Undersurface ablation of the flap for laser in situ keratomileusis retreatment

Comparison of 5468 retreatments after laser in situ keratomileusis by lifting the flap or performing photorefractive keratectomy on the flap

PURPOSE

To assess visual outcomes of retreatment after laser in situ keratomileusis (LASIK) by lifting the flap or performing photorefractive keratectomy (PRK) on the flap, as well as to establish whether there was an increased risk of epithelial ingrowth (EIG) when LASIK and lifting of the flap are separated by a long time interval and to determine the incidence of corneal haze after PRK.

METHODS

Retrospective study of 4077 patients (5468 eyes) who underwent LASIK and subsequent retreatment were reviewed in order to study their visual results and identify cases of EIG and corneal haze.

RESULTS

Enhancements included 5196 eyes from 3876 patients that were retreated by lifting the flap, and 272 eyes from 201 patients that were retreated by PRK on the flap. No statistically significant differences were found between the retreatments in terms of predictability, efficacy, and safety. A total of 704 cases of EIG were found after lifting the flap, for which surgical cleansing was necessary in 70. Surgical cleansing decreased the efficacy index when compared with patients with EIG who did not need cleansing (P=.01). Differences in terms of safety and predictability were not statistically significant. The incidence of corneal haze after ablation of the surface of the previous flap was 14.34%, although none of these cases were clinically relevant.

CONCLUSIONS

Visual outcomes were similar between patients who were retreated by lifting the flap and those who underwent PRK. The incidence of EIG when the flap was lifted was 13.55%. The incidence of EIG increases with the time elapsed between the primary procedure and retreatment.

Flap lift and photorefractive keratectomy enhancements after primary laser in situ keratomileusis using a wavefront-guided ablation profile: Refractive and visual outcomes

PURPOSE

To analyze results of wavefront-guided laser vision correction retreatments performed either by lifting the original flap or by surface ablation over the flap.

SETTING

Optical Express, Glasgow, United Kingdom.

DESIGN

Retrospective case series.

METHODS

This retrospective study included patients grouped according to whether they had flap lift enhancement or photorefractive keratectomy (PRK) performed over the LASIK flap. All retreatment procedures were performed with the Visx Star S4 IR excimer laser with wavefront-guided ablation profile derived from the iDesign aberrometer. Visual acuities, refractive outcomes, vector analysis of refractive cylinder and complications were analyzed in this study. The results of the last available clinical visit are presented.

RESULTS

This retrospective study included 290 eyes of 202 patients divided into 2 groups: 119 eyes that had flap lift enhancement (Group A), and 171 eyes in which photorefractive keratectomy (PRK) was performed over the LASIK flap (Group B). The mean follow-up was 4.0 ± 1.9 months in Group A and 4.2 ± 1.6 in Group B. The mean postoperative manifest spherical equivalent was -0.01 ± 0.35 D and +0.06 ± 0.39 D in Groups A and B, respectively. The percentage of eyes with postenhancement UDVA 20/20 or better was 87.4% in Group A and 79.5 % in Group B (P = .09). In Group A, 22 eyes (18.5%) developed epithelial ingrowth, of which surgical intervention was required in 2 eyes (1.7%). Grade 1 or less haze was noted in 9 (5.3%) eyes in Group B, and resolved in all cases within the first 6 postoperative months.

CONCLUSION

Both retreatment techniques were considered to be effective, predictable, and safe.

FINANCIAL DISCLOSURE

Steven C Schallhorn MD is a consultant to Abbott Medical Optics and Zeiss, and Global Medical Director for Optical Express. None of the other authors have a financial or proprietary interest in the products and materials presented in this paper.

Aspheric Ablation Depth as the Target Depth for Enhanced Wavefront-Guided Myopic Retreatments After Laser-Assisted In Situ Keratomileusis

PURPOSE

To propose a new adjustment method and present the clinical result of wavefront-guided myopic laser-assisted in situ keratomileusis (LASIK) retreatment with an aspheric program-targeted central ablation depth to avoid refractive overcorrection.

METHODS

Thirty-two eyes (of 20 consecutive patients) that underwent wavefront-guided LASIK myopic retreatment between January 2009 and February 2012 after primary wavefront-guided LASIK for myopia were included. Wavefront-guided retreatments were performed using the Bausch and Lomb Technolas 217z100 excimer laser system. Wavefront-guided retreatments were adjusted by setting the ablation depth corresponding to the ablation depth determined by the aspheric program. The refractive outcome, visual outcome, and outcome of high-order aberrations (HOAs) were analyzed. Linear mixed models were also used to evaluate the predicting factors for retreatment offset.

RESULTS

Mean age was 29.5 ± 3.1 years. Spherical equivalent (SE) before retreatment was -1.0 ± 0.44 diopters (D) (range, -2.25 to -0.5). Twelve months postoperatively, SE was -0.03 ± 0.12 D, and 31 of 32 eyes had an uncorrected visual acuity 20/20 or better. All eyes were within ±0.5 D. None of the eyes had lost >2 lines of Snellen visual acuity. Safety and efficacy indices were 1.03 and 1.00, respectively. Total HOA, coma, and trefoil were reduced significantly (P = 0.028, P = 0.036, P = 0.034, respectively). Predictive factors for the amount of offset required are significantly related to preoperative SE (P = 0.006) and spherical aberration (P = 0.03, adjusted by SE).

CONCLUSIONS

Setting the target ablation depth using the aspheric program provided high refractive predictability with a satisfactory visual outcome, significant reduction of HOAs, and no overcorrections.

Management of residual refractive error after laser in situ keratomileusis and photorefractive keratectomy

PURPOSE OF REVIEW

To review the various steps and methods in managing residual refractive error after laser in situ keratomileusis and photorefractive keratectomy (PRK).

RECENT FINDINGS

Past studies have shown the efficacy and safety of flap relifts over recuts and for surface ablation over the flap. Other previous and also more recent studies show the use of a femtosecond laser for side cuts only. Recently, the creation of a femtosecond mini flap has been described. New studies also demonstrate the use of collagen cross-linking in postrefractive surgery ectasia.

SUMMARY

Residual refractive error is a known complication after both laser in situ keratomileusis and PRK. A systematic approach should be taken to manage this complication starting with a thorough evaluation to determine if an enhancement is indicated and if so, which method will be the safest and most efficacious for the patient.

Femtosecond laser-assisted enhancements after laser in situ keratomileusis

We describe a technique of femtosecond laser-assisted enhancement after primary LASIK with a mechanical microkeratome-created flap. The vertical side-cut incision by the femtosecond laser creates a wound configuration that decreases mechanical trauma to the epithelium and prevents epithelial cell migration. These factors may decrease the risk for post-LASIK enhancement epithelial ingrowth.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned. Additional disclosures are found in the footnotes.

Agreement of non-contact pachymetry after LASIK: comparison of combined scanning-slit/Placido disc topography and specular microscopy

PURPOSE

To assess the interchangeability of central corneal thickness (CCT) measurements between combined scanning-slit/Placido disc topography (Orbscan-II) and specular microscopy (Topcon SP-2000P) in patients who underwent laser in situ keratomileusis (LASIK) for myopia.

PATIENTS AND METHODS

We recruited 118 consecutive patients who underwent LASIK for myopia. The CCT was measured using Orbscan-II and Topcon SP-2000P randomly. Orbscan-II and Topcon SP-2000P CCT data were analysed using the paired-sample t-test and the limits of agreement (LoA) were calculated with the method described by Bland-Altman.

RESULTS

The average CCT measurements by Orbscan-II and Topcon SP-2000P were 447.55+/-49.78 microm and 461.38+/-35.35 microm, respectively (P<0.0001; mean difference, 13.83+/-22.31 microm; 95% confidence interval, 9.77-17.09 microm). The Bland-Altman plot showed an inverse association between the average and the difference between the devices: Topcon-Orbscan-II=174.23 -0.353xAverage (P<0.01). The widths of the crude and regression-based 95% limits of agreement were 87.45 and 63.72 microm, respectively.

CONCLUSIONS

Orbscan-II measurements of CCT after myopic LASIK were significantly lower than those obtained using Topcon SP-2000P. The limits of agreement between the two devices were too broad and, therefore, both pachymetric values cannot be used interchangeably. Further, the tendency towards comparably Orbscan-II readings in thinner corneas precludes that one technique can directly replace the other. This is important for the adequate medium- and long-term follow-up of the growing LASIK patient population.

Advances in technologies for laser-assisted in situ keratomileusis (LASIK) surgery

Laser-assisted in situ keratomileusis (LASIK) has become the most widely used form of refractive surgery today. The objective of this surgical technique is to modify the anterior corneal shape by ablating tissue from the stroma by means of the excimer laser after creating a hinged corneal flap. This way, we are able to change the refractive status of the patient, providing better unaided vision. Continuous improvements in the original technique have made the surgical procedure safer, more accurate and repeatable. These progressions are due to the development of novel technologies that are the responsible for new surgical instrumentation, which makes the surgical procedure easier for the surgeon, and better excimer laser ablation algorithms, which increase the optical quality of the ablation and thus the safety of the vision correction procedure. This article aims to describe the more relevant advances in LASIK that have played an important role in the spread and popularity of this technique.

Ablation auf der Unterseite eines LASIK-Flaps

BACKGROUND

The risk of iatrogenic keratectasia after laser in situ keratomileusis (LASIK) increases with thinner posterior stromal beds. Ablations on the undersurface of a LASIK flap could only be performed without the guidance of an eye tracker, which may lead to decentration. A new method for laser ablation with flying spot lasers on the undersurface of a LASIK flap was developed that enables the use of an active eye tracker by utilizing a novel instrument. The first clinical results are reported.

PATIENTS AND METHODS

Patients wishing an enhancement procedure were eligible for a modified repeat LASIK procedure if the flaps cut in the initial procedure were thick enough to perform the intended additional ablation on the undersurface leaving at least 90 microm of flap thickness behind. (1) The horizontal axis and the center of the entrance pupil were marked on the epithelial side of the flap using gentian violet dye. (2) The flap was reflected on a newly designed flap holder which had a donut-shaped black marking. (3) The eye tracker was centered on the mark visible in transparency on the flap. (4) Ablation with a flying spot Bausch & Lomb Technolas 217z laser was performed on the undersurface of the flap with a superior hinge taking into account that in astigmatic ablations the cylinder axis had to be mirrored according to the formula: axis on the undersurface=180 degrees -axis on the stromal bed. (5) The flap was repositioned.

RESULTS

Detection of the marking on the modified flap holder and continuous tracking instead of the real pupil was possible in all of the 12 eyes treated with this technique. It may be necessary to cover the real pupil during ablation in order not to confuse the eye tracker. Ablation could be performed without decentration or loss of best spectacle-corrected visual acuity. Refractive results in minor corrections were good without nomogram adjustment.

CONCLUSIONS

Using this novel flap holder with a marking that is tracked instead of the real pupil, centered ablations with a flying spot laser on the undersurface of a LASIK flap are feasible. Thus, the additional risk of iatrogenic keratectasia associated with stromal enhancement ablations is avoided.

Repeatability and Reproducibility of Posterior Corneal Curvature Measurements by Combined Scanning-Slit and Placido-Disc Topography after LASIK

OBJECTIVE

To assess the repeatability and reproducibility of posterior corneal curvature (PCC) measurements made by combined scanning-slit/Placido-disc topography (Orbscan II) after LASIK.

DESIGN

Experimental instrument validation study.

PARTICIPANTS

We recruited 22 consecutive postmyopic LASIK patients for the repeatability study and another 50 consecutive postmyopic LASIK patients for the reproducibility study.

METHODS

To analyze intrasession repeatability, 1 examiner measured 22 postmyopic LASIK eyes 10 times successively in the shortest time possible. To study intersession reproducibility, the same operator obtained measurements from another 50 eyes with stable refraction in 2 consecutive visits at the same time of the day between 6 and 9 months after myopic LASIK. We explored any association between residual stromal bed thickness and measurement variability.

MAIN OUTCOME MEASURES

Orbscan II scanning-slit PCC data, precision, within-subject coefficient of variation (CV(w)), limits of agreement (LoA), and intraclass correlation coefficient (ICC).

RESULTS

For intrasession repeatability, precision was 0.067 mm (best-fit sphere [BFS]), 0.110 diopters (D; power within 5 mm), 0.158 D (power within 3 mm), and 0.46 (eccentricity). Repeatability was high for PCC BFS and power measurements within 3-mm and 5-mm zones (CV(w) ranged from 0.5%-1.2%) but poor for eccentricity data (CV(w), 31.6%). Correspondingly, ICCs ranged from 0.89 to 0.98 for PCC BFS and power, and the ICC was 0.20 for PCC eccentricity values. For intersession reproducibility, on average, no difference in PCC measurements could be found, indicating that when there is variability, it is due to random factors. The width of the 95% LoA between sessions was clinically acceptable for BFS (0.25 mm) and power (0.4 D [within 5 mm] and 0.6 D [within 3 mm]). Similarly, ICCs indicated good intersession reliability for BFS and power (0.98, 0.96, and 0.85 for BFS, power within 5 mm, and power within 3 mm, respectively) but poor reliability for eccentricity (0.59). Repeatability and reproducibility were unrelated to stromal bed thickness.

CONCLUSIONS

Orbscan II provides reliable post-LASIK PCC data for symmetrical parameters (BFS and power), independent of the residual stromal bed thickness, but is unreliable for measurements that are radially asymmetrical (eccentricity). Orbscan II is useful for monitoring the PCC after LASIK once the early postoperative period is over.

Posterior Corneal Curvature Changes after Undersurface Ablation of the Flap and In-the-Bed LASIK Retreatment

OBJECTIVE

To analyze LASIK retreatment-induced changes in the posterior corneal curvature (PCC) with undersurface ablation of the flap (UAF) and in-the-bed techniques.

DESIGN

Nonrandomized, comparative, interventional study.

PARTICIPANTS

Forty-six eyes with a residual spherical equivalent refraction between -0.37 and -2.75 diopters (D) and astigmatism between 0.0 and -1.25 D were included prospectively. In 23 eyes, the calculated postenhancement flap thickness exceeded 150 microm using micropachymetric optical coherence tomography, whereas with further ablation of the bed, the residual bed thickness (RBT) would have been <250 microm, or <55% of the pre-LASIK central pachymetry. In another 23 eyes, RBT allowed the planned ablation for a calculated post-retreatment RBT exceeding 250 microm, >55% of the pre-LASIK central pachymetry.

INTERVENTION

Eyes with insufficient RBT for further ablation underwent UAF retreatment, whereas those with adequate RBT received conventional in-the-bed LASIK retreatment. Examinations were performed before retreatment and 3 and 6 months postoperatively. No eye was lost to follow-up.

MAIN OUTCOME MEASURES

Micropachymetry, Orbscan II scanning-slit PCC data, and visual acuity (VA).

RESULTS

The groups did not differ in age, intraocular pressure, or retreatment ablation depth, but the UAF eyes had a lower mean pre-retreatment RBT (270.7+/-25.4 microm) than conventional enhancement eyes (353.0+/-41.5 microm) (P = 0.001). Eyes undergoing UAF had no significant change in PCC, whereas eyes undergoing conventional retreatment had an increase in the posterior corneal power within the central 3-mm zone (P = 0.008) 3 months after retreatment. No significant changes occurred thereafter. The amount of change in posterior corneal power within the 3-mm central zone from before to after retreatment differed significantly between the groups (mean difference, 0.135 D; 95% confidence interval, 0.022-0.248 D; P = 0.02). No keratectasia developed clinically, and no retreated eye lost or gained > or =2 lines of best-corrected VA. Six months after retreatment, the efficacy and safety indices for the UAF procedure were 0.96 and 1.01, respectively, and 1 and 1.06 for conventional LASIK enhancement.

CONCLUSION

Undersurface ablation of the flap retreatment appears to have less potential for changing the posterior corneal surface than conventional LASIK enhancement and can help reduce the likelihood of retreatment-induced keratectasia.

Laser in situ keratomileusis: ablation on the flap and stromal bed in a primary treatment

PURPOSE

To analyze outcomes of laser in situ keratomileusis (LASIK) performed on the flap and on the stromal bed at the same time in a primary treatment.

SETTING

Instituto de la Visión, Buenos Aires, Argentina.

METHODS

Twenty-two cases (13 female, 9 male) were studied retrospectively; the mean age of the patients was 33.15 years +/- 10.44 (SD). Inclusion criteria were low pachymetry or topographic asymmetry. Twenty cases (90.9%) presented with low pachymetry (512.2 +/- 21.40 mum), and 2 cases (9.1%) presented with topographic asymmetry (inferior-superior difference more than 1.5 diopters [D]). Ablation was performed on the flap from the back and on the bed. The flap was made using the Technolas Hansatome microkeratome and the ablation by the Technolas 217z excimer laser (both by Bausch & Lomb). Preoperatively, the spherical equivalent (SE) was -5.61 +/- 1.72 D, the cylinder was -1.78 +/- 1.24 D, and the best spectacle-corrected visual acuity (BSCVA) was 0.77 +/- 0.19. Difficulties and complications of the technique, efficacy and safety index, and aberrations were analyzed.

RESULTS

According to the surgical plan and our nomogram, diopters corrected on the flap were -1.73 +/- 1.08 and on the bed were -4.77 +/- 1.89. The mean follow-up was 8.28 +/- 2.19 months. At 6 months, the SE was -0.21 +/- 0.39, vectorial change was 1.69 +/- 0.74, and the BSCVA was 0.77 +/- 0.20. Postoperatively, no eye had an increase in refractive astigmatism. Uncorrected visual acuity was 20/40 or better in all cases (100%) and 20/25 or better in 13 cases (59.1%). Regarding gained and lost lines of BSCVA, 54.5% conserved the lines, 18.2% lost 1 line, 9.1% gained 1 line, and 18.2% gained 2 lines.

CONCLUSIONS

Simultaneous ablation on the flap and on the bed in cases of low pachymetry or topographical asymmetry was predictable, effective, and safe.

Simultaneous laser in situ keratomileusis on the stromal bed and undersurface of the flap in eyes with high myopia and thin corneas

PURPOSE

To evaluate simultaneous laser in situ keratomileusis (LASIK) on the stromal bed and the undersurface of the flap in eyes with high myopia and insufficient corneal thickness for conventional LASIK ablation.

SETTING

21 Century Eye Hospital, Seoul Paik Hospital, Inje University, Seoul, Korea.

METHODS

Using intraoperative pachymetry, the residual stromal bed thickness was evaluated and simultaneous LASIK was performed on the stromal bed and undersurface of the flap without compromising the posterior 300 mum of the stromal bed. In a prospective series, outcomes in 43 eyes of 27 patients with mean spherical equivalent refraction ranging from -12.5 to -3.75 diopters were analyzed 1, 3, and 6 months after surgery.

RESULTS

Postoperative uncorrected visual acuity was 20/30 or better in 35 eyes (81.4%) at 1 month, 36 eyes (83.7%) at 3 months, and 34 eyes (79.1%) at 6 months. During surgery and follow-up, no vision-threatening complications occurred.

CONCLUSION

Simultaneous LASIK appears to be a useful surgical aid in LASIK treatment in eyes with high myopia with or without astigmatism when an adequate residual stromal bed does not exist.

LASIK Enhancement Using Excimer Laser Ablation on the Back of the Flap

PURPOSE

To report our surgical technique for LASIK enhancement by ablating the underside of the flap.

METHODS

Surgical case report of clinical outcomes in three eyes of two patients who had an initial laser ablation in the bed with subsequent enhancements on the underside of the flap.

RESULTS

Following LASIK enhancement on the back of the flap, two eyes gained one line of best spectacle-corrected visual acuity (BSCVA) after treatment compared to preoperatively, going from 20/15 to 20/12, and one eye maintained BSCVA at 20/20.

CONCLUSIONS

Excimer laser ablation of the underside of the flap is a viable alternative to treat corneas with minimal residual tissue whether primary or enhancement procedures are needed. A surgical learning curve exists with this technique.

Cornea-sparing laser in situ keratomileusis: Ablation on the flap

PURPOSE

To evaluate the safety and efficacy of laser ablation on the flap as a treatment for a refractive error.

SETTING

Laser Sight Centres, Sydney, Australia.

METHODS

In this noncomparative case series, 142 treatments were performed in 98 patients using cornea-sparing laser in situ keratomileusis (LASIK) with ablation of the corneal flap and, in some cases, also the stromal bed for spherical equivalent (SE) refractive errors from -0.50 diopter (D) to -12.38 D. The procedure was performed as a primary treatment in 104 eyes, an initial enhancement in 32 eyes, and a second enhancement in 6 eyes. Data were extracted for analysis by retrospective review of patients' charts.

RESULTS

After LASIK, the mean SE was -0.20 D +/- 0.47 (SD) (range +0.87 to -2.35 D) excluding eyes with monovision. The 6 eyes with monovision had a mean SE of -1.90 D with myopia of -1.70 D (range -1.00 to -3.00 D) and mean astigmatism of -0.37 D (range 0 to -0.75 D). Excluding eyes with monovision, 97% of eyes achieved an uncorrected visual acuity of 6/12 or better and 64% of eyes, better than or equal to 6/6. Ninety-six percent were within +/-1.0 D of the intended correction (SE). The safety index was 1.02 and the efficacy index, 0.8.

CONCLUSIONS

Laser ablation of the corneal flap achieved good visual results and enabled preservation of the posterior corneal stroma. This technique may aid the prevention of corneal keratectasia following LASIK.