Purpose:
Recent studies have shown that the scleral biomechanics has an important role for the progression of glaucoma, and is related to the structure of collagen fibers in the sclera. Since the birefringence of collagen fiber is sensitive to the density of collagen fibrils and arrangement of collagen fibers, the ultrastructural and biomechanical characteristics of the sclera are closely related to scleral birefringence. In this study, we investigate the birefringence of the sclera at the anterior segment of the human eye in vivo using polarization-sensitive optical coherence tomography (PS-OCT) and its relationship to standard ocular biometric parameters, which are known as the risk factors of glaucoma.
Methods:
Twenty-one left eyes of healthy human subjects without marked disorder were measured. The refractive power and axial eye length were measured with an autokeratorefractometer (RT-7000, Tomey Corp.) and optical biometer (IOL Master, Carl Zeiss Meditec), respectively. The birefringence of the sclera at a region superior to the cornea was measured by a custom-made prototype PS-OCT. Subsequently, the IOP was measured using Goldmann applanation tonometer.
Results:
Figure 1 (a), (b), and (c) show the plots of birefringence and spherical equivalent, axial eye length, and IOP, respectively. Statistically significant correlation was found between the birefringence and the IOP (two-sided test using Pearson’s correlation coefficient, r = -0.63, p = 0.002). Spherical equivalent and axial eye length did not show statistically significant correlations with the birefringence of the sclera.
Conclusions:
The scleral birefringence of normal eyes had a negative correlation with the IOP. Considering the structural source of the birefringent tissues, this result would indicate that the sclera of healthy eyes with relatively high IOP had low-dense collagen fibrils or irregular orientations of the collagen fibers.
Keywords: sclera • stress response • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)