Topography-Guided Transepithelial Surface Ablation in the Treatment of Moderate to High Astigmatism

Posterior Corneal Astigmatism Does Not Influence Manifest-Treated Topography-guided LASIK Outcomes

PURPOSE

To investigate whether the magnitude of posterior corneal astigmatism (PCA) impacts refractive and visual outcomes of primary topography-guided laser in situ keratomileusis (LASIK) and to provide guidance on treating eyes with high PCA.

METHODS

Comparative retrospective analysis of 4,541 consecutive eyes treated with Contoura (Alcon Laboratories, Inc) on the manifest refractive astigmatism. Standard outcomes of the 1,514 eyes with the lowest PCA (first tercile; low PCA group) were compared to the 1,514 eyes with the highest PCA (last tercile; high PCA group). Pearson correlation coefficient was used to assess relationships between variables.

RESULTS

Preoperatively, 20.9% of eyes presented with PCA of 0.50 diopters (D) or greater. The mean PCA was 0.18 ± 0.07 D in eyes with low PCA, and 0.50 ± 0.11 D in eyes with high PCA. An equivalent number of eyes achieved a cumulative postoperative unilateral uncorrected distance visual acuity of 20/20 in both the low PCA and high PCA groups (95.3% vs 94.7%; P = .4489). The efficacy index of both low and high PCA eyes was identical (0.99 ± 0.06 vs 0.99 ± 0.08; P = .3192), as was the safety index (1.00 ± 0.02 vs 1.00 ± 0.03; P = .0110). The magnitude of preoperative PCA was weakly correlated with postoperative refractive astigmatism (R = 0.1323), but not with postoperative defocus equivalent (R = -0.0414) or spherical equivalent (R = -0.0128).

CONCLUSIONS

PCA does not negatively impact the outcomes of topography-guided LASIK targeting the manifest refraction, having identical accuracy, efficacy, and safety in eyes with both low and high PCA. There is no scientific basis to measure and consider PCA in topography-guided LASIK planning software or nomograms if the excimer laser treatment input targets the manifest refraction. [J Refract Surg. 2022;38(12):780-790.].

The Impact of Epithelial Remodeling on Surgical Techniques Used in Topography-guided Surface Ablation in Irregular Corneas

PURPOSE

To analyze the optical consequences of epithelial remodeling in irregular corneas and their impact on the choice of different surface ablation techniques.

METHODS

Anterior corneal and stromal surface topographies and epithelial thickness maps were analyzed in 24 eyes with irregular corneal optics. On two of the eyes, four different surface ablation techniques were simulated: (1) conventional anterior topography-guided photorefractive keratectomy (PRK), (2) transepithelial phototherapeutic keratectomy (PTK), (3) transepithelial anterior topography-guided PRK, and (4) stromal topography-guided PRK.

RESULTS

Stromal surface topographies showed higher keratometric values, astigmatism, asphericity, and corneal higher order aberrations compared to topographies of anterior corneas covered by epithelium. Transepithelial anterior topography-guided PRK and stromal topography-guided PRK both resulted in regularized stromal surface, transepithelial PTK achieved partial regularization corresponding to the smoothing effect of the epithelial remodeling, and conventional anterior topography-guided PRK delivered after epithelial removal resulted in residual stromal surface irregularities.

CONCLUSIONS

The difference in optical landscapes between the stromal and anterior surfaces in irregular corneas will represent a source of error when anterior topography-guided treatments are delivered on the deepithelialized stroma, as in conventional PRK. In contrast, anterior topography-guided ablations performed as transepithelial PRK and stromal topography-guided PRK delivered after epithelial removal address the full stromal irregularity, whereas transepithelial PTK alone may be used when topography-guided treatments are not possible. The authors conclude topography-guided PRK of irregular corneas should lead to significantly improved regularization only if it includes the effect of epithelial remodeling. [J Refract Surg. 2022;38(8):529-537.].

Large Axis Difference Between Topographic Anterior Corneal Astigmatism and Manifest Refractive Astigmatism: Can Topography-Guided LASIK Target the Manifest Axis?

PURPOSE

To investigate whether the degree of astigmatism axis discrepancy between preoperative manifest refractive astigmatism and anterior corneal astigmatism impacts refractive and visual outcomes of primary topography-guided laser in situ keratomileusis (LASIK) targeting the refractive astigmatism, and to provide guidance on treating eyes with very large axis discrepancy.

METHODS

Comparative retrospective analysis of 25,396 consecutive eyes treated with topography-guided LASIK on the manifest refractive astigmatism. Standard outcomes of the 14,534 eyes with small axis discrepancy (SAD) (Δ in axis ⩽ 10°) were compared to the 2,222 eyes with very large axis discrepancy (VLAD) (Δ in axis ⩾ 45°). Pearson correlation coefficient was used to assess relationships between selected variables.

RESULTS

The mean axis discrepancy was 4.47 ± 2.92° in SAD eyes, and 65.0 ± 13.4° in VLAD eyes. An equivalent number of eyes achieved a cumulative postoperative unilateral uncorrected distance visual acuity of 20/20 in both the SAD and VLAD groups (93.02% vs 93.42%; P = .4892). The efficacy index (0.98 ± 0.13 vs 0.98 ± 0.07; P = .3931) and the safety index (1.00 ± 0.11 vs 1.00 ± 0.03; P = .4757) were identical between groups. There was no clinically meaningful correlation between the preoperative axis discrepancy and preoperative total root mean square anterior corneal coma, postoperative refractive astigmatism, defocus equivalent, spherical equivalent, and angle of error, all with weak correlation coefficients (R = -0.02, -0.03, -0.02, 0.01, and 0.05).

CONCLUSIONS

Large preoperative axis discrepancy (45° to 90°) between refractive astigmatism and topography-measured anterior corneal astigmatism does not negatively impact topography-guided LASIK, having identical refractive and visual outcomes compared to eyes with small (0° to 10°) discrepancy. There is no basis to exclude eyes with large axis discrepancy from topography-guided LASIK, and these eyes should be treated on the manifest refractive astigmatism. [J Refract Surg. 2021;37(10):662-673.].

Effect of Anterior Corneal Higher-Order Aberration Ablation Depth on Primary Topography-Guided LASIK Outcomes

PURPOSE

To investigate the contribution of anterior corneal higher-order aberration ablation depth (HOA-AD) to topography-guided outcomes.

METHODS

This was a retrospective comparative analysis of 9,722 consecutive eyes undergoing laser in situ keratomileusis (LASIK) treated on the clinically measured refractive cylinder with Contoura software (Alcon Laboratories, Inc., Fort Worth, TX). Outcomes of the 3,246 eyes with the shallowest HOA-AD (first tercile: 5.4 ± 0.9 µm) were compared to the 3,362 eyes with the deepest HOA-AD (last tercile: 11.0 ± 1.7 µm).

RESULTS

The HOA-AD followed a left-skewed normal distribution (R² = 0.98) with a mean ± standard deviation of 8.02 ± 3.00 µm, with 1.8% of eyes greater than 15 µm. The efficacy index of shallow versus deep HOA-AD eyes was identical (0.98 ± 0.07 vs 0.98 ± 0.09; P = .99), with a similar percentage having spherical equivalent within ±0.50 diopters (D) (95.2% vs 95.0%; P = .71) and within ±0.75 D (98.9% vs 98.7%; P = .46) of intended target. The safety index (1.00 ± 0.03 vs 1.00 ± 0.04; P = .19) and Alpins correction index (1.00 ± 0.39 vs 1.01 ± 0.43; P = .53) were also identical. The mean postoperative refractive astigmatism difference between the shallow (0.15 D) and deep (0.20 D) groups was 0.05 D. The 3-month laser re-treatment rate was greater in the deep group (0.83% vs 0.37%; P = .02), but less than 1% for both groups.

CONCLUSIONS

The contribution of topography-guided HOA-AD to clinical outcomes in most virgin eyes is negligible, with excellent efficacy, accuracy, and safety in both the deep and shallow ablation groups. Eyes with deep HOA-AD greater than 15 µm trend to lesser outcomes, but should not be excluded from topography-guided surgery. [J Refract Surg. 2019;35(12):754-762].

Primary Topography-Guided LASIK: Refractive, Visual, and Subjective Quality of Vision Outcomes for Astigmatism ⩾2.00 Diopters

PURPOSE

To evaluate the outcomes of primary topography-guided laser in situ keratomileusis (LASIK) in eyes with subjective refractive astigmatism of 2.00 diopters (D) or greater.

METHODS

This was a prospective study in consecutive eyes with cylinder of 2.00 D or greater that had LASIK using the Alcon WaveLight EX500 excimer laser and T-CAT/Contoura software (Alcon Laboratories, Inc., Fort Worth, TX). The accuracy, efficacy, safety, cylinder vector analysis, higher order aberrations, and patients' subjective quality of vision were assessed. Eyes with naturally occurring topographic irregular astigmatism were not excluded.

RESULTS

The mean cylinder was -2.55 D preoperatively and -0.34 D postoperatively; 81% and 95% of eyes were within ±0.50 and ±0.75 D of intended cylinder after LASIK, respectively. The correction index and index of success were 1.00 and 0.13, respectively. The efficacy and safety indexes were 0.98 and 1.04, respectively. The preoperative corneal topography irregularity index, anterior corneal higher order aberrations, and refractive astigmatism magnitude were mildly correlated to postoperative residual astigmatism. Mean ocular and corneal coma were not increased postoperatively. Patients had significant improvements after LASIK in both subjective uncorrected quality of vision and night vision disturbances compared to spectacle- and contact lens-corrected vision before LASIK.

CONCLUSIONS

Topography-guided ablation using the Alcon WaveLight EX500 excimer laser and T-CAT/Contoura software results in excellent accuracy, efficacy, and safety, with improved postoperative subjective quality of vision and reduced night vision disturbances in virgin eyes with refractive astigmatism of 2.00 D or greater, including eyes with topographic naturally occurring irregular astigmatism. [J Refract Surg. 2019;35(2):78-86.].

Small incision lenticule extraction (SMILE) in the correction of myopic astigmatism: outcomes and limitations - an update

Small Incision Lenticule Extraction (SMILE) is a flap-free intrastromal technique for the correction of myopia and myopic astigmatism. To date, this technique lacks automated centration and cyclotorsion control, so several concerns have been raised regarding its capability to correct moderate or high levels of astigmatism. The objective of this paper is to review the reported SMILE outcomes for the correction of myopic astigmatism associated with a cylinder over 0.75 D, and its comparison with the outcomes reported with the excimer laser-based corneal refractive surgery techniques. A total of five studies clearly reporting SMILE astigmatic outcomes were identified. SMILE shows acceptable outcomes for the correction of myopic astigmatism, although a general agreement exists about the superiority of the excimer laser-based techniques for low to moderate levels of astigmatism. Manual correction of the static cyclotorsion should be adopted for any SMILE astigmatic correction over 0.75 D.