|Year : 2019 | Volume
| Issue : 1 | Page : 375-379
Evaluation of femtosecond laser-assisted implantation of intracorneal ring segments in cases of keratoconus
Abd El-Rahman El-Sebaey, Farid M. W. Farid, Alia M Nagy
Department of Ophthalmology, Faculty of Medicine, Menoufia University, Shebin El-Kom, Egypt
|Date of Submission||31-Jan-2018|
|Date of Acceptance||06-Mar-2018|
|Date of Web Publication||17-Apr-2019|
Alia M Nagy
Alsheikh Zayed City, Giza Governorate
Source of Support: None, Conflict of Interest: None
To evaluate the clinical outcomes after implantation of the intracorneal ring segments (ICRSs) by means of femtosecond laser technology in eyes with keratoconus.
Corneal modeling by inserting intrastromal implants has been proposed and investigated as an alternative treatment option in corneal ectasia. Femtosecond laser technology allows the surgeon to program a corneal stromal dissection at a predetermined depth with an extremely high degree of accuracy, which avoids the potential inaccuracies of a mechanical dissection.
Patients and methods
A total of 35 eyes of 28 patients were included in the study. All cases presented with reduced best spectacle corrected visual acuity, contact lens intolerance, and pachy apex of more than 380 μm. ICRSs, selected according to special nomogram depending on spherical and cylindrical correction and site of cone, were implanted in all cases into an intrastromal corneal tunnel created by means of femtosecond technology. Visual, refractive, corneal topography, and pachymetric changes were evaluated during a 1-month follow-up.
Significant improvement in best-corrected visual acuity was observed after surgery (P = 0.0001), which was consistent with the significant reduction in sphere (P = 0.001) and cylinder (P = 0.001). Furthermore, a significant corneal flattening of a mean value of 2.68 D was found (P = 0.001). Corneal thickening was also observed postoperatively in the pachy apex, which was statistically significant (P = 0.001).
ICRSs implantation using femtosecond technology in keratoconus allows significant improvement in visual, refractive, and keratometric outcomes.
Keywords: corneal modeling, femtosecond laser, intracorneal ring segments, keratoconus, WaveLight FS200 Femtosecond Laser
|How to cite this article:|
El-Sebaey AE, Farid FM, Nagy AM. Evaluation of femtosecond laser-assisted implantation of intracorneal ring segments in cases of keratoconus. Menoufia Med J 2019;32:375-9
|How to cite this URL:|
El-Sebaey AE, Farid FM, Nagy AM. Evaluation of femtosecond laser-assisted implantation of intracorneal ring segments in cases of keratoconus. Menoufia Med J [serial online] 2019 [cited 2019 Jul 17];32:375-9. Available from: http://www.mmj.eg.net/text.asp?2019/32/1/375/256114
| Introduction|| |
Keratoconus is an asymmetric, bilateral, progressive, and noninflammatory ectasia due to gradual biomechanical instability of the cornea. Its reported frequency is approximately one in 2000 individuals in the general population. The condition usually begins at puberty and progresses in ∼20% of patients to such an extent that penetrating keratoplasty becomes necessary to preserve vision . Keratoconus management varies depending on the disease severity. Corneal modeling by inserting intrastromal implants has been proposed and investigated as an alternative treatment option in corneal ectasia . The use of these implants is aimed at minimizing the spherocylindrical error by modifying the central corneal curvature and inducing a reduction of corneal higher order aberrations by generating a regularization of the corneal surface . Ring segment is placed within the stroma through a small incision tunnel after creating an almost entirely closed intrastromal pocket. Corneal ring segment implantation using a mechanically guided procedure has been proven to be safe and effective in decreasing myopia, corneal steepness, and decentration of the corneal apex. However, it is well known that femtosecond laser technology allows the surgeon to program a corneal stromal dissection at a predetermined depth with an extremely high degree of accuracy, which avoids the potential inaccuracies of a mechanical dissection that is dependent on the surgeon's manual skills . The use of femtosecond laser for intracorneal ring segments (ICRSs) tunnel creation was widely accepted after FDA approval. Tunnels can be created at 70–80% of the corneal thickness within 15 s with less manipulation. The femtosecond laser acts by delivering laser pulses placed next to each other at a predetermined depth in the stroma. This creates an extending bubble of gas (CO2) and water (a micro-photodisruption), which dissects the tissue and makes a plane of separation and a tunnel for ICRS implantation.
Thus, the aim of this study is to evaluate the clinical outcomes after implantation of the ICRS by means of femtosecond laser technology in eyes of keratoconus regarding visual, refractive, pachymetric, and keratometric outcomes.
| Patients and Methods|| |
The study is a retrospective, nonrandomized, interventional clinical study, that includes a total of 35 eyes of 28 patients with keratoconus diagnosed according to the standard criteria, starting from period November 2015 till June 2016. Diagnosis was based on slit-lamp observation and corneal topography. The creation of the intrastromal tunnel for ICRSs implantation was performed by means of the 150-kHz femtosecond technology (WaveLight FS200 Femtosecond Laser; Alcon, USA; Alcon Laboratories Inc., Fort Worth, Texas, USA) in all cases.
A written informed consent was obtained from each patient after the nature and possible consequences of the study, the procedures involved, the expected duration, the potential risks, benefits involved and any discomfort may be caused were explained to them. Before initiating this study, all procedures were reviewed and approved by the Ethics Committee of the Menoufia University Hospital.
Each patient was informed that participation is voluntary, that is, he or she may withdraw from the study at any time and without giving reasons. The withdrawal did not affect the subsequent medical treatment or relationship with the treating surgeon.
Cases of keratoconus that do not improve with spectacle correction nor contact lenses and Kmax not less than 42 D and not more than 65 D were the inclusion criteria.
The exclusion criteria included the following: unrealistic expectation; corneal scar; pachymetry apex less than 380 μm; Kmax less than 42 D; Kmax more than 65 D; previous corneal surgeries; other ocular pathology such as glaucoma or iridocyclitis; intense atopy that should have been treated previously; patient with systemic diseases that would likely affect wound healing such as insulin-dependent diabetes mellitus; spherical equivalent of plano or hyperopic; patients with collagen vascular diseases, autoimmune, or immune deficiency diseases; pregnant and nursing women; ocular conditions such as corneal erosion syndrome or corneal dystrophies that may predispose the patient to future complications; patients taking medications such as isotretinoin, amiodarone, and sumatriptan.
Surgical procedures were performed by different surgeons. The creation of the intrastromal tunnel for ICRSs implantation was performed by means of the 150-kHz femtosecond technology (WaveLight FS200 Femtosecond Laser) in all cases. In the beginning of the tunnel-making procedure, after the surgeon applies anesthetic, the eye is fixated using a femtosecond LASER's patient interface kit. The WaveLight FS200 Femtosecond Laser's patient interface kit consists of an applanation cone, a suction ring, and vacuum tubing. Afterward an almost entirely closed intrastromal tunnel which has an inner diameter of 5.0 mm and outer diameter 6.1 mm, depth of the pocket differs according to corneal thickness and is usually formed at a depth of 80% of corneal thickness. A corneal incision is made according to the nomogram at the site of the steep meridian; two or one tunnel is created according to the nomogram and whether a single-ring segment or two-ring segments is needed. The tunnel is created, and the ICRS will be inserted into it through the site of incision. Postoperative visits were scheduled for the first postoperative day, the first week, and after first month from surgery. On the first postoperative day, visual acuity measurement and slit-lamp examination (intracorneal segment position and corneal integrity) were performed. First week after surgery, the treatment was adjusted. One month after the surgery, all cases underwent the same examinations as performed preoperatively. Main outcome measures assessed postoperatively were uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), manifest refraction, K readings, corneal thickness, and complications.
Data were stored in an Excel spreadsheet (Microsoft Excel Computer Software 2010; Microsoft Corp., Redmond, Washington, USA). The collected data were computerized and statistically analyzed using statistical package for the social sciences (SPSS) program (Released 2009, PASW Statistics for Windows, version 18.0; SPSS Inc., Chicago, Illinois, USA). Quantitative data were expressed as mean ± SD. Data were tested for normalization using SPSS program according to both mean and SD value. Independent t- test was used to calculate difference between quantitative variables in the two groups in normally distributed data. Paired sample t- test was used to calculate difference between quantitative variables in the same group at different times. Mann–Whitney U-test was used to calculate difference between quantitative variables in the two groups in non-normally distributed data. The significance level for all aforementioned statistical tests was done. The threshold of significance is fixed at 5% level (P value):
P value of less than 0.05 indicates significant results. P value of less than 0.01 indicates highly significant results.
| Results|| |
This retrospective study involved a total of 35 eyes of 28 patients, with a mean age of 20.29 years (SD of 5.83 years); 14 (40%) patients were male and 21 (60%) patients were female. The distribution of right and left eyes was as follows: 18 (51.4%) right eyes versus 17 (48.6%) left eyes.
[Table 1] shows the keratometric changes occurring after ICRS implantation in the sample of eyes analyzed. As shown, a significant central flattening was observed 1 month after surgery. Average K1 preoperatively was 48.96 D (with SD 3.78 D). Average K1 postoperatively was 47.04 D (with SD 3.85 D). Average K2 preoperatively was 54.15 D (with SD 4.70 D). Average K2 postoperatively was 50.45 D (with SD 3.83 D). Average Km preoperatively was 51.47 D (with SD 3.99 D). Average Km postoperatively was 48.77 D (with SD 3.7 D). As shown, a significant central flattening was observed, as there is decrease in K1, which was statistically significant (paired t-test P = 0.001). There is also decrease in K2 which is statistically significant (paired t-test P < 0.001). There is also decrease in Km, which is statistically significant (paired t-test P = 0.001).
[Table 2] shows the pachmymetric changes after ICRS implantation in the sample of eyes analyzed. Average pachy apex preoperatively was 436.14 μm (with SD 38.1 μm). Average pachy apex postoperatively was 449.17 μm (with SD 43.44 μm). Average thinnest location preoperatively was 423.54 μm (with SD 39.41 μm). Average thinnest location postoperatively was 433.69 μm (with SD 41.56 μm). There is a detectable increase in pachy apex, which is statistically significant (paired t-test P = 0.001). There is also increase in corneal thinnest location thickness, which is also statistically significant (paired t-test P = 0.001).
[Table 3] summarizes the visual and refractive outcomes after ICRS implantation. Average preoperative BCVA is 0.38 D (with SD 0.12 D). Average postoperative BCVA is 0.51 D (with SD 0.11 D). Mean sphere preoperatively is −4.00 D (with SD 3.00 D). Mean sphere postoperatively is −2.00 D (with SD 2.00 D). Mean cylinder preoperatively is −5.00 D (with SD 1.00 D). Mean cylinder postoperatively is −3.00 D (with SD 1 D). Mean spherical equivalent preoperatively is −5.65 D (with SD 3.41 D). Mean spherical equivalent postoperatively is −3.16 D (with SD 2.18 D).
There is improvement in BCVA, which is statistically significant (paired t-test P = 0.001). There is decrease in sphere after ICRS implantation, which is statistically significant (paired t-test P = 0.001). There is decrease in cylinder which is also statistically significant (paired t-test P = 0.001).
| Discussion|| |
The study was a retrospective, nonrandomized, interventional clinical study that included a total of 35 eyes of 28 patients with keratoconus diagnosed according to the standard criteria.
Diagnosis was based on slit-lamp observation and corneal topography. Keratoconus cases were classified according to the Amsler–Krumeich grading system. In general, ICRSs act by an arc-shortening effect, flatten the center of the cornea, and provide a biomechanical support for the thin ectatic cornea.
At 1 month after surgery, a statistically significant reduction in myopia and cylinder was observed. These changes were of large magnitude. The mean change in sphere was −2.00 D, and the mean change in refractive cylinder was 2.00 D. These levels of refractive change were consistent with those previously reported after ring segment implantation with mechanical dissection ,. Moreover, it is consistent with those reported by Shetty et al.  who conducted a study on 12 eyes with implantation of ring segments using femtosecond laser, and the mean change in sphere in this study was 4.06 D, and the mean change in cylinder was 4.47 D. It should be considered that ring segment thicknesses implanted in eyes in previous studies on ICRS were even larger than those used in the current study.
As expected, the significant level of refractive correction achieved with ring segments implants in our study was in concordance with a significant improvement in UCVA. As shown in the previous works of Mahmood et al. , the improvement in UCVA was seven lines, and in Daxer et al. , there was an improvement in UCVA by 10 lines. In these two previous studies, ring segment implants were also used for keratoconus management, but mainly in grade II and III cases. However, in our sample, a significant number of keratoconus grade IV cases were included. In the study conducted by Shetty et al. , the mean change in UCVA was by seven lines. Regarding BCVA, there is improvement by two lines of logarithm of the minimum angle of resolution (logMAR), which is in concordance with previous studies.
Regarding corneal topography, a significant central flattening was observed after surgery, which was consistent with the refractive change induced. The mean change in Km was 2.7 D (with SD 3.7 D). This flattening effect is only comparable to that reported by Miranda et al.  (mean change in maximum keratometry of 9.60 D) after Ferrara ring segment implantation in severe keratoconus and to that reported by Mahmood et al. , Daxer et al. , and Shetty et al. , who also used the ring segments in keratoconus. The large flattening effect achieved by Miranda et al.  with Ferrara ring segments was probably owing to the use of thicker implants and reduced diameters, which are factors proven to be related to a potentially more significant flattening.
The analysis of corneal pachymetric changes revealed changes after ring segments implantation which was statistically significant. There was observed thickening of the central cornea as there was increase in the corneal pachy apex, suggesting that corneal tissue redistribution occurs after the implantation of ring segments.
In a study using very high-frequency ultrasound technology, Reinstein et al.  observed a stromal thickening after ring segment implantation, accounting for astigmatic changes ascribable to orthogonal asymmetry. There was an observed increase in thickness in corneal thinnest location, and it was statistically significant (P = 0.001), with mean improvement of 10.16 μm. In the literature, the study by Shetty et al.  detected an increase in corneal thickness after femtosecond laser-assisted ring segment implantation at central, nasal, and temporal parts.
The limitation of our study is the small number of cases. However, improvements were statistically significant in all statistical tests despite this limitation. Although the small study sample did not affect the significance of the refractive and visual results, this limiting factor may prove of relevance with respect to the probable occurrence of complications. Another limiting factor seems to be the 'mixture' of eyes that did and did not undergo corneal cross-linking (CXL). The use of both eyes of some patients in the analysis is another limiting factor. The t-test treats each sample, in this case the eye, as independent, which can falsely inflate the statistical power of the hypothesis test.
| Conclusion|| |
ICRS implantation in keratoconus by means of femtosecond technology allows a significant reduction of myopic spherical error because of the central corneal flattening. The corneal intrastromal implantation system provides a new option for keratoconus management. The technique appears to be safe and effective in decreasing myopia, corneal steepness, and decentration of the corneal apex, and is also potentially reversible.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3]