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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 111  |  Issue : 3  |  Page : 96-101

The ablation depth effect on dry eye after LASIK treatment for myopia


Department of Ophthalmology, Minia University, Minia, Egypt

Date of Submission27-Apr-2018
Date of Acceptance13-Jun-2018
Date of Web Publication22-Nov-2018

Correspondence Address:
Dr. Ahmed Mostafa Eid
Department of Ophthalmology, Minia University Hospital, Minia 61111
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ejos.ejos_21_18

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  Abstract 


Purpose The aim was to investigate the effect of ablation depth on the incidence and severity of the dry eye after laser-assisted in-situ keratomileusis (LASIK) treatment of myopia.
Patients and methods This was a prospective, noncomparative, interventional case series study that included myopic patients who underwent LASIK treatment for myopia ranging from −1.75 to −12.00 D. All patients had a comprehensive preoperative ophthalmologic evaluation. Tear breakup time (TBUT) and Schirmer 1 tests were undertaken for all patients preoperatively and at 1, 3, and 6 months postoperatively. The main outcome measures included the incidence and severity of the dry eye and their correlation with ablation depth at 1, 3, and 6 months postoperatively.
Results 104 eyes of 53 myopic patients (14 males and 39 females) with a mean age of 27.4±6.06 years (range: 21–45 years). At the baseline, the mean spherical equivalent was −6.38±2.82 D (range: −1.5 to −12 D), mean TBUT was 12.93±1.60 s (range: 10–17 s), and the mean Schirmer 1 score was 17.9±62.52 mm (range: 14–30 mm). Mean post-LASIK TBUT was 7.58±4.32, 10.22±5.38, and 12.07±4.02 s at 1, 3, and 6 months, respectively (P<0.001). The mean post-LASIK Schirmer 1 score was 8.50±5.01, 11.4±5.54, and 14.24±3.77 mm at 1, 3, and 6 months, respectively (P<0.001). There was a strong negative correlation between ablation depth and both TBUT and Schirmer 1 values at 1 and 3 follow-up months, but a moderate negative correlation at 6 months.
Conclusions There was moderate to strong negative correlation between ablation depth and the degree of post myopic LASIK dryness assessed objectively by TBUT and Schirmer 1 tests.

Keywords: dry eye, LASIK, myopia, refractive surgery


How to cite this article:
Elfadl MA, Zein HA, Eid AM, Tolba AA. The ablation depth effect on dry eye after LASIK treatment for myopia. J Egypt Ophthalmol Soc 2018;111:96-101

How to cite this URL:
Elfadl MA, Zein HA, Eid AM, Tolba AA. The ablation depth effect on dry eye after LASIK treatment for myopia. J Egypt Ophthalmol Soc [serial online] 2018 [cited 2018 Dec 13];111:96-101. Available from: http://www.jeos.eg.net/text.asp?2018/111/3/96/245978




  Introduction Top


Laser-assisted in-situ keratomileusis (LASIK) is frequently complicated by postoperative dry eye [1],[2],[3],[4]. Post-LASIK dry eye has an incidence that varies widely from 3 to 59% [5],[6]. The transient dry eye develops in almost all eyes in the immediate postoperative period [7],[8]. Corneal afferent sensory nerves are damaged during flap creation and stromal ablation, which subsequently results in diminished corneal sensation. The resultant corneal hypoesthesia has been proposed to reduce both tear secretion and the blinking rate, leading to tear film instability and loss of conjunctival goblet cells. This, in turn, results in symptoms of the dry eye, including pain, photophobia, foreign body sensation, and blink-induced fluctuation of vision [9],[10],[11],[12]. The term LASIK-induced neuroepitheliopathy has been used to describe this condition [13]. The aim of this study was to evaluate the effect of ablation depth on dry eye development after myopic LASIK.


  Patients and methods Top


Study design

This was a prospective, noncomparative interventional case series of eyes undergoing LASIK treatment of myopia. The study was conducted at two sites: The International Eye Center and the Ophthalmology Department of Minia University, Minia, Egypt, between June 2013 and May 2014.

The study protocol was approved by the local Ethics Committee of Minia University and adhered to the tenets of the Declaration of Helsinki. A written informed consent was obtained from all patients after being given a thorough explanation of the nature of the study, involving intervention and potential complications (Clinical Trials.gov Identifier: NCT03228784).

To be included in the study, patients had to be 21 years or older and have a spherical equivalent ranging from −1.50 to −12.00 D. Exclusion criteria were any evidence of corneal ectasia, including keratoconus, forme fruste keratoconus, abnormal corneal elevation maps on Pentacam, corneal thickness less than 500 µm measured at the thinnest corneal location by Pentacam or a calculated residual stromal bed thickness less than 280 µm, symptoms or signs of the dry eye, history of prior use of artificial tears, corneal dystrophy, significant corneal opacification, history of autoimmune disease, crystalline lens opacities, history of prior ocular surgery, and pregnant or lactating females.

Ophthalmologic examination and dry eye evaluation

All patients underwent a comprehensive preoperative ophthalmologic evaluation including the following:
  1. Careful history taking with special emphasis on symptoms suggestive of dry eye disease.
  2. Automated noncycloplegic refraction using NIDEK Auto Ref/Keratometer ARK-1 s (NIDEK Co. LTD, Gamagori, Aichi, Japan).
  3. Snellen uncorrected visual acuity and best spectacle-corrected visual acuity using a Landolt ‘C’ distance chart.
  4. Slit-lamp examination to detect signs of the dry eye, significant corneal opacities, corneal dystrophies, and/or other anterior segment pathologies.
  5. Intraocular pressure measurement using Goldmann applanation tonometer (GAT).
  6. Dilated slit-lamp biomicroscopy using either a 78 or a 90 D noncontact slit-lamp lens and binocular indirect ophthalmoscopy using a 20 D binocular indirect ophthalmoscopy lens.
  7. Oculus Pentacam HR (OCULUS Optikgeräte GmbH, Wetzlar, Germany) imaging of the anterior segment, to assess the corneal front and back elevation and corneal thickness.
  8. Tear film breakup time (TBUT) examination:
    1. More than 10 s was considered normal.
    2. Between 5 and 10 s was considered reduced.
    3. Less than 5 s was considered severely reduced.
  9. Schirmer 1 test:
    1. The test was considered negative or normal if there was greater than or equal to 15 mm wetting of the filter paper after 5 min.
    2. Mild dryness was defined as 14–9 mm wetting of the filter paper after 5 min.
    3. Moderate dryness was defined as 8–4 mm wetting of the filter paper after 5 min.
    4. Severe dryness was defined as less than 4 mm wetting of the filter paper after 5 min.


Both TBUT and Schirmer tests were carried out in a quiet room with relatively constant temperature and humidity. TBUT was performed three times and the results were averaged.

Laser-assisted in-situ keratomileusis procedure and postoperative care

The surgery was performed using VISX Star S4 IR excimer laser (Abbott Laboratories Inc., Abbott Park, Illinois, USA) under topical anesthesia. Moria M2 9.5-mm-diameter suction ring and 110-μm microkeratome head (Moria Inc., Doylestown, Pennsylvania, USA) were used for all patients to create a superior-hinge flap. The ablation zone was 6–6.5 mm with a peripheral blend zone of 8 mm.

After surgery, all patients received topical moxifloxacin 0.5%, topical tobramycin 0.3%/dexamethasone 0.1% combination eye drops four times daily for 15 days. Patients were also instructed to use sodium hyaluronate 0.15% artificial tears five times daily for 1 month. All patients were examined at 1 day and 1 week postoperatively for evidence of flap malposition, striae, epithelial defects, or diffuse lamellar keratitis. Intraocular pressure was measured using GAT at all postoperative visits to detect any steroid-induced ocular hypertension. All eyes underwent slit-lamp examination, GAT, TBUT, and Schirmer 1 testing at 1, 3, and 6 months postoperatively.

The primary outcome measures were the incidence and severity of the dry eye at 1, 3, and 6 months postoperatively based on TBUT and Schirmer 1 test scores. A secondary outcome measure was the correlation between the incidence and severity of the dry eye at the selected follow-up dates with myopic ablation depth.

Statistical analysis

Statistical package for the social sciences, version 22 (SPSS; IBM Corp., Armonk, New York, USA) was used for statistical data analysis. Data were expressed as mean±SD or numbers and percentages. Mean and SD were used as descriptive values for quantitative data. Student’s t-test was used to compare the means between two groups, and χ2-test was used to compare the frequency of qualitative variables. Pearson’s correlation coefficient was used for correlation analysis.


  Results Top


The study included 104 eyes of 53 myopic patients, 14 (26.4%) males and 39 (73.6%) females. The mean age was 27.4±6.1 years (range: 21–45 years). [Table 1] demonstrates the demographic data of the study population. TBUT and Schirmer 1 test results preoperatively and at 1, 3, and 6 months postoperatively are presented in [Table 2].
Table 1 Preoperative data

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Table 2 Preoperative and 1, 3, and 6 months postoperative tear breakup time and Schirmer 1 test

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Incidence of the dry eye

According to tear film breakup time results

TBUT values were normal in 33.7, 54.8, and 88.5% of eyes at 1, 3, and 6 months, respectively. A reduction in TBUT values was observed in 40.4, 26.9, and 6.7% of eyes at 1, 3, and 6 months, respectively. Severely reduced TBUT values were observed in 26, 18.3, and 4.8% of eyes at 1, 3, and 6 months, respectively.

According to Shirmer 1 test results

Schirmer 1 test scores were normal in 32.7, 54.8, and 87.5% of eyes at 1, 3, and 6 months, respectively. Mild dryness was observed in 26.9, 27.9, and 8.7% of eyes at 1, 3, and 6 months, respectively. Moderate dryness affected 35.6, 15.4, and 2.9% of eyes at 1, 3, and 6 months, respectively. Severe dryness was detected in 4.8, 1.9, and 1% of eyes at 1, 3, and 6 months, respectively.

Correlation between ablation depth and dryness

There was a strong negative correlation between ablation depth and TBUT at 1 and 3 months (r=−0.830 and −0.788, respectively). However, this correlation was only moderate at 6 months (r=−0.499; [Table 3] and [Table 4], [Figure 1]). Similarly, there was a strong negative correlation between ablation depth and Schirmer 1 test scores at 1 and 3 months (r=−0.809 and −0.766, respectively) that became moderate at 6 months (r=−0.457; [Table 3] and [Table 4] and [Figure 2]).
Table 3 Correlation between ablation depth and dryness by tear breakup time at 1, 3, and 6 months post laser-assisted in-situ keratomileusis

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Table 4 Correlation between ablation depth and dryness by Schirmer 1 test at 1, 3, and 6 months post laser-assisted in-situ keratomileusis

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Figure 1 Correlation between ablation depth and tear breakup time at 1, 3, and 6 months post laser-assisted in-situ keratomileusis. BUT, tear breakup time.

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Figure 2 Correlation between ablation depth and Schirmer 1 test at 1, 3, and 6 months post laser-assisted in-situ keratomileusis.

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Correlation between ablation depth and tear film breakup time results

At the last follow-up visit 6 months after LASIK, TBUT was severely reduced in five eyes, moderately reduced in seven eyes, and was normal in 92 eyes where mean ablation depth was 141.4±15, 142.14±.52, and 81.9±28.86 µm, respectively. There was a moderate negative correlation between TBUT values and ablation depth (r=−0.499 and P<0.001).

Correlation between ablation depth and Shirmer 1 test results

As regards the Schirmer 1 test, one eye had severe dryness, three eyes had moderate dryness, nine eyes had mild dryness, and 91 eyes were normal at 6 months postoperatively, where the mean ablation depth was 138, 142.3±2.89, 141.5±4.79, and 81.33±28 µm, respectively. There was a moderate negative correlation between the severity of dryness by Schirmer 1 test and ablation depth (r=−0.457; P<0.001).


  Discussion Top


The dry eye is one of the most common postoperative complications of LASIK [14]. Corneal innervation plays a key role in the lacrimal gland–ocular surface functional unit, which is responsible for coordinating basal and reflex tear secretion, blinking, and tear spreading and drainage. Furthermore, corneal nerves release neurotrophic factors that are essential for the corneal epithelial cells to function normally. The term LASIK-induced neuroepitheliopathy has been used to describe the neurotrophic aspect of post-LASIK dry eye that results from severing the nerve fibers during flap formation and stromal ablation [11],[12],[13]. The diminished corneal sensation within the flap area usually recovers gradually over 3–9 months postoperatively. Using confocal microscopy, axonal regeneration could be demonstrated and was found to correlate well with the improvement of the LASIK-induced dry eye [14].

Tuisku et al. [15] investigated the presence of dry eye symptoms and signs 2–5 years after LASIK treatment of high myopia in 20 eyes. They also used a noncontact corneal esthesiometer to assess corneal sensation. Most of their patients reported persistent dry eye symptoms, even in the absence of objective clinical signs of tear insufficiency or corneal hypoesthesia. They hypothesized that these symptoms represented a form of corneal neuropathy rather than a true dry eye disease. However, the small sample size warrants caution in interpreting their results [15].

In the current study, we used an automated microkeratome to create superiorly hinged flaps. A study comparing the use of a mechanical microkeratome to a femtosecond laser in flap creation found that the use of a femtosecond laser was associated with a lower incidence of post-LASIK dry eye and less need for artificial tears in the postoperative period. In the same study, no correlation was found between either flap thickness or the depth of stromal ablation and the incidence of the dry eye. This led to the suggestion that other factors might also be at play, in addition to the neurotrophic effects of corneal nerve damage [14].

We used both TBUT and Schirmer 1 test to quantify the degree of postoperative dry eye. We found a significant reduction in both TBUT values and Schirmer 1 test scores at 1, 3, and 6 months postoperatively compared with the preoperative levels (P<0.001). Persistent dry eye was detected in 12.5% of eyes using Schirmer 1 test and 11.5% of eyes using TBUT at 6 months postoperatively. There was a moderate negative correlation between both TBUT and Schirmer 1 test results and ablation depth at 6 months postoperatively (P=0.001; r=−0.499 and −0.457, respectively).

De Paiva et al. [16] studied the incidence and risk factors for developing the dry eye after myopic LASIK. They divided the study eyes into nasal and superior-hinge groups. The incidence of the dry eye in the nasal-hinge group was 38.9, 25, and 12.5% at 1, 3, and 6 months, respectively, compared with 41.2, 17.7, and 35.3% in the superior-hinge group. The risk for dry eye development was associated with the degree of preoperative myopia [relative risk (RR): 0.88/D; P=0.04], ablation depth (RR: 1.01/µm; P=0.01), and combined flap thickness and ablation depth (RR: 1.01/µm; P=0.01) [16].Using TBUT and Schirmer 1 test, Shoja and Besharati [17] found 20% of eyes to have persistent signs of dry eyes at 6 months after myopic LASIK correction in a series of 190 eyes. A depth of ablation, higher attempted refractive correction, and female sex were all significantly associated with the risk of developing postoperative chronic dryness [17].

In contrast, another study by Ambrósio et al. [9] did not find either flap thickness or ablation depth to be correlated with the incidence of post-LASIK dry eye. This might be explained by the fact that they relied solely on slit-lamp examination for evaluating the signs of the dry eye [14].

We evaluated tear film stability by means of TBUT and tear secretion using Schirmer 1 test. Both were affected by myopic ablation depth and the effect was related to the ablation depth and diminished over time. Most of the patients recovered to their preoperative values by 6 months of follow-up, and only 12% had persistently reduced values.

The limitations of this study included the relatively short follow-up period and the lack of quantitative assessment of corneal sensation. The study did not include a questionnaire or a symptom-based scoring system, as we tried to avoid the bias that could have originated from the presence of subjective symptoms in the absence of TBUT or Schirmer test abnormalities, especially in mild cases. The wide range of myopic error and the use of preoperative Pentacam screening are among the strengths of the study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Wilson SE. Laser in situ keratomileusis-induced (presumed) neurotrophicepitheliopathy. Ophthalmology 2001; 108:1082–1087.  Back to cited text no. 13
    
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Salomão MQ, Ambrósio R Jr, Wilson SE. Dryeye associated with laser in situ keratomileusis: mechanicalmicrokeratome versus femtosecond laser. J Cataract Refract Surg 2009; 35:1756–1760.  Back to cited text no. 14
    
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Tuisku IS, Lindbohm N, Wilson SE, Tervo TM. Dry eye and corneal sensitivity after high myopic LASIK. J Refract Surg 2007; 23:338–342.  Back to cited text no. 15
    
16.
De Paiva CS, Chen Z, Koch DD, Hamill MB, Manuel FK, Hassan SS et al. The incidence and risk factors for developing dry eye after myopic LASIK. Am J Ophthalmol 2006; 141:438–445.  Back to cited text no. 16
    
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    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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