Optical coherence tomography: limits of the retinal-mapping program in age-related macular degeneration

Fibrosis in neovascular age-related macular degeneration: A review of definitions based on clinical imaging

Despite the success of antiangiogenic therapy in controlling exudation in neovascular age-related macular degeneration (nAMD), the involvement of the outer retina in fibrosis results in gradual vision loss over time. The development of drugs that prevent or ameliorate fibrosis in nAMD requires that it is accurately detected and quantified with reliable endpoints and identification of robust biomarkers. Achievement of such an aim is currently challenging due to the lack of a consensus definition of fibrosis in nAMD. As a first step towards the establishment of a clear definition of fibrosis, we provide an extensive overview of the imaging modalities and criteria used to characterize fibrosis in nAMD. We observed variety in the selection of individual and combinations of imaging modalities, and criteria for detection. We also observed heterogeneity in classification systems and severity scales for fibrosis. The most commonly used imaging modalities were color fundus photography, fluorescein angiography and optical coherence tomography (OCT). A multimodal approach was frequently utilized. Our review suggests that OCT offers a more detailed, objective and sensitive characterization than color fundus photography/fluorescein angiography. Thus, we recommend it as a primary modality for fibrosis evaluation. This review provides a basis for future discussions to reach a consensus definition using standardized terms based on a detailed characterization of fibrosis, its presence and evolution, and taking into consideration impact on visual function. Achieving this goal is of paramount importance for the development of antifibrotic therapies.

Macular Hole Detection Using a New Hybrid Method: Using Multilevel Thresholding and Derivation on Optical Coherence Tomographic Images

Optical coherence tomography (OCT) is a noninvasive imaging test. OCT imaging is analogous to ultrasound imaging, except that it uses light instead of sound. In this type of image, microscopic quality intratissue images are provided. In addition, fast and direct imaging of tissue morphology and reproducibility of results are the advantages of this imaging. Macular holes are a common eye disease that leads to visual impairment. The macular perforation is a rupture in the central part of the retina that, if left untreated, can lead to vision loss. A novel method for detecting macular holes using OCT images based on multilevel thresholding and derivation is proposed in this paper. This is a multistep method, which consists of segmentation, feature extraction, and feature selection. A combination of thresholding and derivation is used to diagnose the macular hole. After feature extraction, the features with useful information are selected and finally the output image of the macular hole is obtained. An open-access data set of 200 images with the size of 224 × 224 pixels from Sankara Nethralaya (SN) Eye Hospital, Chennai, India, is used in the experiments. Experimental results show better-diagnosing results than some recent diagnosing methods.

Effect of grid decentration on macular thickness measurements in normal subjects and patients with diabetic macular edema

PURPOSE

To evaluate the effect of optical coherence tomography (OCT) grid decentration on macular thickness measurements in healthy subjects and patients with diabetic macular edema.

METHODS

In this prospective study, 3D spectral-domain OCT images of 51 eyes with clinically significant diabetic macular edema and 29 healthy eyes were assessed. In each eye, the macular Early Treatment Diabetic Retinopathy Study grid was evaluated for decentration. After grid adjustment, changes in central subfield thickness (CST) and central subfield volume (CSV) measurements were recorded. Changes >1 μm and >8.5 μm in CST were considered as grid decentration and clinically significant grid decentration, respectively.

RESULTS

Grid decentration was found in 10 normal eyes (34.6%) and 32 clinically significant macular edema (CSME) eyes (62.7%, p = 0.01). Clinically significant CST changes were found in 3 normal eyes (10.3%) and 23 CSME eyes (45%, p = 0.001). The mean change in CST after grid adjustment was 6.4 ± 5.8 µm and 24.7 ± 27 µm in normal and CSME eyes (p = 0.04). Age, sex, and CST had no statistically significant effect on grid decentration in normal and CSME eyes. Best-corrected visual acuity was significantly worse in eyes with grid decentration (0.75 ± 0.55 vs 0.42 ± 0.22 logMAR, p = 0.02) and clinically significant grid decentration (0.81 ± 0.6 vs 0.45 ± 0.27 logMAR, p = 0.01). Change in CSV was detected in 3 normal eyes (10.3%) and 24 CSME eyes (47%, p = 0.001).

CONCLUSIONS

Grid decentration occurs in a large number of OCT thickness maps and leads to significant error in macular thickness measurements. The effect is more prominent in patients with CSME.

Repeatability of retinal thickness and volume metrics in neovascular age-related macular degeneration using the Topcon 3DOCT-1000

Introduction:

Optical coherence tomography (OCT) is a commonly used imaging modality that provides detailed cross-sectional retinal images. This has revolutionised management of neovascular age-related macular degeneration. The need for repeated anti-vascular endothelial growth factor injections has led to therapy being delivered using OCT-guided retreatment strategies with both qualitative OCT features of disease activity (e.g. macular fluid) and changes in retinal thickness as triggers for retreatment The purpose of this study is to determine the intra-session repeatability of retinal thickness and volume measurements using the Topcon 3DOCT-1000 spectral-domain optical coherence tomography (SDOCT) device in patients with neovascular age-related macular degeneration (nAMD). This is the largest study to date looking specifically at the Topcon 3DOCT-1000.

Materials and Methods:

Two SDOCT raster scans were performed by the same blinded observer in the same sitting in consecutive patients attending for nAMD treatment as part of standard validation of a new device. Retrospective analysis was undertaken, with retinal thickness and volume measurements automatically calculated by the onboard software for each Early Treatment of Diabetic Retinopathy Study subfield for each scan. Bland-Altman methods of analysis were used to assess repeatability.

Results:

Data from the 73 patients were analyzed with a mean age of 78 years (standard deviation 8). The 95% coefficient of repeatability (CR) was 64 μm and 0.050 mm³ for retinal thickness and volume respectively in the central 1 mm macular subfield. The CR did not exceed 85 μm (0.30 mm³) in any subfield. The revised CR for retinal thickness and volume for the subgroup of 37 patients with no segmentation error in the central 1 mm subfield was 53 μm and 0.050 mm³ respectively.

Discussion:

We report relatively modest intra-sessional repeatability of SDOCT retinal thickness and volume metrics in patients with nAMD in a clinical setting. Though useful in detecting clinical change from measurement variability in clinical practice, these results suggest the precision of macular thickness measurement does not approach the theoretical resolution of SDOCT.

Cystoid macular edema: a correlation between macular volumetric parameters and visual acuity

OBJECTIVE

To study in patients with cystoid macular edema (CME) the correlation between macular volumetric parameters on ocular coherence tomography (OCT) and visual acuity (VA).

DESIGN

A retrospective consecutive cohort design was used.

PARTICIPANTS

The sample included 167 examinations of 92 consecutive patients (130 eyes).

METHODS

Patients underwent spectral-domain OCT for CME from the years 2008 to 2010 at a tertiary medical centre. Background and VA data were recorded from the files. The custom-developed Cystometer software was used to calculate volumetric parameters from the OCT videos.

RESULTS

In univariate analyses, VA correlated best with cystoid macular volume (CMVol; R(2) = 8.57) and total macular volume (TMV; R(2) = 7.46). By underlying disease, the strongest correlation was found with CMVol (R(2) = 8.47) in patients with diabetic CME (n = 91) and with TMV (R(2) = 22.18) in patients with branch retinal vein occlusion (n = 46). In multiple regression analyses, TMV, age, and CMVol/TMV accounted for 17.57% of the variation in VA. In the diabetic CME group, CMVol/TMV and age accounted for 15.34% of the variation; in the branch retinal vein occlusion group, TMV accounted for 22.18% of the variation.

CONCLUSIONS

Macular volumetric parameters measured by OCT and Cystometer software significantly correlate with VA in patients with CME, with variations by underlying CME causative factor.

Reliability and reproducibility of spectral and time domain optical coherence tomography images before and after correction for patients with age-related macular degeneration

Purpose: To evaluate the reproducibility and reliability of optical coherence tomography scans obtained using the time domain (TD-OCT) Stratus ^TM OCT, and the Spectral Domain (SD-OCT) Spectralis ^TM and Cirrus ^TM OCT devices before and after manual correction in eyes with either Neovascular (NV-AMD) or Non-Neovascular (NNV-AMD) age-related macular degeneration.

Design: Prospective observational study.

Methods:

Setting: University-based retina practice.

Patients: Thirty-six patients (50 eyes) with NV-AMD or NNV-AMD.

Procedure: OCT scans were taken simultaneously using one TD-OCT and two SD-OCT devices.

Main Outcome Measures: Macular thickness measurements were assessed before and after correction of the algorithm by constructing Bland-Altman plots for agreement and calculating intraclass correlation coefficients (ICCs) and coefficients of repeatability (COR) to evaluate intraclass repeatability.

Results: Spectralis had the highest number of images needing manual correction.  All machines had high ICCs, with Spectralis having the highest.  Also, Bland-Altman plots indicated that there was low agreement between Cirrus™ and Stratus™, Spectralis™ and Stratus™, while there was good agreement between the Cirrus™ and Spectralis™.  The CORs were lowest for Spectralis ^TM and similar and higher for Cirrus ^TM and Stratus ^TM.  Agreement, CORs, and ICCs generally improved after manual correction, but only minimally. 

Conclusion: Agreement is low between devices, except between both SD-OCT machines.  Manual correction tends to improve results.

Is quantitative spectral-domain superior to time-domain optical coherence tomography (OCT) in eyes with age-related macular degeneration?

PURPOSE

The aim of this study was to determine the variability of macular map measurements, for two generations of optical coherence tomography (OCT) instruments, in eyes with wet age related macular degeneration (AMD) and low visual acuity.

METHODS

Patients were examined with Stratus OCT and Cirrus HD-OCT. The macular thickness was assessed with the 'macular thickness map scan' and 'fast protocol' in Stratus and with the 512 × 128 and 200 × 200 cube protocols in Cirrus OCT. Two measurements were taken one directly after the other, at the first visit to analyse repeatability. Approximately 1 week later, a third measurement was taken to analyse reproducibility. In Cirrus OCT, a manual correction of foveal location was also performed. Repeatability and reproducibility were calculated as a coefficient of variance (CoV) and a coefficient of repeatability/reproducibility.

RESULTS

 Repeatability for central macular thickness (expressed as CoV) was about three per cent for all protocols, and the coefficient of repeatability between 34 and 54 μm. Reproducibility (also expressed as CoV) was between four to seven per cent and coefficient of repeatability between 64 and 89 μm. After manual adjustment of foveal location in Cirrus OCT, the coefficient of repeatability improved to 12-18 μm, and the coefficient of reproducibility to 44-47 μm.

CONCLUSIONS

  In eyes affected by wet AMD, there were small differences in repeatability and reproducibility when comparing quantitative maps in Stratus and Cirrus OCT. However, when the software for manual correction of foveal position in Cirrus OCT was used, the variability decreased markedly, and the repeatability was close to what had been reported in normal eyes, demonstrating a significant, potential advantage of spectral-domain over time-domain OCT.

The role of spectral-domain OCT in the diagnosis and management of neovascular age-related macular degeneration

Spectral-domain optical coherence tomography (SD-OCT) has emerged as the ancillary examination of choice to assist the diagnosis and management of neovascular age-related macular degeneration (AMD). SD-OCT provides more detailed images of intraretinal, subretinal, and subretinal pigment epithelium fluid when compared to time-domain technology, leading to higher and earlier detection rates of neovascular AMD activity. Improvements in image analysis and acquisition speed make it important for decision-making in the diagnosis and treatment of this disease. However, this new technology needs to be validated for its role in the improvement of visual outcomes in the context of anti-angiogenic therapy.

Reproducibility of macular thickness measurement among five OCT instruments: effects of image resolution, image registration, and eye tracking

BACKGROUND AND OBJECTIVE

To study the effect of image resolution, eye tracking, and image registration on central macular thickness reproducibility (rCMT) among spectral-domain and time-domain optical coherence tomography (SD-OCT and TD-OCT) instruments.

PATIENTS AND METHODS

Seventy-six eyes were imaged (44 normal, 32 maculopathy) either twice using four SD-OCT and one TD-OCT devices or three times using Spectralis SD-OCT (with and without eye tracking) (Heidelberg Engineering, Inc., Heidelberg, Germany). Cirrus images (Carl Zeiss Meditec, Dublin, CA) were further analyzed with three-point image registration.

RESULTS

All instruments had superior rCMT in normal versus pathologic eyes (P < .001). No difference in rCMT was noted among instruments in normal eyes (P = .92), but TD-OCT was superior to SD-OCT (P = .017) in pathologic eyes. Cirrus image registration improved rCMT for normal eyes (P = .04), with borderline improvement in pathologic eyes (P = .06). Spectralis eye tracking improved rCMT in normal (P = .01) and pathologic (P = .004) eyes.

CONCLUSION

Higher image resolution with SD-OCT may not improve rCMT, but image registration and eye tracking options may improve rCMT.

Transitioning from stratus OCT to cirrus OCT: a comparison and a proposed equation to convert central subfield macular thickness measurements in healthy subjects

BACKGROUND

The purpose of this paper is to study the differences between central subfield macular thickness (CSMT) measurements obtained by time-domain Stratus optical coherence tomography (OCT) and Cirrus spectral domain OCT (Carl Zeiss Meditec, Dublin, CA) and to formulate an equation to convert CSMT values from one to the other.

METHODS

CSMT were measured by both Stratus Macula OCT and Cirrus Macula OCT in 46 healthy subjects. Agreement between measurements was calculated using Lin's concordance coefficient.

RESULTS

The average age of our group was 30 with the logMAR visual acuity of -0.015. The Stratus CSMT measurement (mean ± standard deviation) 193.91 ± 21.7 was statistically significant from the Cirrus CSMT measurement 252.82 ± 28.4 (p < 0.001). The transformation equation 0.76×-0.51 from Cirrus to Stratus resulted in values that best agreed with the observed Stratus OCT values.

CONCLUSIONS

We identified a significant difference of CSMT measurements between Stratus and Cirrus. The Cirrus typically gave a higher value of CSMT. We derived a linear equation to convert the measurements from Cirrus to Stratus which resulted in transformed values that concord with the observed Stratus OCT values.