Heritability of Corneal Curvature and Pentacam Topometric Indices: A Population-Based Study

Heritability of Corneal Parameters in Nuclear Families With Keratoconus

Purpose

This study aimed to investigate the heritability of corneal parameters obtained by Pentacam in nuclear families with keratoconus (KC).

Methods

A total of 82 patients with KC and their biological parents (n = 164) were recruited in the current study. All subjects underwent corneal tomography with Pentacam. Family units were analyzed to calculate the heritability of corneal parameters by linear mixed effects model using the R statistical software.

Results

The pachymetry at apex, pupil, and thinnest point were all significantly heritable at 43.26%, 42.63%, and 43.09%, respectively. The heritability of flat meridian keratometry, steep meridian keratometry, and mean keratometry in the anterior surface were 10.36%, 9.05%, and 10.21%, respectively, and that of flat meridian keratometry, steep meridian keratometry, and mean keratometry in the posterior surface were 8.44%, 9.67%, and 9.06%, respectively. The posterior radius of curvature had higher heritability in comparison with anterior radius of curvature (19.16% vs. 14.37%). Moreover, among combined topometric indices, the heritability of index of vertical asymmetry was the highest (19.49%), and that of central keratoconus index was the lowest (6.64%).

Conclusions

The present study demonstrated a substantial heritability of corneal parameters in nuclear families with KC. The pachymetric indices are heritable and may be suitable as KC endophenotypes, suggesting a necessity to discover the genes associated with corneal thickness in KC.

Translational Relevance

The pachymetric indices are heritable and may be suitable as KC endophenotypes, indicating that the pachymetric indices might be a corneal characteristic to predict the occurrence of KC.

Performances of Corneal Topography and Tomography in the Diagnosis of Subclinical and Clinical Keratoconus

Aim

The purpose of the study was to assess the efficacy of topographical and tomographical indices given by the Pentacam (pachymetric, tomopetric, and aberometric) in clinical and subclinical keratoconus (KCN) diagnosis.

Material and Methods

In this observational analytic retrospective study, patients with abnormal findings in topography and tomography maps but with no signs on clinical examination (subclinical KCN group, sKCN), patients with clinical keratoconus (KCN group), and healthy subjects (Control group) were evaluated.

Results

The KCN group proved significantly different (p < 0.001) values of the investigated parameters than the Control group. Eleven out of 28 investigated parameters proved significantly different in the sKCN group compared to controls (p < 0.001). Two topographic measurements, namely I-S (cut-off = 1.435, a large value indicates the presence of KCN) and CCT (cut-off = 537, a small value indicates the presence of KCN), showed AUCs equal to 1 [0.999 to 1]. Six other Pentacam measurements, including Back maximum keratometry (Back Kmax) proved to be excellent parameters for case-finding and screening. In distinguishing sKCN from normal eyes, Pentacam index of vertical asymmetry (IVA), inferior-superior difference (I-S) value, thinnest point (TP), Belin Ambrosio Enhanced Ectasia Display (BAD_D) and root mean square total (RMS total) performed best.

Conclusions

In distinguishing sKCN from normal eyes, Back Kmax, IVA, I-S, and RMS total values demonstrated higher accuracy and utility. Six indices, namely ISV, IVA, KISA, PRC, RMS-HOA, and Back Kmax demonstrate excellent utility in case-finding and screening for clinical KCN.

Comparison of corneal astigmatism characteristics and prevalence of corneal astigmatism between Turkish individuals and Syrian refugees

PURPOSE

To compare the prevalence, magnitude and type of corneal astigmatism between Turkish individuals and Syrian refugees.

MATERIAL AND METHODS

Data of patients scheduled for cataract surgery between January 2019 and 2020 were reviewed. The patients were randomly stratified according to their ethnicity (Turkish individuals or Syrian refugees). Keratometry was performed with the keratometer of IOLMaster 500. Quantitative analysis was performed using the power vector method (J0 and J45). The association between age and astigmatism in the two groups was explored.

RESULTS

The study included 4085 eyes of 2049 patients (3962 eyes of Turkish individuals and 123 eyes of Syrian refugees). The mean magnitude of corneal astigmatism, J0, J45 and prevalence of against the rule (ATR) astigmatism and with the rule (WTR) astigmatism were 1.01 D, 0.06, 0.01 D, 37.6% and 43.7% in Turkish individuals and 1.13 D, -0.02, 0.07 D, 46.3% and 37.4% in Syrian refugees, respectively. There were no significant differences according to age, sex, right/left eyes, corneal astigmatism magnitude, keratometric values, J0 and J45 (p > 0.05) between the two groups. Below 40 years of age, the mean corneal astigmatism magnitude in Syrian refugees was significantly higher than that in Turkish individuals (p = 0.037). At all ages, ATR astigmatism prevalence was higher in Syrian refugees than in Turkish individuals. ATR astigmatic shift began at a younger age in Syrian refugees (p = 0.037). Age- and sex-adjusted analysis showed that J0 was significantly lower in Syrian refugees than in Turkish individuals (p = 0.013).

CONCLUSION

The prevalence and magnitude of ATR astigmatism were higher and onset earlier in Syrian refugees than in Turkish individuals.

Normative Values of Various Pentacam HR Parameters for Pediatric Corneas

PURPOSE

To provide a normative database of several Pentacam parameters for a healthy pediatric population.

METHODS

This was a retrospective study conducted at Al Watany Eye Hospitals, Cairo, Egypt. We explored the Pentacam HR database and collected the data of 432 normal right eyes of children and teenagers aged 3 to 18 years. The subjects were classified into the following 3 groups: group 1 (3-6 years, 17 eyes), group 2 (6-12 years, 126 eyes), and group 3 (12-18 years, 289 eyes). The parameters of the study cohort were compared with those of a healthy adult cohort.

RESULTS

The mean age of the study cohort was 13.5 (13.2-13.8) years. There were significant differences in the following indices among the 3 age groups: anterior chamber (depth and volume), curvature (index of height decentration, index of vertical asymmetry, and center keratoconus index), elevation (front and back elevations from the best fit toric ellipsoid), and pachymetric (minimum and average pachymetric progression indices and average Ambrosio relational thickness) parameters (P values 0.001, 0.001, 0.002, 0.04, <0.001, <0.001, 0.03, 0.02, 0.01, and 0.03, respectively).

CONCLUSIONS

There were significant differences in the normative values of several Pentacam indices between the pediatric and adult cohorts. Based on this finding, it is more credible to incorporate separate software cutoff values for pediatric patients. However, because there were no clinically significant differences in the parameters of the pediatric subgroups, there is no need to consider a separate cutoff value for each pediatric age range.