Evaluation of the human anterior lens capsule elastic modulus and morphology in different types of cataracts by using nanoindentation

To evaluate and compare the elastic modulus, hardness and mechanical propertiesof the human anterior lens capsule in different types of cataract patients by using nanoindentation device and also to investigate the corelationof these measurementswith patient age. Also capsule thickness was measured by using scanning electron microscope (SEM)to investigate the influence of age, pseudoexfoliation and trypan blueon capsule thickness. The study evaluated 72 patients having cataract surgery between January 2014 and June 2014 at Baskent University Department of Ophthalmology. Patients were investigated in 3 groups. Group 1 consisted of24 patients with normal senile cataract, group 2 patients (n=24) had pseudoexfoliation syndrome and group 3 patients (n=24) had dye-enhanced cataract surgery(0,06% Blue Rhexis).The anterior lens capsules were removedby curvilinear capsulorhexis during routine cataract surgery.Capsules were analyzed by using CSM instrument nanoindentation tester device. Young's Modulus elasticty was measured by Oliver & Pharr method and capsulehardness by Martens Hardess method. In addition the thickness of the anterior lens capsule was measured with FEI Quanta 400F Scanning Electron Microscopy (SEM). There was no significant difference in 3 groups regarding age (p=0.997). The average capsule thickness measured by SEM was 18.19±2.18 µm in Group 1, 18.41±2.64 µm in Group 2 and 18.36±1.95µm in Group 3. In terms of capsule thickness,the difference between the 3 groups was not significant (p=0,975). Young's modulus measured by nano indentation test device with Oliver & Pharr method 7.53±1.07 Gpa in Group 1, 6.007±1.25 Gpa in Group 2 and 8.12±0.98 Gpa in Group 3. Capsules obtained from patients with pseudoexfoliation syndrome were significantly more elastic than the other two groups (p=0.000). Patients with intracameral trypan blue (TB)application (group3) revealed lower elasticity comparinge to the normal group (group1) but the difference was not statistically significant (p = 0.942). Mean capsule stiffnessvalues by Nano indentation device according to Martens Harness method were 326.41±98.40 Mpa for Group 1, 210,5±52.32 Mpa for Group 2 and 315.54±163.15 Mpa for Group 3. Capsule samples from pseudoexfoliation syndrome group displayed less stiffness comparing to the other two groups (p<0.01). There was no significant difference in mean capsule thickness in 3 groups measured by SEM. Capsule thickness displayed an increase correlated with increasing age in all groups. The anterior lens capsules of patients with pseudoexfoliation syndrome had more elasticity and less stiffness comparing to the other two groups. Intracameral TB applicationhad no effect on capsule elasticity and stiffness.