Abstract
Purpose :
To investigate the age dependence of the Brillouin frequency shift in the central cornea in vivo in healthy subjects at 780 nm optical wavelength.
Methods :
Brillouin measurements were made in the central corneas (< 2 mm from the pupil center) of 102 healthy eyes (Caucasian origin, 68 subjects, 49% female, aged 29-82 years, with mean 48 ± 16 years) with a clinically-viable Brillouin imaging system. Inclusion criterion is normal appearing corneas, with less than ± 3 diopters refractive correction, normal corneal topography (no irregular bow-tie, no skewed axis, no scar or other irregularities), and no history of eye diseases, except presbyobia and/or cataract. Eyes that underwent corneal surgery or eyes with pathologies of the anterior ocular segment were not included. Measurements were taken at room temperature (20 – 24°C), with a laser power of 5 mW on the cornea surface. Axial scans over a range of 1.2 mm with a step size of 30 μm were conducted. The Brillouin shift measured in the anterior stroma was averaged over 5 axial scans.
Data analysis was performed with Prism 6.1 (GraphPad software, La Jolla, California, USA).
Results :
The mean Brillouin frequency shift across all ages was 5.726 GHz (SD = 0.015 GHz). Despite significant intersubject variation, a trend towards increasing Brillouin shift with age was observed, with a rate of increase of about ~ 5 MHz/decade (r2 = 0.23), which implies viscoelasticity increase of corneal tissue with age in humans.
Conclusions :
Although the person-to-person variation is large, we observe a pattern of rising Brillouin frequency shift at 780 nm optical wavelength with age, which suggests growing corneal stiffness. This trend is consistent with prior in vitro studies showing a stiffening effect with age in ex vivo human corneas via direct stress-strain measurement (A. Elsheikh et al., CER 32(1), 2007).
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.