Increased central corneal thickness in patients with Turner syndrome

Genetic Correlations Among Corneal Biophysical Parameters and Anthropometric Traits

Purpose

The genetic architecture of corneal dysfunction remains poorly understood. Epidemiological and clinical evidence suggests a relationship between corneal structural features and anthropometric measures. We used global and local genetic similarity analysis to identify genomic features that may underlie structural corneal dysfunction.

Methods

We assembled genome-wide association study summary statistics for corneal features (central corneal thickness, corneal hysteresis [CH], corneal resistance factor [CRF], and the 3 mm index of keratometry) and anthropometric traits (body mass index, weight, and height) in Europeans. We calculated global genetic correlations (rg) between traits using linkage disequilibrium (LD) score regression and local genetic covariance using ρ-HESS, which partitions the genome and performs regression with LD regions. Finally, we identified genes located within regions of significant genetic covariance and analyzed patterns of tissue expression and pathway enrichment.

Results

Global LD score regression revealed significant negative correlations between height and both CH (rg = -0.12; P = 2.0 × 10-7) and CRF (rg = -0.11; P = 6.9 × 10-7). Local analysis revealed 68 genomic regions exhibiting significant local genetic covariance between CRF and height, containing 2874 unique genes. Pathway analysis of genes in regions with significant local rg revealed enrichment among signaling pathways with known keratoconus associations, including cadherin and Wnt signaling, as well as enrichment of genes modulated by copper and zinc ions.

Conclusions

Corneal biophysical parameters and height share a common genomic architecture, which may facilitate identification of disease-associated genes and therapies for corneal ectasias.

Translational Relevance

Local genetic covariance analysis enables the identification of associated genes and therapeutic targets for corneal ectatic disease.

Turner Syndrome: Ocular Manifestations and Considerations for Corneal Refractive Surgery

Turner Syndrome (TS) is the most common sex chromosome abnormality in females and is associated with physical changes, hormone deficiencies, increased risk of autoimmune disease, and ocular complications. In this article, we review the main ocular findings associated with TS and discuss their significance for the patient considering refractive surgery. We also present four cases of TS to highlight the clinical findings that may be present in these patients. The most common ocular manifestations include refractive errors, strabismus, and amblyopia. Less commonly, patients with TS may present with keratoconus, cataracts, glaucoma, uveitis, or other disorders of the posterior segment. When considering corneal refractive surgery in a TS patient, clinicians should perform a thorough ocular history, ask patients about hormone therapy and autoimmune conditions, and pay particular attention to any of the associated ocular symptoms of TS.

Evaluation of anterior segment parameters in patients with Turner syndrome using Scheimpflug imaging

PURPOSE

To compare the anterior segment parameters in patients with Turner syndrome (TS) as measured by the Pentacam HR-Scheimpflug imaging system with those of healthy control subjects.

METHODS

This cross-sectional prospective study included 35 patients with TS and 30 age-matched controls. Corneal topographic analysis was performed using the Pentacam HR-Scheimpflug imaging system (Oculus, Wetzlar, Germany). The power of the corneal astigmatism, mean keratometry (Km) values for the both front and back surfaces of the cornea, maximum keratometry (Kmax), central corneal thickness (CCT), corneal volume (CoV), white-to-white diameter (WTW), chamber volume (CaV), angle and anterior chamber depth (ACD) values were recorded.

RESULTS

The mean age of TS subjects was 17.2 ± 6.1 years; of controls, 16.4 ± 5.7 years. All participants were female. There was a significant difference in the mean values of WTW (11.3 ± 0.5 mm vs 12.0 ± 0.4 mm [P < 0.001]), CaV (148.4 ± 33.5 mm³ vs 191.9 ± 27.6 mm³ [P < 0.001]), and ACD (2.8 ± 0.3 mm vs 3.1 ± 0.2 mm [P < 0.001]) between TS versus group and the control group. The mean values of the power of the corneal astigmatism, Km values for the both front and back of the corneal surface, Kmax, CCT, CoV, and angle values were similar between groups (P > 0.05 for each one).

CONCLUSIONS

There was a reduction in CaV, ACD, and WTW measurements in TS patients compared with controls.

Corneal Thickness Profile and Associations in Chinese Children Aged 7 to 15 Years Old

Corneal thickness (CT) maps of the central (2-mm diameter), para-central (2 to 5-mm diameter), peripheral (5 to 6-mm diameter), and minimum (5-mm diameter) cornea were measured in normal Chinese school children aged 7 to 15 years old using Fourier-domain optical coherence tomography. Multiple regression analyses were performed to explore the effect of associated factors [age, gender, refraction, axial length and corneal curvature radius (CCR)] on CT and the relationship between central corneal thickness (CCT) and intraocular pressure (IOP). A total of 1228 eyes from 614 children were analyzed. The average CCT was 532.96 ± 28.33 μm for right eyes and 532.70 ±28.45 μm for left eyes. With a 10 μm increase in CCT, the IOP was elevated by 0.37 mm Hg, as measured by noncontact tonometry. The CT increased gradually from the center to the periphery. The superior and superior nasal regions had the thickest CTs, while the thinnest points were primarily located in the inferior temporal cornea. The CCT was associated with CCR (p = 0.008) but not with gender (p = 0.075), age (p = 0.286), axial length (p = 0.405), or refraction (p = 0.985). In the para-central region and the peripheral cornea, increased CT was associated with younger age, male gender, and a flatter cornea.

Ethnic Variations in Central Corneal Thickness in a Rural Population in China: The Yunnan Minority Eye Studies

Purpose

To describe the ethnic differences in central corneal thickness (CCT) in population-based samples of ethnic Bai, Yi and Han people living in rural China.

Methods

6504 adults (2119 ethnic Bai, 2202 ethnic Yi and 2183 ethnic Han) aged 50 years or older participated in the study. Each subject underwent standardized ocular examinations and interviewer-administered questionnaires for risk factor assessment. CCT was measured for both eyes using an ultrasound pachymeter. Regression and principal component analysis were performed to examine the relationship of ethnicity and other factors with CCT.

Results

The mean CCT readings were 536.4 ± 34.2 μm in ethnic Bai, 532.1 ± 32.1 μm in ethnic Yi and 529.6 ± 32.7 μm in ethnic Han adults (P<0.001), respectively. There was a decreasing trend of mean CCT with increasing age across all ethnic groups. In multivariate linear regression models, increasing CCT was associated with younger age (P<0.001), male gender (P<0.001), Bai (P<0.001) or Yi (P<0.001) ethnicity, greater body mass index (P<0.001), higher systolic blood pressure (P<0.001), greater corneal curvature (P<0.001), deeper anterior chamber (P < 0.001), and thicker lens (P<0.001). Ethnicity contributed significantly to presence of thin cornea (60%; P< 0.001) compared with other factors. CCT had similar impact on intraocular pressure readings across all ethnic groups.

Conclusions

This study of more than 6500 multiethnic participants demonstrates significant ethnic variations in CCT, with Han ethnicity having the thinnest cornea compared with ethnic minorities. These data are essential to guide future multiethnic clinical trials on CCT-related ocular conditions such as glaucoma.