Abstract
PurposeTo investigate the relationship between scleral mechanical properties, its birefringence, and the anisotropy of birefringence alteration in respect of the direction of the strain by using PS-OCT.MethodsThe scleral birefringence of thirty-nine porcine eyes was measured with a prototype PS-OCT. A rectangle strip of sclera with a width of 4 mm was dissected at the temporal region 5 mm apart from the optic nerve head. The strain and force were measured with a uniaxial tension tester as the sample was stretched with a speed of 1.8 mm/min after preconditioning. The birefringence of the sample was measured by PS-OCT at the center of the sample before applying, denoted as inherent birefringence, and after applying stretching of 6.5% strain. The birefringence alteration was obtained by these two measurements and correlations between birefringence and elastic parameters, tangent modulus, and structural stiffness were examined. Twenty and 19 porcine eyes were stretched in meridional or equatorial directions, respectively.ResultsA moderate positive correlation was found between the inherent birefringence and the structural stiffness. A moderate positive correlation was also found between the inherent birefringence and the tangent modulus. The birefringence increased by strains. Marginal significance was found in the birefringence alteration between meridional and equatorial strains, where the mean birefringence elevation by meridional strain was higher than that by equatorial strain.ConclusionsThe birefringence was found to be altered by applying strain and also be related with inherent birefringence. This implies the birefringence of the sclera of the in vivo eye also could be affected by its mechanical property.
Highlights
Glaucoma is the second leading cause of blindness in the world[1]
The diagnosis of glaucoma is based on characteristic optic nerve cupping which corresponds with the visual field defect
A moderate positive correlation was found between the inherent birefringence and the structural stiffness (Pearson’s correlation coefficient, r = 0.48, P = 0.033 for meridional, and r = 0.50 and P = 0.028 for equatorial strain)
Summary
Glaucoma is the second leading cause of blindness in the world[1]. It is a progressive optic neuropathy due to loss of retinal ganglion cells and the retinal nerve fiber layer that comprises axons of these cells, and is characterized by optic nerve damage and typical visual field loss [2]. Because glaucoma damage is irreversible, early detection and appropriate management of progressive changes are the best ways to prevent loss of visual function. In the diagnosis of glaucoma, structural loss can precede detectable functional loss by up to 5 years [4], and the glaucomatous retinal nerve fiber layer defect can be detected morphologically by redfree fundus photographs earlier than white-on-white visual field defects [5]
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