Keratoconus and quality of life: an updated comprehensive review

Abstract

Keratoconus (KCN), a progressive ectatic corneal disorder, significantly impacts vision-related quality of life (VRQoL) beyond reduced visual acuity. This review aims to comprehensively examine the impact of keratoconus on patients’ quality of life (QoL), considering its economic burden and the effectiveness of various treatment modalities in improving QoL outcomes. KCN profoundly impacts VRQoL, exceeding the effects of reduced visual acuity alone. Multiple factors contribute: refractive errors (leading to challenges with spectacle and contact lens correction, impacting comfort and convenience), decreased contrast sensitivity (hindering daily activities like driving and reading), ocular pain and discomfort (often stemming from the disease itself or treatment), and associated comorbidities (such as vernal keratoconjunctivitis, further compromising ocular health). Disease severity significantly influences VRQoL, with more advanced KCN generally linked to lower QoL scores, although this correlation is not consistently observed across studies. Demographic variations also play a role, with differences noted across genders and age groups in various studies. Nonsurgical options include spectacles (effective in early stages only), contact lenses (soft, rigid gas permeable, and scleral lenses offering varying degrees of visual correction and comfort), each impacting QoL differently based on visual improvement, comfort, and cost. Surgical interventions, such as corneal collagen crosslinking, indirectly improve QoL by stabilizing vision; however, they may not fully restore visual acuity and involve a period of postoperative discomfort. Intracorneal ring segments improve corneal shape and refractive errors, enhancing visual acuity and potentially QoL, but long-term effects and suitability depend on disease stability. Corneal transplantation, reserved for advanced cases, significantly improves vision and QoL for many patients, but it is an invasive procedure with potential complications and a recovery period that can impact QoL. Combined treatment approaches may optimize outcomes, but the optimal strategy remains individualized based on disease severity, patient preferences, and resource access. Ultimately, successful KCN management hinges on a balance of objective visual improvements and subjective QoL enhancements.

Introduction

Keratoconus (KCN) is a non-inflammatory, progressive ectatic corneal disorder characterized by thinning and protrusion of the cornea, resulting in irregular astigmatism and reduced visual acuity [1, 2]. The precise etiology remains unclear, but genetic predisposition, environmental factors (e.g., eye rubbing), and biochemical abnormalities within the cornea are implicated [3, 4]. The prevalence of KCN is notably high in certain regions and populations. Globally, it affects approximately 1.38 individuals per 1000 people [5]. The disease typically manifests during adolescence and young adulthood, with progression often ceasing in the third to fourth decade of life [6].

The lifetime cost of KCN is substantial, imposing a significant economic burden on both patients and healthcare systems. Studies have highlighted the considerable out-of-pocket expenses incurred by patients for treatment and management, including visual aids, medical care, and lost productivity [7, 8]. Chan et al. estimated the annual cost of KCN in Australia to be approximately AUD 44.7 million, emphasizing the disease’s significant public health implications [7]. This economic burden is further amplified by the disease’s early onset, often impacting individuals during their most productive years, and the potential need for multiple interventions, including corneal transplantation [8].

Visual acuity is an important clinical measure, but it does not fully capture the impact of KCN on a patient’s overall well-being. Although KCN is a chronic condition that rarely leads to blindness, National Eye Institute Visual Function Questionnaire (NEI VFQ) results suggest its effect on vision-specific QoL is more severe than expected, given its low prevalence and clinical severity [9]. This condition significantly affects vision-related quality of life (VRQoL), impacting daily activities, social interactions, and psychological well-being [10]. Assessing QoL provides a more holistic understanding of the patient experience, enabling clinicians to effectively tailor management strategies and address unmet needs. Furthermore, QoL assessments are crucial for evaluating the effectiveness of various treatment modalities beyond simple visual acuity improvements.

This review aims to comprehensively examine the impact of KCN on patients’ QoL, considering its increasing prevalence and economic burden. The objective is to analyze the various factors influencing QoL in KCN, including disease severity, visual function (visual acuity, refractive errors, contrast sensitivity, ocular pain), comorbidities, and the effectiveness of different treatment modalities (nonsurgical and surgical interventions) in improving QoL outcomes. The review will also explore the methodological approaches used to assess QoL in KCN, compare QoL outcomes across different populations and severity grades, and discuss the limitations of current research while suggesting future directions for investigation, particularly the need for standardized QoL measures and longitudinal studies.

Method

A literature search was conducted across multiple electronic databases, including PubMed, Scopus, Web of Science, and Google Scholar, to identify relevant studies published up to December 2024. The search strategy utilized a combination of keywords and Medical Subject Headings (MeSH terms) related to KCN and QoL. Example search terms included: “keratoconus,” “quality of life,” “VRQoL,” “patient-reported outcome measures,” “National Eye Institute Visual Function Questionnaire,” “EuroQol Five Dimensions Five Levels,” and specific treatment modalities (e.g., “contact lenses,” “corneal crosslinking,” “intracorneal ring segments,” “keratoplasty”). Additionally, the reference lists of included articles and relevant review articles were manually screened to identify any potentially eligible studies missed by the electronic searches. Studies were selected based on pre-defined inclusion and exclusion criteria, focusing on studies that assessed QoLin patients with KCN using validated questionnaires. A narrative synthesis of the findings was presented, summarizing the impact of KCN and its treatment on various aspects of QoL.

Overview of QoL assessment tools and their application in KCN patient

Several QoL assessment tools have been employed to evaluate the impact of KCN on patients’ lives. These instruments are generally categorized into two groups: vision-specific questionnaires, such as the National Eye Institute Visual Function Questionnaire (NEI VFQ-25) and the KCN Quality of Life Questionnaire (KCQoL); and generic instruments, including the EuroQol Five Dimensions Five Levels (EQ-5D-5 L) and the Short Form Health Survey (SF-36/SF-12). The selection of a QoL instrument is typically guided by the specific objectives of the research and the aspects of quality of life being assessed. The choice of the QoL instrument depends on the specific research question.

Vision-specific tools

National eye Institute Visual Function Questionnaire (NEI VFQ-25)

This widely used questionnaire assesses various aspects of VRQoL, including general vision, near activities, distance activities, social functioning, mental health, role difficulties, dependency, driving, and color vision [11]. Its strengths include its comprehensiveness and validated translations in multiple languages [12–16]. However, it may not capture all aspects of QoL relevant to KCN, such as ocular discomfort or the psychosocial impact of the condition.

KCN Quality of Life Questionnaire (KCQoL)

This disease-specific instrument focuses on the unique challenges faced by KCN patients, including contact lens wear, visual distortions, and psychosocial concerns. This questionnaire is the only validated tool specifically for KCN, boasting excellent psychometric properties. However, it covers only two QoLdomains: activity limitation and symptoms [2, 17]. Also, its availability and validation in different languages may be limited.

Generic tools

EuroQol Five Dimensions Five Levels (EQ-5D-5 L)

This widely used generic QoL instrument assesses five dimensions of health: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression. It provides a single index value for overall health status, facilitating comparisons across different conditions [18, 19]. While it offers a broad perspective on QoL, it may not capture the specific visual impairments experienced by KCN patients.

Short Form Health Survey (SF-36 or SF-12)

The Short Form Health Survey (SF-36 or SF-12) is a widely used generic instrument designed to assess QoL by measuring both physical and mental health components. The SF-36 includes 36 questions that cover eight domains: physical functioning, role limitations due to physical health, bodily pain, general health perceptions, vitality, social functioning, role limitations due to emotional problems, and mental health [20]. The SF-12 is a shorter version with 12 items summarizing the same components, making it quicker to administer [21]. Both surveys are valuable for providing a comprehensive view of a person’s overall health status and are often used in clinical trials and health policy evaluations. However, they might not capture specific vision-related issues.

A key limitation of some QoL instruments is their reliance on patient self-reporting, which can be subject to recall bias and subjective interpretation. Furthermore, cultural differences can influence responses to QoL questionnaires, making cross-cultural comparisons challenging. It seems that using a combination of vision-specific and generic instruments can offer a more comprehensive understanding of the impact of KCN on patients’ lives.

KCN and its impact on VRQoL (VRQoL)

KCN profoundly impacts VRQoL, extending beyond the effects of reduced visual acuity. Factors such as refractive errors, contrast sensitivity, ocular pain and discomfort, comorbidities, and the impact on specific activities all contribute to the overall burden of the disease. Disease severity and demographic variations further influence these outcomes. A comprehensive approach to KCN management should consider visual acuity and broader effects on VRQoL to optimize patient outcomes. While the impact of KCN on visual acuity is well-established, its broader effects on VRQoL are increasingly recognized as significant. This section explores the multifaceted relationship between KCN and VRQoL, considering various visual and non-visual factors, disease severity, and demographic variations.

Visual acuity in KCN and its correlation with VRQoL

Reduced visual acuity is a hallmark of clinical KCN, significantly impacting daily activities and overall VRQoL. Studies consistently demonstrate a strong correlation between worse visual acuity and lower VRQoL scores across various questionnaires, including the NEI-VFQ and the KCN Outcomes Research Questionnaire (KORQ). Kymes et al. found that patients with binocular vision worse than 20/40 experienced reduced QoL across all scales, except for general health and eye pain [22]. Further longitudinal analysis by the same group showed that declining visual acuity over time strongly predicted worsening VRQoL [10]. Similarly, Pinto et al. found a significant association between worse best-corrected visual acuity (BCVA) and lower KORQ scores, highlighting the importance of BCVA in the better eye for overall VRQoL [23]. This underscores the importance of visual acuity as a key determinant of VRQoL in KCN patients.

Refractive errors in KCN and their influence on VRQoL

The irregular astigmatism induced by KCN poses challenges for refractive correction, impacting VRQoL beyond the effects of reduced visual acuity. While spectacles and soft contact lenses may provide adequate correction in early stages [24], the progressive nature of KCN often necessitates rigid gas permeable contact lenses (RGPCLs) or scleral lenses for optimal vision [25, 26]. However, these lenses can be associated with discomfort, inconvenience, and complications, further affecting VRQoL. Steinberg et al. found that even in early-stage KCN with relatively good CDVA, patients experienced a decline in VRQoL compared to emmetropes and myopes, particularly in driving and ocular pain subscales [27]. This suggests that the challenges of refractive correction and associated symptoms contribute to reduced VRQoL even in milder forms of KCN. Fournie et al. further explored the impact of different treatment modalities on VRQoL, finding that patients using RGPCLs reported challenges related to cost, discomfort, and lens loss, highlighting the need for improved management strategies to address these issues [28].

Contrast sensitivity in KCN and its impact on daily activities

Beyond visual acuity and refractive errors, reduced contrast sensitivity is a prominent feature of KCN, further impacting VRQoL [29, 30]. Contrast sensitivity, the ability to distinguish between subtle differences in light and dark, is crucial for various daily activities, including driving, reading, and facial recognition. Although not explicitly addressed in the provided articles, reduced contrast sensitivity is a well-documented consequence of KCN and likely contributes to the difficulties experienced by patients in these specific activities, as highlighted in the studies [31–33]. Further research is needed to directly assess the relationship between contrast sensitivity and VRQoL in KCN patients.

Ocular pain and discomfort: frequency, severity, in KCN and QoL impact

Ocular pain and discomfort are common complaints among KCN patients, contributing significantly to reduced VRQoL. These symptoms can arise from the disease itself, contact lens wear, or surgical interventions. In the early stage, KCN patients reported significantly lower scores on the NEI-VFQ subscale for ocular pain than emmetropes and myopes [27]. Fournie et al. also highlighted discomfort as a prominent themes in patient interviews, particularly among those using RGPCLs [28]. Fan et al. (2024) further detailed the various symptoms experienced by KCN patients, including pain, dryness, irritation, and photophobia, emphasizing their negative impact on daily activities and emotional well-being [33]. These findings underscore the need for effective management strategies to alleviate ocular pain and discomfort in KCN patients to improve their overall VRQoL.

The role of comorbidities in kcn’s impact on QoL

While KCN itself significantly impacts VRQoL, the presence of comorbidities can exacerbate these effects. Vernal keratoconjunctivitis (VKC), often associated with KCN, can increase ocular discomfort, itching, and photophobia [34]. Other conditions, such as Down syndrome, atopic dermatitis, and Leber congenital amaurosis, have also been reported in association with KCN [35]. These comorbidities can introduce additional visual and systemic challenges, further complicating the management of KCN and potentially impacting VRQoL. For instance, atopic dermatitis, with its associated ocular manifestations like blepharitis and keratoconjunctivitis, can worsen ocular surface discomfort and inflammation in KCN patients. Similarly, the presence of Leber congenital amaurosis, a severe retinal dystrophy, can independently and significantly impair vision, compounding the visual challenges posed by KCN. Although the provided articles did not directly address the interplay between KCN and these comorbidities, it is an essential consideration for VRQoL. Most VRQoL instruments currently in use do not distinguish between the effects of KCN and those of coexisting conditions. Consequently, it is often unclear how much of the observed reduction in QoL can be attributed specifically to KCN, as opposed to other comorbidities. To address this limitation, future research should consider strategies such as stratified analyses or the development of more condition-specific QoL tools. These approaches would help to better isolate and quantify the unique impact of keratoconus on patients’ daily functioning and overall well-being.

Impact of KCN on specific activities (Driving, reading, social Interaction)

KCN significantly impacts specific activities crucial for daily living and social participation, including driving, reading, and social interaction. Driving was particularly affected in early-stage KCN, with patients reporting lower scores on the NEI-VFQ subscale for driving compared to controls [27]. Driving difficulties, especially at night, were also highlighted as a major concern for KCN patients [28] Challenges faced by patients in reading, computer use, and social interactions due to blurred vision, distorted vision, and self-consciousness about their eye condition were further detailed [33]. These findings emphasize the wide-ranging impact of KCN on daily activities and the importance of addressing these specific challenges to improve VRQoL.

Comparison of QoL scores across different KCN severity grades

The severity of KCN plays a crucial role in determining its impact on VRQoL. Generally, more severe forms of KCN are associated with greater visual impairment and lower VRQoL scores. Gothwal et al. (2013) found no significant difference in VRQoL between moderate and severe KCN groups in their Indian sample, although this may be attributed to the limitations of the IVI questionnaire used in their study [36]. Other studies, including those by Kymes et al. (2004, 2008) and Pinto et al. suggest a clear relationship between disease severity and VRQoL, with worsening clinical parameters correlating with lower VRQoL scores [22, 23]. Therefore, disease severity is a crucial factor to consider when evaluating and addressing how KCN affects VRQoL.

Comparison of QoL in KCN cases across different populations

While the impact of KCN on VRQoL is generally consistent across populations, some variations may exist due to cultural, socioeconomic, and healthcare access factors. Previously published studies encompass diverse populations geographically, such as India, Taiwan, Jordan, Palestine, and Saudi Arabia. The Saudi Arabian study found that females, patients under 30, and those without vision aids reported significantly lower QoL [37]. The Jordanian study found that males reported lower visual function scores than females [32]. These variations underscore the influence of demographic and cultural factors on the experience of KCN and its impact on QoL.

While all studies acknowledge the progressive nature of KCN, the correlation between disease severity and QoL is not consistently established. The Indian study found no significant correlation between disease severity (based on keratometry) and QoL, while other studies suggest a relationship, although not always statistically significant [36]. The Jordanian [32] and Palestinian [38] studies found no significant correlation between specific corneal tomography indices and QoL, suggesting that visual acuity might be a more significant predictor. However, the Saudi Arabian study did not investigate the correlation between tomography indices and QoL [37].

Impact of treatment modalities on QoL in KCN

KC significantly impacts VRQoL, necessitating various treatment modalities ranging from nonsurgical interventions like contact lenses and spectacles to surgical procedures such as corneal collagen crosslinking (CXL), intracorneal ring segments (ICRS), and corneal transplantation. This section explores the impact of these treatment modalities on VRQoL, considering their effectiveness, comfort, limitations, and complications.

Nonsurgical management

Contact lenses

Contact lenses are a mainstay of nonsurgical KC management, offering improved visual acuity and potentially enhancing VRQoL. Different lens types cater to varying disease severities and patient needs:

Soft and rigid gas permeable contact lenses

The impact of contact lenses on QoL in KCN patients has been the subject of several studies comparing the effects of rigid gas permeable (RGP) lenses and soft silicone-hydrogel (SHCL) lenses designed explicitly for KCN. The findings reveal a complex relationship between lens type, visual acuity, and QoL [33, 39–42]. Yildiz et al. directly compared RGP lenses and SHCLs for KCN using the Contact Lens Impact on Quality of Life (CLIQ) questionnaire. This study found no statistically significant difference in QoL between the two lens types, although RGP lenses showed a slightly better mean CLIQperson measure. However, the visual acuity was better in the RGP group (93.3% with 20/25 or better acuity versus 66.7% in the SHCL group), suggesting that while both lens types provided similar improvements in QoL, RGP lenses might offer superior visual correction in this specific patient population. The study also found a positive correlation between the CLIQperson measure and the steep K value, suggesting that QoL might improve as disease severity increases, possibly due to increased adaptation or the greater impact of the lenses in more severe cases [39].

Another study investigated the relationship between RGP lens wear and QoL in KCN patients stratified by disease severity (mild, moderate, severe). While RGP lenses generally improved QoL compared to no lens wear, patients with severe KCN (steep keratometry > 52 D) experienced significantly reduced lens wearing time and lower QoL scores on the NEI-VFQ-25, particularly in subscales related to ocular pain, mental health, and role difficulties. This suggests that for patients with advanced KCN, RGP lenses may not be sufficient to maintain a good QoL, and alternative lens options might be necessary. This study also highlighted a strong correlation between binocular visual acuity and NEI-VFQ-25 scores, indicating that better visual acuity is associated with better QoL [40].

A further study investigated factors affecting long-term compliance with RGP lens wear in KCN patients. This study found that subjective experiences, such as visual acuity, overall satisfaction, and QoL, were more influential on long-term compliance than objective biometrics. While the study did not directly compare RGP to SHCL lenses, it underscores the importance of patient satisfaction and comfort in determining the success of RGP lens wear [41]. While RGP lenses can improve visual acuity and reduce higher-order aberrations, long-term use may not prevent KCN progression and might even cause corneal epithelial remodeling. Also, RGP lens wear can slightly decrease vision-related QoL, potentially due to discomfort or ocular surface issues [42]. Furthermore, the cost of RGP lenses, especially with frequent replacements due to loss or damage, can pose a financial burden, further affecting VRQoL [33].

Scleral lenses

Scleral lenses offer excellent visual acuity and can significantly improve VRQoL, particularly for patients intolerant to other lens types [33]. However, their larger size and specific handling requirements may pose challenges for some patients. Several studies highlight the positive impact of scleral lenses on QoL in KCN patients [43–46]. These studies suggest that scleral lenses are effective in improving visual parameters and significantly contribute to a better QoL for KCN patients. Hadimani et al., demonstrated significant improvements in various aspects of QoL using the NEI VFQ-25 after three months of scleral lens wear. Specifically, statistically significant improvements were observed in distance and near activities, vision-specific mental health, social functioning, and driving [47]. These findings corroborate other research indicating that the enhanced visual acuity afforded by scleral lenses translates to a measurable increase in patients’ ability to perform daily tasks and participate more fully in social and recreational activities, leading to improved overall well-being [43–46].

However, it’s crucial to consider that while scleral lenses often provide substantial QoL benefits, individual experiences can vary. Factors such as lens fit, handling difficulties, and residual symptoms (e.g., redness, dryness) can influence the overall impact on QoL [44]. Furthermore, the long-term effects of scleral lens wear on QoL require further investigation, as the Hadimani et al. study [47] only assessed outcomes after three months. Larger, longer-term studies are needed to comprehensively assess the sustained impact of scleral lenses on different aspects of QoL and to identify potential predictors of successful outcomes and patient satisfaction. Overall, contact lenses can significantly improve VRQoL in KC patients by enhancing visual acuity. However, comfort, complications, cost, and handling issues can influence the overall impact on VRQoL, varying with lens type and individual patient factors.

Spectacles

Spectacles may provide adequate vision correction in early KC, but their effectiveness diminishes as the disease progresses and irregular astigmatism worsens [46]. The limitations of spectacles in correcting irregular astigmatism can lead to blurred and distorted vision, negatively impacting VRQoL. Even in the early-stage, KC patients may experience reduced VRQoL compared to those with regular refractive errors, suggesting that the limitations of spectacle correction contribute to this decline [27]. In more advanced KC, spectacles become largely ineffective, and patients often transition to contact lenses or surgical interventions for better visual outcomes and improved VRQoL [46].

Surgical management

Corneal collagen crosslinking (CXL)

CXL offers a promising therapeutic approach for managing KCN progression, and emerging evidence suggests a positive correlation with QoL improvements. While the primary aim of CXL is to stabilize the cornea biomechanically, halting disease progression indirectly enhances visual acuity, a key determinant of VRQoL. Studies like that by Chiraples et al., utilizing the NEI VFQ-25 questionnaire, have reported high baseline VRQoL scores in KCN patients treated with accelerated epi-on CXL, suggesting that even before intervention, many individuals maintain a relatively good QoL [48]. Post-CXL, improvements in visual function (near and distance activities, driving) and vision-specific mental health and social functioning have been observed, further supporting the positive impact on overall QoL. However, the immediate postoperative period may involve temporary discomfort and reduced visual acuity, leading to a transient decrease in VRQoL as noted by Marx-Gross et al. [49] Pinto et al., demonstrated improvements in VRQoL following CXL, particularly in subscales related to activity limitations and symptoms [23]. However, CXL does not typically reverse existing corneal changes, and patients may still require contact lenses or other interventions for optimal vision correction. Steinberg et al. found that while CXL stabilized KC progression, VRQoL scores did not significantly improve in their short-term follow-up, suggesting that the psychological burden of the disease may persist even after successful treatment [27].

Despite the potential for QoL enhancement with CXL, several factors warrant consideration. The Cochrane review by Sykakis et al., highlights the limited high-quality evidence available, emphasizing the need for more robust randomized controlled trials (RCTs) with longer follow-up periods to definitively assess the long-term impact on QoL [50]. Furthermore, the type of CXL procedure (epi-on, epi-off, accelerated) may influence the perioperative QoL experience, with epi-off procedures potentially causing more significant short-term discomfort. Individual patient factors, such as age, disease severity, and the presence of comorbidities, also play a role in the overall QoL outcome. Future research should focus on standardizing CXL protocols, investigating the long-term effects on QoL across various patient subgroups, and developing strategies to minimize perioperative discomfort and maximize the long-term benefits of CXL on the QoL of KCN patients.

Intracorneal ring segments (ICRS)

ICRS implantation represents a surgical intervention to improve visual acuity and reduce irregular astigmatism in KCN patients [51], thereby potentially impacting QoL. While studies consistently demonstrate improvements in objective measures like visual acuity, refraction, and keratometry following ICRS implantation [52], the influence on QoL is more nuanced. Paranhos et al., employed the NEI-RQL questionnaire to assess vision-related QoL and found that improvements were significantly correlated with cylinder reduction and normal contrast sensitivity at specific spatial frequencies (3 and 6 cpd). Interestingly, the study highlighted that gender played a role, with males reporting greater QoL improvements than females [53]. This suggests that the subjective experience of visual improvement following ICRS, and its impact on daily life is not solely determined by objective clinical parameters.

In another study, the 4-year follow-up results of 23 KCN patients who underwent ICRS implantation were retrospectively evaluated. A significant improvement was observed in all patients’ best spectacle-corrected and uncorrected visual acuity, along with a decrease in Kmax values. QoL scores, assessed using the NEI-VFQ-25 questionnaire, were generally good, but satisfaction and vision levels did not improve as expected in patients with early-stage KCN. Therefore, they concluded that early ICRS implantation may not be necessary for KCN [54]. Although some studies suggest sustained improvements in visual parameters and QoL for patients with stable KCN [52], the potential for regression of benefits in progressive KCN necessitates careful patient selection.

Corneal transplantation

Corneal transplantation is considered for advanced KC cases where other treatments have failed to provide adequate visual rehabilitation [55]. Previous studies highlighted the psychological impact of corneal transplantation, with patients expressing both fear and hope regarding the procedure [28]. Fan et al. further described the challenges faced by patients after keratoplasty, including postoperative care requirements, fear of ocular trauma, and self-consciousness about the appearance of the graft [33].

Corneal transplantation, while a significant intervention for advanced KCN, presents a complex relationship with QoL. Musch et al. found a strong positive correlation between postoperative BCVA in the better-seeing eye and QoL scores, as measured by the VF-14 and SF-36 questionnaires. This highlights the crucial role of visual function in overall well-being after transplantation. Furthermore, the presence of significant keratometric astigmatism negatively impacted social functioning, underscoring the importance of achieving optimal refractive outcomes to maximize QoL. The study’s findings emphasize the criterion validity of the VF-14 for assessing the impact of corneal transplantation on visual function and the broader influence of visual disability on emotional and social well-being, as evidenced by the SF-36 scores [56].

However, the relationship between postoperative visual acuity in the grafted eye and QoL improvement is not always straightforward. Mendes et al., demonstrated that while postoperative visual function, as measured by a modified VF-14 (PK-VFQ), improved in the majority of patients, this improvement was inversely correlated with preoperative visual acuity in the better-seeing eye [57]. This suggests that patients with initially poorer vision in their unaffected eye experience a greater subjective improvement in visual function after keratoplasty, even if their postoperative acuity in the grafted eye is not exceptionally high. Drzyzga et al., further emphasized the significant impact of corneal transplantation on mental health, showing a reduction in preoperative depression and anxiety symptoms post-surgery. This improvement was directly linked to changes in visual acuity in the grafted eye, but negatively correlated with higher doses of postoperative prednisone, highlighting the importance of managing immunosuppression effectively to optimize both visual and psychological well-being [58]. Despite the challenges and potential for complications, the high patient satisfaction rates reported across these studies (Mendes et al. reporting 97% would undergo the procedure again, Drzyzga et al. reporting 82.5%) underscores the overall positive impact of corneal transplantation on the lives of many KCN patients [57, 58].

Combined treatment modalities

In some cases, a combination of treatment modalities may be employed to optimize visual outcomes and improve VRQoL. For example, CXL may be combined with ICRS or topography-guided photorefractive keratectomy (PRK) to achieve better corneal regularization and visual acuity [59–61]. Similarly, patients undergoing corneal transplantation may still require contact lenses for optimal vision correction. The impact of combined treatment modalities on VRQoL depends on the specific combination used and individual patient factors.

Conclusion

This review comprehensively examines the impact of KCN on VRQoL (VRQoL), considering the disease’s substantial economic burden and its multifaceted effects on patients’ lives. The analysis of various QoL assessment tools (NEI VFQ-25, KCQoL, EQ-5D-5 L, SF-36/SF-12) reveals the limitations of relying mainly on visual acuity to gauge the patient experience. Our examination of KCN’s impact on visual function (Sect. 4) demonstrates the significant influence of reduced visual acuity, irregular refractive errors, contrast sensitivity deficits, and ocular pain and discomfort on VRQoL. The section further highlights the role of comorbidities in exacerbating these effects and the impact on specific daily activities (driving, reading, social interaction). Analysis across different KCN severity grades and populations reveals that while the overall impact on VRQoL is consistent, variations exist due to methodological differences and cultural factors.

The review of treatment modalities shows that nonsurgical interventions like spectacles and contact lenses (soft, RGP, and scleral lenses) provide varying degrees of visual correction and comfort, each influencing QoL differently. Surgical interventions, including CXL, ICRS, and corneal transplantation, offer distinct benefits and limitations regarding VRQoL, with CXL primarily addressing disease progression, ICRS targeting refractive correction, and transplantation offering the most significant visual improvement but with a more invasive procedure and longer recovery period. Combined treatment strategies are also discussed, emphasizing the need for individualized approaches. The review concludes by emphasizing the need for future research to focus on standardized QoL measures, longitudinal studies, and a more holistic understanding of the interplay between KCN, its comorbidities, and the patient experience to optimize treatment outcomes and improve VRQoL.

Authors’ contributions

All authors contributed to the conception and design of the work, literature review, and manuscript writing. Moreover, they approve the submitted version of the manuscript.

Funding

None.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

As this manuscript is a review paper and does not report on any primary research involving human subjects, ethics approval and consent were not obtained prior to conducting the study or writing the manuscript.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.