Corneal Astigmatism Measurement by Ray Tracing Versus Anterior Surface-Based Keratometry in Candidates for Toric Intraocular Lens Implantation

Effectiveness of toric intraocular lens implantation for correcting irregular corneal astigmatism in cataract eyes

A retrospective cohort study was conducted to observe the correction effect of Toric intraocular lens (IOL) implantation in cataract eyes with specific types of irregular corneal astigmatism. Thirty-four eyes with either the "asymmetric bow-tie" pattern (Type I) or the "angled bow-tie" pattern (Type II) were included. Corneal topography was assessed using Pentacam HR, and changes in preoperative corneal astigmatism, visual acuity, manifest refraction, and objective visual quality were measured and compared. The average uncorrected distance visual acuity improved significantly from 0.86 ± 0.40 logMAR to 0.22 ± 0.15 logMAR (P < 0.001). Preoperative corneal astigmatism of 2.05 ± 0.90 D was corrected to a postoperative residual astigmatism of 0.78 ± 0.57 D (P < 0.001), with 32% of eyes within 0.50 D. The residual astigmatism prediction errors in Type I and Type II cases were (0.97 ± 0.68 D) and (0.66 ± 0.37 D), respectively (P = 0.100). The mean spherical equivalent prediction error in Type II cases (0.07 ± 0.36 D) was significantly smaller than that in Type I cases (- 0.29 ± 0.52 D) (P = 0.030). This study concludes that Toric IOL implantation effectively corrects specific types of irregular corneal astigmatism in cataract surgery. Eyes with the "angled bow-tie" pattern show higher accuracy in refractive predictions compared to eyes with the "asymmetric bow-tie" pattern.

Correction of Asymmetric Bowtie Corneal Astigmatism with a Toric Intraocular Lens: Outcomes and Accuracy of Measurement Modes

The outcomes of toric intraocular lens (IOL) implantation in correcting asymmetric bowtie corneal astigmatism remain uncertain. The accurate measurement of corneal astigmatism is essential for surgical planning. In this prospective cohort study, patients with asymmetric or symmetric bowtie corneal astigmatism who underwent toric IOL implantation were recruited. Preoperative corneal astigmatism was measured with an IOLMaster and Pentacam (including the simulated keratometry (SimK), total corneal refractive power (TCRP), and wavefront aberration (WFA) modes). At 3 months after surgery, the refractive outcomes and residual astigmatic refractive errors were compared with patients with symmetric bowtie astigmatism. The prediction errors (the differences between the calculated actual corneal astigmatism and the measured corneal astigmatism) were compared among the different measurement modes in the asymmetric group. There were no differences in residual astigmatism between the asymmetric and symmetric groups. However, the mean absolute residual astigmatic refractive error was greater in the asymmetric group than in the symmetric group (0.72 ± 0.42 D vs. 0.53 ± 0.24 D, p = 0.043). In the asymmetric group, the mean absolute prediction errors for the IOLMaster, SimK, TCRP and WFA modes were 0.53 ± 0.40, 0.56 ± 0.47, 0.68 ± 0.52, and 0.43 ± 0.40 D, respectively. The Pentacam WFA mode was the most accurate mode (p < 0.05). The absolute prediction error of the WFA mode was positively correlated with the total corneal irregular astigmatism higher-order aberrations and coma (r = 0.416 and r = 0.473, respectively; both p < 0.05). Our study suggests toric IOL implantation effectively corrected asymmetric bowtie corneal astigmatism. The Pentacam WFA mode may be the most accurate measurement mode, although its accuracy decreased as asymmetry increased.

Intraocular lens constant optimization in toric intraocular lens calculation using keratometry and total corneal power

PURPOSE

To evaluate intraocular lens (IOL) constant optimization in toric IOL calculation with keratometry (K) and total corneal refractive power (TCRP).

METHODS

Predicted spherical equivalent (SE) and residual astigmatism (RA) with K and TCRP were retrospectively calculated using the Haigis, Holladay 1, and SRK/T formulae and optimized IOL constants. The results of the Barrett calculator and the Abulafia-Koch formula with K were also calculated. The median absolute error in SE (MedAE-SE), mean absolute error in RA (MAE-RA), and centroid error (CE) were analyzed.

RESULTS

Seventy-nine eyes of 71 patients implanted with toric IOLs were included. With K, there were no significant differences between the results before and after constant optimization using all the formulae. With TCRP, constant optimization significantly reduced MedAE-SE; however, significantly increased MAE-RA and CE using the Holladay 1 and SRK/T formulae. MedAE-SE, MAE-RA, and CE using the Haigis formula did not show significant differences. The difference in the predicted RA before and after constant optimization increased with IOL toricity. The MedAE-SE predicted by TCRP was significantly higher than that predicted by K despite constant optimization. The MAE-RA and CE predicted by TCRP were significantly lower than those predicted by K without posterior corneal astigmatism optimization; however, were not significantly different from those predicted by the Barrett and Abulafia-Koch formulae.

CONCLUSIONS

Constant optimization is recommended when using the TCRP in toric IOL calculations, particularly for patients with large astigmatism. However, TCRP did not yield more accurate results than optimized K in toric IOL calculations despite constant optimization.

[The impact of the position of toric intraocular lenses on the functional outcomes of phaco surgery]

The article reviews data on the impact of the position (orientation) of toric intraocular lenses on the functional outcomes of cataract phacoemulsification surgery, discusses the algorithm of astigmatism correction with intraocular lenses including preoperative determination of the size and position of main meridians, calculation of lens parameters, marking of corneal meridians, intraoperative positioning, as well as rotation and/or repositioning of the lens when necessary.

Handling regular and irregular astigmatism during cataract surgery

PURPOSE OF REVIEW

There are several different approaches to handling regular and irregular astigmatism during cataract surgery, but still much debate on which solutions are most effective given unique patient circumstances. In this review, we examine recent literature and studies to highlight some of the most effective ways to plan preoperatively, manage regular and irregular astigmatism during cataract surgery, as well as managing postoperative complications.

RECENT FINDINGS

Recent developments in technology have provided increased courses of action for astigmatism management during cataract surgery. Additional options of toric IOLs with presbyopic platforms, light adjustable lenses, intraocular pinhole lenses, online technological tools and platforms, wavefront or topographic laser technology, and phototherapeutic keratectomy are all effective solutions to managing regular and irregular astigmatism. In this review, we will explore optimal approaches for unique situations.

SUMMARY

With increased technology, research, and methods, correcting regular and irregular astigmatism during cataract surgery is achievable in most patients. With in-depth preoperative planning, analysis of patient-specific factors, and a tailored approach, surgeons can obtain excellent uncorrected vision for patients.

Efficacy of astigmatic correction after femtosecond laser-guided cataract surgery using intraoperative aberrometry in eyes with low-to-moderate levels of corneal astigmatism

PURPOSE

To evaluate the efficacy of astigmatic correction with two types of toric intraocular lenses (IOLs) after femtosecond laser-assisted cataract surgery (FLACS) in eyes with low-to-moderate corneal astigmatism using intraoperative aberrometry for optimizing the position of the toric IOL.

METHODS

Retrospective study includes a total of 99 eyes of 73 patients with anterior keratomeric astigmatism ≤ 3 D and undergoing FLACS (Catalys, Johnson & Johnson Vision) with implantation of a monofocal (Ankoris, PhysIOL) or a multifocal toric IOL with the same platform (Pod FT, PhysIOL). In all cases, intraoperative aberrometry was used (Optiwave refractive analysis, ORA, system, Alcon). Visual and refractive outcomes were evaluated preoperatively and at 4 months after surgery with vector analysis of astigmatic changes.

RESULTS

A total of 89.9%, 93.9% and 97.0% showed a postoperative sphere, cylinder and spherical equivalent within ± 0.50 D, respectively. Mean difference vector (DV) was 0.22 ± 0.27 D, mean magnitude of error (ME) was 0.13 ± 0.29 D, and mean angle of error (AE) was 1.52 ± 11.64°. Poor correlations of preoperative corneal astigmatism with DV (r = - 0.032, p = 0.833), ME (r = - 0.344, p = 0.001) and AE (r = - 0.094, p = 0.377) were found. Likewise, no statistically significant differences were found between monofocal and multifocal toric IOL subgroups in DV (p = 0.580), ME (p = 0.702) and AE (p = 0.499).

CONCLUSIONS

The combination of FLACS and intraoperative aberrometry to optimize the position of a toric IOL allows a very efficacious correction of preexisting low-to-moderate corneal astigmatism.

A New Approach for the Calculation of Total Corneal Astigmatism Considering the Magnitude and Orientation of Posterior Corneal Astigmatism and Thickness

PURPOSE

To evaluate a new method of calculation of total corneal astigmatism based on Gaussian optics and the power design of a spherocylindrical lens (C) in the healthy eye and to compare it with keratometric (K) and power vector (PV) methods.

METHODS

A total of 92 healthy eyes of 92 patients (age, 17-65 years) were enrolled. Corneal astigmatism was calculated in all cases using K, PV, and our new approach C that considers the contribution of corneal thickness. An evaluation of the interchangeability of our new approach with the other 2 methods was performed using Bland-Altman analysis.

RESULTS

Statistically significant differences between methods were found in the magnitude of astigmatism (P < 0.001), with the highest values provided by K. These differences in the magnitude of astigmatism were clinically relevant when K and C were compared [limits of agreement (LoA), -0.40 to 0.62 D), but not for the comparison between PV and C (LoA, -0.03 to 0.01 D). Differences in the axis of astigmatism between methods did not reach statistical significance (P = 0.408). However, they were clinically relevant when comparing K and C (LoA, -5.48 to 15.68 degrees) but not for the comparison between PV and C (LoA, -1.68 to 1.42 degrees).

CONCLUSIONS

The use of our new approach for the calculation of total corneal astigmatism provides astigmatic results comparable to the PV method, which suggests that the effect of pachymetry on total corneal astigmatism is minimal in healthy eyes.

Comparing surgically induced astigmatism calculated by means of simulated keratometry versus total corneal refractive power

Purpose:

To evaluate surgically induced astigmatism as computed by means of either simulated keratometry (KSIM) or total corneal refractive power (TCRP) after temporal incisions.

Methods:

Prospective observational study including 36 right eyes undergoing cataract surgery. Astigmatism was measured preoperatively during the 3-month follow-up period using Pentacam. Surgically induced astigmatism was computed considering anterior corneal surface astigmatism at 3 mm with KSIM and considering both corneal surfaces with TCRP from 1 to 8 mm (TCRP3 for 3 mm). The eyes under study were divided into two balanced groups: LOW with KSIM astigmatism <0.90 D and HIGH with KSIM astigmatism ≥0.90 D. Resulting surgically induced astigmatism values were compared across groups and measuring techniques by means of flattening, steepening, and torque analysis.

Results:

Mean surgically induced astigmatism was higher in the HIGH group (0.31 D @ 102°) than in the LOW group (0.04 D @ 16°). The temporal incision resulted in a steepening in the HIGH group of 0.15 D @ 90°, as estimated with KSIM, versus 0.28 D @ 90° with TCRP3, but no significant differences were found for the steepening in the LOW group or for the torque in either group. Differences between KSIM- and TCRP3-based surgically induced astigmatism values were negligible in LOW group.

Conclusion:

Surgically induced astigmatism was considerably higher in the high-astigmatism group and its value was underestimated with the KSIM approach. Eyes having low astigmatism should not be included for computing the surgically induced astigmatism because steepening would be underestimated.