Linking Microstructure to Mechanics in ICG-Stained Lens Capsules: Insights from Nanoindentation to Electron Microscopy

Purpose To explore the reasons for the mechanical changes of the lens capsule after indocyanine green (ICG) staining through microstructure alterations.Methods A total of 40 anterior capsules were obtained during cataract surgery. Two bands of the same size were prepared for each capsule. One was stained with ICG for 10 s (Group 1) or 1 min (Group 2), and the other was used as a control. The mechanical property measurement was carried out using a nanoindentation instrument. The other anterior capsules were subjected to ultrastructural analysis using scanning electron microscopy and transmission electron microscopy.Results The average elastic modulus and the average hardness of capsule fragments in Group 1 had no significant change after staining. There were significant differences in the average elastic modulus (4.48 ± 0.75 GPa vs.4.08 ± 0.49 GPa, p = 0.04) and average hardness (0.19 ± 0.03 GPa vs.0.15 ± 0.02 GPa, p = 0.01) of capsule fragments after staining in Group 2. Electron microscope observation showed that the cells were swollen, the mitochondrial outer membrane was broken, part of the endoplasmic reticulum was vacuolized, the surface fibers of the capsule were disordered, and the fiber structures were fused and rigid after ICG staining.Conclusions ICG staining significantly affects the mechanical properties and ultrastructure of the human lens capsule. The alteration of the fiber structure on the surface of the capsule might be the cause of the mechanical changes in the capsule.