The genetic and environmental factors for keratoconus

Machine learning with a reduced dimensionality representation of comprehensive Pentacam tomography parameters to identify subclinical keratoconus

PURPOSE

To investigate the performance of a machine learning model based on a reduced dimensionality parameter space derived from complete Pentacam parameters to identify subclinical keratoconus (KC).

METHODS

All 1692 available parameters were obtained from the Pentacam imaging machine on 145 subclinical KC and 122 control eyes. We applied a principal component analysis (PCA) to the complete Pentacam dataset to reduce its parameter dimensionality. Subsequently, we investigated machine learning performance of the random forest algorithm with increasing numbers of components to identify their optimal number for detecting subclinical KC from control eyes.

RESULTS

The dimensionality of the complete set of 1692 Pentacam parameters was reduced to 267 principal components using PCA. Subsequent selection of 15 of these principal components explained over 85% of the variance of the original Pentacam-derived parameters and input to train a random forest machine learning model to achieve the best accuracy of 98% in detecting subclinical KC eyes. The model established also reached a high sensitivity of 97% in identification of subclinical KC and a specificity of 98% in recognizing control eyes.

CONCLUSIONS

A random forest-based model trained using a modest number of components derived from a reduced dimensionality representation of complete Pentacam system parameters allowed for high accuracy of subclinical KC identification.

Oxidative and antioxidative stress markers in keratoconus: a systematic review and meta-analysis

PURPOSE

To conduct a systematic review and meta-analysis on the levels of oxidative stress markers and antioxidants in keratoconus compared to healthy subject.

METHOD

The PubMed, Cochrane Library, Embase, Science Direct and Google Scholar databases were searched on 1st June 2020 for studies reporting oxidative and antioxidative stress markers in keratoconus and healthy controls. Main meta-analysis was stratified by type of biomarkers, type of samples (tears, cornea, aqueous humour and blood) and type of corneal samples (stromal cells, epithelium and endothelium).

RESULTS

We included 36 articles, for a total of 1328 keratoconus patients and 1208 healthy controls. There is an overall increase in oxidative stress markers in keratoconus compared with healthy controls (standard mean deviation (SMD) = 0.94, 95% confidence interval (95% CI) 0.55-1.33), with a significant increase in reactive oxygen and nitrogen species (1.09, 0.41-1.78) and malondialdehyde (1.78, 0.83-2.73). There is an overall decrease in antioxidants in keratoconus compared with healthy controls (-0.63, -0.89 to -0.36), with a significant decrease in total antioxidant capacity/status (-1.65, -2.88 to -0.43), aldehyde/NADPH dehydrogenase (-0.77, -1.38 to -0.17), lactoferrin/transferrin/albumin (-1.92, -2.96 to -0.89) and selenium/zinc (-1.42, -2.23 to -0.61). Oxidative stress markers were higher in tears and in cornea of keratoconus than in aqueous humour, and antioxidants were decreased in tears, aqueous humour and blood without difference between sample type. Oxidative stress markers increased in stromal cells and antioxidants decreased in endothelium.

CONCLUSION

Oxidative stress markers and antioxidants were dysregulated in keratoconus, involving an imbalance of redox homeostasis in tears, cornea, aqueous humour and blood.

Quality-of-Life Improvement After Scleral Lens Fitting in Patients With Keratoconus

OBJECTIVES

To assess the quality-of-life improvement after scleral lens fitting in patients with keratoconus.

METHODS

We conducted a prospective observational study of all consecutive patients with keratoconus starting scleral lens fitting in 2019, from January 2 to December 27, at the Dijon University Hospital, France. Quality of life was assessed before and after wearing scleral lenses for 3 months through the National Eye Institute Visual Function Questionnaire 25 (NEI-VFQ 25) questionnaire. We investigated factors potentially influencing quality of life: final visual acuity, keratoconus stage, and maximum keratometry reading.

RESULTS

In total, 41 eyes of 24 patients were successfully fitted with scleral lenses, 92.9% were 18 mm in diameter and 7.1% were 17 mm. The visual acuity improved by -0.4±0.3 logarithm of the minimum angle of resolution (P<0.001) after scleral lens fitting. Visual gain increased with keratometry and keratoconus severity (P<0.001; P<0.01). The NEI-VFQ 25 score increased by 19.5±19.1 points on average (P<0.001). No association was found between the factors under study and improvement in quality of life.

CONCLUSION

Our study confirms the functional improvement in patients with keratoconus fitted with scleral lenses, especially in patients with more advanced disease. Moreover, it suggests a major role of these lenses in improving quality of life, independently of the severity of the disease and the visual gain.

Evaluation of CorvisST biomechanical parameters and anterior segment optical coherence tomography for diagnosing forme fruste keratoconus

PURPOSE

To investigate the utility of biomechanical property measurements using a Scheimpflug-based tonometer (SBT) and/or anterior segment optical coherence tomography (AS-OCT) for diagnosing forme fruste keratoconus (FFK).

METHODS

In this retrospective interventional case series, 23 eyes with FFK of 23 consecutive patients and 52 eyes of 52 healthy volunteers who visited our keratoconus outpatient clinic were enrolled. Logistic regression analysis was conducted to determine the causal relationship between FFK diagnosis and each parameter.

RESULTS

When only SBT was used, the corneal stiffness parameter, stiffness parameter A1 (SP-A1) and the corneal velocity at first applanation were selected as explanatory variables, and sensitivity, specificity and area under the receiver operating characteristic curve (AUROC) were 82.9%, 86.9% and 0.938, respectively. When only AS-OCT parameters were used, the posterior corneal asymmetric component and central corneal thickness were selected, and the sensitivity, specificity and AUROC were 82.6%, 94.2% and 0.893, respectively. When parameters from both methods were used, SP-A1 and the posterior corneal asymmetry component derived from Fourier analysis were selected as explanatory variables, and sensitivity, specificity and AUROC were 91.30%, 90.38% and 0.947, respectively. No significant differences in AUROC were observed between diagnoses using each device and the combination of both devices (AS-OCT versus SBT, p = 0.314; integrated parameters versus AS-OCT, p = 0.081; integrated parameters versus SBT, p = 0.234).

CONCLUSION

Optimization of SBT and AS-OCT parameters allowed for the diagnosis of FFK at a clinically usable level. Forme fruste keratoconus (FFK) diagnosis integrating biomechanical properties with AS-OCT showed no superiority compared to diagnosis based on a single device.

Estimated Prevalence of Keratoconus in the United States From a Large Vision Insurance Database

PURPOSE

To estimate the prevalence of keratoconus in the United States using a large vision insurance database.

METHODS

We used data from the 2016 vision service plan (VSP) Global claims database to estimate the prevalence of keratoconus among enrollees by state. The VSP Global database includes cross-sectional de-identified claims data summarized by state of residence in predefined age and gender groups. Crude values of prevalence of keratoconus are provided in the VSP Global database. The open-source software package qGIS version 3.12 was used as the geographic information system for geospatial analysis.

RESULTS

The prevalence of keratoconus among VSP enrollees in the United States was estimated to be 0.15% with 95% confidence interval (CI) (0.15%, 0.15%). The prevalence of keratoconus was highest in Western states and among male population. The highest prevalence of keratoconus was in Colorado (0.51%; 95% CI 0.49%-0.52%), with particularly high prevalence for men in the age groups 18 to 39 years (0.90%; 95% CI 0.84%-0.95%) and 40 to 64 years (0.90%; 95% CI 0.85%-0.95%).

CONCLUSION

The average prevalence of keratoconus in the United States in 2016 may be higher than previously reported. Living in Western states and male sex were associated with high prevalence.

Inter-rater Reliability and Repeatability of Manual Anterior Segment Optical Coherence Tomography Image Grading in Keratoconus

OBJECTIVES

To determine the repeatability of corneal measurements from anterior segment optical coherence tomography (AS-OCT) images using ImageJ software in healthy eyes compared with eyes with keratoconus.

METHODS

Anterior segment OCT images of 25 eyes from 14 healthy subjects and 25 eyes from 15 subjects with keratoconus between the ages of 20 and 80 years were evaluated. Two trained observers used ImageJ to measure the central corneal cross-sectional area and anterior and posterior corneal arc lengths. MedCalc statistical software was used to generate the intraclass correlation coefficient (ICC) and Bland-Altman plots (BAPs) for observer measurements.

RESULTS

Observer measurements of the central corneal cross-sectional area and anterior and posterior corneal arc lengths yielded an ICC >0.7. The ICC comparing the 3 parameters ranged from 0.75 to 0.84 for the control and 0.96 to 0.98 for the keratoconus group. No systematic proportional bias was detected by the BAPs. There were minimal differences between the 2 observer's measurements, with a mean of the difference of 0.3 mm2, 0 mm, and 0 mm, for the 3 measurements, respectively.

CONCLUSIONS

This study suggests that ImageJ software is a repeatable and reliable tool in the analysis of corneal parameters from AS-OCT images among patients with keratoconus and may be applicable to AS-OCT imaging protocol development, an area of active keratoconus research.

The Characteristics and Risk Factors of Very Asymmetric Keratoconus

PURPOSE

To characterize very asymmetric keratoconus (KC) in terms of clinical demographics and risk factors in the Japanese population.

METHODS

We retrospectively reviewed the clinical records of patients with very asymmetric KC attending a university hospital. Patients with very asymmetric KC had defined clinical KC in one eye and normal topography in the fellow eye. All patients completed a questionnaire on potential risk factors (family history of KC, atopy, asthma, allergy, heart disease, sleep apnea, Down syndrome, eye rubbing, prone sleep position, and dominant hand). These data were compared with those of patients with clinical or topographic KC in both eyes. Subgroup analysis of very asymmetric KC eyes were performed based on the KC status: mild and severe.

RESULTS

We retrospectively investigated 66 patients with very asymmetric KC and 505 patients with KC. Patients reported eye rubbing (53%-56%), allergy (62%-63%), and atopy (28%-29%) in both groups. There was no significant difference in terms of risk factors between the two groups. Approximately half of the 66 patients with very asymmetric KC had KC eyes ipsilateral to the dominant hand. Subgroup analysis of very asymmetric KC showed that atopy and asthma were more frequent in the mild KC group than in the severe KC group. Forty-four of 60 patients (73.3%) were using corneal, rigid, gas-permeable contact lenses (corneal GPs) for the KC eye, of which 30 patients (68.2%) were also using a corneal GP for the fellow eye.

CONCLUSIONS

The patient-reported frequency of eye rubbing, allergy, and atopy were similar between KC and very asymmetric KC. Furthermore, we found no association between hand dominance and KC laterality.

Update and Review of Diagnosis and Management of Post-Refractive Surgery Ectasia

ABSTRACT

Post-Refractive Surgery Ectasia is a serious, sight-threatening, and highly - avoided complication seen after the following procedures: Laser in situ Keratomileusis, Photorefractive Keratectomy, Small Incision Lenticule Extraction, Radial and/or Arcuate Keratotomy. Specific risk factors may include age, corneal thickness, degree of refractive error, corneal topographic changes including irregular astigmatism, percent tissue ablation, and residual stromal bed. Biomarkers may be a new option to help indicate who is at greatest risk for ectasia. Visual aids including glasses or contacts lenses are often required to achieve optimal vision. Collagen crosslinking is the only treatment thought to stop progression of ectasia and prevent keratoplasty. Other surgical options may include topography-guided phototherapeutic keratectomy and intrastromal corneal ring segments. Ultimately an "ounce of prevention is a pound of cure" so careful preoperative screening and ultimately offering the safest and most effective treatments for patients is arguably the most important job of the refractive surgeon.

Adverse events after riboflavin/UV-A corneal cross-linking: a literature review

BACKGROUND

Riboflavin/UV-A corneal cross-linking (CXL) for treating keratoconus and iatrogenic corneal ectasia has been well-established as first treatment option to stabilize corneal tissue biomechanical instability. Although the plethora of clinical studies has been published into the field, there is no systematic review assessing the type and frequency of adverse events after CXL.

METHODS

A systemic literature review on clinical safety and adverse events after CXL in patients with keratoconus and corneal ectasia was performed using PubMed. A literature search was performed for relevant peer-reviewed publications. The main outcome measures extracted from the articles were adverse events, endothelial cell density, corrected distance visual acuity and maximum simulated keratometry.

RESULTS

The most frequent adverse events after CXL were corneal haze and corneal edema, which were mild and transient. The severe adverse events were infrequent (cumulative incidence: < 1.3%) after CXL. The clinical benefits of CXL highly outweighed the risks for the treatment of keratoconus and corneal ectasia.

CONCLUSIONS

The severe adverse events with permanent sequelae are infrequent after CXL and all are associated with corneal de-epithelialization, such as infectious keratitis and corneal scarring.

Environmental Risk Factors Associated With the Need for Penetrating Keratoplasty in Patients With Keratoconus

Purpose To identify environmental risk factors associated with the need for penetrating keratoplasty (PKP) (full-thickness corneal transplantation) in patients with keratoconus in a Middle Eastern country. Methods This is a retrospective case-control study. This study included patients with keratoconus who underwent PKPor were waitlisted for PKP. Controls were patients diagnosed with keratoconus who did not reach a stage that necessitates PKP. Groups were matched by age and gender. Chi-square test was used to figure out the association between different risk factors including eye rubbing, vernal keratoconjunctivitis (VKC), smoking, paternal consanguinity, eye dryness, family history, asthma, eczema, and diabetes with the need for PKP. Results A total of 111 patients were included in this study, there were 48 (43.26%) men and 63 (56.75%) women. The case group included 42 subjects and the control group included 69 subjects. We found statistically significant differences between the two groups in relation to eye rubbing (p=0.0005), VKC (p=0.005), paternal consanguinity (p=0.02), and smoking rate (p=0.04), all being significant in the group in need of PKP. On the other hand, we did not find out a statistically significant difference between the two groups in relation to family history (p=0.31), dryness (p=0.58), asthma (p=0.15), eczema (p=0.28), or diabetes (p=0.29). Conclusion This study has identified several risk factors associated with the need for PKP in patients with keratoconus, part of which are modifiable. These findings can benefit clinicians in community counseling and give recommendations that can help in preventing or - at least - delaying the need for PKP surgery in keratoconus, such as smoking cessation, aggressive treatment of VKC disease, eye rubbing avoidance, as well as raising awareness regarding the potential risks of paternal consanguinity in this disease entity.

Effect of Thyroxine on Transforming Growth Factor β1, Collagen I, and V Expression in Keratoconus Corneal Fibroblasts and Keratocytes, in Vitro

BACKGROUND

Keratoconus (KC) is a corneal disorder, associated with oxidative stress, hypoxia and as several times discussed, potentially with thyroid gland dysfunction. We aimed to investigate the effect of thyroxine on transforming growth factor β1 (TGF-β1), collagen I and V (Col I and V) expression in human corneal fibroblasts (HCFs) and human keratocytes of KC corneas, in vitro.

METHODS

Primary human KC-keratocytes and normal keratocytes were isolated and cultured as corneal fibroblasts or keratocytes. The effect of 0.1 µg/ml and 1.0 µg/ml thyroxine on TGF-β1, Col I and Col V expression was investigated by qPCR, Western blot, and ELISA. Proliferation assay was performed using BrdU ELISA to observe the 24h effect of 1.0 µg/ml thyroxine on keratocytes, in vitro.

RESULTS

TGFB1 mRNA expression of normal keratocytes increased following 1.0 µg/ml thyroxine stimulation for 24 h (p = .036), without changes in protein expression. Col I protein expression of KC-HCFs increased following 1.0 µg/ml thyroxine stimulation for 24 h (p = .0003). Proliferation of normal and KC keratocytes increased following a 7-day growth period and 24 hours thyroxine administration (p = .018; p = .024).

CONCLUSIONS

Thyroxine may affect the Col I protein expression in KC-HCFs, but not in KC keratocytes, in vitro. Thyroxine administration has no effect on TGF-β1, collagen I and V expression of keratoconus keratocytes. Therefore, an increased thyroxine concentration alone seems not to be causally related to the development of keratoconus.

Risk Factors for Development of Keratoconus: A Matched Pair Case-Control Study

BACKGROUND

Keratoconus, a progressive ectatic corneal disorder, is believed to be multifactorial in etiology with interaction between genetic and environmental factors. To date, risk factors for the development of the disease are extensively debated and need to be identified since they play a critical role in disease prevention and management. This study aimed to analyze associations between several hereditary and environmental predictors and the development of keratoconus.

PATIENTS AND METHODS

This was a retrospective matched pair case-control study. The study was conducted in Ibn-Alhaitham eye teaching hospital between March 2016 and April 2017. Patients with keratoconus (cases) and their age- and gender-matched controls were asked about childhood and early teenage eye rubbing, ocular trauma, obesity, contact lens wear, smoking and sunlight exposure, family history of keratoconus, parental consanguinity and information related to socio-economic status. Univariable and multivariable conditional logistic regression analyses were used to test the significance of associations.

RESULTS

A total of 166 individuals (83 cases and 83 controls; 60.2% female) were included. On univariable analysis, eye rubbing, family history of keratoconus and parental consanguinity were significant risk factors for keratoconus, whereas all other factors were non-significant. On multivariable analysis, eye rubbing (odds ratio: 4.93; P < 0.01), family history of keratoconus (odds ratio: 25.52; P < 0.01) and parental consanguinity (odds ratio: 2.89; P = 0.02), again, emerged as significant risk factors for disease development.

CONCLUSION

Family history of keratoconus, eye rubbing, and parental consanguinity were significant risk factors for keratoconus development. These results support the evidence for multifactorial etiology, the most important factor being hereditary predisposition.

Is keratoconus associated to thyroid diseases? Assessment of the corneal parameters in patients with congenital hypothyroidism

PURPOSE

To investigate the association between keratoconus and congenital hypothyroidism (CH).

PATIENTS AND METHODS

Patients were enrolled in this study and divided into two groups. The first group comprised 31 subjects (11M:20F) with the mean age of 15.2 ± 3.9 years. affected by CH, and the control group was composed by 19 healthy individuals (8M:11F) aged 14.3 ± 4.6 years. All patients underwent complete ophthalmologic examination with visual acuity assessment, refraction, slit lamp examination, and retinoscopy. Corneal parameters were measured using Scheimpflug camera (Pentacam^® Oculus, Germany). The main outcome measures considered for evaluation were: average corneal curvature (K), central corneal thickness (CCT), anterior elevation and posterior elevation at the thinnest point, corneal volume (CV), anterior chamber depth (ACD), and anterior chamber volume (ACV). Additionally, data from Belin/Ambrosio Enhanced Ectasia Display (BAD) and the high order aberrations were evaluated. Kolmogorov-Smirnov test was used to verify the Gaussian distribution, the comparison between the controls and cases group was performed by Mann-Whitney nonparametric test. A p value less than 0.05 was considered to be statistically significant. The odds ratio was performed in order to quantify the relationship between the congenital hypothyroidism and abnormal values displayed on front BAD.

RESULTS

The significant difference in the refractive status between both groups was observed. As to examined corneal and anterior chamber parameters no statistical differences were detected.

CONCLUSIONS

Congenital hypothyroidism diagnosed and treated since the early postnatal life doesn't induce abnormalities of corneal parameters suggestive for keratoconus.

Prevalence and incidence of keratoconus in Norway: a nationwide register study

PURPOSE

To estimate the national prevalence and incidence of keratoconus in Norway.

METHODS

In this epidemiologic study, data were obtained from the Norwegian Patient Registry, which provides information from all publicly funded specialist care in Norway. Prevalence of keratoconus was estimated from the total number of patients registered with this diagnosis and incidence from the annual frequency of first-time registrations of patients up to 40 years of age in the period 2010-2018. Data on age and gender of the keratoconus patients were also gathered.

RESULTS

A total of 9832 keratoconus patients were registered. The estimated prevalence in the general population was 192.1 per 100 000 (95% confidence interval (CI): 188.3-195.9), and the estimated annual incidence was 19.8 per 100 000 (95% CI: 18.1-21.5). There was a predominance of males (73%), and mean age for all patients was 37.5 years at first registration in this period.

CONCLUSION

This study reports the frequency of keratoconus from a national patient register during a time period with available modern diagnostic tools. The estimated prevalence and incidence were higher than most previous estimates and show that keratoconus is not a rare condition. As screening was not part of the study, the true prevalence in the general population may be even higher.

Tomographically normal partner eye in very asymmetrical corneal ectasia: biomechanical analysis

PURPOSE

To point out the biomechanical changes of the topographically and tomographically normal partner eye (NPE) in patients with very asymmetrical corneal ectasia.

SETTING

Department of Ophthalmology, Saarland University Medical Center in Homburg/Saar, Germany.

DESIGN

Retrospective study.

METHODS

The topographical and tomographical results of the NPE were assessed using the Pentacam HR and the biomechanical corneal properties using the Ocular Response Analyzer (keratoconus match index [KMI], corneal hysteresis [CH], and corneal resistance factor [CRF]) and the Corvis ST (topographic biomechanical index [TBI] and Corvis biomechanical index) and compared those results with a normal control group (CG).

RESULTS

The clinical records of 26 patients recruited from the Homburg Keratoconus Center diagnosed with a very asymmetrical corneal ectasia were reviewed. The NPE (8.5 ± 1.5 mm Hg) showed a significantly more pathological CH (P < .001) compared with the CG. The CRF was also significantly more pathological (P = .04) for the NPE (8.3 ± 1.5 mm Hg) compared with the CG. The NPE (0.62 ± 0.32) showed a nonsignificant (P = .08) more pathological KMI compared with the CG. Nineteen (73.1%) of 26 NPE had a KMI less than 0.72 and were considered pathological. Compared with the CG, the TBI of the NPE (0.19 ± 0.25) did not differ significantly overall (P = .57). However, 5 (19.2%) of 26 eyes had a TBI more than 0.29 and were considered pathological.

CONCLUSIONS

Topographically and tomographically NPEs in very asymmetrical corneal ectasia frequently showed biomechanical changes. This should be considered before planning any type of refractive corneal surgery in such patients.

Clinical evaluation of meibomian gland dysfunction in patients with keratoconus

PURPOSE

To investigate the association of keratoconus (KC) with meibomian gland dysfunction (MGD) and to describe the epidemiological characteristics of MGD in this disease.

METHODS

In this observational study, 120 KC patients seen in the Department of Ophthalmology of the Complexo Hospitalario Universitario de Santiago de Compostela and 87 controls were analyzed. The Ocular surface disease index (OSDI) questionnaire was administered and several DED tests and an evaluation of the meibomian glands and lid margin were performed. MGD signs and DED tests were compared between the groups. Symptoms were further analyzed in patients and controls with and without MGD.

RESULTS

KC was significantly associated with MGD after adjusting for age and sex [adjusted odds ratio (ORa), 2.40]. The frequency of MGD in KC patients [59 (49.2%) KC patients and 25 (28.7%) controls had MGD] correlated with the severity of KC (r = 0.206) (P = 0.020). Mean OSDI score in KC patients with and without MGD was 31.1 ± 24.1 and 35.2 ± 26.0 (P = 0.326), and 17.2 ± 22.7 and 13.3 ± 14.1 in controls with and without it (P = 0.366). The most common MGD signs coincided in both groups. Staining with fluorescein (P = 0.000) and lissamine green (P = 0.019) was higher in KC patients, but no differences were detected with TBUT (P = 0.116) or the Schirmer test (P = 0.637). Hypersecretory MGD was the most prevalent variant in both groups.

CONCLUSIONS

MGD and DED are common in KC patients. MGD correlates with the severity of KC and is indistinguishable from MGD in patients without KC. No association was found with symptoms. Patients with KC should be screened for MGD because of its possible clinical implications. Further research is needed to clarify the role of MGD in KC patients.

Diagnosis of Subclinical Keratoconus with a Combined Model of Biomechanical and Topographic Parameters

This study sought to develop a diagnostic model with aberrometry and biomechanical variables for subclinical keratoconus. The design was a cross-sectional study. The topographic data were obtained with a rotating Scheimpflug camera (Pentacam HR), and biomechanical data were obtained with Corvis ST. The study included 81 eyes distributed in 61 healthy corneas and 20 subclinical keratoconus (SCKC), defined as eyes with suspicious topographic findings, normal slit-lamp examination, and a manifestation of keratoconus. Analyses of the topographic and biomechanical data were performed, and a classifying model of SCKC was elaborated. The model for the diagnosis of SCKC includes posterior coma to 90°, Ambrósio's Relational Thickness in the horizontal profile (ARTh), and velocity when the air pulse is off (A2 velocity). The sensitivity was 89.5%, specificity 96.7%, accuracy 94.9%, and precision 89.5%. The area under the curve (AUC) of the receiver operating characteristic (ROC) curve for the model was 0.951. Diagnosis of subclinical keratoconus depends on the aberrometry variable posterior coma to 90° and the biomechanical variables A2 velocity and ARTh.

Contrast sensitivity and higher-order aberrations in Keratoconus subjects

This study analyzes the relationship between contrast-sensitivity and higher-order aberrations (HOA) in mild and subclinical-keratoconus in subjects with good visual-acuity (VA). Keratoconus group (including subclinical-keratoconus) and controls underwent autokeratometry, corneal-tomography, autorefraction and HOA measurement. Contrast-sensitivity was tested using a psychophysical two-alternative forced-choice Gabor patches in three blocks (6, 9, 12 cycles/deg). Controls were compared to the keratoconus group and to a keratoconus subgroup with VA of 0.00 LogMar group ("keratoconus-0.00VA"). Spearman correlation tested association between HOA and contrast-sensitivity. Twenty-two keratoconus subjects (38 eyes: 28 keratoconus, 10 subclinical-keratoconus, 20 keratoconus-0.00VA) and 35 controls were included. There was a significant difference between control and keratoconus, and between control and keratoconus-0.00VA, for keratometry, cylinder, thinnest and central corneal thickness (p < 0.001). Controls showed lower HOA and higher contrast-sensitivity for all spatial-frequencies (p < 0.001). Most HOA were negatively correlated with contrast-sensitivity for all spatial-frequencies for keratoconus group and for 9 and 12 cycles/deg for keratoconus-0.00VA. Keratoconus subjects with good VA showed reduction in contrast-sensitivity and increased HOAs compared to controls. HOA and contrast-sensitivity are inversely correlated in subjects with mild keratoconus despite good VA. This suggests that the main mechanism underlying the decreased vision quality in keratoconus is the increase of HOA.

Effects of Mechanical Compression on Cell Morphology and Function in Human Corneal Fibroblasts

Purpose: To explore the effect of mechanical compression (similar to that induced by eye rubbing) on cell morphology, proliferation, apoptosis, and extracellular matrix synthesis and degradation in human corneal fibroblasts.Materials and methods: Human corneal fibroblasts were isolated from corneal lenticule tissue of 10 patients after small incision lenticule extraction surgery. A system was established to mechanically compress corneal fibroblasts with pressure ranging from 0 to 524 Pa. Morphological changes, cell proliferation, apoptosis, and corneal matrix synthesis and degradation were examined using microscopy imaging, bromodeoxyuridine staining, flow cytometry, and qPCR analysis in human corneal fibroblasts after mechanical compression.Results: Human corneal fibroblasts showed short and thick cytoplasmic extensions, as well as a relatively low aspect ratio, suggesting significant morphological alterations caused by high levels of compressive stress. Mechanical compression inhibited cell proliferation and promoted cell apoptosis. Furthermore, compressive stress led to significant elevation in the expression of genes related to extracellular matrix degradation (matrix metalloproteinases MMP1 and MMP9) as early as 6 h after compression and moderate changes in the expression of tissue inhibitors of metalloproteinases. In addition, the mRNA expression levels of COL1A1, lumican, and vimentin were reduced 24 and 48 h after mechanical compression.Conclusions: Mechanical compression alters cell morphology, inhibits proliferation, induces apoptosis, upregulates genes related to extracellular matrix degradation, and downregulates corneal structural genes in human corneal fibroblasts. This study provides evidence that compressive stress significantly influences corneal keratocytes. Our findings suggest that this mechanical effect may be related to keratoconus associated with chronic eye rubbing.

IL1A and IL1B gene polymorphisms and keratoconus susceptibility: evidence from an updated meta-analysis

Background: Several single-nucleotide polymorphisms (SNPs) in IL1B genes have been associated with KTCN. However, the results of these studies were not conclusive. This meta-analysis association study is aimed to quantitatively estimate the association of IL1B rs16944 (g.4490T>C) and rs1143627 (g.4970C>T), and IL1A rs2071376 (c.615 + 169C>A) polymorphisms with KTCN susceptibility.Materials and Methods: Systematic literature search was performed in Web of Science, MEDLINE, PubMed, Scopus, and Google Scholar databases. The odds ratios (ORs) and 95% confidence intervals (CI) were calculated assuming different contrasted genetic models.Results: The reference T allele of IL1B (g.4490T>C) polymorphism was significantly associated with decreased KTCN risk under all assessed genetic models. Regarding the reference C allele of IL1B (g.4970C>T) polymorphism, decreased risk of KTCN was found. The reference C allele of IL1A (c.615 + 169C>A) polymorphism conferred a decreased risk of KTCN under heterozygous codominant (AC vs. AA), homozygous codominant (CC vs. AA), and dominant (AC+CC vs. AA) genetic models. The pooling estimates showed that the T C haplotype was associated with a significant increase in KTCN risk. In contrast, the T T haplotype was correlated with a decreased risk of KTCN. With the assumption of a prior probability of 0.25, the false-positive report probability (FPRP) values were less than 0.2, indicating the observed significant associations were notable.Conclusion: These findings propose that the studied IL1B polymorphisms and the IL1A variation have opposite effects on KTCN susceptibility. More large-scale replication studies are warranted to illuminate the precise role of these SNPs on the etiology of eye disorders.

IMI Risk Factors for Myopia

Risk factor analysis provides an important basis for developing interventions for any condition. In the case of myopia, evidence for a large number of risk factors has been presented, but they have not been systematically tested for confounding. To be useful for designing preventive interventions, risk factor analysis ideally needs to be carried through to demonstration of a causal connection, with a defined mechanism. Statistical analysis is often complicated by covariation of variables, and demonstration of a causal relationship between a factor and myopia using Mendelian randomization or in a randomized clinical trial should be aimed for. When strict analysis of this kind is applied, associations between various measures of educational pressure and myopia are consistently observed. However, associations between more nearwork and more myopia are generally weak and inconsistent, but have been supported by meta-analysis. Associations between time outdoors and less myopia are stronger and more consistently observed, including by meta-analysis. Measurement of nearwork and time outdoors has traditionally been performed with questionnaires, but is increasingly being pursued with wearable objective devices. A causal link between increased years of education and more myopia has been confirmed by Mendelian randomization, whereas the protective effect of increased time outdoors from the development of myopia has been confirmed in randomized clinical trials. Other proposed risk factors need to be tested to see if they modulate these variables. The evidence linking increased screen time to myopia is weak and inconsistent, although limitations on screen time are increasingly under consideration as interventions to control the epidemic of myopia.

A hospital-based study on clinical data, demographic data and visual function of keratoconus patients in Central China

China is a populous country but lacks epidemiological data on keratoconus (KC). The present study aimed to investigate the clinical data, demographic data, and visual function (VF) data of KC patients in Central China. A total of 524 KC eyes in 307 KC patients (217 bilateral and 90 unilateral) from Henan Eye Hospital were included in the current study. Demographic and VF data were assessed with questionnaires administered by well-trained staff during face-to-face interviews. Visual acuity value was examined by a qualified optometrist, and the clinical data were measured by professional clinicians. The distributions of sex, residence and education level of KC patients were compared by Chi-square tests, and the ratios of people wearing glasses and rigid gas permeable (RGP) lenses were compared by McNemar tests. General linear models/Chi-squared tests were used to compare the clinical and demographic data according to KC severity. Spearman’s correlation analysis was used to test the associations between the data and KC severity. The mean age at diagnosis was 20.98 ± 6.06 years, and males had a higher ratio of KC than females (P < 0.001). Patients in rural areas had a higher rate of KC than those in urban areas (P = 0.039), and the proportion of KC patients with a higher education level (above high school) was high (P < 0.001). A total of 68.40% of the patients reported eye rubbing and 3.52% had a positive family history. The percentage of people wearing glasses was higher than that of patients wearing RGP lenses (P < 0.001). The total VF score of KC patients was 69.35 ± 15.25. The thinnest corneal thickness (TCT) and stiffness parameter at the first applanation (SP-A1) values were inversely correlated with KC severity (P < 0.05). The mean, steep, and max keratometry (Km, Ks and Kmax) values, the RGP lens use and keratoplasty were positively correlated with KC severity (all P < 0.05). The total VF score of the eye with better VA decreased as the severity increased (r = − 0.21, P = 0.002). The present study comprehensively describes various associated features of KC patients from a tertiary hospital in Central China, providing a reference for understanding the characteristics of KC patients in China.

The Association Between Keratoconus and Body Mass Index: A Population-Based Cross-Sectional Study Among Half a Million Adolescents

PURPOSE

To analyze the association between keratoconus and body mass index (BMI) among adolescents.

DESIGN

Cross sectional study.

METHODS

This was a nationwide, population-based study of candidates for military service in Israel attending the draft board in 2006 to 2014 who underwent an ophthalmologic examination. The study population included 579,946 males and females between 16 and 19.9 years of age. Subjects were divided into 4 groups based on adjusted BMI percentiles: underweight (8.3%), normal weight (73.9%), overweight (10.7%), and obese (7.1%). The odds for having keratoconus were compared with the normal weight group. The primary outcome measure was the odds ratio (OR) for the association between BMI groups and keratoconus.

RESULTS

The prevalence of keratoconus in the general population was 164 cases per 100,000, increasing over time (P < .05). There was a greater prevalence of keratoconus among obese adolescents (270/100,000) than of overweight (179/100,000), normal weight (154/100,000), and underweight (141/100,000) adolescents. Compared with the normal weight group, the OR for obese adolescents was 1.50 (95% confidence interval [CI] 1.22-1.83; P < .05), the OR for overweight adolescents was 1.42 (95% CI 1.08-1.92; P < .05), and the OR for underweight adolescents was 0.84 (95% CI 0.65-1.09; P = .18) after adjustment for gender, age, height, country of origin, and socioeconomic status.

CONCLUSIONS

This study provides strong evidence regarding the independent association between BMI and keratoconus. Overweight and obese adolescents have higher odds of having keratoconus compared with normal weight adolescents. BMI should be considered a risk factor for keratoconus and further research should elucidate how obesity is involved in the progress of keratoconus.

Omics analyses in keratoconus: from transcriptomics to proteomics

Purpose of Review

To summarize the recent advances in transcriptomics and proteomics studies of keratoconus using advanced genome-wide gene and protein expression profiling techniques.

Recent Findings

Second-generation sequencing including RNA sequencing has been widely used to characterize the genome-wide gene expression in corneal tissues or cells affected by keratoconus. Due to different sample types, sequencing platforms, and analysis pipeline, different lists of genes have been identified to be differentially expressed in KC-affected samples. Gene ontology and pathway/network analyses have indicated the involvement of genes related with extracellular matrix, WNT-signaling, TGFβ pathway, and NRF2-regulated network. High throughput proteomics studies using mass spectrometry have uncovered many KC-related protein molecules in pathways related with cytoskeleton, cell matrix, TGFβ signaling, and extracellular matrix remodeling, consistent with gene expression profiling.

Summary

Both transcriptomics and proteomics studies using genome-wide gene/protein expression profiling techniques have identified significant genes/proteins that may contribute to the pathogenesis of keratoconus. These molecules may be involved in functional categories related with extracellular matrix and TGFβ signaling. It is necessary to perform comprehensive gene/protein expression studies using larger sample size, same type of samples, up-to-date platform and bioinformatics tools.

Pediatric Keratoconus in A Tertiary Eye Center in Alexandria: A Cross-sectional Study

PURPOSE: To describe the clinical presentation, risk factors, and treatment choices documented in a pediatric keratoconus population treated at a tertiary referral center in Alexandria, Egypt.METHODS: A cross-sectional study of 80 patients with keratoconus aged 18 years or younger referred to the cornea clinic at the Alexandria University Main Hospital between July 2018 and October 2019 was included. Patients' history, initial presentation, best spectacle corrected visual acuity (BSCVA), clinical signs, topographic data, and treatment were recorded.RESULTS: Thirty patients were younger than 14 years and 50 were 14 years or older. Elements of the initial presentation included decreased vision in 26 patients, itching in 20 patients, both visual impairment and itching in 16 patients, accidental discovery during vision screening at school in 15 patients, and hydrops in three patients. All patients had bilateral keratoconus, except for four patients who had previously been treated by keratoplasty (n = 156 eyes). The mean logMAR BSCVA was 0.79 ± 0.63. The mean of the average keratometry (AveK), maximum keratometry (Kmax), central corneal thickness (CCT) and thinnest pachymetry reading were 51.16 ± 7.31 D, 59.18 ± 10.38 D, 458.44 ± 55.87 µ 440.08 ± 60.18 µ, respectively. 57 eyes (36%) had stage 1 disease, 43 eyes (28%) had stage 2 disease, 17 eyes (11%) had stage 3 disease and 39 eyes (25%) had stage 4 disease, respectively. No statistically significant differences in the LogMAR BSCVA, keratometry values, CCT, thinnest pachymetry reading, and the Amsler-Krumeich (AK) staging existed between the two age groups or between boys and girls. Crosslinking was indicated in 69 eyes (44%), while keratoplasty was the only viable solution for 39 eyes (25%), with three patients requiring keratoplasty in both eyes.CONCLUSION: Keratoconus in children can result in severe loss of vision. Keratoconus screening programs in elementary schools should be considered in populations with a high incidence of keratoconus for early detection and adequate intervention.

Fellow Eye as a Predictor for Keratoconus Progression Following Accelerated Corneal Cross-linking

PURPOSE

To assess the fellow eye as a predictor for keratoconus progression following bilateral same-day accelerated corneal cross-linking (A-CXL).

METHODS

This was a post-hoc analysis of data from a prospective study of bilateral A-CXL for progressive keratoconus between 2013 and 2015. The primary outcome measures were absolute change in maximum keratometry (Kmax) (diopters [D]), relative change in Kmax (%), and A-CXL progression (increase in Kmax > 2.00 D). Responses in both eyes were measured by the change in Kmax, with the right eye serving as the "predictor" of progression for the left eye.

RESULTS

Three-hundred ninety-two eyes (196 patients) with a mean age of 26.8 ± 7.7 years were included. There was a significant correlation in absolute and relative Kmax change (r = 0.26, P < .001 and r = 0.32, P < .001, respectively) between right and left eyes. In regression analysis, the only significant predictors of change in Kmax in the left eye were preoperative Kmax of the left eye (P < .02) and change in Kmax of the right eye (P < .001). Eyes that progressed in the right eye were more likely to progress in the left eye (29.4% versus 4.5%, odds ratio = 8.85, P < .001). In multiple regression, right eye progression of greater than 2.00 D was the significant predictor of left eye progression of greater than 2.00 D (odds ratio = 15.15, P < .007).

CONCLUSIONS

This large-scale study of keratoconus following A-CXL indicates that patients with progression in the right eye were 15.5 times more likely to have progression in the left eye. Patients with progression following A-CXL in one eye should be closely observed due to increased risk of progression in the fellow eye. [J Refract Surg. 2021;37(3):186-191.].

Characteristics of Keratoconus Patients in Jordan: Hospital-Based Population

PURPOSE

To study the demographic, clinical and topographic characteristics of keratoconus patients in Jordan.

METHODS

A retrospective study which was conducted at King Abdullah University Hospital, Northern Jordan. The patients who visited our outpatient clinic from March 2015 to September 2020 and had a definite diagnosis of keratoconus were included in this study. Demographic and clinical data, including age, gender, family history, past ocular history, ophthalmic examination, and topographic parameters, were collected and analysed. Keratoconus severity was classified according to K mean readings.

RESULTS

A total of 234 patients with keratoconus were evaluated in this study. The majority of patients (73, 31.2%) were between the ages of 20 and 24. Allergic conjunctivitis was the most frequent past ocular history. Fifty-five patients (23.5%) had a family history of keratoconus. Regarding severity, most of the eyes were mild (63.3%), followed by moderate (24.7%), and then severe (11.9%). The severity of keratoconus was significantly associated with gender (p<0.001). No correlation was found between family history and severity.

CONCLUSION

Most of the Keratoconus patients were young, with a mean age of 25.9 years. The majority were mild in severity, with more females presented in the severe stage. The study reported high rate of family history (23.5%) in comparison to similar studies. Therefore, screening of family members of Keratoconus patients is advisable.

The Sociodemographic and Risk Factors for Keratoconus: Nationwide Matched Case-Control Study in Taiwan, 1998-2015

PURPOSE

The aim of this study was to determine the sociodemographic and risk factors for keratoconus (KC) patients with a nationwide Asian database.

DESIGN

Population-based matched case-control study.

METHODS

We performed a secondary data analysis of the Taiwan National Health Insurance Research Database (NHIRD). Cases were patients with newly diagnosed KC in 1998-2015. Controls were patients without KC and matched 4:1 with the KC cases by age, sex, and index date. Comorbidities diagnosed before KC included diabetes mellitus (DM), asthma, allergic rhinitis, mitral valve prolapse, collagen vascular disease, aortic aneurysm, Down syndrome, sleep apnea, depression, hyperlipidemia, astigmatism, and myopia. Conditional logistic regression with forward selection were used to obtain risk factors for KC.

RESULTS

A total of 5,055 patients with KC were matched with 20,220 controls. The average age at KC first diagnosis was 29.76 years. Individuals who lived in suburban and rural area had lower odds ratio of KC (adjusted odds ratio [OR] 0.86, 95% confidence interval [CI] 0.80-0.94; and 0.73, 95% CI 0.67-0.79; respectively) when comparing with those who lived in urban area. Multivariate analysis revealed that Down syndrome, astigmatism, myopia, allergic rhinitis, and asthma were positively associated with KC with adjusted odds ratios (adjusted OR 8.69, 95% CI 3.74-20.19; 6.23, 95% CI 5.35-7.24; 2.99, 95% CI 2.70-3.32; 1.22, 95% CI 1.14-1.32; and 1.18, 95% CI 1.07-1.30, respectively). On the other hand, hyperlipidemia, depression, and DM (uncomplicated and complicated) were negatively associated with KC (adjusted OR 0.67, 95% CI 0.59-0.77; 0.58, 95% CI 0.48-0.71; 0.77, 95% CI 0.64-0.93; and 0.61, 95% CI 0.44-0.86, respectively).

CONCLUSIONS

Our study found that patients with hyperlipidemia, depression, or DM were less likely to have KC, and patients with asthma, allergic rhinitis, astigmatism, myopia, or Down syndrome had higher odds ratio of KC.

Successful Regression in Patients with Progressive Keratoconus by Corneal Crosslinking

BACKGROUND

Since 2019, corneal collagen crosslinking (CXL) is included in the catalog of procedures covered by statutory health insurance in Germany. CXL is an established ophthalmological procedure for the last 20 years. The aim of this investigation was the measurement of progression before and after CXL.

MATERIAL UND METHODS

65 consecutive eyes with progressive keratoconus from 53 patients were included in the retrospective study, which were observed at the University Eye Hospital Tübingen at least two years before and at least two years after CXL. The time of observation took place from October 2009 until March 2018. Parameters of interest had been the best corrected visual acuity (BCVA) and the keratometric values from the elevation maps measured by a Scheimpflug camera.

RESULTS

65 eyes of 53 patients had been documented. The study population included 46 (86.8%) male and 7 (13.2%) female subjects. The mean age was 24 ± 8 years. The averaged observation time between the primary consultation and CXL showed 25 ± 15 months. Preoperatively the mean BCVA pointed out in a significant increase (0.13 ± 0.17 [first visit] vs. 0.23 ± 0.22 [preOP], p < 0.0001) while the mean Kmax resulted in a statistically significant increase (46.34 ± 3.33 dpt [first visit] vs. 48.78 ± 4.17 dpt [preOP], p < 0.0001). The mean thinnest point of the cornea showed a significant decrease (490.48 ± 34.23 µm [first visit] vs. 468.62 ± 29.84 µm [preop], p < 0.0001). Postoperatively the mean BCVA resulted in a significant improvement at the 12th postoperative month in comparison to the preoperative measurement (0.23 ± 0.22 [preOP] vs. 0.16 ± 0.14 [12 months], p = 0.04 respectively 0.17 ± 0.17 [24 months], p = 0.0006). The mean Kmax demonstrated in the 12th postoperative month a significant reduction (48.78 ± 4.17 dpt [preOP] vs. 47.91 ± 3.41 dpt [12 months], p = 0.0009 respectively 48 ± 4.56 dpt [24 months], p = 0.0051). The mean thinnest point of the cornea indicated a decrease at the 12th postoperative month (468.62 ± 29.84 µm [preOP] vs. 459.82 ± 35.88 µm [12 months], p = 0.0078 respectively 453.47 ± 43.39 µm [24 months], p = 0.0227).

CONCLUSION

CXL is a successful procedure for the therapy of progressive keratoconus.

Keratoconus Indices and their Determinants in Healthy Eyes of a Rural Population

Purpose:

To determine the distribution of keratoconus indices in a 5-93-year-old healthy eyes of a rural population in Iran.

Methods:

In this cross-sectional study, multi-stage cluster sampling was applied to select subjects from two villages in the north and southwest of Iran. After obtaining informed consent, all subjects underwent ophthalmologic and optometric examinations. Corneal imaging by the Pentacam was done in subjects above 5 years between 9 a.m. and 2 p.m., at least 3 h after wakeup. All subjects who had abnormal keratoconus indices were excluded. Our main outcome was keratometry-flat (K_f), keratometry-steep (K_s), keratoconus index (KI), and central keratoconus index (CKI).

Results:

The mean ± standard deviation of K_f, K_s, KI, and CKI was 43.12 ± 1.74, 44.25 ± 1.65, 1.02 ± 0.02, and 1.01 ± 0.01, respectively. According to multiple linear regression analysis, the mean index surface variance (ISV) (b: -1.367, P < 0.001), index vertical asymmetry (IVA) (b: -0.012, P < 0.001), KI (b: -0.011, P < 0.001), CKI (b: -0.001, P < 0.001), index height asymmetry (IHA) (b: -0.491, P: 0.005), and index height decentration (IHD) (b: -0.001, P < 0.001) were lower in men compared to women. Moreover, age had an indirect association with ISV (b: -0.030, P < 0.001) and average pachymetric progression index (RPI_avg) (b: -0.001, P < 0.001), and a direct association with KI, CKI, and IHA. Spherical equivalence had an indirect association with KI (b: -0.001, P < 0.001) and RPI_avg (b: -0.004, P < 0.001) and a direct association with CKI (b: 0.001, P < 0.001). Among all variables, sex had the greatest impact on ISV, IVA, KI, IHA, IHD, and minimum sagittal curvature.

Conclusions:

The Keratoconus indices of our study were similar to other studies. Although age, living place, and type of refractive error were associated with some indices, sex was the strongest determinant of Keratoconus indices in a population of healthy eyes.

Pediatric keratoconus - Current perspectives and clinical challenges

Keratoconus is an ectatic corneal disease characterized by progressive stromal thinning, irregular astigmatism, and defective vision. It can be unilateral or bilateral with asymmetric presentation. It starts at puberty and either progresses rapidly to an advanced stage of the disease or stops in case of delayed onset and slow progression. Pediatric keratoconus is more aggressive than in adults and the management protocols differ because of various rationales such as accelerated progression, advanced stage of disease at the time of diagnosis and co-morbidities. It poses a burden to the society as it affects the quality of life, social, and educational development in children. Hence early diagnosis, recognition of progression, and timely intervention with collagen crosslinking is imperative to arrest the worsening. Association with systemic syndromes and ocular comorbidities can be of concern in pediatric keratoconus. Severe ocular allergy when associated hastens progress and complicates timely intervention of crosslinking treatment and compliance to contact lens wear. Keratoplasty in pediatric keratoconus has good outcomes but can encounter frequent suture-related concerns. This article discusses the epidemiology, etiopathogenesis, clinical challenges, and current perspectives of management of pediatric keratoconus.

Correlation between Keratoconus and Pollution

Introduction: Keratoconus is a corneal ectasia with multifactorial origin. Three risk factors for keratoconus are currently recognized: ultraviolet rays (UV), eye rubbing and atopy. In the current literature, other factors are evoked such as pollution, whose role in the physiopathology of keratoconus is unclear. The effects of particles matter (PM) 2.5 and 10 are the most studied and questioned in the scientific literature.Material and method: A correlation study was carried out to determine the influence of pollution on keratoconus. Fine particulate matter levels were measured according to available WHO data and were correlated with the prevalences of epidemiological studies. These measures were included in the study according to strict selection criteria.Results: The mean pollution rate of the selected studies was 29.1 ± 24.3 μg/m³ for PM_2.5 and 57.2 ± 56.2 μg/m³ for PM₁₀. The Pearson test shows a moderate correlation between the prevalence of keratoconus and the levels of PM_2.5 (R = 0.51; p = .022) and a strong correlation with the levels of PM₁₀ (R = 0.71; p < .001).Discussion: Fine particulate matter appears to be an emerging risk factor for keratoconus. They are thought to act indirectly by exacerbating known risk factors such as atopy and eye rubbing. And could have a direct action on the cornea by increasing the apoptosis of epithelial cells and interacting directly with the structure of collagen of the stroma.

The possible causes for tomography suspect Keratoconus in a Chinese cohort

Background

To explore the possible causes of tomography suspect keratoconus (TSK) marked by Tomography in screening keratoconus in a Chinese cohort, and the reasonable range of corneal horizontal diameter and thickness for decreasing the proportion of TSK.

Methods

Nested case-control study from a single center prospective cohort. All subjects were selected from the Peking University Third Hospital Ectasia Cornea Disease Cohort Project database, which included myopic patients seeking corneal refractive surgical corrections since 2013. Demographic information, basic eye examination, and auxiliary equipment examination including refraction, IOL-master, Pentacam, Sirius, and Topolyzer were recorded. In this study, all cases were classified into two groups: TSK group and normal control (NC) group, and all of them were followed up at least 2 years. The former is consisted of those whose screening examinations of tomography are abnormal, the latter is those whose screening examinations are normal. All of them have already been followed up at least 2 years without abnormalities after excimer laser corneal refractive surgeries. Unpaired t tests and Chi-square tests were used to compare the differences of indices from the tomography between the two groups.

Results

Of 183 TSK eyes (109 patients) and 160 NC eyes (83 patients), the mean age is 28.0 and 26.3 years old respectively. The corneal horizontal diameter is 11.5–11.8 mm in TSK group and 11.8–12.0 mm in NC group. The central corneal thickness is nearly 520 μm in the former and 550 μm in the latter. For Sirius, the TSK ratio of indices of SIf and SIb is 41.5 and 39.9% respectively in TSK group. For Pentacam, the TSK ratio of index IHD is 59.0% and “final D” is 72.7%.

Conclusions

Corneal horizontal diameter and central corneal thickness have great influences on the results of corneal tomography in detecting the suspect keratoconus.

Impact of Scleral Contact Lens Use on the Rate of Corneal Transplantation for Keratoconus

PURPOSE

To evaluate the association of scleral contact lens (SCL) use on the risk for keratoplasty for people with keratoconus.

METHODS

The electronic health records of patients receiving eye care at the University of Michigan Kellogg Eye Center between August 1, 2012, and December 31, 2018, were reviewed. Patients with a diagnostic code of keratoconus or corneal ectasia, no previous history of keratoplasty, and for whom data were available for both eyes were included. Using a multivariable Cox regression model, associations between SCL use and keratoplasty were tested and adjusted for sociodemographic factors, maximum keratometry, and current contact lens (CL) use.

RESULTS

Two thousand eight hundred six eyes met the inclusion criteria. CL use in each eye was 36.2% with no CL, 7.2% soft, 33.9% rigid gas permeable (RGP), and 22.7% scleral. A total of 3.2% of eyes underwent keratoplasty. In the adjusted model, SCL or RGP CL use significantly lowered the hazard of undergoing keratoplasty (HR = 0.19, 95% confidence interval [CI] 0.09-0.39, P < 0.0001 and HR = 0.30, 95% CI 0.17-0.52, P < 0.0001, respectively) when compared with no CL use. Factors associated with increased risk of keratoplasty were black race as compared to white (HR = 1.87, 95% CI 1.10-3.16, P = 0.02), younger age (HR = 0.92 per 5-year increment, 95% CI 0.86-0.99, P = 0.032), and lower socioeconomic status (HR = 1.08 per 5-point increase in the Area Deprivation Index, 95% CI 1.03-1.13, P = 0.0008). Keratoplasty was not associated with sex, insurance, or maximum keratometry.

CONCLUSIONS

Physicians should maximize the use of scleral or RGP CL because patients who successfully use CL have almost one-fifth the risk of undergoing keratoplasty.

Corneal cross-linking versus conventional management for keratoconus: a lifetime economic model

AIMS

To assess the cost-effectiveness of corneal collagen cross-linking (CXL) versus no CXL for keratoconus in the United States (US).

METHODS

A discrete-event microsimulation was developed to assess the cost-effectiveness of corneal cross-linking (CXL, Photrexa + KXL combination product) versus no CXL for patients with keratoconus. The lifetime model was conducted from a US payor perspective. The source for CXL efficacy and safety data was a 12-month randomized, open-label, sham-controlled, multi-center, pivotal trial comparing CXL versus no CXL. Other inputs were sourced from the literature. The primary outcome was the incremental cost per quality-adjusted life year gained. Costs (2019 USD) and effects were discounted 3% annually. The impacts of underlying uncertainty were evaluated by scenario, univariate, and probabilistic analyses.

RESULTS

Starting at a mean baseline age of 31 years and considering a mixed population consisting of 80% slow-progressors and 20% fast-progressors, the CXL group was 25.9% less likely to undergo penetrating keratoplasty (PK) and spent 27.9 fewer years in advanced disease stages. CXL was dominant with lower total direct medical costs (-$8,677; $30,994 versus $39,671) and more QALYs (1.88; 21.80 versus 19.93) compared to no CXL. Considering the impact of reduced productivity loss in an exploratory scenario, CXL was associated with a lifetime cost-savings of $43,759 per patient. CXL was cost-effective within 2 years and cost-saving within 4.5 years.

LIMITATIONS

Limitations include those that are common to similar pharmacoeconomic models that rely on disparate sources for inputs and extrapolation on short-term outcomes to a long-term analytical horizon.

CONCLUSIONS

Keratoconus is a progressive and life-altering disease with substantial clinical, economic, and humanistic consequences. The economic value of cross-linking is maximized when applied earlier in the disease process and/or younger age, and extends to improved work productivity, out-of-pocket costs, and quality of life.

Awareness level of general population regarding keratoconus in Aseer region, Southern of Saudi Arabia

Background

Keratoconus (KC) is a non-inflammatory disease occur to the cornea and cause it to be thin and progressively bulge it into a cone shape which result to blurred vision secondary to irregular astigmatism, frequently eyeglass changing and increase the sensitivity to the bright light, occur usually at second decade of life and stops progressive after fourth decade of life. keratoconus is unknown in aetiology but is a multifactorial disease in causes which divided into genetic and environmental factors, the genetic factors as if patient under ethnic with high prevalence and family history with keratoconus or Atopy.

Aim

to assess the general population awareness regarding keratoconus in Aseer region, southern of Saudi Arabia.

Methodology

A descriptive cross-sectional approach was used targeting all population in Aseer region. The study was conducted during the period from January 2019 to May 2020. Data were collected using structured questionnaire included person's socio-demographic data, Participants' Participants' awareness regarding KC. The questionnaire was uploaded online using social media platforms.

Results

The study included 638 participants who completed the study questionnaire with mean age of 36.8 ± 11.1 years. Exact of 331 (51.9%) of the participants were males. University level of education was reported by 424 participants (66.5%). Fifty-nine participants (9.2%) reported that they had keratoconus.

Conclusions & Recommendations

In conclusion, the study revealed that public awareness in Aseer region regarding keratoconus was moderately poor with defect regarding treatment modalities and its consequences.

Correlation between Corneal Topographic Patterns and Refractive Status of the Eye in an Adult Iranian Population: Tehran Study

Purpose

To evaluate the corneal topographic patterns in an adult Iranian population and investigate its correlation with the refractive status of the eye.

Methods

In a cross-sectional study named "Tehran Study," 1023 samples were selected by the cluster sampling method from the downtown area of Tehran. Eight hundred and forty-nine adults aged over 15 years participated. All selected participants were refracted and underwent topography imaging.

Results

The patients' ages ranged from 15 to 91 years with a mean of 40.33 ± 16 years. The most frequent topographic patterns were symmetric bowtie (SB) (34%), SB with inferior steepening (SB-IS) (14.1%), and round (10.5%). The orders changed in categorization by refractive status: The most frequent pattern in all subgroups (emmetropia, myopia, and hyperopia) was SB with frequencies 32.7%, 35.8%, and 22.5%, respectively. Although the second order was asymmetric bowtie (AB) with AB-IS in the emmetropic and myopic subgroups, in the hyperopic subgroup, round pattern had the second place. The third place was different in all groups. The rarest patterns in the whole were SB with skewed radial axis (SRAX) and AB with SRAX. The first prevalent topographic pattern was SB in all age groups and in both genders. The prevalence of round pattern, irregular pattern, and SRAX significantly increased in older ages, and the prevalence of SB decreased in older ages. The first observed prevalent pattern was SB in both sexes, but the second most prevalent pattern was AB-IS and round in females and males, respectively.

Conclusions

Corneal topographic pattern might be related to the refractive status of the eye. The information about normal topographic patterns provides a reference for comparison with diseased corneas.

Ballistic delivery of compounds to inner layers of the cornea is limited by tough mechanical properties of stromal tissue

The barrier characteristics of the cornea are interrogated using the impact of micro-particles into ex vivo porcine cornea. Using a commercial gene gun (BioRad; PDS1000), microparticles were accelerated and made to embed in target materials: either ballistic gelatin as a reference or corneal tissue. Statistical analysis of penetration of polydisperse spherical microparticles (5-22 μm dia.) with density of 2.5 g/cc, 4.2 g/cc, and 7.8 g/cc (soda-lime glass, barium-titanate glass and stainless steel; more limited examination of 1.1 g/cc polyethylene and 19.2 g/cc tungsten) spanned almost two decades in kinetic energy. Penetration profiles in ballistic gelatin show that the particle embedding depth is sensitive to particle size and density. In the cornea, penetration is a weak function of size and density, and the corneal stroma is an effective stopping medium for high velocity microparticles. Despite the high water content of corneal tissue (76% w/w) compared to the stratum corneum of skin (40% w/w), the resistance to penetration of the cornea is comparable to what is seen in previous research of penetration in skin tissue. Using low density polymer particles with a therapeutic agent payload, it is demonstrated that bulk material can be ballistically delivered to the central 1 cm² of the corneal epithelium in an even layer with high bioavailability of therapeutic compound.

Current perspectives in the management of keratoconus with contact lenses

Our aim is to review current and significant articles on contact lens wear in keratoconus patients. A comprehensive literature search of PubMed was performed for the following topics on contact lens wear in keratoconus patients: (1) characteristics of contact lens wearers, (2) safety and efficacy, (3) complications, (4) fitting techniques, (5) contact lens wear after procedures/surgeries, (6) patient satisfaction. A total of 104 studies were finally selected and reviewed. Gas permeable (GP) lens wear provided significantly better vision than glasses. Special cone design lenses had better patient comfort levels though there was no difference in best corrected visual acuity among the GP lenses. Soft lenses showed good efficacy for the treatment of mild-to-moderate keratoconus with newer designs improving visual performance such as customised hydrogel and novel pinhole lenses. Scleral and hybrid lenses provide good visual acuity and comfort for keratoconic patients previously intolerant to RGP lenses. RGP lens wear post-cross linking (CXL) is relatively well-tolerated. Contact lenses may still be required post intrastromal corneal ring procedures and post keratoplasty. Scheimpflug imaging and anterior segment optical coherent tomography (ASOCT) are useful in contact lens fitting. Computerized contact lens fitting techniques could reduce the chair time of lens fitting as well as improve comfort and visual performance. Contact lenses play an important role in the visual rehabilitation of keratoconus patients. New contact lens designs and materials have significantly expanded the available fitting options for keratoconus patients. Imaging technology can be utilized to guide contact lens fitting.

The Enigma of Environmental Factors in Keratoconus

Keratoconus is an ectatic disorder with highly complex and varied causes including genetic variations and environmental factors. Its prevalence varies widely between regions and countries. Many environmental factors have been proposed to be associated with keratoconus, but the interpretation of their individual contributions is difficult due to the presence of many confounding variables. The current literature was reviewed to evaluate the strength of the associations and the causative effects of environmental factors on keratoconus. Ethnicity and consanguinity have been revealed as important determinants for geographical variations in keratoconus prevalence. Eye rubbing, atopy, floppy eyelid syndrome, contact lens wear, pregnancy, and thyroid hormone disturbances are likely associated with keratoconus. The first 4 factors can induce ocular surface inflammation, matrix metalloproteinase release, and keratocyte apoptosis, consistent with the postulated etiology of keratoconus. The associations of keratoconus with UV exposure, cigarette smoking, personality, and sex were less convincing once confounding factors were considered. Future studies powered for multivariate analysis of factors discussed will hopefully shed light on what is truly important in the development and progression of keratoconus.

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.

Characterization of posterior corneal astigmatism in a population with keratoconus

Background: The curvature of the anterior corneal surface is traditionally used as a surrogate to estimate corneal astigmatism. In recent years, increasing importance has been attributed to posterior corneal astigmatism as an indicator. Our aim is to characterize the posterior corneal surface in a population with keratoconus and investigate its predictive value to keratoconus progression. Methods: Retrospective study from a tertiary care centre (Hospital de Santa Maria, Lisbon, Portugal). Eighty-five patients (85 eyes) with keratoconus were included. All patients had two tomographical examinations ≥12 months apart (Pentacam HR). Vector analysis was used to calculate anterior (ACA), posterior (PCA), and total corneal astigmatism (TCA). Multivariate logistic regression was used to assess the predictive value of PCA to keratoconus progression, adjusting for ACA, TCA and several tomographical indices. Results: Study participants had a mean age of 32 (SD = 12.5) years. Mean tomographical keratoconus classification was 2.16 (SD = 0.95), with a mean Kmax of 55.8D (SD = 7.8). Mean power of PCA, ACA and TCA was, respectively, -0.88D (SD = 0.84), 3.74D (SD = 2.36), and 3.06D (SD = 2.01) and its centroids were 0.44D x 15º, 1.65D x 112º, and 1.61D x 106º, respectively. The power of PCA was ≥0.50, 1.00 and 2.00D in 75.3%, 32.9%, and 3.5% of patients, respectively, inducing against-the-rule astigmatism in 60.0% of patients. On average, ACA overestimated TCA in 0.35D x 151º (p < .01). ACA and TCA were highly correlated but showed a lack of agreement for clinical purposes. A predictive role for PCA was excluded. Conclusions: In this population with keratoconus, PCA contributed substantially to TCA. However, PCA was not a valuable predictor for disease progression.

The Prevalence and Risk Factors for Keratoconus: A Systematic Review and Meta-Analysis

PURPOSE

This study was conducted to determine the prevalence and risk factors for keratoconus worldwide.

METHODS

In this meta-analysis, using a structured search strategy from 2 sources, 4 electronic databases (PubMed, Web of Science, Google Scholar, and Scopus) and the reference lists of the selected articles were searched from inception to June 2018 with no restrictions and filters. The outcome of the study was the prevalence of keratoconus and its risk factors, including eye rubbing, family history of keratoconus, atopy, allergy, asthma, eczema, diabetes type I and type II, and sex.

RESULTS

In this study, 3996 articles were retrieved, of which 29 were analyzed. These 29 articles included 7,158,241 participants from 15 countries. The prevalence of keratoconus in the whole population was 1.38 per 1000 population [95% confidence interval (CI): 1.14-1.62 per 1000]. The prevalence of keratoconus was 20.6 per 1000 (95% CI: 11.68-28.44 per 1000) in men and 18.33 per 1000 (95% CI: 8.66-28.00 per 1000) in women in studies reporting sex. The odds ratio of eye rubbing, family history of keratoconus, allergy, asthma, and eczema was 3.09 (95% CI: 2.17-4.00), 6.42 (95% CI: 2.59-10.24), 1.42 (95% CI: 1.06-1.79), 1.94 (95% CI: 1.30-2.58), and 2.95 (95% CI: 1.30-4.59), respectively.

CONCLUSIONS

The results of this study, as the most comprehensive meta-analysis of keratoconus prevalence and risk factors, showed that keratoconus had a low prevalence in the world and eye rubbing, family history of keratoconus, allergy, asthma, and eczema were the most important risk factors for keratoconus according to the available evidence.

A model of visual limitation in patients with keratoconus

This paper aims to calculate a relevance model of visual limitation (V.L.) in keratoconus patients based on refractive and topographic parameters. A cross-sectional study was carried out in Torrecárdenas Hospital, Almería, Spain, between February 2018 and July 2019. It included 250 keratoconus patients. Two groups were created according to a grading system of V.L. based on RETICS (Red Temática de Investigación Cooperativa en Salud) classification: keratoconus patients with no V.L. (best spectacle-corrected visual acuity (BSCVA) ≤ 0.05 logMAR) and keratoconus patients with V.L. (BSCVA > 0.05 logMAR). Correlations and a binary logistic regression were established. V.L. was correlated with maximum curvature (r = 0.649, p < 0.001) and root mean square higher-order aberrations (HOARMS) (r = 0.625, p < 0.001). Binary logistic regression included V.L. as the dependent variable and spherical equivalent, HOARMS, spherical aberration and interaction between the anterior and posterior vertical coma as independent variables. The model was a good fit. Area under the curve (A.U.C.) of receiver operating characteristic (R.O.C.) curve was 0.924, sensitivity 91.90%, specificity 83.60%, accuracy 88.94%; and precision 91.17%. Binary logistic regression model of V.L. is a good fit model to predict the early loss of visual acuity in keratoconus patients.

Genetics vs chronic corneal mechanical trauma in the etiology of keratoconus

Both genetic and environmental factors have been considered to play a role in the etiology keratoconus. Eye rubbing, and more recently eye compression due to sleeping position, have been identified to be highly related to the condition, and are present in a high percentage of patients. Today, the predominant model is that these factors can provide the "second hit" necessary to generate the condition in a genetically susceptible individual. In addition, the extremely high prevalence in Arab populations, where endogamy could play a role, the high concordance rate in monozygotic twins, and the presence of family history of the condition between 5 and 23% of cases, support a genetic influence. Segregation analysis studies suggest that keratoconus is a complex non-Mendelian disease. Results from linkage analysis, next generation sequencing studies and genome-wide association studies also have suggested that genetic factors are involved in the condition. Recently, it has been proposed that mechanical trauma (i.e. eye rubbing or eye compression at night), is a sine quanon condition for the onset of keratoconus, and quite possibly its only cause. There are various arguments for and against this hypothesis. Indeed, it is possible, as initially suggested around 55 years ago, that the term "keratoconus" include diverse phenotypically similar conditions, which are actually of different etiology.

Survey report on keratoplasty in China: A 5-year review from 2014 to 2018

To provide the general information on corneal transplantation (CT) in China, China Cornea Society designed a questionnaire on CT from 2014 to 2018 and entrusted it to 31 committee members for implementation of the survey nationwide. This article presents the results of the survey and compares the indicators used in the survey and those in the annual statistical report released by the Eye Bank Association of America (EBAA). The number of corneal transplantations completed by the 64 hospitals from 2014 to 2018 was respectively 5377, 6394, 7595, 8270 and 8980, totally 36,616 (22,959 male and 13,657 female). The five largest hospitals by the number of corneal transplantations completed 15,994 surgeries in total, accounting for 43.68% of all the surgeries performed in the 64 hospitals. The most common indication for corneal transplantations was corneal leukoma (7683, 20.98%), followed by bacterial keratitis (4209, 11.49%), corneal dystrophies (4189, 11.44%), keratoconus (3578, 9.77%) and corneal perforation (2839, 7.75%). The main surgical techniques were penetrating keratoplasty (PK) (19,896, 54.34%), anterior lamellar keratoplasty (ALK) (13,869, 37.88%). The proportion of PK decreased from 57.97% in 2014 to 52.88% in 2018 while the proportion of ALK increased from 36.04% in 2014 to 37.92% in 2018. The geographical distribution of keratoplasties performed in China is unbalanced. PK and ALK were the main techniques of CT and corneal leukoma, bacterial keratitis and corneal dystrophies were the main indications for CT in China.

A review of corneal imaging methods for the early diagnosis of pre-clinical Keratoconus

BACKGROUND

Keratoconus (KC) is a corneal ectasia characterised by steepening corneal curvature, changes in refractive error and corneal thickness that result in visual impairment. Early signs of KC include displacement of the thinnest part of the cornea from the central position, changes in the corneal epithelial layer cell distribution, variations in the anterior corneal astigmatism/posterior corneal astigmatism relationship and a variation in corneal thickness. It is important that we review the corneal imaging methods for the diagnosis of preclinical KC.

METHOD

An online literature search was carried out on PubMed. Only publications detailing corneal assessment procedures were considered for this review and any publication on instruments that did not generate KC predictability indices were also excluded from the review. The 308 publications were reviewed.

DISCUSSION

Corneal assessment techniques, with the ability to characterise both the anterior and posterior corneal surfaces, are invaluable in the diagnosis of pre-clinical KC. Reflection based and elevation based corneal imaging systems should be used in conjunction with other assessments such as higher order aberration measuring systems to improve sensitivity and reliability in the diagnosis of pre-clinical KC. Ultra high resolution ultrasound can detect pre-clinical KC. The ability to asses both the epithelium and endothelium makes anterior surface optical coherence tomography a superior technique for pre-clinical KC diagnosis. There is a positive correlation between central corneal thickness and corneal hysteresis. Corneal biomechanics should be considered in conjunction with other corneal assessments in the diagnosis of pre-clinical KC.