Elastic hysteresis in human eyes is an age-dependent value

The elastic hysteresis phenomenon is observed when cyclic loading is applied to a viscoelastic system. The purpose of this study was to quantitatively evaluate elastic hysteresis in living human eyes against an external force.

Prospective case series.

Twenty-four eyes of 24 normal human subjects (mean age: 41.5 ± 10.6 years) were recruited.

A non-contact tonometry process was recorded with a high-speed camera. Central corneal thickness, corneal thickness at 4 mm from the centre, corneal curvature and anterior chamber depth were measured. Intraocular pressure was also measured using Goldmann applanation tonometry and dynamic contour tonometer.

Energy loss due to elastic hysteresis was calculated and graphed.

The mean central corneal thickness was 552.5 ± 36.1 µm, corneal curvature was 7.84 ± 0.26 mm and anterior chamber depth was 2.83 ± 0.29 mm. The mean Goldmann applanation tonometry-intraocular pressure was 14.2 ± 2.7 mmHg and dynamic contour tonometer-intraocular pressure was 16.3 ± 3.5 mmHg. The mean energy loss due to elastic hysteresis was 3.90 × 10(-6) ± 2.49 × 10(-6) Nm. Energy loss due to elastic hysteresis correlated significantly with age (Pearson correlation coefficient = 0.596, P = .0016). There were no significant correlations between energy loss due to elastic hysteresis and other measurements.

Energy loss due to elastic hysteresis in the eyes of subjects was found to positively correlate with age, independent of anterior eye structure or intraocular pressure. Therefore, it is believed that the viscosity of the eye increases with age.