Posterior Corneal Astigmatism Research Articles

Toric intraocular lens: A literature review.

Toric intraocular lenses (IOLs) are universally recommended in cataract cases with preoperative corneal astigmatism ≥1.5 D. An optimal surgical outcome depends on careful patient selection, complete preoperative evaluation, accurate IOL power calculation, precise marking of the axis, meticulous intraoperative approach, and methodical postoperative care. Understanding the importance of posterior corneal astigmatism, surgically induced astigmatism, and effective lens position in IOL power calculation and newer techniques to measure them directly have resulted in better postoperative refractive outcomes. We present a brief overview of toric IOLs along with the preoperative evaluation, IOL power calculation, different marking methods, intraoperative approach, and postoperative outcomes. Functional and anatomical outcomes, including uncorrected visual acuity, residual refractive astigmatism, and postoperative IOL misalignment, which have been reported for both toric IOLs and multifocal toric IOLs, are reviewed.

Toric IOL Calculation in Eyes With High Posterior Corneal Astigmatism.

To evaluate different calculation approaches for toric intraocular lens (IOL) calculation in cases with high posterior corneal astigmatism (PCA). Consecutive patients who underwent cataract extraction with implantation of toric IOLs by a single surgeon were reviewed. Eyes with measured PCA of 0.80 diopters (D) or greater were included. Errors in the predicted postoperative refractive astigmatism were calculated for the Abulafia-Koch formula, vector summation of anterior keratometry with posterior tomography, and the Barrett toric calculator using predicted and measured PCA. One hundred seventy-three consecutive cases of toric IOL implantation were reviewed. Seventeen eyes (10%) had PCA of 0.80 D or greater and were investigated. The mean absolute error was the lowest with Barrett's measured PCA (0.55 ± 0.38) followed by Barrett's predicted PCA mean absolute error (0.65 ± 0.31), vector summation (0.69 ± 0.33), and the Abulafia-Koch formula (0.80 ± 0.36). The rate of eyes with prediction errors within 0.25 D or less was the highest for Barrett's measured PCA (29.4%) followed by Barrett's predicted PCA (5.9%) and no eyes for the Abulafia-Koch formula and vector summation. The mean centroid prediction errors were lowest for Barrett's measured PCA and Barrett's predicted PCA (0.14 ± 0.66 @70, 0.14 ± 0.73 @179, respectively), followed by vector summation (0.35 ± 0.70 @5), and the Abulafia-Koch formula (0.39 ± 0.80 @179). The results suggest that in cases of high PCA, the Barrett toric calculator using direct measurements of PCA may have a potential advantage over predicted PCA in toric IOL calculations and vector summation of the anterior and posterior corneal astigmatism. [J Refract Surg. 2020;36(12):820-825.].

Characteristics of corneal high-order aberrations in adolescents with mild to moderate myopia

BackgroundThis study investigated the characteristics of corneal higher-order aberrations (HOAs) of the anterior surface, posterior surface, and total cornea in adolescents with mild to moderate myopia.MethodsA total of 183 patients with myopia (183 eyes) aged 8 to 18 years were enrolled in this study. The axial length (AL) of the eyes was measured by an IOL-Master, and corneal curvatures (K-values) and HOAs were measured by a Pentacam anterior segment diagnostic analyzer.ResultsResults of this study showed that the anterior, posterior and total corneal horizontal coma Z31 were − 0.1249 ± 0.105 μm, 0.0009 ± 0.001 μm, and − 0.1331 ± 0.116 μm, respectively; the anterior, posterior and total corneal vertical coma Z3− 1 were − 0.0212 ± 0.164 μm, 0.0003 ± 0.043 μm, and − 0.0216 ± 0.168 μm, respectively; and spherical aberration (SA) Z40 values were 0.2244 ± 0.091 μm, 0.1437 ± 0.029 um, and 0.1889 ± 0.090 μm, respectively. Total corneal Z31 was statistically correlated with posterior corneal astigmatism (K2b − K1b) (p = 0.038). Total corneal Z3− 1 was correlated with anterior corneal astigmatism (K2f − K1f) (p = 0.027). Anterior, posterior, and total corneal Z40 were correlated with anterior and posterior corneal curvature (K1f, K2f, K1b, K2b) (p = 0.001). Posterior corneal Z40b was also significantly correlated with AL.ConclusionsIn adolescents with mild to moderate myopia, the posterior corneal surface shape may play a compensatory role in the balance of corneal aberrations, and the posterior corneal SA tended to become less negative as the AL increased. The corneal coma may also play a compensatory role in posterior corneal surface astigmatism, which was valuable for the treatment for improving visual quality. This conclusion still needs to be verified.

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

To characterise the posterior and total corneal astigmatism using colour point-source light-emitting diodes (LED) topography. In a prospective case series 400 eyes from 400 patients were evaluated by colour-LED topography. Only eyes with normal topographies were considered. The following parameters were studied: magnitude and distribution of SimK and posterior corneal astigmatism, correlation between SimK and posterior corneal astigmatism, and differences in magnitude and axis between total and anterior corneal astigmatism. The mean SimK corneal astigmatism was 1.21 ± 0.94 D. The mean posterior corneal astigmatism was 0.37 ± 0.24 D. Posterior astigmatism was vertically oriented in 68% of eyes. Twenty-two percent of eyes showed a posterior corneal astigmatism ≥ 0.50 D. The correlation coefficients between SimK and posterior corneal astigmatism were: r2 = 0.066; p = 0.371 in WTR eyes, r2 = 0.112; p = 0.173 in ATR eyes and r2 = -0.019; p = 0.879 in oblique eyes. A difference between SimK and total corneal astigmatism ≥ 0.50 D was found in 7% of eyes. A difference in axis between SimK and total corneal astigmatism ≥ 10° was found in 24% of eyes. The percentage of eyes with posterior corneal astigmatism ≥ 0.50 D and the differences between anterior and total corneal astigmatism were higher than those previously reported in the literature. Therefore, this study supports the consideration of total corneal astigmatism magnitude and axis is mandatory for a precise surgical correction of astigmatism.

Characterization of posterior corneal astigmatism in a population with keratoconus

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

Recent developments in intraocular lens power calculation methods-update 2020.

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

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

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

Agreement of corneal curvature and central corneal thickness obtained from a swept-source OCT and Pentacam in ectopia lentis patients

To assess the inter-device consistency of corneal curvature and central corneal thickness between Pentacam and a swept-source Fourier-domain anterior segment optical coherence tomography (AS-OCT) in ectopia lentis patients. Totally 72 eyes of ectopia lentis patients were recruited. Central corneal thickness (CCT), corneal curvature values and corneal astigmatism were obtained from both the Pentacam and AS-OCT (CASIA2). Repeatability was evaluated for both devices. The coefficient of repeatability (COR) and the relative COR was calculated. Bland-Altman plots were conducted to evaluate the inter-device agreement of measurement. Orthogonal linear regression was used to examine any proportional bias. The mean difference of CCT, steep anterior corneal curvature (anterior KS), flat anterior corneal curvature (anterior Kf), anterior corneal astigmatism (ACA), steep posterior corneal curvature (posterior KS), flat posterior corneal curvature (posterior Kf), posterior corneal astigmatism (PCA), steep true net power (TNP KS), flat true net power (TNP Kf) and total corneal astigmatism (TCA) between Pentacam and CASIA2 were 7.03±9.70 µm, -0.19±0.41 D, -0.27±0.35 D, 0.04±0.47 D, -0.17±0.23 D, -0.11±0.11 D, -0.02±1.02 D -0.41±0.43 D, -0.52±0.46 D, and -0.15±0.96 D, respectively. For measurement of TNP Kf with the Pentacam and CASIA2, a mean difference of 0.52 D and COR of 0.90 with P=0.02 was detected. There was no significant difference in CCT (P=0.393), anterior Kf (P=0.107), anterior Ks (P=0.414), ACA (P=0.131), posterior Kf (P=0.286), posterior Ks (P=0.418), PCA (P=0.105), TNP Ks (P=0.054), and TCA (P=0.977) between Pentacam and CASIA2. Our study reveals good agreement of CCT, corneal curvature and corneal astigmatism measured by CASIA2 and Pentacam in ectopia lentis patients. However, there was significant difference for CCT and corneal curvature values obtained by the two devices.

Effects of Superficial Keratectomy in Peripheral Hypertrophic Subepithelial Corneal Opacification on Front and Back Corneal Astigmatism

ABSTRACT Purpose To evaluate changes of anterior and posterior corneal astigmatism after superficial keratectomy in peripheral hypertrophic subepithelial corneal opacification (PHSCO). Methods Patients with PHSCO, who had received superficial keratectomy with mitomycin C 0.02%, were included in this retrospective study. Scheimpflug imaging of the cornea (Pentacam®, Oculus, Wetzlar, Germany), best-corrected visual acuity (BCVA) and objective refraction were determined preoperatively and 3 months after superficial keratectomy. Results Fifteen eyes of 15 patients (age: 55 ± 16 years; range: 36–82 years) were included. The mean preoperative BCVA was logMAR 0.4 ± 0.2 and improved to logMAR 0.21 ± 0.3 (p < .01) postoperatively. The median preoperative astigmatism of the anterior corneal surface was 4.67 ± 2.4 D (range: 0.9–13.2 D) and decreased to 1.4 ± 0.4 D (range: 0.8–2.3 D) 3 months after surgery. The median astigmatism of the posterior corneal surface was 0.6 ± 0.5 D (range: 0.1–2.2 D) before surgery and decreased to 0.3 ± 0.2 D (range: 0–0.7 D) 3 months after surgery. Conclusion Superficial keratectomy reduces anterior corneal astigmatism more than posterior corneal astigmatism in patients with PHSCO. Furthermore, a myopic shift and corneal steepening in the peripheral and mid-peripheral cornea was observed after removal of the subepithelial corneal opacification spots.

Assessment of Long-Term Anterior and Posterior Topographic Changes in the Cornea After Ptosis Surgery Using Fourier Harmonic Analysis.

We aimed to assess the corneal refractive changes induced by ptosis surgery in patients with acquired ptosis using Fourier harmonic analysis. This retrospective observational study enrolled consecutive patients who underwent levator aponeurotic surgery for acquired ptosis at the Department of Ophthalmology in the University of Tokyo Hospital from May 2016 to January 2018. Best corrected visual acuity, central corneal thickness, average keratometric corneal power (AvgK), corneal astigmatism, and topographic data using Fourier analysis were analyzed preoperatively and 6 months postoperatively. Thirty-two eyes of 32 patients (age, 72.6 ± 8.5 years) were included in this study. There were no significant differences in best corrected visual acuity and central corneal thickness. However, there were significant decreases in anterior AvgK, anterior corneal astigmatism, and posterior corneal astigmatism 6 months postoperatively (all, P < 0.001). Fourier harmonic analysis showed that the anterior spherical component significantly decreased 6 months postoperatively (P < 0.001). There were no significant differences in other components of the anterior and posterior cornea. There was a significant negative correlation between preoperative posterior AvgK and changes in posterior AvgK (r = -0.891, P < 0.001) and between preoperative posterior corneal astigmatism and changes in posterior corneal astigmatism at 6 months (r = -0.858, P < 0.001). Anterior and posterior corneal keratometry and posterior corneal astigmatism significantly changed 6 months after ptosis surgery for acquired ptosis.

Posterior and total corneal astigmatism measured with optical coherence tomography-based biometer and dual Scheimpflug analyzer.

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.

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

BackgroundIn the present study, we aimed to analyze the effects of cataract surgery using a 1.8-mm steep-axis clear corneal incision (CCI) on the posterior corneal surfaces based on the keratometry from the rotating Scheimpflug imaging device (Pentacam HR) in candidates for toric intraocular lens (IOL) implantation.MethodsPreoperative and at least 1-month postoperative data measured by Pentacam HR were collected in patients for toric IOL implantation. Surgically induced astigmatism on the posterior cornea (P-SIA) was calculated based on the preoperative and postoperative keratometric data, and the related factors of P-SIA were analyzed.ResultsA total of 60 eyes from 56 patients were enrolled. The preoperative anterior, posterior and total corneal astigmatism was 1.58 ± 0.61 D,0.28 ± 0.22 D and 1.70 ± 0.52 D respectively. The postoperative anterior, posterior and total corneal astigmatism was 1.26 ± 0.68 D, 0.41 ± 0.26 D and 1.30 ± 0.51 D respectively. The astigmatism was significantly decreased on anterior surface (P<0.001, paired t-test) and increased on posterior surface (P<0.001, paired t-test). The mean of P-SIA calculated by Holladay–Cravy–Koch method was 0.34 ± 0.20 D, with 0.5 D or greater accounting for 26.7%. A statistically significant correlation was observed between the P-SIA and preoperative anterior corneal astigmatism (r = 0.29, P = 0.024), as well as preoperative posterior corneal astigmatism (r = 0.27, P = 0.038). Multivariate regression analysis showed the preoperative anterior and posterior corneal astigmatism had a significant effect on P-SIA (F = 7.344, P = 0.001).ConclusionsIn candidates for toric IOL implantation with a 1.8-mm steep-axis CCI, the incision caused a significant reduction of the anterior corneal astigmatism but an increase of the posterior corneal astigmatism. P-SIA could not be ignored, and it played a significant role in SIA, especially in cases with higher preoperative anterior or posterior corneal astigmatism.

Refractive outcome of toric intraocular lens calculation in cases of oblique anterior corneal astigmatism.

To establish whether toric intraocular lens (IOL) calculation on the basis of anterior corneal measurements alone, in corneas with oblique anterior astigmatism, will result in a systematic overcorrection or undercorrection of postoperative refractive astigmatism, and to establish whether adjustment of oblique anterior corneal astigmatism to allow for the likely effect of posterior corneal astigmatism is needed in such eyes. The Queen Elizabeth Hospital, Department of Ophthalmology, Adelaide, South Australia. Retrospective case series. Data were collected from consecutive eyes with oblique anterior corneal astigmatism undergoing cataract surgery or refractive lens exchange. Toric IOL calculations were made using unadjusted anterior corneal astigmatism measurements and an astigmatically neutral technique. By comparison of targeted vs achieved astigmatic correction using vector analysis, the astigmatic power prediction error and angle of error were derived. In 50 eyes, the mean postoperatively measured refractive astigmatism was 0.42 diopters (D) (SD 0.33 D), the mean targeted refractive astigmatism was 0.15 (SD 0.18), and the vector-derived mean absolute prediction error was 0.23 D (SD 0.21). All 50 eyes (100%) fell at or within ±1.00 D of the target and 45 eyes (90%) at or within ±0.50 D. The geometric mean astigmatism correction index was 0.98, and the mean absolute angle of error was 8.63 degrees (SD 8.55). There is no systematic error attributable to posterior corneal astigmatism in toric IOL calculation and no need for adjustment of anteriorly measured corneal keratometric values for toric IOL calculation in eyes with oblique anterior corneal astigmatism. To do so may introduce an error in astigmatic outcome.

Total keratometry in intraocular lens power calculations in eyes with previous laser refractive surgery.

Intraocular lens (IOL) calculations in post-refractive cases remain a concern. Our study identifies improved options for surgeons. To evaluate and compare the prediction accuracy of IOL power calculation methods after previous laser refractive surgery using standard keratometry (SK), measured posterior corneal astigmatism (PCA) and total keratometry (TK). Retrospective consecutive cohort. A total of 50 consecutive patients (72 eyes) at a private institution who underwent cataract surgery with prior laser refractive procedures. Methods using SK included ASCRS mean, Barrett True-K no history, Haigis-L and Shammas IOL formulae. Barrett True-K using posterior values (True K TK), Haigis and Holladay 1 Double-K methods using TK were also assessed. Post-surgery refraction was undertaken at minimum 3 weeks following surgery. Arithmetic and absolute IOL refractive prediction errors, variances in mean arithmetic IOL prediction error, and percentage of eyes within ±0.25D, ±0.50D, ±0.75D and ±1.00D of refractive prediction errors were compared. The Barrett True-K (TK) provided the lowest mean refractive prediction error (RPE) and variance for both prior myopes and hyperopes undergoing cataract surgery. The Barrett True-K (TK) exhibited the highest percentages of eyes within ±0.50D, ±0.75D and ±1.00D of the RPE compared to other formulae for prior myopic patients. Accuracy of IOL power calculations in post-laser eyes can be improved by the addition of posterior corneal values as measured by the IOLMaster 700. The use of total keratometry may supplement outcomes when no prior refraction history is known.

Clinical Outcomes of Toric Intraocular Lenses: Differences in Expected Outcomes When Using a Calculator That Considers Effective Lens Position and the Posterior Cornea vs One That Does Not.

PurposeTo compare toric intraocular lens (IOL) outcome accuracy after using an online toric calculator that accounted for posterior corneal astigmatism versus a traditional calculator that only accounted for anterior corneal astigmatism.Patients and MethodsThis was a single-arm, non-masked, non-randomized prospective study in a single private practice in Norfolk, Virginia, USA, evaluating clinical outcomes of toric IOL implantation based on a calculator that considered posterior corneal astigmatism (PCA) and effective lens position (ELP). Of interest was the distribution of the residual refraction (sphere and cylinder) at 40–70 days postoperative. Residual refractive cylinder (RRC) was compared to the back-calculated theoretical results using a legacy calculator that did not consider PCA. Distance visual acuity (best-corrected and uncorrected) and the manifest refraction were also measured, along with preoperative and postoperative keratometry.ResultsForty-six eyes of 34 subjects were available for analysis. All eyes had a spherical equivalent refraction within 0.5D of intended. Uncorrected visual acuity was 20/25 or better in 86% of eyes targeted for emmetropia. Residual cylinder was 0.50D or less in 96% of eyes, with a maximum of 0.75D measured. The difference between residual cylinder and the expected cylinder from calculations was significantly lower for the calculator that included consideration of PCA and ELP relative to the one that did not.ConclusionUse of a toric IOL calculator that includes consideration of posterior corneal astigmatism is recommended to optimize clinical outcomes.

Analysis of the Corneal Anterior and Posterior Surface in Patients With Peripheral Hypertrophic Subepithelial Corneal Opacification.

To characterize the corneal changes in peripheral hypertrophic subepithelial corneal opacification (PHSCO) considering elevation of the anterior and posterior corneal surface, corneal astigmatism, tear secretion, and endothelial cell density. Thirty-eight eyes of 22 patients with PHSCO on at least 1 eye and 38 eyes of 22 age- and sex-matched healthy subjects were included in this retrospective cross-sectional study. Using the Pentacam system (Oculus, Wetzlar, Germany), measurement of the anterior and posterior corneal surface was performed. In addition, the Schirmer test was conducted, and endothelial cells were counted in the central cornea with a specular microscope (SP-3000P; Topcon, Tokyo, Japan). The mean age was 55.2±11.7 years in patients with PHSCO and 54.1±12.4 years in healthy subjects. The corneas of patients with PHSCO showed higher corneal astigmatism of both the corneal anterior and posterior surface (2.9/0.5 vs. 0.8/0.3 D, PHSCO vs. controls, P=<0.001/<0.01). The cornea was thickest in the peripheral 12-o'clock position and the peripheral superior nasal area. Remarkably, central endothelial cell density was markedly reduced in patients with PHSCO (2,372.6 cell/mm±328.1 vs. 2,673 cells/mm±287.6, P<0.01, PHSCO vs. controls). Also, the Schirmer test revealed lower tear secretion in patients with PHSCO (9.8±4.4 mm vs. 14.3±5.7 mm, P<0.001, PHSCO vs. controls). The astigmatism of both the anterior and posterior corneal surface is increased in patients with PHSCO. Intriguingly, tear secretion and central endothelial cell density are reduced in patients with PHSCO. These measurements may become useful to assess the impact of morphological changes on vision and to track disease progression in PHSCO.

Corneal topography, anterior segment and high-order aberration assessments in children with ≥ 2 diopter astigmatism.

To assess topographic findings, anterior segment parameters and high-order aberrations (HOAs) by using corneal tomography in children with 2diopters (dp) or more astigmatism. Children with 2dp or more astigmatism (study group) and children with astigmatism less than 1dp (control group) were recruited. Corneal astigmatism, mean, steep, flat keratometry (K) findings, anterior and posterior K results and anterior segment parameters including anterior chamber depth, kappa distance, horizontal corneal diameter, mean, central, middle, peripheral corneal thicknesses (CT), white-to-white (WTW) distance and pupil diameter were measured by Galilei G4 Dual Scheimpflug corneal tomography. HOAs were also assessed and compared between groups. Fifty-eight eyes of 37 children in the study group and 37 eyes of 37 children in the control group were enrolled. The mean ages of groups were 9.7 ± 2.4years and 9.3 ± 1.6years in study and control groups, respectively. The mean astigmatism was 3.3 ± 1.1dp and 0.5 ± 0.3dp in study and control groups, respectively (p < 0.05). Total corneal astigmatism was 3.3 ± 0.84dp and 1.14 ± 0.47dp in study and control groups, respectively (p < 0.05). There was a significant difference between groups in terms of posterior steep K and posterior astigmatism values. Among anterior segment parameters, mean CT and WTW values were statistically different between groups. HOAs were found to be statistically different between groups. Higher posterior corneal astigmatism, thinner mean CT and lower WTW distance were found in children with 2dp or more astigmatism. Besides, HOAs were much more in these astigmatic children.

Visual and autorefraction outcomes following toric intraocular lens insertion without calculation of posterior corneal astigmatism in the UK National Health Service.

To ascertain visual and refractive outcomes following toric intraocular lens (IOL) implantation in the UK National Health Service (NHS) without posterior corneal astigmatism calculation, with multiple surgeons of different grades, pooled input and output pathways and autorefraction as the refractive outcome measure. Preoperative and 1-month post-operative data were analysed retrospectively in 114 eyes (95 patients) receiving a toric IOL between 2014 and 2016 at Imperial College NHS Trust. Preoperative keratometric astigmatism was ≥2 dioptres (D). Mean preoperative best-corrected visual acuity (BCVA) was 0.50 logMAR (±0.46), improving to a mean uncorrected VA (UCVA) of 0.35 logMAR (±0.36) postoperatively (p < 0.001) with 65% of eyes attaining a UCVA ≤ 0.30 logMAR. Excluding 33 eyes with pre-existing visual comorbidities and one targeting monovision, mean post-operative UCVA was 0.24 logMAR (±0.29) (p < 0.001), and 85% had UCVA ≤ 0.30 logMAR, 62% UCVA ≤ 0.20 logMAR. Mean refractive astigmatism improved from 3.04 D (±1.46) to 1.36 D (±1.13) (p < 0.001). In total, 52% of eyes had post-operative refractive astigmatism ≤1.00 D. The Alpins correction index was 1.05 (±0.22), indicating a tendency to overcorrect. Toric IOL misalignment was noted in two eyes, and two cases of posterior capsule rupture were converted to a non-toric IOL. Visual outcomes of toric IOL implantation in our pooled pathway are comparable to single-surgeon case series where posterior corneal astigmatism has not been accounted for. However, with 1-month post-operative autorefraction, only 52% of eyes had ≤1 D refractive astigmatism, which is lower than previously published series, but may be standard for 1-month autorefraction outcomes.

Changes in anterior segment parameters following insertion of ExPRESS mini glaucoma implant vs. trabeculectomy.

To compare changes in anterior segment parameters following ExPRESS Mini Glaucoma Shunt surgery vs. trabeculectomy using the Pentacam rotating Scheimpflug camera. In this prospective, comparative study, 27 patients with glaucoma treated at the Rabin Medical Center from 2009 to 2013 were enrolled in this prospective comparative study: 19 participants (19 eyes) underwent ExPRESS shunt implantation and 12 (13 eyes) underwent trabeculectomy. Changes in anterior chamber parameters at postoperative day 1 and postoperative month 3 were evaluated on Scheimpflug images. Intraocular pressure decreased significantly from baseline in both groups. The decrease in both groups was similar at postoperative month 3 (p=0.82). ExPRESS surgery caused a transient increase in posterior corneal astigmatism (p=0.008) and a transient decrease in anterior chamber depth (p=0.016) and volume (p=0.006) on postoperative day 1. At postoperative month 3, these parameters were no longer statistically significant (p=0.65, p=0.51, and p=0.57 respectively). Trabeculectomy caused a transient increase in anterior and posterior corneal astigmatism on postoperative day 1 (p=0.003 and p=0.005, respectively), which were not evident at postoperative month 3 (p=1.0 and p=1.0, respectively). At postoperative month 3, both ExPRESS and trabeculectomy showed similar changes in anterior chamber parameters. Both ExPRESS mini glaucoma implant and trabeculectomy significantly decreased intraocular pressure and had transient effects on anterior segment parameters, with minor differences between the methods.

Pentacam Indices in Photorefractive Keratectomy Surgery.

Refractive eye surgeries are one of the most non-emergent ophthalmic surgeries due to the effect on the reduction of refractive errors, increasing visual acuity, enhancing the quality of vision, and indirectly increasing the quality of life of patients. The aim of this study was to determine Pentacam indices in the patients who underwent photorefractive keratectomy (PRK) during 2014-2018, as well as to show their correlation with the type of refractive error. This descriptive cross-sectional study was performed on 2215 eyes of 1125 patients undergoing PRK surgery. The patients’ checklist, including demographic information, refractive index, keratometry, pachymetry, corneal surface zone indices, and progressive corneal thickness indices, was provided. All data were analyzed using the IBM SPSS software, version 25. The findings showed that there was a significant association between posterior corneal astigmatism (PCA) and anterior corneal astigmatism (ACA) (p=0.00). The mean Kmax front was recorded as 44.844 ± 1.58 D, which was significantly correlated with the type of refractive errors (p=0.00). According to the findings, there was a significant relationship between anterior chamber indices and refractive error types and their severity (p=0.00). There was also a significant correlation between the surface zone and keratoconus indices (i.e., index of surface variance - ISV, index of vertical asymmetry - IVA, index of height asymmetry - IHA, and minimum radius of curvature - Rmin) with refractive errors (p=0.00). The findings showed that some of the Pentacam indices could be related to the types of refractive errors in patients undergoing PRK surgery. Therefore, their evaluation is of great importance in this regard.