Central corneal thickness and its relationship to ocular parameters in young adult myopic eyes

Association of myopia and astigmatism with postoperative ocular high order aberration after small incision lenticule extraction

OBJECTIVE

To investigate the correlation between higher-order aberrations (HOA) after small incision lenticule extraction (SMILE) and the severity of myopia and astigmatism, along with the relevant factors. These findings will provide valuable insights for decreasing the occurrence of HOA after SMILE and enhancing visual quality.

METHODS

A total of 75 patients (150 eyes) with myopia and astigmatism who underwent SMILE were categorized into four groups based on the severity of myopia and astigmatism: Myopia Group 1 (Group M1, spherical diopter ranged from -1.00 D to -4.00 D), Myopia Group 2 (Group M2, spherical diopter ranged from -4.10 D to -10.00 D), Astigmatism Group 1 (Group A1, cylindrical diopter ranged from 0 D to -1.00 D), and Astigmatism Group 2 (Group A2, cylindrical diopter ranged from -1.10 D to -3.00 D). A comprehensive assessment was performed to examine the association between HOA and various relevant factors, including a detailed analysis of the subgroups.

RESULTS

Group M1 had significantly lower levels of total eye coma aberration (CA), corneal total HOA (tHOA), internal tHOA, and vertical CA ( Z 3 - 1 ) after SMILE than Group M2 (P < 0.05). Similarly, Group A1 had significantly lower levels of total eye tHOA, CA, trefoil aberration (TA), corneal tHOA, TA, and vertical TA ( Z 3 - 3 ) after SMILE than Group A2 (P < 0.05). Pearson correlation analysis indicated a statistically significant positive relationship between the severity of myopia/astigmatism and most HOA (P < 0.05). Subgroup evaluations demonstrated a notable increase in postoperative HOA associated with myopia and astigmatism in Groups M2 and A2 compared with the control group. Lenticule thickness, postoperative central corneal thickness (CCT), postoperative uncorrected distance visual acuity (UDVA), and postoperative corneal Km and Cyl were strongly correlated with most HOA. Age, eyes, and postoperative intraocular pressure (IOP) were only associated with specific HOA.

CONCLUSION

HOA positively correlated with the severity of myopia and astigmatism after SMILE. However, this relationship was not linear. HOA after SMILE was influenced by various factors, and additional specialized investigations are required to establish its clinical importance.

Associations between corneal curvature and other anterior segment biometrics in young myopic adults

To investigate the associations between corneal curvature (CC) and other anterior segment biometrics in young myopic adults. In this retrospective multi-center study, 7893 young myopic adults were included. CC and other anterior segment biometrics were measured by Scheimpflug imaging (Pentacam). CC was defined as SimK at central 3 mm area, and other anterior segment biometrics included white-to-white corneal diameter (WTW), central corneal thickness (CCT), corneal volume (CV) at 3 mm, 5 mm, and 7 mm area, anterior corneal astigmatism (ACA), posterior corneal astigmatism (PCA), anterior corneal eccentricity (ACE) and asphericity (ACAP), posterior corneal eccentricity (PCE) and asphericity (PCAP), anterior chamber depth (ACD), and anterior chamber volume (ACV). Univariate regression analyses were used to assess the associations between CC and other anterior segment biometrics, and multivariate regression analyses were further performed to adjusted for age, gender and spherical equivalent. CC was higher in patients of female gender and higher myopia (all P < 0.05). Eyes in higher CC quartiles had lower WTW, thinner CCT, lower CV at 3 mm and 5 mm, lower ACD, and lower ACV (all P < 0.001), but had larger ACA, larger PCA, less PCE and less PCAP (all P < 0.001), compared to eyes in lower CC quartiles. The trends of CV at 7 mm, ACE and ACAP were inconsistent in different CC quartiles. After adjusting for age, gender and spherical equivalent with multivariate linear regression, CC was positively correlated to CV at 7 mm (βs = 0.069), ACA (βs = 0.194), PCA (βs = 0.187), ACE (βs = 0.072), PCAP (βs = 0.087), and ACD (βs = 0.027) (all P < 0.05), but was negatively correlated to WTW (βs = - 0.432), CCT (βs = - 0.087), CV-3 mm (βs = - 0.066), ACAP (βs = - 0.043), PCE (βs = - 0.062), and ACV (βs = - 0.188) (all P < 0.05). CC was associated with most of the other anterior segment biometrics in young myopic adults. These associations are important for better understanding of the interactions between different anterior segment structures in young myopic patients, and are also useful for the exploration of the pathogenesis of myopia.

Age- and gender-related characteristics of astigmatism in a myopic population

Purpose

To explore age- and gender-related differences of refractive and corneal astigmatism in myopic patients looking for refractive surgery.

Design

A retrospective cross-sectional study.

Materials and methods

The medical files of candidates looking for corneal refractive surgery between 2019 and 2021 were reviewed, demographic and refractive parameters including age, gender, refractive status, and corneal parameters were analyzed.

Results

A total of 1,417 eyes of 1,417 patients (453 males and 964 females) were included. Males had thicker cornea than females, while females had steeper cornea than males, there was no gender-related difference in refractive and corneal astigmatism depending on patients’ age. There was no difference in refractive astigmatism among different age group from 18 to 50 years, while corneal astigmatism had a shift from with-the rule (WTR) to against-the-rule (ATR) with increasing age. Age, central corneal thickness (CCT), sphere, refractive astigmatism (RA), and corneal curvature (Km) were correlated with corneal astigmatism (CA) (standardized coefficients of are 0.006, p = 0.011 for age, −0.001, p = 0.004 for CCT, and −0.027, p < 0.001 for sphere, 0.61, p < 0.001 for RA, −0.05, p < 0.001 for corneal curvature).

Conclusion

Refractive astigmatism is stable until the age of 50 years in myopic patients looking for refractive surgery, while corneal astigmatism showed a shift from WTR to ATR with advancing age. Age, CCT, sphere, refractive astigmatism and corneal curvature (Km) were correlated with corneal astigmatism.

Interocular Symmetry and Repeatability of Central Corneal Thickness and Corneal Endothelial Cell Morphology and Density in Healthy Eyes of Congolese

PURPOSE

To determine the limits of normal interocular symmetry and the repeatability of central corneal thickness (CCT) and endothelial cell morphology and density.

METHODS

Two hundred and seventy-eight subjects (age: 10.9-80.7 years) with healthy eyes were studied. CCT as well as endothelial cell morphology and density were measured by non-contact specular microscopy. Three measurements were obtained per eye per participant. Upper and lower tolerance limits of normal interocular symmetry were defined as the 2.5th and 97.5th percentiles of the interocular differences in CCT, endothelial cell density (CECD), coefficient of variation (CoV), hexagonality, and cell size. Repeatability was determined using the intraclass coefficient correlation (ICC), the coefficient of variation (CV), and the test-retest variability standard deviation (TRTSD).

RESULTS

The mean interocular differences were -1.05 ± 17.5 µm (p = .32) for CCT and 0.5 ± 90.8 cells/mm² (p = .76) for CECD. The 2.5th and 97.5th percentiles of the interocular differences were -13.9 and 15.4 µm for CCT and -177.4 cells/mm² to 182.0 cells/mm² for CECD. Only interocular difference in CoV correlated weakly with age (r = -0.22, P < .001). ICCs were 0.93 (95% CI: 0.89-0.96, P < .001) for CCT and 0.95 (0.94-0.96, P < .001) for CECD. CV and TRTSD were 1.2% ± 5.3% and 4.4 ± 3.4 µm for CCT and 2.4% ± 3.9% and 17.7 ± 7.7 cells/mm² for CECD, respectively.

CONCLUSIONS

CCT and CECD showed good repeatability and interocular symmetry in normal Congolese subjects. Absolute interocular differences in CCT and CECD exceeding 15.5 µm and 182 cells/mm², respectively, should be considered suspicious and investigated. When comparing two intrasession measurements from the same eye, a difference of approximately 4.5 µm in CCT and 18 cells/mm² or greater may be considered statistically significant.

Refractive error and biometrics of anterior segment of eyes of healthy young university students in Japan

To determine the parameters of the anterior segment of eyes that are significantly associated with the refractive error in healthy young Japanese university students. This was a cross-sectional observational study of 229 healthy Japanese university students (men: women,147:82) whose age ranged between 20 to 29 years. Univariate and multivariate linear regression analyses were performed to identify the factors that were significantly correlated with the refractive error. The independent variables included age, sex, axial length, anterior chamber depth, corneal diameter, curvature of anterior surface of cornea, and central corneal thickness. The mean refractive error (spherical equivalent) was −4.1 ± 2.7 diopters (D) with a range of −12.5 to +0.5 D, and the mean axial length was 25.4 ± 1.3 mm with a range of 22.4 to 29.0 mm. Pearson univariate correlation analysis found that the refractive error was significantly and negatively correlated with the axial length (R = −0.82, P < 0.001), deeper anterior chamber (R = −0.30, P < 0.001), and larger corneal diameter (R = −0.21, P = 0.001). Multiple regression analysis showed that the refractive error was significantly associated with a longer axial length (P < 0.001), a deeper anterior chamber (P < 0.001), and a flatter corneal curvature (P < 0.001).The biometric values of the anterior segment of the eyes should make the eye more hyperopic which would reduce the myopia-inducing lengthening of the axial length.

Effects of Sex Hormones on Ocular Blood Flow and Intraocular Pressure in Primary Open-angle Glaucoma: A Review

Primary open-angle glaucoma (POAG) is a multifactorial optic neuropathy characterized by progressive retinal ganglion cell death and visual field loss. Some speculate that sex plays a role in the risk of developing POAG and that the physiological differences between men and women may be attributed to the variable effects of sex hormones on intraocular pressure, ocular blood flow, and/or neuroprotection. Estrogen, in the form of premenopausal status, pregnancy, and postmenopausal hormone therapy is associated with an increase in ocular blood flow, decrease in intraocular pressure and neuroprotective properties. The vasodilation caused by estrogen and its effects on aqueous humor outflow may contribute. In contrast, although testosterone may have known effects in the cardiovascular and cerebrovascular systems, there is no consensus as to its effects in ocular health or POAG. With a better understanding of sex hormones in POAG, sex hormone-derived preventative and therapeutic considerations in disease management may provide for improved sex-specific patient care.

Effect of age, sex, and refractive errors on central corneal thickness measured by Oculus Pentacam®

BACKGROUND

Central corneal thickness (CCT) can be used to assess the corneal physiological condition as well as the pathological changes associated with ocular diseases. It has an influence on the measurement of intraocular pressure and is being used as a screening tool for refractive surgery candidates. The aim of this study was to determine the median CCT among normal Pakistani population and to correlate CCT with age, sex, and refractive errors.

METHODS

We conducted a retrospective analysis of 5,171 healthy eyes in 2,598 patients who came to Hashmanis Hospital, Karachi, Pakistan. The age of the patients ranged from 6 to 70 years. The refractive error was gauged by an auto-refractometer, and CCT was measured using Oculus Pentacam^®.

RESULTS

The median CCT of our study was 541.0 μm with an interquartile range (IQR) of 44.0 μm. The median age was 26.0 years (IQR: 8.0). Median spherical equivalent (SE) of the patients was -4.3 D (IQR: 3.3) with the median sphere value as -4.0 D (IQR: 3.8). Lastly, the median cylinder was -1.0 D (IQR: 1.3). Age has a weak negative correlation with CCT (r=-0.058) and shows statistical significance (P<0.001). Additionally, males had thinner CCT readings than females (P=0.001). The cylinder values, on the other hand, had a significant (P=0.004) and positive correlation (r=0.154). Three values showed no significant correlation: sphere (P=0.100), SE (P=0.782), and the left or right eye (P=0.151).

CONCLUSION

Among the Pakistani population, CCT was significantly affected by three variables: sex, age, and cylinder. No relationship of CCT was observed with the left or right eye, sphere, and SE.