Noninvasive measurement of scleral stiffness and tangent modulus in porcine eyes.
OBJECTIVE
We investigated an indentation technique to measure the scleral stiffness and tangent modulus of porcine eyes.


METHODS
The scleral load-displacement responses were measured with a universal testing machine as a function of IOP in 15 porcine eyes ex vivo using a 5-mm diameter cylindrical flat-punch indenter. The scleral radius of curvature and scleral thickness were measured using a DSLR camera (Alpha 900) and a camera-mounted stereomicroscope (M205C), respectively. The relationships between scleral stiffness, tangent modulus, and IOP were examined.


RESULTS
The mean local scleral radius of curvature and scleral thickness were 7.86 ± 0.49 and 1.03 ± 0.14 mm, respectively. The average scleral stiffness and scleral tangent modulus of porcine eyes were 0.13 ± 0.02 N/mm and 0.20 ± 0.04 MPa at 15 mm Hg, respectively. The scleral stiffness and scleral tangent modulus were correlated positively with IOP (scleral stiffness, 0.989 < r < 0.999, P < 0.001; scleral tangent modulus, 0.989 < r < 0.999, P < 0.001).


CONCLUSIONS
The scleral indentation technique can provide a noninvasive approach to measure scleral stiffness and tangent modulus.
Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology, Hong Kong, People's Republic of China.
Leo K K
LK
Leung
Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology, Hong Kong, People's Republic of China.
Match W L
MW
Ko
Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong, People's Republic of China.
Cong
C
Ye
Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology, Hong Kong, People's Republic of China.
David C C
DC
Lam
Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong, People's Republic of China.
Christopher K S
CK
Leung
D000818:Animals; D004195:Disease Models, Animal; D004548:Elasticity; D005901:Glaucoma / Q000473:pathology / Q000503:physiopathology*; D007429:Intraocular Pressure; D009216:Myopia / Q000473:pathology / Q000503:physiopathology*; D015203:Reproducibility of Results; D012590:Sclera / Q000473:pathology / Q000503:physiopathology*; D013552:Swine; D041623:Tomography, Optical Coherence; D058609:Visual Field Tests / Q000379:methods*
glaucoma; myopia; noninvasive measurement; sclera; tangent modulus