DW induced cell rupture in hypoosmotic conditions, which could theoretically reduce the survival ratio of LECs. A previous study showed that the LECs exposure to DW for 1 min were markedly swollen with grossly morphologically intact cell membranes, and approximately 2 mins of exposure to DW, the complete cell lysis could be obtained17. Another study suggested that exposure to DW for 1 min, the LECs kept intact, cell membranes markedly swollen, and by 2 mins, no intact cells were visible18. Regrettably, no quantitative analysis was performed in the 2 studies of Crowston et al., the results were observed under microscope.
In this study, quantitative analyses and accurate calculations of the LECs density, the LECs death number, and the LECs mortality were conducted to obtain more precise results by trypan blue-eosin staining and photographing under a microscope19, which could provide a more comprehensive assessment of the effects of DW on LECs viability and clearance. The density of cell population in cataractous lenses varied greatly. The mean number was around 4000/mm2, but there were lenses with even lower cell counts20. In the negative control group of our study, the LECs density was 3829.08±519.16 mm2, which was similar to the conclusion of the study of Laspias et al.20. Therefore, our calculation method could be considered reliable.
Quantitative analysis showed that the LECs mortality was 70.05% in DW immersion for 3 mins, which was 2.35 times higher than that in DW immersion for 1 min. This result was similar to that of Rękas et al.21. There was 70.8% cytolytic destruction of LECs after 3-minute exposure to DW, which was 3.5 times higher than 1-minute exposure to DW21. We also set a negative control group, as well as BSS group acting for the same treatment time, to compare with the DW group. The result suggested that soaking in DW for 2 or 3 mins could effectively cause LECs death, and the effect of DW immersion for 3 mins was better. Naturally, there were different study findings. In the study of Duncan et al., there was 50% cell survival after FHL124 cells exposed for 2 minutes to DW22. This could be due to the different materials and different counting methods. In the study of Rabsilber et al., it suggested that using DW was unable to reduce PCO development significantly23, which was different from ours. This might be caused by the insufficient acting time of DW.
During cataract surgery, the whole capsular bag should be rinsed with irrigation/aspiration (I/A) to remove the lens cortex and viscoelastic agent. Therefore, it might be considered to introduce DW into the capsule combined with stimulated I/A, which could not only fully exploit the capacity of DW to destroy cells, but also the neutrality against DW and clear the LECs with loosened junctions to capsule. In this study, BSS at the height of 70cm was used to rinse the capsule for 1 minute to simulate I/A during the cataract surgery. Results indicated that DW immersion combined with rinse contributed to LECs clearance, and the most effective exposure time was 3 mins. Some research suggested that 360-degree anterior capsular polishing alone was unable to reduce the incidence of PCO24, meaning that mechanical anterior capsular polishing alone was unable to clear all LECs in the capsular bag. Our results indicated that rinsing combined with exposure to hypotonic DW could effectively clear LECs.
To minimize the side effects on intraocular tissues, additional protective measures might be necessary. The sealed capsule irrigation (SCI) was designed to temporarily seal the capsular bag to allow drug injection and saline flush to protect the intraocular tissues8. Rękas et al. infused DW in SCI for 3 mins after the removal of cortical material and rinsed the intracapsular space with 0.9% NaCl25. They recognized that DW irrigated for 3 mins reduced PCO in the long-term follow-up, which was more effective than anterior capsule mechanical cleaning25. After nucleus removal and cortical aspiration, Zhang et al. filled the anterior chamber with a continuous infusion of sterile air, and then injected DW or BSS into the capsule for 3 mins and followed by irrigating the capsular bag with BSS with the assistance of vitrectomy machines13. It was found that the technique could significantly prevent capsular fibrosis and PCO13. However, SCI was inapplicable to patients with deep anterior chamber or a small pupil23, and unsuitable to microincisional (1.8 mm or 2.2 mm) cataract surgery13. What’s more, additional surgical techniques and equipment were necessary in the forementioned methods, which limited their popularized. DW combined with rinse could effectively remove LECs to prevent the occurrence of capsule opacification after cataract surgery, but how this technique could be applied in the clinic still needed further exploration.
Cell death exists in many different forms, such as necrosis, apoptosis, necroptosis, pyroptosis, and autophagy. Necrosis, a common form of pathological cell death, can be identified via hitstopathologic changes in both nuclei and cytoplasm. Our results suggested that soaking in DW not only induced LECs death, but also contributed to LECs clearance. We further considered how the LECs might change as soaking in DW, and cytological observations were carried out on treated LECs. HE staining showed cytolytic destruction and partial shedding of LECs in DW immersion for 2- and 3-mins subgroups. In the study of Rękas et al., basement membrane and LECs were occasionally seen in the specimens prepared for microscopic examination21. The results were the same as our light microscopic results. TEM results showed LECs destruction in DW immersion group, loose junctions between cells and capsule in DW immersion for 1- and 2-mins subgroups, and partial separation of LECs from capsule in DW immersion for 3-mins subgroup. The lysis and rupture of the cell membrane, another symbol of necrosis, could be found in our HE staining and TEM results. Therefore, it can be concluded that DW can cause LECs death via necrosis. Our results suggested that DW could not only cause LECs death, but also loosen the junctions of cells with the capsule, which could shed LECs from capsule partially. Therefore, the shedding percentage of cells increased after soaking in DW. All the above histocytological findings were in agreement with the differences of LECs shedding percentage shown by trypan blue-eosin staining.
Nevertheless, the present study still had some limitations. First, DW could cause LECs death but not enough to kill all LECs. Considering DW frequently was used as a solvent, we did not know whether the trial for combining with other drugs to destroy LECs more fully could have been attempted24. Second, although DW combined rinse was effective on cell shedding but couldn’t make all cell shedding. To this point, part of the reason lied in the fact that partial folding led to some LECs failing to be cleared when the capsule was rinsed with BSS. Third, LECs of anterior capsules were studied in this study, while the cellular morphology and function of LECs of the anterior and equatorial lens capsules were not the same26. Therefore, further animal experiments were necessary to explore the clearance effect of DW on LECs of the equatorial lens capsule. The histopathological changes of treated LECs with DW indicated cellular necrosis, which suggested that there were other operative mechanisms of DW aside from the hypoosmotic mechanism. All these aspects await further investigation.
It was concluded that DW immersion can cause LECs death and DW immersion combined with rinse was an effective method to remove LECs. The histopathology changes of treated DW suggested cellular necrosis was one type of cell death. All of these provided theoretical grounding for preventing lens capsule opacification after cataract surgery via DW.