Predicting Residual Astigmatism in Cataract Surgery

BackgroundTo examine the influence of posterior corneal astigmatism on postoperative refractive astigmatism in pseudophakic eyes after cataract surgery.MethodsThe study enrolled 64 pseudophakic eyes of 50 patients (71.8 ± 9.9 years old, mean ± standard deviation) who had undergone phacoemulsification with non-toric IOL implantation. Refractive astigmatism was measured using an auto ref-keratometer with a 0.01- diopter (D) scale. Two types of corneal astigmatism were calculated using anterior segment optical coherence tomography; keratometric and total corneal astigmatism. Keratometric astigmatism was obtained based on anterior corneal curvature alone and total corneal astigmatism was calculated using both anterior and posterior corneal curvatures. The difference between refractive and corneal astigmatism was computed as the vector difference using 1) refractive and keratometric astigmatism and 2) refractive and total corneal astigmatism.ResultsThe mean refractive, keratometric, and total corneal astigmatism was 0.92 ± 0.48 D, 0.87 ± 0.44 D, and 0.94 ± 0.46 D, respectively. The difference between refractive and keratometric astigmatism (0.70 ± 0.40 D, mean vector of 0.30 D axis 164°) was significantly larger than the difference between refractive and total corneal astigmatism (0.63 ± 0.38 D, mean vector of 0.12 D axis 137°) (P = .019).ConclusionsThe difference between refractive and total corneal astigmatism, calculated using both anterior and posterior corneal curvatures, was significantly smaller than the difference between refractive and keratometric astigmatism using anterior corneal astigmatism alone, implying that the latter overestimates the true postoperative refractive astigmatism and can cause cylindrical inaccuracy after cataract surgery.

To evaluate whether the toric intra-ocular lens (IOL) power calculation based on total corneal astigmatism (TCA) in eyes with high posterior corneal astigmatism (PCA) could result in a systematic over-correction or under-correction after operation. The present study included a mono-centric retrospective study design. The data were collected from 62 consecutive eyes during uncomplicated cataract surgery by a single surgeon with a measured PCA of 0.50 diopters (D) or higher. Toric IOL calculations were made using TCA measurements. The eyes were grouped as either "with-the-rule" (WTR) or "against-the-rule" (ATR) on the basis of the steep anterior corneal meridian. The post-operative refractive astigmatic prediction error was analyzed 1 month post-operatively using the vector analysis by the Alpins method and double-angle plots method. The correction indexes were 1.14 ± 0.29 in the ATR eyes and 1.25 ± 0.18 for the WTR eyes, indicating a tendency toward over-correction. The mean over-correction was 0.22 ± 0.52D in the ATR group and 0.65 ± 0.60D in the WTR group. The magnitude of error (ME) values were significantly different from the ideal value of zero in both groups (ATR: P = 0.03; WTR: P = 0.00). No significant difference in mean absolute error (MAE) in predicted residual astigmatism was found between ATR and WTR groups (0.61 ± 0.42 D versus 0.64 ± 0.39 D; P = 0.54). The ATR group yielded better results, with 48% <0.50D prediction error in the main analysis. The results suggested that in cases of high PCA, the toric IOL calculation, which was performed using TCA, may cause a potential over-correction in the ATR and WTR eyes. For ATR eyes, over-correction led to slight disruption of post-operative visual quality because of the "with-the-rule" residual astigmatism after operation. Therefore, we suggested using TCA for toric IOL calculation in ATR eyes.

PurposeTo investigate the relationship between measured anterior, posterior, and total keratometric astigmatism and post-operative refractive astigmatism (RA) after cataract surgery.Patients and MethodsThis was a retrospective analysis of eyes that consecutively underwent pre-operative measurements of keratometric astigmatism with a swept-source optical coherence tomography (SS-OCT)-based optical biometer and dual-Scheimpflug/Placido disc corneal topographer, cataract surgery with implantation of a monofocal intraocular lens, and post-operative manifest refraction. The difference between post-operative refractive astigmatism and keratometric astigmatism measured using four different ways [Keratometry (K), Simulated Keratometry (SimK), Total Keratometry (TK), and Total Corneal Power (TCP)] was calculated.ResultsFor all 118 eyes, a smaller mean vector difference between post-operative refractive astigmatism and measured keratometric astigmatism was realized with TK (0.08 @ 151) vs TCP2 (0.30 @ 174; p < 0.0006), as well as with K (0.26 @ 173) vs SimK (0.52 @ 177; p = 0.036). The mean vector difference between post-operative refractive astigmatism and TK astigmatism was 0.31 @ 097, 0.21 @ 163, and 0.69 @ 179 in eyes with against-the rule (ATR), oblique, and with-the-rule (WTR) anterior corneal astigmatism, respectively (p < 0.0006). On the other hand, posterior corneal astigmatism did not significantly change with the orientation of anterior corneal astigmatism [0.10 @ 180 for ATR, 0.22 @ 180 for oblique, and 0.28 @ 180 for WTR (p = 0.58)].ConclusionCompared with the other measures of corneal astigmatism, total keratometric astigmatism from the SS-OCT device most closely correlated with post-operative RA. The difference between anterior corneal astigmatism and refractive astigmatism is not completely explained by the contribution from the posterior cornea. Other contributors, such as lens tilt or neuro-adaptation, may be at play.

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.

To evaluate the characteristics of ocular biometric parameters in adult Korean patients with cataract. Department of Ophthalmology, Seoul National University Hospital, Seoul, South Korea. Retrospective case series. Ocular biometric values of 5273 eyes of 5273 Korean patients undergoing cataract surgery measured with the IOLMaster 700 at the Seoul National University Hospital between November 2019 and December 2021 were reviewed. A total of 5273 eyes of 5273 Korean patients were analyzed. The mean ± SD age was 66.1 ± 12.8 years, and 62% were female. Overall, age and ocular biometric parameters were correlated with each other. Particularly, age showed a negative correlation with anterior chamber depth (ACD; r = -0.357), axial length (AL; r = -0.344), and posterior keratometry (PK; r = -0.054) and a positive correlation with lens thickness (LT; r = 0.484), angle α ( r = 0.194), total keratometry (TK; r = 0.137), anterior keratometry (AK; r = 0.129), and angle κ ( r = 0.071). AL showed a positive correlation with ACD ( r = 0.503) and PK ( r = 0.339) and a negative correlation with AK ( r = -0.342), TK ( r = -0.334), LT ( r = -0.288), angle α ( r = -0.220), and angle κ ( r = -0.040). With age, anterior and total corneal astigmatism changed from with-the-rule (WTR) to against-the-rule (ATR) astigmatism. Posterior corneal astigmatism was ATR regardless of age; however, the magnitude decreased with age. Age showed a significant correlation in the order of LT, ACD, and AL. With age, angle α and κ increased, and total corneal astigmatism changes from WTR to ATR, which is mainly affected by changes in anterior corneal astigmatism. AL showed a significant correlation in the order of ACD, AK, PK, and TK. These data are pertinent for improving the result after cataract surgery, especially when using premium intraocular lenses.

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.

PurposeTo determine the percentage of contribution of the magnitude of posterior corneal astigmatism to total corneal astigmatism using Scheimpflug imaging.MethodsThis prospective cross-sectional study was conducted on 356 eyes of 356 patients, where the total corneal astigmatism was calculated by addition of anterior and posterior corneal astigmatism using vector analysis and then the percentage of posterior to total corneal astigmatism was calculated.ResultsThe percentage of contribution of posterior to total corneal astigmatism was about 30% in patients with With The Rule astigmatism and about 8% in patients with Against The Rule astigmatism.ConclusionPosterior corneal astigmatism should not be neglected during calculation of total corneal astigmatism as neglecting posterior corneal astigmatism can result in errors during calculation and correction of astigmatism.

To compare corneal astigmatism obtained from an optical coherence tomography-based biometer (OCT) and dual Scheimpflug analyzer (DSA). Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. Retrospective case series. Consecutive cases with both OCT and DSA measurements were reviewed. Three parameters were analyzed with OCT and DSA: (1) standard keratometric astigmatism (K vs simulated keratometry [SimK]), (2) posterior corneal astigmatism, and (3) total corneal astigmatism (total keratometry [TK] vs total corneal power [TCP]). The magnitudes of corneal astigmatism obtained from the 2 devices were compared. Vector analysis was used to assess differences in corneal astigmatism between devices. In this study 530 corneas in 530 patients were measured. Compared with the DSA, the OCT produced a lower mean magnitude of posterior corneal astigmatism (-0.19 vs -0.29 diopter [D]) and a higher percentage of eyes with magnitude ≤0.25 D (75.5% vs 41.9%) (P < .05). Comparing TK and TCP, (1) TK was greater in magnitudes (1.03 vs 0.98 D); (2) 84.3% of eyes had differences in magnitude of ≤0.50 D; (3) in eyes with TK astigmatism ≥0.5 D, 34.5% and 60.1% of eyes had differences in steep meridian of ≤5 degrees and ≤10 degrees, respectively, and (4) 59.2% of eyes had vector differences of ≤0.50 D. In with-the-rule and against-the-rule eyes, respectively, the vector differences between TK and TCP were 0.16 D @ 83 degrees and 0.17 D @ 12 degrees, and in posterior corneal astigmatism, 0.06 D @ 173 degrees; and 0.15 D @ 175 degrees. There were clinically significant differences in total corneal astigmatism obtained from OCT and DSA devices. Compared with DSA, OCT produced lower values for posterior corneal astigmatism.

Residual astigmatism after toric intraocular lens implantation: Analysis of data from an online toric intraocular lens back-calculator

Purpose:To assess the repeatability of ocular measurements, particularly astigmatism, taken using the latest version of an swept-source optical coherence tomography (SS-OCT) device, IOLMaster 700.Methods:This prospective observational study done in a private eye care centre. Study included 213 eyes of 152 patients diagnosed with cataract. Axial length (AL), Anterior corneal astigmatism (ΔK), Total corneal astigmatism (ΔTK), Aqueous depth (AD), Lens thickness (LT), Iris barycentre distance (IBD) and White to white distance (WTW) were analysed; three measurements were taken for each patient in the same sitting by the same examiner in an undilated state using the SS-OCT device. Repeatability was analysed using intraclass coefficient (ICC) and coefficient of variation (CV) measures, and astigmatism values were transformed into vector components (J0/J45) and categorised based on magnitude.Results:Astigmatism vector components (J0/J45) showed poor repeatability (ICC < 0.5 and CV > 0), while iris coordinates (IBD) and astigmatism magnitude had good correlation (ICC > 0.9) but more variations between the readings which was least for magnitude ≥ 1.5D; however, rest of the parameters demonstrated excellent repeatability (ICC > 0.9 with P value < 0.05).Conclusion:IOLMaster 700 demonstrated good reliability for the parameters measured, although, for astigmatism and iris barycentre distance, more number of readings and cross reference with other devices may be required to get clinically accurate results.

The aim of this study was to compare the effect of corneal irregularity on astigmatism assessment using automated keratometry (AK) (IOLMaster) versus ray tracing keratometry (Pentacam).This is an observational case series approved by the institutional review board of Dongguk University Hospital, Goyang, South Korea.A total of 207 eyes of 207 cataract patients were included. Preoperative corneal astigmatism was measured by both IOLMaster and Pentacam. Corneal irregularity index (IR) was calculated in Fourier analysis map of Pentacam. AK by IOLMaster and total corneal refractive power (TCRP, 3 mm and 4 mm zone analysis with pupil centered) by Pentacam were selected and the difference between the 2 measurements (delta Δ) was calculated using vector analysis. Ocular residual astigmatism (ORA) after cataract surgery was calculated by subtracting 6-month postoperative refractive astigmatism (RA) measurements from corresponding preoperative values (AK, TCRP3, and TCRP4).The mean irregularity index measured was 0.042 ± 0.019 mm (mean ± standard deviation) and was positively correlated with age and magnitude of corneal astigmatism (P < 0.001 and P < 0.05). The difference (Δ) between TCRPs and AK (ΔTCRPs-AK) was 0.43 ± 0.37 (TCRP3) and 0.39 ± 0.35 (TCRP4) diopters. Linear regression analysis revealed that age (P < 0.001), IR (P < 0.001), and AK (P < 0.001) were positively correlated with ΔTCRPs-AK. In highly irregular corneas (IR over 0.77 diopters: mean + 2 standard deviation), postoperative ORAs calculated using TCRPs were significantly lower than ORAs calculated using AK.Corneal irregularities significantly impact astigmatism assessment by IOLMaster (AK) and Pentacam (TCRPs). Compared with AK, TCRPs were more accurate in predicting postoperative residual astigmatism in highly irregular corneas.

To evaluate the efficacy and safety of a new acrylic one-piece toric intraocular lens (IOL). This prospective multicenter clinical trial included 93 eyes of 61 patients that were implanted with a hydrophobic acrylic toric IOL from 2010 to 2012 and followed for 1 year. This IOL uses the platform of a microincision one-piece aspheric IOL, the NY-60 IOL (HOYA, Tokyo, Japan), with three increments in cylindrical power (NHT15, 1.5 diopters [D]; NHT23, 2.25 D; and NHT30, 3.0 D). The inclusion criterion was preoperative corneal astigmatism from 0.75 to 3.00 D. The primary endpoint was uncorrected distance visual acuity (UDVA) of 0.0 logMAR (20/20 Snellen) or better 6 months postoperatively. In addition to UDVA, corrected distance visual acuity (CDVA), residual astigmatism, stability of the IOL alignment, need of realignment, and the rate of Nd:YAG laser capsulotomy were evaluated up to 1 year postoperatively. Errors in astigmatic correction were assessed using Alpin's vector analysis. The primary endpoint was achieved in 54.8% of eyes. One year postoperatively, the logMAR UDVAs were 0.02 ± 0.13, 0.05 ± 0.17, and 0.09 ± 0.14 with models NHT15, NHT23, and NHT30, which corresponds to 0.96 (19/20 Snellen), 0.89 (18/20 Snellen), and 0.82 (16/20 Snellen), respectively. One year postoperatively, the residual astigmatism was 0.66 ± 0.58 D. In each evaluation, the mean absolute change in the position of the axis mark was between 1.93° and 2.32°. Three eyes required repositioning of the IOL axis and 2 eyes received Nd:YAG laser capsulotomy. The correction error showed an undercorrection with against-the-rule astigmatism and overcorrection with with-the-rule astigmatism. The new one-piece toric IOL provided desirable clinical outcomes and stability in eyes with corneal astigmatism.

To evaluate age-related changes in anterior, posterior, and total corneal astigmatism by comparing simulated keratometric astigmatism to total corneal astigmatism. Corneal topography of the anterior and posterior surfaces was evaluated using three-dimensional optical coherence tomography in 419 patients with normal eyes (218 men and 201 women) with ages ranging from 8 to 93 years (mean ± standard deviation: 49.5 ± 23.1 years). Keratometric astigmatism was calculated using the keratometric index (1.3375) and radius of the anterior corneal curvature; anterior and posterior corneal curvature measurements were used to calculate total corneal astigmatism. The keratometric and total astigmatism were 1.08 ± 0.71 diopters (D) and 1.03 ± 0.69 D, respectively. Vector analysis revealed a mean difference between keratometric and total astigmatism of 0.24 ± 0.09 D, which showed a significant correlation to age (P < .0001). In eyes with with-the-rule astigmatism, keratometric astigmatism overestimated total astigmatism. In eyes with against-the-rule astigmatism, keratometric astigmatism underestimated total astigmatism. The anterior corneal surface shifts from with-the-rule to against-the-rule astigmatism with aging, whereas the posterior corneal surface remains as against-the-rule astigmatism in most cases. The variation in the anterior astigmatism is the most important factor contributing to this change. Total corneal astigmatism is a better predictor than keratometric astigmatism for selecting toric intraocular lenses.

Toric Intraocular Lens Calculations Using Ratio of Anterior to Posterior Corneal Cylinder Power.

Phacoemulsification cataract extraction and intraocular lens (IOL) implantation has become the mainstream treatment of cataract.But the postoperative residual astigmatism still influences the postoperative uncorrected visual acuity.Reduce residual astigmatism is currently the ophthalmologists' pursuit.The formation of the residual astigmatism is affected by various factors,which mainly associated with preoperative corneal astigmatism and surgically induced astigmatism.Except for the above reasons,residual astigmatism after Toric IOL implantation has its special reasons.Understanding the reasons of formation of residual astigmatism can provide us the methods how to reduce it.This paper reviewed the causes of the residual astigmatism after phacoemulsification cataract extraction and IOL implantation. Key words: Residual astigmatism; Lens, intraocular; Phacoemulsification