Location and pressure dependent transmission of human and porcine sclera: an anterior to posterior examination.

PURPOSE

For diaphanoscopy or transscleral laser applications, the transmission of the sclera is an essential property. The study aimed to determine the pressure dependent transmission of human sclera from anterior to posterior.

METHODS

Pressure dependent transmission measurements were performed by a pressure inducing setup at the range of 60-2058 kPa. The transmissions were measured within spectral range of 350-1100 nm. Specimens of human sclera were taken from corneo-scleral transplants. Those compounds were obtained at pars plicata residual sclera tissue. For an anterior to posterior examination of transmission, samples were taken from halved eye globes, which were formerly fixed in formalin.

RESULTS

The pressure dependent transmission increased with rising load at all measured wavelengths for human sclera samples. The highest increase was observed for short wavelengths. With rising pressure, the increase of transmission aimed for a steady state. This behavior was fitted by a limited growing function. With an inducing burden of 2058 kPa, the steady state was already reached and exhibited an increase in transmission factor of 4.1 at 400 nm and 1.8 at 1000 nm. The anterior to posterior measurements of human sclera fixed in formalin were not corresponding to the results of the other human samples. For the porcine samples, the transmission increased from anterior to the equator of the eye globe. Further posterior the transmission decreased and rose again to N. opticus. With rising pressure, the transmission increased at all wavelengths and all locations. Posterior from the equator, with higher pressure the transmission became superior compared to anterior.

CONCLUSIONS

The results of human sclera fixed in formalin could be related to formalin-induced cross-linking between the collagen fibers. Because of doubt about the physiological behavior of formalin-fixed samples, formalin-free porcine postmortem eye globes were also probed having a very similar thickness and histological structure as human sclera, so the results could be set in relation to human probes. These results can now be used to create an eye-map to determine maximum possible retina irradiation or illumination durations for transscleral applications in eye surgery.