Corneal Biomechanics and Other Factors Associated with Postoperative Astigmatism after Cataract Surgery

This study aimed to investigate the impact of the cornea's biomechanical properties, corneal hysteresis (CH), and corneal resistance factor (CRF) on postoperative astigmatism after cataract surgery and determine the other factors that influence it. Forty eyes of 40 patients (13M/27F; the median age of 74) were included in this prospective study, underwent 2.75 mm incision cataract surgery, and were followed for 30 days. Visits were scheduled at baseline before surgery (V0), the 1st (V1), the 7th (V2), and the 30th (V3) postoperative days. The main parameters estimated and analyzed with Statistica® 14.0.1 were CH, CRF, astigmatism diopter, and axis. Following the cataract surgery, the CH did not significantly change during the study visits (p = 0.109). However, there was a significant change in the CRF from baseline during the study visits (per protocol set) (p = 0.002). After a slight but insignificant increase from V0 to V1, post hoc analysis found a significant decrease in the mean CRF from V1 to V2 (p = 0.049) with no substantial change from V2 to V3. According to the post hoc analysis, the median astigmatism diopter increased significantly only from V0 to V1 (p = 0.001) and slightly but not significantly decreased to the end of the study with the achievement of a near-baseline value. The main predictors for the final astigmatism diopter (R2 = 0.898) obtained by stepwise regression analysis were its values at V0, V1, and V2 (p < 0.001). The CRF at V1 was marginally significant, with a negative parameter estimate of -0.098303 (p = 0.0623). In conclusion, there was no correlation between preoperative CH and CRF and postoperative astigmatism using 2.75 mm incision cataract surgery. However, the final astigmatism diopter's main predictors were its baseline values before cataract surgery, the first, and the seventh postoperative days.

Prevalence data for total corneal astigmatism in cataract patients

PURPOSE

To report the prevalence data for total corneal astigmatism (TCA) in cataract patients.

METHODS

The authors retrospectively collected and analyzed the preoperative biometric data of the patients who underwent cataract surgery in the Department of Ophthalmology, Peking University Third Hospital, from January 2019 to May 2023.

RESULTS

The mean age of the 10817 patients was 71 ± 10 years; the male/female ratio was 4653/6164. The mean TCA obtained by the IOLMaster 700 (Carl Zeiss Meditec AG, Jena, Germany), the Abulafia-Koch (AK) formula, and the Barrett toric calculator was 1.11 ± 0.81 diopter (D), 1.13 ± 0.75 D, and 1.12 ± 0.74 D respectively, which was significantly greater than the mean standard keratometric (K) astigmatism (0.99 ± 0.75 D) obtained by IOLMaster 700. Against-the-rule (ATR) astigmatism was dominant in all the TCA measurements, and its proportion increased with age. TCA measurements by different methods exhibit high variability, with a total of 1574 (8.9%) data sets from 1016 (9.4%) patients showing a difference larger than 0.5 D in at least one pair of TCA measurements.

CONCLUSION

The use of TCA rather than K astigmatism significantly influenced the choice of intraocular lenses (IOLs) as more patients would be candidates for toric IOLs. It was essential to carefully compare and select TCA obtained with multiple methods for optimal postoperative visual quality.

Revisiting Javal's rule: a fresh and improved power vector approach according to age

PURPOSE

The scientific community has established Javal's rule as a model linking refractive (RA) and keratometric (KA) astigmatism since its appearance more than 100 years ago. The aim was to improve the accuracy of this relationship according to subject's age by applying the power vector analysis. Posterior corneal curvature has also been studied.

METHODS

The IOLMaster 700 optical biometer was used to measure the corneal thickness and the radius of curvature of the anterior and posterior corneal surfaces. Refractive error was determined by a non-cycloplegic subjective refraction process with trial lenses. Linear regression analyses were applied using J0 and J45 power vector components. An evaluation was carried out according to the subject's age resulting into eight regression relationships for each astigmatic vector component for each relationship.

RESULTS

A total of 2254 right eyes from 2254 healthy subjects were evaluated. A trend towards against-the-rule astigmatism (ATR) was found with aging, both for refractive astigmatism (RA) and keratometric astigmatism (KA), with 95.2% of subjects under 20 years old having with-the-rule (WTR) KA, and only 22.8% above 79 years old. The following regression equations were found between RA and KA: [Formula: see text] = 0.73 × [Formula: see text] - 0.18 (R = 0.78) and [Formula: see text] = 0.70 × [Formula: see text] + 0.04 (R = 0.69) and between RA and total corneal astigmatism (TCA): [Formula: see text] = 0.73 × [Formula: see text] + 0.13 (R=0.78) and [Formula: see text] = 0.70 × [Formula: see text] - 0.06 (R = 0.68) for the whole sample, but with sensible differences among age groups, both in the slope and in the intercept.

CONCLUSION

Ignoring the age of the subject when using Javal's rule could lead to an error in the final cylinder calculation that would increase in high astigmatisms. Applying this new power vector approach based on subject's age could improve the accuracy of the astigmatism prediction.

Is Astigmatism Correction Necessary for Patients With Cataract Who Have Corneal Astigmatism of Less Than 0.75 D?

PURPOSE

To investigate the proportion of patients with predicted refractive astigmatism (PRA) of 0.75 diopters (D) or greater and associated risk factors among cataract surgery candidates with low corneal astigmatism.

METHODS

A retrospective cross-sectional study was conducted in Zhongshan Ophthalmic Center, Guangzhou, China. Patients with cataract who had preoperative simulated keratometric astigmatism of less than 0.75 D were recruited. The PRA was calculated by Barrett toric calculator using posterior corneal astigmatism (PCA) measured by the IOLMaster 700 (Carl Zeiss Meditec AG) and corneal surgically induced astigmatism (SIA). Two corneal incision locations (temporal [0°/180°], 135° incision) and varying magnitudes (0.10 to 0.60 D) were considered for SIA. Multiple logistic regression analysis was used to explore risk factors associated with PRA of 0.75 D or greater and build predictive model. Sensitivity analysis was performed using PRA threshold of 0.50 D.

RESULTS

A total of 1,750 eyes from 1,750 patients were included (mean age: 60.14 ± 13.24 years, 42.91% male, 1,010 right eyes and 740 left eyes). The 135° incision (odds ratio [OR]: 17.86) and against-the-rule (ATR) astigmatism (OR: 37.55) are the major risk factors for PRA of 0.75 D or greater. Higher simulated keratometric astigmatism (OR: 2.03), larger PCA (OR: 1.64), and surgically induced astigmatism (OR: 1.29) also significantly increased the risk of PRA of 0.75 D or greater. Nomogram model were constructed with an area under curve of 0.90.

CONCLUSIONS

For patients with corneal astigmatism of less than 0.75 D, temporal incision and measured PCA is preferred. Those patients with ATR astigmatism should be considered for astigmatism correction when using a 135° incision. [J Refract Surg. 2023;39(12):850-855.].

Prevalence and characteristics of oblique astigmatism

OBJECTIVE

To examine the incidence and characteristics of eyes with oblique astigmatism stratified by meridian, age, sex, and eye side (left to right).

METHODS

One thousand eyes of 1000 patients with oblique corneal astigmatism underwent videokeratographic examination and was classified into 4 meridian categories: (1) 31°-45°, (2) 46°-59°, (3) 121°-135°, and (4) 136°-149°. Amounts of regular and irregular astigmatism, and the vertical/horizontal (Rx) and oblique astigmatism components (Ry) decomposed using vector analysis were compared among the 4 categories and age groups, and between sexes and eye sides.

RESULTS

Incidences of the 4 meridian categories were similar and did not differ significantly among age groups or between sexes. The incidence was significantly greater in eyes in meridian categories 1 and 2 in the left eye and categories 3 and 4 in the right eye, and significantly greater in men in their 40 s and 50 s and in women in their 70 s and 80 s (P < 0.0001). The mean regular astigmatism, asymmetry and higher-order irregularity components, and Rx and absolute Ry significantly increased with age (P ≤ 0.0372). The mean regular and irregular astigmatism, and absolute Rx and Ry did not differ significantly among the 4 categories, or between sexes or left and right eyes.

CONCLUSIONS

The incidence of oblique astigmatism was significantly greater in the temporal side meridians, and the incidence in women increased with age. The degree of oblique astigmatism increased with age, with an increase in irregular astigmatism.

Evaluation of long-term clinical outcomes after toric implantable collamer lens implantation

PURPOSE

To evaluate the long-term (8-10 years) outcomes of toric implantable collamer lens (TICL) surgery.

SETTING

Nagoya Eye Clinic, Nagoya, Aichi, Japan.

DESIGN

Retrospective observational study.

METHODS

Patients who underwent TICL surgery from 2005 to 2009 to correct myopia and myopic astigmatism were enrolled. The safety, efficacy, predictability, astigmatism correction efficacy, and complications were evaluated using preoperative, 1-year postoperative, and final examination data.

RESULTS

133 eyes of 77 patients were included. At the final visit, the mean uncorrected and corrected visual acuities were -0.01 ± 0.2 and -0.17 ± 0.05, respectively. The mean safety and efficacy indices were 0.91 ± 0.26 and 0.68 ± 0.21, respectively. The manifest astigmatism was -0.45 ± 0.43 diopters (D). The mean corneal astigmatism change from 1 year postoperatively to the final visit was 0.40 ± 0.26 D. Of the 38 eyes with a change in corneal astigmatism ≥0.5 D, 30 eyes (78.9%) changed to against-the-rule (ATR) astigmatism, 1 (2.6%) changed to oblique astigmatism, and 7 (18.4%) changed to with-the-rule (WTR) astigmatism. The mean manifest astigmatism change from 1 year postoperatively to the final visit was 0.43 ± 0.52 D. Of the 60 eyes with a change in manifest astigmatism ≥0.5 D, 25 (41.7%) changed to ATR astigmatism, 18 (30.0%) changed to oblique astigmatism, and 17 (28.3%) changed to WTR astigmatism. During follow-up, 8 (6.0%) of 133 eyes developed anterior subcapsular cataracts, among which 4 (3.0%) underwent TICL removal and phacoemulsification and aspiration. No vision-threatening complications occurred.

CONCLUSIONS

TICL surgery showed good long-term astigmatism-correcting effects, although the long-term uncorrected visual acuity decreased. The procedure was effective in correcting myopia and astigmatism.

The 10,000 Eyes Study: Analysis of Keratometry, Abulafia-Koch regression transformation, and Biometric Eye Parameters Obtained With Swept-Source Optical Coherence Tomography

PURPOSE

To analyze Abulafia-Koch regression (AKRT), anterior and posterior astigmatism (K and TK), and evaluate biometry data in a large population.

DESIGN

Retrospective cross-sectional study.

METHODS

This multicenter (2 tertiary care centers) study analyzed datasets acquired between 2017 and 2020. Axial length (AL), corneal front and back radii (including meridians for K and TK conversion), horizontal corneal diameter, anterior chamber depth, lens thickness, and central corneal thickness were measured using telecentric keratometry and swept-source optical coherence tomography-based biometry (IOLMaster 700; Carl Zeiss Meditec AG). Cooke-modified axial length (CMAL) and AKRT were calculated. Difference vectors between K and TK astigmatism and between AKRT and TK astigmatism were compared.

RESULTS

A total of 10,300 eyes from 6388 patients were assessed. Difference vectors for K and TK were significantly smaller than for AKRT and TK. K measurement showed a configuration of 51.49% of with-the-rule astigmatism and 30.51% against-the-rule astigmatism, TK measurement showed a configuration of 41.60% of with-the-rule astigmatism and 40.21% against-the-rule astigmatism. Mean total astigmatism was -0.94 ± 0.74 dpt. Mean values for AL and CMAL were 23.70 ± 1.39 mm and 23.70 ± 1.34 mm, respectively. Anterior chamber depth, lens thickness, horizontal corneal diameter, AL, and age were all correlated with each other.

CONCLUSION

Astigmatism analysis showed less difference between K and TK than between AKRT and TK. There were significantly fewer eyes with with-the-rule astigmatism and more eyes with against-the-rule astigmatism configuration in TK-derived than in K-derived keratometry. The study provides data on gender and generational differences in biometry. Significant intersexual differences in AL and CMAL were observed, with CMAL providing lower standard deviation compared with AL.

Effects of Lens-Induced Astigmatism at Near and Far Distances

Purpose

To investigate and compare the degradation of visual acuity (VA) in myopic presbyopes due to lens-induced astigmatism at near and at far distance.

Patients and Methods

Fourteen corrected myopic presbyopes were recruited. VA (logarithm of the minimum angle of resolution) was measured binocularly for different conditions of lens-induced astigmatism: cylindrical powers of -0.25, -0.50, -0.75, -1.00, -1.50, and -2.00 diopters (and positive spherical power of half the cylindrical power) with two axis orientations (with-the-rule WTR and against-the-rule ATR) were added to their optical correction. Measurements were carried out at far and near distance both in photopic and mesopic conditions, and for high and low contrast (HC/LC) stimuli. The paired Wilcoxon signed-rank statistics test was used to evaluate difference between conditions.

Results

The measured VA as a function of the lens-induced astigmatism was described by regression lines in all investigated experimental conditions. The angular coefficients (slopes) of these lines represent the VA degradation, ie, the variation in logMAR corresponding to the addition of 1.00 diopters of cylindrical power. In photopic HC conditions, the VA degradation is significantly more pronounced at far distance than at near distance (0.22±0.06 diopters^-1 vs 0.15±0.05 diopters^-1, p = 0.0061 in WTR conditions; 0.18±0.06 diopters^-1 vs 0.12±0.05 diopters^-1, p = 0.0017 in ATR conditions), although VAs at near and at far with zero cylinder were similar (-0.14±0.10 vs -0.14±0.08, p = 0.824).

Conclusion

The better tolerance to lens-induced astigmatism blur at near than at far distance in photopic conditions with HC stimuli is tentatively attributed to a possible experience-mediated neural compensation associated to the tendency of the eye toward an inherent astigmatism at near.

Predicting Residual Astigmatism in Cataract Surgery

The purpose of this review is to evaluate the prediction of postoperative residual astigmatism and to determine the best prediction method for astigmatism correction. In recent findings for residual astigmatism in non-toric monofocal intraocular lens (IOL) implanted eyes, vector analysis can be used to correctly evaluate residual astigmatism by decomposing it. In predicting residual astigmatism, the with-the-rule (WTR) and against-the-rule (ATR) astigmatism components can now be almost predicted. This may be due to advances in inspection equipment and surgical technique. However, there are still issues with the oblique astigmatism component. In addition, corneal astigmatism is the most important predictor of postoperative residual astigmatism, and other predictors, such as refractive astigmatism, age, and lens thickness, have also been mentioned. However, all but corneal astigmatism are questionable because of the possibility of confounding variables. Total corneal astigmatism is more accurate in predicting residual astigmatism than anterior corneal astigmatism. Several predictions of residual astigmatism have been reported, but complete prediction has not been possible. Further research is needed, especially in predicting oblique astigmatism. However, I emphasize that the accuracy of predicting WTR and ATR astigmatism has improved considerably and can be predicted using regression equations with total corneal astigmatism.

Age- and gender-related characteristics of astigmatism in a myopic population

Purpose

To explore age- and gender-related differences of refractive and corneal astigmatism in myopic patients looking for refractive surgery.

Design

A retrospective cross-sectional study.

Materials and methods

The medical files of candidates looking for corneal refractive surgery between 2019 and 2021 were reviewed, demographic and refractive parameters including age, gender, refractive status, and corneal parameters were analyzed.

Results

A total of 1,417 eyes of 1,417 patients (453 males and 964 females) were included. Males had thicker cornea than females, while females had steeper cornea than males, there was no gender-related difference in refractive and corneal astigmatism depending on patients’ age. There was no difference in refractive astigmatism among different age group from 18 to 50 years, while corneal astigmatism had a shift from with-the rule (WTR) to against-the-rule (ATR) with increasing age. Age, central corneal thickness (CCT), sphere, refractive astigmatism (RA), and corneal curvature (Km) were correlated with corneal astigmatism (CA) (standardized coefficients of are 0.006, p = 0.011 for age, −0.001, p = 0.004 for CCT, and −0.027, p < 0.001 for sphere, 0.61, p < 0.001 for RA, −0.05, p < 0.001 for corneal curvature).

Conclusion

Refractive astigmatism is stable until the age of 50 years in myopic patients looking for refractive surgery, while corneal astigmatism showed a shift from WTR to ATR with advancing age. Age, CCT, sphere, refractive astigmatism and corneal curvature (Km) were correlated with corneal astigmatism.

Comparison of Long-Term Corneal Astigmatic Changes After Cataract Surgery in Eyes with Superior or Horizontal Clear Corneal Incisions

PURPOSE

To compare long-term corneal astigmatic changes after stabilization of surgically induced astigmatism (SIA) subsequent to phacoemulsification between eyes that underwent superior clear corneal incision (CCI) or horizontal CCI.

DESIGN

Retrospective, comparative case series.

METHODS

We examined the anterior corneal astigmatism of eyes that underwent a 2.4 mm-superior CCI (superior CCI group, n=43) or horizontal CCI (horizontal CCI group, n=43) preoperatively, on the postoperative day that SIA stabilized (baseline), and at ≥7 years post-baseline using an autokeratometer. Corneal astigmatic changes from baseline to ≥7 years post-baseline (mean duration 8.74 years in the superior CCI group and 9.05 years in the horizontal CCI group) were decomposed to vertical/horizontal (Rx) and oblique astigmatic change components (Ry), and compared between the 2 groups.

RESULTS

The mean corneal astigmatism components changed significantly toward against-the-rule (ATR) astigmatism in the superior CCI group and with-the-rule astigmatism in the horizontal CCI group within 6 months postoperatively. After stabilization of the SIA, both groups showed a significant increase in the mean Rx and no significant change in the mean Ry over approximately 9 years, indicating a long-term ATR shift. The mean changes in the Rx and Ry did not differ significantly between the superior and horizontal CCI groups. Double angle-plots revealed a similar degree of ATR shift between the 2 groups over the 9 years.

CONCLUSION

After stabilization of the SIA, a similar degree of ATR change occurred subsequent to superior and horizontal CCIs over approximately 9 years, suggesting that CCI direction does not affect long-term astigmatic changes.

Impact of small incision sutureless cataract surgery on the natural course of astigmatism in 10 to 20 years

PURPOSE

To retrospectively assess astigmatic changes over 10- and 20-years after small incision cataract surgery.

SETTING

Five ophthalmic surgical sites in Japan.

DESIGN

Retrospective case series.

METHODS

Data were collected from patients who had undergone phacoemulsification and implantation of an intraocular lens (IOL) through a 2.2- to 2.4-mm incision. Preoperative corneal and postoperative manifest astigmatism were converted to power vector notations: horizontal/vertical (J0) and oblique (J45) astigmatism components.

RESULTS

In 422 eyes of 422 patients who were followed up for 10 years, data before and at 1 month, and 1, 3, 5, 8, and 10 years after surgery were analysed. The mean J0 decreased significantly (p<0.001, repeated measures analysis of variance) with an against-the-rule (ATR) shift of 0.363 ± 0.433 D over 10 years, but the mean J45 did not change significantly (p=0.150). Double-angle plot analyses also showed similar ATR shifts in all astigmatism groups. In the subgroup analysis conducted in 34 patients who were followed up for 20 years, J0 declined significantly (p<0.001) by 0.649 ± 0.576 D over 20-year follow-up, while J45 did not (p=0.516). The postoperative changes in J0 and J45 were not significantly different between eyes with preoperative with-the-rule, ATR, or oblique astigmatism.

CONCLUSIONS

Postoperative astigmatism continued to shift towards ATR during the follow-up period of 20 years after small incision cataract surgery, which appears to reflect the natural course of corneal astigmatic changes that commonly occur with aging. ATR astigmatic shifts were similar in both pattern and magnitude regardless of the type of preoperative astigmatism.

Screening of Keratoconus Using Autokeratometer and Keratometer Keratoconus Index

The keratometer keratoconus index (KKI) is a diagnostic index for the risk of keratoconus calculated from autokeratometer test values. We partially modified the KKI equation and assessed it without limiting the target age and severity of keratoconus. This retrospective study included 179 eyes of 99 patients with keratoconus and 468 eyes from 235 normal controls. In the modified KKI, oblique astigmatism or against-the-rule astigmatism was defined as ≥1D astigmatism. KKI diagnostic power was analyzed in subgroups of <50 and ≥50-year-old patients, and at different keratoconus stages. Although the sensitivity of modified KKI was comparable with that of original KKI (92.7% vs. 95.5%), modified KKI specificity was significantly higher (79.7% vs. 68.6%) (p = 0.0001). Using the modified KKI, sensitivity reached 100% (4/4) and specificity, 63.5% (33/52), in ≥50-year-old patients, while overall sensitivity in keratoconus ≥stage 2 was 100% (30/30). In conclusion, the modified KKI proved to be effective in keratoconus screening at all stages. However, it should be noted that false-positive frequency is higher in ≥50-year-old patients.

Associated factors and distribution of posterior corneal astigmatism in a middle-aged population

CLINICAL RELEVANCE

Posterior corneal astigmatism has an important role in diagnosis and treatment of astigmatism, but it is usually overlooked.

BACKGROUND

This cross-sectional study aimed to investigate the distribution of posterior corneal astigmatism (PCA) and its associated factors in a middle-aged population that participated in the Shahroud Eye Cohort Study (ShECS) phase II.

METHODS

Anterior corneal astigmatism (ACA) and PCA values were measured using rotating Scheimpflug System (Pentacam HR, Oculus). With-the-rule (WTR) astigmatism was considered when the steepest corneal meridian was aligned within 90° ± 30°, and against-the-rule (ATR) astigmatism when the steepest meridian was 0 ± 30°. All the remaining values were considered as oblique astigmatism. Logistic regression models were used for evaluating the association of PCA magnitudes with other factors.

RESULTS

The current study consisted of 3871 eyes with available Pentacam data. Mean age of participants was 55.4 ± 6.1 years and 1557 (40.2%) subjects were male. Means of ACA and PCA were 0.77 ± 0.67 and -0.24 ± 0.15 D, respectively. The majority of PCA consisted of WTR astigmatism (82.43%), while ACA mostly showed ATR astigmatism (55.46%). PCA > 0.3 D was associated with male sex (OR = 1.16, P-value = 0.028) and spherical equivalent (OR = 0.93, P-value = 0.011) in the adjusted model, while PCA > 0.5 dioptre was strongly associated with myopia (OR = 4.6, P-value < 0.001).

CONCLUSION

The most common forms of ACA and PCA in middle-aged Iranian adults were ATR and WTR, respectively. While the shape of posterior corneal surface remained mostly unchanged across ages of 45 to 69 years, ACA was associated with a decrease in ATR proportion. Moreover, the most significant factors associated with higher magnitudes of PCA were male sex and myopia.

Lasting Effects: Seven Year Results of the Castrop Nomogram for Femtosecond Laser-Assisted Paired Corneal Arcuate Incisions

PURPOSE

Long-term results of arcuate incisions are rarely reported. This is unfortunate as long-term stability of astigmatic correction is of great interest to surgeons performing astigmatic correction. This study investigates the 7 year stability of results after application of femtosecond laser-assisted arcuate incisions with the Castrop nomogram.

METHODS

Prospective interventional case series at the Augen- und Laserklinik, Castrop-Rauxel, Germany. Single site, single surgeon study. Seven year results of cataract patients with low to moderate corneal astigmatism receiving femtosecond laser-assisted arcuate incisions using a TechnolasVictus SW 2.7 (Bausch & Lomb Inc, Dornach, Germany) were assessed and compared to 1 year results. Outcome evaluation was based on astigmatic vector analysis, manifest refraction, and visual acuity.

RESULTS

The study analyzed 19 eyes of 19 patients 7 years after surgery. Ocular residual astigmatism changed from -0.26 to -0.39 D. Preoperative corneal astigmatism was -1.51 D. Correction Index changed from 1.0 to 1.16. The magnitude of difference vector changed from 0.26 to 0.39 D. The index of success changed from 0.20 to 0.29. Spherical equivalent remained stable. A slight tendency to change toward astigmatic overcorrection was mainly observed for patients with preoperative with the rule astigmatism, but not with patients with against the rule astigmatism.

CONCLUSIONS

The Castrop nomogram showed stable results 7 years after surgery. Similar to toric IOL surgery, it is advisable to be less aggressive when correcting with the rule astigmatism, to avoid overcorrection over a long period.

Comparison of corneal irregular astigmatism by the type of corneal regular astigmatism

We investigated the relation between corneal regular and irregular astigmatism in normal human eyes. In 951 eyes of 951 patients, corneal irregular astigmatism, such as asymmetry and higher-order irregularity components, was calculated using the Fourier harmonic analysis of corneal topography data within the central 3-mm zone of the anterior corneal surface. The eyes were classified by the type of corneal regular astigmatism into four groups; minimum (< 0.75 diopters), with-the-rule (WTR), against-the-rule (ATR), and oblique astigmatism. The mean age was significantly different among the four groups (P < 0.001); patients with WTR astigmatism were the youngest, followed by those with minimum, oblique, and ATR astigmatism. Significant inter-group differences were found among the four groups in asymmetry (P = 0.005) and higher-order irregularity components (P < 0.001); the largest was in eyes with oblique astigmatism, followed by ATR, WTR, and minimum astigmatism. The stepwise multiple regression analysis revealed that corneal regular astigmatism pattern significantly influenced the amount of corneal irregular astigmatism after controlling for confounding factors (P < 0.001). Corneal irregular astigmatism, such as asymmetry and higher order irregularity components, was the largest in eyes with oblique astigmatism, followed by those with ATR, WTR, and minimum astigmatism, even after adjustment for age of subjects.

Predictive models of aging of the human eye based on ocular anterior segment morphology

Aging is a major risk factor for various eye diseases, such as cataract, glaucoma, and age-related macular degeneration. Age-related changes are observed in almost all structures of the human eye. Considerable individual variations exist within a group of similarly aged individuals, indicating the need for more informative biomarkers for assessing the aging of the eyes. The morphology of the ocular anterior segment has been reported to vary across age groups, focusing on only a few corneal parameters, such as keratometry and thickness of the cornea, which could not provide accurate estimation of age. Thus, the association between eye aging and the morphology of the anterior segment remains elusive. In this study, we aimed to develop a predictive model of age based on a large number of anterior segment morphology-related features, measured via the high-resolution ocular anterior segment analysis system (Pentacam). This approach allows for an integrated assessment of age-related changes in corneal morphology, and the identification of important morphological features associated with different eye aging patterns. Three machine learning methods (neural networks, Lasso regression and extreme gradient boosting) were employed to build predictive models using 276 anterior segment features of 63,753 participants from 10 ophthalmic centers in 10 different cities of China. The best performing age prediction model achieved a median absolute error of 2.80 years and a mean absolute error of 3.89 years in the validation set. An external cohort of 100 volunteers was used to test the performance of the prediction model. The developed neural network model achieved a median absolute error of 3.03 years and a mean absolute error of 3.40 years in the external cohort. In summary, our study revealed that the anterior segment morphology of the human eye may be an informative and non-invasive indicator of eye aging. This could prompt doctors to focus on age-related medical interventions on ocular health.

Evaluation of Astigmatic Correction Using Vector Analysis after Combined Femtosecond Laser-Assisted Phacoemulsification and Intrastromal Arcuate Keratotomy

The aim of this study was to evaluate astigmatic correction in patients with mild to moderate astigmatism after combined femtosecond laser-assisted cataract surgery (FLACS) and intrastromal arcuate keratotomy (ISAK), using vector analysis. This retrospective study included patients with corneal astigmatism of 0.5–3.0 diopters (D) who underwent FLACS and ISAK. Vector analyses of astigmatism were performed using the Alpins method, considering three vectors: target-induced astigmatism (TIA), surgically induced astigmatism (SIA), and difference vector (DV). Magnitude of error (ME), angle of error (AE), correction index (CI), and coefficient of adjustment (CA) were calculated. Subgroup analysis according to the axis of astigmatism, patient age, and white to white (WTW) diameter was conducted. In total, for the 79 eyes of 79 patients, the TIA was 1.21 ± 0.52 D, the SIA was 0.76 ± 0.53 D, and the DV was 0.86 ± 0.50 D. The ME (difference between SIA and TIA) was −0.46 ± 0.45 D, and the CI (ratio of SIA and TIA) was 0.62 ± 0.34; both these parameters demonstrated slight undercorrection. The CA (inverse of the CI) was 2.48 ± 2.61. The AE was 4.02° ± 28.7°, and the absolute AE was 21.7° ± 19.0°. In the univariate regression analyses to identify factors that affected the CI, there was a negative correlation between age and the CI (P=0.022). In conclusion, vector analysis after the combined FLACS and ISAK revealed slight undercorrection, regardless of the astigmatism meridian. The precision of the nomogram should be improved through long-term vector analysis for the results of arcuate keratotomy and through further research on the relationship between patient demographics and CI. Overall, this study has shown that FLACS and ISAK could reduce postoperative corneal astigmatism effectively and safely.

Influence of refractive status and age on corneal higher-order aberration

This study aimed to investigate the influence of refractive status and age of patients on corneal higher-order aberrations (HOAs). Four hundred and twenty-six right eyes of 426 patients were enrolled in this study. The mean and standard deviation of patient age was 47.7 ± 22.1 years. Total HOAs, spherical-like aberration, coma-like aberration, Z^-1₃, Z¹₃, Z^-3₃, Z^-3₃ and spherical aberration (Z⁰₄) for 6-mm pupil were measured using anterior segment optical coherence tomography (AS-OCT). Subjects were classified into three groups according to the amount of spherical equivalent refractive error (SE): myopia (<-0.5 D), emmetropia (-0.5 to 0.5 D), and hyperopia (>0.5 D). The amount of corneal astigmatism was recorded. Relationship between corneal aberrations, refractive status, astigmatism, and age was analyzed. In total, total HOAs, spherical-like aberration and amount of Z^-3₃ and Z⁰₄ were significantly larger in the hyperopia group than in the myopia group. After adjustment for age, however, aberration components did not differ among the three refractive groups. In multiple regression analysis, age and corneal astigmatism showed significant correlation with aberrations, whereas amount of SE and refractive status did not. The current study indicated that age and amount of corneal astigmatism have significant influence on corneal HOAs, but refractive status (myopia, emmetropia, or hyperopia) is not associated with corneal HOAs.

Influence of posterior corneal astigmatism on the outcomes of toric intraocular lens implantation in eyes with oblique astigmatism

PURPOSE

To assess whether the outcomes of toric intraocular lens (IOL) implantation in eyes with oblique astigmatism can be improved by direct measurements of posterior corneal astigmatism using anterior segment optical coherence tomography (AS-OCT) instead of by using anterior corneal measurements alone.

STUDY DESIGN

Retrospective case series.

METHODS

Two toric IOL power calculation methods were compared: anterior corneal astigmatism was used in the keratometry group, whilst total corneal astigmatism determined by ray tracing through the measured anterior and posterior corneal surfaces was used in the AS-OCT group. In a total of 279 eyes of 232 patients, subgroup analysis was conducted for with-the-rule (WTR) (85 eyes in the keratometry group and 34 eyes in the AS-OCT group), against-the-rule (ATR) (73/29 eyes), and oblique (26/32 eyes) astigmatism.

RESULTS

In the WTR and ATR astigmatism groups, the uncorrected distance visual acuity (UDVA) was significantly better in the AS-OCT group than in the keratometry group (P = 0.012 and P < 0.001, Mann-Whitney test), and the residual astigmatism was significantly smaller in the AS-OCT group than in the keratometry group (P = 0.037 and P < 0.001). In eyes with oblique astigmatism, the UDVA (P = 0.299) and residual astigmatism (P = 0.373) of the keratometry and AS-OCT groups did not differ.

CONCLUSION

Incorporation of posterior corneal astigmatism measured with AS-OCT can significantly improve the outcomes of toric IOL implantation in eyes with WTR and ATR astigmatism, but not in eyes with oblique astigmatism.

Five-Year Changes in Corneal Astigmatism After Combined Femtosecond-Assisted Phacoemulsification and Arcuate Keratotomy

PURPOSE

To investigate the long-term stability of corneal astigmatism after combined femtosecond (fs)-assisted phacoemulsification and arcuate keratotomy.

DESIGN

Retrospective, interventional case series.

METHODS

Surgery was performed using a Victus (Bausch & Lomb) platform. A single, 450-μm-deep arcuate keratotomy was paired at the 8-mm zone with the main phacoemulsification incision in the opposite meridian. The keratotomy incisions were not opened. Corneal astigmatism measurements obtained preoperatively and at 2 and 5 years postoperatively were analyzed using vector analysis.

RESULTS

A total of 44 eyes of 44 patients (mean age 66.0 ± 10.1 years) were included. The mean preoperative corneal astigmatism was 1.40 ± 0.66 diopters (D). This was reduced to 0.74 ± 0.54 D at 2 years and 0.70 ± 0.50 at 5 years postoperatively (P < .001). There were no statistically significant differences between postoperative corneal astigmatism at 2 years and at 5 years (P = .609). Both magnitude of error and absolute angle of error were comparable between the 2 postoperative time points (P > .805). At the end of 5 years, 65% of the eyes were within 15 degrees of the preoperative astigmatic meridian. Comparative analysis showed significantly higher surgically induced astigmatism, lower differences in vector and absolute angles of error for the eyes with preoperative with-the-rule (WTR) astigmatism than eyes with against-the-rule (ATR) astigmatism at 5 years (P < .004).

CONCLUSIONS

Our study showed the stability of femtosecond (fs)-assisted arcuate keratotomy was well-maintained over 5 years. There was a tendency of increasing overcorrection of preoperative WTR astigmatism and undercorrection of ATR astigmatism over time.

Multivariate Regression Analysis to Predict Postoperative Refractive Astigmatism in Cataract Surgery

Purpose

To assess the correlation between postoperative refractive astigmatism and preoperative parameters in cataract surgery.

Methods

Left eyes of 100 consecutive patients scheduled for cataract surgery with a 2.4 mm clear corneal incision were examined prospectively. Refractive astigmatism was measured using an autokerato/refractometer. Corneal astigmatism of the total cornea was calculated using a Scheimpflug camera. The vertical/horizontal component (J0) and oblique component (J45) of refractive and total corneal astigmatism were determined using power vector analysis. Refractive astigmatism at 8 weeks postoperatively was estimated using multivariate linear regression analysis. Independent variables analyzed included age, sex, refractive astigmatism, total corneal astigmatism, sphere, intraocular pressure, corneal thickness, anterior chamber depth, lens thickness, axial length, and pupil diameter.

Results

Multivariate regression analysis identified total corneal J0 and age as significant contributors to postoperative refractive J0 (P < 0.001 and P=0.029, respectively). The standard partial regression coefficients in the multiple regression analysis were 0.59 and −0.16 for total corneal J0 and age, respectively. Significant contributors to postoperative refractive J45 were total corneal J45 and lens thickness (P < 0.001 and P=0.015, respectively). The standard partial regression coefficients were 0.79 and −0.15 for total corneal J45 and lens thickness, respectively.

Conclusion

These results suggest that preoperative total corneal astigmatism is the most significant predictor of postoperative refractive astigmatism when performing astigmatism correction in cataract surgery.

Modeling Changes in Corneal Parameters With Age: Implications for Corneal Disease Detection

PURPOSE

To apply computational methods to model normal age-related changes in corneal parameters and to establish their association with demographic factors, thereby providing a framework for improved detection of subclinical corneal ectasia (SCE).

DESIGN

Cross-sectional study.

METHODS

One hundred seventeen healthy participants were enrolled from Centre for Eye Health (Sydney, Australia). Corneal thickness (CT), front surface sagittal curvature (FSSC), and back surface sagittal curvature (BSSC) measurements were extracted from 57 corneal locations from 1 eye per participant using the Pentacam HR. Cluster analyses were performed to identify locations demonstrating similar variations with age. Age-related changes were modeled using polynomial regression with sliding window methods, and model accuracy was verified with Bland-Altman comparisons. Pearson correlations were applied to examine the impacts of demographic factors.

RESULTS

Concentric cluster patterns were observed for CT and FSSC but not for BSSC. Sliding window analyses were best fit with quartic and cubic regression models for CT and FSSC/BSSC, respectively. CT and FSSC sliding window models had narrower 95% limits of agreement compared with decade-based models (0.015 mm vs 0.017 mm and 0.14 mm vs 0.27 mm, respectively), but were wider for BSSC than decade-based models (0.73 mm vs 0.54 mm). Significant correlations were observed between CT and astigmatism (P = .02-.049) and FSSC and BSSC and gender (P = <.001-.049).

CONCLUSIONS

The developed models robustly described aging variations in CT and FSSC; however, other mechanisms appear to contribute to variations in BSSC. These findings and the identified correlations provide a framework that can be applied to future model development and establishment of normal databases to facilitate SCE detection.

Frequency and distribution of corneal astigmatism and keratometry features in adult life: Methodology and findings of the UK Biobank study

PURPOSE

To describe corneal astigmatism in the UK Biobank population and to look for associations with other biometric variables and socio-demographic factors.

METHODS

This analysis included a subsample of 107,452 participants of the UK Biobank study who underwent an enhanced ophthalmic examination including autorefractor keratometry (Tomey RC 5000, Tomey Corp., Nagoya, Japan). Participants were recruited from across the United Kingdom between 2006 and 2010, and all were between 40 to 69 years. After quality control and applying relevant exclusions, data on corneal astigmatism on 83,751 participants were included for analysis. Potential associations were tested through univariable regression and significant parameters carried forward for multivariable analysis.

RESULTS

In univariable analysis, the characteristics significantly associated with higher corneal astigmatism (P<0.001), by order of magnitude were, female gender, white ethnicity, lighter skin colour, use of UV protection, lower alcohol intake, lower corneal-compensated intraocular pressure (ccIOP), older age at completion of education, younger age, higher Townsend deprivation index, lower height and lower systolic blood pressure. After inclusion in the multivariable analysis, gender, skin colour, alcohol intake, age at completion of full-time education, ccIOP, age and Townsend deprivation score remained significant (all P<0.001). Increased corneal astigmatism was also found to be significantly associated with amblyopia or strabismus.

CONCLUSIONS

This analysis confirms previous associations with astigmatism such as younger age and female gender, and identified novel risk factors including lighter skin colour, lower alcohol intake, later age having completed full time education later, lower ccIOP and higher Townsend deprivation index. Further research is needed to investigate these novel associations.

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.

Comparison of using Galilei Dual Scheimpflug Analyzer G4 and Barrett formula in predicting low cylinder preoperatively for cataract surgeries

PURPOSE

To compare corneal astigmatism estimation from Barrett toric calculator, with measurement from Galilei Dual Scheimpflug Analyzer G4 in low corneal cylinder patients.

METHODS

Preoperative corneal astigmatism was measured using Auto Kerato-Refractometer (AutoKM), IOL Master, and Galilei G4 (combined Placido-dual Scheimpflug analyzer) and was processed by Barrett toric calculator with measurements obtained from Auto Kerato-Refractometer and from IOL Master. A total of 42 eyes undergoing cataract surgery with nontoric intraocular lens implantation were included. Corneal astigmatism was calculated based on manifest refractive astigmatism with implications of surgically induced astigmatism. Errors in predicted residual astigmatism were calculated by the difference between postoperative manifest cylindrical refractive error and preoperative corneal cylinder using vector analysis.

RESULTS

Centroid error in predicted residual astigmatism was with-the-rule 0.36 D for AutoKM and 0.48 D for IOL Master, was lower at 0.24 D for the Barrett-IOL Master, and was lowest at 0.21 D for the Barrett-AutoKM (p < .001). The Galilei G4 demonstrated the highest centroid error for SimK (0.53 D) and lower for total corneal power (0.49 D). The Barrett toric calculator obtained the lowest median absolute error in predicted residual astigmatism for AutoKM (0.43 D) and IOL Master (0.54 D). The Barrett-IOL Master demonstrated that 61% and 76% of eyes were within 0.50 and 0.75 D of the predicted residual astigmatism, respectively.

CONCLUSION

The Barrett-IOL Master had more accurate prediction of residual astigmatism for low astigmatism eyes before cataract surgery compared to Galilei Dual Scheimpflug Analyzer G4 in this study.

Gender-differences in age-related changes of corneal astigmatism in Korean cataract patients

Background

This cross-sectional study investigated age-related changes in anterior, posterior, and total corneal astigmatism and evaluated sex differences in corneal astigmatism with increasing age in cataract patients.

Methods

This study evaluated eyes with cataracts from May 2009 and July 2013. All eyes underwent a complete ophthalmological examination and corneal Scheimpflug imaging by a Pentacam camera (Oculus, Wetzlar, Germany). Anterior, posterior, and total corneal astigmatism were determined. Power vector J₀ and linear regression analyses were determined and compared with respect to age and sex.

Results

Four hundred and fifteen patients (217 men, 198 women) aged 20–89 years were evaluated. For anterior corneal astigmatism, 100% of patients who were 20–39 years old had with-the-rule (WTR) in both sexes. WTR was significantly lower in patients 80–89 years old (25.6% of men and 37.8% of women). For total corneal astigmatism, WTR also tended to decrease with increasing age: 93.3% of men and 100% of women 20–39 years old versus 20.9% of men and 31.1% of women 80–89 years old. The regression coefficient of both the anterior corneal and total corneal J₀ vector values analyzed by age were − 0.018 in men and − 0.016 in women (both p < .001).

Conclusions

The against-the-rule shift was faster for total corneal astigmatism than for anterior corneal astigmatism and it occurred earlier in men than in women.

Trial registration

Retrospectively registered. Registration number: KC15RISI0241. Registered April 20, 2016.

Toric intraocular lenses in eyes with with-the-rule, against-the-rule, and oblique astigmatism: One-year results

PURPOSE

To assess 1-year clinical results of toric intraocular lenses (IOLs) in eyes having with-the-rule (WTR), against-the-rule (ATR), or oblique corneal astigmatism.

SETTING

Four ophthalmic surgical sites, Japan.

DESIGN

Prospective case series.

METHODS

One of 3 toric IOLs or 1 nontoric IOL was implanted in eyes having phacoemulsification and IOL implantation.

RESULTS

The study comprised 218 eyes (155 patients). Based on the suggestion of an online toric calculator with anterior corneal curvature data, 63 eyes received the SN6AT3 IOL with a cylinder power of 1.50 diopters [D] at IOL plane (1.50 D cylinder IOL) 55 eyes the SN6AT4 IOL with a cylinder power of 2.25 D at IOL plane (2.25 D cylinder IOL), and 58 eyes the SN6AT5 IOL with a cylinder power of 3.00 D at IOL plane (3.00 D cylinder IOL) (all Acrysof IQ toric), and 42 eyes received the SN60WF IOL (nontoric IOL). One hundred ninety-four eyes (89.0%) completed 1-year of follow-up. The centroid error in predicted residual astigmatism calculated using vector analysis was close to the origin in eyes with WTR astigmatism (0.17 diopter [D] @ 174.9 ± 0.54 D), while those with ATR and oblique astigmatism were significantly shifted toward the ATR direction (P < .001). The distance from the origin was significantly smaller in the WTR group than in ATR and oblique groups (P < .05). The centroid errors were shifted toward ATR in all toric IOL groups (P < .001); however, the distance from the origin was not different between groups (P = .52). Postoperatively, the mean absolute misalignment of the IOLs was 5.92 degrees ± 5.59 (SD) at 1 day and 6.24 ± 5.87 degrees at 1 year. The results of other clinical parameters were excellent, with no significant differences between astigmatism categories or IOL models.

CONCLUSION

Based on anterior corneal curvature alone, toric IOLs undercorrected ATR and oblique astigmatism; however, 1-year clinical results of toric IOLs were highly stable and satisfactory.

FINANCIAL DISCLOSURE

None of the authors has a financial or proprietary interest in any material or method mentioned.

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.

Are There Categories of Corneal Shapes?

This study investigates the possible existence of different natural corneal shape categories. This is important to better describe cornea for both diagnostic and therapeutic assessments. We started by describing corneal shape of different populations as a function of influencing clinical data i.e. age, ametropia and gender. This was done by averaging Zernike polynomial (ZP) decomposition of the anterior surfaces in each subgroup. The results showed small but significant differences of shape that are supported by the literature. This motivated us to examine the feasibility of characterizing the normal corneal shape with an automatic method of clustering independent of any clinical a priori knowledge. Since we did not know beforehand the number of corneal categories, agglomerative hierarchical clustering was applied on ZP coefficients for a large database. The dendrogram based on the Ward's distance was evaluated with two different clustering validity indexes (coefficient of determination R² and semi partial R² (SPR²). The optimal number of categories was around four showing corneal shapes ranging from flatter to steeper.

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.

Corneal shape changes of the total and posterior cornea after temporal versus nasal clear corneal incision cataract surgery

Aim

To compare changes in the shape and astigmatism of the total and posterior cornea between eyes with a nasal clear corneal incision (CCI) and eyes with a temporal CCI in cataract surgery.

Methods

The left eyes of 100 patients undergoing phacoemulsification were randomly assigned to undergo a 2.4 mm nasal (nasal CCI group) or temporal CCI (temporal CCI group). Corneal astigmatic changes were compared between groups using power vector analysis, and corneal shape changes were compared using videokeratography maps at 2 days, and at 2, 4 and 8 weeks postoperatively.

Results

The mean J₀ and J₄₅ values of the total cornea were significantly greater in the nasal CCI group than in the temporal CCI group at 2 and 4 weeks postoperatively (p≤0.0392), but did not differ significantly between groups at 2 days and 8 weeks. The videokeratography maps revealed a wedge-shaped flattening in the total cornea and a steepening in the posterior cornea around the CCIs in both groups at 2 days postoperatively; those were more prominent in the nasal CCI group than in the temporal CCI group. The wound-related changes diminished by 8 weeks postoperatively in the total and posterior cornea, and were not markedly different between groups at 8 weeks postoperatively.

Conclusion

Corneal shape and astigmatic changes were comparable between groups at 8 weeks postoperatively, although the changes were greater after nasal CCI than after temporal CCI in the early postoperative periods, indicating that nasal or temporal CCI can be selected based on the surgeon’s preference.

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.

Corneal Curvature, Astigmatism, and Aberrations in Marfan Syndrome with Lens Subluxation: Evaluation by Pentacam HR System

Marfan syndrome (MFS) is associated with abnormalities of corneal biometric characteristics. We conducted a retrospective case-control study including 55 eyes of the MFS patients with lens subluxation and 53 normal eyes of the control subjects to evaluate the corneal curvature, astigmatism and aberrations using a rotating Scheimpflug camera (Pentacam HR). Compared with the control group, the anterior, posterior, and total corneal curvature were flatter in the MFS group. The anterior and total corneal astigmatism were higher in the MFS patients, whereas the posterior corneal astigmatism was not significantly different between the two groups. Regarding the total corneal aberrations, the root mean square (RMS) aberrations, RMS higher-order aberrations and RMS lower-order aberrations increased, whereas the spherical aberration decreased in the MFS patients. Corneal parameters had potential diagnostic values for MFS patients with lens subluxation and the more reasonable cutoffs were the values of corneal curvature <41.35 D, corneal astigmatism >0.85 D and spherical aberration <0.188 μm. Corneal biometric characteristics of MFS patients with lens subluxation include decreased corneal curvature, higher corneal astigmatism, larger corneal aberrations, and lower spherical aberration. Corneal curvature, corneal astigmatism, and spherical aberration are better diagnostic tools for suspicious MFS.

Evaluating internal and ocular residual astigmatism in Chinese myopic children

PURPOSE

To investigate the nature of internal astigmatism (IA) and ocular residual astigmatism (ORA) in Chinese myopic children and to identify factors that may influence IA and ORA.

METHODS

A total of 206 eyes of 206 myopic children (97 boys and 109 girls; 10.95 ± 2.2 years) were enrolled in this cross sectional study. Total ocular astigmatism (TOA), anterior corneal astigmatism (ACA), posterior corneal astigmatism (PCA) and total corneal astigmatism (TCA) were measured directly using either a Hartmann-Shack wavefront sensor or a Pentacam. IA and ORA were calculated by Fourier vector analyses (the definitions of IA and ORA are: IA = TOA - ACA - PCA, ORA = TOA - ACA). Spearman or Pearson correlation was adopted to detect multiple factors that may influence IA and ORA, which were then predicted by linear regressions. Modified compensation factors were applied to evaluate the inter-relationship between corneal astigmatism and ORA.

RESULTS

While the mean values of IA and ORA were -0.52 DC × 94.8° and -0.63 DC × 93.0°, respectively, the percentage of ORA power over 1.00 D was as high as 28.64%. Full or under-compensation of ACA by ORA predominated in the enrolled subjects. The mean ORA J₀ and J₄₅ were -0.311 ± 0.236 and -0.032 ± 0.156 D, respectively, negatively correlated with the corresponding ACA components (J₀: r = -0.276, J₄₅: r = -0.616, p < 0.001). While age was not correlated with either IA or ORA (p > 0.1), the power of IA or ORA was correlated inversely with the axial length (IA: r = -0.193, p = 0.005; ORA: r = -0.169, p = 0.015) and positively with the spherical equivalent refraction (IA r = 0.195, p = 0.005; ORA r = 0.213, p = 0.002) and power of corneal astigmatism (IA-ACA: r = 0.302, IA-TCA: r = 0.368, ORA-ACA: r = 0.334, ORA-TCA: r = 0.293). Girls had larger IA powers than boys (0.741 ± 0.345 D vs 0.651 ± 0.340, p = 0.036).

CONCLUSIONS

Full or under-compensation of ACA by ORA is common in Chinese myopic children, and the compensation efficiency may decrease with age. Among Chinese children with myopia, a larger ORA is more prevalent with less myopia and greater corneal astigmatism.

Age-Related Changes in Corneal Astigmatism

PURPOSE

To analyze the changes in corneal astigmatism as a function of age and develop a novel model to estimate corneal astigmatic change according to age.

METHODS

This was a cross-sectional study of right eyes of 3,769 individuals. Total corneal astigmatism, keratometric astigmatism, anterior corneal astigmatism, and posterior corneal astigmatism were measured by a Scheimpflug tomographer. Smoothing fitting curves of polar values of corneal astigmatism as a function of age were drawn and average changes in corneal astigmatism at different ages were calculated.

RESULTS

Two turning points of age on total corneal astigmatism were 36 and 69 years. The average change of total corneal astigmatism toward against-the-rule astigmatism was 0.13 diopters (D)/10 years from 18 to 35 years, 0.45 D/10 years from 36 to 68 years, and decreased after 69 years, mainly caused by anterior corneal astigmatism. The mean magnitude of posterior corneal astigmatism was -0.33 D and exceeded 0.50 D in 14.27% of eyes. The vectorial difference between total corneal astigmatism and keratometric astigmatism was correlated with posterior corneal astigmatism, polar value of anterior corneal astigmatism, age, and corneal higher order aberrations (r = 0.636; standard partial regression coefficients were 0.479, -0.466, 0.282, and 0.196, respectively; all P < .001). Based on the non-linear model to estimate corneal astigmatic change with age, a formula was developed to calculate recommended correction of astigmatism according to age and astigmatic type.

CONCLUSIONS

The rate of change of total corneal astigmatism showed a non-linear trend toward against-the-rule astigmatism, which was low at young and old age, high at middle age, and should be taken into account when performing surgery to correct astigmatism. [J Refract Surg. 2017;33(10):696-703.].

Changes in Anterior, Posterior, and Total Corneal Astigmatism after Descemet Membrane Endothelial Keratoplasty

Purpose. To evaluate changes in anterior, posterior, and total corneal astigmatism in patients after Descemet membrane endothelial keratoplasty (DMEK). Methods. We retrospectively included 29 eyes of 23 patients (age 67.6 ± 9.8 years, 13 female, 10 male) after DMEK surgery. The magnitude and axis orientation of anterior, posterior, and total corneal astigmatism before and after DMEK were determined using a rotating Scheimpflug system (Pentacam HR, Oculus). Results. The magnitude of anterior, posterior, and total corneal astigmatism in the central cornea did not change significantly after surgery. Before surgery, we found a significant correlation between the magnitudes of anterior and posterior corneal astigmatism (Spearman's correlation coefficient (r_S) = 0.526, P = 0.003), while after surgery this correlation was no longer significant (r_S = 0.038, P = 0.843). There was a significant correlation between the vector difference between preoperative and postoperative posterior astigmatism and the change in corneal pachymetry (r_P = 0.47, P = 0.010). Conclusions. Posterior corneal astigmatism (especially the orientation) and therefore the relationship between anterior and total corneal astigmatism may change after DMEK. This should be considered to improve the accuracy of toric IOL power calculations following phakic DMEK or in combined procedures.

Toric intraocular lens implantation in children with developmental cataract and preexisting corneal astigmatism

PURPOSE

To evaluate the effect of toric intraocular lens (IOL) implantation on the refractive outcomes in children with cataract and preexisting corneal astigmatism.

METHODS

We included children between the age group of 8-14 years who were randomized into group I (toric) and group II (non-toric), in which toric and spherical IOLs were implanted, respectively, after phacoaspiration. Primary outcome measure was comparison of preoperative keratometric and postoperative refractive cylinder. Secondary outcome measure was comparison of pre- and postoperative visual outcome.

RESULTS

This study included 21 eyes of 17 children with developmental cataract. The mean spherical power of the toric IOLs implanted in the group I was 22.42 ± 4.84 D (range 12.50-29.00 D) and the mean cylindrical power of toric IOL was 3.37 ± 1.43 D (range 1.50-6.00D). The mean spherical power implanted in non-toric (group II) was 20.70 ± 7.09 D (range 10-31D). Mean preoperative keratometric cylinder in group I was 2.99 ± 0.96 D (range 1.85-5.12 D) and in group II it was 3.35 ± 0.63 D (range 2.03D-4.33 D) (p = 0.31) while the mean refractive cylinder at one year postoperatively in group I was 0.50 ± 0.39 D (range 0.00-1.00 D) and in group II it was 2.05 ± 0.39 D (range 1.25D-2.50 D; p = 0.006). Twelve months postoperatively, group I had a mean spherical equivalent (SE) 0.41 ± 0.26 D (range 0.00-0.88 D) and group II had 1.8 ± 1.03 D (range 0.63-4.00 D) (p = 0.002). Uncorrected distance visual acuity (UDVA) improved from 0.94 log MAR ± 0.51 (range 0.60-2.00) to 0.43 log MAR ± 0.33 (range 0.00-1.00) in the group I at the end of 1 year and in group II, it improved from 1.52 log MAR ± 1.12 to 0.75 log MAR ± 0.70 (range 0.00-2.00) at the end of 1 year. Corrected distant visual acuity (CDVA) improved in group I from 0.72 log MAR ± 0.17 (range 0.48-1.00) to 0.19 log MAR ± 0.26 (range 0.00- 0.78) at the end of one year while in group II, it improved from 1.33 ± 1.08 (range 0.18-3.00) to 0.49 log MAR ± 0.80 (range 0.00-2.00) at the end of 1 year.

CONCLUSIONS

Toric IOL implantation in children significantly reduces postoperative astigmatism and thereby improves visual outcome.

Characteristics of Corneal Astigmatism of Anterior and Posterior Surface in a Normal Control Group and Patients With Keratoconus

PURPOSE

To evaluate and compare power and axis orientation of anterior and posterior astigmatism in eyes with keratoconus with healthy eyes.

METHODS

In this retrospective cohort study, we examined 861 eyes of 494 patients diagnosed with keratoconus at the Department of Ophthalmology, University Hospital Frankfurt, and 256 eyes of 256 healthy individuals. Using a Scheimpflug device (Pentacam HR), we measured the magnitude and axis orientation of anterior and posterior corneal astigmatism, corneal thickness, and conus location. The results were compared between different stages of the disease according to the Amsler-Krumeich classification and the control group.

RESULTS

Magnitude of corneal astigmatism was 3.47 ± 2.10 diopters (D) on the anterior surface and 0.69  ± 0.40 D on the posterior surface in eyes across all keratoconus stages. We found a significant increase of anterior and posterior corneal astigmatism with progression of disease (P < 0.01, 1-way analysis of variance) and a significant correlation between anterior and posterior corneal astigmatism (r = 0.77, P < 0.01). In contrast to eyes of healthy individuals, in which posterior corneal axis alignment is vertical in most cases independent of anterior alignment, we found in eyes with keratoconus a match between anterior and posterior alignment when alignment was vertical in 97% of eyes, 46% when oblique and 61% when horizontal (Cohen kappa coefficient κ = 0.55, P < 0.01). With progression of disease, alignment of anterior and posterior corneal astigmatism became increasingly vertical.

CONCLUSIONS

In eyes with keratoconus, posterior axis alignment of corneal astigmatism is in line with alignment of the anterior surface in the majority of cases. Posterior astigmatism axis alignment could potentially be used in algorithms to support diagnosis and staging of keratoconus.

Influence of posterior corneal astigmatism on postoperative refractive astigmatism in pseudophakic eyes after cataract surgery

Background

To examine the influence of posterior corneal astigmatism on postoperative refractive astigmatism in pseudophakic eyes after cataract surgery.

Methods

The 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.

Results

The 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).

Conclusions

The 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.

Influence factors of estimation errors for total corneal astigmatism using keratometric astigmatism in patients before cataract surgery

PURPOSE

To evaluate the influence factors of the estimation errors for total corneal astigmatism using keratometric astigmatism in patients preparing for cataract surgery.

SETTING

EYE and ENT Hospital of Fudan University, Shanghai, China.

DESIGN

Prospective observational study.

METHODS

Eyes of patients preparing for cataract surgery were measured with Pentacam Scheimpflug imaging device. Keratometric astigmatism was obtained using the anterior corneal surface measurement and the keratometric index (1.3375) while neglecting the posterior corneal surface measurement. The Scheimpflug-measured total corneal astigmatism was derived by vector analysis of the astigmatism on both corneal surfaces.

RESULTS

The study comprised 374 eyes of 374 patients 45 to 84 years old. The mean absolute error in magnitude and mean absolute error in angle comparing keratometric astigmatism with Scheimpflug-derived astigmatism was 0.18 ± 0.14 diopter (D) and 7.7 ± 11.0 degrees, respectively. The mean magnitude of the error vector was 0.24 ± 0.14 D. The error in magnitude was significantly larger in eyes with against-the-rule anterior astigmatism, while error in angle was larger in eyes with with-the-rule and oblique anterior astigmatism. Multiple regressions showed that 4 predictors (difference in anterior-posterior astigmatism axis, magnitude of posterior astigmatism, magnitude of keratometric astigmatism, and axial length [AL]) were significantly associated with the absolute error in magnitude. Predictors including the difference in the anterior-posterior astigmatism axis, magnitude of posterior astigmatism, magnitude of keratometric astigmatism, and age were significantly associated with the absolute error in angle and magnitude of the error vector.

CONCLUSIONS

Neglecting posterior corneal astigmatism yielded significant estimation errors in total corneal astigmatism in patients preparing for cataract surgery. Estimation errors were significantly influenced by the difference in the anterior -posterior astigmatism axis, magnitude of posterior astigmatism, keratometric astigmatism, AL, and age.

FINANCIAL DISCLOSURE

None of the authors has any conflicts of interest to disclose.

Posterior Corneal Characteristics of Cataract Patients with High Myopia

Purpose

To evaluate the characteristics of the posterior corneal surface in patients with high myopia before cataract surgery.

Methods

We performed a cross-sectional study at the Eye and ENT Hospital of Fudan University, Shanghai, China. Corneal astigmatism and axial length were measured with a rotating Scheimpflug camera (Pentacam) and partial coherence interferometry (IOLMaster) in a high-myopia study group of 167 eyes (axial length ≥ 26 mm) and a control group of 150 eyes (axial length > 20 mm and < 25 mm).

Results

Total corneal astigmatism and anterior corneal astigmatism values were higher in the high-myopia group than in the control group. There was no significant difference in posterior corneal astigmatism between the high-myopia study group and the control group. In the study group, the mean posterior corneal astigmatism (range 0 – −0.9 diopters) was –0.29 diopters (D) ± 0.17 standard deviations (SD). The steep corneal meridian was aligned vertically (60°–120°) in 87.43% of eyes for the posterior corneal surface, and did not change with increasing age. There was a significant correlation (r = 0.235, p = 0.002) between posterior corneal astigmatism and anterior corneal astigmatism, especially when the anterior corneal surface showed with-the-rule (WTR) astigmatism (r = 0.452, p = 0.000). There was a weak negative correlation between posterior corneal astigmatism and age (r = –0.15, p = 0.053) in the high-myopia group. Compared with total corneal astigmatism values, the anterior corneal measurements alone overestimated WTR astigmatism by a mean of 0.27 ± 0.18 D in 68.75% of eyes, underestimated against-the-rule (ATR) astigmatism by a mean of 0.41 ± 0.28 D in 88.89% of eyes, and underestimated oblique astigmatism by a mean of 0.24 ± 0.13 D in 63.64% of eyes.

Conclusions

Posterior corneal astigmatism decreased with age and remained as ATR astigmatism in most cases of high myopia. There was a significant correlation between posterior corneal astigmatism and anterior corneal astigmatism when anterior corneal astigmatism was WTR. If posterior corneal astigmatism is not accounted for when selecting toric intraocular lenses for high-myopia patients, the use of anterior corneal astigmatism measurements alone will lead to overestimation of WTR astigmatism and underestimation of ATR and oblique astigmatism.

Comparison of clinical outcomes among 3 marking methods for toric intraocular lens implantation

PURPOSE

To compare the clinical outcomes of 3 marking methods for toric intraocular lens (IOL) implantation in cataract patients.

METHODS

This study included 48 eyes of 48 cataract patients who underwent cataract surgery with toric IOL implantation. The rotational errors of 3 marking methods-the iris pattern marking method (iris pattern group), the pendulum marking method (pendulum group), and the 3-point marking method (3-point group)-were assessed.

RESULTS

The respective rotational errors were 4.0° ± 3.1° (mean ± SD), 5.3° ± 4.1°, and 7.3° ± 6.0°. The iris pattern group had significantly (P = 0.048) smaller rotational errors than did the 3-point group; no significant difference was found between the iris pattern and pendulum groups. However, the differences in postoperative uncorrected distance visual acuity and astigmatism did not reach significance among the 3 groups.

CONCLUSION

The refractive and visual results of toric IOL implantation using the 3-point marking method were comparable to the other methods evaluated in this study, although the accuracy of the axis alignment of the toric IOLs was significantly lower than that obtained with the iris pattern method.