Assessment of Anterior, Posterior, and Total Central Corneal Astigmatism in Eyes With Keratoconus

Normative Values for Corneal Tomography and Comparison of Both Eyes in Young Saudi Males with 20/20 Vision Using Pentacam-HR Scheimpflug Imaging

Purpose

Anterior segment evaluation using Scheimpflug imaging with the Pentacam scanner allows the acquisition of a plethora of information. It aids in screening and diagnosing corneal pathologies and determining suitability for keratorefractive procedures. This research has significant benefits in terms of establishing normative tomographic values, which is crucial in countries where Keratoconus (KC) is more prevalent, especially among young age group, along with aiding future research in the field of refractive surgery by providing relevant normative data.

Methods

A retrospective review of digital corneal tomography images for a group of medically and ophthalmologically free males aged between 18 and 21 years with 20/20 unaided distant visual acuity was performed.

Results

A total of 1272 subjects (2544 eyes) were included. Findings revealed a mean maximal corneal curvature (Kmax) of 42.91 ± 1.40D (range 36.90–47.80D). The mean flat keratometry (K1) was 41.87 ± 1.31D (range 36.00–46.40D). The mean steep keratometry (K2) was 42.66 ± 1.35D (range 36.70–47.60D). The mean corneal astigmatism (CA) was 0.79 ± 0.37D (range 0.00D-2.30D). The mean central corneal thickness (CCT) was 558.53 ± 33.84 μm (range 421–677 μm). The mean thinnest corneal location thickness (TCLT) was 551.64 ± 34.08 μm (range 417–669μm). The mean corneal diameter (CD) and anterior chamber depth (ACD) were 12.13 ± 0.39 mm (range 10.50–13.60 mm) and 3.12 ± 0.29 mm (range 2.08–4.08 mm), respectively. The median differences between both eyes of the same subject were as follows: kmax difference of 0.20D (IQR 0.1–0.4); K1, K2 and CA difference of 0.20D (IQR 0.1–0.3) for all 3 parameters; CCT and TCLT difference of 5.00 μm (IQR 3.0–9.0) and 6.00 μm (IQR 3.0–10.0), respectively; CD difference of 0.10 mm (IQR 0.0–0.1); and ACD difference of 0.04 (IQR 0.02–0.06).

Conclusion

We believe our data can aid in establishing normative tomographic values and acceptable differences between both eyes. Our data may also help detect subtle corneal pathology and be useful for researchers and innovators in the field of ophthalmology.

Refractive Outcomes of Non-Toric and Toric Intraocular Lenses in Mild, Moderate and Advanced Keratoconus: A Systematic Review and Meta-Analysis

Background: To perform a systematic review and meta-analysis of the refractive outcomes of non-toric and toric intraocular lenses (IOLs) in keratoconus (KC) using different IOL power calculation formulas. Methods: A systematic search was conducted to identify studies that report on refractive outcomes of different IOL power calculation formulas in KC patients undergoing cataract surgery. Inclusion criteria were primary posterior chamber non-toric and toric monofocal intraocular lens implantation, data on the degree of KC, explicit mention of the formula used for each stage of KC, and the number of eyes in each category. We calculated and compared the absolute and mean prediction errors, percentage of eyes within 0.5 D and 1 D from target, and the weighted absolute prediction errors of IOL formulas, all were given for KC degrees I–III. Results: The bibliographic search yielded 582 studies published between 1996 and 2020, 14 of which (in total 456 eyes) met the criteria: three studies on non-toric IOL (98 eyes), eight studies on toric IOLs (98 eyes) and three studies of unknown separation between non-toric and toric IOLs (260 eyes). The lowest absolute prediction error (APE) for mild, moderate, and advanced KC was seen with Kane’s IOL power formula with keratoconus adjustment. The APE for the top five IOL power formulas ranged 0.49–0.73 diopters (D) for mild (83–94%) of eyes within 1 D from the target), 1.08–1.21 D for moderate (51–57% within 1 D), and 1.44–2.86 D for advanced KC (12–48% within 1 D). Conclusions: Cataract surgery in eyes with mild-to-moderate KC generally achieves satisfactory postoperative refractive results. In patients with advanced KC, a minority of the eyes achieved spherical equivalent refraction within 1 D from the target. The Kane’s formula with keratoconus adjustment showed the best results in all KC stages.

The false positive rates for detecting keratoconus and potential ectatic corneal conditions when evaluating astigmatic eyes with Scheimpflug Technology

PURPOSE

To quantify the false positive rates for keratoconus (KC) and potential ectatic corneal conditions in highly astigmatism eyes when using published parameters/indices obtained from the Pentacam and Galilei units.

SETTING

Oftalmosalud Instituto de Ojos, Lima, Peru.

DESIGN

Prospective cohort study.

METHODS

67 consecutive eyes with corneal astigmatism > 1.5 D, with a minimum follow ups of 36 months after an uneventful LASIK procedure were included. Indices for KC and other potential ectatic corneal conditions (subclinical KC, forme fruste KC, suspect KC) were obtained using the Pentacam and Galilei Scheimpflug cameras.

MAIN OUTCOME MEASURES

The false positive rates for KC and potential ectatic corneal conditions were measured. Cut off values provided by previous studies and company-based parameters were used to assess the rate of false positivity.

RESULTS

The range of false positive rates for a KC diagnosis depending on the lowest and highest cutoff values were: index of height decentration (61% - 1%), index of surface variance (76% - 0%), Posterior elevation (55% - 0%), maximum Ambrosio Relational thickness (100% - 13%), Belin Ambrosio enhanced ectasia display total deviation value (100% - 4%), Average pachymetric progression index (69% - 3%), Pachymetry at the thinnest point (58% - 1%), CSI Center Surround Index (100%), Differential sector index (51%).

CONCLUSION

The false positive rates for KC and ectatic corneal conditions vary dramatically depending on the cut-off values used. Some indexes used for diagnosis of potential ectatic corneal conditions are inaccurate in normal, highly astigmatic eyes.

Astigmatic Vectorial Analysis in Pediatric Keratoconus After Unilateral Cross-Linking Treatment

PURPOSE

The aims of this study were to evaluate the treatment response of pediatric keratoconus (KC) patients to unilateral corneal collagen cross-linking (CXL) in treated eyes, disease progression in untreated eyes, and define the predictive value of astigmatic parameters by astigmatic vectorial analysis.

METHODS

Pediatric patients with KC with CXL-treated progressive eye and untreated fellow eye were included. Patients with other ocular conditions and a history of previous ocular surgery were excluded. Astigmatic changes in anterior and posterior corneal surfaces were evaluated with vectorial analysis. The receiver operating characteristic curves were analyzed to detect the best parameter that discriminates treated and untreated groups.

RESULTS

Thirty-two eyes of 16 patients with at least 2-year follow-up were analyzed. The maximum keratometry (K) in CXL-treated eyes remained stable (from 53.51 ± 2.86-53.41 ± 2.84 diopter (D), P = 0.84) while the steepest K increased in untreated eyes (from 47.82 ± 1.71-49.59 ± 3.32 D, P = 0.03). The oblique components of corneal astigmatism in CXL-treated eyes were higher than those of fellow eyes (all P < 0.05), which significantly decreased in the anterior 3-mm zone after treatment (P = 0.048). The mean differential astigmatism magnitudes were significantly higher in treated eyes (all P < 0.05). The refractive centroid remained unchanged in treated eyes (P = 0.553) and shifted in the oblique direction in untreated eyes (P = 0.04). The oblique differential astigmatism in the anterior 7-mm zone showed the highest area under the curve value in predicting treatment efficacy (0.813, 95% confidence interval: 0.646-0.981, P < 0.001).

CONCLUSIONS

Astigmatic vectorial analysis is an objective tool for longitudinal assessment of clinical outcomes in KC. Changes in the oblique components of corneal astigmatism might predict progression and treatment efficacy.

Refractive outcome and tomographic changes after Descemet membrane endothelial keratoplasty in pseudophakic eyes with Fuchs' endothelial dystrophy

Purpose

To analyze refractive and topographic changes secondary to Descemet membrane endothelial keratoplasty (DMEK) in pseudophakic eyes with Fuchs’ endothelial dystrophy (FED).

Methods

Eighty-seven pseudophakic eyes of 74 patients who underwent subsequent DMEK surgery for corneal endothelial decompensation and associated visual impairment were included. Median post-operative follow-up time was 12 months (range: 3–26 months). Main outcome measures were pre- and post-operative manifest refraction, anterior and posterior corneal astigmatism, simulated keratometry (CA_SimK) and Q value obtained by Scheimpflug imaging. Secondary outcome measures included corrected distance visual acuity (CDVA), central corneal densitometry, central corneal thickness, corneal volume (CV), anterior chamber volume (ACV) and anterior chamber depth (ACD).

Results

After DMEK surgery, mean pre-operative spherical equivalent (± SD) changed from + 0.04 ± 1.73 D to + 0.37 ± 1.30 D post-operatively (p = 0.06). CDVA, proportion of emmetropic eyes, ACV and ACD increased significantly during follow-up. There was also a significant decrease in posterior corneal astigmatism, central corneal densitometry, central corneal thickness and corneal volume over time (p = 0.001). Only anterior corneal astigmatism and simulated keratometry (CA_SimK) remained fairly stable after DMEK.

Conclusion

Despite tendencies toward a hyperopic shift, changes in SE were not significant and refraction remained overall stable in pseudophakic patients undergoing DMEK for FED. Analysis of corneal parameters by Scheimpflug imaging mainly revealed changes in posterior corneal astigmatism pointing out the relevance of posterior corneal profile changes during edema resolution after DMEK.

Influence of rebubbling on anterior segment parameters and refractive outcomes in eyes with DMEK for Fuchs endothelial dystrophy

PURPOSE

To evaluate the potential impact of rebubbling on the anterior segment parameters and refractive outcomes in patients with graft detachment following uneventful DMEK for Fuchs endothelial dystrophy (FED).

METHODS

Retrospective institutional cohort study of comparing 34 eyes of 31 patients with rebubbling for graft detachment following Descemet membrane endothelial keratoplasty (DMEK) to 33 eyes of 28 patients with uneventful DMEK. Main outcome parameters were various corneal parameters obtained by Scheimpflug imaging, refractive outcome, corrected distance visual acuity (CDVA), and endothelial cell density (ECD).

RESULTS

Anterior and posterior corneal astigmatism, corneal densitometry, central corneal thickness, and anterior chamber depth and volume showed no significant differences. Preoperative distribution of astigmatism axis orientations showed a high proportion of anterior corneal with-the-rule astigmatism (71%) in eyes requiring rebubbling. Mean postoperative cylinder in the rebubbling group (1.21 ± 0.85 D) was significantly higher compared to the controls (p = 0.04), while differences in spherical equivalent (SE) were insignificant (p = 0.24). Postoperative CDVA was 0.11 ± 0.11 in the control group compared to 0.21 ± 0.17 in the rebubbling group (p = 0.03). Eyes with subsequent rebubbling demonstrated a significantly higher endothelial cell loss (56% versus 37%) (p < 0.001).

CONCLUSION

Apart from higher cylinder values, refractive outcome and corneal parameters assessed by Scheimpflug imaging were comparable in eyes with rebubbling and controls. However, a reduced visual acuity and an increased endothelial cell loss should be taken into consideration prior to rebubbling especially in eyes with circumscribed graft detachment.

Analysis of total corneal astigmatism with a rotating Scheimpflug camera in keratoconus

Background

To analyze mean corneal powers and astigmatisms on anterior, posterior, and total cornea in patients with keratoconus as calculated according to various keratometric measurements using a Scheimpflug camera.

Methods

We examined the left eyes of 64 patients (41 males and 23 females; mean age 29.94 ± 6.63 years) with keratoconus. We measured simulated K (Sim-K), posterior K, true net power (TNP) and four types of total corneal refractive powers (TCRP). We then used the obtained values to analyze mean K, and corneal astigmatism. TCRP were measured at 2.0 ~ 5.0 mm.

Results

Mean corneal powers from Sim K, posterior K, and TNP were 49.12 ± 3.99, − 7.39 ± 0.79, and 47.78 ± 4.09 diopters, respectively. For TCRP centered on the pupil, mean K tended to decrease with measurement area (all p < 0.01). While, both mean K and astigmatism measured using TCRP centered on the apex decreased with measurement area (all p < 0.001). TCRP centered on the apex were greater than those centered on the pupil for mean K values calculated using TCRP (all p < 0.001). The proportion of WTR was greatest on the anterior and total cornea. As the measurement area moved to the periphery, the proportion of WTR increased.

Conclusions

Mean corneal powers and astigmatisms on total cornea with keratoconus change depending on calculation methods and measurement areas.

Characteristics of preoperative and postoperative astigmatism in patients having Descemet membrane endothelial keratoplasty

PURPOSE

To evaluate the characteristics of preoperative and postoperative astigmatism in patients having Descemet membrane endothelial keratoplasty (DMEK).

SETTING

Department of Ophthalmology, Goethe University, Frankfurt, Germany.

DESIGN

Retrospective case series.

METHODS

Measurements were obtained using a Scheimpflug camera (Pentacam AXL) preoperatively and 3 months and 12 months postoperatively. Values of front and back astigmatism and total astigmatism in the central 4.0 mm diameter zone (TCA4) were analyzed.

RESULTS

Fifty-three eyes of 45 patients were included. The prevalence of TCA4 above 1.0 diopter (D) was considerably higher (79%) and with-the-rule astigmatism was less frequent in this cohort of European patients with Fuchs endothelial dystrophy (mean age 65 years) than that reported in a meta-analysis of healthy European eyes. The TCA4 values correlated with anterior astigmatism preoperatively and postoperatively (P < .001) and with posterior astigmatism at the 1-year follow-up (P < .01). Although, no correlation was found between the preoperative and 1-year results for anterior astigmatism (P = .12), posterior astigmatism (P = .35), or total corneal astigmatism (P = .47), the difference in vector analysis between the two measurements was only 0.01 at 109 degrees, 0.03 at 98 degrees, and 0.02 at 157 degrees, respectively. However, the greater the difference between the preoperative TCA3 and preoperative TCA5 values, the greater the decrease in corneal astigmatism (P < .001).

CONCLUSIONS

The percentage of eyes with corneal astigmatism above 1.0 D was higher preoperatively and postoperatively in patients with Fuchs endothelial dystrophy than in a healthy population. Predicting postoperative astigmatism based on preoperative results is not possible; however, in eyes with a high difference between TCA3 and TCA5, a reduction in corneal astigmatism after DMEK is likely.

Visual Performance in Eyes Undergoing Femtosecond Laser-Assisted Keratoplasty for Advanced Keratoconus

This study was aimed to compare visual performance in eyes having femtosecond laser-assisted keratoplasty (FLAK) for grade 4 keratoconus and keratoconic eyes according to the Amsler-Krumeich classification. We comprised 15 eyes of 15 patients undergoing FLAK for grade 4 keratoconus and 69 of 69 keratoconic patients (grade 1; 26 eyes, 2; 17 eyes, 3; 10 eyes, and 4; 16 eyes), and compared best spectacle-corrected visual acuity (BSCVA), corneal astigmatism (CA), corneal densitometry (CD), and corneal higher-order aberrations (CHOAs) using the Scheimpflug rotating camera. BSCVA in the post-FLAK group was significantly better than that in grade 3 or 4 group, but not than that in grade 1 or 2 group. CA was significantly lower than that in grade 3 or 4 group, but not than that in grade 1 or 2 group. CD was significantly higher than that in grade 1, 2, and 3 group, and significantly lower than that in grade 4 group. CHOAs were significantly lower than that in grade 3 or 4 group, but not than that in grade 1 or 2 group. FLAK showed significantly better BSCVA, and less CA and CHOAs, than grade 3 or 4 keratoconus, and showed less CD than grade 4 keratoconus.

Enantiomorphism and rule similarity in the astigmatism axes of fellow eyes: A population-based study

PURPOSE

To evaluate the relationship patterns between astigmatism axes of fellow eyes (rule similarity and symmetry) and to determine the prevalence of each pattern in the studied population.

METHODS

This population-based study was conducted in 2015 in Iran. All participants had tests for visual acuity, objective refraction, subjective refraction (if cooperative), and assessment of eye health at the slit-lamp. Axis symmetry was based on two different patterns: direct (equal axes) and mirror (mirror image symmetry) or enantiomorphism. Bilateral astigmatism was classified as isorule if fellow eyes had the same orientation (e.g. both eyes were with-the-rule) and as anisorule if otherwise.

RESULTS

Of the total cases of bilateral astigmatism, 80% were isorule, and in the studied population, the prevalence of isorule and anisorule astigmatism was 14.89% and 3.53%, respectively. The prevalence of isorule increased with age (p<0.001). The prevalence of both isorule and anisorule increased at higher degrees of spherical ametropia (p<0.001). Median inter-ocular axis difference was 10° in mirror symmetry and 20° in direct symmetry with no significant difference between two genders (p>0.288). Both symmetry patterns reduced with age (p<0.001). Among cases of bilateral astigmatism, 15.5% and 19.8% had exact direct and mirror symmetry, respectively.

CONCLUSION

Bilateral astigmatism is mainly isorule in the population and anisorule astigmatism is rare. The enantiomorphism is the most common pattern in the population of bilateral astigmatism.

Time Course of Changes in Simulated Keratometry and Total Corneal Refractive Power after Corneal Collagen Cross-Linking for Progressive Keratoconus

Purpose

To assess the simulated keratometry (Sim K) and the total corneal refractive power (TCRP) in eyes undergoing conventional corneal cross-linking (CXL).

Methods

This study comprised 20 eyes of 20 keratoconic patients (14 men and 6 women; median age (25th and 75th percentile), 26.5 (21.8, 38.0) years) who underwent CXL. The Sim K and TCRP were measured with a rotating Scheimpflug system (Pentacam HR, Oculus), preoperatively and 1, 3, 6, and 12 months postoperatively.

Results

The values of Sim K were 52.65 (46.00, 55.70), 52.45 (45.85, 56.88), 51.70 (45.78, 55.83), 51.40 (45.68, 56.80), and 51.25 (46.08, 56.15) D preoperatively and 1, 3, 6, and 12 months postoperatively, respectively. The corresponding figures of TCRP were 52.10 (45.48, 55.08), 51.30 (45.18, 55.20), 50.95 (45.15, 54.50), 50.00 (45.18, 55.08), and 49.80 (45.48, 54.15) D, respectively. The variances of the Sim K and TCRP data were not statistically significant (p=0.994 and p=0.970, respectively, Kruskal-Wallis test). The Sim K was significantly larger than the TCRP before CXL and at 1, 3, 6, and 12 months after CXL (p<0.001, Wilcoxon signed-rank test).

Conclusions

Not only the Sim K but also TCRP was decreased by approximately 1 D after CXL. The Sim K readings may overestimate the TCRP, even after CXL for progressive keratoconus.

Study of Morpho-Geometric Variables to Improve the Diagnosis in Keratoconus with Mild Visual Limitation

The validation of new methods for the diagnosis of incipient cases of Keratoconus (KC) with mild visual limitation is of great interest in the field of ophthalmology. During the asymmetric progression of the disease, the current diagnostic indexes do not record the geometric decompensation of the corneal curvature nor the variation of the spatial profile that occurs in singular points of the cornea. The purpose of this work is to determine the structural characterization of the asymmetry of the disease by using morpho-geometric parameters in KC eyes with mild visual limitation including using an analysis of a patient-specific virtual model with the aid of computer-aided design (CAD) tools. This comparative study included 80 eyes of patients classified as mild KC according to the degree of visual limitation and a control group of 122 eyes of normal patients. The metric with the highest area under the receiver operating characteristic (ROC) curve was the posterior apex deviation. The most prominent correlation was found between the anterior and posterior deviations of the thinnest point for the mild keratoconic cases. This new custom computational approach provides the clinician with a three-dimensional view of the corneal architecture when the visual loss starts to impair.

Mean Posterior Corneal Power and Astigmatism in Normal Versus Keratoconic Eyes

Purpose:

To compare mean posterior corneal power and astigmatism in normal versus keratoconus affected eyes and determine the optimal cut-off points to maximize sensitivity and specificity in discriminating keratoconus from normal corneas.

Methods:

A total of 204 normal eyes and 142 keratoconus affected eyes were enrolled in this prospective comparative study. Mean posterior corneal power and astigmatism were measured using a dual Scheimpflug camera. Correlation coefficients were calculated to assess the relationship between the magnitudes of keratometric and posterior corneal astigmatism in the study groups. Receiver operating characteristic curves were used to compare the sensitivity and specificity of the measured parameters and to identify the optimal cut-off points for discriminating keratoconus from normal corneas.

Results:

The mean posterior corneal power was −6.29 ± 0.20 D in the normal group and −7.77 ± 0.87 D in the keratoconus group (P < 0.001). The mean magnitudes of the posterior corneal astigmatisms were −0.32 ± 0.15 D and −0.94 ± 0.39 D in the normal and keratoconus groups, respectively (P < 0.001). Significant correlations were found between the magnitudes of keratometric and posterior corneal astigmatism in the normal (r=−0.76, P < 0.001) and keratoconus (r=−0.72, P < 0.001) groups. The mean posterior corneal power and astigmatism were highly reliable characteristics that distinguished keratoconus from normal corneas (area under the curve, 0.99 and 0.95, respectively). The optimal cut-off points of mean posterior corneal power and astigmatism were −6.70 D and −0.54 D, respectively.

Conclusion:

Mean posterior corneal power and astigmatism measured using a Galilei analyzer camera might have potential in diagnosing keratoconus. The cut-off points provided can be used for keratoconus screening.

Characteristics of Posterior Corneal Astigmatism in Different Stages of Keratoconus

Purpose

To evaluate the magnitudes and axis orientation of anterior corneal astigmatism (ACA) and posterior corneal astigmatism (PCA), the ratio of ACA to PCA, and the correlation between ACA and PCA in the different stages of keratoconus (KCN).

Methods

This retrospective case series comprised 161 eyes of 161 patients with KCN (104 men, 57 women; mean age, 22.35 ± 6.10 years). The participants were divided into four subgroups according to the Amsler-Krumeich classification. A Scheimpflug imaging system was used to measure the magnitude and axis orientation of ACA and PCA. The posterior-anterior corneal astigmatism ratio was also calculated. The results were compared among different subgroups.

Results

The average amounts of anterior, posterior, and total corneal astigmatism were 4.08 ± 2.21 diopters (D), 0.86 ± 0.46 D, and 3.50 ± 1.94 D, respectively. With-the-rule, against-the-rule, and oblique astigmatisms of the posterior surface of the cornea were found in 61 eyes (37.9%), 67 eyes (41.6%), and 33 eyes (20.5%), respectively; corresponding figures in the anterior corneal surface were 55 eyes (32.4%), 56 eyes (34.8%), and 50 eyes (31.1%), respectively. A strong correlation (P ≤ 0.001, r = 0.839) was found between ACA and PCA in the different stages of KCN; the correlation was weaker in eyes with grade 3 (P ≤ 0.001, r = 0.711) and grade 4 (P ≤ 0.001, r = 0.717) KCN. The maximum posterior-anterior corneal astigmatism ratio (PCA/ACA, 0.246) was found in patients with stage 1 KCN.

Conclusion

Corneal astigmatism in anterior surface was more affected than posterior surface by increasing in the KCN severity, although PCA was more affected than ACA in an early stage of KCN.

Measurement centration and zone diameter in anterior, posterior and total corneal astigmatism in keratoconus

PURPOSE

To investigate the central and paracentral astigmatism and the significance of centration and measurement zone diameter compared to a 3-mm pupil-centred measurement zone in keratoconus and in healthy eyes.

METHODS

Twenty-eight right eyes from 28 KC patients with an inferotemporal cone were selected according to specified criteria based on Oculus Pentacam HR^® measurements and were matched with healthy control eyes. The flat (K1) and steep (K2) keratometry readings were registered from the 'Total Corneal Refractive Power' (TCRP) display as well as the anterior and posterior corneal astigmatism displays (ACA and PCA, respectively). Astigmatic power vectors KP0 and KP45 were calculated and analysed for a 6-mm and two 3-mm zones centred on the corneal apex and the pupil, and for 8 paracentral 3-mm zones.

RESULTS

The astigmatism was generally higher in KC. Many astigmatic values in KC differed between the 3-mm pupil-centred and the 3- and 6-mm apex-centred zones in KC. In the controls, no corresponding differences between measurement zones were seen, apart from PCA, which differed. The magnitude and direction of KP0 and KP45 varied greatly between the paracentral measurements in KC.

CONCLUSION

Centration and measurement zone diameter have great impacts on the astigmatic values in KC. A small pupil-centred measurement zone should be considered when evaluating the astigmatism in KC.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

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.

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 Total Corneal Astigmatism in Eyes With Keratoconus

PURPOSE

To measure posterior corneal astigmatism (PCA) and investigate its influence on total corneal astigmatism (TCA) in eyes with keratoconus.

METHODS

Keratometric astigmatism (KA), PCA, and TCA were investigated by means of a dual Scheimpflug analyzer in patients with keratoconus. Vector analysis was carried out with the Næser polar value method.

RESULTS

We enrolled 119 eyes. PCA magnitude averaged 0.77 ± 0.43 diopters (D) and exceeded 0.50, 1.00, and 2.00 D in 73.9%, 21.8%, and 16.8% of eyes, respectively. PCA averaged 0.95 ± 0.48, 0.55 ± 0.28, and 0.70 ± 0.35 D in eyes with with-the-rule (WTR), against-the-rule (ATR), and oblique astigmatism. The steepest posterior meridian was oriented vertically (between 61 and 119 degrees) in 55.5% of eyes, thus generating ATR astigmatism. The difference between the location of the steepest meridian of KA and that of TCA was >10 degrees in 8.4% of eyes. On average, KA overestimated TCA in eyes with WTR astigmatism by 0.16 D and underestimated TCA in eyes with ATR astigmatism by 0.22 D. The PCA power oriented along the steeper anterior corneal meridian averaged -0.83 ± 0.40, -0.40 ± 0.37, and -0.53 ± 0.43 D for WTR, ATR, and obliquely astigmatic eyes, respectively. Linear regression disclosed a statistically significant correlation (P < 0.0001, r = 0.16) between the meridional powers of TCA and PCA.

CONCLUSIONS

In eyes with keratoconus, PCA displays large, variable values and is correlated to TCA. The influence of PCA on TCA cannot be disregarded when planning astigmatism correction by toric intraocular lenses.

Effects of posterior corneal astigmatism on the accuracy of AcrySof toric intraocular lens astigmatism correction

AIM

To evaluate the effects of posterior corneal surface measurements on the accuracy of total estimated corneal astigmatism.

METHODS

Fifty-seven patients with toric intraocular lens (IOL) implantation and posterior corneal astigmatism exceeding 0.5 diopter were enrolled in this retrospective study. The keratometric astigmatism (KA) and total corneal astigmatism (TA) were measured using a Pentacam rotating Scheimpflug camera to assess the outcomes of AcrySof IOL implantation. Toric IOLs were evaluated in 26 eyes using KA measurements and in 31 eyes using TA measurements. Preoperative corneal astigmatism and postoperative refractive astigmatism were recorded for statistical analysis. The cylindrical power of toric IOLs was estimated in all eyes.

RESULTS

In all cases, the difference of toric IOL astigmatism magnitude between KA and TA measurements for the estimation of preoperative corneal astigmatism was statistically significant. Of a total of 57 cases, the 50.88% decreased from Tn to Tn-1, and 10.53% decreased from Tn to Tn-2. In all cases, 5.26% increased from Tn to Tn+1. The mean postoperative astigmatism within the TA group was significantly lower than that in the KA group.

CONCLUSION

The accuracy of total corneal astigmatism calculations and the efficacy of toric IOL correction can be enhanced by measuring both the anterior and posterior corneal surfaces using a Pentacam rotating Scheimpflug camera.

Distribution of Anterior and Posterior Corneal Astigmatism in Eyes With Keratoconus

PURPOSE

To investigate the magnitude, with-the-rule (WTR) or against-the-rule (ATR) orientation, and vector components (Jackson astigmatic vectors [J0 and J45] and blurring strength) of the anterior and posterior corneal astigmatism (ACA and PCA) in patients with keratoconus (KC) in a retrospective study, and to try to find suitable cutoff points for ACA and PCA in an attempt to discriminate KC from normal corneas.

DESIGN

Retrospective age- and sex-matched case-control study.

METHODS

Using the Pentacam images, the aforementioned parameters were compared between 1273 patients with KC and 1035 normal participants.

RESULTS

The mean magnitude of the ACA and PCA was 4.49 ± 2.16 diopter (D) and 0.90 ± 0.43 D, respectively. The dominant astigmatism orientation of the ACA was ATR in KC patients and WTR in normal participants (P < .001), while for the PCA it was WTR in KC patients and ATR in normal participants (P < .001). There was a significant agreement between the axis orientations of ACA and PCA in KC patients (ĸ = 0.077, P < .001), but not in the normal group (P = .626). ACA and PCA magnitude, M, J0, J45, and blur significantly increased by increasing KC severity. There was a trend for increasing anterior ATR and posterior WTR, and decreasing oblique astigmatism on both corneal surfaces by increasing the KC severity according to the Amsler-Krumeich classification. A cutoff value of 1.8 D for ACA had 90.2% sensitivity and specificity, and that of 0.4 D for PCA had 89.5% sensitivity and 85.0% specificity for discriminating KC from normal corneas.

CONCLUSION

Our findings can help clinicians in the diagnosis of KC and lens manufacturers in designing suitable contact or intraocular lenses.

Eclectic Ocular Comorbidities and Systemic Diseases with Eye Involvement: A Review

Coexistence of several ocular diseases is more frequent than suspected. In spite of the refractive errors, one or more of the following can be detected simultaneously: glaucoma, cataracts, uveitis, age-related macular degeneration, and dry eyes. In addition, as people age, ocular comorbidities are much more usually seen. Specific diseases are openly acknowledged to affect the eyes and vision, such as diabetes mellitus, hypertension blood pressure, arthritis, hyperthyroidism, neurodegenerative disorders, hematologic malignancies, and/or systemic infections. Recent advances in early diagnosis and therapy of the ophthalmic pathologies have reinforced patient options to prevent visual impairment and blindness. Because of this, it is essential not to overlook sight-threatening conditions such as the ocular comorbidities and/or the eye involvement in the context of systemic disorders. Moreover, the important role of the multidisciplinary cooperation to improve and sustain management of patients affected with eclectic ocular comorbidities and/or systemic disorders with eye repercussion is specifically addressed. This review intends to shed light on these topics to help in making opportune diagnosis and appropriately managing the affected patients.