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 selecte

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

Keratoconus (KC) is the most common cornea ectatic disorder. It is characterized by a cone-shaped thin cornea leading to myopia, irregular astigmatism, and vision impairment. It affects all ethnic groups and both genders. Both environmental and genetic factors may contribute to its pathogenesis. This review is to summarize the current research development in KC epidemiology and genetic etiology. Environmental factors include but are not limited to eye rubbing, atopy, sun exposure, and geography. Genetic discoveries have been reviewed with evidence from family-based linkage analysis and fine mapping in linkage region, genome-wide association studies, and candidate genes analyses. A number of genes have been discovered at a relatively rapid pace. The detailed molecular mechanism underlying KC pathogenesis will significantly advance our understanding of KC and promote the development of potential therapies.

/pdf/the-genetic-and-environmental-factors-for-keratoconus-1e06u9jxtq.pdf

The genetic and environmental factors for keratoconus.

/pdf/keratoconus-an-updated-review-1ysvshd8.pdf

Keratoconus: An updated review

Background/aim Keratoconus (KC) is a ectatic corneal disorder with marked progression during childhood and puberty that may lead to severe visual loss. In addition to KC prevalence, estimate shows major geographical variations; recent studies using Scheimpflug technology are in contrast to the 1980s and 1990s literature. The present study aims to determine the prevalence of KC in paediatric patients in Riyadh, Saudi Arabia (KSA). Methods This prospective, cross-sectional, observational, multicentre study collected data from paediatric patients from 6 years and 21 years of age who were seen at multiple non-ophthalmic emergency departments within KSA. Bilateral corneal measurements were performed using a rotational Scheimpflug corneal tomography system. Two masked examiners established the diagnosis of KC using both objective and subjective screening criteria. Cohen’s kappa coefficient (κ) was used to qualitatively analyse the interexaminer agreement. Results There were 522 patients (1044 eyes) evaluated, with an average age of 16.8±4.2 years (range 6–21 years). KC prevalence was 5.56% for examiner 1 and 3.83% for examiner 2. The κ was 0.81 (almost perfect agreement), with discrepancy in nine cases, which were jointly evaluated and consensus obtained. Final KC prevalence was 4.79% (95% CI 2.96 to 6.62) or 1:21 patients. Conclusions The prevalence of KC among paediatric patients in the KSA is considerably higher than numbers reported from earlier studies and from similar studies in other countries. This increase might be due to geographical variations in disease prevalence or due to the ability of screening technology to detect undiagnosed KC with greater accuracy.

https://bjo.bmj.com/content/bjophthalmol/102/10/1436.full.pdf

Prevalence of keratoconus in paediatric patients in Riyadh, Saudi Arabia

Purpose
To describe the epidemiology and prevalence, rates of progression, difference between adult and pediatric populations, and therapeutic approaches to pediatric keratoconus from documented literature.

Pediatric keratoconus: a review of the literature.

Anterior segment optical coherence tomography (AS-OCT) is a non-contact method analogous to ultrasound biomicroscopy (UBM) for the evaluation of the anterior segment structure with a higher resolution that uses infrared instead of ultrasound. In this chapter, we discuss the available types of AS-OCT.

1.

TD-OCT (time-domain AS-OCT) uses a longer wavelength, which results in less scattering and signal loss and deeper structures such as the limbus or scleral spur and angle can be better visualized. It comprises the following.


Visante OCT (Carl Zeiss Meditec, Oberkochen, Germany)


Slit-lamp OCT (Heidelberg Engineering GmbH, Heidelberg, Germany).








2.

Spectral-domain AS-OCT (SD-OCT) or Fourier-domain OCT (FD-OCT) uses a higher speed and shorter wavelength than TD-OCT, which results in better axial resolution and a lesser depth evaluation and limited horizontal scan width. It comprises the following.


Spectralis (Heidelberg Engineering GmbH, Heidelberg, Germany)


RTVue (Optovue, Inc., California, USA)


Cirrus OCT (Carl Zeiss Meditec, Oberkochen, Germany)








3.

Swept-source OCT (SS-OCT), which comprises:


Casia SS-1000 OCT (Tomey, Nagoya, Japan)


DRI OCT-Triton (Topcon Medical Systems)








4.

Ultrahigh-resolution OCT (UHR-OCT), which uses a broad-bandwidth light source and more advanced spectrometer and comprises:


Bioptigen Envisu (Bioptigen Inc., Research Triangle Park, NC, USA)


SOCT Copernicus HR (Optopol Technologies SA, Zawiercie, Poland).

Anterior Segment Optical Coherence Tomography (AS-OCT)

Purpose To assess the diagnostic power of the Corneal Visualization Scheimpflug Technology (Corvis ST) provided corneal biomechanical parameters in keratoconic corneas. Methods The following biomechanical parameters of 48 keratoconic eyes were compared with the corresponding ones in 50 normal eyes: time of the first applanation and time from start to the second applanation [applanation-1 time (A1T) and applanation-2 time (A2T)], time of the highest corneal displacement [highest concavity time (HCT)], magnitude of the displacement [highest concavity deformation amplitude (HCDA)], the length of the flattened segment in the applanations [first applanation length (A1L) and second applanation length (A2L)], velocity of corneal movement during applanations [applanation-1 velocity (A1V) and applanation-2 velocity (A2V)], distance between bending points of the cornea at the highest concavity [highest concavity peak distance (HCPD)], central concave curvature at the highest concavity [highest concavity radius (HCR)]. To assess the change of parameters by disease severity, the keratoconus group was divided into two subgroups, and their biomechanical parameters were compared with each other and with normal group. The parameters' predictive ability was assessed by receiver operating characteristic (ROC) curves. To control the effect of central corneal thickness (CCT) difference between the two groups, two subgroups with similar CCT were selected, and the analyses were repeated. Results Of the 10 parameters compared, the means of the 8 were significantly different between groups ( P P  > 0.05). ROC curve analyses showed excellent distinguishing ability for A1T and HCR [area under the curve (AUC) > 0.9], and good distinguishing ability for A2T, A2V, and HCDA (0.9 > AUC > 0.7). A1T reading was able to correctly identify at least 93% of eyes with keratoconus (cut-off point 7.03). In two CCT matched subgroups, A1T showed an excellent distinguishing ability again. Conclusions The A1T seems a valuable parameter in the diagnosis of keratoconic eyes. It showed excellent diagnostic ability even when controlled for CCT. None of the parameters were reliable index for keratoconus staging.

Keratoconus diagnosis using Corvis ST measured biomechanical parameters.

Aim To evaluate the diagnostic ability of topographic and tomographic indices with Pentacam and Sirius as well as biomechanical parameters with Corvis ST for the detection of clinical and subclinical forms of keratoconus (KCN). Methods In this prospective diagnostic test study, 70 patients with clinical KCN, 79 patients with abnormal findings in topography and tomography maps with no evidence on clinical examination (subclinical KCN), and 68 normal control subjects were enrolled. The accuracy of topographic, tomographic, and biomechanical parameters was evaluated using the area under the receiver operating characteristic curve (AUC) and cross-validation analysis. The Delong method was used for comparing AUCs. Results In distinguishing KCN from normal, all parameters showed statistically significant differences between the two groups (P 0.05). Conclusion In clinical KCN, all topographic, tomographic, and biomechanical indices have acceptable outcomes in terms of sensitivity and specificity. However, in differentiating subclinical forms of KCN from normal corneas, curvature-based parameters (SIb and IS value) followed by integrated indices (PRFI and TBI) are the most powerful tools for early detection of KCN.

/pdf/evaluation-of-corneal-topographic-tomographic-and-149cm8blfo.pdf

Evaluation of corneal topographic, tomographic and biomechanical indices for detecting clinical and subclinical keratoconus: a comprehensive three-device study.

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Anterior Segment Optical Coherence Tomography (AS-OCT)

Keratoconus diagnosis using Corvis ST measured biomechanical parameters.

Evaluation of corneal topographic, tomographic and biomechanical indices for detecting clinical and subclinical keratoconus: a comprehensive three-device study.