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 Table of Contents  
ORIGINAL ARTICLE
Year : 2020  |  Volume : 58  |  Issue : 4  |  Page : 253-257

Preoperative and postoperative comparison of higher order aberrations in individuals 1 month after small incision lenticule extraction


Department of Ophthalmology, Uma Eye Clinic, Chennai, Tamil Nadu, India

Date of Submission08-Sep-2020
Date of Acceptance23-Sep-2020
Date of Web Publication16-Dec-2020

Correspondence Address:
Dr. Aadithreya Varman
Z Block, No. 18, 5th Street, 13th Main Road, Annanagar, Chennai - 600 040, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/tjosr.tjosr_133_20

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  Abstract 


Aim: This study analysed the visual outcomes of patients with myopia and myopic astigmatism following Small Incision Lenticule Extraction (SMILE). Visual outcomes were determined by Post-operative refraction, Uncorrected Visual Acuity and aberrometry estimated with iTrace aberrometer post operatively immediately and upto day 30. Results: On Post-Operative day 1, the spherocylinder group, attained an uncorrected visual acuity of 6/6. Materials and Methods: The final post-operative refraction in all cases was within ±0.25 diopters of sphere in 18 eyes and within ±0.50 diopters of sphere in 10 eyes. The aberrometry values recorded on iTrace at the end of 30 days revealed a decrease in the total higher order aberrations. Mean higher order aberration is significantly (P<0.05) reduced in the post-operative status Similarly the pure cylinder group attained uncorrected visual acuity of 6/6 in all eyes on POD 30, with a decrease in higher order aberrations. Mean higher order aberration is significantly (P<0.05) reduced in the post-operative status. The final post-operative refraction in all cases was within ±0.25 diopters of cylinder in 48 eyes, within ±0.50 diopters of cylinder in 16 eyes and within ±0.75 in 14 eyes. Conclusion: SMILE is a successful procedure in treatment of both myopic spherical and cylindrical refractive errors. The faster healing and flapless advantage along with lesser incidence of dry eyes has an edge over conventional laser vision corrective procedures. The other important advantage is the reduction of higher order aberrations and better quality of vision. To conclude SMILE is safe and effective procedure for correction of myopic refractive errors and is also beneficial in reducing higher order aberrations.

Keywords: Aberrations, refractive surgery, small incision lenticule extraction


How to cite this article:
Varman N V, Varman A, Balakumar D. Preoperative and postoperative comparison of higher order aberrations in individuals 1 month after small incision lenticule extraction. TNOA J Ophthalmic Sci Res 2020;58:253-7

How to cite this URL:
Varman N V, Varman A, Balakumar D. Preoperative and postoperative comparison of higher order aberrations in individuals 1 month after small incision lenticule extraction. TNOA J Ophthalmic Sci Res [serial online] 2020 [cited 2021 Jan 21];58:253-7. Available from: https://www.tnoajosr.com/text.asp?2020/58/4/253/303670




  Introduction Top


Corneal refractive surgeries are performed with high-frequency pulses (femtosecond) for safe and accurate tissue ablation.[1] This technique is employed in the flapless refractive surgical procedure, small incision lenticule extraction (SMILE).[2] SMILE has widely replaced conventional refractive procedures because of its superior advantages of small incision size, lesser damage to corneal nerves, faster recovery, improved strength of the cornea postprocedure, and no flap-related complications.[3],[4],[5],[6] Without eye tracking or registration of iris, SMILE mainly depends on subjective fixation on a central target.


  Materials and Methods Top


A retrospective analysis was conducted on 106 eyes that underwent SMILE over the past 1 year. All patients who were above the age of 18 years to 32 years, adequate central corneal thickness, stable refractive error, normal corneal topography, and normal retinal morphology were included in the study.

Any patient with a corneal scar, media opacities, coexisting glaucoma or other optic nerve abnormalities, and unstable refractive error was excluded from the study.

Patients with myopia and myopic astigmatism were included in the study. All procedures were performed by a single experienced surgeon. VisuMax laser system (Carl Zeiss Meditec AG, Jena, Germany) was utilized for all the corrective refractive procedures. The repetition rate of the laser was 500 kHz and pulse energy was 132 NJ. The diameter of the lenticule was 6.0 mm, the diameter of the cap was 6.5 mm, and the cap thickness intended was 110–130 microns. The anterior surface cut was spiral out and the posterior surface cut was spiral in. The length of the side cuts was 2 mm. The intended refractive lenticule was then gently dissected with a spatula through the side cuts. This was later gently peeled away with a forceps. After surgery, all patients received a topical antibiotic-steroid eye drop combination for 1 week, followed by a steroid eye drop alone for 4 weeks along with topical lubricants to use throughout the day on need basis.

All patients were evaluated immediately postoperatively, postoperative day 1, postoperative day 8, and postoperative day 30. In all visits, patients were evaluated for postoperative refractive outcomes, uncorrected visual acuity, and aberrometry estimated with iTrace aberrometer[Figure 1],[Figure 2],[Figure 3].
Figure 1: The quantitative distribution of spherical and cylindrical powers in the spherocylindrical group

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Figure 2: The quantitative distribution of cylindrical powers in the pure cylinder refractive error group

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Figure 3: The distribution of aberrations in both the groups

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  Results Top


All patients were subjected to reassessment for uncorrected visual acuity estimation at all stipulated periods of postoperative day 1, postoperative day 8, and postoperative day 30. In all visits, patients were evaluated for postoperative refractive outcomes, uncorrected visual acuity, and aberrometry estimated with iTrace aberrometer [Figure 4].
Figure 4: Visual acuity and postoperative refraction in individuals with spherocylindrical refractive errors after small incision lenticule extraction

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When considering 28 eyes with spherocylindrical refractive errors, the following results were noted:

On postoperative day 0, 4 eyes attained an uncorrected visual acuity of 6/18, 22 eyes attained an uncorrected visual acuity of 6/12, and 2 eyes attained an uncorrected visual acuity of 6/9. On postoperative day 1, all the 28 eyes attained an uncorrected visual acuity of 6/6. On postoperative day 10–30, all the 28 eyes maintained an uncorrected visual acuity of 6/6.

The final evaluation after 1 month revealed a stable uncorrected visual acuity of 6/6 in all eyes. The final postoperative refraction in all cases was within ± 0.25 diopters of the sphere in 18 eyes and within ± 0.50 diopters of the sphere in 10 eyes.

iTrace aberrometry values were compared for higher order aberrations before and after SMILE on day 30 [Figure 5].
Figure 5: Comparison of pre operative and post operative reduction in Higher Order Aberrations in the Spherocylinder refractive error group

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The aberrometry values when analyzed at the end of 30 days after an uneventful procedure revealed a decrease in the total higher order aberrations.

The mean higher order aberration is significantly (P < 0.05) reduced in the postoperative status. The mean ± standard deviation (SD) difference is 124.1 ± 103.7 and the 95% confidence interval (CI) of the difference is (83.9–164.3.). All analyses were performed with the paired t-test.

When considering 78 eyes with cylindrical refractive errors, the following results were noted:

On postoperative day 0, 14 eyes attained an uncorrected visual acuity of 6/18, 56 eyes attained an uncorrected visual acuity of 6/12, and 8 eyes attained an uncorrected visual acuity of 6/9.

On postoperative day 1, 10 eyes attained an uncorrected visual acuity of 6/9 and 68 eyes attained an uncorrected visual acuity of 6/6.

On postoperative day 10–30, 4 eyes attained an uncorrected visual acuity of 6/9 and 74 eyes attained an uncorrected visual acuity of 6/6.

The final evaluation after 1 month revealed a stable uncorrected visual acuity of 6/6 in all eyes

The final postoperative refraction in all cases was within ±0.25 diopters of the cylinder in 48 eyes, within ± 0.50 diopters of the cylinder in 16 eyes, and within ± 0.75 in 14 eyes [Figure 6].
Figure 6: Visual acuity and postoperative refraction in individuals with pure cylindrical refractive errors after small incision lenticule extraction

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The aberrometry values when analyzed at the end of 30 days after an uneventful procedure revealed a decrease in the total higher order aberrations.

iTrace aberrometry values were compared for higher order aberrations before and after SMILE on day 30 [Figure 7].
Figure 7: Comparison of pre operative and post operative reduction in Higher Order Aberrations in the Pure Cylinder refractive error group

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The mean higher order aberration is significantly (P < 0.05) reduced in the postoperative status. The mean ± SD difference is 123.8 ± 70.0 and the 95% CI of the difference is 108.1–130.7.

All analyses were performed with the paired t-test.


  Discussion Top


SMILE is a newer alternative to conventional laser vision correction procedures. It is a known fact that visual acuity and quality of vision is delayed in patients who have undergone SMILE. Shah et al. concluded that early visual recovery and refractive outcomes after femtosecond lenticule extraction were affected by the scanning trajectory of the laser and Vestergaard et al. found that CDVA was better than 20/20 in 85% of eyes in the SMILE group and in 83% of eyes in the LASIK group postoperatively;[7],[8] in our case scenario, we have noticed good recovery of visual acuity and lesser higher order aberrations in all patients postoperatively. This is probably due to lesser energy used and also meticulous surgical handling of the tissues and flap. Many studies have reiterated the efficacy, predictability, and index of safety of SMILE in the correction of myopia and myopic astigmatism.[9],[10],[11],[12]

Our study demonstrates the potential benefits of SMILE as a modality of correction of higher order aberrations along with the correction of refractive errors. All the outcomes were repeatable and compared accurately as the surgery was performed by a single surgeon with no alteration in the parameters of the lasers. As far as the efficacy of the procedure was concerned, uncorrected visual acuity was restored to 6/6 and was stable in both the groups when estimated at the end of 1 month. The postoperative refraction ranged from ± 0.25 to ± 0.50 of diopters of the sphere to ± 0.25 to ± 0.75 diopters of the cylinder.

There were no noticeable complications in all cases such as corneal haze, suction loss, tears at the incision edge, cap perforation, difficult lenticule extraction or residue of part of the intrastromal lenticule, and epithelial ingrowth or interphase haze.

The higher order aberrations were studied as a total value of root mean squares which were compared preoperatively and postoperatively at the end of 1 month of the procedure. Our study demonstrated a significant decline in the higher order aberrations in the postoperative period indicating that SMILE is an effective procedure in the correction of higher order aberrations as well as refractive errors.

Other studies concurred with the fact that SMILE induced lesser higher order aberrations and there was no difference in the total higher order aberrations or spherical aberrations with the SMILE or wavefront-guided LASIK (Laser in situ keratomileusis).[13] A comparative study done by Ganesh and Gupta also concluded that with high refractive accuracy and fast postoperative recovery, SMILE provides all of the advantages of LASIK while avoiding the limitations (reduced corneal biomechanical strength, increased postoperative Higher order aberrations (HOAs), low contrast sensitivity under mesopic conditions, and dry eyes) commonly associated with it.[14]

Another study conducted by Lin et al. also concluded that SMILE has a lower induction rate of higher order aberrations and spherical aberration than the FS-LASIK procedure.[15]

Our study was comparable with the studies performed with respect to the overall safety and efficacy of the procedure for the correction of refractive errors and lesser induction of higher order aberrations postoperatively. This provides an edge over conventional refractive procedures.


  Conclusion Top


SMILE is a successful procedure in the treatment of both myopic spherical and cylindrical refractive errors. The faster healing and flapless advantage along with lesser incidence of dry eyes have an edge over conventional laser vision corrective procedures. The other important advantage is the reduction of higher order aberrations and better quality of vision.

To conclude, SMILE is a safe and effective procedure for the correction of myopic refractive errors and is also beneficial in reducing higher order aberrations.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Sugar A. Ultrafast (femtosecond) laser refractive surgery. Curr Opin Ophthalmol 2002;13:246-9.  Back to cited text no. 1
    
2.
Kim P, Sutton GL, Rootman DS. Applications of the femtosecond laser in corneal refractive surgery. Curr Opin Ophthalmol 2011;22:238-44.  Back to cited text no. 2
    
3.
Moshirfar M, McCaughey MV, Reinstein DZ, Shah R, Santiago-Caban L, Fenzl CR. Small-incision lenticule extraction. J Cataract Refract Surg 2015;41:652-65.  Back to cited text no. 3
    
4.
Mohamed-Noriega K, Riau AK, Lwin NC, Chaurasia SS, Tan DT, Mehta JS. Early corneal nerve damage and recovery following small incision lenticule extraction (SMILE) and laser in situ keratomileusis (LASIK). Invest Ophthalmol Vis Sci 2014;55:1823-34.  Back to cited text no. 4
    
5.
Xu Y, Yang Y. Dry eye after small incision lenticule extraction and LASIK for myopia. J Refract Surg 2014;30:186-90.  Back to cited text no. 5
    
6.
Wu D, Wang Y, Zhang L, Wei S, Tang X. Corneal biomechanical effects: small-incision lenticule extraction versus femtosecond laser-assisted laser in situ keratomileusis. J Cataract Refract Surg 2014;40:954-62.  Back to cited text no. 6
    
7.
Shah R, Shah S. Effect of scanning patterns on the results of femtosecond laser lenticule extraction refractive surgery. J Cataract Refract Surg 2011;37:1636-47.  Back to cited text no. 7
    
8.
Vestergaard A, Ivarsen A, Asp S, Hjortdal Jø. Femtosecond (FS) laser vision correction procedure for moderate to high myopia: a prospective study of ReLEx(®) flex and comparison with a retrospective study of FS-laser in situ keratomileusis. Acta Ophthalmol 2013;91:355-62.  Back to cited text no. 8
    
9.
Zhang J, Wang Y, Wu W, Xu L, Li X, Dou R. Vector analysis of low to moderate astigmatism with small incision lenticule extraction (SMILE): results of a 1-year follow-up. BMC Ophthalmol 2015;15:8.  Back to cited text no. 9
    
10.
Fernández J, Valero A, Martínez J, Piñero DP, Rodríguez-Vallejo M. Short-term outcomes of small-incision lenticule extraction (SMILE) for low, medium, and high myopia. Eur J Ophthalmol 2017;27:153-9.  Back to cited text no. 10
    
11.
Reinstein DZ, Carp GI, Archer TJ, Gobbe M. Outcomes of small incision lenticule extraction (SMILE) in low myopia. J Refract Surg 2014;30:812-8.  Back to cited text no. 11
    
12.
Sekundo W, Gertnere J, Bertelmann T, Solomatin I. One-year refractive results, contrast sensitivity, high-order aberrations and complications after myopic small-incision lenticule extraction (ReLEx SMILE). Graefes Arch Clin Exp Ophthalmol 2014;252:837-43.  Back to cited text no. 12
    
13.
Ye MJ, Liu CY, Liao RF, Gu AY, Zhao BY, Liao Y. SMILE and wavefront-guided LASIK out-compete other refractive surgeries in ameliorating the induction of high-order aberrations in anterior corneal surface; hindawi publishing corporation; J Ophthalmol 2016;2016:8702162.  Back to cited text no. 13
    
14.
Ganesh S, Gupta R. Comparison of visual and refractive outcomes following femtosecond laser assisted LASIK with SMILE in patients with myopia or myopic astigmatism. J Refract Surg 2014;30:2014.  Back to cited text no. 14
    
15.
Lin F, Xu Y, Yang Y. Comparison of the visual results after SMILE and femtosecond laser-assisted LASIK for myopia. J Refract Surg 2014;30:248-54.  Back to cited text no. 15
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]



 

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