Posterior corneal surface differences between non-laser in situ keratomileusis (LASIK) and 10-year post-LASIK myopic eyes

Posterior corneal stability after small incision lenticule extraction with different optical zones

BACKGROUND

To assess the changes in the posterior corneal surface following small incision lenticule extraction (SMILE) with different optical zones.

METHODS

In this retrospective study, 106 eyes of 106 patients who underwent SMILE were recruited 3 years after the procedure. Eyes were divided into two groups according to the size of the surgical optical zone: group A (52 eyes, ≤6.2 mm) and group B (54 eyes, ≥6.5 mm). Posterior central elevation (PCE) and 12 other points at 45°, 135°, 225° and 315° with distances of 1 mm, 2 mm and 3 mm from the centre were recorded from Pentacam.

RESULTS

No iatrogenic keratectasia was identified, and eyes in the two groups showed comparable visual results. The overall trend in posterior corneal elevation changes was consistent for both groups. PCE decreased significantly from 1.33 ± 2.32 to 0.75 ± 2.41 in group A (P = 0.024) and from 0.87 ± 2.61 to 0.06 ± 2.74 in group B (P = 0.003). All points in the central 2 mm region in both groups were reduced postoperatively. In the 4 mm and 6 mm corneal annulus, almost all points at 225°and 315° showed backward displacement, with the most prominent change occurring at 315° in the 6 mm annulus (P < 0.001), indicating no forward protrusion in the inferior area.

CONCLUSIONS

No forward protrusion in the posterior corneal surface was observed 3 years after SMILE with different optical zones. Comprehensive preoperative measurements are essential for ensuring corneal stability and avoiding iatrogenic keratectasia.

Regional analysis of posterior corneal elevation after laser refractive surgeries for correction of myopia of different degrees

PURPOSE

To evaluate regional changes in the posterior corneal elevation after three laser refractive surgeries for correction of myopia of different degrees.

SETTINGS AND DESIGN

Retrospective, comparative, and non-randomized study.

METHODS

Two hundred patients (200 eyes) who underwent laser epithelial keratoplasty (LASEK), femtosecond-assisted laser in-situ keratomileusis (FS-LASIK), and small-incision lenticule extraction (SMILE) were included in this study. According to preoperative spherical equivalent (SE), each surgical group was divided into two refractive subgroups: low-to-moderate myopia (LM group) and high myopia (H group). The posterior corneal elevation from Pentacam Scheimpflug tomography was analyzed preoperatively and at 1 month, 3 months, 6 months, and 12 months postoperatively. Three subregions of the posterior cornea were divided in this study as the central, paracentral, and peripheral regions.

STATISTICAL ANALYSIS USED

Generalized Estimating Equations (GEE).

RESULTS

For all three surgical groups, similar changing trends were seen in the two refractive subgroups. H group presented a larger changing magnitude than the LM group in FS-LASIK over time ( P < 0.05), whereas no significant difference was noted in the two refractive subgroups of LASEK or SMILE ( P > 0.05). At 12 months postoperatively, the central posterior corneal elevation returned to the preoperative level in LASEK ( P > 0.05) but shifted forward significantly in FS-LASIK and SMILE ( P < 0.05).

CONCLUSION

Different posterior corneal regions respond differently to corneal refractive surgeries. LASEK, FS-LASIK, and SMILE demonstrate different trends in the regional changes in posterior corneal elevation. The corneal shape seems more stable in LASEK than in FS-LASIK and SMILE.

Two-year stability of posterior corneal surface after transepithelial photorefractive keratectomy with a residual stromal thickness less than 350 μm

PURPOSE

This study aimed to investigate the stability of posterior corneal surface 2 years after transepithelial photorefractive keratectomy (TPRK) in patients with a residual stromal thickness less than 350 μm.

METHODS

In total, 408 eyes of 212 patients (160 women, 52 men) who underwent TPRK were enrolled in this retrospective study. All surgeries were performed in the Amaris 750S excimer laser platform with smart pulse technology. The posterior corneal elevation, anterior chamber depth, Q value, and curvature were measured using Pentacam preoperatively and postoperatively. All patients were followed up for 2 years. The relationship between percent tissue altered (PTA), age, and changes in posterior corneal surface was analyzed.

RESULTS

The mean preoperative spherical equivalent was - 6.80 ± 1.18 D (range: - 9.00 to - 2.63 D). The mean residual stromal thickness was 336.46 ± 7.25 μm (range: 310-348 μm). The mean PTA was 30.93 ± 2.03% (range: 24.29-35.28%). At 2 years after surgery, the elevation of six points in the central area decreased by 1.91 ± 2.97 μm, 2.98 ± 3.23 μm, 1.17 ± 3.85 μm, 1.70 ± 2.88 μm, 1.36 ± 3.19 μm, and 1.65 ± 3.18 μm, compared with the preoperative value (P < 0.05). The elevation of three points in the peripheral area increased by 1.87 ± 6.34 μm, 0.68 ± 6.00 μm, and 0.95 ± 5.50 μm (P < 0.05). There was no significant linear relationship between PTA, age, and changes in posterior corneal surface, anterior chamber depth, and K2 (all P > 0.05).

CONCLUSION

Within 2 years after TPRK, the posterior corneal surface remained stable in patients with a residual stromal thickness between 310 and 350 μm. There was no sign of iatrogenic ectasia during the follow-up period.

Intraocular pressure after myopic laser refractive surgery measured with a new Goldmann convex prism: correlations with GAT and ORA

Background

The purpose of this study is to describe measurements using a newly developed modified Goldmann convex tonometer (CT) 1 year after myopic laser refractive surgery. Intraocular pressure (IOP) measurements were compared with IOP values obtained by Goldmann applanation tonometer (GAT), and Ocular Response Analyzer (ORA).

Methods

Prospective double-masked study performed on thirty eyes of thirty patients that underwent laser in situ keratomileusis (LASIK; n = 19) or photorefractive keratectomy (PRK; n = 11). IOP was measured before and 3 and 12 months after surgery. Intraclass correlation coefficient (ICC) and Bland-Altman plot were calculated to assess the agreement between GAT, CT, IOPg (Goldmann-correlated IOP) and IOPcc (corneal-compensated IOP) from ORA.

Results

Twelve months after LASIK, IOP measured with CT showed the best correlation with IOP measured with GAT before surgery (GATpre) (ICC = 0.886, 95% CI: 0.703–0.956) (15.60 ± 3.27 vs 15.80 ± 3.22; p < 0.000). However, a moderate correlation was found for IOP measured with IOPcc and CT 12 months after LASIK (ICC = 0.568, 95% CI: − 0.185 – 0.843) (15.80 ± 3.22 vs 12.87 ± 2.77; p < 0.004). Twelve months after PRK, CT showed a weak correlation (ICC = − 0.266, 95% CI: − 3.896 – 0.663), compared to GATpre (17.30 ± 3.47 vs 16.01 ± 1.45; p < 0.642), as well as poor correlation (ICC = 0.256, 95% CI: − 0.332 – 0.719) with IOPcc (17.30 ± 3.47 vs 13.38 ± 1.65; p < 0.182).

Conclusions

Twelve months after LASIK, IOP measured with CT strongly correlated with GAT before surgery and could therefore provide an alternative method for measuring IOP after this surgery. More studies regarding this new convex prism are needed to assess its accuracy.

Seven-year observation of posterior corneal elevation after small incision lenticule extraction (SMILE) in patients with moderate and high myopia

Purpose

To investigate the long-term changes in posterior corneal elevation in moderate and high myopia after small incision lenticule extraction (SMILE).

Setting

Eye & ENT Hospital, Fudan University.

Design

Prospective case series.

Methods

Thirty-three eyes of 20 patients (30.1+/-9.5 years, 7 male and 13 female, spherical equivalent [SE] range -4.00 to -8.75 D, average SE -6.25+/-1.29 D) who underwent SMILE were included. Changes in the posterior corneal elevation at central points (PCE), the thinnest point (PTE), the maximal point (PME), and an additional 20 points within the 4-mm area of the best-fit sphere were evaluated with a Pentacam (Oculus Optikgerate GmbH, Wetzlar, Germany) during a 7-year follow-up period. Mixed linear models were used to evaluate changes with P-values <0.05. Correlations of elevation changes and residual bed thickness (RBT) were also evaluated.

Results

No ectasia was observed among the 33 eyes. The safety index was 1.08, and the efficacy index was 1.03. The mean change in PCE at 1, 3, 5, and 7 years was -1.42+/-0.95, -2.67+/-0.98, -2.44+/-1.06, and -1.91+/-0.92 [micro]m, respectively. Significant differences were found at 3, 5, and 7 years (P=0.007, 0.023, and 0.040, respectively). PTE was significantly reduced at each time point compared to baseline. The mean change was -2.82+/-1.19, -3.55+/-1.22, -3.47+/-1.32, and -2.39+/-1.15 [micro]m, respectively (P=0.019, 0.004, 0.010, and 0.039, respectively). PME changed 2.45+/-1.02 [micro]m at 7 years compared to baseline (P=0.017). The changes in PCE and PME negatively correlated with the RBT.

Conclusions

Long-term posterior corneal elevation was stable in moderate and high myopia after SMILE.

Comparison of visual outcomes after femtosecond laser-assisted LASIK versus flap-off epipolis LASIK for myopia

Background

This study clinically evaluated the visual outcomes after refractive surgery for myopia using femtosecond laser-assisted in situ keratomileusis (femto-LASIK) and flap-off epipolis LASIK (epi-LASIK).

Methods

In this retrospective case series study, 40 eyes of 27 patients were divided into two groups depending on the technique used for refractive surgery. Femto-LASIK and flap-off epi-LASIK flaps were created using femtosecond laser and Epi-K™ epikeratome, respectively. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity, manifest refraction, corneal asphericity, and corneal higher-order aberrations (HOAs) were assessed pre- and postoperatively.

Results

The improvement in logarithm of the minimum angle of resolution (logMAR) UDVA after refractive surgery was statistically significant for both groups (P < 0.001 for all groups); it was significant better in UDVA in femto-LASIK than flap-off epi-LASIK, 0.03 ± 0.06 logMAR (femto-LASIK) and 0.54 ± 0.31 logMAR (flap-off epi-LASIK), at 1 day postoperatively; 0.02 ± 0.05 logMAR (femto-LASIK) and 0.14 ± 0.13 logMAR (flap-off epi-LASIK), at 1 week postoperatively (P < 0.001 and P = 0.019). With regard to the corneal HOAs, the increment in spherical aberration (Z_4,0) was greater in flap-off epi-LASIK than femto-LASIK: 0.626 ± 0.232 μm and 0.479 ± 0.139 μm in the front cornea; 0.556 ± 0.227 μm and 0.430 ± 0.137 μm in the total cornea (P = 0.016 and P = 0.017). However, the back corneal HOA changes did not have a significant effect on the total corneal HOA changes.

Conclusion

Femto-LASIK yielded better early visual outcomes than did flap-off epi-LASIK, but there was no significant difference between the outcomes of the two procedures, 1 week postoperatively.

Regional changes in corneal shape over a 6-month follow-up after femtosecond-assisted LASIK

PURPOSE

To assess the regional changes in corneal shape after femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) in patients with different myopia extents.

SETTING

Eye Hospital, Wenzhou Medical University, Wenzhou, China.

DESIGN

Retrospective case series.

METHODS

A retrospective study of myopic eyes treated with FS-LASIK was conducted to assess the shape changes within different corneal regions after surgery. Corneal curvature was measured in the central region (0 mm to 3.0 mm diameter), pericentral region (3.0 mm to 6.0 mm diameter) and peripheral region (6.0 mm to 9.0 mm diameter) preoperatively and from 1 week to 6 months postoperatively.

RESULTS

The study comprised 608 myopic eyes. During the 6-month follow-up, the anterior cornea became steeper in the central and pericentral regions, but flatter in the peripheral region (P < .01), representing a partial, gradual, yet significant reversal of the immediate change in corneal shape after laser ablation. In contrast, the posterior surface experienced significantly less change than the anterior surface, with the cornea becoming slightly flatter (P < .01) in the central region at 1 week postoperatively, and steeper elsewhere (P < .05), and then remaining stable during the rest of the follow-up. On the other hand, the anterior astigmatism had significant decreases in the central region (P < .01) and slight increases in the peripheral region (P < .01) 1 week postoperatively, and that remained stable over the follow-up period. In contrast, there were little or non-significant changes in the posterior astigmatism throughout the follow-up (P > .05).

CONCLUSIONS

Postoperative corneal shape changes were different in different regions. There were shape changes in individual corneal regions during the 6-month follow-up period that represented reverse trends; however, the changes were much smaller than the short-term changes observed 1 week after surgery.