Illumination matters part I: comparative analysis of light sources and illumination in flexible ureteroscopy-fundamental findings from a PEARLS analysis

Purpose Illumination characteristics of flexible ureteroscopes have been evaluated in air, but not in saline, the native operative medium for endourology.

The aim was to evaluate light properties of contemporary ureteroscopes in air versus saline, light distribution analysis, and color temperature.

Methods We evaluated the Storz Flex-Xc and Flex-X2s, Olympus V3 and P7, Pusen 7.5F and 9.2F, and OTU WiScope using a 3D printed black target board in-vitro model submerged in saline.

A spectrometer was used for lux and color temperature measurements at different opening locations.

Results Illuminance was higher in saline compared to air (5679 vs. 5205 lx with Flex-Xc, p = 0.02).

Illuminance in saline differed between ureteroscopes (ANOVA p < 0.001), with highest for the Flex-Xc at 100% brightness setting (5679 lx), followed by Pusen 9.2F (5280 lx), Flex-X2s (4613 lx), P7 (4371 lx), V3 (2374 lx), WiScope (582 lx) and finally Pusen 7.5F (255 lx).

The same ranking was found at 50% brightness setting, with the highest ureteroscope illuminance value 34 times that of the scope with lowest illuminance.

Most scopes had maximum illuminance off center, with skewness.

Three scopes had two light sources, with one light source for all other scopes.

Inter-scope comparisons revealed significant differences of color temperature (ANOVA p < 0.001).

Conclusion The study demonstrates the presence of inhomogeneous light spread as well as large differences in illumination properties of ureteroscopes, possibly impacting on the performance of individual scopes in vivo.

Additionally, the study suggests that future studies on illumination characteristics of flexible ureteroscopes should ideally be done in saline, and no longer in air.