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

Comparative Analysis of Central Corneal Thickness in Four Fish Models

To understand the left-right asymmetry of vertebrate eyes, this study measured the central corneal thickness (CCT) of Oryzias curvinotus, Oryzias melastigma, Oryzias latipes, and zebrafish with optical coherence tomography. The results showed that the CCTs were significant differences among different species and groups, even between the right and left eyes of each fish. The values of the CCTs (mean ± SD, μm) for the four species were 104.71 ± 14.49, 61.88 ± 8.63, 64.76 ± 10.36 and 56.96 ± 10.48, respectively. Moreover, comparing the two wild groups of O. curvinotus from Sanya on N18° and Gaoqiao on N21°, the CCT value for the low-latitude group was 104.71 ± 14.49 μm, greater than the high latitude group 76.13 ± 5.70 μm significantly (t-test, p = 0.0001). Lastly, the paired Student's t-test revealed that significant CCT differences existed between the left and right eye for all four species and groups, of which zebrafish and O. melastigma were belonging to the left thicker type in contrast to the others. This study laid a foundation for understanding the causes of the difference in CCT, and also provided possible fish models for human researches on keratomileusis, glaucoma, and other corneal diseases.

The Underlying Relationship between Keratoconus and Down Syndrome

Keratoconus (KC) is one of the most significant corneal disorders worldwide, characterized by the progressive thinning and cone-shaped protrusion of the cornea, which can lead to severe visual impairment. The prevalence of KC varies greatly by ethnic groups and geographic regions and has been observed to be higher in recent years. Although studies reveal a possible link between KC and genetics, hormonal disturbances, environmental factors, and specific comorbidities such as Down Syndrome (DS), the exact cause of KC remains unknown. The incidence of KC ranges from 0% to 71% in DS patients, implying that as the worldwide population of DS patients grows, the number of KC patients may continue to rise significantly. As a result, this review aims to shed more light on the underlying relationship between KC and DS by examining the genetics relating to the cornea, central corneal thickness (CCT), and mechanical forces on the cornea, such as vigorous eye rubbing. Furthermore, this review discusses KC diagnostic and treatment strategies that may help detect KC in DS patients, as well as the available DS mouse models that could be used in modeling KC in DS patients. In summary, this review will provide improved clinical knowledge of KC in DS patients and promote additional KC-related research in these patients to enhance their eyesight and provide suitable treatment targets.

Asian Race and Primary Open-Angle Glaucoma: Where Do We Stand?

Primary open-angle glaucoma (POAG) is an optic neuropathy characterized by irreversible retinal ganglion cell damage and visual field loss. The global POAG prevalence is estimated to be 3.05%, and near term is expected to significantly rise, especially within aging Asian populations. Primary angle-closure glaucoma disproportionately affects Asians, with up to four times greater prevalence of normal-tension glaucoma reported compared with high-tension glaucoma. Estimates for overall POAG prevalence in Asian populations vary, with Chinese and Indian populations representing the majority of future cases. Structural characteristics associated with glaucoma progression including the optic nerve head, retina, and cornea are distinct in Asians, serving as intermediates between African and European descent populations. Patterns in IOP suggest some similarities between races, with a significant inverse relationship between age and IOP only in Asian populations. Genetic differences have been suggested to play a role in these differences, however, a clear genetic pattern is yet to be established. POAG pathogenesis differs between Asians and other ethnicities, and it may differ within the broad classification of the Asian race. Greater awareness and further research are needed to improve treatment plans and outcomes for the increasingly high prevalence of normal tension glaucoma within aging Asian populations.

Profile of central corneal thickness and corneal endothelial cell morpho-density of in healthy Congolese eyes

Purpose

To determine the pachymetric and corneal endothelial cell morphometric features and their relationship to ocular and systemic factors in healthy Congolese subjects.

Methods

Non-contact specular microscopy was used in 278 healthy eyes (278 subjects) to measure central corneal thickness (CCT), corneal endothelial cell density (CECD) along with cell size, coefficient of variation (CV) in cell size, and hexagonality (HEX). The lower and upper reference limits and average values for each parameter were determined. Correlation and association of average values with anthropo-demographic and clinical variables were assessed.

Results

The mean age was 38.9 ± 17.2 years (10.9–80.7 years). Average values were 504.2 ± 30.7 μm (CCT), 2907.1 ± 290.9 cells/mm² (CECD), 348.5 ± 38.4 μm² (cell size), 32.9 ± 3.6% (CV), and 51.8 ± 7.2% (HEX). CCT was 504.9 ± 33.6 μm in men and 503.6 ± 28.3 μm in women (p = .73); values for CECD were 2917.1 ± 253.5 cells/mm² and 2899.2 ± 317.8 cells/mm² (p = 0.61), respectively. Lower and upper reference limits were 449.6 μm and 566.0 μm for CCT, and 2165.3 cells/mm² and 3414.4 cells/mm² for CECD, respectively. CCT correlated with body mass index (BMI), (r = − 0.12, P = 0.04). CECD decreased with age (r = − 0.49, P < 0.001), BMI (r = − 0.20, P = 0.001), intraocular pressure (r = − 0.13, P = 0.029) and ocular perfusion pressure (r = − 0.28, P = 0.028). CECD decayed by 8.3 cells/mm² or 0.30% per year of age and CCT decreased by 0.72 μm per kg/m².

Conclusions

Mean central cornea was thinner, CECD higher, and references limits lower than reported in other African populations. The CCT and CECD normative values reported herein will be useful for both clinical and research purposes in this population.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12886-021-01947-x.

Reference Values of the Central Corneal Thickness with Different Refractive Errors for the Adult Egyptian Population

AIM

To generate reference values of the central corneal thickness (CCT) with different refractive errors for the adult eastern Egyptian population.

SUBJECTS AND METHODS

This study was a retrospective, observational, and cross-sectional study. It included 1166 eyes (1166 subjects) scheduled for LASIK, who came to private refractive eye centre, Ismailia, Egypt. The study period was from January 2018 to January 2020. The subjects were divided into a broad range of myopia with spherical equivalent (SE) ≤-0.5D and hyperopia (SE) ≥+0.5D. Then, the myopic eyes divided into low (SE>-3.0D), moderate (SE-3.0D to >-6.0D), and high (SE≤-6.0D). Similarly, the hyperopic eyes were divided into low (SE<+3.0D) and moderate (SE+3.0D to <+6.0D) and high ≥+6.0D. The refractive error was measured by an auto-refractometer, and CCT was measured using ultrasonic pachymetry.

RESULTS

The data of 556 myopic eyes in 556 subjects (31.1% males and 68.9% females) and 610 hyperopic subjects (34.4% males and 65.6% females) were included in this study. The mean±SD of CCT for the total myopic subjects was 532.8±32.6μm, range (470 to 627μm). The mean±SD of SE was -4.06±2.50D, range (-0.50 to -14.00D). The mean±SD of CCT for the total hyperopic subjects was 530.8±37.2μm, range (471 to 616μm). The mean±SD of SE was +3.57±1.98D, range (+0.50 to +8.50D). About 16.2% of the myopic eyes and 12.7% of the hyperopic eyes have CCT less than 500μm.

CONCLUSION

The mean of the central corneal thickness of the eastern Egyptian population was 532.8μm for myopic and 530.8μm for hyperopic subjects, respectively. The myopic and hyperopic subjects show a reduction in CCT with age. Females have a thinner cornea than males, 16.2% of the myopic eyes and 12.7% of the hyperopic eyes have CCT less than 500μm.

Central Corneal Thickness and Its Association with Birth Parameters in Chinese Adolescents

Purpose: To examine the distribution and determinants of central corneal thickness (CCT) including birth weight and gestational age in a school-based samples of Grade 7 students in rural China. Methods: 2346 (93.5%) grade 7 students with a mean age of 13.8 years participated in the study. CCT was measured for both eyes using the LenStar LS900. Information regarding birth weight and gestational age was retrieved from the participants' delivery records. A linear regression model was established to examine the relationship of birth weight, gestational age and other factors with CCT. Results: The mean CCT in this population was 534.7 µm and boys had a greater CCT compared with girls (P = .06). CCT was positively related to axial length (r = 0.056) while negatively related to anterior chamber depth (r = -0.076) and corneal power (r = -0.105) . In multivariate analyses, the cornea was 19.35µm thinner in individuals with low birth weight compared with those with normal. In addition, the cornea was 25.25µm thinner in prematurely born adolescents compared with full-term ones. The combined effect of birth weight and gestational age on CCT was not statistically significant (P for interaction = 0.12) Conclusions: Low birth weight and small gestational age are associated with thinner corneas in adolescence. This disparity across groups with different levels of birth parameters should be taken into account by future studies investigating CCT as risk factors or diagnostic tests for glaucoma.

Central corneal thickness in a Jordanian population and its association with different types of Glaucoma: cross-sectional study

BACKGROUND

Central corneal thickness (CCT) has long been implicated to affect glaucoma predisposition. Several reports have identified that thinner CCT is a risk factor for open-angle glaucoma, and that CCT can be very variable between different ethnic groups. In this study, we aim to identify the relation between CCT and different glaucoma parameters in different types of glaucoma in an Arabian ethnicity.

METHODS

We classified our participants into four main groups: primary open-angle glaucoma (POAG), primary angle-closure glaucoma (PACG), pseudoexfoliative glaucoma (PXFG), and a control group. We obtained demographics, intraocular pressure (IOP), cup to disc ratio (CDR), visual field mean deviation (MD) and pattern standard deviation (PSD), CCT, and retinal nerve fiber layer (RNFL) thickness for each participant.

RESULTS

We included A total of 119 eyes with glaucoma, including POAG (54 eyes), PXFG (31 eyes) and PACG (34 eyes), we also included 57 control eyes. We found that PACG eyes have the thinnest CCT. Mean measurements of CCT for our groups were: 538.31 μm (SD = 36.30) in eyes with POAG, 544.45 μm (SD = 28.57) in eyes with PXFG, 506.91 μm (SD = 34.55) in eyes with PACG and 549.63 μm (SD = 42.9) in the control group. We found that CCT is significantly correlated with CDR (p = 0.012, r = - 0.231), MD (p < 0.001, r = 0.327),and RNFL thickness (p = .007, r = .283).

CONCLUSION

In Arabian ethnicity, PACG patients have the thinnest CCT compared to other types of glaucoma, namely POAG and PXFG. We demonstrated that glaucomatous eyes with thinner corneas will probably have more advanced glaucomatous optic neuropathy. Our results emphasize the importance of taking ethnicity into account upon glaucoma management.

Spectacles need and ownership among multiethnic students in rural China

OBJECTIVES

The aim of this study is to describe the prevalence and associated factors of spectacles need and ownership among multiethnic school students in rural China.

STUDY DESIGN

School-based cross-sectional study.

METHODS

This school-based eye study was conducted in Yunnan province located in Southwestern China. Questionnaires were filled out by children with the help of their parents concerning demographic characteristics, spectacles usage, and myopia-related lifestyle exposures. Spectacles need was defined as participants who had an uncorrected visual acuity (VA) of less than 6/12 but could be corrected to more than 6/12 in the better-seeing eye, with myopia of less than -0.5 diopters (D), hyperopia of more than +2.0 D, or astigmatism of more than 0.75 D in both eyes. Definition of spectacles ownership was based on spectacles wearing at school on the examination day.

RESULTS

Among the 7681 students aged 5-16 years participating in this study, 7166 (93.3% of the study participants) successfully completed VA tests and questionnaires. The rate of spectacles need among children with an uncorrected VA of 6/12 or worse in either eye was 68.3% (623/912). Among the students who needed spectacles, only 18.9% owned them. Multivariate analyses revealed that spectacles ownership was significantly associated with increasing age (odds ratio [OR]: 1.30; 95% confidence interval [CI]: 1.08-1.55), more time on reading and writing (OR = 1.66; 95% CI: 1.15-2.40), having myopic friend(s) (OR: 1.90; 95% CI: 1.01-3.56), self-awareness of myopia (OR: 6.67; 95% CI: 2.48-17.92), and poorer uncorrected VA (OR: 4.57; 95% CI: 2.78-7.52).

CONCLUSIONS

We observed a lower rate of spectacles ownership among rural children compared with those of similar ages in urban China. These findings may have important public health implications for China and other countries regarding vision-related health resources allocation.

Longitudinal Change in Central Corneal Thickness in the Tema Eye Survey

PURPOSE

To determine the change and rate of change in central corneal thickness (CCT) and their determinants.

DESIGN

Longitudinal observational population-based study.

METHODS

A total of 758 normal and 58 glaucomatous subjects underwent complete eye examination, with CCT measurements at 2 separate visits. Change and rate of change in CCT were determined. Univariate and multivariate linear regression analyses were performed to determine the factors associated with change and rate of change.

RESULTS

The mean follow-up duration was 8.4 ± 0.7 years. The overall change was -8.9 ± 16.7 μm in OD and -9.8 ± 16.2 μm in OS, both P < .0001. Changes in glaucomatous and normal subjects were -14.1 ± 2.2 μm vs -8.6 ± 0.6 μm in OD (P = .02) and -14.5 ± 2.2 μm vs -9.5 ± 0.6 μm in OS (P = .03), respectively. The overall rate of thinning was -1.1 μm/year (OD) and -1.2 μm/year (OS). Rates in glaucomatous and normal eyes were -1.7 ± 0.3 μm/year vs -1.0 ± 0.1 μm/year in OD (P = .02) and -1.7 ± 0.3 μm/year vs -1.1 ± 0.1 μm/year in OS (P = .03), respectively. Change and rate of change were associated with baseline CCT (ß = -0.1 to -0.09 and -0.011, respectively, all P < .001) and glaucoma (ß = -6.8 to -5.6, P ≤ .009, and -0.75 to -0.69, P ≤ .007, respectively).

CONCLUSION

CCT decreased significantly over time. The change and rate of change were greater in glaucomatous than normal eyes, and were greater than described in cross-sectional studies.

Relationship between Corneal Thickness and Radius to Body Height

PURPOSE

To investigate the possible association between body stature (height) and corneal thickness and radius in younger-adult Caucasians, especially within the context of previously published literature.

METHODS

Body height and weight were measured in 109 healthy subjects, with an average age of 24 ± 6 years (mean ± SD). Subjects underwent an ophthalmic assessment including anterior segment imaging by Scheimpflug topography and specular microscopy. Central and peripheral corneal thickness and corneal radius were analyzed. The relationship between body stature and corneal parameters was assessed using simple and multiple regression analysis. Effect size was determined by generating regression and correlation coefficients.

RESULTS

Body height ranged from 1.54 to 1.86 m (mean ± SD 1.67 ± 0.08 m), central corneal thickness from 465 to 629 μm (554 ± 33 μm), whereas corneal radius measured between 7.16 and 8.49 mm (7.75 ± 0.24 mm). Body height was weakly associated with central corneal thickness and peripheral corneal thickness (r ≥ -0.180), and moderately with corneal radius (r = 0.351). Based on the regression equations, central corneal thickness decreases by 8 μm, whereas corneal radius increases by 0.11 mm for each 0.1-m difference in body height. No significant correlations were found for similar assessments using body weight or body mass index.

CONCLUSIONS

Differences in corneal radius and corneal thickness can be linked to body stature. However, effect sizes were consistently small and no more than 13% of the variability in corneal curvature could be explained by variations in body stature.

Corneal Thickness in Highlanders

Patyal, Sagarika, Amit Arora, Arun Yadav, and Vijay K. Sharma. Corneal thickness in highlanders. High Alt Med Biol. 18:56-60, 2017.

BACKGROUND

Corneal thickness is an important parameter with diagnostic and therapeutic implications. Various studies have highlighted increase in corneal thickness in lowlanders on ascending to high altitude. However, there are no studies in the published literature pertaining to corneal thickness of the highlanders who are inhabitants of such altitudes. Hence, study was carried out with objective to determine the corneal thickness of highlanders living at heights of more than 11,000 feet and compare it with corneal thickness of lowlanders.

MATERIALS AND METHODS

The highlander participants of the study consisted of inhabitants of Ladakh region of India at an altitude of 11,000 feet or more and lowlander participants consisted of inhabitants at an altitude of 1500 feet. A total of 254 highlanders and 212 lowlanders participated. A mean of 25 measurements of central corneal thickness (CCT) of every participant was obtained for each eye using ultrasonic pachymeter.

RESULTS

The mean age of the participants was 41.8 (15.9) and 47.7 (17.7) years among lowlanders and highlanders, respectively. The highlanders had 11.95 μm lower mean CCT reading compared to lowlanders after adjusting for age and sex (p value <0.001). There was no statistically significant difference in mean CCT readings of right eye and left eye in either lowlanders or highlanders. Age also had a significant effect after adjustment for location and gender (p = 0.001). CCT decreased by 0.31 μm with every year increase in the age. Gender had no statistically significant effect.

CONCLUSION

This study found statistically significant difference in CCT measurements between highlanders and lowlanders. The thinner corneas of highlanders may have a bearing on diagnosis and treatment of glaucoma, refractive surgery, contact lens fitting implantation of Intacs, and astigmatic keratectomy done on such patients. The study also opens the scope of further research in the area.

Central Corneal Thickness in Spectral-Domain OCT and Associations with Ocular and Systemic Parameters

Background. Optical coherence tomography (OCT) allows quantitative analysis of the anterior segment of the eye with a noncontact examination. The aim of this study is to analyze associations of central corneal thickness (CCT) as measured by OCT with ocular and systemic cardiovascular parameters. Methods. A cross-sectional study of 734 persons was performed in a working age population. Only healthy eyes were included. A comprehensive ophthalmological examination including refraction, noncontact tonometry, and imaging of the anterior segment by SD-OCT was performed. In parallel, a broad range of systemic cardiovascular parameters were measured. Associations were analyzed using a generalized estimating equations' model. Results. CCT measurements showed a significant association with corneal curvature and intraocular pressure: a thinner CCT was associated with a flatter cornea and with lower intraocular pressure (p < 0.001). Age was positively associated with CCT (p < 0.001); all other cardiovascular parameters were not associated. Conclusion. A thinner cornea is associated with a flatter surface and with lower intraocular pressure readings, while there are no independent associations with refraction and systemic cardiovascular parameters. Our findings highlight the value of SD-OCT CCT measurements as a standard tool in anterior segment analysis.