Retinal assessment using optical coherence tomography

Retinal pigment epithelial changes in chronic Vogt-Koyanagi-Harada disease: fundus autofluorescence and spectral domain-optical coherence tomography findings

PURPOSE

The purpose of this study was to determine whether fundus autofluorescence (FAF) and spectral domain-optical coherence tomography (SD-OCT) imaging allow better assessment of retinal pigment epithelium and the outer retina in subjects with chronic Vogt-Koyanagi-Harada disease compared with examination and angiography alone.

METHODS

A cross-sectional analysis of a series of seven consecutive patients with chronic Vogt-Koyanagi-Harada disease undergoing FAF and SD-OCT was conducted. Chronic disease was defined as duration of intraocular inflammation >3 months. Color fundus photographs were correlated to FAF and SD-OCT images. The images were later correlated to fluorescein angiography and indocyanine green angiography.

RESULTS

All patients had sunset glow fundus, which resulted in no apparent corresponding abnormality on FAF or SD-OCT. Lesions with decreased autofluorescence signal were observed in 11 eyes (85%), being associated with loss of the retinal pigment epithelium and involvement of the outer retina on SD-OCT. In 5 eyes (38%), some of these lesions were very subtle on clinical examination but easily detected by FAF. Lesions with increased autofluorescence signal were seen in 8 eyes (61.5%), showing variable involvement of the outer retina on SD-OCT and corresponding clinically to areas of retinal pigment epithelium proliferation and cystoid macular edema.

CONCLUSION

Combined use of FAF and SD-OCT imaging allowed noninvasive delineation of retinal pigment epithelium/outer retina changes in patients with chronic Vogt-Koyanagi-Harada disease, which were consistent with previous histopathologic reports. Some of these changes were not apparent on clinical examination.

Ophthalmic imaging today: an ophthalmic photographer's viewpoint - a review

Ophthalmic imaging has changed dramatically since the 1960s with increasingly complex technologies now available. Arguably, the greatest changes have been the development of the digital camera and the speed, processing power and storage of electronic data. Already, ophthalmic practices in many major institutions overseas have paperless medium storage and electronically generated reporting from all equipment that use a computer interface. It is hard to remember the widespread use of photographic film with its attendant costs, or even to remember the days before optical coherence tomography (OCT). These latest technical improvements in ophthalmic imaging are now standard in large Australian institutions and becoming more widespread in smaller private practices. The technicians that operate and maintain this ever-increasing plethora of gadgetry have seen their work practices change from the darkroom to the complexities of data-based imaging and storage. It is a fitting time to examine the contemporary state of ophthalmic imaging and what lies on the horizon as we move towards 2020.

OCT reveals regional differences in macular thickness with age

PURPOSE

To assist identification of macular thickness abnormalities by optical coherence tomography (OCT), we use techniques that improve spatial localization across the retina to establish any age-related retinal thickness changes in healthy eyes.

METHODS

Retinal thickness was measured in 30 eyes of 30 healthy subjects aged 13 to 69 years. Using Stratus OCT 3, 12 radial scans centered at the foveola were acquired and points between scans were interpolated to create a topographic map of the central 20 degrees . The thickness map was divided into 37 hexagonal regions. A mean retinal thickness for each hexagon was computed. Retinal thickness vs. age was evaluated for the entire scanned area, five anatomical regions, and within individual hexagons. The retinal nerve fiber layer (RNFL) contribution to total retinal thinning was analyzed in the papillomacular region.

RESULTS

There was a small but significant thinning of the overall macular area with increasing age (2.7 mum/decade; p = 0.027). Comparing the 10 youngest subjects (age 13 to 27 years) with the 10 oldest (age 51 to 68 years), retinal thicknesses in the temporal, superior, inferior, and foveal regions were not significantly different. However, the two age groups differed significantly in retinal thickness in the nasal region (p < 0.008). Across all subjects, retinal thickness in this region was linearly correlated with age, decreasing by 4.1 mum/decade (p < 0.002). Approximately 43% of the retinal thinning in the nasal region was attributed to RNFL loss.

CONCLUSIONS

The method of OCT acquisition and analysis used in this study allows for greater spatial localization of change in retinal thickness associated with aging or pathological processes. Based on the results of this study, the macula thins with increasing age but does so nonuniformly. The greatest amount of thinning occurs nasal to the fovea. RNFL loss accounts for much, but not all the thinning in this area.

Virtual histology of the human heart using optical coherence tomography

Optical coherence tomography (OCT) allows for the visualization of micron-scale structures within nontransparent biological tissues. For the first time, we demonstrate the use of OCT in identifying components of the cardiac conduction system and other structures in the explanted human heart. Reconstructions of cardiac structures up to 2 mm below the tissue surface were achieved and validated with Masson Trichrome histology in atrial, ventricular, sinoatrial nodal, and atrioventricular nodal preparations. The high spatial resolution of OCT provides visualization of cardiac fibers within the myocardium, as well as elements of the cardiac conduction system; however, a limiting factor remains its depth penetration, demonstrated to be approximately 2 mm in cardiac tissues. Despite its currently limited imaging depth, the use of OCT to identify the structural determinants of both normal and abnormal function in the intact human heart is critical in its development as a potential aid to intracardiac arrhythmia diagnosis and therapy.

Adolescents with Type 2 diabetes: early indications of focal retinal neuropathy, retinal thinning, and venular dilation

PURPOSE

The eye provides a unique window into the neural and vascular health of a patient with diabetes. The present study is the first of its kind to examine the neural retinal function, structure, and retinal vascular health in adolescents with Type 2 diabetes.

METHODS

Focal neural responses from 103 discrete retinal regions of the eye were tested using multifocal electroretinography. Optical coherence tomography was utilized to measure retinal thickness. Digital fundus photographs were examined for the presence of retinopathy and to measure vascular caliber using retinal vessel analysis. Fifteen adolescents diagnosed with Type 2 diabetes, aged 13 to 21 years with a mean diabetes duration of 2.1 +/- 1.3 years, were tested. Twenty-six age-matched control subjects were also tested.

RESULTS

Multifocal electroretinograms of the Type 2 diabetic group were significantly (P = 0.03) delayed by 0.49 milliseconds. The diabetic group also showed significant (both; P < or = 0.03) retinal thinning (10.3 microm) and significant venular dilation (16.2 microm).

CONCLUSION

The present study shows early indications of focal retinal neuropathy, retinal thinning, and venular dilation in adolescents with Type 2 diabetes. Early detection of functional and structural changes will hopefully aid in the prevention of permanent damage or further functional loss.

Intravitreal bevacizumab for diabetic macular edema associated with severe capillary loss: one-year results of a pilot study

PURPOSE

To evaluate the effects of intravitreal bevacizumab in patients with diabetic macular edema (DME) associated with severe capillary loss.

DESIGN

Multicenter, open-label, nonrandomized study.

METHODS

SETTING

Two tertiary ophthalmic referral centers in Brazil.

STUDY POPULATION

Ten consecutive patients with DME and "severe" capillary loss.

OBSERVATION PROCEDURES

Intravitreal injection(s) of bevacizumab (1.5 mg). Standardized ophthalmic evaluation was performed at baseline and at weeks 8, 16, 24, and 54.

MAIN OUTCOME MEASURES

Changes in best-corrected visual acuity (BCVA) and in optical coherence tomography variables (central macular thickness [CMT] and total macular volume [TMV]).

RESULTS

Significant changes in BCVA and in CMT/TMV were noted throughout the study (P < .001, P = .009, and P < .001, respectively). The mean logarithm of the minimal angle of resolution Early Treatment Diabetic Retinopathy Study BCVA was 0.786 ( approximately 20/125(+1)) at baseline, 0.646 ( approximately 20/80(-2)) at week 8, 0.580 (20/80(+1)) at week 16, 0.574 ( approximately 20/80(+1)) at week 24, and 0.558 ( approximately 20/80(+2)) at week 54. Compared with baseline, a significant change in BCVA was noted at all follow-up visits (P <or= .008). The mean CMT/TMV values were, respectively, 472.6/10.9 at baseline, 371.4/9.9 at week 8, 359.5/9.8 at week 16, 323.9/9.4 at week 24, and 274.6/8.7 at week 54. Compared with baseline, a significant change in both CMT and TMV was noted only at 24 and 54 weeks (P <or= .007). At 54 weeks, fluorescein angiography demonstrated no change in the extent of macular capillary loss and reduced dye leakage as compared with baseline in all patients.

CONCLUSIONS

Favorable changes in BCVA and in CMT/TMV observed throughout 1 year suggest that intravitreal bevacizumab may be a viable alternative treatment for the management of patients with DME and severe capillary loss.

Correlation in foveal thickness measurements between spectral-domain and time-domain optical coherence tomography in normal individuals

PURPOSE

To compare a time-domain (Stratus) and a spectral-domain (Spectralis) optical coherence tomography (OCT) device in assessing foveal thickness in healthy subjects.

METHODS

In this observational study 40 healthy subjects (40 eyes) underwent Stratus OCT and Spectralis OCT measurements of foveal thickness using three consecutive horizontal and vertical B-scan. Paired samples t-test was used to compare means between Stratus and Spectralis OCT measurements. Coefficient of variation (CoV) was used to compare dispersion in datasets. Pearson's correlation coefficient was used to quantify linear relation between Spectralis and Stratus OCT measurements. To assess agreement between Spectralis and Stratus OCT foveal thickness measurements, the Bland and Altman plots were used.

RESULTS

Sample age ranged from 19 to 49 years (mean 33.25, standard deviation (SD) +/-4.22). The Spectralis OCT foveal thickness measurements resulted significantly higher than those obtained with Stratus OCT (227.64+/-11.74 vs 144.36+/-12.25 microm, and 227.63+/-11.43 vs 144.92+/-12.34 microm, for horizontal and vertical foveal thickness, respectively) (P<0.05). Coefficient of variations were 5.16 and 5.02% using Spectralis OCT, and 8.49 and 8.51% using Stratus OCT. Mean Spectralis/Stratus ratio was 1.58 for both horizontal and vertical measurements. A linear relation between the two technologies was found (r(horiz)=0.899 and r(vert)=0.869) (P<0.001).

CONCLUSIONS

A good correlation between Stratus and Spectralis OCT foveal measurements was found, independently of retinal thickness. This preliminary study suggests the existence of a conversion factor between Stratus and Spectralis OCT when measuring healthy foveal thickness.

Repeatability and reproducibility of macular thickness measurements using fourier domain optical coherence tomography

Aim:

To evaluate repeatability and reproducibility of macular thickness measurements in visually normal eyes using the Topcon 3D OCT-1000.

Methods:

Phase 1 investigated scan repeatability, the effect of age and pupil dilation. Two groups (6 younger and 6 older participants) had one eye scanned 5 times pre and post- dilation by 1 operator. Phase 2 investigated between-operator, within and between-visit reproducibility. 10 participants had 1 un-dilated eye scanned 3 times on 2 separate visits by 2 operators.

Results:

Conclusion:

A high level repeatability, close to 6µm, of macular thickness measurement is possible using the 3D OCT- 1000. Measured differences in macular thickness between successive visits that exceed 6µm in pre-presbyopic individuals are therefore likely to reflect actual structural change. OCT measures are more variable in older individuals and it is advisable to take a series of scans so that outliers can be more easily identified.

A comparison of retinal nerve fiber layer (RNFL) thickness obtained with frequency and time domain optical coherence tomography (OCT)

To diagnose glaucoma and other diseases of the retinal ganglion cell/ optic nerve, the thickness of the retinal nerve fiber layer (RNFL) is routinely measured with optical coherence tomography. Until recently, these OCT measurements were made almost exclusively with a time domain OCT (tdOCT) machine from a single manufacturer. Recently, a number of OCT machines, based upon an improved frequency domain OCT technology (fdOCT), have appeared. We compared measurements made using a new fdOCT machine to those from the older tdOCT machine. The results were comparable. More importantly, we learned that the key factor determining whether results from different machines will be comparable is the algorithm used to segment RNFL thickness, not the type of OCT.

Combined laser and intravitreal triamcinolone for proliferative diabetic retinopathy and macular edema: one-year results of a randomized clinical trial

PURPOSE

To evaluate laser combined with intravitreal triamcinolone acetonide (IVTA) for the management of patients with proliferative diabetic retinopathy (PDR) and clinically significant macular edema (CSME).

DESIGN

Randomized clinical trial.

METHODS

settings: Single center. study population: Twenty-two patients with bilateral treatment-naïve moderate PDR and CSME. intervention: Laser (panretinal and macular) photocoagulation was performed in each eye, followed by IVTA in one randomly assigned eye. Best-corrected visual acuity (BCVA), fundus photography, and optical coherence tomography were performed at baseline and at months 1, 3, 6, 9, and 12. main outcome measures: Changes in BCVA, central macular thickness (CMT), and total macular volume (TMV).

RESULTS

The mean logarithm of the minimal angle of resolution (logMAR) BCVA improved significantly, and mean CMT and TMV were significantly reduced in the IVTA group compared with the laser-only group (controls) at all study follow-up visits (P < .001). The mean logMAR BCVA (Snellen equivalent) was 0.44 (20/50(-2)) for the IVTA group and 0.38 (20/50(+1)) for the controls at baseline, and 0.12 (20/25(-1)) for the IVTA group and 0.32 (20/40(-1)) for the controls at 12 months (P < .001). The mean CMT and TMV were, respectively, 360 microm and 8.59 mm(3) for the IVTA group and 331 microm and 8.44 mm(3) for the controls at baseline, and 236 microm and 7.32 mm(3) for the IVTA group and 266 microm and 7.78 mm(3) for the controls at 12 months (P < .001).

CONCLUSIONS

The combination of laser photocoagulation with IVTA was associated with improved BCVA and decreased CMT and TMV when compared with laser photocoagulation alone for the treatment of moderate PDR with CSME.

Optical coherence tomography-enhanced microlaryngoscopy: preliminary report of a noncontact optical coherence tomography system integrated with a surgical microscope

OBJECTIVES

Optical coherence tomography (OCT) is a new imaging modality that uses near-infrared light to produce cross-sectional images of tissue with a resolution approaching that of light microscopy. We have previously reported use of OCT imaging of the vocal folds (VFs) during direct laryngoscopy with a probe held in contact or near-contact with the VFs. This aim of this study was to develop and evaluate a novel OCT system integrated with a surgical microscope to allow hands-free OCT imaging of the VFs, which could be performed simultaneously with microscopic visualization.

METHODS

We performed a prospective evaluation of a new method of acquiring OCT images of the VFs.

RESULTS

An OCT system was successfully integrated with a surgical microscope to permit noncontact OCT imaging of the VFs of 10 patients. With this novel device we were able to identify VF epithelium and lamina propria; however, the resolution was reduced compared to that achieved with the standard contact or near-contact OCT.

CONCLUSIONS

Optical coherence tomography is able to produce high-resolution images of vocal fold mucosa to a maximum depth of 1.6 mm. It may be used in the diagnosis of VF lesions, particularly early squamous cell carcinoma, in which OCT can show disruption of the basement membrane. Mounting the OCT device directly onto the operating microscope allows hands-free noncontact OCT imaging and simultaneous conventional microscopic visualization of the VFs. However, the lateral resolution of the OCT microscope system is 50 microm, in contrast to the conventional handheld probe system (10 microm). Although such images at this resolution are still useful clinically, improved resolution would enhance the system's performance, potentially enabling real-time OCT-guided microsurgery of the larynx.

Vitreo-retinal traction and anastrozole use

PURPOSE

This study tested a prediction stemming from the hypothesis that anastrozole users experience heightened vitreo-retinal traction. This hypothesis was based on the knowledge that menopause increases the risk of intraocular tractional events such as posterior vitreous detachments (PVDs).

METHODS

Retinal thickness was measured for 3 groups of amenorrheic women: (1) anastrozole users and (2) tamoxifen users undergoing adjuvant therapy for early-stage breast cancer, and (3) control subjects not using hormonal medication. Foveal shape indices were derived for subjects without PVDs.

RESULTS

For anastrozole users, the distance to the temporal side of the fovea became less than the distance to the nasal side at a sufficient height above the foveal base. This effect did not exist for control subjects; the between-group difference was appreciable. Results concerning tamoxifen users were inconclusive.

CONCLUSIONS

The foveas of women using anastrozole appear to be subjected to more tractional force than are the foveas of women not using any hormonal medication.

Retinal nerve fiber layer measures in high- and normal-tension glaucoma

PURPOSE

To use optical coherence tomography (OCT) to investigate the qualitative and quantitative differences in the defects of the retinal nerve fiber layer (RNFL) in subjects with high tension primary open angle glaucoma and subjects with normal tension glaucoma.

METHODS

RNFL was assessed with OCT in 21 eyes with high-tension glaucoma (HTG) and 20 eyes with normal-tension glaucoma (NTG). Regression analyses were performed to investigate the interaction of disease group and location for localized RNFL loss, and to predict diffuse and localized RNFL loss as a function of age, mean defect, spherical equivalent, disease group, and location. Local RNFL thicknesses for superior clock-hour regions were estimated after adjustment for the thicknesses of symmetrically opposed locations.

RESULTS

There were no differences in mean age, visual field defect mean deviation, and refractive error between subjects in HTG and NTG groups. Diffuse RNFL thickness was not significantly different between the two groups [mean RNFL for NTG > HTG by 3.48 mum, 95% confidence interval (CI) -3.9 to 10.9 microm, p = 0.092]. There was no significant interaction of group and location for localized RNFL loss (p = 0.916). Local RNFL thickness at superior regions was not significantly different in the two groups, after adjustment for RNFL thickness at corresponding inferior locations (mean RNFL for NTG > HTG by 6.30 microm, 95% CI -1.08 to 13.7 microm, p = 0.34). RNFL thickness decreased, on average (1.88 microm/dB mean deviation, 95% CI 1.21 to 2.55 microm, p < 0.0001) and locally (1.37 microm/dB mean deviation, 95% CI 0.79 to 1.96 microm, p < 0.0001), with increasing severity of glaucoma.

CONCLUSION

There is no difference in the spatial pattern of RNFL defects, as assessed by the OCT, between HTG and NTG.

Clinical spectrum of lamellar macular defects including pseudoholes and pseudocysts defined by optical coherence tomography

OBJECTIVE

To present the clinical spectrum of lamellar macular defects and describe the different subtypes based on their optical coherence tomography (OCT) configuration and visual prognosis.

METHODS

The retrospective observational case series reviewed OCT scans of 92 eyes with lamellar macular defects. Lamellar macular defects were categorised into subtypes of macular pseudohole (MPH), lamellar macular hole (LMH) and foveal pseudocyst (FP) according to their OCT morphology. The defects were quantitatively characterised in terms of base diameter, depth and central foveal thickness, and examined for the presence of associated epiretinal membranes (ERM).

RESULTS

Visual acuity (VA) was significantly correlated with the central foveal thickness and depth of the lamellar defect. MPH was associated with better VA compared with LMH and FP. MPH was of a smaller base diameter and had a greater central foveal thickness than that of LMH and FP. Fifty-per cent of all lamellar defects had an associated ERM.

CONCLUSIONS

Different profiles of lamellar macular defects were characterised and quantified by OCT. Deeper and wider lamellar defects were associated with poorer visual outcome. Such objective parameters lamellar macular defects are of value when explaining to patients regarding their decreased acuity. Future prospective investigations are required to study the natural history of lamellar defects of different aetiology and surgical indications.

Visual impairment and postural sway among older adults with glaucoma

PURPOSE

To investigate the effect of visual impairment on postural sway among older adults with open-angle glaucoma.

METHODS

This study included 54 community-dwelling participants with open-angle glaucoma, aged 65 and older. Binocular visual field loss was estimated from merged monocular Humphrey Field Analyzer visual field results and retinal nerve fiber layer (RNFL) thickness was obtained from the Stratus Optical Coherence Tomographer. Postural sway was measured under four conditions: eyes open and closed, on a firm, and a foam surface. Data were collected for additional vision measures (visual acuity and contrast sensitivity), physical performance measures (self-reported physical activity levels and 6-min walk test), and demographic measures (age, gender, body mass index, and medical history). Multivariate linear regressions, adjusting for confounding factors, were performed to determine the association between visual loss and postural sway.

RESULTS

Participants with greater binocular visual field loss or thinner RNFL thickness showed increased postural sway, both on firm and foam surfaces, independent of age, gender, body mass index, and physical performance levels. These visual loss measures were significant predictors of postural sway, explaining almost 20% of its variance on the foam surface. Furthermore, participants with greater inferior hemifield visual field loss showed increased postural sway on the foam surface. Increasing glaucomatous visual impairment was accompanied by a steady decrease of the visual contribution to postural control.

CONCLUSION

Among older adults with glaucoma, greater visual field loss or thinner RNFL thickness is associated with reduced postural stability. This postural instability may be a contributing factor in the increased risk of falls among older adults with glaucoma.

Factors affecting perceptual thresholds in epiretinal prostheses

PURPOSE

The goal was to evaluate how perceptual thresholds are related to electrode impedance, electrode size, the distance of electrodes from the retinal surface, and retinal thickness in six subjects blind as a result of retinitis pigmentosa, who received epiretinal prostheses implanted monocularly as part of a U.S. Food and Drug Administration (FDA)-approved clinical trial.

METHODS

The implant consisted of an extraocular unit containing electronics for wireless data, power recovery, and generation of stimulus current, and an intraocular unit containing 16 platinum stimulating electrodes (260- or 520-microm diameter) arranged in a 4 x 4 pattern. The electrode array was held onto the retina by a small tack. Stimulation was controlled by a computer-based external system that allowed independent control over each electrode. Perceptual thresholds (the current necessary to see a percept on 79% of trials) and impedance were measured for each electrode on a biweekly basis. The distance of electrodes from the retinal surface and retinal thickness were measured by optical coherence tomography on a less regular basis.

RESULTS

Stimulation thresholds for detecting phosphenes correlated with the distance of the electrodes from the retinal surface, but not with electrode size, electrode impedance, or retinal thickness.

CONCLUSIONS

Maintaining close proximity between the electrode array and the retinal surface is critical in developing a successful retinal implant. With the development of chronic electrode arrays that are stable and flush on the retinal surface, it is likely that the influence of other factors such as electrode size, retinal degeneration, and subject age will become more apparent. (ClinicalTrials.gov number, NCT00279500.).

Imaging of the pediatric airway using optical coherence tomography

OBJECTIVES

Optical coherence tomography (OCT) is an imaging modality that uses a broadband light source to produce high-resolution cross-sectional images in living tissue (8-20 microm). A prospective study of normal, benign, and pathologic tissues in the pediatric airway was conducted to assess the utility of OCT technology in characterizing the microanatomy of the pediatric upper aerodigestive tract in vivo.

STUDY DESIGN

Prospective clinical trial.

MATERIALS AND METHODS

Fifteen patients from 1 to 17 years of age underwent surgical endoscopy and OCT for various airway disorders. OCT imaging was performed at a frame rate of 1 Hz using a 1.3-microm broadband light source to produce images 1.6 x 6 mm in vertical and horizontal dimensions. The epithelium, lamina propria, and unique tissue microstructures were visualized and then measured using digital micrometry. Direct comparison of OCT images with endoscopic photography was performed.

RESULTS

Systematic imaging of the oral cavity, oropharynx, hypopharynx, and larynx was performed in all 15 patients. Normal microstructures identified included papillae, ducts, glands, and vessels, whereas pathologic conditions included distinct zones of mature scar, granulation tissue, edema, ulceration, and papillomatosis. Endoscopic photographs were well correlated with OCT images.

CONCLUSIONS

OCT is capable of obtaining high-resolution microanatomy images of pediatric airway in vivo tissue. OCT clearly identifies the epithelium and lamina propria while providing detailed structural information on normal and diseased tissues. OCT is a promising emerging imaging modality for use in current pediatric patient populations.

Foveal photoreceptor layer in eyes with persistent cystoid macular edema associated with branch retinal vein occlusion

PURPOSE

To study the correlation of visual acuity and the foveal photoreceptor layer in eyes with persistent cystoid macular edema associated with branch retinal vein occlusion (BRVO).

DESIGN

Retrospective chart review.

METHODS

We studied retrospectively the medical records of 42 eyes of 42 patients with persistent cystoid macular edema secondary to BRVO, eyes in which the foveal thickness was greater than 250 microm at final examination. On the vertical image obtained by optical coherence tomography at the final examination, we measured thickness of the foveal photoreceptor layer that was beneath the foveal cystoid spaces. We also assessed status of the junction between inner and outer segments of the photoreceptors (IS/OS) in the fovea.

RESULTS

The photoreceptor layer beneath the foveal cystoid spaces was detected as a distinct layer with thickness varying between 33 microm and 124 microm (mean, 71.1 +/- 26.8 microm). Final visual acuity showed no correlation with total foveal thickness (r = 0.336, P = .092). However, it did show a close correlation with thickness of the foveal photoreceptor layer (r = -0.571, P < .0001). Of the 42 eyes, 15 showed a continuous IS/OS line in the fovea. Visual acuity in these eyes with a continuous IS/OS line in the fovea was significantly better than that in eyes with a discontinuous or interrupted IS/OS line (P < .0001).

CONCLUSIONS

Both the thickness and the integrity of the foveal photoreceptor layer are associated with visual function in eyes with persistent cystoid macular edema associated with BRVO.

Clinical applications and new developments of optical coherence tomography: an evidence-based review

Optical coherence tomography (OCT) is a new imaging modality that has increasingly become an indispensable tool in clinical practice for the diagnosis and management of ocular diseases involving the macula, optic nerve and anterior segment. The instrument is an advanced imaging technique that provides unprecedented high resolution and cross-sectional tomographic images of the ocular microstructure in situ, and in real time. Since its introduction about four years ago, a multitude of advantages has made OCT an essential instrument in ophthalmic imaging. The technique has fast image acquisition speed and non-contact, non-invasive applicability, allowing a non-excisional 'optical biopsy' to be performed. The purpose of this paper is to provide an evidence-based review of the increasing role of OCT in the diagnosis and management of ocular disorders, particularly in age-related macular degeneration, diabetic macular oedema, macular hole, epiretinal membrane and glaucoma. Being one of the first users of OCT in Australia, our clinical experiences will be highlighted and clinical examples of various conditions will be presented to provide an overview of the immense implications of OCT in practice. The latest developments of the OCT revolution, in relation to combining OCT with fundus photography and scanning laser ophthalmoscopy, will also be described. New developments of three-dimensional visualisation of tissue morphology with future models of ultra-high speed, ultra-high resolution OCT may further enhance the early diagnosis, monitoring of disease progression and assessment of treatment efficacy, facilitated by this powerful technology.

Spectral-domain optical coherence tomography with multiple B-scan averaging for enhanced imaging of retinal diseases

OBJECTIVE

To determine whether multiple B-scan averaging improves the quality of spectral-domain optical coherence tomography (SD OCT) images of the retina.

DESIGN

Prospective cross-sectional study.

PARTICIPANTS

One hundred one eyes of 84 patients with various retinal diseases.

METHODS

A prototype SD OCT system was used with a sensitivity of 98 decibels, air axial resolution of 6.1 mum, and acquisition rate of approximately 18 700 axial scans per second. To evaluate multiple B-scan averaging, a set of 12 B-scan images was obtained at the identical retinal location and the multiple scans were averaged using custom software; some images containing lateral eye motion were rejected. Objective differences in image quality were measured by comparing the contrast-to-noise ratios (CNRs) for key retinal structures in unenhanced and enhanced images using non-repeated-measures analysis of variance and the Dennett post hoc test. Subjective differences in image quality were evaluated by asking trained ophthalmologists independently to rank pairs of unenhanced and enhanced SD OCT images on a 5-point scale (upper or lower image definitely better, slightly better, or equal) and analyzing results using the Scheffe method for paired comparisons.

MAIN OUTCOME MEASURES

Contrast-to-noise ratio in enhanced versus unenhanced SD OCT images, expert comparison of image quality, and retinal pathologic features in enhanced versus unenhanced SD OCT images.

RESULTS

Averaging >4 SD OCT scans achieved significant improvement in CNR and also improved ophthalmologists' ability to distinguish retinal structures. More than 4 scans could be averaged for 100 (99%) of the 101 eyes with retinal diseases in this study. Averaging >4 SD OCT scans improved visualization of structures, such as abnormalities in the photoreceptor layer and sub-retinal pigment epithelium (RPE) lesions, that could not be identified clearly in single-scan SD OCT images because of various retinal pathologic features. These included intraretinal lesions that mask the underlying structures, such as cystoid macular edema and retinal hemorrhage, and inward shifting of the sensory retina because of pigment epithelial detachment and lesions beneath the RPE.

CONCLUSIONS

Multiple B-scan averaging is an easy and practical method to improve the quality of retinal images obtained by SD OCT and thereby to improve the diagnosis and management of retinal diseases.

A framework for comparing structural and functional measures of glaucomatous damage

While it is often said that structural damage due to glaucoma precedes functional damage, it is not always clear what this statement means. This review has two purposes: first, to show that a simple linear relationship describes the data relating a particular functional test (standard automated perimetry (SAP)) to a particular structural test (optical coherence tomography (OCT)); and, second, to propose a general framework for relating structural and functional damage, and for evaluating if one precedes the other. The specific functional and structural tests employed are described in Section 2. To compare SAP sensitivity loss to loss of the retinal nerve fiber layer (RNFL) requires a map that relates local field regions to local regions of the optic disc as described in Section 3. When RNFL thickness in the superior and inferior arcuate sectors of the disc are plotted against SAP sensitivity loss (dB units) in the corresponding arcuate regions of the visual field, RNFL thickness becomes asymptotic for sensitivity losses greater than about 10dB. These data are well described by a simple linear model presented in Section 4. The model assumes that the RNFL thickness measured with OCT has two components. One component is the axons of the retinal ganglion cells and the other, the residual, is everything else (e.g. glial cells, blood vessels). The axon portion is assumed to decrease in a linear fashion with losses in SAP sensitivity (in linear units); the residual portion is assumed to remain constant. Based upon severe SAP losses in anterior ischemic optic neuropathy (AION), the residual RNFL thickness in the arcuate regions is, on average, about one-third of the premorbid (normal) thickness of that region. The model also predicts that, to a first approximation, SAP sensitivity in control subjects does not depend upon RNFL thickness. The data (Section 6) are, in general, consistent with this prediction showing a very weak correlation between RNFL thickness and SAP sensitivity. In Section 7, the model is used to estimate the proportion of patients showing statistical abnormalities (worse than the 5th percentile) on the OCT RNFL test before they show abnormalities on the 24-2 SAP field test. Ignoring measurement error, the patients with a relatively thick RNFL, when healthy, will be more likely to show significant SAP sensitivity loss before statistically significant OCT RNFL loss, while the reverse will be true for those who start with an average or a relatively thin RNFL when healthy. Thus, it is important to understand the implications of the wide variation in RNFL thickness among control subjects. Section 8 describes two of the factors contributing to this variation, variations in the position of blood vessels and variations in the mapping of field regions to disc sectors. Finally, in Sections 7 and 9, the findings are related to the general debate in the literature about the relationship between structural and functional glaucomatous damage and a framework is proposed for understanding what is meant by the question, 'Does structural damage precede functional damage in glaucoma?' An emphasis is placed upon the need to distinguish between "statistical" and "relational" meanings of this question.

Modeling the effects of aging on retinal ganglion cell density and nerve fiber layer thickness

PURPOSE

The effects of aging on retinal nerve fiber layer (RNFL) thickness should reflect the age-related losses in retinal ganglion cells (RGCs), but published data suggest that the relative rate of thinning of RNFL thickness with age is less than predicted by age-related losses of RGCs. Therefore, the present study was undertaken to reconcile the differences in age-dependency on measures of RGCs and axons that are incorporated in normative clinical data.

METHODS

Normative data for RNFL thickness and visual field sensitivities were obtained from the printouts of standard optical coherence tomography (OCT) and standard automated perimetry (SAP) for patients aged between 25 and 95 years, in decade steps. These data were used in models to estimate the number of RGCs underlying each measure.

RESULTS

The age-related losses of RGCs derived from normative perimetry data agreed closely with published histologic data, without an age-dependent variable in the model. In contrast, the age-related losses of RGCs derived from normative total RNFL thickness data required an age-dependent decrease of 0.007 axons/microm(2)/year in axon density in the RNFL to account for the relatively slower rate of RNFL thinning than RGC loss.

CONCLUSIONS

The analysis of normative data suggests a model of age-related thinning of RNFL in which the relationship between RNFL thickness and the density of RGC axons varies with the number of neurons that are lost through normal aging. This model posits that the OCT measurement of total RNFL thickness of a normal retina represents two components: 1) an age-dependent population of RNFL axons, and 2) a non-neural component that partially compensates for the age-related decrease in axons in the nerve fiber layer.

Optical coherence tomography: a review of clinical development from bench to bedside

Since its introduction, optical coherence tomography (OCT) technology has advanced from the laboratory bench to the clinic and back again. Arising from the fields of low coherence interferometry and optical time- and frequency-domain reflectometry, OCT was initially demonstrated for retinal imaging and followed a unique path to commercialization for clinical use. Concurrently, significant technological advances were brought about from within the research community, including improved laser sources, beam delivery instruments, and detection schemes. While many of these technologies improved retinal imaging, they also allowed for the application of OCT to many new clinical areas. As a result, OCT has been clinically demonstrated in a diverse set of medical and surgical specialties, including gastroenterology, dermatology, cardiology, and oncology, among others. The lessons learned in the clinic are currently spurring a new set of advances in the laboratory that will again expand the clinical use of OCT by adding molecular sensitivity, improving image quality, and increasing acquisition speeds. This continuous cycle of laboratory development and clinical application has allowed the OCT technology to grow at a rapid rate and represents a unique model for the translation of biomedical optics to the patient bedside. This work presents a brief history of OCT development, reviews current clinical applications, discusses some clinical translation challenges, and reviews laboratory developments poised for future clinical application.

Thinking inside the graft: applications of optical coherence tomography in coronary artery bypass grafting

Recent advances in catheter-based optical coherence tomography (OCT) have provided the necessary resolution and acquisition speed for high-quality intravascular imaging. Complications associated with clearing blood from the vessel of a living patient have prevented its wider acceptance. We identify a surgical application that takes advantage of the vascular imaging powers of OCT but that circumvents the difficulties. Coronary artery bypass grafting (CABG) is the most commonly performed major surgery in America. A critical determinant of its outcome has been postulated to be injury to the conduit vessel incurred during the harvesting procedure or pathology preexistent in the harvested vessel. As a test of feasibility, intravascular OCT imaging is obtained from the radial arteries (RAs) and/or saphenous veins (SVs) of 35 patients scheduled for CABG. Pathologies detected by OCT are compared to registered histological sections obtained from discarded segments of each graft. OCT reliably detects atherosclerotic lesions in the RAs and discerns plaque morphology as fibrous, fibrocalcific, or fibroatheromatous. OCT is also used to assess intimal trauma and residual thrombi related to endoscopic harvest and the quality of the distal anastomosis. We demonstrate the feasibility of OCT imaging as an intraoperative tool to select conduit vessels for CABG.

Incorporation of regional information in optimal 3-D graph search with application for intraretinal layer segmentation of optical coherence tomography images

We present a method for the incorporation of regional image information in a 3-D graph-theoretic approach for optimal multiple surface segmentation. By transforming the multiple surface segmentation task into finding a minimum-cost closed set in a vertex-weighted graph, the optimal set of feasible surfaces with respect to an objective function can be found. In the past, this family of graph search applications only used objective functions which incorporated "on-surface" costs. Here, novel "in-region" costs are incorporated. Our new approach is applied to the segmentation of seven intraretinal layer surfaces of 24 3-D macular optical coherence tomography images from 12 subjects. Compared to an expert-defined independent standard, unsigned border positioning errors are comparable to the inter-observer variability (7.8 +/- 5.0 microm and 8.1 +/- 3.6 microm, respectively).

Analysis of posterior retinal layers in spectral optical coherence tomography images of the normal retina and retinal pathologies

We present a computationally efficient, semiautomated method for analysis of posterior retinal layers in three-dimensional (3-D) images obtained by spectral optical coherence tomography (SOCT). The method consists of two steps: segmentation of posterior retinal layers and analysis of their thickness and distance from an outer retinal contour (ORC), which is introduced to approximate the normal position of external interface of the healthy retinal pigment epithelium (RPE). The algorithm is shown to effectively segment posterior retina by classifying every pixel in the SOCT tomogram using the similarity of its surroundings to a reference set of model pixels from user-selected area(s). Operator intervention is required to assess the quality of segmentation. Thickness and distance maps from the segmented layers and their analysis are presented for healthy and pathological retinas.

Intravitreal bevacizumab (avastin) for central and hemicentral retinal vein occlusions: IBeVO study

PURPOSE

To evaluate the safety, visual acuity changes, and morphologic effects associated with intravitreal bevacizumab injections for the management of macular edema due to ischemic central or hemicentral retinal vein occlusion (RVO).

METHODS

In this prospective, open-label study, 7 consecutive patients (7 eyes) with macular edema associated with ischemic central or hemicentral RVO were treated with intravitreal injections of 2.0 mg (0.08 mL) of bevacizumab at 12-week intervals. Standardized ophthalmic evaluation was performed at baseline and at weeks 1, 6, and 12 after each injection. Clinical evidence of toxicity and complications as well as changes in logarithm of minimum angle of resolution Early Treatment Diabetic Retinopathy Study best-corrected visual acuity (BCVA), central macular thickness (CMT) and total macular volume (TMV) shown by optical coherence tomography (OCT), and dye leakage shown by fluorescein angiography were evaluated.

RESULTS

The median age of the 7 patients was 65 years (range, 58-74 years), and the median duration of symptoms before injection was 7 months (range, 2.5-16 months). At baseline, mean BCVA was 1.21 (Snellen equivalent, approximately 20/320) in the affected eye. Mean baseline CMT and TMV were 730.1 microm and 17.1 mm(3), respectively. Fluorescein leakage was observed in the macula and affected retinal quadrants in all seven eyes. Six patients completed the 25-week follow-up examination with reinjections performed at weeks 12 and 24. The most common adverse events were conjunctival hyperemia and subconjunctival hemorrhage at the injection site. At the last follow-up, mean BCVA in the affected eye was 0.68 (Snellen equivalent, 20/100(+1). No patient had a decrease in BCVA. Mean CMT and TMV at the 25-week follow-up were 260.3 microm and 9.0 mm(3), respectively; fluorescein leakage within the macula and affected retinal quadrants as compared with baseline was markedly reduced in all patients. Coupled with fluorescein angiographic findings, OCT data suggest a trend of macular edema recurrence between 6 weeks and 12 weeks after injection.

CONCLUSIONS

Intravitreal bevacizumab injections of 2.0 mg at 12-week intervals were well tolerated and were associated with short-term BCVA stabilization or improvement and favorable macular changes in all patients with ischemic RVO and associated macular edema.

Retinal imaging by spectral optical coherence tomography

PURPOSE

To demonstrate applicability of high speed spectral optical coherence tomography (SOCT) method for imaging retinal pathologies in clinical conditions.

METHODS

SOCT was performed in 67 eyes with different macular diseases. Examinations were carried out with the prototype SOCT instrument constructed in the Institute of Physics, Nicolaus Copernicus University, Toruń, Poland. A broadband superluminescent diode was used as a light source.

RESULTS

The disturbances of retinal layer structure concerning mainly outer segments of photoreceptors were observed in case of central serous chorioretinopathy and choroidal neovascularization in age-related macular degeneration. Large drusen were often related to significant changes of outer nuclear layer thickness and reflectivity.

CONCLUSIONS

SOCT detects small disturbances of the retinal structure and helps to precisely determine layers involved in different pathologies.

Optical Coherence Tomography for Artwork Diagnostics

An overview of the optical coherence tomography (OCT) technique is given. Time domain, spectral and sweep source modalities are briefly described, and important physical parameters of the OCT instrument are discussed. Examples of the application of OCT to diagnosis of various art objects such as oil paintings on canvas (imaging of glaze and varnish layers), porcelain, faience, and parchment are presented. Applications to surface profilometry of painting on canvas are also discussed.