| 1.PrefaceWith the improvement of equipment and technology, excimer laser corneal refractive surgery for myopia has become a high security, good predictive and rapid visual acuity recovery method. However, in some patients, even their postoperative uncorrected visual acuity is at or better than 1.0, blurred vision, glare, halo or night vision decrease and other complications may appear.that means increased aberrations of eye, reduced retinal image quality, resulting in decrease of visual quality.As awareness of the optometry systems and the advancement of technology, "customized ablation" for different corneal and refractive state comes into being. At present, main clinical customized ablations include wavefront-guided customized ablation, topography-guided customized ablation and Q-value Adjusted customized ablation and so on.Wavefront-guided customized ablation is based on the building mathematical model with data of wavefront aberrations of the eye, then cut cornea using excimer laser to eliminate the human eye aberrations and achieve better visual quality. In theory, wavefront instrument has advantages than comprehensive refractometer and retinoscopy in the optical properties of eyes, it can measure apart from spherical and cylinder other than many other parameters, these parameters can be more precise assessment of the whole eye of the optical properties and visual symptoms. However, there are many factors affecting wavefront-guided customized ablation technique, such as tear film, pupil size and accommodation, corneal flap thickness, laser cutting depth and diameter, corneal wound healing response (matrix remodeling and epithelial hyperplasia) and biomechanical changes. To improve visual quality after excimer laser corneal refractive surgery and carry out wavefront-guided customized ablation surgery, there are many issues to be studied.At present, the eye tracking and iris recognition technology has been considered an important factor to ensure ablation surgery. Pupil center shift and physiological eyeball rotation can lead to laser-cutting center position deviation, refraction not to be fully corrected and not achieve the best-corrected visual acuity, or new aberrations. Besides, other factors, such as operating room light, pupil diameter, head position, eye movement, corneal light reflex and dry eye also affect iris recognition application in the wavefront-guided customized ablation. To observe the clinical efficacy of wavefront-guided LASIK with technology of iris recognition and without recognition technology in myopia or myopic astigmatism, a prospective study was done.2 Materials and Methods2.1 Patients and MethodsFrom July 2008 to September 2009,158 eyes (85 cases) received wavefront-guided LASIK treatment because of myopia or myopic astigmatism in our hospital. They were divided into two groups:one group underwent wavefront-guided LASIK with iris recognition(81 eyes)(iris recognition group), with an average of (23.0±4.7) years; another group underwent wavefront-guided LASIK treatment without iris recognition through the limbus marking point (77 eyes) (non-iris recognition group), averaged (22.5±3.9) years. The two groups show no statistical significance in patient's age (P≥0.05). Iris recognition group had spherical equivalent of (-6.72±1.93) D, spherical (-6.35±1.82) D, Cylinder (-0.74±0.53) D; Non-iris recognition group had spherical equivalent of (-6.28±1.41) D, spherical (-6.22±1.28) D, Cylinder(-0.75±0.58) D. The were no statistical significance (P≥0.05) between two groups for the spherical, cylinder and spherical equivalent refraction. 2.2 Preoperative examination:routine examination included uncorrected visual acuity, best corrected visual acuity, refractive examination, silt-lamp biomicroscopy of the anterior segment,, direct ophthalmoscopy fundus, non-contact tonometer measurement of intraocular pressure, corneal thickness, Orbscan II anterior segment analysis system and Zywave wavefront aberration measurement.2.3 Surgical design2.3.1 Surgical design of wavefront-guided LASIK with iris recognition:The eyes were examined by OrbscanⅡanterior segment analysis system, selected the Zyoptix type, output OTE files from Zyoptix Export.Zywave wavefront aberration examination:which underwent at normal light or dark light when pupil diameter is maintained at 4-6mm each eye received examination for two times, similarly dark or compound tropicamide dilation pupil when pupil diameter is maintained at 6.0-7.5mm, each eye was examined three times. From the dilated zywave wavefront aberration examination choose a result, output iris recognition ATE+IR file, and then with the non-dilated zywave examination results were compared to identify. Require the mydriasis and the pupil is not scattered large with the pupil center in X, Y the moving scope and the eye rotation degrees within the required standards.If not within the required standards, or can not identify the pupil shift, to re-examine, or abandon the surgical method. Open Zylink treatment software, looking for OTE files and ATE files of patients, calculations, select the Personalized Treatment, adjusting the cutting diopter (residual corneal thickness> 250μm and not less than half of the entire corneal thickness) and optical zone (> 6mm), output the TLS files, write in 3.5-inch floppy disk (A drive).2.3.2 Surgical design of wavefront-guided LASIK without iris recognition:The eyes for OrbscanⅡanterior segment analysis system, select the Zyoptix type, based on the results click on Zyoptix Export, then output OTE files. From dilated zywave wavefront aberration test results, select the raw data correct image, then directly output non-iris recognition ATE files, It is not need to iris recognition with the non-dilated Zywave examination results, The remaining steps are the same with surgery design of wavefront-guided LASIK with iris recognition. But need for slit-lamp microscopy before surgery testimony was 3:00 and 9:00 limbus marking point.2.4 Laser in situ keratomileusis surgical methodsBausch-Lomb Technolas 217z excimer laser machine was used, chose Zyoptix, inserted 3.5-inch floppy disk (A disk), identified patients TLS file, verified the treatment data.Inserted Personalized Treatment card, tested to excimer laser energy. While preparing for surgery, with Hansatome microkeratome 160 Segment produced corneal flap, before open corneal flap, first to iris recognition, dimming interior lighting and surgical vision lighting, so that pupil diameter is similar to the undilated Zywave aberration measured size, enable patients look above directly that corneal surface to achieve better transparency. If can not carry out iris recognition, it should be to re-adjust the patient's head position, Close assisted laser ore drip a drop of BSS in the corneal surface, and then carry out iris recognition. After the iris recognition, adjust the iris tracking system that allows tracking of light and central corneal reflex points overlapped, open corneal flap for laser treatment.Wavefront-guided LASIK without iris recognition not required for iris recognition step, but need to adjust the patient's head position, markers of corneal flap alignment horizontal, the remaining steps are same as wavefront-guided LASIK with iris recognition.2.5 Statistical analysis:Postoperatively the patients were followed-up for 3 months, and recorded with uncorrected visual acuity, best corrected visual acuity, refraction and RMS of aberrations were recorded. The data were analyzed by the 17.0 statistical software, t test for the paired data, Kruskal Wallis (rank sum) test for multiple samples pairwise comparison, P<0.05 as considered significant.3 Results3.1 Vision(Logarithmic visual acuity) and refractionIris recognition group:preoperative uncorrected visual acuity was 4.25±0.22, best corrected visual acuity was 4.95±0.07; postoperative 10 days of uncorrected visual acuity was 4.98±0.14, best corrected visual acuity was 5.28±0.15; postoperative 1 month uncorrected visual acuity was 4.99±0.11, the best corrected visual acuity was 5.24±0.21; postoperative 3 month uncorrected visual acuity was 4.99±0.31, best corrected visual acuity was 5.23±0.26. Non-iris recognition group: preoperative uncorrected visual acuity was 4.27±0.23, best corrected visual acuity was 4.96±0.08; postoperative 10 days of uncorrected visual acuity was 4.98±0.12, best corrected visual acuity was 5.12±0.16; postoperative 1 month uncorrected visual acuity was 4.98±0.12, best corrected visual acuity was 5.18±0.22; postoperative 3 month uncorrected visual acuity was 4.94±0.21, best corrected visual acuity was 5.11±0.25. The average uncorrected visual acuity and best corrected visual acuity all increased at postoperative 10 days,1 month and 3 month and there was no statistical significance between two groups.Iris recognition group:spherical equivalent was (-0.25±0.32) D, spherical (-0.05±0.36) D, Cylinder (-0.24±0.13) D postoperative 10 days; spherical equivalent was (-0.32±0.23)D, spherical(-0.07±0.34)D, Cylinder (-0.32±0.17) D postoperative 1 month; spherical equivalent was (-0.45±0.42) D, spherical (-0.35±0.42) D, Cylinder (-0.33±0.20) D postoperative 3month.Non-iris recognition group:spherical equivalent was (-0.34±0.35) D, spherical (-0.09±0.43) D, Cylinder (-0.32±0.18) D postoperative 10 days; spherical equivalent was (-0.38±0.26) D, spherical (-0.25±0.31) D, Cylinder (-0.35±0.24) D postoperative 1 month; spherical equivalent was (-0.48±0.46) D, spherical (-0.36±0.47) D, Cylinder (-0.38±0.23) D postoperative 3month. Residual refraction (spherical equivalent, spherical and cylinder) in the two groups at postoperative 10 days,1 month and 3 month show no statistically significant.3.2 Safety, efficacy and predictability of the surgeryThe average best corrected visual acuity at postoperative 10 days,1 month and 3 month between iris recognition group 81 eyes and non-iris recognition group 77 eyes were no statistically significant. Iris recognition group 80 eyes (98.77%) and non-iris recognition group 74 eyes (96.10%) best corrected visual acuity reached or exceeded the preoperative best corrected visual acuity at postoperative 3 month. Iris recognition group 1 eye (1.34%) and non-iris recognition group 3 eyes (3.90%) best corrected visual acuity decreased by 1 line than the preoperative, the two groups the best corrected visual acuity were not decreased 2 lines or more than 2 lines. The security index of iris recognition group at postoperative 3 month was 1.06 and non-iris recognition group was 1.03, there was no statistically significant (P=0.432)The average uncorrected visual acuity at postoperative 10 days,1 month and 3 month between iris recognition group 81 eyes and non-iris recognition group 77 eyes were no statistically significan. The average uncorrected visual acuity of iris recognition group from preoperative 4.25±0.22 increased to 4.99±0.31 at postoperative 3 month, and non-iris recognition group from preoperative 4.27±0.23 increased to 4.94±0.21. The average uncorrected visual acuity of iris recognition group and non-iris recognition group all at 0.5 or above at postoperative 3 month, Iris recognition group 69 eyes (85.19%) and non-iris recognition group 63 eyes (81.82%) uncorrected visual acuity equal to or exceeded the preoperative best corrected visual acuity at postoperative 3 month. The validity index of iris recognition group is 1.01 and non-iris recognition group was 0.96 at postoperative 3 month., there was no statistically significant (P=0.487)Postoperative 3 month iris recognition group 76 eyes (93.83%) and non-iris recognition group of 70 eyes (90.91%)spherical equivalent within±0.5D, iris recognition group 80 eyes (98.77%) and non-iris recognition group of 75 eyes (97.40%) spherical equivalent within±1.0D, the difference between the two groups were no statistically significant (P=0.643,0.626).3.3 The pupil center shift and the eye rotation degrees3.3.1 Preoperative pupil center shift and the eye rotation degrees:Iris recognition group:81 eyes of preoperative examination by Zywave wave-front aberration measured pupil from 4.5-5.5 mm to 6.0-7.5 mm the pupil average horizontal (X axis) displacement (55.81±56.25)μm, range (0-244)μm, average vertical direction (Y axis) displacement (74.01±53.75)μm, range (5-246)μm, the average vector direction of displacement (99.65±67.32)μm, range (12-260)μm; preoperative right eye, left eye the mean pupil center shift was no significant difference (P≥0.05). Eyeball rotation 1.15°±0.98°, the range of 0-4.34°; right eye, left eye rotation degrees was no statistically significant (P≥0.05).3.3.2 Pupil center shift and the eye rotation degrees during operation:Iris recognition group 81 eyes conducted iris recognition during surgery, measure the average of the pupil center (X-axis) displacement (59.23±51.38)μm, range (0～244)μm, average vertical direction (Y axis) displacement of 73.12±56.08μm, range (1～250)μm, the average vector direction of the shift (100.04±64.68)μm, range (13～265)μm. During surgery right eye, left eye the mean pupil center shift was no significant difference (P≥0.05).Degrees rotation of eye during surgery is a dilated and non-dilated Zywave examination rotation+not dilated Zywave inspection and under excimer laser the overall rotation. If the degree in excess of 10°, need to re-adjust the eye position, and then carry out iris recognition. The average eye rotation 3.81°± 2.75°during surgery, the range of 0～9.9°,27 eyes with eyeballs rotated beyond 5°accounted for 33.33%. degrees of rotation during surgery between the right eye and left eye show no statistically significant (P≥0.05).3.4 Comparison of wavefront aberrationIris recognition group and non-iris recognition group preoperative in general higher-order aberrations,3-order aberrations,4-order aberrations, and 5-order aberration root mean square value (RMS) show no statistically significant (P≥0.05). Two groups higher-order aberrations all increased than preoperative, the higher-order aberrations increased the most obvious is after 10 days, after 1 month and 3 months a gradual decline in higher-order aberrations, but all higher than preoperative. Non-iris recognition group postoperative 1 month and postoperative 3 months 3rd order aberrations higher than the iris recognition group increased, the difference between the two groups show statistically significant (P≤0.05), between the two groups general higher-order aberrations,4-order aberrations, and 5-order aberrations show no statistically significant (P≥0.05)There were no statistically significant between iris recognition group and non-iris recognition group in preoperative root mean square value (RMS) of coma, trefoil(Z3-3,Z33) and spherical aberration (P≥0.05). The two groups root mean square value (RMS) of level coma and vertical coma postoperative 1 month and preoperative 3 months show statistically significant (P≤0.05).4 Conclusion4.1 wavefront-guided LASIK with or without iris recognition through the limbus marking point for myopia or myopic astigmatism are equally safety, effectiveness and predictability.4.2 Wavefront-guided LASIK application of iris recognition technology induces smaller postoperative coma than wavefront-guided LASIK without iris recognition technology through the limbus marking point, suggesting application of iris recognition technology may be more accurate positioning of laser cutting center during surgery.
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