Reproducibility of diabetic macular edema estimates from SD-OCT is affected by the choice of image analysis algorithm

Progressive inner retinal neurodegeneration in non-proliferative macular telangiectasia type 2

PURPOSE

Patients with non-proliferative macular telangiectasia type 2 (MacTel) have ganglion cell layer (GCL) and nerve fibre layer (NFL) loss, but it is unclear whether the thinning is progressive. We quantified the change in retinal layer thickness over time in MacTel with and without diabetes.

METHODS

In this retrospective, multicentre, comparative case series, subjects with MacTel with at least two optical coherence tomographic (OCT) scans separated by >9 months OCTs were segmented using the Iowa Reference Algorithms. Mean NFL and GCL thickness was computed across the total area of the early treatment diabetic retinopathy study grid and for the inner temporal region to determine the rate of thinning over time. Mixed effects models were fit to each layer and region to determine retinal thinning for each sublayer over time.

RESULTS

115 patients with MacTel were included; 57 patients (50%) had diabetes and 21 (18%) had a history of carbonic anhydrase inhibitor (CAI) treatment. MacTel patients with and without diabetes had similar rates of thinning. In patients without diabetes and untreated with CAIs, the temporal parafoveal NFL thinned at a rate of -0.25±0.09 µm/year (95% CI [-0.42 to -0.09]; p=0.003). The GCL in subfield 4 thinned faster in the eyes treated with CAI (-1.23±0.21 µm/year; 95% CI [-1.64 to -0.82]) than in untreated eyes (-0.19±0.16; 95% CI [-0.50, 0.11]; p<0.001), an effect also seen for the inner nuclear layer. Progressive outer retinal thinning was observed.

CONCLUSIONS

Patients with MacTel sustain progressive inner retinal neurodegeneration similar to those with diabetes without diabetic retinopathy. Further research is needed to understand the consequences of retinal thinning in MacTel.

Protocol for Multi-modality MEdical imaging sTudy bAsed on KaiLuan Study (META-KLS): rationale, design and database building

INTRODUCTION

Multi-modality medical imaging study, especially brain MRI, greatly facilitates the research on subclinical brain disease. However, there is still a lack of such studies with a wider age span of participants. The Multi-modality MEdical imaging sTudy bAsed on KaiLuan Study (META-KLS) was designed to address this issue with a large sample size population.

METHODS AND ANALYSIS

We aim to enrol at least 1000 subjects in META-KLS. All the participants without contraindications will perform multi-modality medical imaging, including brain MRI, retinal fundus photograph, fundus optical coherence tomography (OCT) and ultrasonography of the internal carotid artery (ICA) every 2-4 years. The acquired medical imaging will be further processed with a standardised and validated workflow. The clinical data at baseline and follow-up will be collected from the KaiLuan Study. The associations between multiple risk factors and subclinical brain disease are able to be fully investigated. Researches based on META-KLS will provide a series of state-of-the-art evidence for the prevention of neurological diseases and common chronic diseases.

ETHICS AND DISSEMINATION

The Kailuan Study and META-KLS have been approved by the Medical Ethics Committee of Kailuan General Hospital (IRB number: 2008 No. 1 and 2021002, respectively). Written informed consent will be acquired from each participant. Results are expected to be published in professional peer-reviewed journals beginning in 2023.

TRIAL REGISTRATION NUMBER

NCT05453877.

Total retinal thickness: a neglected factor in the evaluation of inner retinal thickness

AIM

To determine whether macular retinal nerve fibre layer (mRNFL) and ganglion cell-inner plexiform layer (GC-IPL) thicknesses vary by ethnicity after accounting for total retinal thickness.

METHODS

We included healthy participants from the UK Biobank cohort who underwent macula-centred spectral domain-optical coherence tomography scans. mRNFL and GC-IPL thicknesses were determined for groups from different self-reported ethnic backgrounds. Multivariable regression models adjusting for covariables including age, gender, ethnicity and refractive error were built, with and without adjusting for total retinal thickness.

RESULTS

20237 participants were analysed. Prior to accounting for total retinal thickness, mRNFL thickness was on average 0.9 μm (-1.2, -0.6; p<0.001) lower among Asians and 1.5 μm (-2.3, -0.6; p<0.001) lower among black participants compared with white participants. Prior to accounting for total retinal thickness, the average GC-IPL thickness was 1.9 μm (-2.5, -1.4; p<0.001) lower among Asians compared with white participants, and 2.4 μm (-3.9, -1.0; p=0.001) lower among black participants compared with white participants. After accounting for total retinal thickness, the layer thicknesses were not significantly different among ethnic groups. When considered as a proportion of total retinal thickness, mRNFL thickness was ~0.1 and GC-IPL thickness was ~0.2 across age, gender and ethnic groups.

CONCLUSIONS

The previously reported ethnic differences in layer thickness among groups are likely driven by differences in total retinal thickness. Our results suggest using layer thickness ratio (retinal layer thicknesses/total retinal thickness) rather than absolute thickness values when comparing retinal layer thicknesses across groups.

Short-Term Outcomes of Switching to Ranibizumab in Polypoidal Choroidal Vasculopathy Resistant to Aflibercept Therapy

Background: To evaluate the short-term outcomes of switching to ranibizumab in aflibercept-resistant polypoidal choroidal vasculopathy (PCV). Methods: This retrospective study included 18 eyes diagnosed with aflibercept-resistant PCV. All patients were treated with two to four consecutive ranibizumab injections at 4–5-week intervals. The best-corrected visual acuity (BCVA), and central retinal thickness (CRT) values before and after switching to ranibizumab were compared. The proportion of eyes showing ≥100 µm decrease in retinal thickness and/or complete resolution of fluid after switching was identified. Results: The mean number of aflibercept injections before switching was 5.7 ± 3.3. After switching, a mean of 2.8 ± 0.6 consecutive ranibizumab injections was performed. The mean logarithm of minimal angle of resolution (logMAR) BCVA was 0.41 ± 0.26 (Snellen equivalents = 20/51) before switching, and 0.40 ± 0.30 (20/50) after switching (p = 0.574). The mean CRT was 422.2 ± 152.4 µm before switching, and 400.7 ± 182.0 µm after switching (p = 0.236). A decrease in CRT of ≥100 µm, and/or complete resolution of fluid was noted in three eyes (16.7%). Conclusions: Switching to ranibizumab in aflibercept-resistant polypoidal choroidal vasculopathy was not effective in most patients, suggesting the need for further investigation to seek more effective treatment options for this condition.

Detecting retinal neurodegeneration in people with diabetes: Findings from the UK Biobank

Importance

Efforts are underway to incorporate retinal neurodegeneration in the diabetic retinopathy severity scale. However, there is no established measure to quantify diabetic retinal neurodegeneration (DRN).

Objective

We compared total retinal, macular retinal nerve fiber layer (mRNFL) and ganglion cell-inner plexiform layer (GC-IPL) thickness among participants with and without diabetes (DM) in a population-based cohort.

Design/setting/participants

Cross-sectional analysis, using the UK Biobank data resource. Separate general linear mixed models (GLMM) were created using DM and glycated hemoglobin as predictor variables for retinal thickness. Sub-analyses included comparing thickness measurements for patients with no/mild diabetic retinopathy (DR) and evaluating factors associated with retinal thickness in participants with and without diabetes. Factors found to be significantly associated with DM or thickness were included in a multiple GLMM.

Exposure

Diagnosis of DM was determined via self-report of diagnosis, medication use, DM-related complications or glycated hemoglobin level of ≥ 6.5%.

Main outcomes and measures

Total retinal, mRNFL and GC-IPL thickness.

Results

74,422 participants (69,985 with no DM; 4,437 with DM) were included. Median age was 59 years, 46% were men and 92% were white. Participants with DM had lower total retinal thickness (-4.57 μm, 95% CI: -5.00, -4.14; p<0.001), GC-IPL thickness (-1.73 μm, 95% CI: -1.86, -1.59; p<0.001) and mRNFL thickness (-0.68 μm, 95% CI: -0.81, -0.54; p<0.001) compared to those without DM. After adjusting for co-variates, in the GLMM, total retinal thickness was 1.99 um lower (95% CI: -2.47, -1.50; p<0.001) and GC-IPL was 1.02 μm lower (95% CI: -1.18, -0.87; p<0.001) among those with DM compared to without. mRNFL was no longer significantly different (p = 0.369). GC-IPL remained significantly lower, after adjusting for co-variates, among those with DM compared to those without DM when including only participants with no/mild DR (-0.80 μm, 95% CI: -0.98, -0.62; p<0.001). Total retinal thickness decreased 0.40 μm (95% CI: -0.61, -0.20; p<0.001), mRNFL thickness increased 0.20 μm (95% CI: 0.14, 0.27; p<0.001) and GC-IPL decreased 0.26 μm (95% CI: -0.33, -0.20; p<0.001) per unit increase in A1c after adjusting for co-variates. Among participants with diabetes, age, DR grade, ethnicity, body mass index, glaucoma, spherical equivalent, and visual acuity were significantly associated with GC-IPL thickness.

Conclusion

GC-IPL was thinner among participants with DM, compared to without DM. This difference persisted after adjusting for confounding variables and when considering only those with no/mild DR. This confirms that GC-IPL thinning occurs early in DM and can serve as a useful marker of DRN.

Association of Macular Thickness With Age and Age-Related Macular Degeneration in the Carotenoids in Age-Related Eye Disease Study 2 (CAREDS2), An Ancillary Study of the Women's Health Initiative

Purpose

To evaluate the relationship of retinal layer thickness with age and age-related macular degeneration (AMD) in the Carotenoids in Age-Related Eye Disease Study 2.

Methods

Total retinal thickness within the macular area, and individual layer thickness was determined for CAREDS2 participants (n = 906 eyes, 473 women) from the Women's Health Initiative using Heidelberg optical coherence tomography (OCT). Mean measurements within the OCT grid were compared across age tertiles (69–78, 78–83, and 83–101 years) and AMD outcomes.

Results

Mean retinal thickness in the central circle, inner ring, and outer ring were 277 ± 34 µm, 326 ± 20 µm, and 282 ± 15 µm, respectively. Thickness did not vary by age in the central circle, but decreased with age in the inner and outer circles (P ≤ 0.004). Specifically, ganglion cell (GCL), inner plexiform, and outer nuclear (ONL) layer thickness decreased with age (P ≤ 0.003). Age-adjusted retinal thickness in all three circles did not vary by AMD outcomes (486 without AMD and 413 with AMD). However, individual layers showed changes with GCL and photoreceptor thinning and retinal pigment epithelial thicknening in eyes with late AMD. After controlling for age and AMD, higher ONL thickness was associated with better visual acuity.

Conclusions

In this cohort of older women, a decrease in perifoveal thickness was associated with increasing age, particularly in the inner retinal layers. Variabilty in thickness in AMD eyes was primarily due to outer retinal layers. Among all retinal layers, the ONL plays an important role in preserving visual acuity.

Translational Relevance

The study provides a deeper understanding of age related changes to the retinal layers and their effect on visual loss.

Macular Microvasculature and Associated Retinal Layer Thickness in Pediatric Amblyopia: Magnification-Corrected Analyses

Purpose

The purpose of this study was to characterize macular microvasculature and structural retinal layers using magnification-corrected optical coherence tomography angiography (OCTA) images in children with amblyopia.

Methods

This prospective cross-sectional study included 22 children with unilateral amblyopia (4–11 years of age) receiving spectral-domain OCTA. Vessel densities in foveal and parafoveal regions of the superficial capillary plexus (SCP) and deep capillary plexus (DCP) were measured in amblyopic and fellow eyes using a customized image analysis program correcting the scale of retinal image with axial length. Iowa Reference Algorithms (Iowa Institute for Biomedical Imaging) were used to measure mean thickness values of 10 intra-retinal layers rescaled for image size correction.

Results

Foveal and parafoveal vessel densities in amblyopic eyes were lower than that of the fellow eyes in the SCP (fovea: P = 0.006 and parafovea: P = 0.003) and the DCP (P = 0.024 and P = 0.025, respectively). Amblyopic eyes had significantly smaller foveal avascular zone (FAZ) area than fellow eyes (P < 0.001). There were significant differences in retinal layer thickness between paired eyes, particularly in the inner retina in both foveal and parafoveal regions; retinal nerve fiber layer (RNFL) (P = 0.024 and P = 0.095, respectively), ganglion cell layer (P < 0.001 and P = 0.008), inner plexiform layer (IPL; P = 0.12 and P = 0.037), inner nuclear layer (P = 0.005 and P = 0.005), and outer plexiform layer (OPL; P = 0.02 and P = 0.057), except in the foveal IPL, the parafoveal RNFL, and OPL.

Conclusions

Unilateral amblyopic eyes demonstrate reduced macular vessel density and thicker inner retinal layers compared with fellow eyes even after correcting for image magnification. Changes in macular microvasculature and structural layers may offer valuable insights in the development of amblyopia.

Diagnostic Ability of Individual Macular Layers by Spectral-Domain OCT in Different Stages of Glaucoma

PURPOSE

To compare the diagnostic ability of macular intraretinal layer thickness with circumpapillary retinal nerve fiber layer (cpRNFL) thickness, either when used individually or in combination with cpRNFL for detecting early, moderate, and advanced glaucoma.

DESIGN

Cross-sectional study.

PARTICIPANTS

A total of 423 glaucoma participants and 423 age- and gender-matched normal participants.

METHODS

Participants underwent Cirrus spectral-domain OCT (SD-OCT) imaging (Carl Zeiss Meditec, Dublin, CA) using the optic disc and macular scanning protocols. Iowa Reference Algorithms (version 3.8.0) were used for intraretinal layer segmentation, and mean thickness of intraretinal layers was rescaled with magnification correction using axial length value. Thickness measurements of each layer/sector and their corresponding areas under the receiver operating characteristic curve (AUCs) were obtained. Glaucoma eyes were subdivided based on of their visual field severity (early, n = 234; moderate, n = 107; advanced, n = 82).

MAIN OUTCOME MEASURES

Intraretinal layers.

RESULTS

Some 67% of participants were male, their average ± standard deviation age was 65±9 years. Circumpapillary retinal nerve fiber layer, macular ganglion cell layer (mGCL), and macular inner plexiform layer (mIPL) were significantly thinner in the glaucoma groups (P < 0.0005). The 2 best parameters for detecting normal eyes from early glaucoma was cpRNFL (AUC = 0.861) and mGCL (AUC = 0.842), from moderate glaucoma was mGCL combined with inner plexiform layer (IPL) (AUC = 0.915) and cpRNFL (AUC = 0 .914), and from advanced glaucoma was mGCL-IPL (AUC = 0.984) and cpRNFL (AUC = 0.977). There was no statistical significance between AUCs for the macular parameter and cpRNFL thickness measurement at any of the severities (P > 0.05). Combining macular and cpRNFL parameters improved the diagnostic performance for early glaucoma (AUC = 0.908; P = 0.002) and moderate glaucoma (AUC = 0.944; P = 0.031) but not for advanced glaucoma (AUC = 0.991; P > 0.05).

CONCLUSIONS

Single-layer mGCL thickness is comparable to the traditional cpRNFL thickness for the diagnosis of early/moderate glaucoma, whereas cpRNFL thickness remains the most efficient for advanced glaucoma. Combining macular measurements (GCL and GCL-IPL) and cpRNFL improved the discrimination of early/moderate glaucoma but not of advanced glaucoma. For the diagnosis of early glaucoma, both macular and optic disc scans should be used.

Association between individual retinal layer thickness and visual acuity in patients with epiretinal membrane: a pilot study

Purpose

We investigated the correlation between visual acuity (VA) and individual retinal layer thickness in the foveal, parafoveal, and perifoveal regions of patients with an idiopathic epiretinal membrane (ERM).

Methods

One hundred and five subjects presenting with unilateral idiopathic ERM were included in this study. We segmented each patient’s optical coherence tomography (OCT) image into seven layers and calculated the mean layer thickness in the foveal, parafoveal, and perifoveal regions using the Iowa Reference Algorithm. In 105 patients with ERM, we detected correlations between their macular regions’ individual retinal layer thickness and their best corrected VA. Thirty-one of the 105 patients with ERM underwent vitrectomy and completed six months of follow-up. We then compared the 31 surgical patients’ preoperative and postoperative individual retinal layer thickness in each macular region. Additionally, the association between preoperative individual retinal layer thickness in each macular region and VA six months post-surgery in patients with ≥ two Snellen lines of visual improvement was determined.

Results

Multiple linear regression analysis showed that the inner nuclear layer (INL) thickness in the foveal, parafoveal, and perifoveal region were all associated with VA in the 105 patients (R² = 0.344, P < 0.001; R² = 0.427, P < 0.001; and R² = 0.340, P < 0.001, respectively). Thirty-one surgical patients 6 months post-surgery showed significantly decreased thicknesses (P ≤ 0.012) of the foveal INL, inner plexiform layer (IPL), and outer nuclear layer (ONL); the parafoveal retina nerve fiber layer (RNFL), IPL, INL, and ONL; and the perifoveal RNFL, IPL, INL, ganglion cell layer (GCL), outer plexiform layer (OPL), and photoreceptor layer (PRL). We found a weak correlation between postoperative VA and preoperative foveal and perifoveal RNFL thickness (r = 0.404 and r = 0.359, respectively), and a moderate correlation between postoperative VA and preoperative foveal and parafoveal INL thickness (r = 0.529 and r = 0.583, respectively) in the 31 surgical patients (P ≤ 0.047). The preoperative INL thickness in the foveal, parafoveal, and perifoveal regions showed a moderate to strong correlation (r = 0.507, 0.644, and 0.548, respectively), with postoperative VA in patients with ≥ 2 lines of visual improvement (P ≤ 0.038).

Conclusion

We detected a correlation between retinal damage and VA in the parafoveal, perifoveal, and foveal regions. Our results suggest that INL thickness in all macular regions may be a prognostic factor for postoperative VA in ERM patients.

Comparison of the Iowa Reference Algorithm to the Heidelberg Spectralis optical coherence tomography segmentation algorithm

For spectral-domain optical coherence tomography (SD-OCT) studies of neurodegeneration, it is important to understand how segmentation algorithms differ in retinal layer thickness measurements, segmentation error locations and the impact of manual correction. Using macular SD-OCT images of frontotemporal degeneration patients and controls, we compare the individual and aggregate retinal layer thickness measurements provided by two commonly used algorithms, the Iowa Reference Algorithm and Heidelberg Spectralis, with manual correction of significant segmentation errors. We demonstrate small differences of most retinal layer thickness measurements between these algorithms. Outer sectors of the Early Treatment Diabetic Retinopathy Study grid require a greater percent of eyes to be corrected than inner sectors of the retinal nerve fiber layer (RNFL). Manual corrections affect thickness measurements mildly, resulting in at most a 5% change in RNFL thickness. Our findings can inform researchers how to best use different segmentation algorithms when comparing retinal layer thicknesses.

Detection of Diabetic Macular Edema in Optical Coherence Tomography Image Using an Improved Level Set Algorithm

Diabetic macular edema (DME) is a major cause of visual loss in the patients with diabetic retinopathy. DME detection in Optical Coherence Tomography (OCT) image contributes to the early diagnosis of diabetic retinopathy and blindness prevention. Currently, DME detection in the OCT image mainly relies on the handwork by the experienced clinician. It is a laborious, time-consuming, and challenging work to organize a comprehensive DME screening for diabetic patients. In this study, we proposed a novel algorithm for the detection and segmentation of DME region in OCT image based on the K-means clustering algorithm and improved Selective Binary and Gaussian Filtering regularized level set (SBGFRLS) algorithm named as SBGFRLS-OCT algorithm. SBGFRLS-OCT algorithm was compared with the current level set algorithms, including C-V (Chan-Vese), GAC (geodesic active contour), and SBGFRLS, to estimate the performance of DME detection. SBGFRLS-OCT algorithm was also compared with the clinician to estimate the precision, sensitivity, and specificity of DME segmentation. Compared with C-V, GAC, and SBGFRLS algorithm, the SBGFRLS-OCT algorithm enhanced the accuracy and reduces the processing time of DME detection. Compared with manual DME segmentation, the SBGFRLS-OCT algorithm achieved a comparable precision (97.7%), sensitivity (91.8%), and specificity (99.2%). Collectively, this study presents a novel algorithm for DME detection in the OCT image, which can be used for mass diabetic retinopathy screening.

Impact of manual correction over automated segmentation of spectral domain optical coherence tomography

Objective

To study the automated segmentation of retinal layers using spectral domain optical coherence tomography (OCT) and the impact of manual correction over segmentation mistakes.

Methods

This was a retrospective, cross-sectional, comparative study that compared the automated segmentation of macular thickness using Spectralis™ OCT technology (Heidelberg Engineering, Heidelberg, Germany) versus manual segmentation in eyes with no macular changes, macular cystoid edema (CME), and choroidal neovascularization (CNV). Automated segmentation of macular thickness was manually corrected by two independent examiners and reanalyzed by them together in case of disagreement.

Results

In total, 306 eyes of 254 consecutive patients were evaluated. No statistically significant differences were noted between automated and manual macular thickness measurements in patients with normal maculas, while a statistically significant difference was found in central thickness in patients with CNV and with CME. Segmentation mistakes in macular OCTs were present in 5.3% (5 of 95) in the normal macula group, 16.4% (23 of 140) in the CME group, and 66.2% (47 of 71) in CNV group. The difference between automated and manual macular thickness was higher than 10% in 1.4% (2 of 140) in the CME group and in 28.17% (20 of 71) in the CNV group. Only one case in the normal group had a higher than 10% segmentation error (1 of 95).

Conclusion

The evaluation of automated segmented OCT images revealed appropriate delimitation of macular thickness in patients with no macular changes or with CME, since the frequency and magnitude of the segmentation mistakes had low impact over clinical evaluation of the images. Conversely, automated macular thickness segmentation in patients with CNV showed a high frequency and magnitude of mistakes, with potential impact on clinical analysis.

Age-related changes of individual macular retinal layers among Asians

We characterized the age-related changes of the intra-retinal layers measured with spectral-domain optical coherence tomography (SD-OCT; Cirrus high-definition OCT [Carl Zeiss Meditec]. The Singapore Epidemiology of Eye Diseases is a population-based, cross-sectional study of Chinese, Malays and Indians living in Singapore. Iowa Reference Algorithms (Iowa Institute for Biomedical Imaging) were used for intra-retinal layer segmentation and mean thickness of 10 intra-retinal layers rescaled with magnification correction using axial length value. Linear regression models were performed to investigate the association of retinal layers with risk factors. After excluding participants with history of diabetes or ocular diseases, high-quality macular SD-OCT images were available for 2,047 participants (44–89 years old). Most of the retinal layers decreased with age except for foveal retinal nerve fiber layer (RNFL) and the inner/outer segments of photoreceptors where they increased with age. Men generally had thicker retinal layers than women. Chinese have the thickest RNFL and retinal pigment epithelium amongst the ethnic groups. Axial length and refractive error remained correlated with retinal layers in spite of magnification correction. Our data show pronounced age-related changes in retinal morphology. Age, gender, ethnicity and axial length need be considered when establishing OCT imaging biomarkers for ocular or systemic disease.

Longitudinal Macular Structure-Function Relationships in Glaucoma and Their Sources of Variability

PURPOSE

To review central structure-function (SF) relationships in glaucoma; to compare contributions of within-session and between-session variability to total variability of macular optical coherence tomography (OCT) thickness measurements; and to test the hypothesis that longitudinal within-eye variability of central SF relationships is smaller than between-individual variability.

METHODS

We reviewed the pertinent literature on central SF relationships in glaucoma. Thirty-eight eyes (20 normal or glaucoma subjects) had ×3 macular images per session over 3 sessions, and superpixels thickness measurements for ganglion cell layer (GCL), ganglion cell/inner plexiform layer (GCIPL), ganglion cell complex (GCC), and full macular thickness (FMT) were exported. Linear mixed models were used for estimating contributions of between- and within-session variability to total thickness variability. One hundred twenty eyes with ≥3 10° visual fields (VFs)/OCT images were enrolled for the longitudinal study. We investigated within-eye longitudinal SF relationships (GCIPL thickness vs VF total deviations) with a change-point regression model and compared within-eye to between-individual variabilities with components-of-variance models.

RESULTS

In the cross-sectional study, the between-session component contributed 8%, 11%, 11%, and 36% of total variability for GCL, GCIPL, GCC, and FMT, respectively. In the longitudinal study, between-individual variability explained 78%, 77%, and 67% of total SF variability at 3.4°, 5.6°, and 6.8° eccentricities, respectively (P < .05). SF relationships remained stable over time within individual eyes.

CONCLUSIONS

Within-session variability accounts for most of macular thickness variability over time. Longitudinal within-eye SF variability is smaller than between-individual variability. Study of within-eye SF relationships could help clinicians better understand SF linking in glaucoma and help refine progression algorithms. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

Central retinal thickness following panretinal photocoagulation using a multispot semi-automated pattern-scanning laser to treat ischaemic diabetic retinopathy: Treatment in one session compared with four monthly sessions

PURPOSE

To compare central retinal thickness (CRT) after panretinal photocoagulation (PRP) with a multispot semi-automated PAttern-SCAnning Laser (PASCAL) in one session (SS-PRP) versus four monthly sessions (MS-PRP) in diabetic retinopathy.

METHODS

Multicentre, prospective, randomized, single-blinded, controlled trial evaluating the noninferiority of SS-PRP versus MS-PRP for CRT measured with macular spectral-domain optical coherence tomography (SD-OCT), with a 9-month follow-up in patients presenting severe nonproliferative diabetic retinopathy (DR) or mild proliferative DR without macular oedema (ME) at baseline.

RESULTS

Ninety-seven eyes of 97 participants with a mean age of 57.0 ± 14.2 years were included. The mean change of CRT from baseline to 9 months was not statistically different in SS-PRP or in MS-PRP: +16.9 ± 28.3 μm versus +24.7 ± 31.8 μm, respectively (p = 0.224). The variation in mean best-corrected visual acuity (BCVA) from baseline to 9 months was similar in both groups: -1.1 ± 6.5 letters versus -0.6 ± 6.2 letters (p = 0.684). The number of patients with stabilization of DR was not statistically different between the two groups. No severe complication was recorded in either group.

CONCLUSION

This study showed the noninferiority of PRP performed in one session versus four monthly sessions with a PASCAL concerning central retinal thickness for treating mild proliferative or severe nonproliferative DR without ME at baseline.

Assessment of Global and Local Alterations in Retinal Layer Thickness in Ins2 (Akita) Diabetic Mice by Spectral Domain Optical Coherence Tomography

PURPOSE/AIM

The Ins2 (Akita) mouse is a spontaneous diabetic mouse model with a heterozygous mutation in the insulin 2 gene that results in sustained hyperglycemia. The purpose of the study was to assess global and local retinal layer thickness alterations in Akita mice by analysis of spectral domain optical coherence tomography (SD-OCT) images.

MATERIALS AND METHODS

SD-OCT imaging was performed in Akita and wild-type mice at 12 and 24 weeks of age. Inner retinal thickness (IRT), outer retinal thickness (ORT), total retinal thickness (TRT), and photoreceptor outer segment length (OSL) were measured. Mean global thickness values were compared between Akita and wild-type mice. Local thickness variations in Akita mice were assessed based on normative values in wild-type mice.

RESULTS

Akita mice had higher blood glucose levels and lower body weights (p < 0.001). On average, IRT, ORT, and TRT were approximately 2% lower in Akita mice than in wild-type mice (p ≤ 0.02). In Akita mice, the percent difference between retinal areas with thickness below and above normative values for IRT, ORT, and TRT was 22%, 32%, and 38%, respectively.

CONCLUSIONS

These findings support the use of the Akita mouse model to study the retinal neurodegenerative effects of hyperglycemia.

Avoiding Clinical Misinterpretation and Artifacts of Optical Coherence Tomography Analysis of the Optic Nerve, Retinal Nerve Fiber Layer, and Ganglion Cell Layer

Background:

Optical coherence tomography (OCT) has become an important tool for diagnosing optic nerve disease. The structural details and reproducibility of OCT continues to improve with further advances in technology. However, artifacts and misinterpretation of OCT can lead to clinical misdiagnosis of diseases if they go unrecognized.

Evidence Acquisition:

A literature review using PubMed combined with clinical and research experience.

Results:

We describe the most common artifacts and errors in interpretation seen on OCT in both optic nerve and ganglion cell analyses. We provide examples of the artifacts, discuss the causes, and provide methods of detecting them. In addition, we discuss a systematic approach to OCT analysis to facilitate the recognition of artifacts and to avoid clinical misinterpretation.

Conclusions:

While OCT is invaluable in diagnosing optic nerve disease, we need to be cognizant of the artifacts that can occur with OCT. Failure to recognize some of these artifacts can lead to misdiagnoses and inappropriate investigations.

GANGLION CELL LAYER THICKNESS AND VISUAL IMPROVEMENT AFTER EPIRETINAL MEMBRANE SURGERY

PURPOSE

To evaluate the possible prognostic value of preoperative individual retinal layer thicknesses measured by an automated algorithm from spectral domain optical coherence tomography and visual acuity or improvement after epiretinal membrane surgery.

METHODS

Data from 76 eyes with idiopathic epiretinal membrane that underwent pars plana vitrectomy for idiopathic epiretinal membrane removal were analyzed. The preoperative thicknesses of the ganglion cell layer, inner plexiform layer, and other layers were measured using the Iowa Reference Algorithm. Each retinal layer thickness and its ratio of the central foveal thickness were compared between eyes with (Group 1) or without (Group 2) 2 or more Snellen lines of visual improvement at 3, 6, and 12 months after surgery.

RESULTS

Higher mean central foveal thickness/ganglion cell layer ratio and symptom duration of ≤1 year were significantly more common in Group 1 (P = 0.03 and 0.04, respectively). After adjusting for age and symptom duration, lens status, and preoperative visual acuity, higher central foveal thickness/ganglion cell layer ratio was associated with ≥2 lines of visual improvement after surgery (odds ratio: 6.57, 95% confidence interval: 1.29-33.40).

CONCLUSION

The preoperative inner retinal layer changes may have a role independent of outer retinal layer parameters in the visual prognosis after epiretinal membrane peeling.

Automated Retinal Layer Segmentation Using Spectral Domain Optical Coherence Tomography: Evaluation of Inter-Session Repeatability and Agreement between Devices

Retinal and intra-retinal layer thicknesses are routinely generated from optical coherence tomography (OCT) images, but on-board software capabilities and image scaling assumptions are not consistent across devices. This study evaluates the device-independent Iowa Reference Algorithms (Iowa Institute for Biomedical Imaging) for automated intra-retinal layer segmentation and image scaling for three OCT systems. Healthy participants (n = 25) underwent macular volume scans using a Cirrus HD-OCT (Zeiss), 3D-OCT 1000 (Topcon), and a non-commercial long-wavelength (1040nm) OCT on two occasions. Mean thickness of 10 intra-retinal layers was measured in three ETDRS subfields (fovea, inner ring and outer ring) using the Iowa Reference Algorithms. Where available, total retinal thicknesses were measured using on-board software. Measured axial eye length (AEL)-dependent scaling was used throughout, with a comparison made to the system-specific fixed-AEL scaling. Inter-session repeatability and agreement between OCT systems and segmentation methods was assessed. Inter-session coefficient of repeatability (CoR) for the foveal subfield total retinal thickness was 3.43μm, 4.76μm, and 5.98μm for the Zeiss, Topcon, and long-wavelength images respectively. For the commercial software, CoR was 4.63μm (Zeiss) and 7.63μm (Topcon). The Iowa Reference Algorithms demonstrated higher repeatability than the on-board software and, in addition, reliably segmented all 10 intra-retinal layers. With fixed-AEL scaling, the algorithm produced significantly different thickness values for the three OCT devices (P<0.05), with these discrepancies generally characterized by an overall offset (bias) and correlations with axial eye length for the foveal subfield and outer ring (P<0.05). This correlation was reduced to an insignificant level in all cases when AEL-dependent scaling was used. Overall, the Iowa Reference Algorithms are viable for clinical and research use in healthy eyes imaged with these devices, however ocular biometry is required for accurate quantification of OCT images.

Improved repeatability of retinal thickness measurements using line-scan ophthalmoscope image-based retinal tracking

BACKGROUND AND OBJECTIVE

To assess repeatability and speed of a line-scan ophthalmoscope (LSO) image-based tracking system and compare to the point-scanning approach.

PATIENTS AND METHODS

Thirty-five eyes with retinal diseases underwent volume scans using two spectral-domain optical coherence tomography (OCT) devices: a line-scan tracking Cirrus HD-OCT (Carl Zeiss Meditec; Dublin, CA) and point-scan tracking Spectralis HRA+OCT (Heidelberg Engineering, Heidelberg, Germany). Eyes were also imaged on the Cirrus HD-OCT with tracking disabled.

RESULTS

Mean difference in central subfield thickness (CST) between consecutive scans was 2.6 µm for the Cirrus without tracking, 1.7 µm with tracking, and 3.6 µm for the Spectralis. The repeatability standard deviation was 3.0 µm for the Cirrus without tracking, 1.5 µm with tracking, and 4.0 µm for the Spectralis. Coefficient of variation for the CST was 1.1% for the Cirrus without tracking, 0.5% with tracking, and 1.4% for the Spectralis. Mean scan acquisition time was 12.3 ± 6.2 seconds for the Spectralis, 7.8 ± 6.7 for the Cirrus with tracking, and 4.3 ± 0.6 for the Cirrus without tracking.

CONCLUSION

Real-time LSO image-based retinal tracking appears to improve repeatability of OCT retinal thickness measurements.

Interobserver agreement in detecting spectral-domain optical coherence tomography features of diabetic macular edema

Purpose

To evaluate interobserver agreement for the detection of spectral-domain optical coherence tomography (SDOCT) features of diabetic macular edema (DME).

Method

Cross-sectional study in which 2 retinal specialists evaluated SDOCT scans from eyes receiving treatment for DME. Scans from 50 eyes with DME of 39 patients were graded for features of DME including intra-retinal fluid (IRF), diffuse retinal oedema (DRE), hyper-reflective foci (HRF), subretinal fluid (SRF), macular fluid and vitreomacular traction (VMT). Features were graded as present or absent at zones involving the fovea, 1mm from the fovea and the whole scan of 49 line scans. Analysis was performed using cross-tabulations for percentage concordance and kappa values (κ).

Results

In the 2950 line scans analysed, there was an increase in percentage concordance for DRE and HRF when moving from a foveal line scan, 1mm zone and then to a whole scan analysis (88% vs 94% vs 96%) and (88% vs 94% vs 94%) respectively with κ ranging from substantial to almost perfect. Percentage concordance for SRF was 96% at all 3 regions analysed, whilst IRF was 96% at fovea and 98% at higher number of line-scans analysed. Concordance for MF was 100% at fovea and 98% at 1mm zone and whole scan with almost perfect and substantial κ respectively. κ agreement was substantial for VMT at all regions analysed.

Conclusion

We report a high level of interobserver agreement in the detection of SDOCT features of DME. This finding is important as detection of macular fluid is used to guide retreatment with anti-angiogenic agents.

Kernel regression based segmentation of optical coherence tomography images with diabetic macular edema

We present a fully automatic algorithm to identify fluid-filled regions and seven retinal layers on spectral domain optical coherence tomography images of eyes with diabetic macular edema (DME). To achieve this, we developed a kernel regression (KR)-based classification method to estimate fluid and retinal layer positions. We then used these classification estimates as a guide to more accurately segment the retinal layer boundaries using our previously described graph theory and dynamic programming (GTDP) framework. We validated our algorithm on 110 B-scans from ten patients with severe DME pathology, showing an overall mean Dice coefficient of 0.78 when comparing our KR + GTDP algorithm to an expert grader. This is comparable to the inter-observer Dice coefficient of 0.79. The entire data set is available online, including our automatic and manual segmentation results. To the best of our knowledge, this is the first validated, fully-automated, seven-layer and fluid segmentation method which has been applied to real-world images containing severe DME.

Changes in Central Macular Thickness following Single Session Multispot Panretinal Photocoagulation

Purpose. To determine changes in central subfield (CSF) macular thickness and best corrected visual acuity (BCVA) following single session, multispot panretinal photocoagulation (PRP). Methods. Forty eyes of 33 patients with newly diagnosed proliferative diabetic retinopathy were treated with single session, 20-millisecond, multispot PRP. Changes in central macular thickness and BCVA at 4- and 12-week follow-up were compared to baseline measurements. Results. Each eye received a mean (SD) of 2,750 (686.7) laser spots. At 4-week follow-up, there was a statistically significant 24.0 μm increase in mean CSF thickness (P = 0.001), with a 17.4 μm increase from baseline at 12-week follow-up (P = 0.002). Mean logMAR BCVA increased by 0.05 logMAR units (P = 0.03) at 4-week follow-up. At 12-week follow-up, BCVA had almost returned to normal with only an increase of 0.02 logMAR units compared to baseline (P = 0.39). Macular edema occurred in 2 eyes (5%) at 12-week follow-up. Conclusions. Macular thickening occurs following single session, 20-millisecond, multispot PRP, with a corresponding, mild change in BCVA. However, the incidence of macular edema appears to be low in these patients. Single session, 20-millisecond, multispot PRP appears to be a safe treatment for patients with proliferative diabetic retinopathy.

Reproducibility of spectral-domain optical coherence tomography retinal thickness measurements and conversion to equivalent time-domain metrics in diabetic macular edema

IMPORTANCE

Understanding measurement variability and relationships between measurements obtained on different optical coherence tomography (OCT) machines is critical for clinical trials and clinical settings.

OBJECTIVE

To evaluate the reproducibility of retinal thickness measurements from OCT images obtained by time-domain (TD) (Stratus; Carl Zeiss Meditec) and spectral-domain (SD) (Cirrus; Carl Zeiss Meditec, and Spectralis; Heidelberg Engineering) instruments and formulate equations to convert retinal thickness measurements from SD-OCT to equivalent values on TD-OCT.

DESIGN, SETTING, AND PARTICIPANTS

A cross-sectional observational study was conducted in private and institutional practices. Persons with diabetes mellitus who had at least 1 eye with central-involved diabetic macular edema, defined as Stratus central subfield thickness (CST) of 250 μm or greater, participated. An additional normative cohort (individuals with diabetes but without diabetic macular edema) was enrolled. Each study eye underwent 2 replicate Stratus scans followed by 2 replicate Cirrus or Spectralis scans (real-time image registration used) centered on the fovea.

MAIN OUTCOMES AND MEASURES

Optical coherence tomography CST and macular volume.

RESULTS

The Bland-Altman coefficient of repeatability for relative change in CST (the degree of change that could be expected from measurement variability) was lower with Spectralis (7%) compared with Cirrus (14%) and Stratus (12% and 15% within Cirrus/Stratus and Spectralis/Stratus groups, respectively). For each cohort, the initial Stratus CST was within 10% of the replicate Stratus measurement nearly all of the time; the conversion equations predicted a Stratus CST within 10% of the observed thickness 86% and 89% of the time for Cirrus/Stratus and Spectralis/Stratus groups, respectively, which is similar to the agreement on Stratus test-retest. The Bland-Altman limits of agreement for relative change in CST between machines (the degree of change that could be expected from measurement variability [combining within and between instrument variability]) were 21% for Cirrus and 19% for Spectralis when comparing predicted vs actual Stratus measurement.

CONCLUSIONS AND RELEVANCE

Reproducibility appears to be better with Spectralis than with Cirrus and Stratus. Conversion equations to transform Cirrus or Spectralis measurements to Stratus-equivalent values, within 10% of the observed Stratus thickness values, appear feasible. Central subfield thickness changes beyond 10% when using the same machine or 20% when switching machines, after conversion to Stratus equivalents, are likely due to a change in retinal thickness rather than measurement error.