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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 110  |  Issue : 2  |  Page : 59-64

Retreatment of residual error after femtosecond laser-assisted in-situ keratomileusis in correcting high hyperopia


Department of Ophthalmology, Faculty of Medicine, Suez Canal University, Ismailia, Egypt

Date of Submission20-Nov-2016
Date of Acceptance30-Mar-2017
Date of Web Publication20-Jul-2017

Correspondence Address:
Amr A Gab-Alla
Lecturer of Ophthalmology, Faculty of Medicine, Suez Canal University, Ring Road, Ismailia, 41522
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ejos.ejos_17_17

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  Abstract 

Purpose
The aim of the present study was to evaluate the results of femtosecond laser-assisted in-situ keratomileusis (LASIK) in correcting high hyperopia.
Patients and methods
The study was carried out at El-Gowhara Eye Center, Ismailia, Egypt. A prospective case series study was carried out. Hyperopic eyes with a spherical equivalent (SE) greater than or equal to +3.00 D were corrected by LASIK. The flaps were created with the VisuMax femtosecond laser. The refractive ablations were performed with the 500-kHz Amaris excimer laser. Full cycloplegic refraction was the target refraction. Patients were divided into two groups. Group A included patients with residual refractive errors less than or equal to +0.50 D of the target refractions and had no further LASIK retreatment, and group B included patients with residual refractive errors greater than +0.50 D of the target refractions along with retreatment 1 month after the primary LASIK. The refractive predictability and stability of the treated and retreated eyes were followed-up for 6 months after LASIK.
Results
Sixty-four patients (115 eyes) received primary hyperopic femtosecond LASIK. The mean±SD age of all patients was 40.30±13.4 years with a range of 21–64 years. The preoperative mean±SD cycloplegic SE refraction was +4.29±1.5 D with a range from +3.00 to +9.00 D. One month after the primary LASIK treatment, 79.1% (91 eyes) of the treated patients had a mean cycloplegic SE refraction of +0.36±0.13 D (group A). After 6 months of follow-up, 62.6% of eyes (n=72) had an uncorrected distance visual acuity of 0.3±0.21 log MAR. Four (3.5%) eyes lost one line of corrected distance visual acuity (CDVA) (Snellen). Five (4.3%) eyes lost two lines of CDVA (Snellen). Seven (6.1%) eyes gained one line of CDVA (Snellen). Twenty-one (18.3%) eyes gained two lines of CDVA (Snellen). The mean±SD cycloplegic SE refraction was +0.41±0.32 D. In group B (20.9%) (24 eyes), patients had a mean±SD cycloplegic SE refraction of +2.41±0.96 D at the first month after primary LASIK. These patients required a second-stage LASIK retreatment by lifting the original flap. After 6 months of follow-up, 83.3% of eyes (n=20) had an uncorrected distance visual acuity of 0.6±0.13 log MAR. Seven (29.2%) eyes gained one line of CDVA (Snellen). Two (8.3%) eyes lost one line of CDVA, and two (8.3%) eyes lost two lines of CDVA (Snellen). The mean±SD cycloplegic SE refraction was +0.25±0.21 D. No epithelial ingrowth was recorded in both groups.
Conclusion
Femtosecond LASIK for the correction of high hyperopia is predictable and safe; 79.1% of the patients underwent correction during the primary treatments, and 20.9% were totally corrected after retreatments. No cases of epithelial ingrowth were recorded over the 6-month follow-up period.

Keywords: femtosecond, hyperopia, laser-assisted in-situ keratomileusis


How to cite this article:
Gab-Alla AA. Retreatment of residual error after femtosecond laser-assisted in-situ keratomileusis in correcting high hyperopia. J Egypt Ophthalmol Soc 2017;110:59-64

How to cite this URL:
Gab-Alla AA. Retreatment of residual error after femtosecond laser-assisted in-situ keratomileusis in correcting high hyperopia. J Egypt Ophthalmol Soc [serial online] 2017 [cited 2017 Oct 23];110:59-64. Available from: http://www.jeos.eg.net/text.asp?2017/110/2/59/211141


  Introduction Top


Correction of high hyperopia by the excimer laser is a challenge [1]. This challenge includes the need to steepen the cornea significantly, which causes increased sensitivity to minor decentration, greater dryness, and high risk of residual refractive errors up to 29% that require retreatment between the third and the sixth month postoperatively [1]. Furthermore, surface smoothing due to wound healing, epithelial remodulation, and biomechanical changes can cause less accurate refractive predictability and unwanted regression [2],[3].

Refractive stability after laser-assisted in-situ keratomileusis (LASIK) for hyperopia is still controversial. It has been followed-up for 1 [4], 3 [5], and 6 months after LASIK [6]. Regression represents a substantial clinical problem, needing retreatment in a significant percentage of cases [7].

Several techniques have been investigated to improve the results of hyperopic LASIK treatments, including nomogram refinement and increasing the size of the optical zone and the size of the corneal flap [8].

Femtosecond laser technology has some advantages compared with mechanical microkeratomes such as higher predictable flap thickness, more uniformity throughout the whole flap, regularity, and accuracy [9],[10],[11],[12],[13]. Published studies on lifting femtosecond laser-created corneal flaps and retreatment of hyperopic residual refractive errors after previous LASIK treatment are still limited. In the present study, we evaluated the refractive predictability and stability results of two stages of femtosecond laser-assisted hyperopic laser in-situ keratomileusis to treat high hyperopia.


  Patients and methods Top


This prospective case series study included patients undergoing femtosecond LASIK for correcting hyperopia greater than or equal to +3.00 D. Patients were followed-up for 6 months postoperatively.

Inclusion criteria were age more than 21 years, cycloplegic spherical equivalent (SE) greater than or equal to +3.00, central corneal thickness more than 500 μm, regular corneal topography (Sirius; CSO, Scandicci, Italy), no previous refractive or lens surgery, and absence of connective tissue diseases and diabetes. Keratoconus and keratoconus suspect were ruled out by corneal topography. Preoperative corrected distance visual acuity (CDVA) was recorded. Patients were divided into two groups. Group A patients with residual refractive errors less than or equal to +0.50 D of the target refractions had no further LASIK retreatment. Group B patients with residual refractive errors greater than +0.50 D of the target refractions were retreated after the first month following primary LASIK.

Surgical technique

The corneal flap was created with a Visumax femtosecond laser (Carl Zeiss Meditec, Jena, Germany). Flaps thicknesses were of 120 μm, with a superior hinge, and a 90° side-cut angle. The flap diameter (determined by the diameter of the applanation glass) was 9.5 mm in eyes with a white-to-white diameter greater than 12.0 mm (measured by topography) and 9.0 mm in eyes with a white-to-white diameter of 12.0 mm or less.

After completion of the femtosecond treatment, the flap was lifted superiorly, and the stromal bed was dried with a microsponge. The refractive ablation treatment was performed using 500-kHz Amaris excimer laser (Schwind Eye-tech Solutions, Kleinostheim, Germany). Eye tracking and a 6-mm optical zone were used. Full cycloplegic refraction was the target refraction. Next, the flap was repositioned, and the interface was irrigated with a balanced salt solution.

The postoperative follow-up visits were on the first day, first week, the first, the third, and the sixth month postoperatively. All visits included slit-lamp examination, uncorrected distance visual acuity (UDVA), and manifest and cycloplegic refractions. Visual acuity was measured and averaged in log MAR units. Patients with residual refractive errors more than +0.50 D of the target refractions were revaluated using the Sirius corneal topography (CSO) and retreated at the first month after primary LASIK.

All retreatments were performed by lifting the original flap. First, the flap edge was identified using a slit lamp and then marked with a pen marker after the eye was anesthetized using two drops of 0.4% benoxinate hydrochloride at 5-min intervals. The patient was then moved to the laser room. The flap edge was separated from the bed in its entirety using a flat spatula. The flap was then separated from the bed by a sweep movement from the flap pedicle to the periphery. The excimer laser treatment was applied and then the flap was replaced. The patients were re-evaluated for refractive errors again and followed-up for 6 months after retreatments. LASIK retreatments were performed only when the estimated residual stromal thickness was greater than 300 μm. All treatments were performed by the same surgeon (A.A.G.-A.).

Postoperative predictability was assessed by the percentage of eyes within +0.5 D of the target correction using the mean cycloplegic SE. Stability was assessed by comparing postoperative cycloplegic SE refractions at follow-up times. Efficacy was assessed by the percentage of postoperative UCVA to the preoperative CDVA. Postoperative safety was assessed by the percentage of the eyes that gained/lost lines compared with preoperative CDVA.

The study was reviewed and approved by the institutional review board of Suez Canal University in agreement with the Declaration of Helsinki. Written informed consent was obtained from all patients after explaining the procedures and the surgical techniques used.

Statistical analysis

Collected data were coded, entered, and analyzed using Microsoft Excel software. Data were then imported into statistical package for the social sciences (SPSS, version 20; IBM, Armonk, NY, USA) software for analysis. Baseline characteristics of the study population are presented as frequencies and percentages for categorical (qualitative) data or as mean values and SD (normal data) for continuous (quantitative) data. Differences between means were compared by the t-test. Statistical significance tests were used; a P value of less than or equal to 0.05 was considered statistically significant at the 95% level of confidence, and a P value of less than or equal 0.01 was considered statistically highly significant at the 99% level of confidence.


  Results Top


In this study, 64 patients (115 eyes) received primary hyperopic femtosecond LASIK. The mean±SD age of all the patients was 40.30±13.4 years with a range of 21–64 years. The preoperative mean±SD cycloplegic SE refraction was +4.29±1.5 D, with a range from +3.00 to +9.00 D. This study included 44 (68.7%) females and 20 (31.3%) males. LASIK treatment was bilateral in 51 (79.7%) patients and unilateral in 13 (20.3%) patients ([Table 1]).
Table 1 Baseline characteristics of all patients

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At the first month after primary LASIK treatment, 79.1% (91 eyes) of the treated patients had a mean±SD cycloplegic SE refraction of +0.36±0.13 D of the target postoperative refractions (group A) ([Figure 1]). These patients did not require further LASIK retreatment. Their mean±SD age was 42.36±13.21 years with a range of 21–63 years. Their preoperative mean±SD cycloplegic SE refraction was +4.19±1.41 D, with a range of +3.00 to +6.50 D. These patients included 36 (70.59%) females and 15 (29.41%) males. LASIK treatment was bilateral in 40 (78.4%) patients and unilateral in 11 (21.6%) patients ([Table 2]). After the 6-month follow-up period, 62.6% of eyes (n=72) had an UDVA of 0.3+0.21 log MAR. Four (3.5%) eyes lost one line of CDVA (Snellen). Five (4.3%) eyes lost two lines of CDVA (Snellen). Seven (6.1%) eyes gained one line of CDVA (Snellen). Twenty-one (18.3%) eyes gained two lines of CDVA (Snellen) ([Figure 2]). The mean±SD cycloplegic SE refraction was +0.41+0.32 ([Table 3] and [Figure 3]).
Figure 1 Scattergram of attempted versus achieved spherical equivalent correction one month post-primary LASIK in group A

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Table 2 Preoperative characteristics of both groups

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Figure 2 Percentage of group A gained and lost log MAR lines of CDVA at the 6th month post-primary LASIK (CDVA: corrected distance visual acuity)

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Table 3 Follow-up of the cycloplegic refraction spherical equivalent before and after primary laser-assisted in-situ keratomileusis in group A

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Figure 3 Follow-up of cycloplegic refraction SE before and after primary LASIK in group A

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At the first month after primary LASIK, 13 (20.9%) patients (24 eyes) had a mean±SD cycloplegic SE refraction of +2.41±0.96 D (range: +1.00 to +4.75 D). Although the changes were statistically significant (P<0.0001) compared with their preoperative values, these patients needed LASIK retreatments by lifting the original flap (group B). Their mean±SD age was 32.58±11.14 years with a range of 21–53 years. Their preoperative mean±SD cycloplegic SE refraction was +5.30±1.82 D, with a range of +5.50 to +9.00 D. These patients included eight (61.5%) females and five (38.5%) males. LASIK retreatment was bilateral in 11 (84.6%) patients and unilateral in two (15.4%) patients ([Table 2]). After 6 months of follow up, 83.3% of eyes (n=20) had an UDVA of 0.6±0.13 log MAR. Seven (29.2%) eyes gained one line of CDVA (Snellen). Two (8.3%) eyes lost one line, and two (8.3%) eyes lost two lines of CDVA (Snellen) ([Figure 4]). The cycloplegic SE refractions of all patients were within +0.5 D of the target postoperative refractions ([Figure 5]) with a mean±SD of +0.25±0.21 ([Table 4] and [Figure 6]). Group B patients were younger in age (P=0.017) and had higher hyperopia (P=0.002) compared with group A ([Table 2]). No cases of epithelial ingrowth were recorded in both groups.
Figure 4 Percentage of group B gained and lost log MAR lines of CDVA at the 6th month post-LASIK retreatment (CDVA: corrected distance visual acuity)

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Figure 5 Scattergram of attempted versus achieved spherical equivalent correction 6-month post-LASIK retreatment in group B

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Table 4 Follow-up of cycloplegic refraction spherical equivalent after primary laser-assisted in-situ keratomileusis and 6 months after retreatment in group B

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Figure 6 Follow-up of cycloplegic refraction SE post-primary LASIK and 6-months after retreatment in group B

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  Discussion Top


Femtosecond laser-created corneal flaps have several advantages that can affect the results of laser ablation and postoperative refractive stability. It is planar, predictable in the intended flap thickness, has uniform thickness [14],[15], and its size is precisely created independently of the corneal anatomy [16]. On the other hand, flaps created by the microkeratome are less predictable [14],[15], thicker in the periphery and thinner in the center (meniscus in shape) [14], and have more variable diameters because of the dependence on corneal diameter and keratometry [16].

In hyperopia treatments, a uniform, large, and predicted corneal flap created by femtosecond laser allows adequate peripheral laser ablation, leading to a more accurate and potentially more stable ablation. According to the model created by Dupps and Roberts [17], the nonuniform cutting (meniscal flap) of the microkeratome during the flap creation produce a deeper peripheral disruption of collagen fibers attached to the sclera. This could result in more lamellar retraction and central flattening and result in a hyperopic undercorrection. In addition, the stroma is less hydrated after femtosecond laser flap creation than after microkeratome flap creation, which limits the effectiveness of laser ablation and causes undercorrection [18].

Evaluating refractive outcomes in hyperopic LASIK is a challenge. This is because postoperative recording results as a percentage of eyes within ±0.50 D of the manifest refraction can be misleading [19]; many hyperopic eyes undergo some intended overcorrection in anticipation of regression. Therefore, postoperative SE deviation from the target refraction is better than the simple postoperative manifest refraction SE [8].

In the present study, corneal flaps were created by Visumax femtosecond laser with 90° side-cut angle to permit adequate peripheral laser ablation with predicted corneal flaps and to decrease the possibilities of epithelial ingrowth in the retreated patients by lifting the corneal flaps. Cycloplegic refraction was the target refraction for the included patients. This is because, with age, manifest refraction can be increased because of the reduced accommodation for latent hyperopia, and falsely can be interpreted as a regression. LASIK retreatment was performed in a month after the primary LASIK treatment to have stable refractions. However, Durrie and Aziz [20] recommended that retreatment can be done shortly after the primary LASIK in patients with residual refractive error and decreased visual acuity on the first day and the first week postoperatively. In the present study, patients who required LASIK retreatments were younger and had higher hyperopia compared with other patients who underwent total correction in the primary treatments.

By assessing the morphology of LASIK flaps, created by a 60 kHz femtosecond laser and a mechanical microkeratome by the anterior segment optical coherence tomography (OCT), Von Jagow and Kohnen [21] reported that the general morphology and regularity of femtosecond laser flaps were planar and symmetrical in all cases. They also concluded that the junction of the side cuts and the lamellar cut was well discernible and angled. Moreover, the femtosecond laser flaps had a relatively constant peripheral thickness compared with the periphery of the microkeratome flaps, which showed higher variations in thickness and a deviation from the intended flap thickness. Von Jagow and Kohnen [21] also concluded that hyperopic ablation profiles have major functional areas in the periphery of the optical zone, and hence the importance of the corneal flaps.

Caster et al. [22] analyzed the risk for epithelial ingrowth after primary LASIK retreatment. All retreatments were performed by lifting the original flap. They reported that, when the flap lift retreatment was performed before three years after primary LASIK, the risk for clinically significant epithelial ingrowth was much lower than 1%. The present study found no case of epithelial ingrowth after LASIK retreatment when the original flaps were created by femtosecond laser with 90° side-cut angle. Wilson and Santhiago [23] did not report any epithelial ingrowth after LASIK retreatment (160 eyes with a femtosecond laser) with at least 1-year follow-up. In addition, this study showed that there was no any case of epithelial ingrowth after LASIK retreatment when the original flap was created with a femtosecond laser.

On the other hand, Kamburoglu and Ertan [24] in their study to evaluate the incidence of epithelial ingrowth after femtosecond LASIK reported that two eyes of the 108 eyes after enhancement procedure developed clinically significant epithelial ingrowth. They also concluded that the lower incidence of epithelial ingrowth after femtosecond LASIK might be due to the side-cut created by the femtosecond laser and the less peripheral trauma at the time of flap creation. Moreover, Letko et al. [25] reported that in 140 retreatments of femtosecond-created corneal flaps, only one patient (both eyes) with epithelial ingrowth was identified. They also concluded that the femtosecond laser-created flap edge is nearly vertical, which makes a more effective barrier for the epithelium. In addition, mechanical microkeratomes cut the flap by sliding the blade on the stromal interface, which increases the risk of inoculating the epithelium; however, the femtosecond laser creates the flap by cavitation bubbles that coalesce to create a resection plane.

Finally, in conclusion, femtosecond LASIK for the correction of high hyperopia is predictable and safe. Of the patients, 79.1% were corrected within 0.5 D of the target postoperative refraction in the primary treatments, and 20.9% were totally corrected in the retreatments without any cases of epithelial ingrowth recorded over the 6 months of follow-up.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
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21.
Von Jagow B, Kohnen T. Corneal architecture of femtosecond laser and microkeratome flaps imaged by anterior segment optical coherence tomography. J Cataract Refract Surg 2009; 35:35–41.  Back to cited text no. 21
    
22.
Caster AI, Friess DW, Schwendeman FJ. Incidence of epithelial ingrowth in primary and retreatment laser in situ keratomileusis. J Cataract Refract Surg 2010; 36:97–101.  Back to cited text no. 22
    
23.
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24.
Kamburoglu G, Ertan A. Epithelial ingrowth after femtosecond laser assisted in situ keratomileusis. Cornea, 2008; 27:1122–1125.  Back to cited text no. 24
    
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    Figures

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

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



 

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