helsinki. Informed consent of the patients and approval of the local ethics committee were obtained. The study is listed in the German Clinical Trials Register (DRKS; DRKS00030330).

The diagnosis of clinically manifest KC in our study was made after thorough clinical evaluation by two experienced corneal specialists (JS, SL) based on slit-lamp findings and at least one of the following objective topography data: KISA-Index > 100, I-S > 1.4D, Kmax > 47D [12, 13]. The definition of progressive keratoconus included an increase in Kmax and/or refractive astigmatism ≥ 1 D within 1 year [14, 15]. Exclusion criteria were previous ocular surgery or trauma, contact lens wearing within 5 days (soft CL) or 7 days (hard CL) before examination.

To analyze the vision-related quality of life (vr-QoL) in our patients, two different questionnaires were used: the “National Eye Institute Visual Functioning Questionnaire – 25” [NEI-25] and the “Keratoconus Outcomes Research Questionnaire” [KORQ]). Both were evaluated and used in former studies for measuring vr-QoL in patients with keratoconus [6–8, 16, 17]. The questionnaires were completed after informing the patients about the study rational and obtaining their written consent by one of the authors (PF). All KC patients knew about their disease and its progression in one eye beforehand and were scheduled for an epi-off corneal cross-linking treatment (CXL) as well as the regular follow-up examinations at the Hamburg Vision Clinic. Both questionnaires were completed before, three and six months after CXL.

The changes in refractive, visual acuity and topographic parameters were estimated using mixed regression with subject random effect. The differences in estimates between time periods were tested with Tukey post hoc method. For testing differences of glare-test-data, the Wilcoxon signed-rang-test was applied. Spearman correlation analyses were used to identify potential correlations between the KORQ results and the measured topographic and VA-data.

The data from the KORQ were evaluated using the “ready to use excel-spreadsheet” provided and recommended by Khadka et al. [10]. Additionally, we evaluated how sufficient the KORQ measures psychometric properties in our patients by running Rasch analysis. Thereby, the precision can be estimated by testing the one-dimensionality and ordering of category and expressed in Rasch outputs for person and item separation and reliability [9, 18]. The NEI-25 data were evaluated as recommended by the Mangione et al. [19].

In total, we included 41 patients (33 male, 8 female, mean age: 25 (range 18 to 50) with progressive KC into our study. Their respective refraction, visual acuity and topography data for both eyes are displayed in Table 1.

Table 1

Descriptivs
	Before surgery			3 months follow-up			6 months follow-up
	N	Range	Mean (SD)^a	N	Range	Mean (SD)^a	N	Range	Mean (SD)^a	P-Value^b
Treatment-Eye
ISV (D)	36	-0.09 to 12.89	6.53 (± 3.63)	31	-0.9 to 13.4	6.72 (± 3.63)	35	-0.26 to 11.8	6.51 (± 3.63)	0.410
KMax (D)	36	45.77 to 74.92	56.42 (± 7.46)	31	46.18 to 72.96	56.19 (± 7.45)	35	44.9 to 74.76	55.82 (± 7.45)	0.330
RMS	36	0.33 to 6.33	2.90 (± 1.35)	31	0.58 to 5.96	2.86 (± 1.35)	35	0.67 to 6.12	2.80 (± 1.35)	0.430
Sphere (D)	37	-10 to 3.5	-1.15 (± 2.64)	40	-12 to 4.5	-0.74 (± 2.64)	39	-10 to 2.75	-1.23 (± 2.64)	0.510
Cylinder (D)	37	-7.75 to 0.25	-2.89 (± 1.89)	40	-8 to -0.5	-3.48 (± 1.88)	39	-7.5 to -0.75	-3.27 (± 1.87)	0.220
Spherical Equiv. (D)	37	-10.62 to 2.25	-2.59 (± 3.15)	40	-16 to 3	-2.49 (± 3.16)	39	-13.5 to 1	-2.86 (± 3.16)	0.730
UDVA (LogMar)	25	0.15 to 2	0.86 (± 0.40)	33	0.15 to 2	0.75 (± 0.33)	30	0.15 to 2	0.66 (± 0.29)	0.010
CDVA (LogMar)	36	0 to 2	0.28 (± 0.17)	40	0 to 1	0.26 (± 0.17)	39	0 to 0.82	0.26 (± 0.17)	0.560
Fellow Eye
ISV	36	-1.8 to 20.83	4.33 (± 3.97)	31	-0.32 to 20.47	4.67 (± 3.97)	34	-9.46 to 11.01	3.51 (± 4.07)	0.140
KMax	36	41.62 to 94.52	52.70 (± 9.81)	31	41.98 to 84.94	52.56 (± 9.88)	34	42.03 to 89.57	52.12 (± 9.81)	0.720
RMS	36	0.23 to 7.08	2.10 (± 1.63)	31	0.33 to 7.14	2.11 (± 1.62)	34	0.26 to 15.55	2.37 (± 1.64)	0.600
Sphere (D)	37	-14.5 to 8	-0.58 (± 2.79)	39	-13 to 4.75	-0.53 (± 2.79)	38	-11.5 to 8	-0.23 (± 2.80)	0.460
Cylinder (D)	37	-5 to 0	-1.44 (± 1.30)	39	-5 to 0.25	-1.45 (± 1.29)	38	-6 to 0	-1.75 (± 1.30)	0.130
Spherical Equiv. (D)	37	-16.25 to 6.25	-1.28 (± 2.90)	39	-15.5 to 3.38	-1.26 (± 2.90)	38	-14.25 to 7	-1.10 (± 2.91)	0.850
UDVA (LogMar)	25	0 to 2.3	0.54 (± 0.30)	31	0 to 2	0.48 (± 0.28)	30	0 to 2	0.41 (± 0.16)	0.040
CDVA (LogMar)	36	0 to 2.3	0.13 (± 0.12)	39	0 to 2	0.13 (± 0.13)	38	0 to 2	0.12 (± 0.11)	0.490
^a Estimated with Mixed Regression Model with subject random effect
^b Adjusted with Tukey method

Table 1Descriptivs

Regarding the refractive, topographic and visual acuity data, we could identify statistically significant differences only for the UDVA (treatment- and fellow-eye). The pairwise comparison revealed statistically significant differences only for the comparison before and six months after the treatment with improvement in both eyes (treatment-eye: mean UDVA (LogMar) before/ after treatment: 0.86/0.66, P = 0.009; fellow-eye: 0.66/0.45, P = 0.029). We also conducted contrast and glare VA – test (Mesotest®, Oculus, Wetzlar Germany) with all patients failed to identify any optotypes either before or after the treatment.

Psychometric analyzes

KORQ

The KORQ and the NEI-25 were completed on the day of surgery, three months ([mean/SD]: 93 days ± 13) and six months (189 days ± 15) after CXL.

Analyzing the psychometric properties data obtained from the KORQ during follow-up, we found statistically significant differences only for one of the 18 items in the “visual ability” section: “How much does your vision interfere with using a computer screen?” (improvement pre to 6-month follow-up, P = 0.033). Within the “activity” section, two of the 11 items demonstrated statistically significant differences: “How much are you troubled by distorted vision?” (improvement pre – 6-months follow-up, P = 0.004) and “With respect to your eyes and vision: How much are you troubled by dry days?” (decline pre − 6 months follow-up, P = 0.015). The combined “activity” and “symptoms”-scores didn`t display any statistically significant differences (activity [pre/3month post/ 6 months post]: -1.18 (+-0.98)/-1.23(+-0.99)/-1.27(+-1.04) P = 0.799; symptoms: -1.25(+-0.98)/-1.3(+-0.93)/-1.24(+-1.01) P = 0.738, (for further data see supplement file 1). We did not demonstrate any statistically significant correlations between either “symptoms” or “activity”-scores and the analyzed topographic or visual acuity data before or after the treatment.

To evaluate measurement - precision of the KORQ in our study population, we additionally run Rasch analyses. The output numbers for our study collective (Table 2) demonstrate a high measurement precision (the cut-offs displayed in Table 2 are based on the study by Khadka et al. [10]).

Table 2

Rasch analysis results to evaluate the psychometric properties of the KORQ in our study population.
	Domains
Categories	Symptoms	Activity
Person separation (> 2.0)	2.07	2.83
Person reliability (> 0.8)	0.81	0.89
Item separation (> 2.0)	3.03	7.15
Item reliability (> 0.8)	0.9	0.98

Table 2

NEI-25

Analyzing potential differences between the vr-QoL of KC patients with the NEI-25, we did not find statistically significant differences of items before and after the treatment (see supplement file 2).

In our current study, using a prospective study design with a higher number of included patients, we confirm our previous findings of a stable vr-QoL in KC-patients after CXL [11]. These results are in line with the findings of other studies analyzing the vr-QoL in progressive KC after CXL using the NEI-25 [20, 21]. Kandel et al published a comprehensive review about the measurement of QoL in KC clearly emphasizing the importance of using a comprehensive and high-quality patient-reported outcome to achieve reliable results. The NEI-25, developed in 2001, “was designed to measure the dimensions of self-reported vision-targeted health status that are most important for persons who have chronic eye diseases. The content was identified during a series of condition-specific focus groups with patients who had age-related cataracts, glaucoma, age-related macular degeneration, diabetic retinopathy, or CMV retinitis” [19, 22]. Next to the content-related inaccuracies when using a questionnaire originally designed by analyzing patients with different pathologies, also the method of designing the questionnaire is important to achieve reliable results.

Many questionnaires like the NEI-25 use traditional Likert (summary) scoring without the application of statistical validation derived from item response theory [23]. Important components of these statistical validation options include Rasch weighting, which converts standard Likert scales into linear data and helps to remove redundant items, or principal component analysis, which helps to establish whether items on a scale all measure the same trait, or whether a scale is unidimensional [24, 25]. In 2017, based on these principles (importance of pathological specific content and statistical validation implementation), Khadka et al. developed a keratoconus outcome research questionnaire (KORQ), which has been termed by Kandel et al as “the only validated keratoconus- specific questionnaire”, which provides “the most superior psychometric properties” [8, 10]. Consequently, in more recent studies, the KORQ has been predominantly used to analyse vr-QoL in KC patients [6, 7, 26, 27].

To ensure the reliability of our results, we not only used the NEI-25 as we did in our previous study, but also the KORQ and did additional Rasch analysis to validate the precision of the KORQ when applied to our study population. Despite single items of the KORQ display statistically significant differences before – after CXL (in total 3 of 29, whereby 2 items displayed improvement of VA-related tasks and one a worsening of dry eye symptoms), neither the combined “activity” or “symptoms” scores demonstrated differences of statistical significance. The Rasch analysis revealed a good measurement precision using the KORQ in our population.

The two studies we found analysing the vr-QoL in KC patients pre and post CXL using the KORQ, reporting either an improvement or an equal vr-QoL [6, 7]. As done in our study, Kandel et al. and Ferrini et al included 39 or 38 patients with a follow up of 6 months. However, other than in their studies, we couldn`t find any correlation of visual- or morphology– parameters with the KORQ-scores. This was completely unexpected because most studies report, as expected, high correlation between vr-QoL scores and the visual acuity [6, 7, 10]. Looking at the data given in the respective studies, the most obvious biasing factors leading to different correlation-results might be a distinct heterogeneity of the age and the used VA-data: The mean age of the patients analyzed in the study by Khadka et al. was 45 years of age, which at least almost double the mean age of the patients included in our and the studies by Ferrini et al. (20.5) and Kandel et al. (24,2). Regarding the influence of the visual acuity data, Ferrini et al report a mean BCVA of the treatment eye of 0.2 before the treatment without giving information about the BCVA of the fellow eye. Their correlations analysis, conducted for both eyes of the patient, revealed significant correlations of the KORQ scores and the treated eye before, but not 6 months after the treatment. The untreated eye didn`t show any significant correlations between the BCVA and the KORQ scores “symptoms” or “activity”. Kandel et al. reporting a mean BCVA of the treatment eye of 0.4 before the treatment, without giving data of the untreated eye. The initial BCVA of 0.4 is much lower than in similar studies. Khadka et al. analyzing KC patients, but not before and after CXL, reported about the worse-, and better-eye, whereby the “better eye” of the patient was used for statistical analysis (mean BCVA better eye: 0.2, worse eye: 0.3).

Independently of the heterogeneity of the BCVA reported in the different studies, it seems to be not completely clear which eye should be used for correlation analysis: The one of the treatment eye? The one of the “better” eye or the binocular visual acuity? A recent study by Kandel et al., conducted to get more insight in the relationship between the QoL scores and the standard clinical variables, reported that the correlations of QoL scores with most clinical parameters and visual acuity were similar when considered either better eye or worse eye [28]. They also demonstrated statistically significant correlations between clinical and QoL scores, but only with “low magnitudes” suggesting a more complex relationship between clinical parameters and patient-reported outcomes [28].

A potential drawback of our study could be the heterogeneity of the VA of the included patients. Usually, we perform CXL in patients with a “still good enough vision for daily tasks”. Otherwise, we use a combined approach (PRK/ CXL), implant rings (MyoRing®) or do keratoplasty. However, some patients didn`t follow our recommendation and decided for the “more basic” (CXL) treatment which is usually also the only treatment option fully covered by their insurance company. On the one hand we could have decided to excluded these patients, on the other hand, we intentionally wanted to include all the patients treated in our facilities to avoid unrecognized bias and to get a “unfiltered” insight in the “general” vr-QoL of (our) KC patients.

In summary, we could confirm our previous findings of a stable (not-improving) vr-QoL after CXL in progressive KC patients. These findings are especially important considering the fact of a known lower vr-QoL in KC patients with a diagnosed progression compared to patients with a stable disease [11, 29]. Our findings underline the importance of an early stabilizing treatment of KC patients not only from a morphological/ functional, but also from a psychological perspective [11]. Based on this knowledge, we recommend to consider initial stabilizing treatment in young patients with a high risk of progression and not to wait until progression can be confirmed by morphological changes.

The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

The authors have no relevant financial or non-financial interests to disclose.

Author contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Johannes Steinberg, Paul Fischer and Vasyl Druchkiv. The first draft of the manuscript was written by Johannes Steinberg and Paul Fischer and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Ethics approval

This study was performed in line with the principles of the Declaration of Helsinki. Approval was granted by the local Ethics Committee Hamburg (17^th of august 2020, No PV5720). Informed consent was obtained from all individual participants included in the study. The study is listed in the German Clinical Trials Register (DRKS; DRKS00030330).

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

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Abstract

Purpose

Methods

Results

Conclusion

Introduction

Materials and Methods

Results

Psychometric analyzes

KORQ

NEI-25

Discussion

Conclusions

Declarations

References

Additional Declarations

Supplementary Files

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Version 1