Vital dyes may increase lens capsule stiffness

This experimental study found that staining with brilliant blue, indocyanine green (ICG) and trypan blue significantly increases the stiffness of the human lens capsule.

The authors used atomic force microscopy to assess potential changes in lens capsule stiffness after staining using brilliant blue, ICG and trypan blue in commercially available concentrations.

Human lens capsules were obtained during routine cataract surgery after a curvilinear capsulorhexis was created using a bent needle. The 15 lens capsules were immediately placed in a balanced salt solution and handed over to a technician. They were then dissected into 7 wedge-shaped parts. Three fragments were stained with brilliant blue 0.025%, ICG 0.05% or trypan blue 0.06% for one minute. Another three specimens were additionally illuminated using a standard light source. The seventh part served as an untreated control.

Tissue stiffness increased after staining using brilliant blue, ICG and—to a lesser degree—trypan blue. Illumination using a standard surgical light source did not increase the mechanical properties of the lens capsule in a statistically significant manner. However, the observed increase in stiffness was quite consistent for all three dyes tested, with an increase of approximately 1.2-fold.

They write that the rim of a capsulorhexis after a curvilinear capsulorhexis created on a stained anterior capsule may be more stable than on an unstained capsule. Therefore, in addition to improved contrast, the increased mechanical properties of the stained anterior capsule may contribute to successful cataract surgery in complex cases, such as in eyes with white cataract with liquefied cortex.

They also note that the increase in lens capsule stiffness differed between the dyes; thus, it might be interesting to use dyes that provide a more pronounced stiffening effect in situations in which increased tissue stiffness may be helpful. Nevertheless, one may hypothesize that increased stiffness of stained tissue might be disadvantageous in other surgical interventions, such as posterior lamellar keratoplasty, where trypan blue is used during the preparation of the donor tissue.