Taneri S, Azar D T
Department of Ophthalmology, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, USA.
Ophthalmologe. 2007 Feb;104(2):132-6. doi: 10.1007/s00347-006-1433-5.
The risk of iatrogenic keratectasia after laser in situ keratomileusis (LASIK) increases with thinner posterior stromal beds. Ablations on the undersurface of a LASIK flap could only be performed without the guidance of an eye tracker, which may lead to decentration. A new method for laser ablation with flying spot lasers on the undersurface of a LASIK flap was developed that enables the use of an active eye tracker by utilizing a novel instrument. The first clinical results are reported.
Patients wishing an enhancement procedure were eligible for a modified repeat LASIK procedure if the flaps cut in the initial procedure were thick enough to perform the intended additional ablation on the undersurface leaving at least 90 microm of flap thickness behind. (1) The horizontal axis and the center of the entrance pupil were marked on the epithelial side of the flap using gentian violet dye. (2) The flap was reflected on a newly designed flap holder which had a donut-shaped black marking. (3) The eye tracker was centered on the mark visible in transparency on the flap. (4) Ablation with a flying spot Bausch & Lomb Technolas 217z laser was performed on the undersurface of the flap with a superior hinge taking into account that in astigmatic ablations the cylinder axis had to be mirrored according to the formula: axis on the undersurface=180 degrees -axis on the stromal bed. (5) The flap was repositioned.
Detection of the marking on the modified flap holder and continuous tracking instead of the real pupil was possible in all of the 12 eyes treated with this technique. It may be necessary to cover the real pupil during ablation in order not to confuse the eye tracker. Ablation could be performed without decentration or loss of best spectacle-corrected visual acuity. Refractive results in minor corrections were good without nomogram adjustment.
Using this novel flap holder with a marking that is tracked instead of the real pupil, centered ablations with a flying spot laser on the undersurface of a LASIK flap are feasible. Thus, the additional risk of iatrogenic keratectasia associated with stromal enhancement ablations is avoided.
准分子原位角膜磨镶术（LASIK）后医源性角膜扩张的风险随着后弹力层基质床变薄而增加。在LASIK角膜瓣下表面进行消融时，只能在没有眼动追踪仪引导的情况下进行，这可能会导致偏心。一种利用新型仪器在LASIK角膜瓣下表面使用飞点激光进行激光消融的新方法被开发出来，该方法能够使用主动眼动追踪仪。本文报告了首批临床结果。
希望接受增效手术的患者，若初次手术中制作的角膜瓣足够厚，能够在其下表面进行预期的额外消融且剩余至少90微米的角膜瓣厚度，则符合改良重复LASIK手术的条件。（1）使用龙胆紫染料在角膜瓣的上皮侧标记水平轴和入瞳中心。（2）将角膜瓣翻转至一个新设计的带有环形黑色标记的角膜瓣固定器上。（3）将眼动追踪仪对准角膜瓣上透过透明部分可见的标记使其居中。（4）使用博士伦Technolas 217z飞点激光在角膜瓣下表面进行消融，采用上方铰链，考虑到在散光消融中，柱镜轴必须根据公式进行镜像：下表面轴=180度-基质床轴。（5）将角膜瓣复位。
在使用该技术治疗的所有12只眼中，均能够检测到改良角膜瓣固定器上的标记并进行连续追踪，而非追踪真实瞳孔。在消融过程中可能需要遮盖真实瞳孔，以免干扰眼动追踪仪。消融过程中未出现偏心或最佳矫正视力丧失的情况。在无需调整列线图的情况下，小度数矫正的屈光结果良好。
使用这种带有可被追踪标记而非真实瞳孔的新型角膜瓣固定器，在LASIK角膜瓣下表面使用飞点激光进行中心消融是可行的。因此，避免了与基质增强消融相关的医源性角膜扩张的额外风险。
