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

Comparison between two multimodal imaging platforms: Nidek Mirante and Heidelberg Spectralis

PURPOSE

To investigate the reliability and comparability of retinal measurements obtained with spectral-domain optical coherence tomography (OCT), optical coherence tomography angiography (OCTA), confocal scanning laser ophthalmoscopy (cSLO) colour images, and fundus autofluorescence (FAF) between two multimodal imaging platforms in eyes with macular pathology and normal, healthy volunteers.

METHODS

This cross-sectional, multi-centre, instrument validation study recruited 94 consecutive subjects. All participants underwent a dilated examination and were scanned consecutively on the Heidelberg Spectralis (Heidelberg Engineering, Heidelberg, Germany) and Nidek Mirante (Nidek Co. Ltd., Gamagori, Japan) devices. Agreement between device images were evaluated from measures of the central retinal thickness (CRT), presence of segmentation and fixation imaging artefacts (IA), foveal avascular zone (FAZ) measurements; as well as sensitivity and specificity values from the detection of atrophy on fundus autofluorescence (FAF), drusen, subretinal drusenoid deposits, geographic atrophy, epiretinal membrane, fibrosis and haemorrhage on multicolour imaging, and agreement between devices and groups.

RESULTS

Compared with reference clinical examination, sensitivity values for the identification of retinal features using sole device images ranged from 100% for epiretinal membranes to 66.7% for subretinal drusenoid deposits (SSD). Mean absolute difference for CRT between OCT devices was 3.78 μm (95% confidence interval [CI]: - 21.39 to 28.95, P = 0.809). Differences in the superficial and deep capillary plexus FAZ area on OCTA between devices were not statistically significant (P = 0.881 and P = 0.595, respectively). IAs were significantly increased in the presence of macular pathology.

CONCLUSION

Comparison of retinal measurements between the OCT devices did not differ significantly. Common ultrastructural biomarkers of multiple macular pathologies were identified with high sensitivities and specificities, with good agreement between graders, indicating that they can be identified with comparable confidence in retinal imaging between the two devices.

TWELVE-MONTH EFFICACY OF INTRAVITREAL BEVACIZUMAB INJECTION FOR CHRONIC, ATYPICAL, OR RECURRENT CENTRAL SEROUS CHORIORETINOPATHY

PURPOSE

To evaluate intravitreal bevacizumab (IVB) injection efficacy for the treatment of chronic, atypical, or recurrent central serous chorioretinopathy (CSC).

METHODS

Clinical data from 77 eyes of 71 patients with chronic, atypical, or recurrent CSC treated with IVB were retrospectively analyzed. After initial 6-weekly IVB administration until no subretinal fluid remained at the fovea, additional as-needed IVBs were administered, based on optical coherence tomography findings. Best-corrected visual acuity and central retinal thickness (CRT) were analyzed at baseline and 3, 6, 9, and 12 months after initial IVB.

RESULTS

The significant improvement of baseline logarithm of minimum angle of resolution best-corrected visual acuity and CRT at 3 months (both P < 0.001) was maintained throughout the 12-month follow-up period. Best-corrected visual acuity improved significantly in patients with chronic and recurrent CSC, at all time points (all P < 0.05), but not in patients with atypical CSC. The CRT reduction was significant in all subgroups during the follow-up period (all P < 0.05). Definite leakage on initial fluorescein angiography correlated with improved reduction in CRT (P = 0.039).

CONCLUSION

As-needed optical coherence tomography-based IVB was effective for reducing CRT in patients with chronic, atypical, or recurrent CSC, and for vision improvement in chronic and recurrent CSC over the 1-year follow-up period.

Foveal Abnormality associated with epiretinal Tissue of medium reflectivity and Increased blue-light fundus Autofluorescence Signal (FATIAS)

PURPOSE

To describe a distinct vitreomacular interface disorder (VMID) termed Foveal Abnormality associated with epiretinal Tissue of medium reflectivity and Increased blue-light fundus Autofluorescence Signal (FATIAS).

METHODS

A case series including forty-seven eyes of 47 patients. The included eyes must present an irregular foveal contour on optical coherence tomography (OCT) and a pathologically increased autofluorescent signal at the fovea on blue-light fundus autofluorescence (B-FAF). Main outcome measures were morphologic characteristics of the lesions, logarithm of minimum angle of resolution (logMAR) best-corrected visual acuity (BCVA), and central foveal thickness (CFT).

RESULTS

The following two types of FATIAS were identified: (1) the step type characterized by an asymmetric contour of the foveal pit and by a tissue of medium reflectivity on the foveal surface and (2) the rail type characterized by a shallow foveal pit and a rail of tissue of medium reflectivity on the foveal surface. The outer retinal bands were continuous in all cases. Both types presented with an area of increased B-FAF signal, usually bilobed in the step type and round and centered on the foveal pit in the rail type. LogMAR BCVA was 0.09 ± 0.1 and 0.1 ± 0.1 (P = 0.91), and CFT was 197.8 ± 9.7 and 202.2 ± 13.2 (P = 0.19) in the step and in the rail group, respectively.

CONCLUSIONS

We describe a distinct VMID named FATIAS. Two types of FATIAS may be appreciated with SD-OCT and B-FAF analyses, the step and the rail type. Both are characterized by abnormal foveal contour and autofluorescence signal.

Variability in the ocular phenotype in mucopolysaccharidosis

PURPOSE

Mucopolysaccharidoses (MPSs) are a heterogeneous group of lysosomal storage disorders. Ocular complications (such as corneal clouding, retinopathy and optic neuropathy) are common. Notably, there is a paucity of data on the effect of genotype and systemic treatments (enzyme replacement therapy or haematopoietic stem cell transplantation) on the ocular phenotype in MPS. We prospectively studied the ocular features of patients with MPSI (Hurler/Hurler-Scheie/Scheie), MPSIV (Morquio) and MPSVI (Maroteaux-Lamy), to evaluate the effect of different therapeutic interventions and to correlate the findings with genetic and biomarker data.

METHODS

Prospective observational cohort study. Study participants underwent detailed ocular examination including visual acuity; assessment of corneal clouding (Iris camera Corneal Opacification Measure score and Pentacam densitometry) and retinal and optic nerve imaging (optical coherence tomography and wide-field fundus imaging). Data on genotype, biomarkers and delivered therapies (type and length of treatment) were also collected for each patient where available.

RESULTS

Overall, 21 patients with MPSI, 4 patients with MPSIV and 3 patients with MPSVI were recruited. Corneal clouding scores were higher in MPSI compared with MPSIV and MPSVI. Retinopathy was evident in patients with MPSI only. Association was observed between corneal clouding and biomarkers in MPSI, MPSIV and MPSVI. However, no clear association was seen between genotype or treatment type and ocular phenotype.

CONCLUSIONS

The ocular phenotype in MPS is variable, with corneal clouding occurring in MPSI, MPSIV and MPSVI, and retinopathy in MPSI only. There was an association between corneal clouding and efficacy of systemic treatment as measured by biomarkers.

Foveal avascular zone area and parafoveal vessel density measurements in different stages of diabetic retinopathy by optical coherence tomography angiography

AIM

To investigate foveal avascular zone (FAZ) and parafoveal vessel densities (PRVD) by means of optical coherence tomography angiography (OCTA) in diabetic patients with or without diabetic retinopathy (DR) and to assess the reproducibility of FAZ and PRVD measurements.

METHODS

Sixty diabetic patients (60 eyes) with different stage of DR (graded according to the International Clinical Severity Scale for DR) and 20 healthy subjects underwent FAZ area and PRVD measurements using OCTA by two experienced examiners. FAZ area in all patients was also assessed using fluorescein angiography (FA).

RESULTS

In subject with proliferative DR and with moderate-severe non proliferative DR, FAZ area was significantly increased compared to healthy controls (P=0.025 and P=0.050 respectively measured with OCTA and P=0.025 and P=0.048 respectively measured with FA). OCTA showed significantly less inter-observer variability compared to FA. Concordance correlation coefficient (CCC) for FAZ area measurements was 0.829 (95%CI: 0.736-0.891) P<0.001 with FA and 1.000 (95%CI: 0.999-1.000) P<0.001 with OCTA. CCC was 0.834 (95%CI: 0.746-0.893) P<0.001 and 0.890 (95%CI: 0.828-0.930) P<0.001 for parafoveal superficial and deep vessel density measurements, respectively.

CONCLUSION

OCTA shows progressive increase of FAZ area and reduction of PRVD in both superficial and deep plexus at increasing DR severity. FAZ area and PRVD measurements using OCTA are highly reproducible.

Comparability of retinal thickness measurements using different scanning protocols on spectral-domain optical coherence tomography

Retinal thickness measurements obtained using optical coherence tomography (OCT) play an essential role both in multi-center clinical trials and in normal clinical practice. Different scanning protocols are available on most OCT devices, and it is important to ascertain whether the retinal thickness measurements obtained from these are comparable. This study aimed to compare retinal thickness measurements between raster and radial scanning protocols using spectral-domain OCT (SD-OCT). In a prospective study, 32 healthy subjects were scanned sequentially using raster and radial protocols from a SD-OCT device. For both the raster and radial OCT scans, retinal thicknesses were measured manually subfoveally and at 12 other points at 0.5 mm intervals temporally and nasally on the horizontal OCT B-scan passing through the fovea. The retinal thickness measurements were compared using intraclass correlation (ICC) and Bland-Altman plots. Subfoveal retinal thickness was 227.0 µm when measured on the raster scan and 229.2 µm on the radial scan, with a mean difference of 2.2 µm (P = 0.141).The ICC for agreement was 0.889 (95 % confidence interval 0.818-0.933). Similar results were observed for retinal thickness measurements at all other points, with mean differences ranging from -3.37 to 2.59 µm, and ICC values ranging from 0.837 to 0.972. The retinal thickness measurements obtained by the raster and radial scans of the same SD-OCT device are comparable, with differences of less than 4 µm. This is of relevance when measurements made using different OCT scan protocols are compared.

Repeatability of Foveal Measurements Using Spectralis Optical Coherence Tomography Segmentation Software

Purpose

To investigate repeatability and reproducibility of thickness of eight individual retinal layers at axial and lateral foveal locations, as well as foveal width, measured from Spectralis spectral domain optical coherence tomography (SD-OCT) scans using newly available retinal layer segmentation software.

Methods

High-resolution SD-OCT scans were acquired for 40 eyes of 40 young healthy volunteers. Two scans were obtained in a single visit for each participant. Using new Spectralis segmentation software, two investigators independently obtained thickness of each of eight individual retinal layers at 0°, 2° and 5° eccentricities nasal and temporal to foveal centre, as well as foveal width measurements. Bland-Altman Coefficient of Repeatability (CoR) was calculated for inter-investigator and inter-scan agreement of all retinal measurements. Spearman's ρ indicated correlation of manually located central retinal thickness (RT₀) with automated minimum foveal thickness (MFT) measurements. In addition, we investigated nasal-temporal symmetry of individual retinal layer thickness within the foveal pit.

Results

Inter-scan CoR values ranged from 3.1μm for axial retinal nerve fibre layer thickness to 15.0μm for the ganglion cell layer at 5° eccentricity. Mean foveal width was 2550μm ± 322μm with a CoR of 13μm for inter-investigator and 40μm for inter-scan agreement. Correlation of RT₀ and MFT was very good (ρ = 0.97, P < 0.0005). There were no significant differences in thickness of any individual retinal layers at 2° nasal compared to temporal to fovea (P > 0.05); however this symmetry could not be found at 5° eccentricity.

Conclusions

We demonstrate excellent repeatability and reproducibility of each of eight individual retinal layer thickness measurements within the fovea as well as foveal width using Spectralis SD-OCT segmentation software in a young, healthy cohort. Thickness of all individual retinal layers were symmetrical at 2°, but not at 5° eccentricity away from the fovea.

The effects of ocular magnification on Spectralis spectral domain optical coherence tomography scan length

PURPOSE

The purpose of this study was to assess the effects of incorporating individual ocular biometry measures of corneal curvature, refractive error, and axial length on scan length obtained using Spectralis spectral domain optical coherence tomography (SD-OCT).

METHODS

Two SD-OCT scans were acquired for 50 eyes of 50 healthy participants, first using the Spectralis default keratometry (K) setting followed by incorporating individual mean-K values. Resulting scan lengths were compared to predicted scan lengths produced by image simulation software, based on individual ocular biometry measures including axial length.

RESULTS

Axial length varied from 21.41 to 29.04 mm. Spectralis SD-OCT scan lengths obtained with default-K ranged from 5.7 to 7.3 mm, and with mean-K from 5.6 to 7.6 mm. We report a stronger correlation of simulated scan lengths incorporating the subject's mean-K value (ρ = 0.926, P < 0.0005) compared to Spectralis default settings (ρ = 0.663, P < 0.0005).

CONCLUSIONS

Ocular magnification appears to be better accounted for when individual mean-K values are incorporated into Spectralis SD-OCT scan acquisition versus using the device's default-K setting. This must be considered when taking area measurements and lateral measurements parallel to the retinal surface.

Evaluation of Central Macular Thickness and Retinal Nerve Fiber Layer Thickness using Spectral Domain Optical Coherence Tomography in a Tertiary Care Hospital

Purpose: To evaluate the normative data of macular thickness and retinal nerve fiber layer thickness (RNFL) among normal subjects using spectral domain optical coherence tomography (OCT).

Materials and methods: Normal subjects presenting to a tertiary medical hospital were included in the study. All patient underwent clinical examination followed by study of macular thickness and RN FL thick ness by spectral domain Topc on OCT. The data was collected and analyzed for variations in gender and age. The data was also compared with available literature.

Results: Total numbers of patients enrolled in the study were 154 (308 eyes). Numbers of males were 79 (158 eyes) and numbers of females were 75 (150 eyes). The mean age among males was 42.67 ± 12.15 years and mean age among females was 42.88 ± 11.73 years.

Overall the mean mac ular thickness (central 1 mm zone) with SD - OCT was 241.75 ± 17.3 microns. The mean macular volume was 7.6 cu. mm ± 0.33. On analysis of the RNFL thickness, we observed that the RNFL was thickest in the inferior quadrant (138.58) followed by superior (122.30) nasal (116.32) and temporal quadrant (73.04).

Gender-wise comparison of the data revealed no statistically significant difference for age, macular thickness parameters, volume and RFNL values except outer temporal thickness among males and females. No age-related difference was noted in the above parameters. On comparison with available norma tive data from India and elsewhere, we found significant variations with different machines.

Conclusion: The study is the first to provide normative data using SD-OCT from central India. The data from spectral domain OCT correlated well with the values obtained from similar studies with SD - OCT. Values obtained from time domain OCT machines are different and are not comparable.

How to cite this article: Agarwal P, Saini VK, Gupta S, Sharma A. Evaluation of Central Macular Thickness and Retinal Nerve Fiber Layer Thickness using Spectral Domain Optical

Coherence Tomography in a Tertiary Care Hospital. J Curr Glaucoma Pract 2014;8(2):75-81.

Spectral- and time-domain optical coherence tomography measurements of macular thickness in normal eyes and in eyes with diabetic macular edema

PURPOSE

To report macular thickness values in normal eyes and eyes with diabetic macular edema (DME) using time-domain (TD) and spectral-domain (SD) optical coherence tomography (OCT), and to derive a conversion equation.

METHODS

The index study was a prospective investigation conducted on 80 eyes from 40 normal subjects and 130 eyes from 118 patients with DME seen in our clinic. Retinal thickness values from the central 1 mm of the macula and surrounding four ETDRS subfields were acquired using TD-OCT (Stratus OCT) and SD-OCT (SPECTRALIS HRA+OCT). Measurements of the central (C) subfield from both devices were used to derive a conversion equation. The equation was used to predict SD-OCT values using measurements from TD-OCT. Agreement between predicted and actual SD-OCT measurements was assessed.

RESULTS

In normal eyes, the mean difference between TD-OCT and SD-OCT measurements of the C subfield was 76 μm (CI(95)=74 and 77, respectively). The conversion equation, y=1.029x+72.49, was derived. In eyes with DME, using the equation, SPECTRALIS-predicted values were 5% higher than actual measurements, with 95% of predicted values falling within 9% of the actual measurements. Relocating SD-OCT grids to match the location on TD-OCT resulted in predicted values falling within 7% of actual measurements.

CONCLUSIONS

The percent difference between actual thickness measurements from SPECTRALIS and predicted thickness measurements, using the conversion equation, was within reported limits of repeatability of Stratus in eyes with DME. Our equation may help correlate OCT values from both devices in standard care and clinical trials for DME.

The functional significance of foveal abnormalities in albinism measured using spectral-domain optical coherence tomography

PURPOSE

The relationship between foveal abnormalities in albinism and best-corrected visual acuity (BCVA) is unclear. High-resolution spectral-domain optical coherence tomography (SD OCT) was used to quantify foveal retinal layer thicknesses and to assess the functional significance of foveal morphologic features in patients with albinism.

DESIGN

Cross-sectional study.

PARTICIPANTS

Forty-seven patients with albinism and 20 healthy control volunteers were recruited to the study.

METHODS

Using high-resolution SD OCT, 7×7×2-mm volumetric scans of the fovea were acquired (3-μm axial resolution). The B scan nearest the center of the fovea was identified using signs of foveal development. The thickness of each retinal layer at the fovea and foveal pit depth were quantified manually using ImageJ software and were compared with BCVA.

MAIN OUTCOME MEASURES

Total retinal thickness, foveal pit depth, photoreceptor layer thickness, and processing layer thickness in relation to BCVA.

RESULTS

Total photoreceptor layer thickness at the fovea was correlated highly to BCVA (P = 0.0008; r = -0.501). Of the photoreceptor layers, the outer segment length was correlated most strongly to BCVA (P<0.0001; r = -0.641). In contrast, there was no significant correlation between either total retinal thickness or pit depth and BCVA (P>0.05). This was because of an inverse correlation between total photoreceptor layer thickness and total processing layer thickness (P<0.0001; r = -0.696).

CONCLUSIONS

Neither the total retinal thickness nor the pit depth are reliable indicators of visual deficit, because patients with similar overall retinal thickness had widely varying foveal morphologic features. In albinism, the size of the photoreceptor outer segment was found to be the strongest predictor of BCVA. These results suggest that detailed SD OCT images of photoreceptor anatomic features provide a useful tool in assessing the visual potential in patients with albinism.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Reproducibility and agreement in evaluating retinal nerve fibre layer thickness between Stratus and Spectralis OCT

PURPOSE

To evaluate intra-device reproducibility of retinal nerve fibre layer (RNFL) measurements obtained using Stratus and Spectralis optical coherence tomography, and to analyze inter-device correlation and agreement for these measurements.

DESIGN

Prospective observational study.

METHODS

A total of 30 normal individuals participated in the study. One eye of each participant was scanned three times during one session by the same operator using Spectralis and Stratus. Intra-class correlation coefficients (ICCs), correlation coefficients (R), and Bland-Altman plots (BAPs) were used to assess reproducibility, correlation, and agreement between the two devices, respectively.

RESULTS

A significant difference in mean RNFL thickness was seen between Stratus and Spectralis (106.2 ± 6.9 μm vs 100.0 ± 7.3 μm, P = 0.0001). ICCs of RNFL thickness measurements ranged from 0.69 (clock hour 2; 95% confidence interval (95% CI): 0.54, 0.85) to 0.91 (inferior quadrant; 95% CI: 0.86, 0.96) for Stratus and were higher for Spectralis, ranging from 0.87 (temporal-superior sector; 95% CI: 0.79, 0.94) to 0.96 (global and nasal-inferior sector; 95% CI: 0.94, 0.99). Rs of RNFL thickness measurements between the two instruments ranged from 0.61 (temporal quadrant) to 0.87 (superior quadrant). BAPs demonstrated a systematic difference in RNFL values between the two devices, with Spectralis producing thinner RNFL values than Stratus.

CONCLUSIONS

Spectralis demonstrated higher ICCs and thinner RNFL measurements than Stratus. Although the inter-device correlation was good, differences in RNFL measurements obtained by the two devices indicate that these measurements would not be interchangeable in clinical evaluations.