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Research Article
Vol. 54, No. 25 / September 1 2015 / Applied Optics
Statistical characteristics of aberrations of human eyes after small incision lenticule extraction surgery and analysis of visual performance with individual eye model QIQI LOU,1,2 YAN WANG,3,* ZHAOQI WANG,1,2 YONGJI LIU,1,2 LIN ZHANG,3
AND
HUI FANG1,2
1
Institute of Modern Optics, Nankai University, Tianjin 300071, China Key Laboratory of Optical Information Science and Technology, Ministry of Education, Tianjin 300071, China 3 Tianjin Eye Hospital & Eye Institute, Tianjin Key Lab of Ophthalmology and Visual Science, Tianjin Medical University, Tianjin 300020, China *Corresponding author:
[email protected] 2
Received 7 July 2015; revised 3 August 2015; accepted 3 August 2015; posted 4 August 2015 (Doc. ID 245546); published 21 August 2015
Preoperative and postoperative wavefront aberrations of 73 myopic eyes with small incision lenticule extraction surgery are analyzed in this paper. Twenty-eight postoperative individual eye models are constructed to investigate the visual acuity (VA) of human eyes. Results show that in photopic condition, residual defocus, residual astigmatism, and higher-order aberrations are relatively small. 100% of eyes reach a VA of 0.8 or better, and 89.3% of eyes reach a VA of 1.0 or better. In scotopic condition, the residual defocus and the higher-order aberrations are, respectively, 1.9 and 8.5 times the amount of that in photopic condition, and the defocus becomes the main factor attenuating visual performance. © 2015 Optical Society of America OCIS codes: (330.7326) Visual optics, modeling; (330.1070) Vision - acuity; (330.7335) Visual optics, refractive surgery. http://dx.doi.org/10.1364/AO.54.007490
1. INTRODUCTION Recently, as a flap-free corneal refractive surgery, compared with laser-assisted in situ keratomileusis (LASIK), small incision lenticule extraction (SMILE) surgery has received extensive interest of clinicians and researchers because of its relatively few intraoperative and postoperative complications. Lin et al. [1] compared SMILE surgery with femtosecond laser-assisted LASIK surgery and found that SMILE surgery had a lower induction rate of higher-order aberrations. Shah et al. [2] analyzed preoperative and postoperative variation of main aberrations of 47 eyes with SMILE surgery at 5.4 mm pupil diameter and pointed that higher-order aberrations increased from 0.19 to 0.32 μm. Shah et al. [2] also investigated the uncorrected distance visual acuity (UDVA) of 51 eyes which received SMILE surgery and found that 70% of these eyes reached an UDVA of 0.8 or better. Sekundo et al. [3] studied the postoperative UDVA of 91 myopic eyes with SMILE surgery and showed that 83.5% of these eyes had an UDVA of 1.0 or better. Vestergaard et al. [4] measured the postoperative UDVA of highly myopic eyes (the mean spherical equivalent refraction is −7.19 D) which accepted SMILE surgery, and the results showed that the UDVA of 84% of the eyes reached 0.8 or 1559-128X/15/257490-04$15/0$15.00 © 2015 Optical Society of America
better. Results mentioned above are all based on experimental measurement, and investigations of postoperative visual acuity (VA) with individual eye model have not been reported yet. As an important method of analyzing visual performance of human eyes, individual eye model has gotten great development. Li et al. [5] designed aspherical spectacles to correct the higher-order aberrations of human eyes based on the individual eye model. He et al. [6] constructed individual eye models to analyze the characteristics of chromatic aberration in a population of eyes. Zhai et al. [7] established individual eye models to investigate the interaction between chromatic and higher-order aberrations. Lou et al. [8] constructed the individual eye model of large visual field to study the distribution of peripheral aberrations. In this paper, we analyze preoperative and postoperative wavefront aberrations of 73 myopic eyes with SMILE surgery at different visual conditions. Then the influencing factors on visual performance at different visual conditions are investigated. Postoperative individual eye models which meet photopic condition are constructed to investigate the VA of human eyes, with modulation transfer function (MTF) curve and aerial image modulation (AIM) curve.
Research Article
Vol. 54, No. 25 / September 1 2015 / Applied Optics
Table 1 demonstrates that after SMILE surgery, defocus decreases from −4.57 1.13 D to −0.36 0.54 D and astigmatism decreases from −0.44 0.42 D to −0.25 0.19 D at 2.8 mm pupil diameter. The decreases of defocus and astigmatism from preoperative to 3 month postoperative are statistically significant (p < 0.01), which reflects the advancement and effectiveness of SMILE surgery in correcting defocus and astigmatism. RMSH of 2.8 mm pupil diameter increases from 0.038 0.015 to 0.054 0.021 μm which is still a quite small value. At 6 mm pupil diameter, the postoperative residual defocus and RMSH are, respectively, −0.69 0.52 D and 0.459 0.123 μm, which are, respectively, 1.9 and 8.5 times the amount of that at 2.8 mm pupil diameter. The residual astigmatism is basically the same for two different pupil diameters.
2. STATISTICAL ANALYSES OF MAIN ABERRATIONS BEFORE AND AFTER SMILE SURGERY AT DIFFERENT PUPIL DIAMETERS Tianjin Eye Hospital introduced SMILE surgery in August 2011 and has successfully cured approximately 4000 myopic eyes. The inclusion criteria for SMILE surgery comprises of ages ranging from 18 to 45 years old, the spherical equivalent refraction ranging from −2 to −10 D, a stable refractive error within 2 years, a corrected distance visual acuity of 0.8 or better, the minimum corneal thickness of 480 mm, intraocular pressure smaller than 21 mm Hg and absence of ocular disease or corneal surgery. To investigate characteristics of aberrations before and after SMILE surgery in this research, 73 myopic eyes are selected to receive additional wavefront aberration tests. The inclusion criteria of these eyes is the preoperative refractive errors, with the sphere and cylinder ranging from −2.33 D to −7.46 D and from −0.02 D to −1.90 D, respectively. The study protocol adheres to the tenets of the Declaration of Helsinki, and is approved by the Institutional Review Board of Tianjin Eye Hospital. Informed consents are obtained from all participants. A femtosecond laser system (VisuMax, Carl Zeiss Meditec AG, Germany) with 500 kHZ repetition rate and 110–120 nJ energy is utilized during the whole operation process. Preoperative and 3- month postoperative wavefront aberrations are measured by Hartman–Shack wavefront aberrometer of Wavescan (VISX, Santa Clara, CA, USA) [9] in Tianjin Eye Hospital with the pupil diameter ranging from 6 to 7 mm in a darkroom. Based on the wavefront aberrations, the statistical analyses of defocus, astigmatism and root-meansquare of higher-order aberrations (RMSH ) at 2.8 and 6 mm pupil diameters are carried out by SPSS software (IBM SPSS Statistic 19). The transform of wavefront aberrations at different pupil diameters is accomplished by MATLAB procedure [10]. The comparisons of above aberrations between preoperation and postoperation are conducted using Paired Samples t Test. Statistical results are given in Table 1 where the P value is the statistical probability. In hypothesis testing, it is of highly statistical significance when the P value is smaller than 0.01. Table 1.
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3. INFLUENCING FACTORS ON VISUAL PERFORMANCE AT DIFFERENT PUPIL DIAMETERS The ideal eye model is constructed in ZEMAX environment with the Gullstrand–Lee eye model as the fundamental structure which parameters are shown in Table 2. For 2.8 mm pupil diameter of photopic vision, the stop diameter is set to be 2.7 mm, and it is set to be 5.8 mm for 6 mm pupil diameter of scotopic vision. To correct the residual aberrations of the fundamental eye model, we set the “thickness” of vitreous and “conic” of posterior surface of crystalline lens as variables and execute optimization. After optimization, the ideal eye model is established. Based on the postoperative statistical data, we introduce mean defocus, mean astigmatism, and mean higher-order aberrations into the ideal eye model, respectively, and calculate the radial averaged MTF for different pupil diameters. The results are shown in Fig. 1, where the solid line, dashed line, short-dashed line, and dash-dotted line denote the MTF of defocus-only, astigmatism-only, RMSH -only, and diffraction limit, respectively, with: (a) in the case of 2.8 mm pupil diameter, and (b) in the case of 6 mm pupil diameter. It can be seen
Statistics of Aberrations Before and After SMILE Surgery (Preop: Preoperative, Postop: Postoperative) 2.8 mm
6 mm
Parameter
Defocus (D)
Astigmatism (D)
RMSH (μm)
Defocus (D)
Astigmatism (D)
RMSH (μm)
Preop mean Postop mean p
−4.57 1.13 −0.36 0.54
