Structure and Function of Lens Suture Examined by 2-photon Fluorescence Microscopic Imaging.

We have applied 2-photon fluorescence microscopy (2PFM) to investigate the structures and functions of mouse eye lenses, especially lens sutures, using wildtype (WT) and KLPH-KO suture-cataract lenses in vivo. Dynamic structures of lens sutures have been hypothesized to act as pathways carrying fluid containing ions, nutrients, and other factors as part of microcirculation for maintaining lens homeostasis and transparency. 3D imaging results show both typical "Y" and "double Y" shaped suture structures in WT lenses, diverse suture patterns including "star" shapes with variations appearing at different depths, and misaligned suture planes in KLPH-KO lenses. The variability in suture patterns, quantified using the mean of image stacks' similarity indices (SSIM) to the mean projection of the stack, reveals a significant increase (p<0.05) in pattern randomization for KLPH-KO lenses. Both WT and KLPH-KO lenses exhibit voids around sutures and enlarged vacuoles throughout the lens structure in vivo. Pathological features like irregular and larger central voids containing 2~5-μm-diameter amorphous structures that might result from membrane protein remnants/aggregates in the KLPH-KO mouse eye lens were observed. In conclusion, this work provides new morphological markers for characterizing suture cataract and fiber pathological features. Lens sutures are stabilized structures that are impermeable to dyes, and the extracellular spaces of lens peripheral fibers provide efficient diffusion pathways for lens microcirculation.