Asymmetry in keratoconus and vision-related quality of life

Mendelian randomization analysis does not reveal a causal influence between keratoconus and three major mental disorders

Background

Observational studies have suggested at a possible link between keratoconus (KC) and various mental disorders, but the exact direction of causation in these associations remains unclear. This study aims to investigate the potential causal link between KC and three prominent mental conditions: Anxiety, Depression, and Schizophrenia.

Methods

Using instrumental variables identified from Genome-wide association study (GWAS) data of European individuals, we conducted bidirectional two-sample Mendelian Randomization (MR) analyses to explore potential causal relationships between KC and the three major mental disorders. We primarily employed the Inverse-Variance Weighted (IVW) method to evaluate causality. In addition, we performed four supplementary MR methods (MR-Egger, Weighted Median, Simple Mode, and Weighted Mode). Furthermore, we conducted various sensitivity analyses to assess heterogeneity, horizontal pleiotropy, and result stability.

Results

Our findings did not reveal any concrete evidence of a causal link between KC and the three major mental disorders, namely anxiety, depression, and schizophrenia [anxiety: odds ratio (OR)=0.997, 95% confidence interval (CI)=0.988-1.008, p = 0.621; depression: OR=1.008, 95% CI=0.999-1.017, p = 0.084; schizophrenia: OR=1.002, 95% CI= 0.984-1.020, p = 0.840]. Similarly, the three major mental disorders were not caustically associated with KC [anxiety: OR=1.014, 95% CI=0.635-1.620, p = 0.953; depression: OR=1.109, 95% CI= 0.749-1.643, p = 0.604; schizophrenia: OR= 0.969, 95% CI= 0.884-1.062, p = 0.497]. The sensitivity analyses indicated that the results remained robust, with no signs of pleiotropy or heterogeneity.

Conclusions

Our study does not support a genetically determined significant causal connection between KC and the three major mental disorders. The increased occurrence of mental disorders observed in KC patients in observational reports likely arises from factors that can be modified. Further research is warranted to unveil the underlying mechanisms behind the associations observed in observational studies.

Exploring the causal relationship between body mass index and keratoconus: a Mendelian randomization study

Background

Despite reports suggesting a link between obesity and keratoconus, the causal relationship is not fully understood.

Methods

We used genome-wide association study (GWAS) data from public databases for a two-sample Mendelian randomization analysis to investigate the causal link between body mass index (BMI) and keratoconus. The primary method was inverse variance weighted (IVW), complemented by different analytical techniques and sensitivity analyses to ensure result robustness. A meta-analysis was also performed to bolster the findings' reliability.

Results

Our study identified a significant causal relationship between BMI and keratoconus. Out of 20 Mendelian randomization (MR) analyses conducted, 9 showed heterogeneity or pleiotropy. Among the 11 analyses that met all three MR assumptions, 4 demonstrated a significant causal difference between BMI and keratoconus, while the remaining 7 showed a positive trend but were not statistically significant. Meta-analysis confirmed a significant causal relationship between BMI and keratoconus.

Conclusion

There is a significant causal relationship between BMI and keratoconus, suggesting that obesity may be a risk factor for keratoconus.

[Effect of keratoplasty on the quality of life of keratoconus patients]

Corneal deformations caused by keratoconus produce high levels of optical aberration (OA). Despite appropriate optical correction, these alter the quality of vision and diminish the patient's quality of life, especially since the affected population is predominantly young and of working age. When thinning is too severe or corneal transparency too impaired, a corneal transplant may be considered. In this study, we compare the quality of life of patients with keratoconus in the early (stages 1 and 2) or advanced (stages 3 and 4) stages of the Krumeich classification, as well as patients who have had keratoconus treated by keratoplasty. Quality of life was assessed using the NEI-VFQ 25 questionnaire, the most widely used for keratoconus. An aberrometric examination (OQAS®; HD Analyser, Visiometrics, Terrassa, Spain) was also performed to assess patients' quality of vision. Our results show that keratoplasty provides an improvement in quality of life compared with advanced-stage keratoconus in the areas of distance (p=0.0083) and near vision (p=0.029) activities. This improvement also applies to Best-Corrected Visual Acuity (BCVA) (p=0.032) and transparency (OSI) (p=0.049). Our study shows that keratoplasty improves corneal transparency, and it is interesting to note that it improves patients' quality of life over the long term.

Vision-Related Quality of Life in Patients With Keratoconus With Enantiomorphic Topography After Bilateral Intrastromal Corneal Ring Implantation

PURPOSE

The aim of this study was to evaluate the quality of life (QOL) after intrastromal ring implantation in patients with keratoconus.

METHODS

This was a prospective, randomized, interventional study. We analyzed 60 eyes of 30 patients aged 16 to 35 years who were treated at the Department of Ophthalmology and Visual Sciences, Federal University of São Paulo, Brazil. The Visual Function Questionnaire (VFQ-25) and Short-Form 36 Questionnaire (SF-36) were used before intracorneal ring segment (ICRS) implantation and at 3, 6, and 12 months after surgical intervention.

RESULTS

The mean corrected visual acuity improved from a mean of 0.32 ± 0.2 logMAR (20/40) preoperatively to 0.14 ± 0.11 logMAR (20/25) 1 year postoperatively ( P = 0.001). The mean spherical equivalent varied from -7.24 ± 3.47 preoperatively to -4.13 ± 2.41 postoperatively ( P = 0.001). The overall composite score for the VFQ-25 improved from 55.1 preoperatively to 80.4 1 postoperatively ( P = 0.001). SF-36 showed statistically significant improvement in all scores. When analyzing the correlation between visual acuity and VFQ composite score, a significant correlation was found between both variables (Pearson correlation coefficient of -0.40, P = 0.001).

CONCLUSIONS

Patients with keratoconus had increased psychological symptoms and lower QOL and improved psychosocial criteria associated with corneal remodeling and decreased visual dependence on others after surgery. Extrapolation of these data to the whole keratoconus population suggests that ICRS implantation could improve QOL in these patients.

Investigating the Link Between Visual Quality and Vision-Related Quality of Life in Patients With Keratoconus

PURPOSE

The purpose of the study was to investigate the optical and visual determinants of vision-related quality of life (VR-QoL) in patients with keratoconus.

METHODS

A cross-sectional case-control study was conducted at the Department of Ophthalmology, Antwerp University Hospital, Belgium. Patients previously diagnosed with keratoconus and healthy emmetropic or ametropic volunteers were included. Patients younger than 18 years, with ametropia of more than ±10 D, or with a history of corneal surgery or relevant ocular comorbidity limiting visual acuity were excluded. Assessment included autorefraction, high-contrast visual acuity testing, corneal imaging, intraocular straylight analysis, contrast sensitivity, aberrometry, and the National Eye Institute Visual Functioning Questionnaire (NEI VFQ-25). The Rasch-modified visual functioning scale (VFS) and socio-emotional scale were used to quantify VR-QoL. Stepwise linear regression was used to investigate the association between the clinical variables and VR-QoL.

RESULTS

Seventy-seven patients with keratoconus (77 pairs of eyes) and 77 age-matched and sex-matched controls were included in the study. The scores on the VFS and the SES were significantly lower in patients with keratoconus compared with controls ( P < 0.001). Higher-order and lower-order aberrations, high-contrast visual acuity, and contrast sensitivity were poorer in patients with keratoconus ( P < 0.001). Bivariate analyses showed that spectacle-corrected high-contrast visual acuity, higher spatial frequency contrast sensitivity, and higher-order aberration metrics were strong predictors of SES ( P < 0.001) and of VFS ( P < 0.001). Higher-order aberration of the worse eye was the strongest predictor for both SES (b = 0.310, P < 0.001) and VFS (b = 0.638, P < 0.001) on stepwise regression. Contrast sensitivity was not included in the stepwise regression because of insufficient data in the keratoconus group (33/77 patients; 42.9%).

CONCLUSIONS

Both higher and lower aberration showed a strong correlation with VR-QoL, surpassing high-contrast visual acuity. These findings underline the importance of visual quality measures within keratoconus research and clinical care.

Prevalence of Psychiatric Illness Among Keratoconus Patients

Background  Keratoconus is a chronic corneal disorder characterized by progressive thinning of the cornea resulting in visual deterioration. Keratoconus patients have a higher rate of psychiatric morbidities. Therefore, this study will assess the prevalence of psychiatric illness among keratoconus patients. Methods We conducted a quantitative retrospective study in three centers across Saudi Arabia from June 2016 to February 2023. We included all patients previously diagnosed with keratoconus and any psychiatric illness. We excluded patients with other ocular diseases in addition to keratoconus. After we extracted the data, we coded and analyzed them using IBM SPSS Statistics for Windows, Version 21.0 (2012; IBM Corp., Armonk, New York, United States) and GraphPad Prism Version 8.4.2 (Dotmatics, Boston, Massachusetts, United States). Results The study included 57 keratoconus patients, with the majority being Saudi (96.5%), female (2:1), in the age group of 31-40 years (40.4%), and with a high-school level of education. The majority of patients were also obese (42.4%) and non-smokers (82%). Most patients had comorbid medical disorders. Of the 57 patients, 63.2% had anxiety disorders, 56.1% had depression, 10.5% had schizophrenia, and 1.8% had bipolar disorder. Patients with only a primary-school level of education were significantly more likely to be diagnosed with bipolar disorder, whereas those who were single were significantly more likely to be diagnosed with schizophrenia. Corneal transplant was also significantly associated with schizophrenia. Most patients (51%) were diagnosed with a psychiatric illness before keratoconus was diagnosed. Conclusion Among the keratoconus patients, single relationship status, primary-school level of education, and comorbidities were significantly associated with schizophrenia, bipolar disorder, and anxiety disorder, respectively. In addition, corneal transplant was significantly associated with schizophrenia. Lastly, the occurrence of psychiatric illness before keratoconus diagnosis was observed in the majority of patients.

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.

YouTube as a source of information on keratoconus: a social media analysis

CLINICAL RELEVANCE

Keratoconus (KC) treatment in the early stage is usually with glasses or soft toric contact lenses, in advanced stages rigid gas-permeable corneal or scleral contact lenses are used. Optometrists should be aware of misleading information from online platforms when providing information to keratoconus patients.

BACKGROUND

Keratoconus is a progressive corneal disease characterised by stromal thinning and corneal ectasia. To the best of our knowledge, there is no study evaluating the popularity, quality, and reliability of videos about keratoconus disease and its treatment published on YouTube. In our study, we aimed to evaluate the credibility, quality, and popularity of YouTube videos about keratoconus.

METHODS

This is a retrospective, cross-sectional, register-based study. A YouTube search was performed using the keywords 'keratoconus', 'keratoconus disease', 'keratoconus treatment', 'keratoconus cross linking'. The quality and reliability of video content were measured using the DISCERN questionnaire, the Journal of the American Medical Association (JAMA) score, and the Global Quality Score (GQS). The video power index was used to evaluate the popularity of the videos.

RESULTS

One hundred videos were included in the study. The average duration was 6.33 min and average total number of views was 14,940. The mean DISCERN, JAMA, and GQS scores were 42.57 ± 12.04 (intermediate quality), 1.77 ± 0.51 (poor quality), and 3.63 ± 1.03 (intermediate quality), respectively. The mean video power index was 11.02 ± 24.55 (range, 0-193). The DISCERN score was significantly positively correlated with GQS and JAMA scores (p ≤ 0.001).

CONCLUSIONS

This study showed that YouTube videos about keratoconus contain moderately useful information for patients. So, physicians, being aware of the quality and diversity of online information, should correct any misinformation they encounter while face-to-face with patients.

Advances in artificial intelligence models and algorithms in the field of optometry

The rapid development of computer science over the past few decades has led to unprecedented progress in the field of artificial intelligence (AI). Its wide application in ophthalmology, especially image processing and data analysis, is particularly extensive and its performance excellent. In recent years, AI has been increasingly applied in optometry with remarkable results. This review is a summary of the application progress of different AI models and algorithms used in optometry (for problems such as myopia, strabismus, amblyopia, keratoconus, and intraocular lens) and includes a discussion of the limitations and challenges associated with its application in this field.

Determining the center of a keratoconus: Comparison of different tomographic parameters and impact of disease severity

Purpose

There exists remarkable variation in definitions for the location of the center of a keratoconus. The objective of this study was to analyze deviations between locations obtained by different tomographic maps for that purpose. Furthermore, it was investigated whether these deviations are influenced by disease severity.

Methods

In 162 eyes with keratoconus, corneal tomographic maps derived by Scheimpflug technology were retrospectively analyzed to determine the cone location with 5 different methods: maximum axial curvature of the front surface (Kmax), maximum tangential curvature of the front surface (tKmax), minimum pachymetry (Pachymin), maximum elevation of the front surface (ELEF), and maximum elevation of the back surface (ELEB). Distances between the locations were calculated and tested for a correlation with keratoconus severity and distance between cone and corneal vertex.

Results

Cone locations derived from the curvature maps (Kmax, tKmax) showed the lowest agreement with the locations determined by pachymetry or elevation maps. The largest distances were found between Kmax and Pachymin [Median and Interquartile range: 1.19 mm (0.87, 1.60)], Kmax and ELEB [1.12 mm (0.79, 1.41)], and Kmax and ELEF [0.97 mm (0.64, 1.27)]. Low distances (<0.5 mm) were calculated between ELEB and ELEF, and ELEB and Pachymin. All of the calculated distances between the locations showed a significant negative correlation with keratoconus severity and most of them increased significantly with a more peripheral position of the cone (p < 0.05).

Conclusions

There was low consistency between different methods for describing the location of a keratoconus. Curvature-based determinations of the cone center (Kmax, tKmax) showed the highest deviations and should not be used for that purpose. However, the discrepancies between different cone location methods diminished with increasing disease severity and more central position of the cone.

Single-cell atlas of keratoconus corneas revealed aberrant transcriptional signatures and implicated mechanical stretch as a trigger for keratoconus pathogenesis

Keratoconus is a common ectatic corneal disorder in adolescents and young adults that can lead to progressive visual impairment or even legal blindness. Despite the high prevalence, its etiology is not fully understood. In this study, we performed single-cell RNA sequencing (scRNA-Seq) analysis on 39,214 cells from central corneas of patients with keratoconus and healthy individuals, to define the involvement of each cell type during disease progression. We confirmed the central role of corneal stromal cells in this disease, where dysregulation of collagen and extracellular matrix (ECM) occurred. Differential gene expression and histological analyses revealed two potential novel markers for keratoconus stromal cells, namely CTSD and CTSK. Intriguingly, we detected elevated levels of YAP1 and TEAD1, the master regulators of biomechanical homeostasis, in keratoconus stromal cells. Cyclical mechanical experiments implicated the mechanical stretch in prompting protease production in corneal stromal cells during keratoconus progression. In the epithelial cells of keratoconus corneas, we observed reduced basal cells and abnormally differentiated superficial cells, unraveling the corneal epithelial lesions that were usually neglected in clinical diagnosis. In addition, several elevated cytokines in immune cells of keratoconus samples supported the involvement of inflammatory response in the progression of keratoconus. Finally, we revealed the dysregulated cell-cell communications in keratoconus, and found that only few ligand-receptor interactions were gained but a large fraction of interactional pairs was erased in keratoconus, especially for those related to protease inhibition and anti-inflammatory process. Taken together, this study facilitates the understanding of molecular mechanisms underlying keratoconus pathogenesis, providing insights into keratoconus diagnosis and potential interventions.

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.

Keratoconus: An updated review

Keratoconus is a bilateral and asymmetric disease which results in progressive thinning and steeping of the cornea leading to irregular astigmatism and decreased visual acuity. Traditionally, the condition has been described as a noninflammatory disease; however, more recently it has been associated with ocular inflammation. Keratoconus normally develops in the second and third decades of life and progresses until the fourth decade. The condition affects all ethnicities and both sexes. The prevalence and incidence rates of keratoconus have been estimated to be between 0.2 and 4,790 per 100,000 persons and 1.5 and 25 cases per 100,000 persons/year, respectively, with highest rates typically occurring in 20- to 30-year-olds and Middle Eastern and Asian ethnicities. Progressive stromal thinning, rupture of the anterior limiting membrane, and subsequent ectasia of the central/paracentral cornea are the most commonly observed histopathological findings. A family history of keratoconus, eye rubbing, eczema, asthma, and allergy are risk factors for developing keratoconus. Detecting keratoconus in its earliest stages remains a challenge. Corneal topography is the primary diagnostic tool for keratoconus detection. In incipient cases, however, the use of a single parameter to diagnose keratoconus is insufficient, and in addition to corneal topography, corneal pachymetry and higher order aberration data are now commonly used. Keratoconus severity and progression may be classified based on morphological features and disease evolution, ocular signs, and index-based systems. Keratoconus treatment varies depending on disease severity and progression. Mild cases are typically treated with spectacles, moderate cases with contact lenses, while severe cases that cannot be managed with scleral contact lenses may require corneal surgery. Mild to moderate cases of progressive keratoconus may also be treated surgically, most commonly with corneal cross-linking. This article provides an updated review on the definition, epidemiology, histopathology, aetiology and pathogenesis, clinical features, detection, classification, and management and treatment strategies for keratoconus.

Spectrum of Binocular Vision Anomalies in Keratoconus Subjects

Keratoconus (KC) is typically a bilateral asymmetric corneal condition associated with anisometropia. A detailed evaluation of binocular vision function is therefore a critical component of ocular examination in these patients for early detection and treatment of binocular vision anomalies.

PURPOSE

The purposes of this study were to measure the various parameters of binocular vision (BV) in patients with KC and to identify the factors that possibly influence them.

METHODS

This was a prospective, observational study of BV in patients with KC and with best-corrected visual acuity ≤0.4 logMAR in each eye. Age-matched, nonstrabismic normal patients served as controls. Binocular vision examination included motor assessment, accommodation parameters, and fusional vergence.

RESULTS

Binocular vision parameters of 84 KC patients were compared with those of 71 normal controls. The KC group showed statistically significant differences between fellow eyes in refractive cylinder (0.44 ± 2.1 D, P = .03), best-corrected visual acuity (0.06 ± 0.09 logMAR, P = .001), and maximum keratometry (6.64 ± 8.2D, P = .005). The control group showed no significant difference in any refractive or keratometric parameter between fellow eyes. Sixty-six (78.6%) of 84 KC patients had various combinations of BV anomalies: 48.8% had impaired stereopsis, 44% had abnormal fusional vergence, and 39.3% had accommodative infacility. Among individual parameters, all except accommodative amplitudes and negative distance fusional vergence showed statistically significant impairment compared with controls (P < .001). Median (interquartile range) stereoacuity was 70 (50 to 550) arc sec in the KC group and 40 (30 to 50) arc sec in control (P < .0001). There was a statistically significant but weak correlation between stereoacuity and positive fusional vergence for near (P = .008; Spearman coefficient, -0.28) and weak but significant negative correlation between phoria status and negative fusional vergence for near (P = .03; Spearman coefficient, -0.24).

CONCLUSIONS

A large proportion of KC patients have BV anomalies. Assessment of BV function should be included in the clinical examination of all KC patients.

Keratoconus in Africa: A systematic review and meta-analysis

PURPOSE

The aim of this review is to evaluate the prevalence of and factors associated with keratoconus in Africa.

METHOD

A systematic online literature search was conducted for articles on keratoconus in Africa. Meta-analysis was performed to estimate the prevalence of keratoconus in Africa. The Freeman-Tukey double arcsine transformation was used to minimize the effects of studies with extremely high or low prevalence estimates on the overall pooled estimates. Leave-one-out sensitivity analysis was used to assess the robustness of the pooled effects and potential outliers. Meta-regression was performed to explore associations between keratoconus, gender and age.

RESULTS

Twelve studies were included in the review; 5 from Egypt, 2 from South Africa, 2 from Kenya, 1 from Sudan, 1 from Ghana and 1 from Nigeria. Two studies were conducted in allergic conjunctivitis patients, 4 in keratoconus patients, 1 in contact lens service seekers, 1 in pre-LASIK patients, 1 in refractive patients and 1 in a student population. Eight studies were included in the meta-analysis. The overall prevalence estimate of keratoconus in Africa was 7.9% (95% CI: 2.5%-16.0%). The prevalence of keratoconus among males and females in Africa was estimated to be 9.3% (95% CI: 2.5%-19.5%) and 5.8% (95% CI: 1.5%-12.7%) respectively. The estimated prevalence of unilateral and bilateral keratoconus was 2.6% (95% CI: 0.4%-6.5%) and 5.8% (95% CI: 1.6%-12.3%), respectively. The estimated prevalence of mild keratoconus was 2.2% (95% CI: 0.7%-4.7%), moderate keratoconus was 3.5% (95% CI: 0.0%-11.8%) and severe keratoconus was 4.0% (95% CI: 0.0%-19.6%). There was no significant association between gender and the prevalence of keratoconus in Africa (p = 0.63), and age and the prevalence of keratoconus in Africa (p = 0.78).

CONCLUSION

The estimated prevalence of keratoconus reported here is higher than prevalence values reported in other meta-analyses or different geographical locations. This is mainly because studies included in this meta-analysis were either conducted on a cohort at high risk of keratoconus or a population with high possibility of finding keratoconus patients. There is a dearth of well-designed population-based studies on keratoconus in Africa, resulting in a lack of epidemiological information. This highlights the urgent need for research on keratoconus in Africa.

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

OBJECTIVE

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

MATERIAL AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Evaluation of vision-related quality of life in keratoconus patients, and associated impact of keratoconus severity indicators

PURPOSE

To evaluate vision-related quality of life in keratoconus patients and associated impact of keratoconus severity indicators using the National Eye Institute Visual Function Questionnaire (NEI-VFQ-25).

METHODS

This was a prospective cross-sectional study carried out from November 1, 2014, to April 30, 2015, in the corneal service of the Hôtel-Dieu hospital, Paris, France. A hundred and one keratoconus patients were consecutively enrolled. Participants completed a French-validated version of the National Eye Institute Visual Function Questionnaire (NEI-VFQ-25). Manifest refraction, maximum keratometry value, and corneal thinnest point were recorded. Associations between clinical and demographic factors, previous medical or surgical treatment, and NEI-VFQ-25 scale scores were evaluated.

RESULTS

Vision-related quality of life was no better in patients managed with rigid gas permeable contact lens, collagen cross-linking, or intracorneal ring segment implantation, compared with untreated patients. In advanced keratoconus (stages II, III, and IV of Amsler-Krumeich classification), rigid gas permeable contact lens wearers had better general vision but more ocular pain. Distance-corrected visual acuity worse than 20/40, mean refractive cylinder > 2.5 diopters, and corneal thinnest point < 460 μm in the better eye were associated with a lower vision-related quality of life. In multivariate analysis, only the uncorrected and distance-corrected visual acuity of the better eye remained significantly correlated with vision-related quality of life.

CONCLUSIONS

Low distance-corrected visual acuity in the better eye was the strongest predictor of low vision-related quality of life.

LogMAR and Stereoacuity in Keratoconus Corrected with Spectacles and Rigid Gas-permeable Contact Lenses

SIGNIFICANCE

This study showed an improvement in three-dimensional depth perception of subjects with bilateral and unilateral keratoconus with rigid gas-permeable (RGP) contact lens wear, relative to spectacles. This novel information will aid clinicians to consider RGP contact lenses as a management modality in keratoconic patients complaining of depth-related difficulties with their spectacles.

PURPOSE

The aim of this study was to systematically compare changes in logMAR acuity and stereoacuity from best-corrected spherocylindrical spectacles to RGP contact lenses in bilateral and unilateral keratoconus vis-à-vis age-matched control subjects.

METHODS

Monocular and binocular logMAR acuity and random-dot stereoacuity were determined in subjects with bilateral (n = 30; 18 to 24 years) and unilateral (n = 10; 18 to 24 years) keratoconus and 20 control subjects using standard psychophysical protocols.

RESULTS

Median (25th to 75th interquartile range) monocular (right eye) and binocular logMAR acuity and stereoacuity improved significantly from spectacles to RGP contact lenses in the bilateral keratoconus cohort (P < .001). Only monocular logMAR acuity of affected eye and stereoacuity improved from spectacles to RGP contact lenses in the unilateral keratoconus cohort (P < .001). There was no significant change in the binocular logMAR acuity from spectacles to RGP contact lenses in the unilateral keratoconus cohort. The magnitude of improvement in binocular logMAR acuity and stereoacuity was also greater for the bilateral compared with the unilateral keratoconus cohort. All outcome measures of cases with RGP contact lenses remained poorer than control subjects (P < .001).

CONCLUSIONS

Binocular resolution and stereoacuity improve from spectacles to RGP contact lenses in bilateral keratoconus, whereas only stereoacuity improves from spectacles to RGP contact lenses in unilateral keratoconus. The magnitude of improvement in visual performance is greater for the binocular compared with the unilateral keratoconus cohort.

Demographic profile, clinical, and topographic characteristics of keratoconus patients attending at a tertiary eye center

Purpose

To evaluate the demographic profile, clinical, and topographic characteristics of keratoconus (KCN) patients attending at a subspecialty eye hospital in Tehran, Iran.

Methods

In this cross-sectional study, all patients who attended Noor Eye Hospital between March 2011 and March 2017 and had a diagnosis of KCN were identified, and the required number of patients was randomly selected. The following data were extracted from patient's records: age, sex, visual acuity, refraction, keratometry, pachymetry, and treatment procedures. The data of KCN laterality, severity, morphology, and cone location were also extracted by analyzing the corneal imaging maps.

Results

The records of 1080 eyes of 540 patients were evaluated. The mean age of the participants was 31.04 ± 8.54 years (range, 13–63 years), and 69.3% of the patients were male. The highest and lowest frequency of KCN was seen in the age group 20–30 years and above 50 years, respectively. Bilateral KCN was detected in 93.3% [95% confidence interval (CI): 91.68–94.75] of the subjects. 43.7% (95%CI: 32.88–54.48), 55.6% (95%CI: 44.73–66.38), and 0.8% (95%CI: 0.75–0.78) of the cases had nipple, oval, and globus cones, respectively. The cone was central in 52.1% (95%CI: 41.10–63.11), paracentral in 43.6% (95%CI: 36.13–51.04), and peripheral in 4.3% (95%CI: 00.76–7.86) of the cases. The frequency percentage of KCN according to severity was 15.2% (95%CI: 13.09–17.46), 56.4% (95%CI: 53.37–59.37), and 28.4% (95%CI: 25.75–31.21) for mild, moderate, and severe KCN, respectively. Among different parameters, only cone location had a significant association with age as the frequency of paracentral and peripheral cones increased with ageing (P = 0.002).

Conclusions

The mean age of KCN patients in our study was higher than similar studies in other Asian countries. KCN was bilateral in most cases with an oval morphology and central cone location. Most of the patients had moderate to severe KCN.

Genetic Aspects of Keratoconus: A Literature Review Exploring Potential Genetic Contributions and Possible Genetic Relationships with Comorbidities

INTRODUCTION

Keratoconus (KC) is a complex, genetically heterogeneous, multifactorial degenerative disorder that is accompanied by corneal ectasia which usually progresses asymmetrically. With an incidence of approximately 1 per 2000 and 2 cases per 100,000 population presenting annually, KC follows an autosomal recessive or dominant pattern of inheritance and is, apparently, associated with genes that interact with environmental, genetic, and/or other factors. This is an important consideration in refractive surgery in the case of familial KC, given the association of KC with other genetic disorders and the imbalance between dizygotic twins. The present review attempts to identify the genetic loci contributing to the different KC clinical presentations and relate them to the common genetically determined comorbidities associated with KC.

METHODS

The PubMed, MEDLINE, Google Scholar, and GeneCards databases were screened for KC-related articles published in English between January 2006 and November 2017. Keyword combinations of "keratoconus," "risk factor(s)," "genetics," "genes," "genetic association(s)," and "cornea" were used. In total, 217 articles were retrieved and analyzed, with greater weight placed on the more recent literature. Further bibliographic research based on the 217 articles revealed another 124 relevant articles that were included in this review. Using the reviewed literature, an attempt was made to correlate genes and genetic risk factors with KC characteristics and genetically related comorbidities associated with KC based on genome-wide association studies, family-based linkage analysis, and candidate-gene approaches.

RESULTS

An association matrix between known KC-related genes and KC symptoms and/or clinical signs together with an association matrix between identified KC genes and genetically related KC comorbidities/syndromes were constructed.

CONCLUSION

Twenty-four genes were identified as potential contributors to KC and 49 KC-related comorbidities/syndromes were found. More than 85% of the known KC-related genes are involved in glaucoma, Down syndrome, connective tissue disorders, endothelial dystrophy, posterior polymorphous corneal dystrophy, and cataract.

Evaluation of keratoconus progression

AIM

To define variables for the evaluation of keratoconus progression and to determine cut-off values.

METHODS

In this retrospective cohort study (2010-2016), 265 eyes of 165 patients diagnosed with keratoconus underwent two Scheimpflug measurements (Pentacam) that took place 1 year apart ±3 months. Variables used for keratoconus detection were evaluated for progression and a correlation analysis was performed. By logistic regression analysis, a keratoconus progression index (KPI) was defined. Receiver-operating characteristic curve (ROC) analysis was performed and Youden Index calculated to determine cut-off values.

RESULTS

Variables used for keratoconus detection showed a weak correlation with each other (eg, correlation r=0.245 between RPImin and Kmax, p<0.001). Therefore, we used parameters that took several variables into consideration (eg, D-index, index of surface variance, index for height asymmetry, KPI). KPI was defined by logistic regression and consisted of a Pachymin coefficient of -0.78 (p=0.001), a maximum elevation of back surface coefficient of 0.27 and coefficient of corneal curvature at the zone 3 mm away from the thinnest point on the posterior corneal surface of -12.44 (both p<0.001). The two variables with the highest Youden Index in the ROC analysis were D-index and KPI: D-index had a cut-off of 0.4175 (70.6% sensitivity) and Youden Index of 0.606. Cut-off for KPI was -0.78196 (84.7% sensitivity) and a Youden Index of 0.747; both 90% specificity.

CONCLUSIONS

Keratoconus progression should be defined by evaluating parameters that consider several corneal changes; we suggest D-index and KPI to detect progression.

Asymmetry between Left and Right Eyes in Keratoconus Patients Increases with the Severity of the Worse Eye

PURPOSE

To evaluate whether the inter-eye asymmetry of keratoconus (KC) patients is different from a healthy control group and to investigate how asymmetry changes with increasing severity of the disease.

METHODS

In this retrospective study, we included both eyes of 350 patients with KC (age 35 ± 13 years) and 68 candidates planned for refractive surgery (control group, age 37 ± 11 years). Inclusion criteria for the KC group were keratoconus in at least one eye with Pentacam Topographical Keratoconus Classification (TKC) of at least 0.5. Patients eligible for refractive surgery in both eyes were included in the control group. Corneal tomography as well as Ocular Response Analyzer measurements were compared between both groups. Subgroup analysis was performed with respect to the TKC staging. Asymmetry was provided as worse eye (defined by higher TKC) minus fellow eye.

RESULTS

In the KC group, both eyes showed the same TKC staging in 30.6%, a difference of one stage in 34.0% and of two stages in 24.6% of the patients. The inter-eye asymmetry in the keratoconus group was significantly larger than that in the control group. Corneal power showed an asymmetry of 3.8 ± 4.0 D in keratoconus eyes versus 0.22 ± 0.17 D in the control group. Central corneal thickness (CCT) asymmetry was 34 ± 30 µm versus 6 ± 5 µm, respectively. The Keratoconus Match Index showed an asymmetry of 0.40 ± 0.35 versus 0.15 ± 0.14. The difference between both eyes increased with increasing TKC of the worse eye.

CONCLUSIONS

Inter-eye asymmetry is larger in keratoconus than in normal eyes, and it increases with keratoconus severity in the worse eye.

Correlation between visual function and refractive, topographic, pachymetric and aberrometric data in eyes with keratoconus

AIM

To analyze the relationship between two visual functions and refractive, topographic, pachymetric and aberrometric indicators in eyes with keratoconus.

METHODS

Corrected distance visual acuity (CDVA), and letter contrast sensitivity (CS) were correlated with refraction, corneal topography, pachymetry, and total corneal wavefront data prospectively in 71 eyes with keratoconus. The topographic indices assessed were simulated keratometry for the flattest and steepest meridians (SimK1 and SimK2), posterior steeper K (Ks), elevation value in best-fit sphere (BFS) maps, squared eccentricity (Є(2)), aspheric asymmetric index (AAI), pachymetry, thickness progression index (TPI), the amount of pachymetric decentralization (APD), and GalileiTM-keratoconus indices.

RESULTS

The mean CDVA (expressed as logMAR) were 0.25±0.21. The mean CS was 1.25±0.46. The spherical refraction correlated well with CDVA (r=-0.526, P<0.001). From topographic indices, SRI correlated with CS (r=-0.695), and IAI with CS (r=-0.672) (P<0.001 for all). Root mean square (RMS) was 4.3±1.81 µm, spherical aberration (SA) was -0.4±0.67 µm, vertical and horizontal coma were -2.1±1.47 and -0.4±0.72 µm. All wavefront data (except horizontal coma), AAI, Є(2) and maximum BFS correlated significantly with the visual function (P≤0.001 for all).

CONCLUSION

In this study, CS is more affected than CDVA as a visual function. The quantity and quality of vision is significantly correlated with well-known and new topographic indices. There is not a significant correlation between visual function and pachymetric parameters. The significantly correlated indices can be used in staging keratoconus and to follow the outcome of a treatment.

Impact of Collagen Cross-linking on Psychological Distress and Vision and Health-Related Quality of Life in Patients With Keratoconus

OBJECTIVE

To evaluate the changes in psychological distress level and quality of life (QoL) scores of keratoconus (KC) patients 1 year after corneal collagen cross-linking (CXL).

METHODS

Observational cross-sectional study. Thirty-three, consecutive progressive KC patients who received CXL treatment were enrolled in the study. All patients were evaluated before and 1 year after CXL ophthalmologically and psychologically. Main outcome measures were the visual, refractive, and topographic changes and the Beck Depression Inventory, State-Trait Anxiety Inventory (STAI), Short Form-36 (SF-36), and The National Eye Institute Visual Function Questionnaire (NEI-VFQ-25).

RESULTS

There were significant improvements in the keratometric readings at flat axis, steep axis, the mean keratometric reading, the corneal astigmatism (Kast), and the maximum keratometric reading. State-Trait Anxiety Inventory-II scores, QoL dimensions, such as physical role difficulty, general health, mental health, ocular pain, near activities, distance activities, peripheral vision, and mental health scores, and the composite score of NEI-VFQ-25, were higher after surgery. There was a positive correlation between the changes observed in Kast and mental health; a negative correlation between the changes in Kast and STAI-II, and a negative correlation between the changes in mental health and STAI-II. Change in STAI-II has significantly predicted the improvement observed in general health.

CONCLUSIONS

Our results suggested lower trait anxiety and better vision-related and health-related QoL in KC patients 1 year after successful CXL treatment. Better QoL in these patients seems to be related not only with the visual and refractive results but also improvement observed in trait anxiety.

Differences in central and non-central keratoconus, and their effect on the objective screening thresholds for keratoconus

PURPOSE

To evaluate the differences in central and non-central keratoconus (based on cone location), and their effect on the objective screening thresholds for keratoconus.

METHODS

This comparative case series was performed at tertiary care cornea and refractive surgery service. Three groups were made: KC apex within central 2 mm (central keratoconus, n = 50), apex outside central 2mm (non-central keratoconus, n = 50) and normal controls (n = 100, with 50 cases each with apex within and outside central 2 mm). All cases underwent clinical evaluation and corneal topography (CSO, Sirius, Italy). Apex keratometry (ApexK), simulated keratometry at 3 mm (SimK), central corneal thickness (CCT) and minimum corneal thickness (MCT), anterior corneal higher-order aberrations root mean square (HOARMS), and Zernike's coefficients up to fourth order at different zones were measured.

RESULTS

In spite of the keratoconic groups having comparable ApexK (p > 0.05), central keratoconus had higher SimK and thinner CCT and MCT (p < 0.001). HOARMS was significantly more for central keratoconus at 3 mm zones. These findings had moderate to large effect size (Cohen's d). Receiver operating curve analysis was carried out to compare central keratoconus and non-central keratoconus with control group. ApexK and HOARMS had best discriminative parameters. Using single parametric suspicion cut-offs of 'either SimK steep >47.2 D or CCT < 491.6 μ' had a good sensitivity (0.98) for central keratoconus, but not for non-central keratoconus (0.80). Changing this cut-off to 'either SimK steep K ≥ 45.8 D or CCT ≤ 503 μ' gave a sensitivity and specificity of 0.95 and 0.87 for non-central keratoconus and 0.99 and 0.87 for central keratoconus.

CONCLUSION

Non-central keratoconus has lesser effect on SimK, pachymetry and smaller-aperture HOARMS. Using 'SimK steep >47.2 D or CCT < 491.6 μ' may miss timely referral for topography in many of these cases. Using more stringent criteria of SimK steep K ≥ 45.8 D or CCT ≤ 503 μ to get a corneal topography done to rule out keratoconus is recommended, especially in cohorts with higher risk.

Replication and meta-analysis of candidate loci identified variation at RAB3GAP1 associated with keratoconus

PURPOSE

Keratoconus is a common complex corneal ectasia that can lead to severe visual impairment. Although a genetic component is well recognized, the genetic risk factors for keratoconus are yet to be fully elucidated. A recent genome-wide association study (GWAS) by Li et al. identified 15 potentially associated single nucleotide polymorphisms (SNPs). Here, we aimed to replicate these associations, and conduct a meta-analysis of the current and previous studies.

METHODS

We genotyped the 15 reported associated SNPs in 524 Australian Caucasian cases with keratoconus and 2761 controls. Association analysis was conducted in PLINK. A meta-analysis of this study with the adjusted P values of the previously published GWAS was conducted using the method of Fisher to combine P values.

RESULTS

Our Australian cohort showed association (P < 0.003) at SNPs near RAB3GAP1, KCND3, IMMPL2, and in a gene desert on chromosome 13q33.3, providing evidence of replication of the published results. The meta-analysis showed SNP rs4954218 near RAB3GAP1 gene was associated significantly with keratoconus, with P = 9.26 × 10(-9) passing the genome-wide significance level.

CONCLUSIONS

Although the mechanism of disease association is yet to be determined, SNP rs4954218 is associated consistently with keratoconus and likely tags a functional variant that contributes to disease susceptibility.

Revisiting keratoconus diagnosis and progression classification based on evaluation of corneal asymmetry indices, derived from Scheimpflug imaging in keratoconic and suspect cases

PURPOSE

To survey the standard keratoconus grading scale (Pentacam®-derived Amsler-Krumeich stages) compared to corneal irregularity indices and best spectacle-corrected distance visual acuity (CDVA).

PATIENTS AND METHODS

Two-hundred and twelve keratoconus cases were evaluated for keratoconus grading, anterior surface irregularity indices (measured by Pentacam imaging), and subjective refraction (measured by CDVA). The correlations between CDVA, keratometry, and the Scheimpflug keratoconus grading and the seven anterior surface Pentacam-derived topometric indices - index of surface variance, index of vertical asymmetry, keratoconus index, central keratoconus index, index of height asymmetry, index of height decentration, and index of minimum radius of curvature - were analyzed using paired two-tailed t-tests, coefficient of determination (r(2)), and trendline linearity.

RESULTS

The average ± standard deviation CDVA (expressed decimally) was 0.626 ± 0.244 for all eyes (range 0.10-1.00). The average flat meridian keratometry was (K1) 46.7 ± 5.89 D; the average steep keratometry (K2) was 51.05 ± 6.59 D. The index of surface variance and the index of height decentration had the strongest correlation with topographic keratoconus grading (P < 0.001). CDVA and keratometry correlated poorly with keratoconus severity.

CONCLUSION

It is reported here for the first time that the index of surface variance and the index of height decentration may be the most sensitive and specific criteria in the diagnosis, progression, and surgical follow-up of keratoconus. The classification proposed herein may present a novel benchmark in clinical work and future studies.

Comparison of Placido disc and Scheimpflug image-derived topography-guided excimer laser surface normalization combined with higher fluence CXL: the Athens Protocol, in progressive keratoconus

Background

The purpose of this study was to compare the safety and efficacy of two alternative corneal topography data sources used in topography-guided excimer laser normalization, combined with corneal collagen cross-linking in the management of keratoconus using the Athens protocol, ie, a Placido disc imaging device and a Scheimpflug imaging device.

Methods

A total of 181 consecutive patients with keratoconus who underwent the Athens protocol between 2008 and 2011 were studied preoperatively and at months 1, 3, 6, and 12 postoperatively for visual acuity, keratometry, and anterior surface corneal irregularity indices. Two groups were formed, depending on the primary source used for topoguided photoablation, ie, group A (Placido disc) and group B (Scheimpflug rotating camera). One-year changes in visual acuity, keratometry, and seven anterior surface corneal irregularity indices were studied in each group.

Results

Changes in visual acuity, expressed as the difference between postoperative and preoperative corrected distance visual acuity were +0.12 ± 0.20 (range +0.60 to −0.45) for group A and +0.19 ± 0.20 (range +0.75 to −0.30) for group B. In group A, K1 (flat keratometry) changed from 45.202 ± 3.782 D to 43.022 ± 3.819 D, indicating a flattening of −2.18 D, and K2 (steep keratometry) changed from 48.670 ± 4.066 D to 45.865 ± 4.794 D, indicating a flattening of −2.805 D. In group B, K1 (flat keratometry) changed from 46.213 ± 4.082 D to 43.190 ± 4.398 D, indicating a flattening of −3.023 D, and K2 (steep keratometry) changed from 50.774 ± 5.210 D to 46.380 ± 5.006 D, indicating a flattening of −4.394 D. For group A, the index of surface variance decreased to −5.07% and the index of height decentration to −26.81%. In group B, the index of surface variance decreased to −18.35% and the index of height decentration to −39.03%. These reductions indicate that the corneal surface became less irregular (index of surface variance) and the “cone” flatter and more central (index of height decentration) postoperatively.

Conclusion

Of the two sources of primary corneal data, the Scheimpflug rotating camera (Oculyzer™) for topography-guided normalization treatment with the WaveLight excimer laser platform appeared to provide more statistically significant improvement than the Placido disc topographer (Topolyzer™). Overall, the Athens protocol, aiming both to halt progression of keratoconic ectasia and to improve corneal topometry and visual performance, produced safe and satisfactory refractive, keratometric, and topometric results. The observed changes in visual acuity, along with keratometric flattening and topometric improvement, are suggestive of overall postoperative improvement.