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Cataract and Refractive Surgery - part 7

thổi khí nitơ trong khi cắt bỏ đã làm giảm sự xuất hiện của hòn đảo trung tâm. Hòn đảo trung tâm thường được đặc trưng bởi undercorrection kèm theo nhìn đôi bằng một mắt. Với địa hình, trung tâm cao | 104 Complications of Excimer Laser Surgery blows nitrogen gas during ablation has decreased the occurrence of central islands. Central islands are usually characterized by undercorrection accompanied by monocular diplopia. With topography the central elevated area is clear. These symptoms often disappear in 3 to 6 months. Several attempts have been made to treat symptomatic central islands 9 21 . The topography-linked or wavefront-guided laser ablation is a helpful tool. 8 Fig. 8.2 Retinal images. Top wavefront analysis. The higher order aberration is 1.14 pm. Bottom the retinal image evaluated by wavefront analysis pupil size 3 mm . The blurred image left improved after surgery right 8.3 Intraoperative Complications 105 Fig. 8.3 Orbscan irregular astigmatism . Top kera-tometric map shows irregular astigmatism. The visual acuity is 0.7 1.5 X sphere -0.5 D cylinder -2.0 D axis 153 . The patient complained of monocular dip- lopia during the day and at night. Bottom after wavefront-guided laser ablation the uncorrected visual acuity improved to 1.5 106 Complications of Excimer Laser Surgery 8 Fig. 8.4 Retinal images. Top wavefront analysis. The higher order aberration is 0.66 pm. Bottom the retinal image evaluated by wavefront analysis pupil size 3 mm . The blurred image left improved after surgery right 8.3.4 Undercorrection Undercorrection is the result of incorrect preoperative evaluation of refraction excessive moisture in the stromal bed decentration and problems with laser calibration. If the preoperative refraction is unstable the refraction should .