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Christopher M Pruet, Arash Kazemi, Xiaoming Zhang, Jay W McLaren, Arthur J Sit; Relationships between Axial Length and Ocular Biomechanical Properties. Invest. Ophthalmol. Vis. Sci. 2016;57(12):3553.
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© ARVO (1962-2015); The Authors (2016-present)
Glaucoma is associated with increased axial length and myopia, but it is not known if this is because of unique biomechanical properties of longer eyes. In this study, we investigated the relationships between axial length and ocular rigidity, Young’s modulus of the cornea, intraocular pressure (IOP), and other biomechanical variables.
Axial length was measured by ultrasonography in 28 eyes from 14 healthy participants (ages 34.3±10.7 years, mean±SD), and IOP was measured by Goldmann applanation tonometry (GAT) in the sitting position. Ocular rigidity was estimated from the Friedenwald equation and IOP measured by pneumatometry in the sitting position, and in the supine position with and without a 10-gram weight added to the tonometer probe. Corneal hysteresis, the corneal resistance factor, and cornea-corrected IOP were measured by using the Ocular Response Analyzer (ORA, Reichert). Central corneal thickness was measured from Scheimpflug images (Pentacam HR, Oculus). Young’s modulus was determined by measuring the wave propagation in the cornea using the surface wave elastography. The wave propagation in the eye was generated noninvasively for 0.1 seconds at 100 Hz by using a handled device on the closed eyelids. The relationships between axial length and other variables were explored by Pearson correlation for right eyes.
Axial length was 24.2±1.2 and 24.1±1.2 mm for right and left eyes respectively, ocular rigidity was 0.024±0.005 and 0.025±0.004 mmHg/µL, IOP by GAT was 15.3±2.4 and 15.0±2.4 mmHg, and the corneal Young’s modulus was 752±115 and 713±141 kPa. Axial length was correlated with ocular rigidity (r=-0.70, p=0.006 right and r=-0.68, p=0.007 left). Axial length was not correlated with measurements from the ORA, Young’s modulus of the cornea, IOP, or central corneal thickness (p>0.08).
The strong negative correlation between ocular rigidity with axial length is consistent with published invasive measurements of ocular rigidity and estimates of rigidity based on Schiotz tonometry. In healthy eyes, corneal elasticity is not related to axial length, suggesting that the increased glaucoma risk associated with myopia is not related to unique corneal biomechanical properties in long eyes. Further research is needed to determine if scleral elasticity is altered with glaucoma.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Ocular rigidity vs. Axial length. p<0.008
Corneal Young's modulus vs. Axial Length. p>0.08.
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