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Postoperative ocular higher-order aberrations and contrast sensitivity: Femtosecond lenticule extraction versus pseudo small-incision lenticule extraction
ARTICLE
Postoperative ocular higher-order aberrations and contrast sensitivity: Femtosecond lenticule extraction versus pseudo small-incision lenticule extraction Deborah K.L. Tan, MB BS, Wan Ting Tay, MAppStat, Cordelia Chan, FRCSEd, Donald T.H. Tan, FRCOphth, FAMS, Jodhbir S. Mehta, FRCSEd
PURPOSE: To evaluate and compare changes in contrast sensitivity and ocular higher-order aberrations (HOAs) after femtosecond lenticule extraction (FLEx) and pseudo small-incision lenticule extraction (SMILE). SETTING: Singapore National Eye Centre, Singapore. DESIGN: Retrospective case series. METHOD: Patients had femtosecond lenticule extraction (Group 1) or pseudo small-incision lenticule extraction (Group 2) between March 2010 and December 2011. The main outcome measures were manifest refraction, HOAs, and contrast sensitivity 1, 3, 6, and 12 months postoperatively. RESULTS: Fifty-two consecutive patients (102 eyes) were recruited, 21 patients (42 eyes) in Group 1 and the 31 patients (60 eyes) in Group 2. The uncorrected and corrected distance visual acuities were significantly better in Group 2 than in Group 1 at 12 months (P Z .032). There was no significant increase in 3rd- or 4th-order aberrations at 1 year and no significant difference between the 2 groups preoperatively or postoperatively. At 1 year, there was a significant increase in mesopic contrast sensitivity in Group 2 at 1.5 cycles per degree (cpd) (P Z .008) that was not found in Group 1, and photopic contrast sensitivity at 6.0 cpd was higher in Group 2 (P Z .027). CONCLUSIONS: These results indicate that refractive lenticule extraction is safe and effective with no significant induction of HOAs or deterioration in contrast sensitivity at 1 year. Induction of HOAs was not significantly different between both variants of refractive lenticule extraction. However, there was significant improvement in photopic contrast sensitivity after pseudo small-incision lenticule extraction, which persisted through 1 year. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2015; 41:623–634 Q 2015 ASCRS and ESCRS
The femtosecond laser is a near-infrared neodymium: YAG laser that causes photodisruption of the cornea by producing ultrashort pulses of light (10 15 of a second or femtosecond) at high repetition rates, thereby eliciting cleavage of the stroma lamellae with surgical precision.1,2 Femtosecond lasers have been widely used in laser in situ keratomileusis (LASIK) to enable nonmechanical creation of a corneal flap.3 Their advantage over manual microkeratomes include increased precision,4,5 a reduced incidence of buttonholes or free Q 2015 ASCRS and ESCRS Published by Elsevier Inc.
caps,6,7 and a reduced incidence of flap-related complications.8,9 Refractive lenticule extraction (ReLEx, Carl Zeiss Meditec AG) is a new corneal refractive procedure in which the femtosecond laser cuts an intrastromal lenticule corresponding to the patients' refractive correction without the use of a microkeratome or excimer laser.10 The lenticule is then removed through a surface incision of varying size depending on whether the femtosecond lenticule extraction (FLEx, Carl Zeiss http://dx.doi.org/10.1016/j.jcrs.2014.07.032 0886-3350
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HOAS AFTER FEMTOSECOND LENTICULE EXTRACTION VS PSEUDO SMALL-INCISION LENTICULE EXTRACTION
Meditec AG)11 or small-incision lenticule extraction (SMILE, Carl Zeiss Meditec AG)12,13 procedure is being performed. The first involves cutting and lifting a complete LASIK-type hinged flap to remove the intrastromal lenticule; the latter is a flapless procedure that involves removing the same lenticule through a small 2.0 to 4.0 mm pocket incision.10 Pseudo small-incision lenticule extraction is generally performed during the learning curve and transition from femtosecond lenticule extraction to small-incision lenticule extraction, whereby the laser is used exactly as in femtosecond lenticule extraction (ie, the laser performs the flap cut); however, the flap is not lifted and only a smaller incision (5.0 to 6.0 mm) is opened. Next, the lenticule is extracted akin to small-incision lenticule extraction. Initial clinical results of refractive lenticule extraction have been promising.10,14–16 The postoperative refractive outcomes, stability of refraction, predictability, efficacy, and safety have been shown to be similar if not better than in LASIK, with fewer complications.14,15 It has been well documented that LASIK compromises contrast sensitivity after surgery,17–20 and reports have also shown that higher-order aberrations (HOAs) increase after LASIK.21–23 In a comparative study between femtosecond lenticule extraction and LASIK, contrast sensitivity and the induction of HOAs were reported to be similar to or better than in LASIK.14,15,24 In the transitional learning curve from femtosecond lenticule extraction, pseudo small-incision lenticule extraction is a good intermediary procedure before conversion to full small-incision lenticule extraction because it allows the surgeon to gain familiarity with the visualization of the lenticule without lifting the flap. It also allows the surgeon to perform the lamellar separation required in the small-incision lenticule extraction procedure with the knowledge that if unsuccessful, the flap can be simply lifted and the lenticule removed vis- a-vis a standard femtosecond
Submitted: January 14, 2014. Final revision submitted: June 29, 2014. Accepted: July 10, 2014.
lenticule extraction procedure. Another potential advantage of pseudo small-incision lenticule extraction over small-incision lenticule extraction is that in the event of the need for refractive retreatment, it might be possible to lift the flap fully to perform excimer ablation on the stromal bed. A review of the current literature showed a lack of studies that compared the visual outcomes between the 2 procedures of refractive lenticule extraction. Because pseudo small-incision lenticule extraction might be considered an important transitional procedure, the purpose of this study was to evaluate and compare changes in contrast sensitivity and ocular HOAs after femtosecond lenticule extraction and pseudo small-incision lenticule extraction. PATIENTS AND METHODS Study Population This was a retrospective study that included all patients who had refractive lenticule extraction–femtosecond lenticule extraction and pseudo small-incision lenticule extraction between March 2010 and December 2011 at the Singapore National Eye Centre. The study group represented our learning curve with refractive lenticule extraction, which included initial experience with femtosecond lenticule extraction followed by a transition to performing pseudo small-incision lenticule extraction. This study was performed in accordance with the tenets of the Declaration of Helsinki, as revised in 1989. Written informed consent was obtained from all patients, and ethics approval was obtained from the Institutional Review Board of the Singapore Eye Research Institute. Inclusion criteria for the study were age 21 years or older, spherical myopia between 1.00 diopter (D) and 9.00 D and myopic astigmatism less than 3.00 D, stable refractive error for 12 months, minimum corneal thickness of 480 mm with minimum calculated residual stromal bed (RSB) after treatment of 250 mm, and regular corneal topography (Orbscan II, Bausch & Lomb/Orbtek Inc.). Exclusion criteria were residual, recurrent, or active ocular diseases such as uveitis, severe dry eye, severe allergic eye disease, glaucoma, visually significant cataract, retinal disease, previous corneal surgery or trauma within the corneal flap zone; patent vascularization within 1.0 mm of the corneal flap zone; any active systemic disease; or the use of systemic medications that are likely to affect corneal wound healing, such as corticosteroids and antimetabolites.
Surgical Technique
From the Singapore Eye Research Institute (D.K.L. Tan, Tay, Chan, D.T.H. Tan, Mehta), the Department of Ophthalmology (D.T.H. Tan), Yong Loo Lin School of Medicine, National University of Singapore, the Singapore National Eye Center (D.K.L. Tan, Chan, D.T.H. Tan), the Department of Clinical Sciences (Mehta), Duke-NUS Graduate Medical School, and the Lee Kong Chian School of Medicine (D.T.H. Tan), Nanyang Technological University, Singapore. Corresponding author: Jodhbir S. Mehta, FRCSEd, Singapore National Eye Center, 11 Third Hospital Avenue, Singapore 168751. E-mail: [email protected].
The refractive lenticule extraction procedures were performed by 1 of 3 experienced corneal refractive surgeons (D.T.H.T, C.C., J.S.M) using a previously described technique10,12 All refractive lenticule extraction procedures share similar surgical steps at the beginning of the procedure. After these common steps, there were specific steps for femtosecond lenticule extraction and pseudo small-incision lenticule extraction. After application of topical anesthesia, standard sterile draping, and insertion of a speculum, the patient's eye was positioned under the femtosecond surgical microscope
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Table 1. Demographic and preoperative information.
Parameter Patients (n) Age (y) Mean G SD Range Male sex, n (%) Eyes (n) Sphere (D) Mean G SD Range Cylinder (D) Mean G SD Range SE (D) Mean G SD Range
Femtosecond Lenticule Extraction
Pseudo Small-Incision Lenticule Extraction
21
31
32.26 G 7.10 20.83, 45.51 12 (57.1) 42
31.56 G 5.71 23.01, 41.13 20 (64.5) 60
5.32 G 2.08 1.00, 9.00
5.85 G 1.91 0.50, 10.00
.183
0.97 G 0.57 0.00, 2.75
0.77 G 0.72 0.00, 3.00
.129
5.80 G 2.08 1.38, 9.75
6.23 G 1.84 1.50, 10.13
.271
P Value
.697 .592
SE Z spherical equivalent
(Visumax, Carl Zeiss Meditec AG). Under patient fixation, the cornea was docked under the curved suction contact glass before application of suction as centration was achieved. Femtosecond laser treatment was then initiated. First, the posterior lamellar surface of the refractive lenticule was incised (spiral-in pattern); second, a vertical 15 mm lenticule side cut at the outer border of the lamellar dissection was performed to outline the outer edge of the lenticule. Next, the anterior lamellar surface of the refractive lenticule was cut (spiral-out pattern), which extended beyond the posterior lenticule diameter by 0.5 mm to form an overlapping anterior flap.25 The following femtosecond laser parameters were used: 120 mm flap thickness, 7.5 mm anterior flap diameter, 6.5 mm optical zone of lenticule, and 145 nJ of power with side-cut angles at 90 degrees. The spot distance and tracking spacing were 3/3 mm for the lenticule, 2.5/2.5 mm for the lenticule side cut, 3/3 mm for the flap, and 2/2 mm for the flap side cut.
Steps Specific to the Femtosecond Lenticule Extraction Procedure After the formation of the anterior flap, the vertical flap side cut through to the corneal surface was created, leaving a superior hinge 50 degrees in chord length, similar to a standard LASIK flap in configuration. The suction was then released, and a Seibel spatula (Rhein Medical, Inc.) was inserted under the flap near the hinge before the flap was separated and reflected, again similar to a LASIK procedure. The inner edge of the lenticule was then identified and separated from the RSB with a Sinskey hook, and the posterior border of the lenticule was gently separated from the stromal bed with the Seibel spatula. The free end of the lenticule was then grasped with a nontoothed serrated forceps and peeled off, after which the flap was repositioned.
Steps Specific to the Pseudo Small-Incision Lenticule Extraction Procedure In pseudo small-incision lenticule extraction, the hinge position was rotated to the upper temporal quadrant; otherwise, the vertical laser side cut was similar to femtosecond lenticule extraction. After release of suction, the Seibel spatula was used to separate the cut edge of the flap at the 12 o'clock position to form a superior opening of
approximately 5.0 to 6.0 mm. A blunt-tipped lamellar dissector was then used to perform lamellar dissection in the posterior, then the anterior laser dissection planes to separate the lenticule completely. Care was taken at this stage not to inadvertently further widen the 5.0 to 6.0 mm opening. The lenticule was then grasped with a forceps and removed from the pocket incision.
Outcome Measures The preoperative and 1-, 3-, 6-, and 12-month postoperative ophthalmic examinations included manifest refraction and HOAs, which were measured with an aberrometer system (Technolas Zywave aberrometer with Zywave software version 4.45, Zyoptix Diagnostic Workstation, Bausch & Lomb) with a 5.0 mm pupil without pharmacological intervention. Examinations also included contrast sensitivity, which was assessed with the Optec 6500P (Stereo Optical Co., Inc.) using the Functional Acuity Contrast Test sinewave contrast sensitivity slides. It was performed with corrected distance visual acuity (CDVA) under photopic as well as mesopic conditions, with dark adaptation of 10 minutes and without glare.
Statistical Analysis Statistical analysis was performed using SPSS software (version 16, SPSS, Inc.). A paired-sample t test was used for preoperative and postoperative comparisons. An independent-sample t test was used for comparisons between the femtosecond lenticule extraction group and pseudo small-incision lenticule extraction group. A P value less than 0.05 was considered statistically significant.
RESULTS Fifty-two consecutive patients (102 eyes) were sequentially recruited for the study. Table 1 shows the patients' demographic and preoperative data. There was no
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Table 2. Comparison of preoperative and postoperative visual acuity and SE. Postoperative Preoperative Parameter Snellen UDVA Mean G SD Range Snellen CDVA Mean G SD Range Mean SE (D) G SD
Group 1
Group 2
1 Month P Value
Group 1
Group 2
P Value
0.06 G 0.09 0.01, 0.50
0.05 G 0.06 0.01, 0.33
.413
0.85 G 0.19 0.33, 1.00
0.85 G 0.22 0.29, 1.33
.906
1.00 G 0.10 0.80, 1.33 5.80 G 2.08
1.01 G 0.06 1.00, 1.33 6.23 G 1.84
.394
0.97 G 0.15 0.50, 1.25 0.19 G 0.63
1.01 G 0.13 0.67, 1.33 0.20 G 0.54
.15
.271
.992
CDVA Z corrected distance visual acuity; Group 1 Z femtosecond lenticule extraction; Group 2 Z pseudo small-incision lenticule extraction; SE Z spherical equivalent; UDVA Z uncorrected distance visual acuity
statistically significant difference between the 2 groups in mean age, sex, mean sphere, mean cylinder, or mean spherical equivalent (SE) (P range 0.129 to 0.697).
The uncorrected distance visual acuity (UDVA) and CDVA showed a general trend toward improvement in the pseudo small-incision lenticule extraction group
Figure 1. A: Preoperative CDVA and postoperative UDVA in femtosecond lenticule extraction patients. B: Preoperative CDVA and postoperative UDVA in pseudo smallincision lenticule extraction patients (CDVA Z corrected distance visual acuity; UDVA Z uncorrected distance visual acuity).
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Table 2. (Cont.) Postoperative 3 Months
6 Months
1 Year
Group 1
Group 2
P Value
Group 1
Group 2
P Value
Group 1
Group 2
P Value
0.91 G 0.17 0.33, 1.33
0.91 G 0.18 0.40, 1.33
.904
0.91 G 0.15 0.50, 1.00
0.93 G 0.19 0.25, 1.33
.489
0.93 G 0.19 0.50, 1.33
0.97 G 0.20 0.63, 1.33
.345
1.04 G 0.13 0.80, 1.33 0.11 G 0.54
1.06 G 0.14 0.80, 1.33 0.01 G 0.49
.379
1.04 G 0.09 1.00, 1.30 0.11 G 0.41
1.05 G 0.18 0.63, 1.33 0.06 G 0.44
.83
1.09 G 0.16 0.80, 1.33 0.09 G 0.33
1.19 G 0.17 1.00, 1.33 0.02 G 0.45
.032
.335
compared with the femtosecond lenticule extraction group 1, 3, 6, and 12 months after surgery; however, the difference in CDVA was statistically significant at 12 months only (PZ.032) (Table 2). The mean spherical equivalent (SE) was not statistically significantly different between the 2 groups at any postoperative visit (Table 2). Figure 1 shows the safety of femtosecond lenticule extraction and pseudo small-incision lenticule extraction and Figure 2, their efficacy. Using intention-to-treat analysis, a significant increase in the root mean square (RMS) of total HOAs from preoperatively to 1 and 3 months postoperatively occurred in both the femtosecond lenticule extraction and pseudo small-incision lenticule extraction groups (both P ! .05) (Table 3). However, 6 months postoperatively, the increase was significant in the pseudo small-incision lenticule extraction group (P ! .001) but not the femtosecond lenticule extraction group (P Z .068) compared with preoperatively. A statistically significant increase in 3rd-order aberrations was observed in the pseudo small-incision lenticule extraction group 1 month (P Z .003) and in both groups 3 months postoperatively (both P ! .05) compared with preoperative values. However, this increase was not significant at 6 months or 1 year. A statistically significant increase in 3rd-order vertical trefoil was found from preoperatively to 3 months postoperatively in the femtosecond lenticule extraction group; however, the difference was not significant at 6 months or 1 year. A significant increase in 3rd-order vertical coma aberration occurred in both groups 1, 3, and 6 months postoperatively, but not at 1 year. There was no difference in preoperative and postoperative 3rd-order horizontal trefoil and horizontal coma, total 4th-order aberrations, and spherical aberration at any timepoint between the 2 groups. Table 4 compares the HOAs between the 2 groups preoperatively and postoperatively. The RMS of total
.830
.665
HOAs was not significantly different between the 2 groups preoperatively (P Z .664) or postoperatively at 1, 3, or 6 months (P Z .225 to P Z .586). Total 3rdorder aberrations, 3rd-order vertical and horizontal trefoil aberration, 3rd-order vertical and horizontal
Figure 2. A: Change in CDVA in femtosecond lenticule extraction patients. B: Change in CDVA in pseudo small-incision lenticule extraction patients (CDVA Z corrected distance visual acuity).
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Table 3. Preoperative versus postoperative HOAs after femtosecond lenticule extraction and of pseudo small-incision lenticule extraction.
Surgery/Parameters Femtosecond lenticule extraction HOA RMS Total 3rd order Trefoil (vertical) Trefoil (horizontal) Coma (vertical) Coma (horizontal) Total 4th order Spherical aberration Pseudo small-incision lenticule extraction HOA RMS Total 3rd order Trefoil (vertical) Trefoil (horizontal) Coma (vertical) Coma (horizontal) Total 4th order Spherical aberration
n
1 Mo Vs Preop
3 Mo Vs Preop
6 Mo Vs Preop
1 Y Vs Preop
Mean Difference (mm)
Mean Difference (mm)
Mean Difference (mm)
Mean Difference (mm)
P Value n
.012 .097 .882 .857 .015 .839 .913 .958
P Value n
P Value n
.068 .075 .25 .863 .017 .754 .076 .311
P Value
33 20 20 20 20 20 20 20
0.073 G 0.027 0.036 G 0.02 0.004 G 0.026 0.007 G 0.036 0.137 G 0.051 0.009 G 0.041 0.001 G 0.007 0.001 G 0.009
28 26 26 26 26 26 26 26
0.069 G 0.023 .006 20 0.043 G 0.017 .018 17 0.06 G 0.025 .024 17 0.012 G 0.027 .673 17 0.218 G 0.048 !.001 17 0.003 G 0.035 .939 17 0.004 G 0.005 .425 17 0.007 G 0.012 .554 17
0.061 G 0.031 0.036 G 0.019 0.031 G 0.026 0.005 G 0.027 0.159 G 0.06 0.013 G 0.041 0.01 G 0.005 0.019 G 0.018
d 8 8 8 8 8 8 8
d 0.067 G 0.038 0.004 G 0.044 0.013 G 0.043 0.213 G 0.104 0.049 G 0.062 0.002 G 0.008 0.029 G 0.028
d .118 .928 .782 .081 .456 .798 .34
43 50 50 50 50 50 50 50
0.098 G 0.029 .002 36 0.028 G 0.009 .003 50 0.023 G 0.022 .302 50 0.029 G 0.016 .08 50 0.115 G 0.026 !.001 50 0.008 G 0.019 .661 50 0.001 G 0.005 .898 50 0.009 G 0.008 .228 50
0.126 G 0.029 !.001 19 0.025 G 0.011 .037 43 0.024 G 0.019 .224 43 0.031 G 0.018 .099 43 0.117 G 0.035 .001 43 0.025 G 0.02 .215 43 0.031 G 0.022 .165 43 0.062 G 0.08 .447 43
0.175 G 0.039 !.001 d 0.017 G 0.012 .173 28 0.034 G 0.023 .135 28 0.032 G 0.018 .082 28 0.099 G 0.035 .007 28 0.03 G 0.022 .183 28 0.012 G 0.018 .505 28 0.008 G 0.011 .476 28
d 0 G 0.016 0.029 G 0.029 0.003 G 0.024 0.055 G 0.041 0.029 G 0.033 0.02 G 0.01 0.006 G 0.008
d .998 .324 .899 .186 .396 .071 .475
HOA Z higher-order aberrations; RMS Z root mean square Means G SD
coma aberration, total 4th-order aberrations, and spherical aberration were not significantly different between the 2 groups preoperatively or postoperatively at 1, 3, 6, and 12 months (P Z .201 to P Z .978). Table 5 compares the preoperative and 3-month and 12-month postoperative contrast sensitivity. The
mesopic contrast sensitivity decreased at 3, 6, 12, and 18 cycles per degree (cpd) in the femtosecond lenticule extraction group at 3 months (all P ! .05), although the difference was not significant at 1 year (P Z .341 to P Z .872). In the pseudo small-incision lenticule extraction group, the mesopic contrast sensitivity
Table 4. Comparison of preoperative and postoperative HOAs after femtosecond lenticule extraction and pseudo small-incision lenticule extraction. Postoperative Preoperative
1 Month
Mean G SD Parameter (mm) HOA RMS Total 3rd order Trefoil (vertical) Trefoil (horizontal) Coma (vertical) Coma (horizontal) Total 4th order Spherical aberration
Group 1 0.306 G 0.157 0.002 G 0.062 0.078 G 0.120 0.023 G 0.141 0.088 G 0.21 0.023 G 0.080 0.01 G 0.02 0.001 G 0.04
Mean G SD Group 2
0.291 G 0.154 0.001 G 0.047 0.079 G 0.131 0.004 G 0.100 0.076 G 0.175 0.003 G 0.090 0.026 G 0.107 0.007 G 0.042
P Value .664 .910 .964 .306 .781 .341 .480 .413
Group 1 0.378 G 0.166 0.026 G 0.088 0.099 G 0.183 0.008 G 0.101 0.011 G 0.300 0.013 G 0.163 0.010 G 0.028 0.002 G 0.042
Group 2 0.397 G 0.147 0.027 G 0.052 0.061 G 0.170 0.018 G 0.120 0.044 G 0.189 0.012 G 0.123 0.009 G 0.04 0.013 G 0.058
P Value .586 .941 .396 .730 .586 .978 .918 .302
Group 1 Z femtosecond lenticule extraction; Group 2 Z pseudo small-incision lenticule extraction; HOA Z higher-order aberrations; RMS Z root mean square
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increased at all measured spatial frequencies but was only significant at 3 cpd at 3 months (P Z .015) and at 1.5 cpd at 1 year (P Z .008). The photopic contrast sensitivity decreased at 6, 12, and 18 cpd in the femtosecond lenticule extraction group at 3 months (all P ! .05), although the difference was not significant at 1 year (P Z .152 to P Z .634); there was no significant difference in photopic contrast sensitivity in the pseudo small-incision lenticule extraction group at 3 months and 12 months compared with preoperatively. Figure 3 shows the mesopic and photopic contrast sensitivity over time in both groups. There was no significant difference in mesopic or photopic contrast sensitivity at any spatial frequency between the 2 groups preoperatively (P Z .138 to P Z .926) (Table 6). At 3 months, mesopic contrast sensitivity at 3 cpd was significantly higher in the pseudo small-incision lenticule extraction group than in the femtosecond lenticule extraction group (P Z .003); photopic contrast sensitivity at 6 cpd was also higher in the pseudo small-incision lenticule extraction group than in the femtosecond lenticule extraction group (P Z .004). This difference in photopic contrast sensitivity at 6 cpd persisted to 1 year (P Z .027), although the difference in mesopic contrast sensitivity at 3 cpd did not persist (P Z .336).
studies of the induction of HOAs after refractive lenticule extraction.11,13 In a study by Sekundo et al.,11 no eye had a significant increase in HOAs after femtosecond lenticule extraction; however, they did not perform a detailed numerical analysis in their study. Shah et al.13 found a significant increase in the RMS of total HOAs, higher-order coma aberrations, spherical aberrations, and 4th-order aberrations 6 months after small-incision lenticule extraction. Similarly, in our study the RMS of total HOAs and 3rd-order vertical coma aberration were significantly increased at 6 months in the pseudo small-incision lenticule extraction group. However, there was no significant change in total 4th-order or spherical aberrations. In the femtosecond lenticule extraction group at 6 months, only 3rd-order vertical coma aberration was significantly increased. Of note, at 1 year there was no significant change in the total as well as in different types of HOAs in the femtosecond lenticule extraction group or the pseudo small-incision lenticule extraction group. Therefore, our results indicate that refractive lenticule extraction is safe and effective in preventing a significant induction of HOAs over the long term. However, it appears that there is a change in HOAs over time in refractive lenticule extraction, with a period of about 6 months to 1 year before visual quality improves. This is unlike in LASIK, where visual quality usually remains constant postoperatively.14,29 We hypothesize that the return of HOAs to baseline in refractive lenticule extraction and not in LASIK could be the result of several factors, including wider effective optical zones in refractive lenticule extraction (O6.5 mm) than in LASIK, a wider transition in the refractive lenticule, and differences in corneal
DISCUSSION Higher-order aberrations commonly increase after LASIK procedures.21–23 Several studies have shown less induction of HOAs with the use of femtosecond lasers than with the use of microkeratomes during LASIK.26–28 However, there have been few published
Table 4. (Cont.) Postoperative 3 Months
6 Months
Mean G SD Group 1 0.369 G 0.106 0.030 G 0.071 0.044 G 0.159 0.019 G 0.091 0.081 G 0.269 0.024 G 0.160 0.012 G 0.024 0.001 G 0.057
Group 2 0.399 G 0.137 0.025 G 0.078 0.061 G 0.157 0.025 G 0.126 0.037 G 0.292 0.023 G 0.144 0.002 G 0.116 0.055 G 0.567
1 Year
Mean G SD P Value .323 .772 .603 .803 .473 .972 .472 .544
Group 1 0.353 G 0.163 0.026 G 0.070 0.042 G 0.160 0.029 G 0.081 0.046 G 0.274 0.006 G 0.151 0.015 G 0.027 0.025 G 0.066
Group 2 0.416 G 0.167 0.021 G 0.066 0.041 G 0.152 0.034 G 0.117 0.038 G 0.241 0.030 G 0.144 0.015 G 0.041 0.014 G 0.064
Mean G SD P Value
Group 1
.225 .762 .973 .589 .900 .486 .930 .495
d 0.021 G 0.109 0.017 G 0.102 0.020 G 0.111 0.045 G 0.421 0.002 G 0.163 -0.013 G 0.022 -0.026 G 0.061
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Group 2 d 0.002 G 0.071 0.052 G 0.142 0.003 G 0.121 0.028 G 0.247 0.035 G 0.143 0.029 G 0.054 0.011 G 0.049
P Value d .369 .339 .614 .443 .398 .201 .332
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Table 5. Preoperative versus postoperative mesopic and photopic contrast sensitivities. Group 1 3 Months Vs Preop CS/Spatial Frequency n Mesopic 1.5 cpd 3 cpd 6 cpd 12 cpd 18 cpd Photopic 1.5 cpd 3 cpd 6 cpd 12 cpd 18 cpd
Mean Difference
Group 2 1 Year Vs Preop
P Value n
Mean Difference
3 Months Vs Preop
P Value n
Mean Difference
1 Year Vs Preop
P Value n
Mean Difference
P Value
40 40 40 40 40
0.250 G 0.195 0.700 G 0.289 0.800 G 0.388 0.900 G 0.303 0.525 G 0.261
.208 .02 .046 .005 .051
28 28 28 28 28
0.286 G 0.295 0.179 G 0.277 0.214 G 0.419 0.071 G 0.439 0.143 G 0.384
.341 .525 .613 .872 .713
56 56 56 56 56
0.054 G 0.156 0.464 G 0.185 0.250 G 0.312 0.054 G 0.307 0.089 G 0.26
.732 .015 .427 .862 .733
24 24 24 24 24
0.625 G 0.215 0.542 G 0.269 0.208 G 0.289 0.000 G 0.341 0.125 G 0.435
.008 .056 .478 .999 .777
40 40 40 40 40
0.125 G 0.224 0.375 G 0.231 0.725 G 0.349 0.950 G 0.343 0.800 G 0.336
.58 .113 .044 .009 .022
28 28 28 28 28
0.179 G 0.282 0.179 G 0.257 0.179 G 0.371 0.500 G 0.339 0.179 G 0.326
.532 .494 .634 .152 .588
56 56 56 56 56
0.143 G 0.166 0.143 G 0.185 0.054 G 0.205 0.071 G 0.286 0.179 G 0.387
.393 .442 .794 .804 .646
24 24 24 24 24
0.542 G 0.361 0.583 G 0.300 0.542 G 0.313 0.417 G 0.394 0.083 G 0.564
.147 .065 .097 .302 .884
cpd Z cycles per degree; CS Z contrast sensitivity; Group 1 Z femtosecond lenticule extraction; Group 2 Z pseudo small-incision lenticule extraction Means G SE
biomechanical stability between refractive lenticule extraction and LASIK. Our group recently found significantly less inflammation and stromal remodeling after refractive lenticule extraction than after LASIK, which might contribute to recovery of HOAs to baseline levels in refractive lenticule extraction.30 Comparing refractive lenticule extraction and femtosecond lenticule extraction with wavefrontoptimized femtosecond LASIK, Gertnere et al.15 found that refractive lenticule extraction and femtosecond lenticule extraction induced significantly less HOAs than LASIK, indicating that HOAs were likely induced by the excimer laser rather than the by corneal flap. In our study comparing the 2 variants of refractive lenticule extraction, we found that the increase in the RMS of total HOAs, total 3rd-order aberrations, 3rd-order vertical and horizontal trefoil aberrations, 3rd-order vertical and horizontal coma aberrations, total 4thorder aberrations, and spherical aberrations were not significantly different between femtosecond lenticule extraction and pseudo small-incision lenticule extraction groups from preoperatively to 1, 3, 6, and 12 months postoperatively (P range 0.201 to 0.978). Therefore, despite the small incision, lack of flap lifting, and potential for a more difficult lenticule extraction because of the learning curve for lamellar separation, pseudo small-incision lenticule extraction did not induce significantly more HOAs than femtosecond lenticule extraction. However, Tay et al.31 noted differences in corneal flap and stromal bed edema between femtosecond lenticule extraction and pseudo small-incision lenticule extraction
postoperatively on anterior segment optical coherence tomography; anatomic stabilization occurred 3 months postoperatively. Contrast sensitivity is the ability to detect differences in luminance between adjacent areas and reflects the quality of vision.17–20,32 Numerous studies have shown that contrast sensitivity function declines after corneal refractive surgeries such as photorefractive keratectomy33–36 and LASIK,17,18,34,36–38 although the effects are often temporary and contrast sensitivity generally recovers to preoperative levels within 3 to 12 months after surgery.17,18,34,36–38 Comparing refractive lenticule extraction with femtosecond-assisted LASIK, Gertnere et al.15 found that photopic contrast sensitivity increased similarly after both procedures but that mesopic contrast sensitivity significantly improved after refractive lenticule extraction but not after femtosecond-assisted LASIK. In our study, both mesopic and photopic contrast sensitivities decreased significantly 3 months after femtosecond lenticule extraction at the higher frequencies (6, 12, 18 cpd) but recovered by 1 year. In contrast, mesopic and photopic contrast sensitivities were generally improved after pseudo small-incision lenticule extraction at all frequencies at 3 months and at 1 year, although the only significantly improvement in mesopic contrast sensitivity was at 3 cpd at 3 months and 1.5 cpd at 1 year. Because HOAs have been found to inadvertently affect contrast sensitivity after refractive surgery,33,35,37 the recovery of HOAs to preoperative levels at 1 year explains the similar trend in contrast sensitivity at 1 year in our study.
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Figure 3. Femtosecond lenticule extraction mesopic (A) and photopic (C) contrast sensitivities over time and pseudo small-incision lenticule extraction mesopic (B) and photopic (D) contrast sensitivities over time (cpd Z cycles per degree).
The improvement in both mesopic and photopic contrast sensitivities in the pseudo small-incision lenticule extraction group, despite of the increase in HOAs at 3 months, was not found in the femtosecond lenticule extraction group. We hypothesize that after flap creation and lifting in femtosecond lenticule extraction, the ocular surface is more neurotrophic than after pseudo small-incision lenticule extraction, in which there is no flap lifting. The effect of a less neurotrophic surface is a superior ocular surface and tear film, hence equating to a better quality of vision. This might have negated some of the effects of HOAs in pseudo smallincision lenticule extraction patients, resulting in improved contrast sensitivity. Comparing the 2 variants of refractive lenticule extraction, both photopic and mesopic contrast sensitivities were better in the pseudo small-incision lenticule extraction group than in femtosecond lenticule extraction group at all frequencies except at 12 cpd
under mesopic conditions at 3 months and 1 year. However, this was significant only for 3 cpd under mesopic conditions and 6 cpd under photopic conditions at 3 months. This significant improvement in photopic contrast sensitivity at 6 cpd persisted to 1 year after pseudo small-incision lenticule extraction. Therefore, we postulate that pseudo small-incision lenticule extraction with a small incision and lack of a lifted flap might have led to fewer induced aberrations, which might have contributed to better contrast sensitivity. This study has several limitations. First, this was a retrospective analysis and in this process, there was a risk for bias. However, there were no statistically significant differences in the demographics or preoperative data between the 2 groups. The authenticity of the results would probably have been better confirmed with a randomized controlled study, which is currently in progress. Second, multiple surgeons
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Table 6. Between-group comparison of preoperative and postoperative mesopic and photopic contrast sensitivities. Preoperative
Postoperative
3 Months CS/Spatial Frequency Mesopic 1.5 cpd 3 cpd 6 cpd 12 cpd 18 cpd Photopic 1.5 cpd 3 cpd 6 cpd 12 cpd 18 cpd
1 Year
Group 1
Group 2
P Value
Group 1
Group 2
P Value
Group 1
Group 2
P Value
6.24 G 1.10 5.55 G 1.29 4.40 G 1.55 2.95 G 1.38 1.33 G 1.44
6.26 G 1.07 5.24 G 1.05 4.02 G 1.63 2.53 G 1.61 1.12 G 1.61
.926 .194 .233 .178 .498
5.95 G 1.41 4.83 G 1.57 3.58 G 1.93 2.00 G 1.62 0.70 G 1.14
6.30 G 1.19 5.70 G 1.26 4.23 G 1.85 2.52 G 1.81 1.21 G 1.57
.188 .003 .095 .152 .066
6.57 G 1.48 5.61 G 1.57 4.32 G 1.93 3.07 G 2.34 1.61 G 1.73
6.75 G 0.99 5.96 G 1.12 4.75 G 1.29 3.04 G 1.30 1.63 G 1.69
.617 .366 .359 .954 .970
5.88 G 0.97 5.83 G 1.01 5.36 G 1.41 4.86 G 1.51 3.48 G 1.49
5.79 G 1.12 5.66 G 0.98 5.45 G 1.31 4.40 G 1.53 3.41 G 1.86
.683 .379 .741 .138 .858
5.70 G 1.32 5.40 G 1.46 4.55 G 1.74 3.80 G 1.62 2.50 G 1.88
5.95 G 1.10 5.77 G 1.01 5.46 G 1.31 4.30 G 1.39 3.16 G 1.95
.324 .174 .004 .106 .1
6.07 G 1.18 5.75 G 1.40 5.18 G 1.61 4.36 G 1.87 3.54 G 1.73
6.21 G 1.59 6.25 G 1.29 6.08 G 1.18 5.00 G 1.38 3.63 G 2.08
.724 .191 .027 .171 .867
cpd Z cycles per degree; CS Z contrast sensitivity; Group 1 Z femtosecond lenticule extraction; Group 2 Z pseudo small-incision lenticule extraction Means G SD
performed the operations. This might have affected the results of the achieved visual outcomes, especially because pseudo small-incision lenticule extraction involves a more potentially challenging lamellar dissection technique than femtosecond lenticule extraction. However, all 3 surgeons in this study were corneal trained and used to performing corneal lamellar surgery, and the transition from femtosecond lenticule extraction to pseudo small-incision lenticule extraction was smooth and well controlled. At present, we are collecting data on the small-incision lenticule extraction procedure, the results of which will be subsequently published. Third, we assessed the HOAs and contrast sensitivity before and after surgery but did not assess subjective symptoms in the study. A standardized questionnaire measuring patients' quality of vision and an assessment of the relationship between these symptoms and HOAs and contrast sensitivity would be useful. Last, patients with missing preoperative or postoperative data were excluded in our analysis because we analyzed our data by the intention-to-treat approach to provide unbiased comparisons of the patients in each group. These missing data might reduce the representativeness of the sample; however, they are missing at random and therefore unlikely to distort inferences about our study population. In summary, our results indicate that refractive lenticule extraction is safe and effective with no significant induction of HOAs and deterioration in contrast sensitivity at 1 year postoperatively. In the comparative arm of the study between the 2 variants of refractive lenticule extraction, which also describes our initial learning curve with this new form of refractive
surgery, we found that the induction of HOAs was not significantly different between femtosecond lenticule extraction and pseudo small-incision lenticule extraction. However, there was a significant improvement in photopic contrast sensitivity after pseudo small-incision lenticule extraction that persisted through 1 year. WHAT WAS KNOWN In refractive lenticule extraction, the femtosecond laser cuts an intrastromal lenticule. The lenticule is then removed through a surface incision of varying size depending on whether it is femtosecond lenticule extraction, small-incision lenticule extraction, or pseudo smallincision lenticule extraction, which is a transitional procedure. Initial clinical results of both procedures have been promising; however, there is a lack of studies comparing the visual outcomes between refractive lenticule extraction procedures. WHAT THIS PAPER ADDS Refractive lenticule extraction was safe and effective with no significant induction of HOAs or deterioration in contrast sensitivity 1 year postoperatively. Induction of HOAs was not significantly different between femtosecond lenticule extraction and pseudo smallincision lenticule extraction, although there was significant improvement in photopic contrast sensitivity after pseudo small-incision lenticule extraction.
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REFERENCES 1. Soong HK, Malta JB. Femtosecond lasers in ophthalmology. Am J Ophthalmol 2009; 147:189–197 2. Kullman G, Pineda R. Alternative applications of the femtosecond laser in ophthalmology. Semin Ophthalmol 2010; 25:256–264 3. Kim P, Sutton GL, Rootman DS. Applications of the femtosecond laser in corneal refractive surgery. Curr Opin Ophthalmol 2011; 22:238–244 4. Binder PS. One thousand consecutive IntraLase laser in situ keratomileusis flaps. J Cataract Refract Surg 2006; 32:962–969 5. Kezirian GM, Stonecipher KG. Comparison of the IntraLase femtosecond laser and mechanical keratomes for laser in situ keratomileusis. J Cataract Refract Surg 2004; 30:804–811 ~o MQ, Wilson SE. Femtosecond laser in laser in situ ker6. Saloma atomileusis. J Cataract Refract Surg 2010; 36:1024–1032 7. Moshirfar M, Gardiner JP, Schliesser JA, Espandar L, Feiz V, Mifflin MD, Chang JC. Laser in situ keratomileusis flap complications using mechanical microkeratome versus femtosecond laser: retrospective comparison. J Cataract Refract Surg 2010; 36:1925–1933 8. Holtzer MP, Rabsilber TM, Auffarth GU. Femtosecond laser-assisted corneal flap cuts: morphology, accuracy, and histopathology. Invest Ophthalmol Vis Sci 2006; 47:2828–2831. Available at: http://www.iovs.org/cgi/reprint/47/7/2828. Accessed September 7, 2014 9. Lee JK, Nkyekyer EW, Chuck RS. Microkeratome complications. Curr Opin Ophthalmol 2009; 20:260–263 € der M, Sekundo W. Femtosecond lenti10. Blum M, Kunert K, Schro cule extraction for the correction of myopia: preliminary 6-month results. Graefes Arch Clin Exp Ophthalmol 2010; 248:1019–1027 11. Sekundo W, Kunert K, Russmann C, Gille A, Bissmann W, Stobrawa G, Sticker M, Bischoff M, Blum M. First efficacy and safety study of femtosecond lenticule extraction for the correction of myopia: six-month results. J Cataract Refract Surg 2008; 34:1513–1520; erratum, 1819 12. Sekundo W, Kunert KS, Blum M. Small incision corneal refractive surgery using the small incision lenticule extraction (SMILE) procedure for the correction of myopia and myopic astigmatism: results of a 6 month prospective study. Br J Ophthalmol 2011; 95:335–339 13. Shah R, Shah S, Sengupta S. Results of small incision lenticule extraction: all-in-one femtosecond laser refractive surgery. J Cataract Refract Surg 2011; 37:127–137 14. Vestergaard A, Ivarsen A, Asp S, Hjortdal JØ. Femtosecond (FS) laser vision correction procedure for moderate to high myopia: a prospective study of ReLExÒ flex, and comparison with a retrospective study of FS-laser in situ keratomileusis. Acta Ophthalmol 2013; 91:355–362. Available at: http://onlinelibrary.wiley.com/doi/ 10.1111/j.1755-3768.2012.02406.x/pdf. Accessed September 7, 2014 15. Gertnere J, Solomatin I, Sekundo W. Refractive lenticule extraction (ReLEx flex) and wavefront-optimized femto-LASIK: comparison of contrast sensitivity and high-order aberrations at 1 year. Graefes Arch Clin Exp Ophthalmol 2013; 251:1437–1442 16. Ang M, Chaurasia SS, Angunawela RI, Poh R, Riau A, Tan D, Mehta JS. Femtosecond lenticule extraction (FLEx): clinical results, interface evaluation, and intraocular pressure variation. Invest Ophthalmol Vis Sci 2012; 53:1414–1421. Available at: http://www.iovs.org/content/53/3/1414.full.pdf. Accessed September 7, 2014 17. Mutyala S, McDonald MB, Scheinblum KA, Ostrick MD, Brint SF, Thompson H. Contrast sensitivity evaluation after laser in situ keratomileusis. Ophthalmology 2000; 107:1864–1867
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18. Chan JWW, Edwards MH, Woo GC, Woo VCP. Contrast sensitivity after laser in situ keratomileusis; one-year follow-up. J Cataract Refract Surg 2002; 28:1774–1779 19. Holladay JT, Dudeja DR, Chang J. Functional vision and corneal changes after laser in situ keratomileusis determined by contrast sensitivity, glare testing, and corneal topography. J Cataract Refract Surg 1999; 25:663–669 20. Nakamura K, Bissen-Miyajima H, Toda I, Hori Y, Tsubota K. Effect of laser in situ keratomileusis correction on contrast visual acuity. J Cataract Refract Surg 2001; 27:357–361 21. Oshika T, Miyata K, Tokunaga T, Samejima T, Amano S, Tanaka S, Hirohara Y, Mihashi T, Maeda N, Fujikado T. Higher order wavefront aberrations of cornea and magnitude of refractive correction in laser in situ keratomileusis. Ophthalmology 2002; 109:1154–1158 22. Miller JM, Anwaruddin R, Straub J, Schwiegerling J. Higher order aberrations in normal, dilated, intraocular lens, and laser in situ keratomileusis corneas. J Refract Surg 2002; 18: S579–S583 23. Pallikaris IG, Kymionis GD, Panagopoulou SI, Siganos CS, Theodorakis MA, Pallikaris AI. Induced optical aberrations following formation of a laser in situ keratomileusis flap. J Cataract Refract Surg 2002; 28:1737–1741 24. Kamiya K, Shimizu K, Igarashi A, Kobashi H, Komatsu M. Comparison of visual acuity, higher-order aberrations and corneal asphericity after refractive lenticule extraction and wavefrontguided laser-assisted in situ keratomileusis for myopia. Br J Ophthalmol 2013; 97:968–975 25. Riau A, Angunawela RI, Chaurasia SS, Tan DT, Mehta JS. Effect of different femtosecond laser-firing patterns on collagen disruption during refractive lenticule extraction. J Cataract Refract Surg 2012; 38:1467–1475 26. Buzzonetti L, Petrocelli G, Valente P, Tamburrelli C, Mosca L, Laborante A, Balestrazzi E. Comparison of corneal aberration changes after laser in situ keratomileusis performed with mechanical microkeratome and IntraLase femtosecond laser: 1year follow-up. Cornea 2008; 27:174–179 27. Medeiros FW, Stapleton WM, Hammel J, Krueger RR, Netto MV, Wilson SE. Wavefront analysis comparison of LASIK outcomes with the femtosecond laser and mechanical microkeratomes. J Refract Surg 2007; 23:880–887 28. Tran DB, Sarayba MA, Bor Z, Garufis C, Duh Y-J, Soltes CR, Juhasz T, Kurtz RM. Randomized prospective clinical study comparing induced aberrations with IntraLase and Hansatome flap creation in fellow eyes; potential impact on wavefrontguided laser in situ keratomileusis. J Cataract Refract Surg 2005; 31:97–105 29. Au JD, Krueger RR. Optimized femto-LASIK maintains preexisting spherical aberration independent of refractive error. J Refract Surg 2012; 28(suppl):S821–S825. Available at: http://www.healio.com/ w/media/journals/jrs/2012/11_november_supplement/10_3928_ 1081597x_20121005_02/10_3928_1081597x_20121005_02.pdf. Accessed September 7, 2014 30. Riau AK, Angunawela RI, Chaurasia SS, Lee WS, Tan DT, Mehta JS. Early corneal wound healing and inflammatory responses following refractive lenticule extraction (ReLEx). Invest Ophthalmol Vis Sci 2011; 52:6213–6221. Available at: http:// www.iovs.org/content/52/9/6213.full.pdf. Accessed September 7, 2014 31. Tay E, Li X, Chan C, Tan DT, Mehta JS. Refractive lenticule extraction flap and stromal bed morphology assessment with anterior segment optical coherence tomography. J Cataract Refract Surg 2012; 38:1544–1551 32. Marcos S. Aberrations and visual performance following standard laser vision correction. J Refract Surg 2001; 17:S596–S601
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33. Tanabe T, Miyata K, Samejima T, Hirohara Y, Mihashi T, Oshika T. Influence of wavefront aberration and corneal subepithelial haze on low-contrast visual acuity after photorefractive keratectomy. Am J Ophthalmol 2004; 138:620–624 s-Mico R, Charman WN. Choice of spatial frequency for 34. Monte contrast sensitivity evaluation after corneal refractive surgery. J Refract Surg 2001; 17:646–651 35. Seiler T, Kaemmerer M, Mierdel P, Krinke H-E. Ocular optical aberrations after photorefractive keratectomy for myopia and myopic astigmatism. Arch Ophthalmol 2000; 118:17–21. Available at: http://archopht.jamanetwork.com/data/Journals/ OPHTH/9867/ecs90164.pdf. Accessed September 7, 2014 36. Wang Z, Chen J, Yang B. Comparison of laser in situ keratomileusis and photorefractive keratectomy to correct myopia from 1.25 to 6.00 diopters. J Refract Surg 1997; 13:528–534 37. Yamane N, Miyata K, Samejima T, Hiraoka T, Kiuchi T, Okamoto F, Hirohara Y, Mihashi T, Oshika T. Ocular higherorder aberrations and contrast sensitivity after conventional
laser in situ keratomileusis. Invest Ophthalmol Vis Sci 2004; 45:3986–3990. Available at: http://www.iovs.org/cgi/reprint/45/ 11/3986. Accessed September 7, 2014 rez-Santonja JJ, Sakla HF, Alio JL. Contrast sensitivity after 38. Pe laser in situ keratomileusis. J Cataract Refract Surg 1998; 24:183–189
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First author: Deborah K.L. Tan, MB BS Singapore Eye Research Institute, Singapore
Postoperative ocular higher-order aberrations and contrast sensitivity: Femtosecond lenticule extraction versus pseudo small-incision lenticule extraction Deborah K.L. Tan, MB BS, Wan Ting Tay, MAppStat, Cordelia Chan, FRCSEd, Donald T.H. Tan, FRCOphth, FAMS, Jodhbir S. Mehta, FRCSEd
PURPOSE: To evaluate and compare changes in contrast sensitivity and ocular higher-order aberrations (HOAs) after femtosecond lenticule extraction (FLEx) and pseudo small-incision lenticule extraction (SMILE). SETTING: Singapore National Eye Centre, Singapore. DESIGN: Retrospective case series. METHOD: Patients had femtosecond lenticule extraction (Group 1) or pseudo small-incision lenticule extraction (Group 2) between March 2010 and December 2011. The main outcome measures were manifest refraction, HOAs, and contrast sensitivity 1, 3, 6, and 12 months postoperatively. RESULTS: Fifty-two consecutive patients (102 eyes) were recruited, 21 patients (42 eyes) in Group 1 and the 31 patients (60 eyes) in Group 2. The uncorrected and corrected distance visual acuities were significantly better in Group 2 than in Group 1 at 12 months (P Z .032). There was no significant increase in 3rd- or 4th-order aberrations at 1 year and no significant difference between the 2 groups preoperatively or postoperatively. At 1 year, there was a significant increase in mesopic contrast sensitivity in Group 2 at 1.5 cycles per degree (cpd) (P Z .008) that was not found in Group 1, and photopic contrast sensitivity at 6.0 cpd was higher in Group 2 (P Z .027). CONCLUSIONS: These results indicate that refractive lenticule extraction is safe and effective with no significant induction of HOAs or deterioration in contrast sensitivity at 1 year. Induction of HOAs was not significantly different between both variants of refractive lenticule extraction. However, there was significant improvement in photopic contrast sensitivity after pseudo small-incision lenticule extraction, which persisted through 1 year. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2015; 41:623–634 Q 2015 ASCRS and ESCRS
The femtosecond laser is a near-infrared neodymium: YAG laser that causes photodisruption of the cornea by producing ultrashort pulses of light (10 15 of a second or femtosecond) at high repetition rates, thereby eliciting cleavage of the stroma lamellae with surgical precision.1,2 Femtosecond lasers have been widely used in laser in situ keratomileusis (LASIK) to enable nonmechanical creation of a corneal flap.3 Their advantage over manual microkeratomes include increased precision,4,5 a reduced incidence of buttonholes or free Q 2015 ASCRS and ESCRS Published by Elsevier Inc.
caps,6,7 and a reduced incidence of flap-related complications.8,9 Refractive lenticule extraction (ReLEx, Carl Zeiss Meditec AG) is a new corneal refractive procedure in which the femtosecond laser cuts an intrastromal lenticule corresponding to the patients' refractive correction without the use of a microkeratome or excimer laser.10 The lenticule is then removed through a surface incision of varying size depending on whether the femtosecond lenticule extraction (FLEx, Carl Zeiss http://dx.doi.org/10.1016/j.jcrs.2014.07.032 0886-3350
623
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HOAS AFTER FEMTOSECOND LENTICULE EXTRACTION VS PSEUDO SMALL-INCISION LENTICULE EXTRACTION
Meditec AG)11 or small-incision lenticule extraction (SMILE, Carl Zeiss Meditec AG)12,13 procedure is being performed. The first involves cutting and lifting a complete LASIK-type hinged flap to remove the intrastromal lenticule; the latter is a flapless procedure that involves removing the same lenticule through a small 2.0 to 4.0 mm pocket incision.10 Pseudo small-incision lenticule extraction is generally performed during the learning curve and transition from femtosecond lenticule extraction to small-incision lenticule extraction, whereby the laser is used exactly as in femtosecond lenticule extraction (ie, the laser performs the flap cut); however, the flap is not lifted and only a smaller incision (5.0 to 6.0 mm) is opened. Next, the lenticule is extracted akin to small-incision lenticule extraction. Initial clinical results of refractive lenticule extraction have been promising.10,14–16 The postoperative refractive outcomes, stability of refraction, predictability, efficacy, and safety have been shown to be similar if not better than in LASIK, with fewer complications.14,15 It has been well documented that LASIK compromises contrast sensitivity after surgery,17–20 and reports have also shown that higher-order aberrations (HOAs) increase after LASIK.21–23 In a comparative study between femtosecond lenticule extraction and LASIK, contrast sensitivity and the induction of HOAs were reported to be similar to or better than in LASIK.14,15,24 In the transitional learning curve from femtosecond lenticule extraction, pseudo small-incision lenticule extraction is a good intermediary procedure before conversion to full small-incision lenticule extraction because it allows the surgeon to gain familiarity with the visualization of the lenticule without lifting the flap. It also allows the surgeon to perform the lamellar separation required in the small-incision lenticule extraction procedure with the knowledge that if unsuccessful, the flap can be simply lifted and the lenticule removed vis- a-vis a standard femtosecond
Submitted: January 14, 2014. Final revision submitted: June 29, 2014. Accepted: July 10, 2014.
lenticule extraction procedure. Another potential advantage of pseudo small-incision lenticule extraction over small-incision lenticule extraction is that in the event of the need for refractive retreatment, it might be possible to lift the flap fully to perform excimer ablation on the stromal bed. A review of the current literature showed a lack of studies that compared the visual outcomes between the 2 procedures of refractive lenticule extraction. Because pseudo small-incision lenticule extraction might be considered an important transitional procedure, the purpose of this study was to evaluate and compare changes in contrast sensitivity and ocular HOAs after femtosecond lenticule extraction and pseudo small-incision lenticule extraction. PATIENTS AND METHODS Study Population This was a retrospective study that included all patients who had refractive lenticule extraction–femtosecond lenticule extraction and pseudo small-incision lenticule extraction between March 2010 and December 2011 at the Singapore National Eye Centre. The study group represented our learning curve with refractive lenticule extraction, which included initial experience with femtosecond lenticule extraction followed by a transition to performing pseudo small-incision lenticule extraction. This study was performed in accordance with the tenets of the Declaration of Helsinki, as revised in 1989. Written informed consent was obtained from all patients, and ethics approval was obtained from the Institutional Review Board of the Singapore Eye Research Institute. Inclusion criteria for the study were age 21 years or older, spherical myopia between 1.00 diopter (D) and 9.00 D and myopic astigmatism less than 3.00 D, stable refractive error for 12 months, minimum corneal thickness of 480 mm with minimum calculated residual stromal bed (RSB) after treatment of 250 mm, and regular corneal topography (Orbscan II, Bausch & Lomb/Orbtek Inc.). Exclusion criteria were residual, recurrent, or active ocular diseases such as uveitis, severe dry eye, severe allergic eye disease, glaucoma, visually significant cataract, retinal disease, previous corneal surgery or trauma within the corneal flap zone; patent vascularization within 1.0 mm of the corneal flap zone; any active systemic disease; or the use of systemic medications that are likely to affect corneal wound healing, such as corticosteroids and antimetabolites.
Surgical Technique
From the Singapore Eye Research Institute (D.K.L. Tan, Tay, Chan, D.T.H. Tan, Mehta), the Department of Ophthalmology (D.T.H. Tan), Yong Loo Lin School of Medicine, National University of Singapore, the Singapore National Eye Center (D.K.L. Tan, Chan, D.T.H. Tan), the Department of Clinical Sciences (Mehta), Duke-NUS Graduate Medical School, and the Lee Kong Chian School of Medicine (D.T.H. Tan), Nanyang Technological University, Singapore. Corresponding author: Jodhbir S. Mehta, FRCSEd, Singapore National Eye Center, 11 Third Hospital Avenue, Singapore 168751. E-mail: [email protected].
The refractive lenticule extraction procedures were performed by 1 of 3 experienced corneal refractive surgeons (D.T.H.T, C.C., J.S.M) using a previously described technique10,12 All refractive lenticule extraction procedures share similar surgical steps at the beginning of the procedure. After these common steps, there were specific steps for femtosecond lenticule extraction and pseudo small-incision lenticule extraction. After application of topical anesthesia, standard sterile draping, and insertion of a speculum, the patient's eye was positioned under the femtosecond surgical microscope
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Table 1. Demographic and preoperative information.
Parameter Patients (n) Age (y) Mean G SD Range Male sex, n (%) Eyes (n) Sphere (D) Mean G SD Range Cylinder (D) Mean G SD Range SE (D) Mean G SD Range
Femtosecond Lenticule Extraction
Pseudo Small-Incision Lenticule Extraction
21
31
32.26 G 7.10 20.83, 45.51 12 (57.1) 42
31.56 G 5.71 23.01, 41.13 20 (64.5) 60
5.32 G 2.08 1.00, 9.00
5.85 G 1.91 0.50, 10.00
.183
0.97 G 0.57 0.00, 2.75
0.77 G 0.72 0.00, 3.00
.129
5.80 G 2.08 1.38, 9.75
6.23 G 1.84 1.50, 10.13
.271
P Value
.697 .592
SE Z spherical equivalent
(Visumax, Carl Zeiss Meditec AG). Under patient fixation, the cornea was docked under the curved suction contact glass before application of suction as centration was achieved. Femtosecond laser treatment was then initiated. First, the posterior lamellar surface of the refractive lenticule was incised (spiral-in pattern); second, a vertical 15 mm lenticule side cut at the outer border of the lamellar dissection was performed to outline the outer edge of the lenticule. Next, the anterior lamellar surface of the refractive lenticule was cut (spiral-out pattern), which extended beyond the posterior lenticule diameter by 0.5 mm to form an overlapping anterior flap.25 The following femtosecond laser parameters were used: 120 mm flap thickness, 7.5 mm anterior flap diameter, 6.5 mm optical zone of lenticule, and 145 nJ of power with side-cut angles at 90 degrees. The spot distance and tracking spacing were 3/3 mm for the lenticule, 2.5/2.5 mm for the lenticule side cut, 3/3 mm for the flap, and 2/2 mm for the flap side cut.
Steps Specific to the Femtosecond Lenticule Extraction Procedure After the formation of the anterior flap, the vertical flap side cut through to the corneal surface was created, leaving a superior hinge 50 degrees in chord length, similar to a standard LASIK flap in configuration. The suction was then released, and a Seibel spatula (Rhein Medical, Inc.) was inserted under the flap near the hinge before the flap was separated and reflected, again similar to a LASIK procedure. The inner edge of the lenticule was then identified and separated from the RSB with a Sinskey hook, and the posterior border of the lenticule was gently separated from the stromal bed with the Seibel spatula. The free end of the lenticule was then grasped with a nontoothed serrated forceps and peeled off, after which the flap was repositioned.
Steps Specific to the Pseudo Small-Incision Lenticule Extraction Procedure In pseudo small-incision lenticule extraction, the hinge position was rotated to the upper temporal quadrant; otherwise, the vertical laser side cut was similar to femtosecond lenticule extraction. After release of suction, the Seibel spatula was used to separate the cut edge of the flap at the 12 o'clock position to form a superior opening of
approximately 5.0 to 6.0 mm. A blunt-tipped lamellar dissector was then used to perform lamellar dissection in the posterior, then the anterior laser dissection planes to separate the lenticule completely. Care was taken at this stage not to inadvertently further widen the 5.0 to 6.0 mm opening. The lenticule was then grasped with a forceps and removed from the pocket incision.
Outcome Measures The preoperative and 1-, 3-, 6-, and 12-month postoperative ophthalmic examinations included manifest refraction and HOAs, which were measured with an aberrometer system (Technolas Zywave aberrometer with Zywave software version 4.45, Zyoptix Diagnostic Workstation, Bausch & Lomb) with a 5.0 mm pupil without pharmacological intervention. Examinations also included contrast sensitivity, which was assessed with the Optec 6500P (Stereo Optical Co., Inc.) using the Functional Acuity Contrast Test sinewave contrast sensitivity slides. It was performed with corrected distance visual acuity (CDVA) under photopic as well as mesopic conditions, with dark adaptation of 10 minutes and without glare.
Statistical Analysis Statistical analysis was performed using SPSS software (version 16, SPSS, Inc.). A paired-sample t test was used for preoperative and postoperative comparisons. An independent-sample t test was used for comparisons between the femtosecond lenticule extraction group and pseudo small-incision lenticule extraction group. A P value less than 0.05 was considered statistically significant.
RESULTS Fifty-two consecutive patients (102 eyes) were sequentially recruited for the study. Table 1 shows the patients' demographic and preoperative data. There was no
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Table 2. Comparison of preoperative and postoperative visual acuity and SE. Postoperative Preoperative Parameter Snellen UDVA Mean G SD Range Snellen CDVA Mean G SD Range Mean SE (D) G SD
Group 1
Group 2
1 Month P Value
Group 1
Group 2
P Value
0.06 G 0.09 0.01, 0.50
0.05 G 0.06 0.01, 0.33
.413
0.85 G 0.19 0.33, 1.00
0.85 G 0.22 0.29, 1.33
.906
1.00 G 0.10 0.80, 1.33 5.80 G 2.08
1.01 G 0.06 1.00, 1.33 6.23 G 1.84
.394
0.97 G 0.15 0.50, 1.25 0.19 G 0.63
1.01 G 0.13 0.67, 1.33 0.20 G 0.54
.15
.271
.992
CDVA Z corrected distance visual acuity; Group 1 Z femtosecond lenticule extraction; Group 2 Z pseudo small-incision lenticule extraction; SE Z spherical equivalent; UDVA Z uncorrected distance visual acuity
statistically significant difference between the 2 groups in mean age, sex, mean sphere, mean cylinder, or mean spherical equivalent (SE) (P range 0.129 to 0.697).
The uncorrected distance visual acuity (UDVA) and CDVA showed a general trend toward improvement in the pseudo small-incision lenticule extraction group
Figure 1. A: Preoperative CDVA and postoperative UDVA in femtosecond lenticule extraction patients. B: Preoperative CDVA and postoperative UDVA in pseudo smallincision lenticule extraction patients (CDVA Z corrected distance visual acuity; UDVA Z uncorrected distance visual acuity).
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Table 2. (Cont.) Postoperative 3 Months
6 Months
1 Year
Group 1
Group 2
P Value
Group 1
Group 2
P Value
Group 1
Group 2
P Value
0.91 G 0.17 0.33, 1.33
0.91 G 0.18 0.40, 1.33
.904
0.91 G 0.15 0.50, 1.00
0.93 G 0.19 0.25, 1.33
.489
0.93 G 0.19 0.50, 1.33
0.97 G 0.20 0.63, 1.33
.345
1.04 G 0.13 0.80, 1.33 0.11 G 0.54
1.06 G 0.14 0.80, 1.33 0.01 G 0.49
.379
1.04 G 0.09 1.00, 1.30 0.11 G 0.41
1.05 G 0.18 0.63, 1.33 0.06 G 0.44
.83
1.09 G 0.16 0.80, 1.33 0.09 G 0.33
1.19 G 0.17 1.00, 1.33 0.02 G 0.45
.032
.335
compared with the femtosecond lenticule extraction group 1, 3, 6, and 12 months after surgery; however, the difference in CDVA was statistically significant at 12 months only (PZ.032) (Table 2). The mean spherical equivalent (SE) was not statistically significantly different between the 2 groups at any postoperative visit (Table 2). Figure 1 shows the safety of femtosecond lenticule extraction and pseudo small-incision lenticule extraction and Figure 2, their efficacy. Using intention-to-treat analysis, a significant increase in the root mean square (RMS) of total HOAs from preoperatively to 1 and 3 months postoperatively occurred in both the femtosecond lenticule extraction and pseudo small-incision lenticule extraction groups (both P ! .05) (Table 3). However, 6 months postoperatively, the increase was significant in the pseudo small-incision lenticule extraction group (P ! .001) but not the femtosecond lenticule extraction group (P Z .068) compared with preoperatively. A statistically significant increase in 3rd-order aberrations was observed in the pseudo small-incision lenticule extraction group 1 month (P Z .003) and in both groups 3 months postoperatively (both P ! .05) compared with preoperative values. However, this increase was not significant at 6 months or 1 year. A statistically significant increase in 3rd-order vertical trefoil was found from preoperatively to 3 months postoperatively in the femtosecond lenticule extraction group; however, the difference was not significant at 6 months or 1 year. A significant increase in 3rd-order vertical coma aberration occurred in both groups 1, 3, and 6 months postoperatively, but not at 1 year. There was no difference in preoperative and postoperative 3rd-order horizontal trefoil and horizontal coma, total 4th-order aberrations, and spherical aberration at any timepoint between the 2 groups. Table 4 compares the HOAs between the 2 groups preoperatively and postoperatively. The RMS of total
.830
.665
HOAs was not significantly different between the 2 groups preoperatively (P Z .664) or postoperatively at 1, 3, or 6 months (P Z .225 to P Z .586). Total 3rdorder aberrations, 3rd-order vertical and horizontal trefoil aberration, 3rd-order vertical and horizontal
Figure 2. A: Change in CDVA in femtosecond lenticule extraction patients. B: Change in CDVA in pseudo small-incision lenticule extraction patients (CDVA Z corrected distance visual acuity).
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Table 3. Preoperative versus postoperative HOAs after femtosecond lenticule extraction and of pseudo small-incision lenticule extraction.
Surgery/Parameters Femtosecond lenticule extraction HOA RMS Total 3rd order Trefoil (vertical) Trefoil (horizontal) Coma (vertical) Coma (horizontal) Total 4th order Spherical aberration Pseudo small-incision lenticule extraction HOA RMS Total 3rd order Trefoil (vertical) Trefoil (horizontal) Coma (vertical) Coma (horizontal) Total 4th order Spherical aberration
n
1 Mo Vs Preop
3 Mo Vs Preop
6 Mo Vs Preop
1 Y Vs Preop
Mean Difference (mm)
Mean Difference (mm)
Mean Difference (mm)
Mean Difference (mm)
P Value n
.012 .097 .882 .857 .015 .839 .913 .958
P Value n
P Value n
.068 .075 .25 .863 .017 .754 .076 .311
P Value
33 20 20 20 20 20 20 20
0.073 G 0.027 0.036 G 0.02 0.004 G 0.026 0.007 G 0.036 0.137 G 0.051 0.009 G 0.041 0.001 G 0.007 0.001 G 0.009
28 26 26 26 26 26 26 26
0.069 G 0.023 .006 20 0.043 G 0.017 .018 17 0.06 G 0.025 .024 17 0.012 G 0.027 .673 17 0.218 G 0.048 !.001 17 0.003 G 0.035 .939 17 0.004 G 0.005 .425 17 0.007 G 0.012 .554 17
0.061 G 0.031 0.036 G 0.019 0.031 G 0.026 0.005 G 0.027 0.159 G 0.06 0.013 G 0.041 0.01 G 0.005 0.019 G 0.018
d 8 8 8 8 8 8 8
d 0.067 G 0.038 0.004 G 0.044 0.013 G 0.043 0.213 G 0.104 0.049 G 0.062 0.002 G 0.008 0.029 G 0.028
d .118 .928 .782 .081 .456 .798 .34
43 50 50 50 50 50 50 50
0.098 G 0.029 .002 36 0.028 G 0.009 .003 50 0.023 G 0.022 .302 50 0.029 G 0.016 .08 50 0.115 G 0.026 !.001 50 0.008 G 0.019 .661 50 0.001 G 0.005 .898 50 0.009 G 0.008 .228 50
0.126 G 0.029 !.001 19 0.025 G 0.011 .037 43 0.024 G 0.019 .224 43 0.031 G 0.018 .099 43 0.117 G 0.035 .001 43 0.025 G 0.02 .215 43 0.031 G 0.022 .165 43 0.062 G 0.08 .447 43
0.175 G 0.039 !.001 d 0.017 G 0.012 .173 28 0.034 G 0.023 .135 28 0.032 G 0.018 .082 28 0.099 G 0.035 .007 28 0.03 G 0.022 .183 28 0.012 G 0.018 .505 28 0.008 G 0.011 .476 28
d 0 G 0.016 0.029 G 0.029 0.003 G 0.024 0.055 G 0.041 0.029 G 0.033 0.02 G 0.01 0.006 G 0.008
d .998 .324 .899 .186 .396 .071 .475
HOA Z higher-order aberrations; RMS Z root mean square Means G SD
coma aberration, total 4th-order aberrations, and spherical aberration were not significantly different between the 2 groups preoperatively or postoperatively at 1, 3, 6, and 12 months (P Z .201 to P Z .978). Table 5 compares the preoperative and 3-month and 12-month postoperative contrast sensitivity. The
mesopic contrast sensitivity decreased at 3, 6, 12, and 18 cycles per degree (cpd) in the femtosecond lenticule extraction group at 3 months (all P ! .05), although the difference was not significant at 1 year (P Z .341 to P Z .872). In the pseudo small-incision lenticule extraction group, the mesopic contrast sensitivity
Table 4. Comparison of preoperative and postoperative HOAs after femtosecond lenticule extraction and pseudo small-incision lenticule extraction. Postoperative Preoperative
1 Month
Mean G SD Parameter (mm) HOA RMS Total 3rd order Trefoil (vertical) Trefoil (horizontal) Coma (vertical) Coma (horizontal) Total 4th order Spherical aberration
Group 1 0.306 G 0.157 0.002 G 0.062 0.078 G 0.120 0.023 G 0.141 0.088 G 0.21 0.023 G 0.080 0.01 G 0.02 0.001 G 0.04
Mean G SD Group 2
0.291 G 0.154 0.001 G 0.047 0.079 G 0.131 0.004 G 0.100 0.076 G 0.175 0.003 G 0.090 0.026 G 0.107 0.007 G 0.042
P Value .664 .910 .964 .306 .781 .341 .480 .413
Group 1 0.378 G 0.166 0.026 G 0.088 0.099 G 0.183 0.008 G 0.101 0.011 G 0.300 0.013 G 0.163 0.010 G 0.028 0.002 G 0.042
Group 2 0.397 G 0.147 0.027 G 0.052 0.061 G 0.170 0.018 G 0.120 0.044 G 0.189 0.012 G 0.123 0.009 G 0.04 0.013 G 0.058
P Value .586 .941 .396 .730 .586 .978 .918 .302
Group 1 Z femtosecond lenticule extraction; Group 2 Z pseudo small-incision lenticule extraction; HOA Z higher-order aberrations; RMS Z root mean square
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increased at all measured spatial frequencies but was only significant at 3 cpd at 3 months (P Z .015) and at 1.5 cpd at 1 year (P Z .008). The photopic contrast sensitivity decreased at 6, 12, and 18 cpd in the femtosecond lenticule extraction group at 3 months (all P ! .05), although the difference was not significant at 1 year (P Z .152 to P Z .634); there was no significant difference in photopic contrast sensitivity in the pseudo small-incision lenticule extraction group at 3 months and 12 months compared with preoperatively. Figure 3 shows the mesopic and photopic contrast sensitivity over time in both groups. There was no significant difference in mesopic or photopic contrast sensitivity at any spatial frequency between the 2 groups preoperatively (P Z .138 to P Z .926) (Table 6). At 3 months, mesopic contrast sensitivity at 3 cpd was significantly higher in the pseudo small-incision lenticule extraction group than in the femtosecond lenticule extraction group (P Z .003); photopic contrast sensitivity at 6 cpd was also higher in the pseudo small-incision lenticule extraction group than in the femtosecond lenticule extraction group (P Z .004). This difference in photopic contrast sensitivity at 6 cpd persisted to 1 year (P Z .027), although the difference in mesopic contrast sensitivity at 3 cpd did not persist (P Z .336).
studies of the induction of HOAs after refractive lenticule extraction.11,13 In a study by Sekundo et al.,11 no eye had a significant increase in HOAs after femtosecond lenticule extraction; however, they did not perform a detailed numerical analysis in their study. Shah et al.13 found a significant increase in the RMS of total HOAs, higher-order coma aberrations, spherical aberrations, and 4th-order aberrations 6 months after small-incision lenticule extraction. Similarly, in our study the RMS of total HOAs and 3rd-order vertical coma aberration were significantly increased at 6 months in the pseudo small-incision lenticule extraction group. However, there was no significant change in total 4th-order or spherical aberrations. In the femtosecond lenticule extraction group at 6 months, only 3rd-order vertical coma aberration was significantly increased. Of note, at 1 year there was no significant change in the total as well as in different types of HOAs in the femtosecond lenticule extraction group or the pseudo small-incision lenticule extraction group. Therefore, our results indicate that refractive lenticule extraction is safe and effective in preventing a significant induction of HOAs over the long term. However, it appears that there is a change in HOAs over time in refractive lenticule extraction, with a period of about 6 months to 1 year before visual quality improves. This is unlike in LASIK, where visual quality usually remains constant postoperatively.14,29 We hypothesize that the return of HOAs to baseline in refractive lenticule extraction and not in LASIK could be the result of several factors, including wider effective optical zones in refractive lenticule extraction (O6.5 mm) than in LASIK, a wider transition in the refractive lenticule, and differences in corneal
DISCUSSION Higher-order aberrations commonly increase after LASIK procedures.21–23 Several studies have shown less induction of HOAs with the use of femtosecond lasers than with the use of microkeratomes during LASIK.26–28 However, there have been few published
Table 4. (Cont.) Postoperative 3 Months
6 Months
Mean G SD Group 1 0.369 G 0.106 0.030 G 0.071 0.044 G 0.159 0.019 G 0.091 0.081 G 0.269 0.024 G 0.160 0.012 G 0.024 0.001 G 0.057
Group 2 0.399 G 0.137 0.025 G 0.078 0.061 G 0.157 0.025 G 0.126 0.037 G 0.292 0.023 G 0.144 0.002 G 0.116 0.055 G 0.567
1 Year
Mean G SD P Value .323 .772 .603 .803 .473 .972 .472 .544
Group 1 0.353 G 0.163 0.026 G 0.070 0.042 G 0.160 0.029 G 0.081 0.046 G 0.274 0.006 G 0.151 0.015 G 0.027 0.025 G 0.066
Group 2 0.416 G 0.167 0.021 G 0.066 0.041 G 0.152 0.034 G 0.117 0.038 G 0.241 0.030 G 0.144 0.015 G 0.041 0.014 G 0.064
Mean G SD P Value
Group 1
.225 .762 .973 .589 .900 .486 .930 .495
d 0.021 G 0.109 0.017 G 0.102 0.020 G 0.111 0.045 G 0.421 0.002 G 0.163 -0.013 G 0.022 -0.026 G 0.061
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Group 2 d 0.002 G 0.071 0.052 G 0.142 0.003 G 0.121 0.028 G 0.247 0.035 G 0.143 0.029 G 0.054 0.011 G 0.049
P Value d .369 .339 .614 .443 .398 .201 .332
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Table 5. Preoperative versus postoperative mesopic and photopic contrast sensitivities. Group 1 3 Months Vs Preop CS/Spatial Frequency n Mesopic 1.5 cpd 3 cpd 6 cpd 12 cpd 18 cpd Photopic 1.5 cpd 3 cpd 6 cpd 12 cpd 18 cpd
Mean Difference
Group 2 1 Year Vs Preop
P Value n
Mean Difference
3 Months Vs Preop
P Value n
Mean Difference
1 Year Vs Preop
P Value n
Mean Difference
P Value
40 40 40 40 40
0.250 G 0.195 0.700 G 0.289 0.800 G 0.388 0.900 G 0.303 0.525 G 0.261
.208 .02 .046 .005 .051
28 28 28 28 28
0.286 G 0.295 0.179 G 0.277 0.214 G 0.419 0.071 G 0.439 0.143 G 0.384
.341 .525 .613 .872 .713
56 56 56 56 56
0.054 G 0.156 0.464 G 0.185 0.250 G 0.312 0.054 G 0.307 0.089 G 0.26
.732 .015 .427 .862 .733
24 24 24 24 24
0.625 G 0.215 0.542 G 0.269 0.208 G 0.289 0.000 G 0.341 0.125 G 0.435
.008 .056 .478 .999 .777
40 40 40 40 40
0.125 G 0.224 0.375 G 0.231 0.725 G 0.349 0.950 G 0.343 0.800 G 0.336
.58 .113 .044 .009 .022
28 28 28 28 28
0.179 G 0.282 0.179 G 0.257 0.179 G 0.371 0.500 G 0.339 0.179 G 0.326
.532 .494 .634 .152 .588
56 56 56 56 56
0.143 G 0.166 0.143 G 0.185 0.054 G 0.205 0.071 G 0.286 0.179 G 0.387
.393 .442 .794 .804 .646
24 24 24 24 24
0.542 G 0.361 0.583 G 0.300 0.542 G 0.313 0.417 G 0.394 0.083 G 0.564
.147 .065 .097 .302 .884
cpd Z cycles per degree; CS Z contrast sensitivity; Group 1 Z femtosecond lenticule extraction; Group 2 Z pseudo small-incision lenticule extraction Means G SE
biomechanical stability between refractive lenticule extraction and LASIK. Our group recently found significantly less inflammation and stromal remodeling after refractive lenticule extraction than after LASIK, which might contribute to recovery of HOAs to baseline levels in refractive lenticule extraction.30 Comparing refractive lenticule extraction and femtosecond lenticule extraction with wavefrontoptimized femtosecond LASIK, Gertnere et al.15 found that refractive lenticule extraction and femtosecond lenticule extraction induced significantly less HOAs than LASIK, indicating that HOAs were likely induced by the excimer laser rather than the by corneal flap. In our study comparing the 2 variants of refractive lenticule extraction, we found that the increase in the RMS of total HOAs, total 3rd-order aberrations, 3rd-order vertical and horizontal trefoil aberrations, 3rd-order vertical and horizontal coma aberrations, total 4thorder aberrations, and spherical aberrations were not significantly different between femtosecond lenticule extraction and pseudo small-incision lenticule extraction groups from preoperatively to 1, 3, 6, and 12 months postoperatively (P range 0.201 to 0.978). Therefore, despite the small incision, lack of flap lifting, and potential for a more difficult lenticule extraction because of the learning curve for lamellar separation, pseudo small-incision lenticule extraction did not induce significantly more HOAs than femtosecond lenticule extraction. However, Tay et al.31 noted differences in corneal flap and stromal bed edema between femtosecond lenticule extraction and pseudo small-incision lenticule extraction
postoperatively on anterior segment optical coherence tomography; anatomic stabilization occurred 3 months postoperatively. Contrast sensitivity is the ability to detect differences in luminance between adjacent areas and reflects the quality of vision.17–20,32 Numerous studies have shown that contrast sensitivity function declines after corneal refractive surgeries such as photorefractive keratectomy33–36 and LASIK,17,18,34,36–38 although the effects are often temporary and contrast sensitivity generally recovers to preoperative levels within 3 to 12 months after surgery.17,18,34,36–38 Comparing refractive lenticule extraction with femtosecond-assisted LASIK, Gertnere et al.15 found that photopic contrast sensitivity increased similarly after both procedures but that mesopic contrast sensitivity significantly improved after refractive lenticule extraction but not after femtosecond-assisted LASIK. In our study, both mesopic and photopic contrast sensitivities decreased significantly 3 months after femtosecond lenticule extraction at the higher frequencies (6, 12, 18 cpd) but recovered by 1 year. In contrast, mesopic and photopic contrast sensitivities were generally improved after pseudo small-incision lenticule extraction at all frequencies at 3 months and at 1 year, although the only significantly improvement in mesopic contrast sensitivity was at 3 cpd at 3 months and 1.5 cpd at 1 year. Because HOAs have been found to inadvertently affect contrast sensitivity after refractive surgery,33,35,37 the recovery of HOAs to preoperative levels at 1 year explains the similar trend in contrast sensitivity at 1 year in our study.
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631
Figure 3. Femtosecond lenticule extraction mesopic (A) and photopic (C) contrast sensitivities over time and pseudo small-incision lenticule extraction mesopic (B) and photopic (D) contrast sensitivities over time (cpd Z cycles per degree).
The improvement in both mesopic and photopic contrast sensitivities in the pseudo small-incision lenticule extraction group, despite of the increase in HOAs at 3 months, was not found in the femtosecond lenticule extraction group. We hypothesize that after flap creation and lifting in femtosecond lenticule extraction, the ocular surface is more neurotrophic than after pseudo small-incision lenticule extraction, in which there is no flap lifting. The effect of a less neurotrophic surface is a superior ocular surface and tear film, hence equating to a better quality of vision. This might have negated some of the effects of HOAs in pseudo smallincision lenticule extraction patients, resulting in improved contrast sensitivity. Comparing the 2 variants of refractive lenticule extraction, both photopic and mesopic contrast sensitivities were better in the pseudo small-incision lenticule extraction group than in femtosecond lenticule extraction group at all frequencies except at 12 cpd
under mesopic conditions at 3 months and 1 year. However, this was significant only for 3 cpd under mesopic conditions and 6 cpd under photopic conditions at 3 months. This significant improvement in photopic contrast sensitivity at 6 cpd persisted to 1 year after pseudo small-incision lenticule extraction. Therefore, we postulate that pseudo small-incision lenticule extraction with a small incision and lack of a lifted flap might have led to fewer induced aberrations, which might have contributed to better contrast sensitivity. This study has several limitations. First, this was a retrospective analysis and in this process, there was a risk for bias. However, there were no statistically significant differences in the demographics or preoperative data between the 2 groups. The authenticity of the results would probably have been better confirmed with a randomized controlled study, which is currently in progress. Second, multiple surgeons
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Table 6. Between-group comparison of preoperative and postoperative mesopic and photopic contrast sensitivities. Preoperative
Postoperative
3 Months CS/Spatial Frequency Mesopic 1.5 cpd 3 cpd 6 cpd 12 cpd 18 cpd Photopic 1.5 cpd 3 cpd 6 cpd 12 cpd 18 cpd
1 Year
Group 1
Group 2
P Value
Group 1
Group 2
P Value
Group 1
Group 2
P Value
6.24 G 1.10 5.55 G 1.29 4.40 G 1.55 2.95 G 1.38 1.33 G 1.44
6.26 G 1.07 5.24 G 1.05 4.02 G 1.63 2.53 G 1.61 1.12 G 1.61
.926 .194 .233 .178 .498
5.95 G 1.41 4.83 G 1.57 3.58 G 1.93 2.00 G 1.62 0.70 G 1.14
6.30 G 1.19 5.70 G 1.26 4.23 G 1.85 2.52 G 1.81 1.21 G 1.57
.188 .003 .095 .152 .066
6.57 G 1.48 5.61 G 1.57 4.32 G 1.93 3.07 G 2.34 1.61 G 1.73
6.75 G 0.99 5.96 G 1.12 4.75 G 1.29 3.04 G 1.30 1.63 G 1.69
.617 .366 .359 .954 .970
5.88 G 0.97 5.83 G 1.01 5.36 G 1.41 4.86 G 1.51 3.48 G 1.49
5.79 G 1.12 5.66 G 0.98 5.45 G 1.31 4.40 G 1.53 3.41 G 1.86
.683 .379 .741 .138 .858
5.70 G 1.32 5.40 G 1.46 4.55 G 1.74 3.80 G 1.62 2.50 G 1.88
5.95 G 1.10 5.77 G 1.01 5.46 G 1.31 4.30 G 1.39 3.16 G 1.95
.324 .174 .004 .106 .1
6.07 G 1.18 5.75 G 1.40 5.18 G 1.61 4.36 G 1.87 3.54 G 1.73
6.21 G 1.59 6.25 G 1.29 6.08 G 1.18 5.00 G 1.38 3.63 G 2.08
.724 .191 .027 .171 .867
cpd Z cycles per degree; CS Z contrast sensitivity; Group 1 Z femtosecond lenticule extraction; Group 2 Z pseudo small-incision lenticule extraction Means G SD
performed the operations. This might have affected the results of the achieved visual outcomes, especially because pseudo small-incision lenticule extraction involves a more potentially challenging lamellar dissection technique than femtosecond lenticule extraction. However, all 3 surgeons in this study were corneal trained and used to performing corneal lamellar surgery, and the transition from femtosecond lenticule extraction to pseudo small-incision lenticule extraction was smooth and well controlled. At present, we are collecting data on the small-incision lenticule extraction procedure, the results of which will be subsequently published. Third, we assessed the HOAs and contrast sensitivity before and after surgery but did not assess subjective symptoms in the study. A standardized questionnaire measuring patients' quality of vision and an assessment of the relationship between these symptoms and HOAs and contrast sensitivity would be useful. Last, patients with missing preoperative or postoperative data were excluded in our analysis because we analyzed our data by the intention-to-treat approach to provide unbiased comparisons of the patients in each group. These missing data might reduce the representativeness of the sample; however, they are missing at random and therefore unlikely to distort inferences about our study population. In summary, our results indicate that refractive lenticule extraction is safe and effective with no significant induction of HOAs and deterioration in contrast sensitivity at 1 year postoperatively. In the comparative arm of the study between the 2 variants of refractive lenticule extraction, which also describes our initial learning curve with this new form of refractive
surgery, we found that the induction of HOAs was not significantly different between femtosecond lenticule extraction and pseudo small-incision lenticule extraction. However, there was a significant improvement in photopic contrast sensitivity after pseudo small-incision lenticule extraction that persisted through 1 year. WHAT WAS KNOWN In refractive lenticule extraction, the femtosecond laser cuts an intrastromal lenticule. The lenticule is then removed through a surface incision of varying size depending on whether it is femtosecond lenticule extraction, small-incision lenticule extraction, or pseudo smallincision lenticule extraction, which is a transitional procedure. Initial clinical results of both procedures have been promising; however, there is a lack of studies comparing the visual outcomes between refractive lenticule extraction procedures. WHAT THIS PAPER ADDS Refractive lenticule extraction was safe and effective with no significant induction of HOAs or deterioration in contrast sensitivity 1 year postoperatively. Induction of HOAs was not significantly different between femtosecond lenticule extraction and pseudo smallincision lenticule extraction, although there was significant improvement in photopic contrast sensitivity after pseudo small-incision lenticule extraction.
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HOAS AFTER FEMTOSECOND LENTICULE EXTRACTION VS PSEUDO SMALL-INCISION LENTICULE EXTRACTION
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First author: Deborah K.L. Tan, MB BS Singapore Eye Research Institute, Singapore