Time-domain Optical Coherence Tomography Research Articles

Analysis of the signal measured in spectral-domain optical coherence tomography based on nonlinear interferometers

We analyze and compare the output signals obtained in three different configurations of optical coherence tomography (OCT). After appropriate processing, these signals are used to retrieve an image of the sample under investigation. One of the configurations considered is the common choice in most OCT applications and is based on the use of a Michelson interferometer. For brevity, here we refer to it as standard OCT. The other two configurations are two types of optical coherence tomography based on the use of so-called nonlinear interferometers, interferometers that contain optical parametric amplifiers inside. The goal is to highlight the differences and similarities between the output signals measured in standard OCT and in these two OCT schemes, with the aim of evaluating if retrieval of information about the sample can be better done in one case over the others. We consider schemes where the optical sectioning of the sample is obtained by measuring the output signal spectrum (spectral or Fourier-domain OCT), since it shows better performance in terms of speed and sensitivity than the counterpart time-domain OCT.

A STUDY TO COMPARE THE RETINAL NERVE FIBER LAYER (RNFL) MEASUREMENTS USING THE TD OCT 'STRATUS' AND THE SD OCT 'RTVUE' IN HEALTHY PARTICIPANTS AND GLAUCOMA PATIENTS

Background: To compare the RNFL measurements using the conventional Time Domain Optical Coherence Tomography (TD-OCT) 'Stratus' and the Spectral Domain Optical Coherence Tomography (SD OCT) 'RTVue' in healthy participants and glaucoma patients. ThisMethods: prospective cross-sectional study included 50 eyes in each of the two study groups as, healthy eyes and eyes of established glaucoma patients. Peripapillary RNFL thickness was measured by both machines in random order by the same operator on the same day with pupils uniformly dilated to over 5.0 mm. Three separate fast RNFL Scans were acquired with Stratus OCT, from which the most reliable scan was chosen for comparison. For RTVue, “RNFL3.45” scan protocol was used, which consists of four sets of 1024 “A-scans” along a 3.45 mm-diameter circle centered on the optic disc. There was a signicant difference in RNFL measurements between the two methods ,which was maximum in the superiorResults: quadrant and minimum in the nasal quadrant in both the groups In both the groups, RTVue RNFL measurements are thicker as. Conclusion: compared to that of Stratus with maximum quadrant mean RNFL measurement in the inferior quadrant and minimum in the nasal quadrant. Maximum difference in RNFL measurement between the two machines was at superior quadrant in both the groups.

Evaluation of Signal Degradation Due to Birefringence in a Multiple Reference Optical Coherence Tomography System With Polarization-Based Balanced Detection

Although time-domain optical coherence tomography (TD-OCT) systems are straightforward to realize, the imaging speed, sensitivity, and imaging depth limit their range of applications. Multiple reference optical coherence tomography (MR-OCT) based on TD-OCT increases imaging range by about tenfold while providing sensitivity to image highly scattering biological samples. The multiple path-delays and free-space construction make MR-OCT also interesting for hybrid and compact systems, filling the gap between fibre-based and wafer-level integrated optical systems. We describe an optical configuration using a balanced detection scheme and the resulting signal properties due to the required use of polarizing optical components. We numerically simulate the signal properties using Jones calculus and compare the results with measurements. We discuss the origin of signal degradation due to birefringence of the sample in OCT and show that the quarter-wave plate in the sample arm of the Michelson interferometer can be adjusted to optimize the signal returning from a birefringent sample thereby improving the visibility of structures of interest. The theory discussed will be useful to understand and minimize signal degradation due to birefringence in Time-Domain and Fourier-Domain OCT systems.

Reliability of Time Domain AS-OCT in Measuring the Extraocular Rectus Muscle Insertion-Limbus Distances: A Systematic Review and Meta-Analysis.

PurposeThe insertion-limbus distances of the extraocular muscles are clinically relevant in the preoperative planning of strabismus surgeries, especially in reoperations when information regarding insertion sites is not accessible to the surgeon. In this systematic review, we assess the reliability of time-domain anterior segment optical coherence tomography (TD AS-OCT) in determining insertion-limbus distances preoperatively by investigating prior studies that compare preoperative TD AS-OCT measurements of the insertion-limbus distances to those of calipers, which are assumed to be the gold standard.MethodsSystematically reviewing EMBASE, PubMed, Google Scholar, Science Direct, and Web of Science, 2 members screened for studies that compared preoperative TD AS-OCT measurements to those of intraoperative calipers, the gold standard. To assess the risk of bias for individual studies, the reviewers utilized the ROBINS-I tool, a Cochrane’s collaboration tool used to assess bias in studies that are not randomized. For the meta-analysis, parallel forms reliability was examined and estimated as the Pearson product-moment correlation between TD AS-OCT measurements and surgical caliper measurements.ResultsSix out of the seven eligible studies provided measures of reliability that were >0.7. These six records were eligible for meta-analysis. There was no evidence of a difference between means of TD AS-OCT and caliper measurements (n{hat mu _{AS - oct}}n = 6.81, 95% CI [6.41, 7.22]; n{hat mu _{calipers}}n = 6.73, 95% CI [6.18, 7.29]; n{rm{hat Delta }}n = 0.08, 95% CI [−0.44, 0.61]). Reliability was estimated to be good (n{hat rho _{xx}}n = 0.91) though the lower limit was slightly below the recommended minimum acceptable level of 0.70 (95% CI [0.65, >0.99]).ConclusionIn the setting of primary surgeries, TD AS-OCT has an acceptable reliability. However, there is insufficient data to conclude whether TD AS-OCT has an acceptable reliability in the setting of reoperations.

Retinal nerve fiber layer thickness in amblyopia.

To report retinal nerve fiber layer thickness (RNFLT) in eyes with amblyopia compared with contralateral healthy eyes. In this cross-sectional study, we included patients with anisometropic amblyopia, strabismic amblyopia, and mixed amblyopia. All subjects underwent complete ophthalmic examination, including RNFLT measurement with time-domain OCT (Stratus OCT) and scanning laser polarimeter (GDX VCC). A paired "t" test was used to compare average and quadrant-wise RNFL thickness between the amblyopic and contralateral normal eyes. In addition, an analysis of variance test was used to compare various RNFL thickness parameters between the three groups. A total of 33 eyes of 33 subjects with anisometropic amblyopia, 20 eyes of 20 subjects with strabismic amblyopia, and 38 eyes of 38 subjects with mixed amblyopia were included. In the anisometropic amblyopia group, the average RNFLT in the amblyopic eye was 98.2 μm and 99.8 μm in the fellow normal eye (P = 0.5), the total foveal thickness was 152.82 μm (26.78) in the anisometropic eye and 150.42 μm (23.84) in the fellow eye (P = 0.38). The difference between amblyopic and contralateral normal eye for RNFL and macular parameters was statistically insignificant in all three groups. The RNFL thickness in four quadrants was similar in the amblyopic and non-amblyopic eye between all three groups and statistically non-significant. Our study showed that RNFL thickness was similar in amblyopic and non-amblyopic eyes between all three amblyopia groups.

Optical phase modulation by natural eye movements: application to time-domain FF-OCT image retrieval.

Eye movements are commonly seen as an obstacle to high-resolution ophthalmic imaging. In this context we study the natural axial movements of the in vivo human eye and show that they can be used to modulate the optical phase and retrieve tomographic images via time-domain full-field optical coherence tomography (TD-FF-OCT). This approach opens a path to a simplified ophthalmic TD-FF-OCT device, operating without the usual piezo motor-camera synchronization. The device demonstrates in vivo human corneal images under the different image retrieval schemes (2-phase and 4-phase) and different exposure times (3.5 ms, 10 ms, 20 ms). Data on eye movements, acquired with a spectral-domain OCT with axial eye tracking (180 B-scans/s), are used to study the influence of ocular motion on the probability of capturing high-signal tomographic images without phase washout. The optimal combinations of camera acquisition speed and amplitude of piezo modulation are proposed and discussed.

Evaluation of Choroidal Thickness Using Optical Coherent Tomography: A Review.

The choroid is the main source of blood and nourishment supply to the eye. The dysfunction of the choroid has been implicated in various retinal and choroidal diseases. The identification and in-depth understanding of pachychoroid spectrum disorders are based on the tremendous progress of optical coherence tomography (OCT) technology in recent years, although visibility of choroid is challenging in the era of the time or spectral domain OCT. The recent rapid revolution of OCTs, such as the enhanced depth imaging OCT and the swept-source OCT, has greatly contributed to the significant improvement in the analysis of the morphology and physiology of the choroid precisely, especially to the choroid–scleral boundary and vasculature. The present review highlights the recently available evidence on the measurement methodology and the clinical significance of choroidal thickness in retinal or choroidal disorders.

Acute syphilitic posterior placoid chorioretinitis: a case report

Purpose: To present a case of acute syphilitic posterior placoid chorioretinitis (ASPPC), one of the possible ocular manifestations of syphilis, and alert clinicians to the reemergence of syphilis worldwide.
 Methods: Clinical findings, fluorescein angiography, indocyanine green angiography, autofluorescence imaging, time domain optical coherence tomography features, and management of the patient are presented.
 Results: A 39–year–old male presented as an otherwise healthy man with a 3–day history of blurred vision in his right eye. Clinical examination revealed signs of posterior uveitis. Clinical features and additional imaging findings were consistent with the descripton of ASPPC. Syphilis was confirmed with a positive serological test for syphilis. Additional human immunodeficiency virus (HIV) testing was intended and the patient only then disclosed his medical history of being HIV positive and receiving antiretroviral therapy. Cerebrospinal fluid examination revealed neurosyphilis. He was treated with a 2– week course of intravenous penicillin and his visual acuity recovered fully.
 Conclusions: Ocular findings may be the presenting feature of syphilis. Physicians' awareness of the variety of clinical presentations of syphilis is important for prompt recognition and early management of this curable disease, which can cause substantial morbidity and increased mortality if left untreated.

Optical Coherence Tomography for Diagnosis and Treatment of Corneal Diseases

Optical coherence tomography (OCT) is a modern non-contact real-time imaging of anterior and posterior eye’s segments. Based on the principle of low-coherence interferometry, it provides the analysis of tissue structures. In this review, we discuss technical aspects of two different OCT platforms: Time-Domain OCT (TD-OCT), and Spectral-Domain (SD-OCT) with the use of Fourier transformation — Fourier-Domain (FD-OCT). Over the last several years, the development of OCT has increased the resolution of images by different ways of optical filtering. The usage of tunable swept laser instead of superluminescent diode in modern Swept-Source OCT (SS-OCT) provides the sufficient quality of image. Anterior segment OCT can detect the pathological changes in different ocular structures and may be a key tool for monitoring of their progression. In pterygium OCT shows the true extent of fibrovascular granulation tissue in stromal layers, whereas in keratitis it provides imaging of corneal infiltration. Frequently, OCT-pachymetry can be advantageous in the detection of subclinical keratectasias. In patients with bullous keratopathy OCT can help to distinguish corneal edema and fibrosis. The new era of OCT is characterized by application of this method in keratorefractive surgery. Microscope-mounted (portable) and microscopeintegrated OCT systems have been developed. During LASIK surgery intraoperative OCT (iOCT) helps to assess flap interface, measure flap and residual bed thickness. It is a useful tool to reveal the structural changes during corneal collagen crosslinking. At the beginning of keratoplasty, iOCT helps to determine the corneal thickness, extent and depth of opacity, Descemet membrane perforation. iOCT guides decision-making regarding keratoplasty modification, depth and diameter of trephination. Furthermore, a real-time visualization of ocular structures during keratoplasty decreases the frequency of intra- and postsurgical complications.

Time-Domain Optical Coherence Tomography System for Determining The Extinction Coefficient and Group Refractive Index of Gelatin-based Skin Phantoms

Optical Coherence Tomography (OCT) is a non-invasive, non-destructive optical imaging technique that uses a low coherence interferometer to obtain real-time cross-sectional images of samples. OCT is notably used in biomedical applications including ophthalmology and dermatology. Aside from generating cross-sectional images, axial scans can also provide additional information about its optical properties such as extinction coefficient and refractive index. This study determines the extinction coefficients and group refractive indices of gelatin-based skin phantoms using a portable time-domain (TD) – OCT system. The gelatin-based skin phantoms were fabricated with varying concentrations of titanium dioxide (TiO2), while keeping the amount of both gelatin and water constant. By changing the proportion of the gelatin powder and TiO2, skin phantoms can then be fabricated to mimic various skin conditions, both pathologic and non-pathologic. Results of the study found a positive correlation of extinction coefficient and refractive index with TiO2 concentration. Thus, increasing TiO2 concentration also increases both extinction coefficient and group refractive index. The median extinction coefficient values of the phantoms ranged from 4.29 mm−1 to 8.48 mm−1. Literature showed that the epidermis can have extinction coefficients of 1.64-7.3 mm−1. For refractive indices of the fabricated phantoms, values ranged from 1.32 to 1.48, while studies on human participants showed that human skin has refractive index values of 1.34-1.56. Based on these properties, it is feasible to fabricate phantoms simulating the optical properties of human skin.

Jitter Correction and SNR Improvement of A-Scan Signal Using Wavelet Denoising and Signal Averaging for a Portable Time-Domain Optical Coherence Tomography System

<p class='IJASEITAbtract'>Optical coherence tomography (OCT) is used to probe surface cross-sections of various materials in manufacturing, anatomy, and agriculture, among others. In any OCT system, signals have embedded noise in various forms, such as electrical noise and Jitter, which affect the depth profile (A-scan) and image quality. A signal processing method for correcting the Jitter and improving the signal-to-noise ratios (SNR) and image quality was developed in this study for a portable time-domain (TD) OCT system that utilizes a pc-based oscilloscope for data acquisition. A stack of five glass coverslips was used as a sample. Each signal from the oscilloscope consists of an A-scan coupled with a trigger signal. Jitter correction was done by first denoising the trigger signal using a combination of moving average and wavelet denoising. A reference trigger was selected, and all other trigger signals were adjusted, including the A-scans. Once jitter was corrected, the denoising method on the OCT A-scans was employed. The signal averaging method and various wavelet denoising methods were applied to the A-scans of the sample to identify which will give the highest SNR and improved image quality. Combining averaging of fifty signals and Daubechies 7 (Db7) with hard thresholding reduced the acquisition time and storage space by 50%, improved the SNR by 18 dB, improved the depth profile and image quality of a stack of five glass coverslips. This signal processing method will allow us to characterize and properly visualize cross-sectional images of other samples in the future using our TD-OCT system.

Optical Coherence Tomography for Three-Dimensional Imaging in the Biomedical Field: A Review

Optical coherence tomography (OCT) has become a novel approach to noninvasive imaging in the past three decades, bringing a significant potential to biological research and medical biopsy in situ, particularly in three-dimensional (3D) in vivo conditions. Specifically, OCT systems using broad bandwidth sources, mainly centered at near-infrared-II, allow significantly higher imaging depth, as well as maintain a high-resolution and better signal-to-noise ratio than the traditional microscope, which avoids the scattering blur and thus obtains more details from delicate biological structures not just limited to the surface. Furthermore, OCT systems combined the spectrometer with novel light sources, such as multiplexed superluminescent diodes or ultra-broadband supercontinuum laser sources, to obtain sub-micron resolution imaging with high-speed achieve widespread clinical applications. Besides improving OCT performance, the functional extensions of OCT with other designs and instrumentations, taking polarization state or birefringence into account, have further improved OCT properties and functions. We summarized the conventional principle of OCT systems, including time-domain OCT, Fourier-domain OCT, and several typical OCT extensions, compared their different components and properties, and analyzed factors that affect OCT performance. We also reviewed current applications of OCT in the biomedical field, especially in hearing science, discussed existing limitations and challenges, and looked forward to future development, which may provide a guideline for those with 3D in vivo imaging desires.

Condition diagnosing easel tempera paintings by the high-resolution optical coherence tomography method

Peculiarities of using optical coherence tomography for examining the condition of valuable paintings are considered. A full-field optoelectronic system for determination of the internal microstructure of inhomogeneous media with high resolution and operation speed using a Wiener adaptive filtering algorithm for dynamic signal processing in time-domain optical coherence tomography is presented. Examples of determination of specific features of the microstructure of antique easel tempera paintings, such as thickness of the varnish layer and characteristics of its craquelure, morphology of the subsequent overpaint of the author layer, and loss of the varnish-and-paint layer by shelling, for determining the condition of an art object are presented.

Optical Coherence Tomography and Glaucoma.

Early detection and monitoring are critical to the diagnosis and management of glaucoma, a progressive optic neuropathy that causes irreversible blindness. Optical coherence tomography (OCT) has become a commonly utilized imaging modality that aids in the detection and monitoring of structural glaucomatous damage. Since its inception in 1991, OCT has progressed through multiple iterations, from time-domain OCT, to spectral-domain OCT, to swept-source OCT, all of which have progressively improved the resolution and speed of scans. Even newer technological advancements and OCT applications, such as adaptive optics, visible-light OCT, and OCT-angiography, have enriched the use of OCT in the evaluation of glaucoma. This article reviews current commercial and state-of-the-art OCT technologies and analytic techniques in the context of their utility for glaucoma diagnosis and management, as well as promising future directions.

EVALUATION OF GLAUCOMA MODULE PREMIUM EDITION IN EGYPT

The mean prevalence of high myopia increases over time in Egypt Prevalence of high myopia in Egypt which was 0.2%, in 1960 increased to 7.4% in 1976 and 10.8% in 2015. Optical coherence tomography (OCT) is a noninvasive, painless and quick precise technology that can be used for interpreting tissue structure and function. Time-domain OCT was fast enough to scan a circle centered on the optic nerve head (circumpapillary) to assess the retinal nerve fiber layer (RNFL) thickness. Glaucoma Module Premium Edition (GMPE) is a new, objective method of ONH analysis using BMO. The termination of Bruch's membrane at the ONH marks the opening through which RGC axons exit the eye to form the choroidal and scleral portions of the neural canal, this anatomic opening, termed Bruch's membrane opening (BMO). The minimum distance from the BMO to the internal limiting membrane represents the most geometrically accurate measurement of neuroretinal rim width. This neuroretinal rim measurement has been termed Bruch's Membrane Opening-Minimum Rim Width (BMO-MRW).

Three-dimensional measurement for spherical and nonspherical shapes of contact lenses.

In recent years, with the development of precise lathe-cutting equipment, special shaped contact lenses (CL) have been crafted. However, while it is possible to manufacture such a lens, its shape evaluation has not been well-established. We conducted a basic optical experiment using special lenses to measure a spherical lens and nonspherical mold. As the measurement sample, a metal ball, special CL, and a toric-shaped mold were adopted. In order to accurately measure those real shapes, we proposed an algorithm in which the probe light is vertically incident to the sample surface within a numerical aperture of the optical probe. For this algorithm, we developed the specialized time-domain optical coherence tomography (TD-OCT), which was designed to conduct circular scanning while maintaining vertical incidence by driving a two-axis (vertical and horizontal) micro-electromechanical system mirror with a phase difference of 90°. The shape, thickness distribution, and curvature radii of both front and back surfaces of a CL were estimated with this OCT signal analysis and sphere fitting. The shape and curvature radius were evaluated by using the simulated data under the same experimental conditions. They were sufficiently accurate based on the resolution of this OCT. Also, a toric-shaped mold was evaluated by comparing the relationship between each coordinate and intensity of the interference signal. As a result, it is confirmed that the experimental result and the simulated matched well.

Prevalence of Vitreoretinal Interface Disorders in an Australian Population: The Blue Mountains Eye Study.

PurposeTo describe the prevalence, risk factors, and associations of vitreoretinal interface (VRI) abnormalities in a population-based study of older adults.DesignCross-sectional analysis of cohort study participants.ParticipantsOf the 1149 participants (mean age, 76.1 ± 6.9 years) in the 15-year Blue Mountains Eye Study follow-up examination from 2007 through 2009, 905 (1791 eyes) had gradable time-domain or spectral-domain OCT scans of the macula from at least 1 eye.MethodsOCT scans were graded according to the International Vitreomacular Traction Study Group classification system of VRI abnormalities. Best-corrected visual acuity (BCVA) was recorded.Main Outcome MeasuresPrevalence of VRIs.ResultsOverall, 451 participants showed any VRI abnormality (49.8%). Prevalence of VRI abnormality by person was: vitreomacular adhesion (VMA), 33.6%; vitreomacular traction (VMT), 1.6%; epiretinal membrane (ERM), 21.4%; full-thickness macular hole (FTMH), 0.7%; and lamellar macular hole (LMH), 0.7%. Twenty-two percent of VMAs were focal, and 78% were broad based; 76% of VMTs were focal, and 24% were broad based. All FTMHs observed were large (>400 μm), with mean aperture size of 573 μm (range, 459–771 μm). Increased age was associated with higher ERM and lower VMA prevalence (P < 0.001 for both). Pseudophakia and myopia were associated with ERM (age- and sex-adjusted odds ratios [ORs], 1.48 [95% confidence interval (CI), 1.01–2.17] and 1.72 [95% CI, 1.05–2.81], respectively). Moderate or severe ERM and FTMH were associated with worse BCVA of 9.2 Early Treatment Diabetic Retinopathy Study (ETDRS) letters (95% CI, 3.4–15.0 ETDRS letters; P = 0.008) and 26.0 ETDRS letters (95% CI, 10.9–41.1 ETDRS letters; P = 0.001), respectively.ConclusionsThe prevalence of VRI abnormalities is high in older individuals. Epiretinal membrane was associated with increasing age, pseudophakia, and myopia. Epiretinal membrane and FTMH may account for significant visual loss in the affected eye. This study provided useful population-based data on the prevalence of VRI abnormalities in older individuals.

Endodontic fillings evaluated using en face OCT, microCT and SEM.

Objectives: The goal of endodontic therapy is mechanically cleaning and shaping the root canal system, the removal of organic and inorganic debris followed by sealing with permanent filling materials. Materials and Methods: Therefore, the aim of this in vitro study was to engage three imagistic methods: (i) en face (ef) time domain (TD) optical coherence tomography (OCT), (ii) micro-computed tomography (μCT), and (iii) scanning electron microscopy (SEM), in terms of their efficiency in assessing the quality of endodontic fillings. So far, is settled that efOCT images can identify defects/voids in several of the investigated root canal fillings and identify gaps of 50 μm. Results: The results delivered by μCT technology also showed several imperfections of the endodontic filling but also at the interfaces formed by the sealer and the root canal walls. SEM investigations highlights the complex form of the interface formed the endodontic filling material and the walls of the root canal, as well as shortcomings of the materials from several samples. Gaps of 50 μm are identified with efOCT. Conclusions: The net advantage of OCT technology, in respect to the other two technologies consists in its non-invasiveness. The OCT axial resolution is also sufficient to see the material gaps. Another advantage of efOCT investigations is that they allow real-time imaging of complex arrangement at the interfaces of the filling material with dentinal root.

Agreement Between Angle-to-Angle Distance and Aqueous Depth Obtained With Two Different Optical Coherence Tomographers and a Scheimpflug Camera.

To compare angle-to-angle (ATA) distance and aqueous depth (AQD) readings produced by two different optical coherence tomography (OCT) devices and a Scheimpflug camera. ATA distance and AQD were measured in 60 eyes using the Visante time-domain OCT (TD-OCT) (Carl Zeiss Meditec AG), the Anterion swept-source OCT (SS-OCT) (Heidelberg Engineering GmbH), and the Pentacam HR Scheimpflug camera (Oculus Optikgeräte GmbH). Moreover, ATA distance was measured along the horizontal and vertical meridians. Bland-Altman analysis was used to assess the agreement between devices. All three devices did not yield similar horizontal ATA distance: 11.96 ± 0.47 mm (TD-OCT), 11.96 ± 0.42 mm (SS-OCT), and 11.05 ± 0.52 mm (Pentacam). More specifically, the Pentacam yielded significantly smaller values (approximately 0.9 mm, P < .001). Mean vertical ATA distance was 12.61 ± 0.65 and 12 ± 0.65 mm for the TD-OCT and SS-OCT, respectively (P = .983). Vertical ATA distance was significantly larger than horizontal ATA distance for both OCT devices (approximately 0.6 mm, P < .001). The lowest mean difference was found between both OCT devices (0.0068 and -0.0415 mm, for horizontal and vertical meridians, respectively) and the highest between the Pentacam and the two OCT devices (approximately 0.9 mm). As for AQD, inter-device mean values were also statistically significant: 2.89 ± 0.48, 2.82 ± 0.49, and 2.79 ± 0.50 mm, for the TD-OCT, SS-OCT, and Pentacam, respectively (P < .001). Mean differences were similar for the TD-OCT versus SS-OCT and SS-OCT versus Pentacam (approximately 0.02 mm), and larger between the TD-OCT and Pentacam (approximately 0.05 mm). The results show that the TD-OCT and SS-OCT are interchangeable instruments for ATA distance measurement but the Pentacam is not with either of the two OCT devices. A clinical criterion should assess whether these three devices could be used interchangeably for AQD measurement. [J Refract Surg. 2021;37(2):133-140.].

Retinal nerve fiber layer changes in migraine: a systematic review and meta-analysis.

Migraine is one of the most common disabling diseases in the world. Its recurrent attacks may lead to abnormalities in the structure of the brain and retina. An increasing number of studies have investigated retinal nerve fiber layer (RNFL) thickness alterations in migraine by the optical coherence tomography (OCT); however, no consensus has yet reached. We searched Pubmed, Embase, and Web of Science databases to identify studies that investigated RNFL thickness in migraine by OCT measurement and performed a meta-analysis of eligible studies. Twenty-six studies were included in the meta-analysis, comprising 1530 migraine patients and 1105 healthy controls. The mean RNFL thickness was thinner in the migraine group compared to the control group (SMD =- 0.53). In the subgroup analyses, RNFL thickness were decreased most significantly in the superior (SMD = - 0.71) and inferior (SMD = - 0.63) quadrants among all quadrants. Migraine with aura (SMD = - 0.91) showed a greater effect size of RNFL thickness reduction than migraine without aura (SMD =- 0.47). Spectral-domain OCT (SMD = - 0.55) seems more sensitive to detect RNFL thickness reduction than time-domain OCT (SMD = - 0.44). In addition, age, sex, disease duration, attack frequency, and intraocular pressure were not significantly associated with RNFL thickness. The findings from our comprehensive meta-analysis with large datasets strengthen the clinical evidence of the RNFL thickness reduction in migraine. RNFL thickness via spectral-domain OCT measurement demonstrates the potential role in differentiating patients with migraine, especially migraine with aura, from healthy controls.