# Behavior of Generated Gas during Femtosecond Laser Lens Irradiation in Porcine Cadaver Eyes
## 4 Discussion  
The present results suggest that femtosecond laser lens irradiation generates gas that expands towards the posterior capsule in conjunction with the amount of laser energy, which subsequently leads to the expansion of the posterior capsule. Although the sample size was small, the reason for not finding correlation between ACD change ratio and the amount of laser irradiation energy may be related to the fact that gas distribution is predominantly on the posterior capsule side, and the difference in distensibility between anterior and posterior capsules. During laser irradiation, generated gas causes an increase in the IOP by raising the lens capsule's internal pressure, with the increase in the IOP dependent on the amount of the laser energy [5]. The increases in the lens capsule's internal pressure caused by the generated gas can lead to intraoperative CBS. Although the laser irradiation settings used in this experiment were within the range that can be set in usual surgery, as the amount of laser energy increased, this led to an excessive amount of generated gas and potential ruptures in the capsule due to the occurrence of CBS during laser irradiation. Therefore, laser irradiation needs to be set at a level that avoids the generation of excessive gas. In addition, careful attention needs to be paid to intraoperative CBS avoidance to prevent pressure-handling issues that can occur in procedures such as hydrodissection, in which there could be an increase in inner lens capsule pressure after laser irradiation [3, 6, 7]. This study focused on the behavior of gas found inside the lens capsule, which is the visible part of the generated gas, along with examining its influence on the lens capsule. However, pH acidification occurs in the aqueous humor due to the invisible part of the gas (carbon dioxide) [8]. This finding suggests that FLACS may influence ocular tissue due to currently unknown chemical changes and generated substances [9]. Since these changes are not reported for conventional cataract surgeries, additional investigations into these issues need to be undertaken. There are several limitations in this study. First, it is possible that the size of the crystalline lens of the porcine eye may not be the same for individuals, and between the left and right eyes. However, it is difficult to accurately measure changes in lens diameter before and after laser irradiation, as laser crystalline lens irradiation by a clinical FLACS device cannot be performed after extracting a crystalline lens and accurately measuring the lens diameter. Second, in order to observe the extracted lens in this experiment, lens fragmentation was performed without performing anterior capsulotomy. If anterior capsulotomy had been performed, the behavior of the gas and the amount of energy that causes the capsule to burst might have been different from that observed in the actual experiment. However, since a large amount of the gas was distributed towards the  
Figure 7: Although the laser irradiation caused significantly longer average equatorial perimeter, there was no correlation with the amount of laser irradiation energy. (**a**) Box-plot diagram showing mean values of equatorial perimeter length in control lens and laser-irradiated lens. Boxes, interquartile range (difference between upper 75% and lower 25% quartiles); thick black lines, median; whiskers, highest and lowest values that were not outliers or extreme values. There was significant difference between these two groups (\(p=0.001<0.05\)). (**b**) No correlation was found between amount of laser irradiation energy and equatorial perimeter of laser-irradiated lens (\(p=0.899>0.05\)). back during actual clinical FLACS in combination with anterior capsulotomy and lens fragmentation, the phenomenon in this experiment was not wrong as a whole. In summary, femtosecond laser porcine lens irradiation generated gas in the lens, with the extent of this increase dependent on the amount of laser irradiation energy.