Influence of posterior corneal astigmatism on total corneal astigmatism in eyes with moderate to high astigmatism

Using Total Corneal Astigmatism With Femtosecond Laser Cataract Surgery and Arcuate Keratotomy(ies) to Treat Low Amounts of Astigmatism

PURPOSE

The aim of this study was to evaluate outcomes using total corneal astigmatism (TCA) to calculate arcuate keratotomy(ies) (AK) parameters performed with femtosecond laser-assisted cataract surgery to reduce low corneal astigmatism.

METHODS

Patients who had femtosecond laser-assisted cataract surgery and AK with 0.50 diopter (D) to 1.30 D of TCA were included. Exclusion criteria were intraoperative complications, preexisting corneal surgery, and comorbidities that might adversely affect outcomes. Corneal tomography (Galilei G4, Zeimer Ophthalmic Systems AG) was performed preoperatively and 1 month postoperatively. TCA was input into the Donnenfeld limbal relaxing incisions nomogram to calculate the AK parameters. Preoperative and postoperative tomographic and subjective refractive measurements were compared. The Alpins method for vector analysis evaluated results.

RESULTS

Eighty-two eyes of 82 patients were included. Mean preoperative TCA was significantly reduced from 0.80 ± 0.19 D to 0.51 D ± 0.26 D ( P < 0.001). Preoperative posterior corneal astigmatism, -0.28 ± 0.13 D, was unchanged, postoperative posterior corneal astigmatism, -0.28 ± 0.14 D ( P = 0.653). Target-induced astigmatism arithmetic mean (0.82 ± 0.21 D) was greater than that of the surgically induced astigmatism (0.70 ± 0.40 D), resulting in an arithmetic mean difference vector of 0.51 ± 0.27 D with a summated mean at 0.16 D at 20 degrees. The correction index was 0.87, indicating undercorrection. Angle of error arithmetic mean, -1.27 ± 23.27 degrees, indicated good alignment.

CONCLUSIONS

Inputting TCA for calculation of femtosecond laser AK parameters can reduce low amounts of preoperative corneal astigmatism, thereby improving uncorrected vision.

Accuracy of Toric Intraocular Lens Calculators with Predicted and Measured Posterior Corneal Astigmatism Across Different Types of Astigmatism

INTRODUCTION

This study is a retrospective case series to compare the accuracy of the Barrett toric calculator using predicted posterior corneal astigmatism (PCA) and PCA measurements using swept-source optical coherence tomography (SS-OCT) and a Scheimpflug camera. This evaluation was conducted across different types of anterior and posterior astigmatism.

METHODS

A total of 146 eyes from 146 patients implanted with toric intraocular lenses were included. Mean absolute prediction error, standard deviation of prediction error, and the percentage of eyes with prediction errors within ±0.50 diopters (D) were calculated using vector analysis. Biometric measurements were conducted using the IOLMaster 700 and Pentacam HR. A subgroup analysis was conducted based on the orientation of both anterior and posterior corneal astigmatism.

RESULTS

The Barrett toric calculator with predicted PCA yielded the best results, with 78.1% having a prediction error ≤ 0.50 D, which was a significantly higher percentage than the Barrett formula with the two versions of measured PCA (P < 0.05). In the subgroup with a horizontally steep meridian PCA using the IOLMaster 700, the Barrett formula with predicted PCA yielded the best results, with 78.3% of cases having a prediction error of less than 0.5 D. This percentage was significantly higher than the other two measured PCA subgroups (P < 0.05).

CONCLUSION

The Barrett toric formula with predicted PCA demonstrated a statistically significantly higher proportion of cases with a prediction error ≤ 0.5 D compared to the two measured PCA formulas (from the IOLMaster 700 or Pentacam). This trend persisted even when the posterior corneal astigmatism was horizontally steep.

Predictive accuracy of Barrett TK toric calculator compared to measured posterior corneal astigmatism using Pentacam in toric IOL power calculation

PURPOSE

To compare the predictive accuracy of Barrett total keratometry (Barrett TK) toric calculator with the measured posterior corneal astigmatism (PCA) by using Pentacam in toric intraocular lens (IOL) power calculation.

METHODS

A prospective analysis was done on 118 eyes requiring toric IOL power implantation. The absolute prediction error of the Barrett TK toric calculator and the measured PCA in the online toric calculator were assessed and compared to the standard Alcon toric calculator (with Barrett toric calculator incorporated).

RESULTS

The mean absolute prediction error of the online toric calculator (0.32 D) (with Barrett toric calculator incorporated), Barrett TK Toric (0.34 D), and measured PCA of Pentacam in Barrett toric calculator (0.33 D) were found to be similar with no statistically significant difference. Subanalysis in eyes with with-the-rule astigmatism, against-the-rule astigmatism, and oblique astigmatism showed similar results. Alpins analysis showed that all three methods overcorrected corneal astigmatism.

CONCLUSION

The Barrett TK toric calculator and the measured PCA of Pentacam in the Barrett toric calculator have similar predictive accuracy to the online toric calculator (with Barrett toric calculator incorporated).

Comparison of Automated Keratometer and Scheimpflug Tomography for Predicting Refractive Astigmatism in Pseudophakic Eyes

PURPOSE

To analyse the correspondence between refractive astigmatism and corneal astigmatism in pseudophakic eyes with non-toric intraocular lenses.

SETTING

Yeouido St. Mary hospital, Seoul, Republic of Korea.

DESIGN

Evaluation of a diagnostic test instrument.

METHODS

This retrospective study included 95 eyes of 95 patients. Corneal astigmatism was measured with an automated keratometer (RK-5, Canon) and Scheimpflug tomography (Pentacam HR, Oculus). Refractive astigmatism was compared to keratometric astigmatism (based on anterior corneal measurements only), equivalent K-reading, and total corneal astigmatism (both based on anterior and posterior corneal measurements). Vector analysis was carried out by Næser's polar value method. The accuracy was defined as the average magnitude of the vectorial difference in astigmatism (DA). Each corneal measurement was optimized in retrospect by a multiple linear regression equation between refractive and corneal astigmatism.

RESULTS

Keratometric astigmatism overestimated with-the-rule (WTR) refractive astigmatism and underestimated against-the-rule (ATR) refractive astigmatism. Several measurements based on both corneal surfaces' values did not show any statistically significant difference with respect to refractive astigmatism. The mean corneal astigmatism by total corneal refractive power (TCRP) at 4.0 mm (zone/pupil) produced the lowest mean arithmetic DA and the highest percentage of eyes with a DA ≤ 0.50 dioptre. After optimization, the accuracies of automated KA and TCRP 4.0 mm (zone/pupil) were similar.

CONCLUSIONS

Total corneal astigmatism measured by Scheimpflug tomography at a 4.0 mm zone centered on the pupil accurately reflects the refractive astigmatism in pseudophakic eyes. However, the accuracy of total corneal astigmatism is not different from automated KA after optimization.

Descemet membrane endothelial keratoplasty combined with presbyopia-correcting and toric intraocular lenses - a narrative review

Fuchs endothelial corneal dystrophy (FECD) is the leading indication for EK and may coexist with cataract and presbyopia. Notably, the outcomes of phacoemulsification in FECD patients are not as favorable as those in eyes without this condition. Historically, only monofocal intraocular lenses (IOLs) were recommended for these patients. However, recent reports have described the implantation of Premium-IOLs (such as Multifocal IOLs, Enhanced Depth of Focus IOLs, and Toric IOLs) in FECD eyes undergoing cataract surgery and Descemet membrane endothelial keratoplasty (DMEK). While the results are encouraging, they are not as optimal as those from unoperated eyes, especially when comparing simultaneous procedures to sequential ones. It's advised to perform the DMEK first to improve the accuracy of IOL calculations. Still, even successfully operated eyes may experience secondary graft failure or graft rejection after DMEK. The success rate of a secondary DMEK is typically lower than that of the initial procedure. Furthermore, if the postoperative thickness after DMEK is less than anticipated, laser enhancements might not be an option. There's a pressing need for more controlled and randomized clinical trials to ascertain the safety and effectiveness of Premium-IOLs for FECD eyes. This narrative review aims to collate evidence on the use of Premium IOL technologies in eyes receiving EK and to underscore key points for surgeons performing EK combined with cataract surgery.

Normative Topographic Anterior and Posterior Corneal Astigmatism: Axis Distribution and Its Relations with Ocular and Biometric Parameters

Corneal astigmatism correction is a key factor when planning refractive treatment for ametropies with intraocular lenses. We aim to obtain normative anterior and posterior corneal astigmatism (ACA and PCA, respectively) data in a local population and to describe their axis distribution and their association with other parameters. A total of 795 patients with no ocular diseases were evaluated with corneal tomography and optical biometry. Only data of the right eye were included. Mean ACA and PCA were 1.01 ± 0.79 and 0.34 ± 0.17 D, respectively. Vertical steep axis distribution was 73.5% for ACA and 93.3% for PCA. Axis orientation between ACA and PCA matched best for vertical orientation (especially 90° to 120°). Vertical ACA orientation frequency decreased with age, with a more positive sphere and less ACA. Vertical PCA orientation frequency increased with higher PCA. Eyes with vertical ACA orientation were younger and showed a greater white-to-white (WTW) measurement, anterior corneal elevations, ACA and PCA. Eyes with vertical PCA orientation were younger and showed greater anterior corneal elevations and PCA. Normative ACA and PCA data in a Spanish population were presented. Steep axis orientations presented differences with age, WTW, anterior corneal elevations and 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.].

Measurements of Anterior and Posterior Corneal Curvatures with OCT and Scheimpflug Biometers in Patients with Low Total Corneal Astigmatism

Background: Posterior keratometry measurements are evolving features of the optical biometers. The differences between devices have bigger impact for the low astigmatism values. The majority of adults present the corneal astigmatism below 1.5 D. Objectives: To compare the total corneal astigmatism measured with two different technologies in cataract patients with corneal astigmatism below 1.5 D. Material and Methods: Three automated exams were performed on each of the two devices: swept-source optical coherence tomography (SS-OCT) and Scheimpflug biometers. The anterior and total corneal astigmatism and power were analysed. Statistical comparisons were performed for within-subject standard deviation, repeatability, Bland−Altman and vector analysis. Results: Twenty-nine eyes of twenty-seven patients were included. The limits of agreement between anterior and total corneal astigmatism were narrower for the SS-OCT than for the Scheimpflug biometer (−0.16 to 0.29 D and −0.40 to 0.39 D, respectively). The >0.5 D difference between SS-OCT and Scheimpflug total astigmatism was noticed in 5 (17%) of cases. The difference between mean total keratometric power for both devices was statistically significant (0.2 D, p < 0.001). SS-OCT total corneal flat measurements had worse repeatability than Scheimpflug (p = 0.007). Conclusions: For the corneal astigmatism <1.5 D, the difference between anterior and total corneal astigmatism measured with SS-OCT was clinically not significant. The mean anterior and total keratometry values obtained with Scheimpflug and SS-OCT biometers are not interchangeable.

Accuracy of the Goggin Nomogram for 0.50 D Steps in Toric IOL Cylinder Power Calculation

PURPOSE

To examine the accuracy of the cylinder power choice for toric intraocular lenses (IOLs) using the Goggin Nomogram, which adjusts anterior keratometric astigmatic power values for the likely effect of posterior corneal and non-corneal, non-lenticular astigmatism.

METHODS

A consecutive, retrospective case series was based at the Queen Elizabeth Hospital and Ashford Advanced Eye Care in Adelaide, Australia. A total of 586 consecutive eyes of 586 patients underwent phacoemulsification surgery with implantation of a Zeiss AT TORBI 709MP or AT LISA Tri Toric 939 MP toric IOL, calculated using the Goggin Nomogram. The median absolute magnitude of error and geometric mean astigmatic correction index in consecutive eyes with toric IOL cylinder powers of 1.00 to 3.00 diopters (D) were analyzed.

RESULTS

Overall, all eyes receiving IOL cylinder powers of 1.00 to 3.00 D inclusive had a median magnitude of error value of 0.19 D (IQR: 0.31) and astigmatic correction index value of 1.03 (IQR: 0.33). For eyes with with-the-rule, against-the-rule, and oblique astigmatism, the median magnitude of error was 0.18 D (interquartile range [IQR]: 0.29), 0.19 D (IQR: 0.31), and 0.17 D (IQR: 0.39), respectively, and the astigmatic correction index was 1.06 (IQR: 0.28), 1.01 (IQR: 0.35) and 1.08 (IQR: 0.32), respectively.

CONCLUSIONS

Goggin Nomogram adjusted keratometry provided optimal refractive astigmatic outcome in IOL cylinder powers of 1.00 to 3.00 D in eyes with with-the-rule, against-the-rule, and oblique astigmatism. Goggin Nomogram adjusted keratometry compensates for both posterior corneal astigmatism and any other source of ocular astigmatism. [J Refract Surg. 2022;38(5):298-303.].

Agreement between swept-source optical biometry and Scheimpflug-based topography measurements of posterior corneal curvature

PURPOSE

To evaluate agreement of posterior corneal curvature parameters between a swept-source optical coherence tomography-based biometer (IOLMaster 700) and Scheimpflug topography (Pentacam HR) in healthy, myopic eyes.

SETTING

Department of Ophthalmology, Osmangazi Aritmi Hospital, Bursa, Turkey.

DESIGN

Retrospective study.

METHODS

In this study, 59 eyes of 59 patients who applied as candidates for refractive surgery were included. Measurements of the posterior corneal curvature were performed using IOLMaster 700 and Pentacam HR. J0 and J45 vector components were calculated using astigmatic values. Posterior corneal keratometry (K) measurements at flat (K flat) and steep (K steep) axes and J0 and J45 values were compared between the 2 devices. The agreement between the devices was analyzed using the Bland-Altman method. Intraclass correlation coefficients and within-subject SD were calculated to assess the repeatability.

RESULTS

59 eyes of 59 patients were included in this study. The IOLMaster 700 provided significantly flatter K flat and K steep values (P < .001, for both). Significant differences were found in J0 and J45 values (P = 0.13 and P < .001, respectively). The mean differences between K flat, K steep, and J0 and J45 values were 0.49 diopter (D), 0.53 D, 0.04 D, and -0.05 D, respectively.

CONCLUSIONS

The IOLMaster 700 and the Pentacam HR could not be used interchangeably to measure K flat, K steep, and J0 and J45 values of the posterior corneal curvature in healthy, myopic eyes. Both devices showed high repeatability for posterior corneal curvature measurement.

Toric IOL Calculation in Eyes With High Posterior Corneal Astigmatism

PURPOSE

To evaluate different calculation approaches for toric intraocular lens (IOL) calculation in cases with high posterior corneal astigmatism (PCA).

METHODS

Consecutive patients who underwent cataract extraction with implantation of toric IOLs by a single surgeon were reviewed. Eyes with measured PCA of 0.80 diopters (D) or greater were included. Errors in the predicted postoperative refractive astigmatism were calculated for the Abulafia-Koch formula, vector summation of anterior keratometry with posterior tomography, and the Barrett toric calculator using predicted and measured PCA.

RESULTS

One hundred seventy-three consecutive cases of toric IOL implantation were reviewed. Seventeen eyes (10%) had PCA of 0.80 D or greater and were investigated. The mean absolute error was the lowest with Barrett's measured PCA (0.55 ± 0.38) followed by Barrett's predicted PCA mean absolute error (0.65 ± 0.31), vector summation (0.69 ± 0.33), and the Abulafia-Koch formula (0.80 ± 0.36). The rate of eyes with prediction errors within 0.25 D or less was the highest for Barrett's measured PCA (29.4%) followed by Barrett's predicted PCA (5.9%) and no eyes for the Abulafia-Koch formula and vector summation. The mean centroid prediction errors were lowest for Barrett's measured PCA and Barrett's predicted PCA (0.14 ± 0.66 @70, 0.14 ± 0.73 @179, respectively), followed by vector summation (0.35 ± 0.70 @5), and the Abulafia-Koch formula (0.39 ± 0.80 @179).

CONCLUSIONS

The results suggest that in cases of high PCA, the Barrett toric calculator using direct measurements of PCA may have a potential advantage over predicted PCA in toric IOL calculations and vector summation of the anterior and posterior corneal astigmatism. [J Refract Surg. 2020;36(12):820-825.].

Spotlight on the Corneal Back Surface Astigmatism: A Review

Recent evidence indicates that the corneal back surface astigmatism (CBSA) contributes to the refractive state of the eye in cataract surgery, especially with the implantation of toric intraocular lenses. But this has been met with some scepticism. A review of key studies performed over the past three decades shows that the mean CBSA power ranges from 0.18(±0.16)D to 1.04(±0.20)D. The clinical assessment of CBSA is problematic. There is poor agreement between the current automated systems for assessment of CBSA and it is assumed that these systems directly measure the CBSA. But CBSA cannot be measured directly in vivo. A historical review of methods used to quantify the curvature of the posterior corneal surface reveals that CBSA estimated by current systems is based on values for corneal front surface astigmatism, corneal refractive index, central corneal thickness, corneal thickness at peripheral locations and the exact distance between the corneal apex and each one of these peripheral locations. Doubts and errors in these values, coupled with the precise details of the algorithm incorporated to estimate CBSA, are the likely sources of the lack of agreement between current systems. These systematic errors cloud the assessment of CBSA. Mean CBSA may be low, but it varies from case to case. There is a clear need for a realistic, practical procedure for clinicians to independently calibrate systems for estimating CBSA. This would help to reduce uncertainty and the discrepancies between instruments designed to measure the same parameter.

Predicted and Measured Changes in Posterior Corneal Astigmatism after Uncomplicated Femtosecond Assisted LASIK (FsLASIK) and Microkeratome LASIK Correction for Myopia and Low Astigmatism

Purpose: To compare predicted and measured changes in astigmatism at the posterior corneal surface (PCS) after FsLASIK or LASIK.Methods: Astigmatism was measured at both corneal surfaces (Pentacam^TM) before and 3 months after unremarkable FFsLASIK (roup 1,n = 100) or LLASIK (roup 2,n = 100) for myopia (-7.25DS to -0.75DS) and low astigmatism (≤1.00DC). Photoablation was achieved using Schwind Amaris750S^TM laser (Aberration Free profile, centered on corneal vertex). Pre-and postop astigmatic data, according to subjective refraction and estimates for the corneal surfaces (over the central 3.2 mm zone), were subjected to vector analysis to calculate surgically induced astigmatism (SIA) by refraction (SIA_R), at the anterior (SIA_Fact) and posterior corneal surfaces (SIA_Bact). The difference vector between SIA_R and SIA_Fact was regarded as the predicted SIA at the PCS (SIA_Best).Results: Reporting key findings. Mean(±sd,95%CI) SIA_Best and SIA_Bact powers in group 1 were -0.52DC(±0.35,-0.56 to -0.45) and -0.11DC(±0.08,-0.13 to -0.10) in group 1, -0.35DC(0.20,-0.39 to -0.32) and -0.08DC(0.07,-0.09 to -0.06) in group 2. Differences between SIA_Best and SIA_Bact were significant for powers but not axes. Significant correlations(p < .01) were revealed between (I) SIA_R and SIA_Fact powers [Group 1, SIA_R = 0.370.SIA_Fact-0.292,r = 0.299. Group 2, SIA_R = 0.484.SIA_Fact-0.394,r = 0.519] but not the axes and (II) ΔC (difference between pre-[x1] and postop measured PCS astigmatic powers) and x1 [Group 1, ΔC = 0.384x1 + 0.119,r = 0.423. Group 2, ΔC = 0.135x1 + 0.047,r = 0.229,p = .022]. There was no correlation between SIA_Best and SIA_Bact powers or axes.Conclusion: The changes in posterior corneal astigmatic powers according to Pentacam measurements are small and do not account for the deficit between SIA_R and SIA_Fact after FsLASIK or LASIK.

Repeatability of total Keratometry and standard Keratometry by the IOLMaster 700 and comparison to total corneal astigmatism by Scheimpflug imaging

OBJECTIVES

We aimed (1) to assess the repeatability of Total Keratometry (TK) and standard keratometry (K) measurements, as provided by the IOLMaster 700 (Carl Zeiss Meditec), and (2) to compare the corneal astigmatism measured by TK to the total corneal astigmatism (TCA) measured by a Scheimpflug camera (Pentacam AXL, Oculus).

METHODS

Two groups of patients were prospectively enrolled: Group A included previously unoperated eyes undergoing cataract surgery, and Group B eyes with previous myopic corneal excimer laser surgery. TK and K were measured three times by the same examiner. Repeatability was assessed based on the within-subject standard deviation (Sw), test-retest variability, coefficient of variation and intraclass correlation coefficient (ICC). In Group A, TCA was measured once and compared to TK astigmatism. Vector analysis was performed according to Næser.

RESULTS

In Group A (69 eyes) the mean K and TK were, respectively, 43.14 ± 1.37 D and 43.18 ± 1.37 D. In Group B (51 eyes) the mean K and TK were, respectively, 40.14 ± 2.20 D and 39.71 ± 2.35 D. The repeatability of the average K and TK was high (Sw < 0.10D). All measurements revealed an ICC > 0.9. For most measurements the variance of K and TK did not show any statistically significant difference either within groups or between groups. Vectors KP(45) were significantly different between TK astigmatism and TCA.

CONCLUSIONS

TK measurements offer high repeatability in unoperated and post-excimer laser surgery eyes. TK astigmatism and TCA measurements could not be considered interchangeable.

Polar value analysis of astigmatic change and rotational stability after implantation of V4c toric implantable collamer lens

Background

To evaluate the clinical results and rotational stability of V4c toric implantable collamer lens (TICL, STAAR Surgical Company, Monrovia, CA, USA) in patients with moderate to high myopic astigmatism. Retrospective, interventional case series was performed at Shenzhen Eye Hospital, Shenzhen, Guangdong, China.

Methods

This study enrolled 43 patients (72 eyes) who received TICL implantation to correct myopia and myopic astigmatism. The patients underwent visual and refractive examinations before and 1 month after surgery. Astigmatic changes were estimated using polar value analysis. The difference between the achieved axis and the intended axis at the last follow-up was taken as the rotation of the V4c TICL.

Results

At 1 month postoperatively, the mean safety and efficacy indices were 1.17 and 1.13, respectively. A significant reduction of 8.92±2.58 D was observed in the spherical equivalent refraction (SER), which decreased from −9.29±2.41 D preoperatively to −0.37±0.55 D postoperatively. The astigmatic error of treatment in cylinder format was calculated to 0.50±0.41 @ 15.08° relative to the preoperative stronger meridian at 1 month, postoperatively. At 1 month postoperatively, the mean absolute rotation was 8.30±10.00 degrees (median =5.46 degrees; range, 0.00–58.88 degrees).

Conclusions

TICL could achieve good astigmatic outcomes for correcting moderate to high myopic astigmatism. After TICL implantation, corneal astigmatism remained unchanged. To optimize postoperative astigmatic outcomes in TICL, polar value analysis can be used to build a nomogram.

Effect of femtosecond laser-assisted steepest-meridian clear corneal incisions on preexisting corneal regular astigmatism at the time of cataract surgery

AIM

To investigate the clinical efficacy and safety of femtosecond laser-assisted steepest-meridian clear corneal incisions for correcting preexisting corneal astigmatism performed at the time of cataract surgery.

METHODS

This prospective case series study comprised consecutive age-related cataract patients with corneal regular astigmatism (range: +0.75 to +2.50 D) who had femtosecond laser-assisted steepest-meridian clear corneal incisions (single or paired). Corneal astigmatism was performed with the Pentacam preoperatively and 3mo postoperatively. Total corneal astigmatism and steepest-meridian measured in the 3-mm central zone were used to guide the location, size and number of clear corneal incision. The vector analysis of astigmatic change was performed using the Alpins method.

RESULTS

Totally 138 eyes of 138 patients were included. The mean preoperative corneal astigmatism was 1.31±0.41 D, and was significantly reduced to 0.69±0.34 D (equivalent to difference vector) after surgery (P<0.01). The surgically-induced astigmatism was 1.02±0.54 D. The correction index (ratio of target induced astigmatism and surgically-induced astigmatism: 0.72±0.36) as well as the magnitude of error (difference between surgically-induced astigmatism and target induced astigmatism: -0.29±0.51) represented a slight under correction. For angle of error, the arithmetic mean was 1.11±13.70, indicating no significant systematic alignment errors.

CONCLUSION

Femtosecond-assisted steepest-meridian clear corneal incision is a fast, customizable, adjustable, precise, and safe technique for the reduction of low to moderate corneal astigmatism during cataract surgery.

Evaluation of posterior and total corneal astigmatism with colour-LED topography

PURPOSE

To characterise the posterior and total corneal astigmatism using colour point-source light-emitting diodes (LED) topography.

METHODS

In a prospective case series 400 eyes from 400 patients were evaluated by colour-LED topography. Only eyes with normal topographies were considered. The following parameters were studied: magnitude and distribution of SimK and posterior corneal astigmatism, correlation between SimK and posterior corneal astigmatism, and differences in magnitude and axis between total and anterior corneal astigmatism.

RESULTS

The mean SimK corneal astigmatism was 1.21 ± 0.94 D. The mean posterior corneal astigmatism was 0.37 ± 0.24 D. Posterior astigmatism was vertically oriented in 68% of eyes. Twenty-two percent of eyes showed a posterior corneal astigmatism ≥ 0.50 D. The correlation coefficients between SimK and posterior corneal astigmatism were: r² = 0.066; p = 0.371 in WTR eyes, r² = 0.112; p = 0.173 in ATR eyes and r² = -0.019; p = 0.879 in oblique eyes. A difference between SimK and total corneal astigmatism ≥ 0.50 D was found in 7% of eyes. A difference in axis between SimK and total corneal astigmatism ≥ 10° was found in 24% of eyes.

CONCLUSIONS

The percentage of eyes with posterior corneal astigmatism ≥ 0.50 D and the differences between anterior and total corneal astigmatism were higher than those previously reported in the literature. Therefore, this study supports the consideration of total corneal astigmatism magnitude and axis is mandatory for a precise surgical correction of astigmatism.

Characterization of posterior corneal astigmatism in a population with keratoconus

Background: The curvature of the anterior corneal surface is traditionally used as a surrogate to estimate corneal astigmatism. In recent years, increasing importance has been attributed to posterior corneal astigmatism as an indicator. Our aim is to characterize the posterior corneal surface in a population with keratoconus and investigate its predictive value to keratoconus progression. Methods: Retrospective study from a tertiary care centre (Hospital de Santa Maria, Lisbon, Portugal). Eighty-five patients (85 eyes) with keratoconus were included. All patients had two tomographical examinations ≥12 months apart (Pentacam HR). Vector analysis was used to calculate anterior (ACA), posterior (PCA), and total corneal astigmatism (TCA). Multivariate logistic regression was used to assess the predictive value of PCA to keratoconus progression, adjusting for ACA, TCA and several tomographical indices. Results: Study participants had a mean age of 32 (SD = 12.5) years. Mean tomographical keratoconus classification was 2.16 (SD = 0.95), with a mean Kmax of 55.8D (SD = 7.8). Mean power of PCA, ACA and TCA was, respectively, -0.88D (SD = 0.84), 3.74D (SD = 2.36), and 3.06D (SD = 2.01) and its centroids were 0.44D x 15º, 1.65D x 112º, and 1.61D x 106º, respectively. The power of PCA was ≥0.50, 1.00 and 2.00D in 75.3%, 32.9%, and 3.5% of patients, respectively, inducing against-the-rule astigmatism in 60.0% of patients. On average, ACA overestimated TCA in 0.35D x 151º (p < .01). ACA and TCA were highly correlated but showed a lack of agreement for clinical purposes. A predictive role for PCA was excluded. Conclusions: In this population with keratoconus, PCA contributed substantially to TCA. However, PCA was not a valuable predictor for disease progression.

Recent developments in intraocular lens power calculation methods-update 2020

For many decades only a few formulas have been available to calculate the intraocular lens (IOL) power for patients undergoing cataract surgery: the Haigis, Hoffer Q, Holladay 1 and 2 and SRK/T. In recent years, several new formulas for IOL power calculation have been introduced with the aim of improving the accuracy of refraction prediction in eyes undergoing cataract surgery. These include the Barrett Universal II, the Emmetropia Verifying Optical (EVO), the Kane, the Næser 2, the Olsen, the Panacea, the Pearl DGS, the Radial Basis Function (RBF), the T2 and the VRF formulas. Although most of them are unpublished so that their structure is unknown, we give an overview of each formula and report the results of the studies that have compared them. Their performance in short and long eyes is provided and a special focus is given on the issue of segmented axial length, which is a promising method to obtain more accurate outcomes in short and long eyes. Here, the group refractive index originally developed for the IOLMaster may not represent the best method to convert the optical path length into a physical distance. The issue of posterior and total corneal astigmatism (TCA) is discussed in relation to toric IOLs; the latest formulas for toric IOLs and their results are also reported.

A multicenter study of the distribution pattern of posterior corneal astigmatism in Chinese myopic patients having corneal refractive surgery

Including posterior corneal astigmatism (PCA) into consideration may increase the accuracy of astigmatism correction after corneal refractive surgery. In the present study we aim to investigate the distribution pattern of PCA in a large number of myopic patients from multiple ophthalmic centers. There were 7829 eyes retrospectively included in the study. Pentacam data of the eyes were retrieved from the machine and only results with image quality labelled with ‘OK’ were included. Distribution of PCA was slightly positively skewed (Skewness = 0.419, Kurtosis = 0.435, KS P < 0.0001). Mean PCA was 0.34 ± 0.14 D (range: 0.00 D-0.99 D). PCA was ≥ 0.25 D in 74.91% of the eyes and was ≥ 0.50 D in 11.61% of the eyes. In 97.55% of the eyes the steep meridian of PCA was vertical (SMV). PCA magnitude was significantly higher in eyes with SMV PCA (P < 0.0001) or high manifest astigmatism (MA, P < 0.0001). There was a significant correlation between anterior corneal astigmatism (ACA) magnitude and PCA magnitude in all of the eyes (r = 0.704, P < 0.0001). There was also a trend of decreasing frequency and magnitude of SMV PCA with aging (both P < 0.0001). In conclusion, PCA is present in myopic patients having corneal refractive surgery and PCA magnitude is increased with higher MA or ACA. Consideration of the impact of PCA on laser astigmatism correction may be necessary.

The Impact of Changes in Corneal Back Surface Astigmatism on the Residual Astigmatic Refractive Error following Routine Uncomplicated Phacoemulsification

Purpose

To determine the significance of any association between intersessional changes in ocular residual astigmatism (RA) and astigmatism at corneal front (FSA) and back (BSA) surfaces following uneventful routine phacoemulsification.

Methods

Astigmatism was evaluated by autorefractometry and subjective refraction and at both the corneal surfaces with Orbscan II™ (Bausch & Lomb) over central 3 mm and 5 mm optical zones at 1, 2, and 3 months after routine phacoemulsification in 103 patients implanted with monofocal nontoric intraocular lenses (IOLs, one eye/patient). Data were subjected to vector analysis to determine the actual change (Δ) in astigmatism (power and axis) for the refractive and Orbscan II findings.

Results

The number of cases that attended where ΔRA was ≥0.50 DC between 1 and 2 months was 52 by autorefractometry and 36 by subjective refraction and between 2 and 3 months was 24 by autorefractometry and 19 by subjective refraction. Vector analysis revealed significant correlations between ΔFSA and ΔRA for data obtained by autorefractometry but not by subjective refraction. At all times, ΔBSA was greater than ΔFSA (p < 0.01). Key findings for ΔBSA values over the central 3 mm zone were between (A) the sine of the axis of ΔRA (y) and sine of the axis of ΔBSA (x) for the data obtained by autorefractometry (between 1 and 2 months, y = 0.749 - 0.303x, r = 0.299, n = 52, p=0.031) and subjective refraction (between 2 and 3 months, y = 0.6614 - 0.4755x, r = 0.474, n = 19, p=0.040) and (B) ΔRA (y) and ΔBSA (x) powers between 2 and 3 months postoperatively for the data obtained by autorefractometry (ΔRA = 0.118 ΔBSA + 0.681 r = 0.467, n = 24, p=0.021) and subjective refraction (ΔRA = 0.072 ΔBSA + 0.545 r = 0.510, n = 19, p=0.026).

Conclusion

Changes in the ocular residual refractive astigmatic error after implanting a monofocal nontoric IOL are associated with changes in astigmatism at the back surface of the cornea within the central optical zone.

Effect of 1.8-mm steep-axis clear corneal incision on the posterior corneal astigmatism in candidates for toric IOL implantation

Background

In the present study, we aimed to analyze the effects of cataract surgery using a 1.8-mm steep-axis clear corneal incision (CCI) on the posterior corneal surfaces based on the keratometry from the rotating Scheimpflug imaging device (Pentacam HR) in candidates for toric intraocular lens (IOL) implantation.

Methods

Preoperative and at least 1-month postoperative data measured by Pentacam HR were collected in patients for toric IOL implantation. Surgically induced astigmatism on the posterior cornea (P-SIA) was calculated based on the preoperative and postoperative keratometric data, and the related factors of P-SIA were analyzed.

Results

A total of 60 eyes from 56 patients were enrolled. The preoperative anterior, posterior and total corneal astigmatism was 1.58 ± 0.61 D,0.28 ± 0.22 D and 1.70 ± 0.52 D respectively. The postoperative anterior, posterior and total corneal astigmatism was 1.26 ± 0.68 D, 0.41 ± 0.26 D and 1.30 ± 0.51 D respectively. The astigmatism was significantly decreased on anterior surface (P<0.001, paired t-test) and increased on posterior surface (P<0.001, paired t-test). The mean of P-SIA calculated by Holladay–Cravy–Koch method was 0.34 ± 0.20 D, with 0.5 D or greater accounting for 26.7%. A statistically significant correlation was observed between the P-SIA and preoperative anterior corneal astigmatism (r = 0.29, P = 0.024), as well as preoperative posterior corneal astigmatism (r = 0.27, P = 0.038). Multivariate regression analysis showed the preoperative anterior and posterior corneal astigmatism had a significant effect on P-SIA (F = 7.344, P = 0.001).

Conclusions

In candidates for toric IOL implantation with a 1.8-mm steep-axis CCI, the incision caused a significant reduction of the anterior corneal astigmatism but an increase of the posterior corneal astigmatism. P-SIA could not be ignored, and it played a significant role in SIA, especially in cases with higher preoperative anterior or posterior corneal astigmatism.

Management of Cataract in Patients with Irregular Astigmatism with Regular Central Component by Phacoemulsification Combined with Toric Intraocular Lens Implantation

Purpose

To evaluate visual acuity (VA) and refractive status in patients with cataract and irregular astigmatism with a regular central component after phacoemulsification with implantation of a toric intraocular lens (IOL).

Methods

Patients with cataract associated with irregular astigmatism with a regular central component were enrolled. All patients underwent phacoemulsification and toric IOL implantation. Postoperative visual acuity, residual astigmatism, toric IOL rotation, higher-order aberration, and objective and subjective visual quality were measured 3 months after surgery.

Results

Twenty-three eyes were included in the study. The logMAR corrected and uncorrected distance visual acuity values were decreased at 3 months postoperatively (p  <  0.005). The preoperative average corneal astigmatism and postoperative residual astigmatism were 1.15–6.97 D (1.99 ± 1.26 D) and 0–2.75 D (0.65 ± 0.57 D), respectively. The average IOL rotation was 3.17 ± 2.01°. Some objective indicators of visual quality, including the modulation transfer function (p  <  0.05), Strehl ratio (p  <  0.005), 100% VA (p  <  0.005), 20% VA (p  <  0.005), and 9% VA (p  <  0.005), were significantly higher than the corresponding preoperative values. The objective scatter index (p  <  0.005) was significantly lower than that before surgery. The postoperative VF-14 scale score was 83.99 ± 14.58.

Conclusion

Toric IOL implantation has a good corrective effect on certain specific types of corneal irregular astigmatism with cataract. This effect can be attributed to its ability to correct the regular component of irregular astigmatism. The indications for toric IOL implantation could be expanded to some extent, thereby bringing benefit to more patients.

García Á, Piñero DP. Comparison of Standard and Total Keratometry Astigmatism Measured with three Different Technologies

Purpose:

To compare the keratometric and total corneal astigmatism measures provided by three different technologies as well as to assess the level of interchangeability among them.

Methods:

A Prospective, comparative study enrolling 94 eyes from 53 patients (age, 29-77 years) was carried out. All participants were patients with the diagnosis of cataract or patients with a transparent crystalline lens but seeking surgical presbyopia correction. A complete eye examination was performed in all eyes, including corneal analysis with three different devices: IOL-Master 700 (Carl Zeiss Meditec), Cassini (i-Optics), and Pentacam (Oculus Optikgeräte GmbH). Interchangeability of standard and total keratometric readings (equivalent keratometric readings for Pentacam) and astigmatism measures with these three systems were evaluated with the Bland-Altman analysis.

Results:

Significantly higher standard and total keratometric readings were obtained with the IOL-Master compared to the other two systems (p<0.001). Likewise, a significantly higher magnitude of standard and total keratometric astigmatism was obtained with the Cassini system (p<0.001). Ranges of the agreement for corneal power measurements between devices varied from 0.58 D to 1.53 D, whereas they ranged from 0.46 D to 1.37 D for standard and total astigmatism measurements.

Conclusion:

Corneal power and astigmatism measures obtained with IOL-Master 700, Cassini, and Pentacam systems cannot be used interchangeably. The impact of these differences on the refractive predictability achieved with different types of intraocular lenses (IOL) should be evaluated in the future in order to define which is the best corneal evaluation approach for optimizing the IOL power calculations.

Rotational stability and refractive outcomes of a single-piece aspheric toric intraocular lens with 4 fenestrated haptics

PURPOSE

To assess the outcomes of implantation of a single-piece toric intraocular lens (IOL) with 4 fenestrated haptics.

SETTING

IRCCS Fondazione Bietti, Rome, Italy.

DESIGN

Prospective case series.

METHODS

All patients who had implantation of the Mini Toric Ready IOL were consecutively enrolled. Intraoperatively, the IOL was aligned using an automated system. Follow-up visits were performed at 1 day, 1 week, and 1, 3, and 6 months. At each visit, retroillumination pictures were taken to assess IOL orientation; visual acuity and refraction were also measured.

RESULTS

The final analysis comprised 63 eyes (63 patients). From the first to the last follow-up, the mean arithmetic rotation was -0.2 degrees ± 3.5 (SD) (range -13 to +10 degrees) and the mean absolute rotation was 1.6 ± 3.1 degrees. Intraocular lens rotation from the first to the last examination was within 5 degrees in 92.1% of eyes and on consecutive visits, within 5 degrees in 98.4% or more of eyes. By 6 months, 10 IOLs (15.9%) had rotated clockwise and 10 counterclockwise. Linear regression did not show a statistically significant relationship between rotational stability and the axis of placement with any preoperative parameter (eg, axial length). The mean magnitude of preexisting corneal astigmatism was 1.9 ± 0.7 diopters (D) (range 0.76 to 3.72 D). At the last follow-up, the mean magnitude of refractive astigmatism was 0.5 ± 0.4 D (range 0.0 to 1.5 D); the difference was statistically significant (P < .05).

CONCLUSION

The toric IOL showed good rotational stability and is an option for correcting corneal astigmatism at the time of cataract surgery.

Effects of steep-axis incision on corneal curvature in one-handed phacoemulsification

AIM

To examine the effects of one-handed phacoemulsification with steep-axis incision on corneal curvature and analyze surgically induced astigmatism (SIA) on the true net power, anterior and posterior corneal surfaces.

METHODS

Patients with cataracts underwent one-handed phacoemulsification with a 2.4-mm steep-axis of clear corneal incision (CCI) based on true net power. CCI was created under the guidance of Verion. Central corneal thickness (CCT), keratometry readings of the true net power and anterior and posterior corneal surface were obtained using Pentacam. Biometry, such as axial length, anterior chamber depth (ACD) and white-to-white (WTW) were performed using Lenstar pre- and 3mo post-operatively.

RESULTS

The study evaluated 68 eyes of 65 patients. The mean age was 65.93±9.40y; CCT was 529.21±37.40 µm; WTW was 11.59±0.35 mm. Regarding true net power, keratometric value at the flattest corneal meridian for the 3-mm central zone (Ks) was significantly decreased postoperatively (P=0.031). Keratometric value at the steepest corneal meridian for the 3-mm central zone (Kf) was increased postoperatively (P>0.05). Astigmatism of true net power was 1.21±0.56 D preoperatively and significantly decreased to 1.02±0.58 D postoperatively (P=0.021). On the anterior corneal surface, no significant difference in Ks and Kf was noted pre- versus postoperatively. Anterior corneal astigmatism was 1.08±0.51 D preoperatively and significantly decreased to 0.87±0.46 D postoperatively (P=0.002). On the posterior corneal surface, Ks and Kf were significantly increased postoperatively (all P<0.05), and posterior corneal astigmatism also increased (P=0.008). The SIA values of true net power and the anterior and posterior corneal surfaces at 3mo postoperatively were 1.26±0.63 D (range: 0.11 to 2.80 D), 1.05±0.54 D (range: 0.23 to 2.40 D), and 0.21±0.17 D (range: 0.01 to 0.07 D), respectively.

CONCLUSION

One-handed phacoemulsification with steep-axis incision can effectively decrease astigmatism of true net power and anterior corneal astigmatism. In the same surgery, the difference in personal SIA potentially originated from a difference in personal corneal thickness and diameter, both CCT and WTW distance should always be measured preoperatively when planning steep-axis phacoemulsification.

Posterior corneal astigmatism: a review article

Most human eyes show at least a small degree of corneal astigmatism and it can arise from both surfaces of the cornea. The shape of the anterior corneal surface provides no definitive basis for knowing the toricity of the posterior surface. In the previous studies, average astigmatism of the posterior corneal surface was -0.26 to -0.78 diopter. The radius of the posterior corneal surface is less than the radius of the anterior corneal surface. Most studies have found a clear correlation between the anterior and posterior corneal asphericities and the asphericity of the posterior surface is independent of the vertex radius of curvature, refractive error and gender. In contrast to the anterior corneal surface, the asphericity of the posterior corneal surface varies significantly between meridians. The anterior and posterior corneal surface would have approximately parallel principal meridians and both of these surfaces are often flatter in the horizontal meridian than the vertical one. This is especially true in the higher degrees of corneal astigmatism, and then about 10% of any anterior corneal astigmatism is neutralized by an astigmatism arising from the posterior corneal surface. Although the second corneal surface only contributes to about 10% of the total refractive power of the eye, a precise knowledge of its morphology is needed for the correct diagnosis and monitoring the corneal diseases or the surgical interventions and in many eyes neglecting the posterior corneal surface measurement may lead to significant deviations from the corneal astigmatism estimation. In this article, we have reviewed the shape and the toricity of the posterior corneal surface and also the effect of age on it. We investigated the contribution of posterior corneal astigmatism to the total corneal astigmatism and evaluated the accuracy of corneal astigmatism estimation by neglecting the posterior corneal surface measurement.

Distribution and related factors of corneal regularity and posterior corneal astigmatism in cataract patients

Purpose

To study the distribution of posterior corneal astigmatism (PCA) and its influencing factors in Chinese patients before cataract surgery.

Patients and methods

A retrospective study was conducted in the First Affiliated Hospital of Soochow University, Suzhou, China. In all, this study enrolled 121 eligible eyes of 121 cataract patients. The astigmatism, aberrations and Q value of anterior, posterior and total cornea and anterior segment parameters (ACD, CCT, WTW, ATA) were measured by the Sirius System, and AL was measured by Lenstar LS 900. Cataract was diagnosed using slit-lamp examination.

Results

The mean age of patients was 67.44±10.66 years old. Mean PCA was 0.31±0.17 (range 0.05–1.09) D and 85.9% eyes had PCA values <0.5 D. With-the-rule (WTR) astigmatism predominated the anterior cornea astigmatism (ACA) (48.8%) and total corneal astigmatism (TCA) (61.2%), while against-the-rule (ATR) astigmatism predominated posterior (86.0%). Significant positive correlation was found between the astigmatic power vector (APV) of ACA and PCA (Pearson correlation=0.318, P<0.001); TCA and PCA (Pearson correlation=0.204, P=0.025); keratometric astigmatism and PCA (Pearson correlation=0.356, P<0.001); this study also found a positive correlation between primary spherical aberration (Z4°) of the total cornea and PCA (Pearson correlation=0.266, P=0.003); primary spherical aberration (Z4°) of the corneal front surface and PCA (Pearson correlation=0.260, P=0.004); total corneal aberrations (Total cornea root mean square [RMS]) and PCA (Pearson correlation=0.327, P<0.001); total corneal higher-order aberrations (Total HOA RMS) (Pearson correlation=0.232, P=0.011); total corneal lower-order aberrations (Total LOA RMS) (Pearson correlation=0.250, P=0.006). A positive linear correlation between Q value of corneal front surface and PCA, either 6 mm pupil diameter (Pearson correlation=0.264, P=0.003) or 8 mm pupil diameter (Pearson correlation=0.184, P=0.043) was found in this study.

Conclusion

Corneal aberration, Q value (front surface specifically) was essential that we need to take into consideration when we conduct PCA and intraocular lens measurement in clinics.

Corneal dioptric power and astigmatism: A comparison between colour light-emitting diode based (CassiniTM) and Scheimpgflug technology (PentacamTM) topography

AIM

To determine the agreement and to compare the measurements obtained from a colour light-emitting diode based (Cassini^TM) and Scheimpflug (Pentacam^TM) based topography in the evaluation of the anterior, posterior, and total corneal power and astigmatism.

METHODS

A total of 30 eyes from 30 healthy patients were consecutively measured using Pentacam^TM and Cassini^TM. The main evaluated parameters were the anterior, posterior, and total dioptric power, and a power vector analysis of the astigmatism. The agreement between both devices was analysed using the intraclass correlation coefficient (ICC) and performing Bland-Altman plots. The comparison of means was performed using paired Student t-test.

RESULTS

The agreement between both devices when comparing the anterior and total corneal dioptric power was very high (ICC>0.85), but not when studying the posterior cornea (ICC<0.5). In the astigmatism analysis, measurements from the anterior cornea also showed an excellent agreement (ICC>0.78), but was poor for the corneal posterior surface (ICC<0.31). When studying the corneal dioptric power, no statistically significant differences were found for the anterior surface (P>.05), but Pentacam^TM obtained higher values for posterior and total surfaces (P<.001). As regards the magnitude of the astigmatism, no significant differences were found between both devices.

CONCLUSION

Both devices were highly comparable when studying the anterior cornea, but the agreement was poor-moderate when measuring posterior cornea. Therefore, the data obtained by both topographers are not interchangeable.

Consensus on the management of astigmatism in cataract surgery

This project was aimed at achieving consensus on the management of astigmatism during cataract surgery by ophthalmologists from Latin America using modified Delphi technique. Relevant peer-reviewed literature was identified, and 21 clinical research questions associated with the definition, classification, measurement, and treatment of astigmatism during cataract surgery were formulated. Twenty participants were divided into seven groups, and each group was assigned three questions to which they had to respond in written form, after thoroughly reviewing the literature. The assigned questions with corresponding responses by each group were discussed with other participants in round 4 – presentation of findings. The consensus was achieved if approval was obtained from at least 80% of participants. The present paper provides several agreements and recommendations for management of astigmatism during cataract surgery, which could potentially minimize the variability in practice patterns and help ophthalmologists adopt optimal practices for cataract patients with astigmatism and improve patient satisfaction.

Comparison of Color Light-Emitting Diode Corneal Topographer and Dual Rotating Scheimpflug-Placido Topographer

Purpose

To compare measurements of anterior and posterior keratometric values, using a color light-emitting diode corneal topographer and a dual rotating Scheimpflug-Placido topographer.

Methods

Anterior and posterior corneal index measurements were performed using a color light-emitting diode corneal topographer (Cassini) and a dual rotating Scheimpflug-Placido topographer (Galilei G4) and then compared. The paired t-test, intraclass correlation coefficients (ICCs), and Bland-Altman plots were used to evaluate the agreement between measurements.

Results

Sixty postrefractive surgery eyes and 60 normal eyes were evaluated. Both the color light-emitting diode corneal topographer and the dual rotating Scheimpflug-Placido topographer provided highly repeatable corneal measurements (ICC > 0.969). The agreement levels between the 2 devices for anterior corneal power, astigmatism magnitude, and J0 and J45 values were ICC > 0.906 for the total group. However, the ICC values for posterior corneal power, astigmatism magnitude, and J0 and J45 values were lower than 0.681 for the total group.

Conclusions

The anterior keratometric values obtained by the color light-emitting diode corneal topographer and the dual rotating Scheimpflug-Placido topographer showed high agreement levels, but the posterior keratometric values showed lower agreement levels.

Agreement Between Internal Astigmatism and Posterior Corneal Astigmatism in Pseudophakic Eyes

PURPOSE

To directly measure internal astigmatism and evaluate its agreement with posterior corneal astigmatism in pseudophakic eyes.

METHODS

This prospective study enrolled 32 eyes of 32 patients (18 women, 56.3%) who underwent phacoemulsification with implantation of a non-toric monofocal intraocular lens (IOL). Two months postoperatively, posterior corneal astigmatism was measured using a Pentacam Scheimpflug analyzer (Oculus Optikgeräte GmbH, Wetzlar, Germany). Manifest refractive astigmatism was measured after fitting a spherical hard contact lens. This refractive astigmatism that was vertexed to the corneal plane was considered internal astigmatism. The magnitudes of internal and posterior corneal astigmatism were compared. The relationship and agreement between these two astigmatisms were investigated using the Spearman correlation coefficient and Bland-Altman plots, respectively.

RESULTS

The mean patient age was 56.3 ± 9.6 years. IOL decentration or tilt and posterior segment abnormalities were not encountered in any cases postoperatively. The mean refractive astigmatism measured before fitting the hard contact lens was -0.81 ± 0.56 diopters (D). Internal astigmatism (-0.17 ± 0.21 D) was significantly different from posterior corneal astigmatism (-0.30 ± 0.15 D; P = .046). Regression analysis demonstrated a weak association between internal astigmatism and posterior corneal astigmatism (r² = 0.22, P = .013). Bland-Altman plots produced 95% limits of agreement for these two astigmatisms from -0.49 to 0.75 D.

CONCLUSIONS

A significant but weak correlation was found between the magnitudes of internal astigmatism and posterior corneal astigmatism in the pseudophakic eyes. This result indicates that Pentacam measurement of the posterior cornea did not compare well with a "gold standard" of refraction-derived values. [J Refract Surg. 2018;34(6):379-386.].

Age-related changes in with-the-rule and oblique corneal astigmatism

PURPOSE

To describe the age-related changes in with-the-rule (WTR) and oblique keratometric astigmatism (KA), posterior corneal astigmatism (PCA) and total corneal astigmatism (TCA).

METHODS

We used a Pentacam HR (high-resolution) rotating Scheimpflug camera to determine the KA, PCA and TCA in the right eyes of 710 patients, aged from 20 to 88 years. The age-related changes along the vertical, horizontal and oblique meridians were analyzed with Naeser's polar value method in a cross-sectional study.

RESULTS

In the whole group, all meridional astigmatic powers and polar values were stable in the age groups from 20 to 49 years, followed by a 1.0 dioptre (D) against-the-rule (ATR) change in KA and TCA, and a 0.12 D reduction in against-the-rule PCA. A nasal rotation of the steep meridian in KA and TCA was noted in the 70-88 years old. The PCA averaged approximately 0.25 D ATR in all age groups. Females displayed the same early astigmatic stability as in the whole group, while male eyes demonstrated a linear decay from 1.5 D WTR at 20 years to 0.5 D ATR astigmatism for the oldest patients.

CONCLUSION

Corneal astigmatism is stable until the age of 50 years; thereafter both keratometric and total corneal astigmatism show a 0.25 D ATR change per 10 years. The average 0.25 D ATR PCA compensates the predominant keratometric WTR astigmatism in the younger patients and increases the TCA in the elderly with keratometric ATR astigmatism. The gender-based differences in age-related astigmatism require further studies.

Distribution of posterior corneal astigmatism and aberration before cataract surgery in Chinese patients

PURPOSE

To study the prevalence of posterior corneal astigmatism (PCA) and aberration in Chinese eyes before cataract surgery.

METHODS

A cross-sectional study was conducted in Eye and ENT Hospital of Fudan University, Shanghai. In all, we enrolled 1976 eligible eyes of 1976 cataract patients. The astigmatism and aberrations of anterior and posterior cornea were measured by the rotating Scheimpflug System (Pentacam HR, Oculus). Cataract was diagnosed using slit-lamp examination.

RESULTS

The mean age of patients was 61.82 ± 13.67 years old. Mean PCA was 0.28 ± 0.16 (range 0-1.0) D and 87.04% eyes had PCA values <0.5 D. WTR astigmatism predominated the anterior cornea astigmatism (43.1%), while ATR astigmatism predominated posterior (85.4%) and total corneal astigmatism (47.2%). We found a shift tendency of WTR to ATR with aging in anterior corneal astigmatism, while PCA remains ATR. A positive correlation between the magnitude of anterior and posterior corneal astigmatism (r² = 0.089, P < 0.001) was found, especially in WTR anterior cornea astigmatism eyes (r² = 0.298, P < 0.001). Compared with total corneal astigmatism, anterior corneal measurements overestimated WTR astigmatism by a mean of 0.24 ± 0.13 (D), and underestimated ATR astigmatism and oblique astigmatism in most eyes. Furthermore, anterior corneal aberrations measurements overestimated the total corneal aberration in most eyes.

CONCLUSIONS

About 12.96% of eyes had PCA ≥0.5 D. The posterior surface remained ATR astigmatism in most cases with aging. Neglecting the posterior cornea would result in overestimation in WTR anterior corneal eyes and underestimation in ATR and oblique anterior corneal eyes. Also, the posterior corneal aberration was also essential in clinics.

Customized Toric Intraocular Lens Implantation in Eyes with Cataract and Corneal Astigmatism after Deep Anterior Lamellar Keratoplasty: A Prospective Study

Purpose

To investigate the effectiveness of toric intraocular lenses (IOLs) for treating corneal astigmatism in patients with cataract and previous deep anterior lamellar keratoplasty (DALK).

Setting

San Giovanni-Addolorata Hospital, Rome, Italy.

Design

Prospective interventional case series.

Methods

Patients undergoing cataract surgery after DALK for keratoconus were enrolled. Total corneal astigmatism (TCA) was assessed by a rotating Scheimpflug camera combined with Placido-disk corneal topography (Sirius; CSO, Firenze, Italy). A customized toric IOL (FIL 611 T, Soleko, Rome, Italy) was implanted in all eyes. One year postoperatively, refraction was measured, the IOL position was recorded, and vectorial and nonvectorial analyses were performed to evaluate the correction of astigmatism.

Results

Ten eyes of 10 patients were analyzed. The mean preoperative TCA magnitude was 4.92 ± 1.99 diopters (D), and the mean cylinder of the IOL was 6.18 ± 2.44. After surgery, the difference between the planned axis of orientation of the IOL and the observed axis was ≤10° in all eyes. The mean surgically induced corneal astigmatism was 0.35 D at 20°. The mean postoperative refractive astigmatism power was 1.13 ± 0.94 D; with respect to preoperative TCA, the reduction was statistically significant (p < 0.0001). The mean change in astigmatism power was 3.80 ± 1.60 D, corresponding to a correction of 77% of preoperative TCA power. Nine eyes out of 10 had a postoperative refractive astigmatism power ≤ 2D.

Conclusions

Toric IOLs can effectively correct corneal astigmatism in eyes with previous DALK. The predictability of cylinder correction is partially lowered by the variability of the surgically induced changes of TCA. This trial is registered with NCT03398109.

Effect of the posterior corneal surface on total corneal astigmatism in patients with age-related cataract

AIM

To explore the effect of the posterior astigmatism on total corneal astigmatism and evaluate the error caused by substituting the corneal astigmatism of the simulated keratometriy (simulated K) for the total corneal astigmatism in age-related cataract patients.

METHODS

A total of 211 eyes with age-related cataract from 164 patients (mean age: 66.8±9.0y, range: 45-83y) were examined using a multi-colored spot reflection topographer, and the total corneal astigmatism was measured. The power vector components J₀ and J₄₅ were analyzed. Correlations between the magnitude difference of the simulated K and total cornea astigmatism (magnitude difference_SimK-Tca), anterior J₀, and absolute meridian difference (AMD) between the anterior and posterior astigmatisms were calculated. To compare the astigmatism of the simulated K and total cornea both in magnitude and axial orientation, we drew double-angle plots and calculated the vector difference between the two measures using vector analysis. A corrective regression formula was used to adjust the magnitude of the simulated K astigmatism to approach that of the total cornea.

RESULTS

The magnitude difference_SimK-Tca was positively correlated with the anterior corneal J₀ (Spearman's rho= 0.539; P<0.001) and negatively correlated with the AMDR (Spearman's rho=-0.875, P<0.001). When the anterior J₀ value was larger than 1.3 D or smaller than -0.8 D, the errors caused by determining the total corneal astigmatism with the karatometric calculation tended to be greater than 0.25 D. An underestimation by 16% was observed for against the rule (ATR) astigmatism and an overestimation by 9% was observed for with the rule (WTR) astigmatism when ignoring the posterior measurements.

CONCLUSION

Posterior corneal astigmatism should be valued for more precise corneal astigmatism management, especially for higher ATR astigmatism of the anterior corneal surface. We suggest a 9% reduction in the magnitude of the simulated K in eyes with WTR astigmatism, and a 16% addition of the magnitude of the simulated K in eyes with ATR 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.

Assessment of Corneal Keratometric and Astigmatism Measurements Using Verion System and Other Instruments in Cataract Patient

PURPOSE

To compare keratometry and corneal astigmatism measurements obtained by the Verion Image Guided System to those obtained by automated keratometry (IOLMaster), manual keratometry (YZ38, Suzhou 66 visual Polytron Technologies Inc., China), and Scheimpflug imaging (Pentacam HR) in eyes with cataract.

METHODS

A total of 149 cataractous eyes of 149 patients were examined and categorized as low astigmatism (<1.0 D, N = 50), moderate astigmatism (1.0-2.0 D, N = 49), and high astigmatism (>2.0 D, N = 50). The flattest and the steepest keratometric values (Kf and Ks), the magnitude of astigmatism (Ast), the orientation of the steepest meridian (Axis), and power vectors J₀ and J₄₅ were compared.

RESULTS

Keratometry readings (Kf, Ks, and Km) obtained by the Verion system showed statistically significant differences as compared to the other three devices. The magnitude of astigmatism (Ast) measured by the Verion (1.50 ± 0.85 D) was similar to that measured by the YZ38 (1.45 ± 0.82 D, P = 0.110) and slightly lower than that by the IOLMaster (1.56 ± 0.87 D, P = 0.014), but much higher than that by the Pentacam (1.36 ± 0.81 D, P = 0.000) significantly. However, no statistically significant differences were observed in the J₀ and J₄₅ vectors in the whole sample, besides moderate and high astigmatism subgroups. A difference in astigmatism magnitude of 0.50 D or more was detected between the Verion system and other three devices most commonly in moderate astigmatism eyes (16.3-24.5%). The difference in the location of the steep meridian was greater than 10 degrees most frequently in the low astigmatism eyes (26.0-52.0%).

CONCLUSIONS

Keratometric and astigmatic results obtained with Verion were not completely interchangeable with those obtained with IOLMaster, manual keratometry, and Pentacam. The individual differences in power and orientation of the corneal cylinder should be considered while selecting the appropriate toric intraocular lens.

Agreement between total corneal astigmatism calculated by vector summation and total corneal astigmatism measured by ray tracing using Galilei double Scheimpflug analyzer

PURPOSE

To evaluate the agreement between total corneal astigmatism calculated by vector summation of anterior and posterior corneal astigmatism (TCA_Vec) and total corneal astigmatism measured by ray tracing (TCA_Ray).

METHODS

This study enrolled a total of 204 right eyes of 204 normal subjects. The eyes were measured using a Galilei double Scheimpflug analyzer. The measured parameters included simulated keratometric astigmatism using the keratometric index, anterior corneal astigmatism using the corneal refractive index, posterior corneal astigmatism, and TCA_Ray. TCA_Vec was derived by vector summation of the astigmatism on the anterior and posterior corneal surfaces. The magnitudes and axes of TCA_Vec and TCA_Ray were compared. The Pearson correlation coefficient and Bland-Altman plots were used to assess the relationship and agreement between TCA_Vec and TCA_Ray, respectively.

RESULTS

The mean TCA_Vec and TCA_Ray magnitudes were 0.76±0.57D and 1.00±0.78D, respectively (P<0.001). The mean axis orientations were 85.12±30.26° and 89.67±36.76°, respectively (P=0.02). Strong correlations were found between the TCA_Vec and TCA_Ray magnitudes (r=0.96, P<0.001). Moderate associations were observed between the TCA_Vec and TCA_Ray axes (r=0.75, P<0.001). Bland-Altman plots produced the 95% limits of agreement for the TCA_Vec and TCA_Ray magnitudes from -0.33 to 0.82D. The 95% limits of agreement between the TCA_Vec and TCA_Ray axes was -43.0 to 52.1°.

CONCLUSION

The magnitudes and axes of astigmatisms measured by the vector summation and ray tracing methods cannot be used interchangeably. There was a systematic error between the TCA_Vec and TCA_Ray magnitudes.

Estimating Total Corneal Astigmatism From Anterior Corneal Data

PURPOSE

To determine keratometric astigmatism (KA), posterior corneal astigmatism (PCA), and total corneal astigmatism (TCA) in 951 normal eyes, to establish a model for estimating TCA from anterior corneal data, and to test this method in a new group of eyes with toric intraocular lenses (TIOLs).

METHODS

We used a Pentacam HR (high-resolution) Scheimpflug camera to determine KA, PCA, and TCA in 951 normal eyes. A model to estimate TCA from anterior corneal data was evaluated by the difference (=error) between the measured TCA and the estimated value. The model was tested in 40 eyes with TIOLs.

RESULTS

KA, TCA, and PCA averaged 1.06 (±0.85) D, 1.05 (±0.83) D, and 0.33 (±0.17) D. The error of the model to estimate TCA averaged zero with an SD of ±0.21 D. Application of this model and of direct Pentacam TCA measurements in TIOL calculation gave similar results, namely a slight reduction of overcorrection in with-the-rule astigmatism, but an eradication of undercorrection in against-the-rule astigmatism.

CONCLUSIONS

It was possible to estimate TCA accurately from anterior corneal data with a new formula. However, application of both this model on keratometric data and of direct Pentacam measurements in a group of 40 eyes with TIOLs did not completely eradicate the refractive error in TIOL calculation. More studies comparing Pentacam TCA and refractive astigmatism are required.

Total Corneal Astigmatism Measurements: Agreement Between 2 Rotating Scheimpflug Cameras

PURPOSE

To investigate agreement between rotating Scheimpflug camera (Pentacam HR, Oculus) and rotating Scheimpflug camera combined with Placido disc corneal topography (Sirius, CSO) in measuring total corneal astigmatism (TCA).

METHODS

In this observational study, all patients undergoing cataract surgery with preoperative measurement of TCA by both devices and a validated corneal topographer (Keratron, Optikon 2000) were retrospectively evaluated. Astigmatism analysis was performed with and without vector analysis separately in eyes with with-the-rule, against-the-rule, and oblique astigmatism. Vector analysis was performed using the Næser polar system.

RESULTS

In 130 eyes of 130 subjects, nonvectorial analysis revealed that the mean TCA values obtained with the Sirius were higher than the corresponding values given by the Pentacam HR in all subgroups, although the difference was statistically significant only in eyes with against-the-rule astigmatism (P = 0.0009). This finding was confirmed by vector analysis. A TCA magnitude difference greater than 0.5 diopters was observed in 20.8% of cases, and a TCA axis difference greater than 10 degrees was observed in 45.4% of cases. Axis differences dropped to 18.5% when only eyes with astigmatism >0.75 diopters were analyzed and 3 measurements were averaged. The mean difference in the meridional and torsional power of TCA was close to zero in all subgroups, but with relatively large standard deviations (approximately 0.5 D).

CONCLUSIONS

Agreement between both devices in measuring TCA is only moderate with respect to both magnitude and axis orientation.

Polar Value Analysis of Low to Moderate Astigmatism with Wavefront-Guided Sub-Bowman Keratomileusis

Purpose

To evaluate the astigmatic outcomes of wavefront-guided sub-Bowman keratomileusis (WFG-SBK) for low to moderate myopic astigmatism.

Methods

This study enrolled 100 right eyes from 100 patients who underwent WFG-SBK for the correction of myopia and astigmatism. The polar value method was performed with anterior and posterior corneal astigmatism measured with Scheimpflug camera combined with Placido corneal topography (Sirius, CSO) and refractive astigmatism preoperatively and 1 month, 3 months, and 6 months postoperatively.

Results

Similar results for surgically induced astigmatism (SIA) and error of the procedure in both anterior corneal astigmatism (ACA) and total ocular astigmatism (TOA). There was a minor undercorrection of the cylinder in both ACA and TOA. Posterior corneal astigmatism (PCA) showed no significant change.

Conclusions

Wavefront-guided SBK could provide good astigmatic outcomes for the correction of low to moderate myopic astigmatism. The surgical effects were largely attributed to the astigmatic correction of the anterior corneal surface. Posterior corneal astigmatism remained unchanged even after WFG-SBK for myopic astigmatism. Polar value analysis can be used to guide adjustments to the treatment cylinder alongside a nomogram designed to optimize postoperative astigmatic outcomes in myopic WFG-SBK.

Tomographic Analysis of Anterior and Posterior and Total Corneal Refractive Power Changes After Femtosecond Laser-Assisted Keratotomy

PURPOSE

To analyze the effect of penetrating femtosecond laser-assisted keratotomy (pFLAK) during laser lens surgery on anterior and posterior corneal astigmatism and total corneal refractive power (TCRP) astigmatism (CA_ant, CA_post, CA_TCRP) measured with Scheimpflug tomography.

DESIGN

Prospective, interventional case series.

METHODS

This institutional study included 27 eyes of 23 patients (aged 65 ± 8 years) with low-to-moderate CA_TCRP determined with Scheimpflug tomography (Pentacam HR; Oculus, Wetzlar, Germany) after penetrating femtosecond laser-assisted keratotomy (pFLAK) and laser lens surgery. The CA_ant, CA_post, and CA_TCRP were determined before and 1 and 3 months after surgery. Vector analysis according to the Alpins method was used to calculate surgically induced astigmatism (SIA).

RESULTS

The mean preoperative CA_ant (0.97 ± 0.30 diopter [D]) was significantly reduced to 0.63 ± 0.34 D (P < .001). SIA_ant was 0.71 ± 0.37 D. The CA_post showed no significant change, from preoperative 0.26 ± 0.12 D to 0.26 ± 0.10 D postoperatively (P = .625). In line with this finding, SIA_post was low (0.12 ± 0.07 D). The CA_TCRP showed similar results as CA_ant.

CONCLUSION

pFLAKs planned according to Scheimpflug-based CA_TCRP result in a significant reduction of the CA_ant and CA_TCRP, but do not affect the posterior corneal curvature significantly, as measured by Scheimpflug tomography. Further research is required to develop a new valid nomogram for laser-assisted lens surgery.

The Effect of the Degree of Astigmatism on Optical Quality in Children

PURPOSE

To investigate the effect of the degree of astigmatism on optical quality in children. The important objective evaluation parameters we focus on include the RMS of the high-order aberrations, MTF, and PSF.

METHODS

The children, age ranging from 7 to 10 years old, underwent an optometry examination. Fifty-nine children who met the inclusion criteria were divided into three groups: A (1.0 D ≤ astigmatism < 2.0 D), B (2.0 D ≤ astigmatism < 3.0 D), and C (3.0 D ≤ astigmatism < 4.0 D). The OPD-SCAN-III aberrometer was used to measure PSF, MTF, and other optical parameters. Total higher-order aberrations, total coma aberrations, total spherical aberrations, and total trefoil aberrations corresponding to the RMS value, the AR value of MTF, and the SR value of PSF with a 4 mm pupil diameter were assessed.

RESULTS

RMS-HO, RMS-T.Coma, RMS-T.Tre, and RMS-T.Sph in the three groups were significantly increased with increasing the degree of astigmatism, while there were no significant differences in RMS-T.Sph between the groups. The AR value and the SR value decreased with increasing degree of astigmatism, and there were significant differences in the AR value and the SR value.

CONCLUSION

Astigmatism has a significant influence on the higher-order aberrations, MTF, and PSF in the children. The effect of astigmatism value on the optical quality is mainly reflected in the change in these three parameters.

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

PURPOSE

To compare corneal astigmatism derived from total corneal refractive power (CA_TCRP), a ray-tracing method, with that derived from simulated keratometry (CA_SimK), an anterior surface-based method, in candidates for toric intraocular lens (IOL) implantation.

DESIGN

Reliability analysis.

METHODS

In 1 eye of 200 consecutive patients (mean age 71 ± 9 years) with cataract, a Pentacam HR (Oculus) was used to measure CA_TCRP and CA_SimK. Eyes with CA_TCRP >1 diopter (D) were defined as candidates for toric IOL implantation. The estimation difference between CA_TCRP and CA_SimK was analyzed by calculating the arithmetic, absolute, and vector differences between the 2 methods.

RESULTS

Seventy-seven candidates were identified. In the candidates, CA_SimK was <1 D in 22% of cases and underestimated the astigmatism magnitude, on average, by -0.15 ± 0.34 D. The mean absolute and vector difference between CA_TCRP and CA_SimK was 0.31 ± 0.29 D and 0.30 ± 0.29 D × 180 degrees, respectively. The absolute and vector differences between the 2 methods were >0.50 D in 21 of 77 (27.2%) and 25 of 77 (32.5%) eyes, respectively; the proportions were significantly (P < .001) higher than in the eyes with CA_TCRP ≤1 D (0.8% and 9.8%, respectively). The difference in steep meridian alignment between CA_TCRP and CA_SimK was >5 degrees in 22.1% and >10 degrees in 2.6% of cases.

CONCLUSION

The difference between CA_TCRP and CA_SimK, as calculated by Pentacam HR, is greater in candidates for toric IOL implantation than in the general population. That difference considerably influences the candidate and toric IOL power selection in a large proportion of cases.