Journal of Refractive Surgery

Original Article Supplemental Data

Dry Eye After Small Incision Lenticule Extraction and LASIK for Myopia

Yesheng Xu, MD; Yabo Yang, MD, PhD

Abstract

PURPOSE:

To compare the effects of small incision lenticule extraction (SMILE) and LASIK with either femtosecond laser or mechanical microkeratome on dry eye.

METHODS:

A total of 176 patients (338 eyes) who underwent refractive procedures for myopia were observed in this nonrandomized, interventional, prospective study. To evaluate dry eye, the Schirmer secretion test without anesthesia, tear break-up time, and the McMonnies questionnaire were used preoperatively and at 1, 3, and 6 months postoperatively.

RESULTS:

In all groups, there was no significant decrease in the results from the Schirmer secretion test without anesthesia after surgery. The value in the LASIK group was significantly lower than any other group at 3 and 6 months postoperatively. In all groups, the tear break-up time decreased significantly after surgery and did not return to preoperative levels within 6 months; the SMILE group time lasted significantly longer than the LASIK group at 1 month. The McMonnies score increased significantly in all groups after surgery. The preoperative levels returned within 6 months in all groups except the LASIK group. The mean McMonnies score in the SMILE group was better than other groups.

CONCLUSIONS:

Dry eye after corneal refractive surgery usually occurs transiently. The SMILE procedure had better dry eye parameters and relatively fewer subjective symptoms than LASIK.

[J Refract Surg. 2014;30(3):186–190.]

From the Department of Ophthalmology, The Second Hospital Affiliated to Zhejiang University, Hangzhou, China.

The authors have no financial or proprietary interest in the materials presented herein.

AUTHOR CONTRIBUTIONS

Conception and design (YY); data collection (YY, YX); analysis and interpretation (YX); writing the manuscript (YX); critical revision of the manuscript (YY)

Correspondence: Yabo Yang, MD, PhD, Department of Ophthalmology, The Second Hospital Affiliated to Zhejiang University, Hangzhou 310009, China. E-mail: yabyang@hotmail.com

Received: August 22, 2013
Accepted: November 11, 2013
Posted Online: February 28, 2014

Abstract

PURPOSE:

To compare the effects of small incision lenticule extraction (SMILE) and LASIK with either femtosecond laser or mechanical microkeratome on dry eye.

METHODS:

A total of 176 patients (338 eyes) who underwent refractive procedures for myopia were observed in this nonrandomized, interventional, prospective study. To evaluate dry eye, the Schirmer secretion test without anesthesia, tear break-up time, and the McMonnies questionnaire were used preoperatively and at 1, 3, and 6 months postoperatively.

RESULTS:

In all groups, there was no significant decrease in the results from the Schirmer secretion test without anesthesia after surgery. The value in the LASIK group was significantly lower than any other group at 3 and 6 months postoperatively. In all groups, the tear break-up time decreased significantly after surgery and did not return to preoperative levels within 6 months; the SMILE group time lasted significantly longer than the LASIK group at 1 month. The McMonnies score increased significantly in all groups after surgery. The preoperative levels returned within 6 months in all groups except the LASIK group. The mean McMonnies score in the SMILE group was better than other groups.

CONCLUSIONS:

Dry eye after corneal refractive surgery usually occurs transiently. The SMILE procedure had better dry eye parameters and relatively fewer subjective symptoms than LASIK.

[J Refract Surg. 2014;30(3):186–190.]

From the Department of Ophthalmology, The Second Hospital Affiliated to Zhejiang University, Hangzhou, China.

The authors have no financial or proprietary interest in the materials presented herein.

AUTHOR CONTRIBUTIONS

Conception and design (YY); data collection (YY, YX); analysis and interpretation (YX); writing the manuscript (YX); critical revision of the manuscript (YY)

Correspondence: Yabo Yang, MD, PhD, Department of Ophthalmology, The Second Hospital Affiliated to Zhejiang University, Hangzhou 310009, China. E-mail: yabyang@hotmail.com

Received: August 22, 2013
Accepted: November 11, 2013
Posted Online: February 28, 2014

Dry eye is one of the most common complications of LASIK.1–5 Some perceive dry eye symptoms as a major contributor to patient dissatisfaction after LASIK. Several studies provided different incidences of this complication, ranging from 20% to more than 50% in patients who had LASIK.1–5 Thin-flap LASIK is also associated with transient postoperative dry eye symptoms.6,7 A comparison study of dry eye after normal and thin-flap LASIK showed that there were no significant differences in dry eye disease markers or tear osmolarity at any stage up to 1 year after surgery.8 Several studies have assessed the effect of femtosecond laser use on the incidence of dry eye after femtosecond laser-assisted LASIK (femto-LASIK), with some evidence showing decreased signs and symptoms9 or no significant difference.10 The femtosecond laser may generate more consistent and predictable flap diameters and thicknesses than microkeratomes.11 There may also be fewer flap-related complications, including reduced epithelial injury.12,13

Because it is a new technique introduced into corneal refractive surgery, the effect of SMILE on dry eye requires further investigation. Theoretically, SMILE is a minimally invasive approach to corneal refractive surgery. Instead of a corneal flap, an intrastromal lenticule that corresponds to the desired refractive correction is created with a femtosecond laser and then removed from a small incision. Flapless laser-correcting surgery requires only a small incision, which means that fewer corneal nerves are severed. This may lead to fewer side effects after surgery, including less dry eye.

This study compares the change in and recovery of dry eye symptoms and signs among patients undergoing LASIK and SMILE.

Patients and Methods

This nonrandomized, interventional, prospective study took place at a single center (Eye Center, Second Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, China). We enrolled 338 eyes of 176 patients who were scheduled for laser refractive surgery between April and December 2012. All patients were enrolled once they agreed to participate in our study and promised to adhere to the follow-up appointments. The patients selected the procedure group depending on the refractive error degree, central corneal thickness, and ability to pay for the procedure. The research was approved by the Institutional Review Board at Zhejiang University College of Medicine and followed the tenets of the Declaration of Helsinki. Informed consent was obtained from all participants after explaining the nature and possible consequences.

Inclusion criteria were as follows: 18 years of age or older, qualified for laser refractive surgery for myopia (normal ophthalmic examination except for refractive error, stable refraction, and minimum calculated residual corneal stromal bed thickness > 250 μm). Patients also had to agree to fill out dry eye questionnaires and be observed on subsequent visits. Patients were excluded from the study if they had severe dry eye with Schirmer test values without anesthesia of 5 mm, a history of arthritis or connective tissue disease, were pregnant, or were part of another dry eye study.

All patients had preoperative and postoperative examinations (within 2 weeks before laser refractive surgery and at 1, 3, and 6 months postoperatively) in the following sequence by the same observer (YX): Schirmer test without anesthesia, break-up time (BUT), and the McMonnies questionnaire,14 which contains 12 questions evaluating dry eye under specific conditions.

After surgery, topical 0.3% ofloxacin eye drops (Tarivid; Santen, Inc., Tokyo, Japan) and 0.1% sodium hyaluronate (Hycosan, Ursapharm, Germany) combined with 0.1% fluorometholone (Flumetholon; Santen, Inc.) were used for 2 weeks per the standard procedure for all refractive procedures at our center.

Surgical Technique

The same surgeon (YY) performed all procedures. All surgical procedures were performed with anesthesia preoperatively with oxybuprocaine (Benoxil; Santen, Inc.). After standard sterile draping and insertion of the aspirating speculum to keep the eye open, the patient’s eye was positioned under an excimer laser system (MEL 80; Carl Zeiss Meditec, Inc., Jena, Germany) or the femtosecond laser system (VisuMax; Carl Zeiss Meditec, Inc.) integrated surgical microscope.

SMILE Procedure With Refractive Lenticule Extraction

In the SMILE group, a small tunnel incision (4 mm) was created at a 120° angle, and the refractive lenticule was extracted through the incision using a spatula. For all myopic corrections, the optical zone size was 6.0 to 6.5 mm. The depth of the lenticule’s anterior surface to the corneal anterior surface was 100 μm.

Femto-LASIK Procedure

In the femto-LASIK group, the flap diameter was 7.9 mm and flap thickness was set to 100 μm with a 90° hinge angle. The flaps were created by laser scanning in spirals from the periphery to the center of the pupil. The excimer laser system was used in the subsequent ablation of the stromal bed with a 6.0- to 6.5-mm optical zone.

90-m LASIK Flap Procedure

In the 90-μm flap group, the flap was created by the Moria One Use-Plus SBK microkeratome (Moria S.A., Antony, France). The flap thickness was approximately 90 μm with a nasal hinge. The excimer laser system was used in the subsequent ablation of the stromal bed with a 6.0-mm optical zone.

110-m LASIK Flap Procedure

In this group, the flap was created by the Moria M2 110 microkeratome (Moria S.A.). The flap thickness was approximately 110 μm with a superior hinge. The excimer laser system was used in the subsequent ablation of the stromal bed with a 6.0 to 6.5 mm optical zone.

Schirmer Secretion Test

A sterile standardized Schirmer tear test strip (HESSEN Biotechnology, Inc., Beijing, China) was placed at the junction of the lateral and middle third of the inferior fornix without anesthesia. The length of the wet portion of the strip was measured at 5 minutes and recorded in millimeters.

Tear Break-Up Time

To measure tear BUT, one drop of physiological saline was placed on the fluorescein sodium ophthalmic strip (HESSEN Biotechnology Inc.), which was placed into the lower conjunctival sac for 1 second. The tear film was observed under cobalt blue filtered light. The interval between the last complete blink and the first appearance of randomly distributed dry spots was measured. The average of three measurements was obtained.

Subjective Dry Eye Symptoms

Subjective symptoms were evaluated using the McMonnies questionnaire, a reliable and validated 12-item questionnaire used to assess subjective symptoms of dry eye syndrome.14,15 The total possible score ranged from 0 to 45. A high score on the McMonnies questionnaire indicates dry eye problems. A score higher than 14.5 could be defined as dry eye.14

Statistical Analysis

Comparisons of dry eye outcome variables between different laser refractive surgeries and preoperative and postoperative within-eye comparisons were performed using a one-way analysis of variance followed by Bonferroni’s multiple comparisons test. Data are presented as mean ± standard deviation. A P value less than .05 was considered statistically significant.

Results

Patients

Patient preoperative parameters are listed in Table 1. Patient ages ranged from 18 to 40 years (mean: 23.77 ± 5.72 years). Preoperative spherical equivalents ranged from −2.00 to −10.00 diopters (mean: −5.42 ± 1.91 diopters). All patients completed all follow-up examinations.

Preoperative and Surgical Parameters

Table 1:

Preoperative and Surgical Parameters

Among the refractive laser procedures, only preoperative central corneal thickness was significantly different, being thinner in the 90-μm LASIK group than other groups (P < .001).

Corrected distance visual acuity ranged from 20/30 to 20/15 postoperatively and from 20/30 to 20/12.5 at 6 months postoperatively. The percentage of eyes that gained or lost lines of acuity in each group is shown in Figure A (available in the online version of this article). No significant difference was found between groups.

Time-Dependent Changes in Dry Eye Characteristics

Before surgery, the mean Schirmer secretion test without anesthesia in the SMILE group was 17.49 ± 7.48 mm; this value decreased 1 month after surgery and recovered to the preoperative value at 3 months. In the femto-LASIK group, the Schirmer secretion test without anesthesia followed the same postoperative pattern. In the 90-μm LASIK group, the Schirmer secretion test without anesthesia decreased 1 month after surgery and decreased further at 3 months, then the values returned slightly at 6 months. The 110-μm LASIK group followed the same postoperative pattern (Figure 1, Table A, available in the online version of this article).

(A) The Schirmer test time. The value in the LASIK group was significantly lower than in the small incision lenticule extraction (SMILE) group, femtosecond laser-assisted LASIK (femto-LASIK), and 90-μm LASIK groups at 3 and 6 months. (B) The tear break-up time for all groups was significantly lower than preoperative scores at 1, 3, and 6 months postoperatively. The value in the SMILE group was significantly higher than the 110-μm LASIK (LASIK) group at 1 month postoperatively. (C) The McMonnies questionnaire scores. The 110-μm LASIK group score was significantly higher than the preoperative score at 6 months postoperatively. Scores of the femto-LASIK and the 110-μm LASIK groups at 3 months postoperatively were significantly higher than preoperative scores. Scores in all groups increased significantly at 1 month postoperatively. Scores in the 110-μm LASIK and femto-LASIK groups were significantly lower than the 90-μm LASIK group at 1 month postoperatively. The score in the SMILE group was significantly lower than the 90-μm LASIK and 110-μm LASIK groups. The score in the femto-LASIK group was significantly lower than the 90-μm LASIK and 110-μm LASIK groups at 6 months postoperatively.

Figure 1.

(A) The Schirmer test time. The value in the LASIK group was significantly lower than in the small incision lenticule extraction (SMILE) group, femtosecond laser-assisted LASIK (femto-LASIK), and 90-μm LASIK groups at 3 and 6 months. (B) The tear break-up time for all groups was significantly lower than preoperative scores at 1, 3, and 6 months postoperatively. The value in the SMILE group was significantly higher than the 110-μm LASIK (LASIK) group at 1 month postoperatively. (C) The McMonnies questionnaire scores. The 110-μm LASIK group score was significantly higher than the preoperative score at 6 months postoperatively. Scores of the femto-LASIK and the 110-μm LASIK groups at 3 months postoperatively were significantly higher than preoperative scores. Scores in all groups increased significantly at 1 month postoperatively. Scores in the 110-μm LASIK and femto-LASIK groups were significantly lower than the 90-μm LASIK group at 1 month postoperatively. The score in the SMILE group was significantly lower than the 90-μm LASIK and 110-μm LASIK groups. The score in the femto-LASIK group was significantly lower than the 90-μm LASIK and 110-μm LASIK groups at 6 months postoperatively.

The mean preoperative BUT was 10.35 ± 3.28 seconds in the SMILE group; this value decreased significantly 1 month after surgery and then lowered significantly again at 3 months; it recovered close to the preoperative value but was still significantly lower at 6 months. In the femto-LASIK, 90-μm LASIK, and 110-μm LASIK groups, the BUT followed the same postoperative pattern (Figure 1, Table A).

McMonnies questionnaire scores from all four groups increased significantly (P < .01 for all groups) at 1 month. By 3 months postoperatively, the scores recovered to their preoperative values in the SMILE and 90-μm LASIK groups (P = .08 and .16, respectively). By 6 months postoperatively, the McMonnies questionnaire scores recovered to their preoperative values in the femto-LASIK group (P = .17). In the 110-μm LASIK group, the score increased during the 3-month follow-up and was still significantly higher than the preoperative level (P < .01) (Figure 1, Table A).

Discussion

In this study, we observed time-dependent changes in the clinical parameters of tear function before and after SMILE and LASIK. Transient changes in all parameters occurred that were consistent with the development of transient dry eye after surgery. Within 3 months, the BUT and subjective symptoms changed significantly, and the SMILE group recovered 6 months after surgery in all parameters. The Schirmer secretion test without anesthesia in all groups had no significant decrease after surgery. The value of the Schirmer secretion test in the LASIK group was significantly lower than any other group and lasted longer postoperatively. The LASIK group always had the lowest ranking, whereas the SMILE group frequently had the highest ranking. By 6 months postoperatively, all groups had satisfactory visual outcomes. There was no significant deteriorative effect of dry eye on visual acuity in all groups.

To ensure homogeneity of our study, we selected patients in each group with preoperative spherical equivalents that ranged from −2.00 to −10.00 diopters and with age, sex, drinking and smoking habits, body mass index, and screen time that were statistically equal. However, the central corneal thickness could not be balanced because the choice of thin-flap LASIK always depended on a thin central corneal thickness. Under these conditions, we compared these procedures and witnessed the differences in dry eye signs and symptoms mainly because of flap or flapless, ablation or no ablation, suction, and corneal stromal bed interface approaches.

The small incision with SMILE means that there is a smaller likelihood of cutting corneal nerves, perhaps leading to less dry eye postoperatively than after conventional flap surgery. This is compatible with our results. Flap thickness, hinge, and formation were all essential, influential factors. Creation of a thinner, wider nasal hinge may be ideal. Using a mechanical microkeratome, dry eye was better in thin-flap LASIK than LASIK, mainly due to a thinner flap with nasal hinge. Femto-LASIK creates a flap with a high level of reproducibility and maintains epithelial integrity, which improves safety and efficacy.13 Flaps created with a femtosecond laser sever all superficial corneal nerves except for those at the hinge.

The application of the microkeratome suction ring has been shown in other studies to induce changes in the perilimbic conjunctiva, especially on goblet cell density, which contributes to the pathology of dry eye.16 In femto-LASIK and SMILE procedures, the control suction is longer and lighter. The effect on goblet cells needs to be investigated in future studies.

The mechanism for dry eye syndrome after LASIK can be explained by two theories: neurogenic and inflammatory, chained together in a vicious circle.17 With two different kinds of lasers, the wound surface and nearby tissues would show different structures, consequently inducing different types of wound healing. Eyes with femtosecond laser flaps had a lower incidence of LASIK-associated dry eye and required less treatment for the disorder.18

Dry eye after four types of surgery mainly occurred transiently. SMILE had better dry eye parameters and relatively fewer subjective symptoms. Femto-LASIK or thin-flap LASIK are also good choices to reduce dry eye signs and symptoms.

References

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The change in Snellen lines of best-corrected visual acuity (BCVA) at 6 months postoperatively.

Figure A. The change in Snellen lines of best-corrected visual acuity (BCVA) at 6 months postoperatively.

Preoperative and Surgical Parameters

Parameter SMILE (n = 81) FS-LASIK (n = 97) 90-μm LASIK (n = 82) 110-μm LASIK (n = 78) P
Age (y) 24.10 ± 6.03 23.96 ± 5.14 25.15 ± 6.34 24.74 ± 4.91 .21
Female/male 37/44 41/56 37/45 29/49 .69
IOP (mm Hg) 15.46 ± 0.50 15.14 ± 2.68 14.73 ± 2.31 15.57 ± 2.29 .12
CCT (μm) 554.78 ± 28.97 537.68 ± 31.08 530.04 ± 34.33 549.47 ± 22.90 < .001
Spherical equivalent (D) −5.70 ± 1.71 −5.80 ± 2.01 −5.53 ± 1.99 −5.31 ± 1.41 .08
Calculated cut/ablation depth (μm) 103.04 ± 0.36 99.97 ± 19.34 94.80 ± 18.85 98.90 ± 16.38 .27
Body mass index 20.42 ± 2.61 21.01 ± 2.88 20.82 ± 3.54 21.64 ± 2.67 .10
Screen time (hr/day) 9.63 ± 4.96 8.70 ± 3.55 9.84 ± 4.15 8.72 ± 4.31 .27
Smoker (%) 22.22 13.40 18.29 20.51 .37
Drinker (%) 6.17 7.22 6.10 7.69 .15
Break-up time (seconds) 10.35 ± 3.28 11.09 ± 3.15 11.23 ± 3.23 11.18 ± 2.89 .24
Schirmer test (mm) 17.49 ± 7.48 18.55 ± 7.75 17.91 ± 7.09 18.19 ± 8.23 .83
McMonnies score 9.09 ± 5.78 8.60 ± 4.99 9.16 ± 5.07 7.03 ± 3.82 .07

10.3928/1081597X-20140219-02

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