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Blades không bao giờ được tái sử dụng, trừ khi được thiết kế để sử dụng bởi nhà sản xuất rõ ràng. Nó đã được chứng minh lưỡi ngu si đần độn sản xuất cánh tà mỏng hơn và làm tăng nguy cơ của đột xuất cánh tà (5,6). Nhiều trung tâm cho phép cùng một lưỡi dao được sử dụng trên cả hai mắt cùng một bệnh nhân | 194 Lahners and Hardten vary from unit to unit and poor quality blades should uniformly be rejected and replaced. Blades should never be reused unless expressly designed for such use by the manufacturer. It has been shown that dull blades produce thinner flaps and increase the risk of irregular flaps 5 6 . Many centers allow for the same blade to be used on both eyes of the same patient but not more than this. Even in this usage it has been demonstrated that the second flap cut is somewhat thinner than the first 6 . C. GUIDELINES FOR LASER SETTINGS It is a popular misconception that lasers are computer-controlled devices that are incapable of producing a less than perfect outcome. In reality these devices while capable of great accuracy must be carefully maintained and calibrated to achieve proper performance. When setting up the excimer laser the following parameters merit special attention laser room environment fluence testing and beam homogeneity. The laser room environment is an important variable that must be controlled. The room should be kept cool for optimal laser performance. This varies from laser to laser but a temperature of 18 to 24 degrees Celsius should be maintained. The ambient humidity should be kept low 40 to 50 relative humidity and as steady as possible. Humidity can significantly affect the ablation rate of corneal tissue with overcorrections more likely in very dry conditions and undercorrections more likely in more humid conditions 13 . The room should be kept free from particulate debris which can adversely affect ablation regularity if it is deposited on the optical system of the laser. This can be achieved with an active filtration system using a HEPA high efficiency particulate air filter. These systems are capable of removing particles as small as 0.1 micron including bacteria. The system should be in operation continuously as shutdown periods will allow particulate matter to coat the optics of the laser system. Laser fluence is a .
