The present study investigated changes in corneal epithelial thickness after small incision lenticule extraction (SMILE) in patients with long-term preoperative soft contact lens (SCL) wear, the impact of SCL wear on the efficacy of surgical outcomes and the effects of long-term SCL wear on postoperative corneal aberrations. Patients were assigned to three groups according to the duration of SCL wear: Group A, the non-SCL-wearing group; group B, those with SCL wear ≤1 year; and group C, those with SCL wear >1 year. Epithelial thickness was recorded in nine zones by anterior segment optical coherence tomography across a 5-mm diameter before surgery and at 1 week, and 1, 3 and 6 months post-surgery. Corneal epithelial thickness and corneal aberrations among the three groups were compared, as well as the effects of changes in corneal epithelial thickness on postoperative visual acuity and manifest refraction. No significant differences were noted with regard to age or preoperative spherical equivalent among groups A (22 eyes), B (17 eyes) and C (18 eyes). Preoperative corneal epithelial thickness in the inferonasal, inferior and inferotemporal zones was thinner in group B compared with that in group A, and corneal epithelial thickness was thinner in all nine zones in group C compared with that in group A (P<0.05). At all follow-up time points, in the central, nasal, inferonasal, inferior, inferotemporal and temporal areas, the epithelial thickness was thinner in group C compared with that in group A (P<0.05). At 3 months postoperatively, the epithelial thickness was thinner in the inferonasal and inferior sectors in group C compared with that in group B (P<0.05), and at 6 months postoperatively, the epithelial thickness in the inferior region was thinner in group C compared with that in group B (P<0.05). There were no significant differences in visual acuity or manifest refraction among the three groups at all postoperative time points. The total higher-order aberrations were greater in group C compared with those in group A for all time points (P<0.05) and were greater in group C at 1 and 3 months postoperatively compared with those in group B (P<0.05). The spherical aberrations at 3 and 6 months postoperatively were greater in group C compared with those in group A (P<0.05). The coma aberrations were greater in group C compared with those in groups A and B for all time points (P<0.05). In conclusion, long-term SCL wear will result in corneal epithelial thinning, which does not impact visual acuity or manifest refraction after SMILE.
The number of teenagers who exhibit myopia and myopic astigmatism is increasing each year. Numerous patients choose soft contact lenses (SCLs) to manage the problem of refractive error. The normal physiology of the ocular surface (
In recent years, methods of corneal refractive surgery have been improving. Corneal refractive surgery provided another option for the correction of visual acuity, particularly in myopic patients with the experience of SCL wear. Small incision lenticule extraction (SMILE) is a relatively new surgical method of corneal refractive surgery, which realizes the flapless surgical mode, leaving the epithelium and the Bowman's layer undamaged except for the small side cut incision to extract the lenticule (
Previous studies have been performed to evaluate the central region of the cornea (
This retrospective observational study included 57 eyes of 30 patients (16 male and 14 female; mean age 25.90±5.90 years; range 16-34 years) who were scheduled for SMILE as treatment for myopia or myopia astigmatism at The First Affiliated Hospital of Soochow University (Suzhou, China) between June 2017 and April 2018. A complete ophthalmic examination was performed to screen for corneal abnormalities and determine the eligibility of the patients for refractive surgery. The inclusion criteria were: Age >18 years; spherical equivalent refraction converted by preoperative optometry of -2.00 to -6.00 diopters; intraocular pressure ranging from 10-21 mmHg; no history of hard contact lens wear; and a normal corneal topograghy examination. Patients with ocular pathological conditions such as corneal opacity and keratoconus were excluded. Additionally, patients with other ocular diseases and systemic organic diseases affecting the recovery from surgery were excluded from the study.
A previous study found that a 2-week contact lens-free period seemed to be adequate for the cornea to stabilize (
The corneal epithelial thickness data were obtained preoperatively and then at 1 week, and 1, 3 and 6 months postoperatively using the RTVue-100 anterior segment optical coherence tomography system (Optovue, Inc.). Each measurement was performed by one experienced technician in a room where light levels were reduced by half. All patients were forbidden from using any eye drops for 2 h prior to the measurements.
The anterior segment optical coherence tomography obtained the epithelial thickness of a circular region over a 6-mm diameter centered at the pupil center. The maps were divided into 3 zones by the annular rings: Central zone (2-mm diameter), paracentral zone (2- to 5-mm diameter) and mid-peripheral zone (5- to 6-mm diameter). The paracentral and mid-peripheral zones were each divided into the following 8 sectors: Superior, superonasal, nasal, inferonasal, inferior, inferotemporal, temporal and superotemporal (
Corneal topography measurements were acquired using a Sirius Corneal Topographer (CSO, Inc.). Three consecutive scans were taken and the best quality scan was selected for further analysis. For this, the Scheimpflug image area needed to be >90%, the centration positioning needed to be >90% and the Placido disk needed to cover an area of >90%. The total higher order aberrations, spherical aberrations and coma aberrations were noted for analysis.
All myopic operations were performed by one experienced surgeon (from Department of Ophthalmology, The First Affiliated Hospital of Soochow University). Preoperative medication included topical 0.5% levofloxacin (Santen Pharmaceutical Co., Ltd.) three times for 3 days.
All SMILE procedures were performed by VisuMax 500-kHz femtosecond laser (Carl Zeiss AG). The diameter of the cap was 7.3-7.5 mm (7.48±0.05 mm) and the intended cap thickness was 120 µm. A 3-mm incision was made at the 90˚ meridian to extract the lenticule and the side-cut angle was 90˚. The optical zone diameter was 6.3-6.8 mm (6.60±0.13 mm). The maximum thickness of the lenticule was 59-135 µm (108.5±17.9 µm) and the lenticule side-cut angle was 90˚. The data were described as mean ± SD.
Postoperative medications included topical tobramycin dexamethason (Novartis International AG) four times for 30 min after surgery, 0.5% levofloxacin (Santen Pharmaceutical Co., Ltd.) four times every day for 7 days, 0.1% fluorometholone (Santen Pharmaceutical Co., Ltd.) four times every day, which decreased one time each week until once a day for one week. Patients were followed up at postoperative week 1, and months 1, 3 and 6. Uncorrected distance visual acuity (UDVA), manifest refraction and intraocular pressure (IOP) were measured, and anterior segment optical coherence tomography and corneal topography were performed at every visit.
SPSS for Windows software (version 17.0; SPSS, Inc.) was used for statistical analysis. Preoperative examinations among groups were analyzed by one-way ANOVA followed by Bonferroni's correction. The corneal aberrations within groups, the epithelial thickness and the difference in epithelial thickness, the corneal aberrations and the difference in corneal aberrations and the max-min and SD values of corneal epithelial thickness across a 5-mm diameter among three groups were compared with a two-way mixed ANOVA followed by Bonferroni's correction. Kruskal-Wallis H test was used to analyze UDVA and spherical equivalent among three groups. P<0.05 was considered to indicate a significant difference.
The study cohort consisted of 30 patients with 57 eyes undergoing SMILE for myopia correction. A total of 8 eyes were treated in group B in patients who had worn one-day disposable hydrogel SCLs (Johnson & Johnson) and 9 eyes in patients who had worn monthly disposable hydrogel SCLs (Johnson & Johnson or Bausch & Lomb). A total of 8 eyes were treated in group C in patients who had worn one-day disposable hydrogel SCLs (Johnson & Johnson) and 10 eyes in patients who had worn monthly disposable hydrogel SCLs (Johnson & Johnson or Bausch & Lomb). The ratio of daily and monthly disposable lens in group B was consistent with that in group C. The mean age, preoperative spherical equivalent refractive power and preoperative epithelial thickness of the central 5-mm zone were similar among the three groups. There were no statistically significant differences in baseline measurements among the three groups, except epithelial thickness (P<0.05). The preoperative mean corneal epithelial thickness was thinner in group C than in group A (P<0.05), whereas no significant difference in preoperative epithelial thickness was observed in group B compared with groups A and C (P>0.05) (
Visual acuity values (in logMAR) at postoperative week 1, and months 1, 3 and 6 were similar among the three groups. Analysis with the Kruskal-Wallis H test revealed no statistically significant differences in UDVA among the three groups at all postoperative time points (P>0.05;
Spherical equivalent was compared at postoperative week 1, and months 1, 3 and 6 among the three groups. Analysis with the Kruskal-Wallis H test revealed no statistically significant differences in spherical equivalent among the three groups at each pair of consecutive time points (P>0.05) (
The preoperative superior epithelial thickness was thinner than the preoperative inferior epithelial thickness of the nine sectors in group A (
At postoperative week 1 and month 1, the epithelial thicknesses in the central, nasal, inferonasal, inferior, inferotemporal and temporal segments were thinner in group C than in group A (P<0.05). At postoperative month 3, the epithelial thicknesses in the central, nasal, inferonasal, inferior, inferotemporal and temporal regions were significantly thinner in group C than in group A (P<0.05); the inferonasal and inferior regions were thinner in group C than in group B. At postoperative month 6, the epithelial thicknesses in the central, nasal, inferonasal, inferior, inferotemporal and temporal segments were significantly thinner in group C than in group A (P<0.05); the epithelial thicknesses in the inferior segment were thinner in group C than in group B (
In the superior and superonasal regions of the cornea, the change in epithelial thickness at postoperative week 1 and month 1 was greater in group C than in group A (P<0.05) In the superotemporal region, the change in epithelial thickness was greater in group C than in group A at postoperative week 1 and month 1 (P<0.05); it was also greater in group C than in group B at postoperative week 1 (P<0.05;
It should be noted that at all examined time points, the epithelial thickness in the central, nasal, inferonasal, inferior, inferotemporal and temporal segments was less in group C than in group A, but in the superior, superotemporal and superonasal zones had no statistically significant difference between group A and group C at all postoperative time points which the epithelial thickness difference of the three zones was more in group C than in group A at postoperative week 1 and month 1 (
The total higher-order aberrations of the three groups were increased postoperatively, compared with preoperatively (P<0.05). Preoperatively and at postoperative months 1, 3 and 6, the total higher-order aberrations were greater in group C than in group A (P<0.05). At postoperative month 1 and 3, the total higher-order aberrations were greater in group C than group B (P<0.05). However, there were no statistically significant differences in the numbers of total higher-order aberrations difference among the three groups after surgery (P>0.05).
Postoperatively, spherical aberrations were increased among the three groups, compared with preoperative measurements (P<0.05;
Coma aberrations in group A at postoperative month 3, in group B at postoperative month 6, as well as in group C at postoperative at all time points, were greater than preoperative values (P<0.05;
No postoperative complications (e.g., refraction regression, epithelial defects or diffuse lamellar keratitis) were observed during the first 6 months postoperatively in any of the eyes.
Previous studies have demonstrated that contact lens wear can lead to corneal epithelial thinning (
Preoperatively, the corneal epithelial thickness is not evenly distributed; it is characterized by a thinner epithelium superiorly compared with that inferiorly (
The underlying mechanisms of corneal epithelial thinning after contact lens wear have been investigated in multiple studies. Corneal oxygen uptake plays an important role in corneal metabolism and the maintenance of corneal transparency (
To the best of our knowledge, there have been no studies focusing on changes in corneal epithelial thickness following SCL wear after corneal refractive surgery. To recover the smooth corneal anterior surface, the corneal epithelium itself undergoes remodeling in response to corneal refractive surgery; this remodeling is characterized by uneven thickening of the corneal epithelium. The present results confirmed the findings of previous studies (
No differences were found in terms of visual acuity or manifest refraction among the three groups at all postoperative time points after SMILE. The visual quality after SMILE did not appear to be affected by the thinning of the corneal epithelium induced by contact lens wear and corneal surgery. Considering that the postoperative epithelial healing response caused by SMILE is mild (
In the present study, the total higher-order and coma aberrations of the long-term wear group were greater than those of the non-wearing and short-term wear groups preoperatively, which was consistent with the results after surgery. By contrast, there were no significant differences in spherical aberrations among the three groups, while spherical aberrations at 3 and 6 months postoperatively were greater in the long-term wear group than in the non-wearing group. Consistent with this, the changes in spherical aberrations at 1, 3 and 6 months postoperatively were greater in the long-term wear group than in the non-wearing group. Larger corneal aberrations observed in the long-term wear group may have been related to the influence of contact lenses on the normal physiology of the corneal epithelium (
The present study has a few limitations. Investigation of corneal epithelial thickness was limited to a region 5 mm in diameter. Furthermore, the thickness of the peripheral corneal epithelium may have been affected by the size of the palpebral fissure and the compression of the upper and lower eyelids on the cornea, which led to decreased accuracy and reliability of the measurement of peripheral corneal epithelial thickness and may have affected the comprehensive assessment of corneal epithelial thickness. With the possible development of more accurate high-resolution anterior segment optical coherence tomography technology, the epithelial thickness over the entire cornea can be studied to fully evaluate changes in epithelial thickness.
In summary, the present results indicate that long-term SCL wear will lead to epithelial thinning. However, uneven thickening of the corneal epithelium after SMILE and discontinuation of SCL wear do not impact visual acuity or manifest refraction after SMILE.
Not applicable.
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.
YX, YW and XY made substantial contributions to acquisition of data and analysis of data. YW was involved in drafting the manuscript. YQ, BL and XZ made substantial contributions to conception and design, and revised the manuscript critically for important intellectual content. XZ and YX confirm the authenticity of all the raw data. All authors read and approved the final manuscript.
Clinical trials registration reference ID: 2019-049 (The First Affiliated Hospital of Soochow University Institutional Review Board, Suzhou, China). This retrospective study was approved by the Ethics Committee of The First Affiliated Hospital of Soochow University, and all patients provided consent at the time of the surgery.
Not applicable.
The authors declare that they have no competing interests.
Zoning of corneal epithelium (diameter of central 6 mm). C, central; S, superior; SN, superonasal; N, nasal; IN, inferonasal; I, inferior; IT, inferotemporal; T, temporal; ST, superotemporal; OD, oculus dexter; OS, oculus sinister.
Corneal epithelial thickness in (A) preoperative, (B) 1 week, (C) 1 month, (D) 3 month and (E) 6 month of group A (non-SCL-wearing), group B (wearing SCL ≤1 year) and group C (wearing SCL >1 year; *P<0.05). Two-way ANOVA (Bonferroni's correction). SCL, soft contact lens.
Corneal epithelial thickness difference in (A) superior, (B) superonasal and (C) superotemporal sectors of group A (non-SCL-wearing), group B (wearing SCL ≤1 year) and group C (wearing SCL >1 year) preoperatively and at postoperative week 1, and months 1, 3 and 6 (*P<0.05, comparing between group A and group C; #P<0.05, comparing between group B and group C). Two-way mixed ANOVA (Bonferroni's correction). SCL, soft contact lens.
(A) Preoperative corneal aberrations of group A (non-SCL-wearing), group B (wearing SCL ≤1 year) and group C (wearing SCL >1 year). (B) Total high order aberration difference, (C) spherical aberration difference and (D) coma difference of three groups at all postoperative time points. *P<0.05. Two-way mixed ANOVA (Bonferroni's correction). SCL, soft contact lens; tHOA, total high order aberration.
Nine sectors of corneal epithelial thickness of group A (non-SCL-wearing), group B (wearing SCL ≤1 year) and group C (wearing SCL >1 year) for each pair of consecutive time points.
Preoperative comparative data for all three study groups
Parameters | Group A | Group B | Group C | F-value | P-value |
---|---|---|---|---|---|
Eyes, n | 22 | 17 | 18 | - | - |
Age, years | 23.55±6.46 | 26.78±5.07 | 28.30±4.16 | 2.156 | 0.135 |
Sphere, D | -4.25±1.10 | -4.43±1.12 | -4.61±1.15 | 0.511 | 0.603 |
Cylinder, Dcyl | -0.80±0.37 | -0.75±0.40 | -0.57±0.55 | 1.407 | 0.254 |
SE, D | -4.65±1.11 | -4.80±1.13 | -4.90±1.08 | 0.259 | 0.772 |
ET, µm | 57.10±2.90 | 55.52±2.59 | 54.05±1.71 | 7.462 | 0.001 |
aValues expressed as mean ± standard deviation.
bP<0.01; one-way ANOVA (Bonferroni's correction). Group A, non-wearing SCL; group B, wearing SCL ≤1 year; group C, wearing SCL >1 year; D, diopters; Dcyl, diopters cylinder; SE; spherical equivalent; ET, corneal epithelial thickness; SCL, soft contact lens.
Comparative data of UDVA and SE among three groups
Parameters | Time | Group A (n=22) | Group B (n=17) | Group C (n=18) | U | P-value |
---|---|---|---|---|---|---|
UDVA, logMAR | 1 week postoperative | -0.05±0.06 | -0.05±0.06 | -0.04±0.06 | 0.402 | 0.818 |
1 month postoperative | -0.06±0.06 | -0.05±0.06 | -0.06±0.07 | 0.475 | 0.789 | |
3 months postoperative | -0.05±0.05 | -0.04±0.08 | -0.04±0.04 | 0.142 | 0.932 | |
6 months postoperative | -0.09±0.07 | -0.07±0.06 | -0.04±0.07 | 4.018 | 0.134 | |
SE, D | 1 week postoperative | 0.05±0.30 | 0.07±0.49 | -0.20±0.43 | 2.978 | 0.226 |
1 month postoperative | 0.01±0.42 | 0.10±0.39 | 0.19±0.26 | 1.696 | 0.428 | |
3 months postoperative | 0.03±0.35 | 0.05±0.37 | -0.13±0.46 | 1.637 | 0.441 | |
6 months postoperative | 0.02±0.28 | 0.05±0.49 | 0.02±0.28 | 0.103 | 0.950 |
aValues expressed as mean ± standard deviation. Kruskal-Wallis H test. Group A, non-wearing SCL; group B, wearing SCL ≤1 year; group C, wearing SCL >1 year; SCL, soft contact lens; UDVA, uncorrected distance visual acuity; SE, spherical equivalent.
Comparative data of corneal epithelial map within central 5-mm uniformity indices among three groups
Parameters | Group A (n=22) | Group B (n=17) | Group C (n=18) |
---|---|---|---|
Preoperative | |||
Max-min, µm | 6.36±1.68 | 5.47±2.45 | 5.06±0.80 |
SD |
1.51±0.45 | 1.27±0.68 | 1.10±0.22 |
1 week postoperative | |||
Max-min, µm |
9.82±2.32 | 8.82±3.13 | 7.83±1.50 |
SD |
2.39±0.72 | 2.14±0.83 | 1.76±0.29 |
1 month postoperative | |||
Max-min, µm | 9.77±2.99 | 9.71±3.58 | 8.33±1.81 |
SD | 2.42±0.71 | 2.28±0.58 | 1.90±0.37 |
3 months postoperative | |||
Max-min, µm |
10.77±2.69 | 9.53±2.72 | 8.11±1.57 |
SD |
2.58±0.64 | 2.22±0.61 | 2.04±0.41 |
6 months postoperative | |||
Max-min, µm |
10.82±3.00 | 9.76±3.49 | 8.22±1.73 |
SD |
2.70±0.75 | 2.31±0.79 | 1.96±0.34 |
aValues expressed as mean ± SD.
bP<0.05, comparison of three groups.
cP<0.05 compared with group A.
dP<0.01, comparison of three groups. Two-way mixed-design ANOVA (Bonferroni's correction). Group A, non-wearing SCL; group B, wearing SCL ≤1 year; group C=wearing SCL >1 year; SCL, soft contact lens; SD, standard deviation.
Comparative data of corneal aberrations among three groups
Aberrations | Time | Group A (n=22) | Group B (n=17) | Group C (n=18) |
---|---|---|---|---|
tHOA | Preoperative |
0.38±0.10 |
0.40±0.12 | 0.51±0.15 |
1 month postoperative |
0.64±0.15 |
0.69±0.17 |
0.85±0.24 |
|
3 months postoperative |
0.65±0.15 |
0.69±0.22 |
0.78±0.20 |
|
6 months postoperative |
0.65±0.18 |
0.68±0.22 |
0.76±0.18 |
|
Spherical aberration | Preoperative | 0.22±0.07 | 0.19±0.08 | 0.21±0.08 |
1 month postoperative | 0.39±0.12 |
0.42±0.17 |
0.48±0.13 |
|
3 months postoperative |
0.37±0.10 |
0.39±0.15 |
0.48±0.12 |
|
6 months postoperative |
0.38±0.12 |
0.41±0.16 |
0.47±0.12 |
|
Coma | Preoperative |
0.18±0.07 |
0.23±0.12 |
0.37±0.12 |
1 month postoperative |
0.35±0.17 |
0.38±0.21 |
0.61±0.22 |
|
3 months postoperative |
0.36±0.15 |
0.42±0.24 |
0.51±0.18 |
|
6 months postoperative |
0.39±0.19 |
0.42±0.21 |
0.51±0.17 |
aValues expressed as mean ± standard deviation.
bP<0.05 comparison of three groups.
cP<0.05, compared with group C.
dP<0.01 comparison of three groups.
eP<0.05 postoperative vs. preoperative.
fP<0.001 comparison of three groups. Two-way mixed-design ANOVA (Bonferroni's correction). Group A, non-wearing SCL; group B, wearing SCL ≤1 year; group C, wearing SCL >1 year; tHOA, total high order aberration; SCL, soft contact lens.