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Arun Kumar Narayanaswamy, Nai Mui Hoon, Chwee Teck Lim, Tin Aung; Young’s Modulus Determination of Normal and Glaucomatous Human Irides. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):6139. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the biomechanical properties (Young’s modulus) of normal (control) and glaucomatous human iris using atomic force microscopy (AFM)
Iris tissue obtained from 18 glaucomatous subjects (9 eyes each with Primary open angle and angle closure glaucoma) and 5 normal subjects undergoing elective eye surgery were subject to estimation of Young’s modulus by atomic force microscopy (AFM). Force measurements were carried out at room temperature using Nanowizard II BioAFM (JPK instruments AG, Germany). The iris samples were immersed in the liquid media (Phosphate-Buffered Saline, PBS with 0.1 % Bovine Serum Albumin, BSA) during force measurements. The probe consisted of a 4.5 μm diameter polystyrene bead attached to a silicon nitride cantilever (Novascan Technologies, Inc., Ames, IA). The spring constants of the cantilever used was determined by the thermal tune method 13 and was typically in the range of 0.03 ± 0.003 N/m. A maximum force of 3 nN and loading rate of 5 μm/s were applied. A hundred force-distance curves in an area of 10 μm x 10 μm and an average of 15 reference areas from each sample were used to estimate the modulus values. Young’s modulus values were calculated for each recorded curve using JPK Data Processing Software (JPK instruments AG, Germany), which employs a Hertz model for spherical indenters (diameter 4.5 μm; Poisson ratio 0.5) fitted to the extend curves.
The iris from the normal controls had the least modulus (0.85 ± 0.31 kPa) while iris from PACG patients had the highest modulus (2.4 ± 0.82 kPa). The modulus of PACG iris was significantly higher (p < 0.05) compared to the normal controls and POAG iris. However, there was no significant difference in the modulus of POAG iris (1.13± 0.36 kPa) compared to the normal controls.
PACG iris were stiffer compared to POAG and normal control iris which could be due to variations in the composition of extracellular matrix proteins and this needs further evaluation.Variations in biomechanical properties of iris may have a significant role in the pathogenesis of angle closure glaucoma.
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