Clinical applications of wavefront aberrometry - a review

Innervation in corneal bioengineering

Given the crucial role nerves play in maintaining corneal function and integrity, the ability of bioengineered cornea to demonstrate functional nerve regeneration directly influences their longevity and stability. Despite advances in biofabrication techniques and an increasing appreciation of the importance of neural innervation, to this day none have completely replicated the complexity and functionality of the cornea with successful innervation. This review evaluates the materials and fabrication techniques used to produce and enhance innervation in bioengineered cornea. Approaches to facilitating innervation are discussed and methods of assessing innervation compared. Finally, current challenges and future directions for innervated bioengineered cornea are presented, providing guidance for future work. STATEMENT OF SIGNIFICANCE: The functional nerve regeneration in bioengineered corneas directly influences their longevity and stability. Despite advancements in biofabrication techniques and growing recognition of the importance of neural innervation for bioengineered cornea, there remains a lack of comprehensive reviews on this topic. This review addresses the critical gap by evaluating the materials and fabrication techniques employed to promote innervation in bioengineered corneas. Additionally, we discuss various approaches to enhancing innervation, compare assessment methods, and examine both in vitro and in vivo responses. By providing a comprehensive overview of the current state of research and highlighting challenges and future directions, this review aims to provide guidance for inducing innervation of bioengineered cornea.

Risk Factors for Corneal Monochromatic Aberrations and Implications for Multifocal and Extended Depth-of-Focus Intraocular Lens Implantation

PURPOSE

To discuss factors influencing corneal aberrations that might influence the optical quality after intraocular lens (IOL) implantation.

METHODS

PubMed and Scopus were the main resources used to search the medical literature. An extensive search was performed to identify relevant articles concerning factors influencing the level of corneal aberrations as of August 27, 2023. The following keywords were used in various combinations: corneal, aberrations, defocus, astigmatism, spherical aberration, coma, trefoil, quadrafoil, intraocular lens, and IOL.

RESULTS

Conclusive evidence is lacking regarding the correlation between age and changes in corneal aberrations. Patients with astigmatism have greater corneal higher-order aberrations than those with minimal astigmatism, particularly concerning trefoil and coma. Increased levels of corneal higher-order aberrations are noted following contact lens wear, in patients with dry eye disease, and with pterygium. Increased higher-order aberrations have been reported following corneal refractive surgery and for 3 months following trabeculectomy; regarding intraocular lens surgery, the results remain controversial.

CONCLUSIONS

Several factors influence the level of corneal higher-order aberrations. Multifocal and extended depth-of-focus IOLs can share similarities in their optical properties, and the main difference arises in their design and performance with respect to spherical aberration. Preoperative evaluation is critical for proper IOL choice, particularly in corneas with risk of high levels of aberrations. [J Refract Surg. 2024;40(6):e420-e434.].

The effect of transepithelial corneal collagen cross-linking treatment on optical quality of the cornea in keratoconus: 12-month clinical results

PURPOSE

To evaluate the effect of transepithelial corneal collagen crosslinking (CXL) treatment on the optical performance of the cornea at 12-month follow-up after CXL in patients with progressive keratoconus.

METHODS

One hundred and ten eyes of 67 patients were included. The following corneal optical aberrations over the 4-mm-diameter pupil were recorded via Sirius dual-scanning corneal tomography: total, anterior and posterior amount of corneal higher order aberrations [HOAs], vertical coma, horizontal coma, vertical trefoil, oblique trefoil, and spherical aberration, and Strehl ratio of point spread function (PSF).

RESULTS

There were significant improvements in mean root mean square error values for corneal total HOA, total coma, anterior HOA, anterior coma, and vertical coma following CXL (P > 0.05, for all). No significant changes were found in the posterior aberometric parameters. PSF value did not change after CXL (P > 0.05). The corneal topographic measurements not revealed a change in the mean simulated keratometry-1, simulated keratometry-2, and maximum keratometry compared with the baseline measurements (P > 0.05, for all). At 12 months, there was a significant improvement in the uncorrected (UCVA) and best corrected (BCVA) visual acuity (P < 0.001, both). Most corneal aberrations correlated significantly with postoperative BCVA, but changes in HOAs were not statistically associated with improvements in visual acuity.

CONCLUSIONS

Transepithelial CXL was effective in stabilizing the keratometric indices and improving the most corneal aberrations in keratoconic eyes 1 year after the procedure. While the healing effect on aberrations after CXL was in total and anterior parameters, no significant changes were observed in the posterior surface. In addition, it was observed that transepithelial CXL treatment did not cause a significant change in PSF distribution data.

The visual impact of higher-order aberrations in patients with pediatric blepharokeratoconjunctivitis

PURPOSE

To analyze higher-order aberrations (HOAs) and their visual impact in a pediatric blepharokeratoconjunctivitis (PBKC) cohort compared with healthy controls.

METHODS

Prospective case-control study of pediatric patients (≤ 16 years old). Subjects underwent wavefront aberrometry analysis to compare HOAs and their impact on visual quality.

RESULTS

A total of 150 eyes from 76 patients were included in the analysis. The PBKC group consisted of 50 eyes and the control group of 100 healthy eyes. Mean age was 10.39 ± 3.81 years for the PBKC group and 10.80 ± 3.61 years for the controls. Mean corrected-distance visual acuity (CDVA) was 0.24 ± 0.21 logMAR in the PBKC group and 0.07 ± 0.1 in the controls (P < 0.001). Mean astigmatism was 1.6 ± 1.98D in the PBKC group vs. 0.67 ± 0.76D in the control group (P = 0.01). Mean RMS of HOAs was 1.05 ± 1.7mm in the PBKC group and 0.41 ± 0.18mm in the controls (P < 0.001). The mean modulation transfer function (MTF) in the PBKC group was significantly lower (16.37 ± 16.32) than controls (30.3 ± 23.57) (P < 0.001). Corneal leukomas, stromal vascularization, peripheral nummular subepithelial scars, and pannus formation are associated with increased HOAs.

CONCLUSIONS

There was a significant increase in total HOAs of eyes with PBKC compared to healthy controls. Corneal opacity, vascularization, and scarring are associated with increased HOAs. The PBKC eye aberration profile: coma, secondary astigmatism, quadrafoil, and pentafoil, were associated with decreased CDVA and visual quality (PSF and MTF).

A Comprehensive Wavefront Assessment of Keratoconus Using an Integrated Scheimpflug Corneal Tomographer/Hartmann-Shack Wavefront Aberrometer

OBJECTIVES

To characterize higher-order aberrations (HOAs) in different severities of keratoconus (KC) from the anterior and posterior corneal surfaces and whole eye using an integrated Scheimpflug corneal tomographer/Hartmann-Shack wavefront aberrometer.

METHODS

This study included eyes with clinical KC, topographic KC (no clinical signs), fellow eyes with very asymmetric ectasia with normal topography and no clinical signs (VAE-NT), and control eyes. Corneal and ocular wavefront aberrations were obtained using an integrated Scheimpflug tomographer/Hartmann-Shack wavefront aberrometer. The diagnostic capability of distinguishing VAE-NT from the control was also tested.

RESULTS

This study included 68 eyes with clinical KC, 44 with topographic KC, 26 with VAE-NT, and 45 controls. Clinical KC had significantly greater total HOAs and coma from the anterior and posterior corneal surfaces and whole eye than the other groups ( P <0.05). Although topographic KC had significantly greater values in all wavefront parameters than the control ( P <0.05), ocular and corneal HOAs did not differ between the VAE-NT and control groups. The coma from the anterior cornea in topographic KC was significantly greater than that in VAE-NT ( P <0.05); the coma from the posterior cornea and whole eye did not differ. Total HOAs from the anterior corneal surface exhibited the highest area under the receiver operating characteristic curve value of 0.774 (sensitivity, 73%; specificity, 78%).

CONCLUSION

A comprehensive wavefront assessment can be used to quantitatively evaluate corneal and ocular HOAs across various severity of KC. Total HOAs from the anterior corneal surface exhibited the potential ability in distinguishing VAE-NT from the control eyes.

Multimodal diagnostics for keratoconus and ectatic corneal diseases: a paradigm shift

Different diagnostic approaches for ectatic corneal diseases (ECD) include screening, diagnosis confirmation, classification of the ECD type, severity staging, prognostic evaluation, and clinical follow-up. The comprehensive assessment must start with a directed clinical history. However, multimodal imaging tools, including Placido-disk topography, Scheimpflug three-dimensional (3D) tomography, corneal biomechanical evaluations, and layered (or segmental) tomography with epithelial thickness by optical coherence tomography (OCT), or digital very high-frequency ultrasound (dVHF-US) serve as fundamental complementary exams for measuring different characteristics of the cornea. Also, ocular wavefront analysis, axial length measurements, corneal specular or confocal microscopy, and genetic or molecular biology tests are relevant for clinical decisions. Artificial intelligence enhances interpretation and enables combining such a plethora of data, boosting accuracy and facilitating clinical decisions. The applications of diagnostic information for individualized treatments became relevant concerning the therapeutic refractive procedures that emerged as alternatives to keratoplasty. The first paradigm shift concerns the surgical management of patients with ECD with different techniques, such as crosslinking and intrastromal corneal ring segments. A second paradigm shift involved the quest for identifying patients at higher risk of progressive iatrogenic ectasia after elective refractive corrections on the cornea. Beyond augmenting the sensitivity to detect very mild (subclinical or fruste) forms of ECD, ectasia risk assessment evolved to characterize the inherent susceptibility for ectasia development and progression. Furthermore, ectasia risk is also related to environmental factors, including eye rubbing and the relational impact of the surgical procedure on the cornea.

Spherical aberrations and their role in modern ophthalmology

Spherical aberration is an imperfection of the optical system of the human eye. The role of spherical aberration of the human eye in the quality of vision and pseudoaccommodation is reviewed. Spherical aberration is an imperfection of the optical system of the human eye. In most cases, due to well-developed neuroadaptation, it is insignificant for the perception of the image. Nevertheless, its role in modern ophthalmology is far from straightforward. On the one hand, there are clinical scenarios in which an excess of spherical aberration degrades the retinal image and leads to a high dissatisfaction rate among patients.©Recently, there is a growing interest in the modulation of spherical aberration in the clinical setting. Modern intraocular lenses as well as laser refractive procedures are aimed at interfering with spherical aberrations of the optical system in order to increase range of pseudoaccommodation. Here, we review the role of spherical aberration of the human eye in the quality of vision and pseudoaccommodation.

Comparison of Ocular Wavefront Aberration Measurements Obtained Using Two Hartmann-Shack Wavefront Aberrometers

OBJECTIVES

To assess agreement between measurements of ocular wavefront aberrations obtained using the Pentacam AXL Wave (Oculus Optikgeräte GmbH) (Aberrometer A) and KR-1W (Topcon Corp) (Aberrometer B), both of which are based on the Hartmann-Shack principle.

METHODS

In this prospective case-control study, ocular wavefront aberrations measurements were obtained using both aberrometers in patients with keratoconus (KC) and control participants. Ocular wavefront aberrations were measured through the natural pupil without dilation using both devices in a dark room. For both aberrometers, accommodation was inhibited by automatically adding fogging. The individual Zernike coefficients from the second to fourth order were compared between the two aberrometers for a 4-mm pupil diameter.

RESULTS

Twenty-six KC and 29 control eyes were assessed. Statistically significant correlations ( P <0.05) were observed for all Zernike coefficients, except for Z 4-2 in the control group. Bland-Altman analysis indicated good agreement between aberrometers and no statistically significant differences in the control group. However, in the KC group, patterns of proportional error were observed in vertical coma Z 3-1 (r=0.338, P =0.008), trefoil Z 4-4 (r=0.701, P =0.003), secondary astigmatism Z 4-2 (r=0.348, P =0.025), and spherical aberrations Z 40 (r=0.407, P =0.012).

CONCLUSIONS

The Zernike coefficient values measured by the two aberrometers were well correlated in the control and KC groups. However, in eyes with KC, Aberrometer B tended to present greater values in several Zernike coefficients than Aberrometer A, suggesting that wavefront measurements obtained using the two aberrometers are not interchangeable in patients with KC.

Advanced Optical Wavefront Technologies to Improve Patient Quality of Vision and Meet Clinical Requests

Adaptive optics (AO) is employed for the continuous measurement and correction of ocular aberrations. Human eye refractive errors (lower-order aberrations such as myopia and astigmatism) are corrected with contact lenses and excimer laser surgery. Under twilight vision conditions, when the pupil of the human eye dilates to 5-7 mm in diameter, higher-order aberrations affect the visual acuity. The combined use of wavefront (WF) technology and AO systems allows the pre-operative evaluation of refractive surgical procedures to compensate for the higher-order optical aberrations of the human eye, guiding the surgeon in choosing the procedure parameters. Here, we report a brief history of AO, starting from the description of the Shack-Hartmann method, which allowed the first in vivo measurement of the eye's wave aberration, the wavefront sensing technologies (WSTs), and their principles. Then, the limitations of the ocular wavefront ascribed to the IOL polymeric materials and design, as well as future perspectives on improving patient vision quality and meeting clinical requests, are described.

Agreement of wavefront-based refraction, dry and cycloplegic autorefraction with subjective refraction

PURPOSE

To evaluate the agreement of dry, and cycloplegic autorefraction and wavefront-based refraction with subjective refraction.

METHOD

83 subjects aged 19-57 years were included in this cross-sectional study. Refractive status was determined using four methods including subjective refraction, wavefront-based refraction, dry and cycloplegic autorefraction. Refractive data were recorded as sphere, cylinder and spherical equivalent (SE). Power vector components were used to compare the astigmatism obtained using the different methods of refraction.

RESULTS

The more negative spherical, cylindrical and SE components were obtained using dry autorefraction, wavefront-based refraction and dry autorefraction, respectively. The less negative spherical, cylindrical and SE components were obtained using cycloplegic autorefraction, subjective refraction and cycloplegic autorefraction, respectively. Considering the spherical component, there was a statistically significant hyperopic shift (0.12 ± 0.29 D, p = 0.001) with cycloplegic autorefraction and a significant myopic shift (-0.17 ± 0.32 D, p < 0.001) with dry autorefraction compared to subjective refraction, while the difference between wavefront-based and subjective refraction was not significant statistically (p = 0.145). The calculated cylindrical component using subjective refraction showed statistically significant difference with dry auto-refraction (p < 0.001), cycloplegic auto-refraction (p = 0.041) and wavefront refraction (p < 0.001). The highest correlation with subjective refraction in sphere, cylinder and SE was observed for cycloplegic auto-refraction (rs = 0.967), dry auto-refraction (rs = 0.983) and cycloplegic auto-refraction (rs = 0.982), respectively.

CONCLUSIONS

As subjective refraction is gold standard in our study, sphere in cycloplegic auto-refraction and astigmatism in dry auto-refraction showed better agreement and correlation.

Advances in the Noninvasive Diagnosis of Dry Eye Disease

Dry eye disease (DED) is a multifactorial disease that represents one of the most common ophthalmologic conditions encountered in everyday clinical practice. Traditional diagnostic tests for DED, such as subjective questionnaires, tear film break-up time and the Schirmer test, are often associated with poor reproducibility and reliability, which make the diagnosis, follow-up, and management of the disease challenging. New advances in imaging technologies enable objective and reproducible measurements of DED parameters, thus making the diagnosis a multimodal imaging-based process. The aim of this review is to summarize all the current and emerging diagnostic tools available for the diagnosis and monitoring of DED, such as non-invasive tear breakup time, thermography, anterior segment optical coherence tomography, meibography, interferometry, in vivo confocal microscopy, and optical quality assessment. Although there is not a gold standard imaging technique, new multi-imaging-integrated devices are precious instruments to help clinicians to better cope with the diagnostic complexity of DED.

Repeatability and Agreement of Wavefront aberrations of Pentacam AXL Wave- a new hybrid topographer and aberrometer with ITrace in healthy eyes

PURPOSE

To assess repeatability and agreement of Pentacam AXL Wave, with iTrace aberrometer.

SETTING

Narayana Nethralaya, Bangalore, India.

DESIGN

Prospective ,cross-sectional study.

METHODS

One hundred eyes of 100 patients underwent three sets of measurements, at a single visit, using Pentacam AXL Wave (Oculus, Germany) and iTrace (Tracey Technologies, USA).Lower-order aberration (LOA), higher-order aberration (HOA), Coma and Spherical Aberrations (SA) were analyzed. Repeatability was assessed using within-subject standard deviation (Sw), test-retest variability (TRT), within-subject coefficient of variation (COV) and Intraclass Correlation Coefficient (ICC). The Bland-Altman analysis was used to assess 95% limits of agreement (LoA) and the correlation coefficient (r) to determine strength of relationship between measurements.

RESULTS

All measurements with Pentacam AXL Wave had repeatability with an ICC for total ocular aberrations ranging from 0.84 for HOAto 0.92 for LOA and corneal from 0.76 for HOA to 0.86 for LOA The Sw, TRT, COV of all aberrations were significantly lower (better) than those of iTrace (p < 0.001). The mean differences between 2 devices were insignificant for the comparison of all parameters, except for spherical aberration (0.011(0.002571 to 0.02008; P= 0.01). Both devices showed excellent corelations for ocular aberrations (tHOA (P=0.12,LoA= -0.52 to 0.025; r= 0.89); LOA (P=0.14, LoA = -2.71 to 2.61  ; r= 0.96) coma (P=0.27, LoA = -0.11 to 0.12; r= 0.89) and in SA (P=0.01,  LoA = -0.09 to 0.07;r=0.97)).

CONCLUSIONS

The repeatability estimates for wavefront aberrations using Pentacam AXL Wave were significantly better than that using iTrace. Both devices showed excellent corelations for total ocular aberrations.

Impact of asteroid hyalosis on internal higher-order aberrations in eyes with cataract accompanied by acoustic shadows on swept-source optical coherence tomography examination

Increased internal higher-order aberrations (HOAs) have been reported in eyes with asteroid hyalosis, which is usually asymptomatic. This report describes 2 patients with cataract and concurrent asteroid hyalosis. In the first case, internal HOAs were within the normal range, and swept-source optical coherence tomography (SS-OCT) did not show acoustic shadows. After cataract surgery, visual acuity improved and internal HOAs remained within normal limits. However, in the second case, SS-OCT revealed multiple acoustic shadows, presumably due to asteroid hyalosis, and internal HOAs increased in both eyes. After combined vitrectomy and cataract surgery, visual acuity and the internal HOA values improved in both eyes, and acoustic shadows disappeared on SS-OCT. Phacovitrectomy should be considered if the cause of visual impairment is cataract and asteroid hyalosis. Objective assessment of internal HOAs by a wavefront sensor and checking for acoustic shadows on SS-OCT might be useful in detecting this combination of ophthalmic conditions.

Efficacy of Toric Intraocular Lens and Prevention of Axis Misalignment by Optic Capture in Pediatric Cataract Surgery

PURPOSE

To compare the outcomes of intraocular lens (IOL) implantation using toric (T)-IOL and non-toric (N)-IOL in pediatric cataract patients with astigmatism, and to examine the effect of optic capture (OC) on the axis misalignment (AM) of the T-IOLs.

SETTING

Department of Ophthalmology, Kindai University Hospital, Osaka, Japan.

DESIGN

Interventional, comparative case study.

METHODS

Consecutive pediatric patients implanted with T-IOLs or N-IOLs were retrospectively reviewed. In the T-IOL group, the preoperative and postoperative corrected distance visual acuity (CDVA) and AM were compared in patients with and without OC.

RESULTS

The T-IOL group included 14 eyes of 11 patients, while the N-IOL group included 22 eyes of 15 patients. One year after surgery, the mean ocular cylinder (1.38 ± 0.80 D) was significantly smaller than the average corneal cylinder (3.33 ± 1.24 D) in the T-IOL group (P = .00012, Wilcoxon signed-rank test). The mean preoperative and 1-year postoperative CDVA (logMAR) were 0.57/0.003 (T-IOL) and 0.71/0.09 (N-IOL), respectively. The AM at 1 week and 1 year after surgery was 2.6° ± 3.7° and 4.4° ± 3.1° for the OC group, and 13.3° ± 8.8° and 18.5° ± 14.8°, for the non-OC group, respectively. The AM was significantly smaller in the OC group than that in non-OC group (P = .009, Mann-Whitney U test) at postoperative 1 week.

CONCLUSION

T-IOL implantation is effective in correcting astigmatism in pediatric cataract patients with astigmatism, and the OC technique is likely to achieve lower AM of the T-IOL.

Case Report: What Are We Doing for Our "20/20 Unhappy" Scleral Lens Patients?

SIGNIFICANCE

Scleral lenses (SLs) partially mask higher-order aberrations (HOAs) in highly aberrated eyes. Although visual acuity (VA) may show satisfactory quantitative clinical outcomes during SL wear, residual (uncorrected) HOAs can leave subjective visual quality goals unmet.

PURPOSE

The purpose of this study was to report a case where a "20/20 unhappy" patient with SLs was able to meet visual goals with wavefront-guided SLs.

CASE REPORT

A 40-year-old male with bilateral keratoconus, whose Snellen VA with SLs was 20/20 right eye (OD) 20/16 left eye (OS), reported halos and glare at night and perceptual smearing. When viewing a point of light, a "Ferris wheel" shadowing was observed OD and a U-shaped shadowing OS. Residual higher-order root mean square wavefront error was 0.49 μm OD and 0.39 μm OS; visual image quality measured by visual Strehl ratio was 0.067 OD and 0.092 OS (pupil size, 4.00 mm). Wavefront-guided SLs reduced residual higher-order root mean square to 0.19 μm OD and 0.25 μm OS, VA improved to 20/10 OD and 20/13 OS, and visual Strehl improved to 0.150 OD and 0.121 OS. The patient reported reduced smearing, shadowing, and night vision concerns, meeting his visual expectations and goals.

CONCLUSIONS

Wavefront sensing quantifies both lower and HOAs, which can cause visual dissatisfaction in individuals with highly aberrated eyes, despite sometimes reaching typical levels of VA. As wavefront-guided SLs targeting these residual aberrations to improve visual image quality become more available, they should be considered for 20/20 unhappy patients when conventional clinical options are unsatisfactory.

Novel Approaches for Imaging-Based Diagnosis of Ocular Surface Disease

Imaging has become indispensable in the diagnosis and management of diseases in the posterior part of the eye. In recent years, imaging techniques for the anterior segment are also gaining importance and are nowadays routinely used in clinical practice. Ocular surface disease is often synonymous with dry eye disease, but also refers to other conditions of the ocular surface, such as Meibomian gland dysfunction or keratitis and conjunctivitis with different underlying causes, i.e., allergies or infections. Therefore, correct differential diagnosis and treatment of ocular surface diseases is crucial, for which imaging can be a helpful tool. A variety of imaging techniques have been introduced to study the ocular surface, such as anterior segment optical coherence tomography, in vivo confocal microscopy, or non-contact meibography. The present review provides an overview on how these techniques can be used in the diagnosis and management of ocular surface disease and compares them to clinical standard methods such as slit lamp examination or staining of the cornea or conjunctiva. Although being more cost-intensive in the short term, in the long term, the use of ocular imaging can lead to more individualized diagnoses and treatment decisions, which in turn are beneficial for affected patients as well as for the healthcare system. In addition, imaging is more objective and provides good documentation, leading to an improvement in patient follow-up and education.

Using Artificial Intelligence and Novel Polynomials to Predict Subjective Refraction

This work aimed to use artificial intelligence to predict subjective refraction from wavefront aberrometry data processed with a novel polynomial decomposition basis. Subjective refraction was converted to power vectors (M, J0, J45). Three gradient boosted trees (XGBoost) algorithms were trained to predict each power vector using data from 3729 eyes. The model was validated by predicting subjective refraction power vectors of 350 other eyes, unknown to the model. The machine learning models were significantly better than the paraxial matching method for producing a spectacle correction, resulting in a mean absolute error of 0.301 ± 0.252 Diopters (D) for the M vector, 0.120 ± 0.094 D for the J0 vector and 0.094 ± 0.084 D for the J45 vector. Our results suggest that subjective refraction can be accurately and precisely predicted from novel polynomial wavefront data using machine learning algorithms. We anticipate that the combination of machine learning and aberrometry based on this novel wavefront decomposition basis will aid the development of refined algorithms which could become a new gold standard to predict refraction objectively.

Wavefront sensing, novel lower degree/higher degree polynomial decomposition and its recent clinical applications: A review

We are in the midst of a shift towards using novel polynomials to decompose wavefront aberrations in a more ophthalmologically relevant way. Zernike polynomials have useful mathematical properties but fail to provide clinically relevant wavefront interpretation and predictions. We compared the distribution of the eye's aberrations and demonstrate some clinical applications of this using case studies comparing the results produced by the Zernike decomposition and evaluating them against the lower degree/higher degree (LD/HD) polynomial decomposition basis which clearly dissociates the higher and lower aberrations. In addition, innovative applications validate the LD/HD polynomial basis. Absence of artificial reduction of some higher order aberrations coefficients lead to a more realistic analysis. Here we summarize how wavefront analysis has evolved and demonstrate some of its new clinical applications.

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.

Precision and agreement of higher order aberrations measured with ray tracing and Hartmann-Shack aberrometers

BACKGROUND

To assess the precision and agreement of measurements of higher order aberrations (HOAs) obtained with a ray tracing aberrometer (iTrace) and a Hartmann-Shack aberrometer (Topcon KR-1 W).

METHODS

Prospective evaluation of the diagnostic test. Data from the right eyes of 92 normal subjects obtained using the two devices were included in this study. Two observers performed 3 consecutive scans to determine the intraobserver repeatability and interobserver reproducibility. About one week later, one observer performed an additional 3 consecutive scans to obtain the intersession reproducibility. The within-subject standard deviation (Sw), test-retest repeatability (TRT) and intraclass correlation coefficient (ICC) were used to assess the precision, while Bland-Altman plots were performed to assess the agreement.

RESULTS

For intraobserver repeatability of the ocular, corneal and internal HOAs, Topcon KR-1 W showed a 2.77Sw of 0.079 μm or less and ICCs of 0.761 or more; and iTrace showed a 2.77Sw of 0.105 μm or less and ICCs of 0.805 or more. The ICCs of the internal HOAs of interobserver reproducibility were less than 0.75 except for spherical aberration (SA) (0.862), and interobserver reproducibility of the counterpart showed similar but lower results. For the ocular, corneal and internal HOA measurements, statistically significant differences existed between the Topcon KR-1 W and iTrace (all P < 0.05). No significant differences were observed in the ocular SA and internal coma.

CONCLUSIONS

The ray tracing and Hartmann-Shack method aberrometers provided excellent repeatability but less reliable reproducibility in the measurement of HOAs (except for SA). The two aberrometers should not be interchangeable in clinical application because of the significant differences in HOA measurements between them.

Surgical Workflow Management Schemata for Cataract Procedures

Objective: Workflow guidance of surgical activities is a challenging task. Because of variations in patient properties and applied surgical techniques, surgical processes have a high variability. The objective of this study was the design and implementation of a surgical workflow management system (SWFMS) that can provide a robust guidance for surgical activities. We investigated how many surgical process models are needed to develop a SWFMS that can guide cataract surgeries robustly.

Methods: We used 100 cases of cataract surgeries and acquired patient-individual surgical process models (iSPMs) from them. Of these, randomized subsets iSPMs were selected as learning sets to create a generic surgical process model (gSPM). These gSPMs were mapped onto workflow nets as work-flow schemata to define the behavior of the SWFMS. Finally, 10 iSPMs from the disjoint set were simulated to validate the workflow schema for the surgical processes. The measurement was the successful guidance of an iSPM.

Results: We demonstrated that a SWFMS with a workflow schema that was generated from a subset of 10 iSPMs is sufficient to guide approximately 65% of all surgical processes in the total set, and that a subset of 50 iSPMs is sufficient to guide approx. 80% of all processes.

Conclusion: We designed a SWFMS that is able to guide surgical activities on a detailed level. The study demonstrated that the high inter-patient variability of surgical processes can be considered by our approach.

Real-Time Measurement of Ocular Wavefront Aberrations in Symptomatic Subjects

The purpose of this work was to study the real-time changes of the optical properties of the eye with accommodation in subjects with symptoms of accommodative disorders. From ocular aberrations, it is possible to compute several parameters like the response and lag of accommodation. The ocular aberrations were measured in 4 subjects, with different accommodative disorders, during several cycles of accommodation/disaccommodation and for different accommodative stimuli. The measurement was done continuously and in real time during different accommodative stimuli. It was possible to see the changes in accommodative response during the several stimuli of accommodation. Subjects with accommodative disorders showed different accommodative responses. The use of wavefront ocular aberrations can be a tool to diagnose accommodative disorders. In some subjects with complaints, this method showed irregularities even when the results of the usual clinical exams were normal.

Comparison of Ocular Monochromatic Higher-order Aberrations in Normal Refractive Surgery Candidates of Arab and South Asian Origin

PURPOSE

To compare the ocular monochromatic higher-order aberration. (HOA) profile in normal refractive surgery candidates of Arab and South Asian origin.

METHODS

This cross-sectional, observational, comparative study was performed in the cornea department of a specialty hospital. Normal refractive surgery candidates with no ocular morbidity except refractive error were recruited. Refractive surgery candidates underwent a preoperative evaluation, including wavefront aberrometry with the iDesign aberrometer (AMO, Inc., Santa Ana, California, United States). The HOA from right eyes were analyzed for HOA signed, absolute, and polar Zernike coefficients.

RESULTS

Two hundred Arab participants (group 1) and 200 participants of South-Asian origin (group 2) comprised the study sample. The age and refractive status were comparable between groups. The mean of the HOA root mean square (RMS) was 0.36 ± 17 μ and 0.38 ± 18 μ for Arab and South-Asian eyes, respectively (P < 0.05, rank sum test [RST]). Of the 22 higher order signed Zernike modes, only Z3 (-3), Z3 (-1),3 (1), Z4 (-4), Z4 (-2), Z4 (0), Z4 (4), and Z5 (-5) were significantly different from zero (one sample t-test, P < 0.002, with a Bonferroni correction of 0.05/22). All the signed and absolute Zernike terms were comparable between groups (RST, P > 0.002 [0.05/22]). The polar coefficients for coma, trefoil, spherical aberration, and tetrafoil were comparable between groups (P > 0.05, RST). Combined RMS values of third, fourth, fifth, and sixth order also were comparable between groups (P > 0.05, RST).

CONCLUSIONS

Preoperative whole eye HOA were similar for refractive surgery candidates of Arab and South-Asian origin. The values were comparable to historical data for Caucasian eyes and were lower than Asian (Chinese) eyes. These findings may aid in refining refractive nomograms for wavefront ablations.

Correlation of higher order aberrations in the anterior corneal surface and degree of keratoconus measured with a Scheimpflug camera

OBJECTIVE

To determine the correlation of higher order aberrations in anterior corneal surface and degree of keratoconus measured with a Scheimpflug camera.

MATERIAL AND METHODS

A descriptive, cross-sectional study was conducted on 152 eyes (both eyes of each patient) of patients with keratoconus, from January 2009 to April 2014. An examination was performed on the corneal aberrometry in the anterior corneal surface, and topographic mapping (by Amsler and Muckenhirn classification) was used to determine the degree of keratoconus. The correlation between high-order aberrations in anterior corneal surface and the degree of keratoconus was determined.

RESULTS

Coma aberration significantly correlated with keratoconus severity (r=.60, P<.01), as well as with the high order aberration (r=.61, P<.01). Trefoil and keratoconus were weakly correlated (r=.34, P<.01).

CONCLUSION

Higher order aberrations in anterior corneal surface were positively correlated with the degree of keratoconus in a similar way to the entire optical system.

Effect of Single Administration of Coffee on Pupil Size and Ocular Wavefront Aberration Measurements in Healthy Subjects

No study has so far evaluated the impact of coffee drinking on ocular wavefront aberration (OWA) measurements. This study presents novel findings regarding the OWA of the eye following coffee intake. We aimed to evaluate the acute changes in pupil size and OWA of the eye after single administration of coffee. A total of 30 otherwise healthy participants were included in this prospective study. All subjects drank a cup of coffee containing 57 mg caffeine. Measurements of pupil size, total coma (TC), total trefoil (TF), total spherical aberration (TSA), and total higher order aberration (HOA) were performed before and at 5 minutes, at 30 minutes, and at 4 hours after coffee drinking using a wavefront aberrometer device (Irx3, Imagine Eyes, Orsay, France). The mean age of the study population was 20.30 ± 2.74 years. Pupil size did not show a significant change during the measurements (p > 0.05). A significant increase was observed in TF and HOA measurements following coffee intake (p = 0.029 and p = 0.009, resp.). Single administration of coffee results in significant increase in TF and total HOAs in healthy subjects without any effect on pupil diameter. Ultrastructural changes in the cornea following coffee intake might be of relevance to the alterations in ocular aberrations in healthy subjects.

Comparison of the Orbscan II topographer and the iTrace aberrometer for the measurements of keratometry and corneal diameter in myopic patients

Background

The purpose of this study was to compare corneal power and horizontal corneal diameter (white-to-white [WTW] distance) readings obtained by the Orbscan II topographer and the iTrace aberrometer.

Methods

Keratometry readings in the flat (Kf) and steep (Ks) meridians and WTW distance were measured with the Orbscan II and iTrace systems in 100 myopic patients. Statistical evaluation was performed using the paired t test, Pearson correlation, and Bland-Altman analysis for comparison of measurement techniques.

Results

The mean keratometry values with the Orbscan II and iTrace were 43.16 ± 1.44 and 42.64 ± 1.43 diopter (D), respectively (P < 0.0001). The mean WTW distance measurements with the Orbscan II and iTrace were 11.57 ± 0.34 and 11.33 ± 0.36 mm, respectively (P < 0.0001). For the measurement of corneal power, the 95 % limits of agreement (LoA) between the Orbscan II and iTrace were − 0.21 to 1.21 D for the flat meridian and − 0.15 to 1.25 D for the steep meridian. For the measurement of WTW distance, the range of the 95 % LoA between the two devices was 0.47 mm.

Conclusions

For some clinical applications, the keratometry and WTW distance measurements obtained by the Orbscan II topographer and the iTrace aberrometer differed greatly and therefore were not interchangeable.

Trial registration

Clinical trials number: ChiCTR-OCS-14005077 (August 2nd, 2014).

The Role of Aberrometry in Accommodative Spasm After Myopic Photorefractive Keratectomy

PURPOSE

To report the role of aberrometry in a case of accommodative spasm following myopic photorefractive keratectomy (PRK).

METHODS

Observational case report.

RESULTS

One month following myopic PRK, a 33-year-old healthy woman complained of seeing multiple images and headache that interfered with her daily activities. Her corrected distance visual acuity (CDVA) was 20/40 in the right eye and 20/25 in the left eye with a manifest refraction of -0.75 -0.50 × 165° in the right eye and plano -0.50 × 20° in the left eye. Cycloplegic refraction was plano -0.50 × 165° in the right eye and plano -0.5 × 20° in the left eye. Ray tracing aberrometry showed variable refraction with increase in internal defocus, which after cycloplegia reduced from 1.019 to 0.142 µm in the right eye and 0.366 to 0.230 µm in the left eye. Total ocular aberrations decreased by 53.16% in the right eye (range: 1.511 to 0.708 µm) and 18.77% (range: 0.671 to 0.545 µm) in the left eye; corresponding simulated Snellen visual acuity charts also showed improvement. The patient was treated with one drop of cyclopentolate 1% three times a day for 6 weeks, following which headache and ghosting of images completely resolved.

CONCLUSIONS

Accommodative spasm should be considered in patients with visual disturbances of uncertain causes following myopic refractive surgery. Ray tracing aberrometry can serve as a diagnostic and educative tool in managing such patients.

Comparing the effect of two different intraocular lenses on optical aberrations in bilaterally operated eyes for cataract

OBJECTIVE

To assess high order and spherical aberrations results of hydrophobic acrylic AMO Sensar AR40E and hydrophobic acrylic Alcon AcrySof SA60AT intraocular lenses after implantation in cases with bilateral cataract.

METHODS

Cases diagnosed as bilateral cataract were included in the study and preoperative aberration measurements were recorded by using Nidek OPD SCAN-ARK 1000. Groups were created by implanting AMO Sensar AR40E to one eye of the patients, while Alcon AcrySof SA60AT into the other in a prospective and randomized manner. Aberration measurements were recorded after one and two months of surgery.

RESULTS

Overall, 40 eyes in 20 patients (11 women and 9 men) were included in the study. All patients underwent bilateral phacoemulsification surgery due to cataract. There were 20 eyes in both groups. Mean age was 62.4 (range: 31-82) years. There was no significant difference in aberrations recorded before surgery and one and two months after surgery in both groups. (p<0.05).

CONCLUSION

There was no difference among spherical intraocular lenses used in this study.

Analysis of four aberrometers for evaluating lower and higher order aberrations

PURPOSE

To compare the measurements of lower and higher order aberrations (HOA) of 4 commonly used aberrometers.

SETTING

Massachusetts Eye & Ear Infirmary, Boston, USA.

DESIGN

Prospective, cross-sectional study, in a controlled, single-blinded fashion.

METHODS

Multiple readings were obtained in 42 eyes of 21 healthy volunteers, at a single visit, with each of the following aberrometers: Alcon LADARWave®, Visx WaveScan®, B & L Zywave®, and Wavelight Allegro Analyzer®. Results were compared and analyzed in regards to the lower and HOA, to the different wavefront sensing devices and software, Tscherning and Hartmann-Shack and between the Fourier and Zernike algorithms. Statistical analysis included Bland-Altman plots, Intraclass Correlation Coefficient (ICC), multiple comparison tests with Analysis of Variance and Kruskal-Wallis. Significant level was set to p<0.05 and alpha level correction was adjusted under the Bonferroni criteria.

RESULTS

Most measurements of all 4 aberrometers were comparable. However, statistically significant differences were found between the aberrometers in total HOA (tHOA), spherical aberration (SA), horizontal coma and astigmatism (2,2). LADARwave and Wavescan showed significant differences in tHOA (P<0.001, ICC = 0.549, LoA = 0.19±0.5) and in SA (P<0.001, ICC = 0.733, LoA = 0.16±0.37). Wavescan showed a significant difference compared to Zywave (p<0.001, ICC = 0.920, LoA = 0.09±0.13) in SA. Comparisons between Allegro Analyzer and Zywave demonstrated significant differences in both Horizontal Coma (3,1) (p<0.001, ICC = -0.207, LoA = -0.15±0.48) and Astigmatism (2,2) (P = 0.003, ICC = -0.965, LoA = 0.2±2.5). Allegro Analyzer also differed from Wavescan in Horizontal Coma (3,1) (P<0.001, ICC = 0.725, LoA = -0.07±0.25).

CONCLUSIONS

Although some measurements were comparable predominately in the lower order aberrations, significant differences were found in the tHOA, SA, horizontal coma and astigmatism. Our analysis suggests that sensor design contributes to agreement in lower order aberrations, and Fourier and Zernike expansion might disagree in higher order aberrations. Therefore, comparison between aberrometers was generally possible with some exceptions in higher order measurements.

Precision of higher-order aberration measurements with a new Placido-disk topographer and Hartmann-Shack wavefront sensor

PURPOSE

To assess the intrasession and intersession precision of ocular, corneal, and internal higher-order aberrations (HOAs) measured using an integrated topographer and Hartmann-Shack wavefront sensor (Topcon KR-1W) in refractive surgery candidates.

SETTING

IOBA-Eye Institute, Valladolid, Spain.

DESIGN

Evaluation of diagnostic technology.

METHODS

To analyze intrasession repeatability, 1 experienced examiner measured eyes 9 times successively. To study intersession reproducibility, the same clinician obtained measurements from another set of eyes in 2 consecutive sessions 1 week apart. Ocular, corneal, and internal HOAs were obtained. Coma and spherical aberrations, 3rd- and 4th-order aberrations, and total HOAs were calculated for a 6.0 mm pupil diameter.

RESULTS

For intrasession repeatability (75 eyes), excellent intraclass correlation coefficients (ICCs) were obtained (ICC >0.87), except for internal primary coma (ICC = 0.75) and 3rd-order (ICC = 0.72) HOAs. Repeatability precision (1.96 × S(w)) values ranged from 0.03 μm (corneal primary spherical) to 0.08 μm (ocular primary coma). For intersession reproducibility (50 eyes), ICCs were good (>0.8) for ocular primary spherical, 3rd-order, and total higher-order aberrations; reproducibility precision values ranged from 0.06 μm (corneal primary spherical) to 0.21 μm (internal 3rd order), with internal HOAs having the lowest precision (≥0.12 μm). No systematic bias was found between examinations on different days.

CONCLUSIONS

The intrasession repeatability was high; therefore, the device's ability to measure HOAs in a reliable way was excellent. Under intersession reproducibility conditions, dependable corneal primary spherical aberrations were provided.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Corneal higher-order aberrations after Descemet's membrane endothelial keratoplasty

PURPOSE

We compared corneal higher-order aberrations (HOAs) in eyes after Descemet's membrane endothelial keratoplasty (DMEK), Descemet's stripping automated endothelial keratoplasty (DSAEK), and penetrating keratoplasty (PK), and in a control group that had not undergone surgery.

DESIGN

Retrospective analysis of clinical data.

PARTICIPANTS

Thirty eyes of 30 patients who had undergone standard DMEK, 20 eyes of 20 patients after DSAEK, 20 eyes of 20 patients after PK, and 20 eyes of 20 controls were analyzed.

METHODS

In addition to standard postoperative examinations, each participant was analyzed with the Pentacam high-resolution rotating Scheimpflug imaging system (Pentacam HR, Oculus, Wetzlar, Germany). Data were compared between groups.

MAIN OUTCOME MEASURES

Visual acuity and HOAs.

RESULTS

The mean follow-up was 6.5 ± 1.2 months after DMEK, 22.6 ± 11.8 months after DSAEK, and 103.1 ± 74.2 months after PK. There were no statistically significant differences for the anterior 4.0-mm zones between the DMEK group and the controls or between the DMEK and DSAEK groups. The DMEK procedure compared with PK showed statistically significant differences in all terms for the 4.0-mm zones. All combined Zernike terms for mean posterior aberrations of the central 4.0-mm zones showed statistically significant higher aberrations for DMEK compared with controls. The DMEK procedure compared with DSAEK showed statistically significant lower mean values for all combined Zernike terms, except for coma and coma-like terms in the central 4.0-mm zones of the posterior corneal surface. Compared with PK, DMEK showed statistically significant lower mean values for all combined Zernike terms for the central 4.0-mm zones of the posterior corneal surface, except for spherical aberration (SA) and SA-like terms. Best spectacle-corrected visual acuity (BSCVA) after DMEK was statistically significantly better than after DSAEK (P=0.001) and PK (P=0.005). There was no statistically significant difference when BSCVA was compared with controls (P=0.998).

CONCLUSIONS

Both DSAEK and PK exhibit increased posterior corneal HOAs even years after surgery. Patients receiving DMEK display only slight changes in posterior corneal HOAs.

Ocular response analyzer measurements in keratoconus with normal central corneal thickness compared with matched normal control eyes

PURPOSE

To compare corneal hysteresis (CH) and corneal resistance factor (CRF) in eyes with keratoconus with a central corneal thickness (CCT) ≥ 520 μm with CH and CRF in matched controls, and to estimate the sensitivity and specificity of these parameters for discriminating between the two groups.

METHODS

This prospective, comparative case series comprised 19 eyes of 19 patients with keratoconus with CCT ≥ 520 μm and 19 eyes of 19 healthy sex-, age-, and CCT-matched patients who underwent a complete clinical eye examination, corneal topography, tomography, and biomechanical evaluation. The receiver operating characteristic (ROC) curve was used to identify cutoff points that maximized the sensitivity and specificity for discriminating between groups.

RESULTS

Central corneal thickness was 543.1 ± 13.9 μm (range: 520 to 568 μm) in the keratoconus group and 545 ± 12.5 μm (range: 527 to 575 μm) in the control group (P=.6017). Corneal hysteresis was 9.22 ± 1.44 mmHg (range: 6.2 to 11.35 mmHg) in the keratoconus group and 10.58 ± 1.91 mmHg (range: 7.34 to 13.53 mmHg) in the control group (P=.0075). Corneal resistance factor was 8.62 ± 1.52 mmHg (range: 5.60 to 11.20 mmHg) in the keratoconus group and 10.30 ± 1.92 mmHg (range: 6.95 to 14.12 mmHg) in the control group (P=.0049). The ROC curve analyses showed a poor overall predictive accuracy of CH (cutoff, 9.90 mmHg; sensitivity, 78.9%; specificity, 63.2%; test accuracy, 71.05%) and CRF (cutoff, 8.90 mmHg; sensitivity, 68.4%; specificity, 78.9%; test accuracy, 73.65%) for detecting keratoconus in the eyes studied.

CONCLUSIONS

Corneal hysteresis and CRF were statistically lower in the keratoconus group compared with the control group. Given the large overlap, both CH and CRF had low sensitivity and specificity for discriminating between groups.