Image courtesy IntraLase.
图片由 IntraLase 提供。
Image courtesy IntraLase.
图片由 IntraLase 提供。
Figure 3. Photodisruption with a femtosecond laser.
图3.飞秒激光的光干扰。
Advantages of Mechanical Microkeratomes
机械显微角膜磨的优点
1. Proven history 1. 久经考验的历史Microkeratome technology is more than 20 years old (beginning with the ALK procedure) with many surgeons having performed thousands of procedures with very low complication rates.1,2 Femotsecond laser technology is a more recent development with clinical use approaching 9 years currently.
显微角膜刀技术已有 20 多年的历史（从 ALK 手术开始），许多外科医生已经以非常低的并发症率进行了数千次手术。 1,2 Femotsecond 激光技术是最近发展起来的，目前临床应用已接近 9 年。
2. Lower cost 2.成本更低Mechanical microkeratome systems are relatively inexpensive compared with a femtosecond laser system.
与飞秒激光系统相比，机械微型角膜刀系统相对便宜。
3. More efficient surgical flow
3. 更高效的手术流程Creation of a microkeratome flap typically takes less than 30 seconds from the time of suction-on to suction-off and is done just prior to the excimer ablation without moving the patient. The fourth-generation 60kHz IntraLase system typically requires about 30 to 45 seconds of suction-on time to create the flap (the laser portion of the flap creation takes only 15 to 20 seconds). Some excimer system designs, however, do not allow the same surgical bed to be used for the femtosecond laser flap creation and the excimer ablation. This necessitates moving the patient, sometimes between rooms, after the flap creation, before the excimer ablation, when the femtosecond laser is used.
从吸入到抽出，微型角膜膜皮瓣的创建通常需要不到 30 秒的时间，并且在准分子消融之前完成，无需移动患者。第四代 60kHz IntraLase 系统通常需要大约 30 到 45 秒的吸力时间来创建襟翼（创建襟翼的激光部分只需要 15 到 20 秒）。然而，一些准分子系统设计不允许使用相同的手术床进行飞秒激光皮瓣的创建和准分子消融。这需要在皮瓣创建后、准分子消融之前、使用飞秒激光时移动患者，有时在房间之间移动。
4. Ability to create flap in eye with anterior stromal opacity/scar
4. 能够在眼前质混浊/瘢痕中形成皮瓣A mechanical system can cut through opacities in many cases without difficulty or complication. Femtosecond laser flap creation is susceptible to vertical gas breakthrough in corneas with anterior stromal opacities or previous incisional surgery. This occurs because the gas that develops from cavitation following each laser pulse builds pressure and must escape from the cornea through the path of least resistance. A previous incision or scar anterior to the interface may represent the path of least resistance, thus leading to gas escaping to the surface of the flap in an undesirable location. Should this occur towards the center of the optical zone, consideration should be given to not lifting the flap. Once the cornea has healed, the surgeon can determine whether a mechanical microkeratome or a surface ablation is the most appropriate subsequent procedure. Use caution in setting a flap thickness less than 100 µm using the IntraLase as there is a higher chance of vertical gas breakthrough, even in the absence of scars/opacities evident at the slit lamp.
在许多情况下，机械系统可以毫无困难或复杂地消除不透明度。飞秒激光皮瓣的产生容易在前基质混浊或既往切口手术的角膜中发生垂直气体穿透。这是因为每个激光脉冲后空化产生的气体会产生压力，并且必须通过阻力最小的路径从角膜逸出。界面前方的先前切口或疤痕可能代表阻力最小的路径，从而导致气体在不需要的位置逸出到皮瓣表面。如果这种情况发生在光学区域的中心，应考虑不要抬起襟翼。角膜愈合后，外科医生可以确定机械显微角膜切术还是表面消融术是最合适的后续手术。使用 IntraLase 将皮瓣厚度设置为小于 100 μm 时要小心，因为即使在裂隙灯上没有明显的疤痕/混浊的情况下，垂直气体穿透的可能性也更高。
5. Potential for epikeratome epithelial flap creation
5. 表角膜上皮皮瓣的产生潜力Several mechanical microkeratome systems have auxiliary equipment that allows for automated epithelial flap creation or removal (eg, epi-LASIK). This type of epithelial flap creation is not possible currently with the femtosecond laser.
一些机械显微角膜切术系统具有辅助设备，可以自动创建或切除上皮瓣（例如，epi-LASIK）。目前，飞秒激光无法产生这种类型的上皮瓣。
6. Less inflammation induced
6.较少的炎症诱发Diffuse lamellar keratitis (DLK), sterile inflammation confined to the lamellar interface following LASIK, is quite rare with today’s sterilization protocols in LASIK using a microkeratome. Early generation femtosecond lasers required significantly higher energy settings to create the flap in a clinically acceptable time due to the lower repetition rate. This led to opaque bubble layer (OBL) formation and increased incidence of DLK following surgery, requiring higher dosing of more potent corticosteroid drops than what is typically used for LASIK using a microkeratome. In addition, occasionally patients would note transient light-sensitivity (TLS) around 2 to 6 weeks following surgery. The latest generation IntraLase system operates at 60 kHz. This increased speed allows for lower energy settings with smaller spot sizes and less induced inflammation, essentially resolving the DLK, OBL, and TLS issues. OBL that occurs with the 60 kHz system is of a lower magnitude, resolves more quickly, and does not appear to be associated with increased incidence of DLK.
弥漫性层状角膜炎 （DLK） 是 LASIK 术后局限于层状界面的无菌炎症，在当今使用显微角膜膜切术的 LASIK 绝育方案中非常罕见。由于重复率较低，早期飞秒激光器需要更高的能量设置才能在临床可接受的时间内创建皮瓣。这导致了不透明气泡层 （OBL） 的形成和手术后 DLK 的发生率增加，与通常使用显微角膜镜进行 LASIK 相比，需要更高剂量的更有效的皮质类固醇滴剂。此外，偶尔患者会在手术后 2 至 6 周左右注意到短暂性光敏 （TLS）。最新一代的 IntraLase 系统工作频率为 60 kHz。这种速度的提高允许更低的能量设置，更小的斑点尺寸和更少的诱发炎症，从根本上解决了 DLK、OBL 和 TLS 问题。60 kHz 系统发生的 OBL 幅度较小，消退速度更快，并且似乎与 DLK 发生率增加无关。
Advantages of Femtosecond Laser
飞秒激光器的优势
1. Fewer flap-related complications
1. 减少皮瓣相关并发症
Mechanical blade systems are susceptible to malfunction due to loss of power, jamming of mechanical parts, loss of suction during the pass, and operator error in use or assembly (improper assembly is mainly an issue with older mechanical systems). In addition, unusually shaped eyes are at risk for irregular flap creation. With very rare exceptions, these complications are either not possible to obtain or are clinically insignificant when using a femtosecond laser system.
机械叶片系统容易因功率损失、机械部件卡住、通过过程中的吸力损失以及操作人员在使用或组装中的错误而发生故障（组装不当主要是旧机械系统的问题）。此外，形状异常的眼睛有产生不规则皮瓣的风险。除了极少数例外，当使用飞秒激光系统时，这些并发症要么无法获得，要么在临床上无关紧要。
Incomplete flap. A partial flap may be created if the mechanical microkeratome movement is compromised during the pass. This can occur if the oscillating blade stops functioning, the translation or pivoting motor malfunctions (eg, an eyelid drape binds in the translating mechanism), or if suction is lost. The presence of an incomplete flap usually contraindicates the excimer laser ablation at the time of surgery due to insufficient stromal bed exposure.3,4
襟翼不完整。如果机械微型角膜切机运动在通过过程中受到损害，则可能会产生部分皮瓣。如果摆动叶片停止工作，平移或旋转电机发生故障（例如，眼睑悬垂在平移机构中），或者如果失去吸力，就会发生这种情况。由于基质床暴露不足，手术时存在不完全皮瓣通常禁忌准分子激光消融。 3,4
Buttonhole flap. A buttonhole is a flap with a full-thickness incision from the interface to the surface located central to the intended flap edge. This can occur in eyes that have a relatively small white-to-white and/or steep central keratometry reading. The presence of a buttonhole flap contraindicates the excimer laser ablation at the time of surgery due to the irregular stromal ablation that will occur in the area of the buttonhole. In addition, the patient would be at increased risk of visually significant epithelial ingrowth in the future.5
扣眼翻盖。扣眼是一种襟翼，从界面到位于预期襟翼边缘中心的表面具有全厚切口。这可能发生在白到白和/或陡峭的中央角膜测量读数相对较小的眼睛中。由于扣眼区域会发生不规则的间质消融，因此在手术时存在扣眼皮瓣禁忌准分子激光消融。此外，患者将来出现视觉上显着的上皮向内生长的风险增加。 5
Free flap. A free flap is a flap without a hinge resulting in a free-floating cap. This can occur in eyes that have large white-to-white and/or flat central keratometry reading. The presence of a free flap usually does not contraindicate the excimer laser ablation at the time of surgery due to adequate stromal exposure for the treatment. However, orienting the free cap can be challenging following ablation, particularly if the cornea was not marked prior to the pass or if the marks have worn off. A rotated free cap can induce irregular astigmatism.6
自由翻盖。自由襟翼是没有铰链的襟翼，可产生自由浮动的盖子。这可能发生在具有大白到白和/或平坦中央角膜测量读数的眼睛中。游离皮瓣的存在通常不禁忌手术时准分子激光消融，因为治疗时有足够的基质暴露。然而，消融后游离帽的方向可能具有挑战性，特别是如果角膜在通过前没有标记或标记已经消失。旋转的自由帽会引起不规则散光。 6
Irregular flap shape/contour. If a mechanical system binds and slows its translation and then releases and speeds up, both the edge of the flap and the thickness of the flap can become irregular. Upon lifting, it may be evident that there are areas of the flap that are much thinner than other areas, possibly with an incursion into Bowman’s layer (eg, a pseudobutton hole). Excimer laser ablation in these situations may result in an irregular ablation leading to induced aberrations and irregular astigmatism.
不规则的皮瓣形状/轮廓。如果机械系统束缚并减慢其平移速度，然后松开并加速，则襟翼的边缘和襟翼的厚度都可能变得不规则。抬起后，可以明显地发现皮瓣的某些区域比其他区域薄得多，可能侵入了Bowman层（例如，假纽扣孔）。在这些情况下，准分子激光烧蚀可能会导致不规则烧蚀，从而导致诱发像差和不规则散光。
2. Hinge position flexibility
2.铰链位置灵活性
A mechanical microkeratome typically does not allow the surgeon to switch the position of the hinge (eg, nasal, superior, temporal) without switching to a different system. It may be advantageous to customize the hinge position in certain patients (eg, patient with high with-the-rule astigmatism may benefit from superior hinge position due to the deeper ablation required peripherally at 3 and 9 o’clock; dry eye patient may benefit from nasal or temporal hinge position due to decreased severing of afferent nerve trunks;7 hyperopic patient may benefit from temporal hinge position due to nasal angle kappa). The femtosecond laser systems allow flexibility in the hinge location for each patient through the software interface.
机械显微角膜切术通常不允许外科医生在不切换到其他系统的情况下切换铰链的位置（例如，鼻铰链、上颞铰链）。在某些患者中，定制铰链位置可能是有利的（例如，高散光患者可能受益于优越的铰链位置，因为在3点钟和9点钟位置需要外周更深的消融;干眼症患者可能受益于鼻铰链位置，因为传入神经干的切断减少; 7 由于鼻角 kappa，远视患者可能受益于颞铰链位置）。飞秒激光系统通过软件界面为每位患者提供灵活的铰链位置。
3. Lower incidence of epithelial ingrowth
3.上皮向内生长的发生率降低
Epithelial ingrowth may be seen more commonly in a microkeratome created flap than with a femtosecond laser created flap.8,9 This may occur due to the difference in the flap morphology at the edge. A mechanical microkeratome has a flatter entrance angle and a shallower transition angle between the side cut and the interface. The femtosecond laser allows the surgeon to program precisely the side cut angle, allowing for angles up to 90 degrees. One hypothesis is that the steeper transition angle created by the femtosecond laser system may inhibit the passage of epithelial cells into the interface.
上皮向内生长在显微角膜刀皮瓣中可能比飞秒激光皮瓣更常见。 8,9 这可能是由于边缘襟翼形态的差异而发生的。机械微型角膜刀具有更平坦的入射角和侧切口和界面之间的较浅过渡角。飞秒激光允许外科医生精确编程侧切角度，允许角度高达 90 度。一种假设是，飞秒激光系统产生的更陡峭的过渡角可能会抑制上皮细胞进入界面。
4. Less variability in flap thickness
4. 襟翼厚度变化小
Although this is an extremely controversial topic, the general consensus in the literature is that there is a tighter standard deviation on flap thickness with the femtosecond laser vs. mechanical microkeratome.10-14 Flap thickness is a difficult parameter to measure as there is significant variability in ultrasound measurements based on position of the probe, stromal bed hydration, hydration status of the flap, etc. At our center, regardless of the method of flap creation, we have always measured flap thickness using the same subtraction ultrasound pachymetry technique and found that the measurements are tighter using a femtosecond laser (standard deviation of 11 µm) vs. a mechanical microkeratome (standard deviation of 14µm).
尽管这是一个极具争议的话题，但文献中的普遍共识是，飞秒激光与机械微角膜化术相比，皮瓣厚度的标准偏差更严格。 10-14 皮瓣厚度是一个难以测量的参数，因为根据探头的位置、基质床水化、皮瓣的水化状态等，超声测量存在显着差异。在我们的中心，无论采用何种皮瓣制作方法，我们始终使用相同的减法超声测厚技术测量皮瓣厚度，并发现使用飞秒激光（标准偏差为 11 μm）与机械微型角膜刀（标准偏差为 14μm）的测量更严格。
5. Precise control of flap diameter and hinge width
5.精确控制襟翼直径和铰链宽度
Although mechanical microkeratomes offer adjustable parameters to alter flap diameter (eg, suction ring size, suction ring thickness, stop setting, and changeable width head), variability in flap diameter and hinge width is largely out of the surgeon’s control, determined primarily by the corneal curvature and white-to-white measurement. In general, flap diameters and hinge widths are smaller on flat, large corneas and larger on steep, narrow corneas. The femtosecond laser allows the surgeon to precisely control both the flap diameter and the hinge width. This allows for customization of flap sizes for different corneal sizes as well as different refractive errors where ablation patterns may extend further peripherally and nasally (eg, hyperopia) or more at 3 and 9 o’clock (high with-the-rule astigmatism). In addition, recent studies in corneal biomechanics suggest that the anterior, peripheral cornea provides the most biomechanical support (Paper presented at: the XXIV Congress of the ESCRS; September 9, 2006; London, England). Consequently, there may be safety advantages to smaller, more central flaps that can be precisely specified only by the femtosecond laser.
虽然机械显微角膜刀提供了可调节的参数来改变角膜瓣直径（例如，吸环尺寸、吸环厚度、止动装置和可变宽度头），但皮瓣直径和铰链宽度的变化在很大程度上超出了外科医生的控制范围，主要由角膜曲率和白光测量决定。一般来说，扁平、大角膜的皮瓣直径和铰链宽度较小，而陡峭、狭窄的角膜较大。飞秒激光使外科医生能够精确控制皮瓣直径和铰链宽度。这允许针对不同的角膜尺寸以及不同的屈光不正定制皮瓣尺寸，其中消融模式可能在3点钟和9点钟位置进一步向周边和鼻部延伸（例如，远视）或更多（高散光）。此外，最近在角膜生物力学方面的研究表明，前外周角膜提供了最多的生物力学支持（论文发表于：ESCRS第二十四届大会;2006年9月9日;英国伦敦）。因此，只有飞秒激光器才能精确指定更小、更中心的襟翼可能具有安全优势。
6. Patient preference 6. 患者偏好
Subjective questionnaires have shown that patients prefer the laser flap creation to the blade system (Figure 4), removing some of the anxiety associated with the procedure.15
主观问卷调查表明，与刀片系统相比，患者更喜欢激光皮瓣的创建（图4），从而消除了与手术相关的一些焦虑。 15