Biomechanical changes in the anterior lens capsule after trypan blue staining

To examine the effect of trypan blue staining on the biomechanical behavior of the porcine anterior lens capsule.

Department of Ophthalmology, Technical University of Dresden, Dresden, Germany.

Fifty-five anterior lens capsules from porcine cadaver eyes were used. Two parallel 8.0 mm x 4.0 mm large capsule strips were prepared from each capsule. After trypan blue staining for various time intervals combined with exposure to white light (6000 lux) or with no light exposure, biomechanical stress-strain measurements were performed using an automated material tester. Untreated specimens and specimens treated with glutaraldehyde 0.1% were used as controls. The absorption spectrum of trypan blue 0.1% solution and the emission spectrum of the light source were measured.

After treatment with light and trypan blue, at 25% strain, there was a statistically significant increase in stress of up to 70.1% and in elastic stiffness of 47% and a decrease in the ultimate mechanical strain of up to 13%. There were no biomechanical changes in capsules with trypan blue staining in the absence of light or after a short illumination time of 30 seconds, indicating a light-dependent process. After 30 minutes of glutaraldehyde 0.1% treatment, there was an increase in stress of 321.6% at 25% strain and a decrease in the ultimate strain of 47.6%. The emission spectrum of the light source included the absorption peak for trypan blue at 580 nm.

Trypan blue staining of the lens capsule combined with light irradiation for at least 1 minute led to an increase in elastic stiffness at 25% strain and a reduction in the ultimate extensibility. This effect is probably due to the photosensitizing action of trypan blue, leading to light-induced collagen crosslinking of the capsule collagen similar to age-related crosslinking. Nucleus expression might be impeded by the increased capsule stiffness. Continuous curvilinear capsulorhexis is facilitated.