Age-dependency of ocular parameters: a cross sectional study of young and elderly healthy subjects

Corneal Biomechanical Parameters after 60-Year-Old

Purpose

To determine the distribution of corneal biomechanical parameters in an elderly population.

Methods

This cross-sectional study was conducted in subjects above 60 years living in Tehran. The participants were selected using multi-stage cluster sampling. Corneal biomechanical parameters were measured in a randomly selected subsample of this population using the Reichert Ocular Response Analyzer (Reichert Ophthalmic Instruments, Inc., Buffalo, NY, USA).

Results

Of 470 subjects, the data of 420 participants aged over 60 years were analyzed (mean age: 69.3 ± 6.5 years and range: 61-88 years), 363 (86.4%) of whom were male. The mean and standard deviation of corneal hysteresis (CH) and corneal resistance factor (CRF) were 8.37 ± 1.55 mmHg (95% confidence interval [CI]: 8.02-8.72) and 9.06 ± 1.70 mmHg (95% CI: 8.69-9.44), respectively. The mean CH was 8.27 ± 1.54 mmHg in men and 9.25 ± 1.28 mmHg in women, and the mean CRF was 9.00 ± 1.71 mmHg in men and 9.63 ± 1.37 mmHg in women. According to the results of multiple linear logistic regression analysis, CH had a significant association with younger age (β = -0.05, P = 0.032), female sex (β = 1.83, P < 0.001), reduced maximum keratometry (β = -0.22, P = 0.06), and increased anterior chamber volume (β = 0.01, P = 0.007). CRF had a significant correlation with a younger age (β = -0.06, P = 0.02), female sex (β = 1.01, P = 0.05), central corneal thickness (β = 0.02, P < 0.001), and reduced maximum keratometry (β = -0.39, P = 0.010).

Conclusion

The mean CH and CRF values were low in this sample of the Iranian population aged over 60 years indicating the weaker elasticity of the corneal connective tissue.

Distribution of Anterior Chamber Parameters in Normal Chinese Children and the Associated Factors

PURPOSE

To describe the distribution of anterior chamber depth (ACD), anterior chamber volume (ACV), and anterior chamber angle (ACA) and establish the associated factors in the pediatric population in Shanghai, China.

MATERIALS AND METHODS

In this cross-sectional study, children aged 6 to 18 years from 9 primary and middle schools in Shanghai were enrolled. The Pentacam Scheimpflug camera was used to measure anterior eye chamber parameters. The distribution of ACD, ACV, ACA, and their associations with age, sex, body mass index, cycloplegic refractive error, axial length, intraocular pressure, and other parameters were analyzed.

RESULTS

A total of 1321 children were included, with a mean age of 9.65±2.95 years. The mean ACA, ACD, and ACV values were 37.95±7.96 degrees, 3.22±0.23 mm and 194.89±28.95 mm, respectively, and were higher in boys than in girls. ACV and ACD had similar growth trend curves with age, whereas ACA was stable. Overall, 5% of the tested children had ACA values ≤24.91 degrees. Greater ACV, deeper ACD, shorter pupil diameter, shorter axial length, and thinner apex corneal thickness were the independent factors associated with wider ACA (R=13.0%, P<0.001).

CONCLUSIONS

As one of diagnostic indicators of angle closure, ACA was stable with age. The results of this study should improve the current understanding of the distribution of anterior chamber parameters and the main factors affecting their variation.

Corneal Biomechanics and Visual Field Progression in Eyes with Seemingly Well-Controlled Intraocular Pressure

PURPOSE

To investigate the incidence and risk factors for glaucomatous visual field progression in eyes with well-controlled intraocular pressure (IOP).

DESIGN

Prospective cohort.

PARTICIPANTS

A total of 460 eyes of 334 patients with glaucoma under treatment.

METHODS

Study subjects had a mean follow-up of 4.3±0.8 years. Patients were classified as well controlled if all IOP measurements were less than 18 mmHg. Rates of visual field progression were calculated using ordinary least-squares linear regression of standard automated perimetry (SAP) mean deviation (MD) values over time. Progression was defined as a significantly negative MD slope (alpha = 0.05).

MAIN OUTCOME MEASURES

Rates of SAP MD change; mean and peak IOP, and IOP fluctuation; and corneal biomechanics: corneal hysteresis (CH), central corneal thickness (CCT), and corneal index.

RESULTS

Of the 179 eyes with well-controlled IOP, 42 (23.5%) demonstrated visual field progression. There was no significant difference between progressing and stable patients in baseline MD (-6.4±7.1 decibels [dB] vs. -6.0±6.2 dB; P = 0.346), mean IOP (11.7±2.0 mmHg vs. 12.1±2.3 mmHg; P = 0.405), IOP fluctuation (1.6±0.6 mmHg vs. 1.6±0.5 mmHg; P = 0.402), or peak IOP (14.3±1.9 mmHg vs. 14.6±2.1 mmHg; P = 0.926). Progressing eyes had significantly lower CH (8.6±1.3 mmHg vs. 9.4±1.6 mmHg; P = 0.014) and thinner CCT (515.1±33.1 μm vs. 531.1±42.4 μm; P = 0.018, respectively) compared with stable eyes. In the multivariate analysis, a 1 standard deviation lower corneal index, a summation of normalized versions of CH and CCT, resulted in a 68% higher risk of progression (odds ratio, 1.68; 95% confidence interval, 1.08-2.62; P = 0.021).

CONCLUSIONS

Approximately one-quarter of eyes with well-controlled IOP may show visual field progression over time. Thin cornea and low CH are main risk factors.

The Mechanical Interpretation of Ocular Response Analyzer Parameters

Purpose

Ocular Response Analyzer (ORA) is one of the most widely used devices in clinic, while the mechanical interpretations of parameters obtained from ORA have not been understood completely. The aim of this research is to explore the mechanical interpretation of ORA parameters.

Methods

Rabbits aged 3-24 months were measured with ORA in vivo and corneal strips uniaxial tensile tests to get ORA parameters and corneal biomechanical parameters (corneal elastic modulus, relaxation time, and relaxation limit). The mechanical interpretation of ORA parameters was cognized preliminarily by analyzing the correlation between ORA parameters and corneal biomechanical parameters. On the other hand, finite element method was applied to simulate ORA measurements with different corneal biomechanical parameters to obtain quantitative relationship between ORA parameters and corneal biomechanical parameters further.

Results

Biomechanical experimental results showed that Corneal Resistance Factor (CRF) was correlated with corneal elastic modulus and relaxation limit significantly, while the significant correlations between Corneal Hysteresis (CH) and corneal biomechanical parameters were not observed. Results of finite element analysis showed that both CH and CRF were correlated with corneal elastic modulus, relaxation limit, and relaxation time significantly. Besides, corneal elastic modulus was positively correlated with upslop1 and upslop2 and negatively correlated with w2.

Conclusions

For all ORA parameters, CH, CRF, the upslope, and the width of the peaks are parameters which may reflect corneal elastic properties. It is viable to cognize mechanical interpretation of ORA parameters by the comparisons of the data from ORA and biomechanical tests of rabbits with different ages and the simulations of ORA based on finite element methods. Further studies are needed to confirm the mechanical interpretation.

Age-Related Variations of Rabbit Corneal Geometrical and Clinical Biomechanical Parameters

Purpose

To study the variations in corneal clinical biomechanical parameters (CCBP) and corneal geometrical parameters of rabbit in relation to age.

Methods

Rabbits aged 3, 7, 12, 18, and 24 months were enrolled. Each eye of the rabbits was tested with Ocular Response Analyzer (ORA), Optical Coherence Tomography (OCT), and Pachymeter to obtain the intraocular pressure (IOP): Goldmann-correlated IOP (IOPg) and Corneal Compensated Intraocular Pressure (IOPcc); CCBP: Corneal Hysteresis (CH) and Corneal Resistance Factor (CRF); corneal geometric parameters: corneal curvature radius (CCR) and central corneal thickness (CCT).

Results

The IOP of the rabbits changes slightly from 3 to 7 months of age, while it significantly decreases from 7 to 18 months of age and increases from 18 to 24 months of age; CH and CRF decrease with the increase of age; CCT increases from 7 to 18 months and decreases from 3 to 7 months of age and from 18 to 24 months of age; CCR presents an upward trend from 3 to 18 months and a significant decrease between 18 and 24 months of age.

Conclusion

CH and CRF are negatively correlated with age. CCT and CCR are positively correlated with age.

Measurement of and Factors Associated with the Anterior Chamber Volume in Healthy Chinese Adults

Purpose. To measure the anterior chamber volume (ACV) and determine factors associated with the ACV in healthy Chinese adults. Methods. In this cross-sectional study, we used swept-source optical coherence tomography (SS-OCT) to measure ACV and other anterior segment parameters. Factors associated with ACV were also determined. Results. A total of 313 healthy Chinese adults were enrolled. The anterior segment parameters, including ACV, could be measured by SS-OCT with excellent repeatability and reproducibility. There was a significant difference between the horizontal and vertical anterior chamber widths (ACW) (P < 0.05), with a mean difference of 390 μm. The ACV (mean 153.83 ± 32.42 mm³) was correlated with most of the anterior segment parameters, especially anterior chamber depth (ACD), which accounted for about 85% of the variation of ACV. Most of the anterior segment parameters were significantly correlated with age, and the relative changes in ACV and ACD were greatest in subjects aged 41–50 years. Conclusion. ACV was correlated with most of the anterior segment parameters measured in this study, particularly ACD. The relatively large difference between horizontal and vertical ACW suggests that the ACV could and should be measured using multiple OCT scans.

Relationship among Corneal Biomechanics, Anterior Segment Parameters, and Geometric Corneal Parameters

Purpose. To investigate the relationship between corneal biomechanical parameters, anterior segment parameters, and geometric corneal parameters in a healthy Caucasian group. Methods. This retrospective study included the healthy eyes with best corrected visual acuity of at least 20/40 of 122 Caucasian subjects. The anterior segment parameters and geometric corneal parameters such as corneal volume, central corneal thickness, horizontal and vertical corneal radii, anterior and posterior steep, and flat keratometric values were measured with a Scheimpflug camera. The biomechanical properties were measured with Ocular Response Analyzer. Results. One hundred and twenty-two healthy Caucasian subjects (67 males, 55 females) with a mean age of 45.32 ± 20.23 were enrolled. Both corneal hysteresis and corneal resistance factor were positively correlated with CCT (r = 0.529, p < 0.001; r = 0.638, p < 0.001) and CV (r = 0.635, p < 0.001; r = 0.579, p < 0.001) and negatively correlated with age (r = −0.373, p < 0.001; r = −0.249, p < 0.001). Both in age-gender and multivariate models, CH and CRF had statistically significant negative association with the posterior steep K value. Conclusions. CH and CRF are negatively correlated with posterior steep and average posterior K values.