Topcon 3D Research Articles

Évaluation de l’épaisseur maculaire moyenne par la tomographie en cohérence optique (SD OCT) chez le sujet mélanoderme sénégalais

Our goal was to evaluate the normal macular thickness in Blacks by OCT and to determine socio-demographic and clinical parameters which may influence it. This was a multicenter, prospective, descriptive study over 6 months. It included Black adults followed in the ophthalmology departments of Abass Ndao and Aristide-Le-Dantec hospitals in Dakar. Included subjects had corrected visual acuity of 10/10 (0 logMAR) and P2 (+0.1 logMAR), clear ocular media, and no retinal abnormalities. We used the Topcon 3D 2000OCT to measure the central thicknesses of the cornea (CT) and of the macula (MT), and cup to disc ratio (C/D) in each eye. Socio-demographic, clinical and tomographic data were collected on a survey form and correlated to the MT. The analysis was carried out by the Epi info 7 software. We used the Chi2 comparison test with a P value˂0.05. One hundred and nine patients were included. The mean age was 27.39 years with a male/female ratio of 0.65. The subjects were emmetropic in 54.13% of cases. The mean CT was 519.97μm, the mean C/D was 0.23, and the mean MT was 264.35μm. The P-value (P) was greater than or equal to 0.1 for all the factors studied. MT in our study was lower than that of Whites, and the various parameters studied did not demonstrate a statistically significant influence on MT.

Development of a new algorithm based on FDT Matrix perimetry and SD-OCT to improve early glaucoma detection in primary care.

PurposeThe purpose of this study was to develop an objective algorithm to discriminate the earliest stages of glaucoma using frequency doubling technology (FDT) Matrix perimetry and spectral domain-optical coherence tomography (OCT) technology to improve primary care detection.Materials and methodsThree hundred six eyes (mean age 58.67±15.12) from 161 patients were included and classified in the following three groups: 101 nonglaucoma (GI-NG), 100 glaucoma suspect (GII-SG), and 105 open-angle glaucoma (GIII-OAG). All participants underwent a visual field exploration using the Humphrey Matrix visual field instrument and retinal nerve fiber layer evaluation using the Topcon 3D OCT-2000. Pattern deviation plot was divided into 19 areas and five aggrupation or quadrants and ranked with a value between 0 and 4 according to its likelihood of normality, and differences among three groups were analyzed. Principal component analysis (PCA) was also used to extract the most notable features of FDT and OCT, and a logistic regression analysis was applied to obtain the classification rules.ResultsOnly area numbers 7 and 12 and the central zone of FDT Matrix showed statistical differences (P<0.05) between GI-NG and GII-SG. The classification rules were estimated by the four PCA obtained from FDT Matrix and 3D OCT-2000 in a separate and combined use. Area under the receiver operating characteristic curve was 78.88% with FDT-PCA, 82.09% with OCT-PCA, and 94.27% with combined use of FDT and OCT-PCA to discriminate GI-NG and GII-SG.ConclusionThe predictive rules based on FDT-PCA or OCT-PCA provide a high sensitivity and specificity to detect the earliest stages of glaucoma and even better in combined use. These predictive rules may help the future development of software for FDT Matrix perimetry and 3D OCT-2000, which will greatly improve their diagnostic ability, making them useful in daily practice in a primary care setting.

Local comparison of cup to disc ratio in right and left eyes based on fusion of color fundus images and OCT B-scans

Symmetry analysis of Optical Coherence Tomography (OCT) images in right and left eyes can lead to introduction of new biomarkers for early detection of eye diseases. In this study, we investigate the symmetry between two eyes by calculating local cup to disc ratio (CDR) from each B-scan based on fusion of fundus images and OCT B-scans. For this purpose, in the first phase, the OCT data of Optic Nerve Head (ONH) in right and left eyes are aligned by finding the equivalent B-scans of both eyes based on the fovea-ONH axes. Since the fovea-ONH axes in OCT data are not available, at first, left and right fundus images are aligned according to their automatically detected fovea-ONH axes. Then, OCT data are registered to corresponding fundus images based on maximum similarity between en-face OCT data and fundus image in each eye. This two-stage alignment procedure depends on 1) the blood vessels, automatically extracted by Hessian analysis of directional curvelet sub-bands, and 2) the disc contour of ONH in fundus images, detected by Distance Regularized Level Set Evolution (DRLSE) algorithm. In the second phase, in order to calculate the local CDRs, the disc and cup boundaries are extracted from the aligned B-scans in left and right eyes. The disc boundary is limited by Bruch-Membrane opening, and the cup boundary is defined by retinal layer border. Therefore, Inner Limiting Membrane (ILM) and Retinal Pigment Epithelium (RPE) layers are extracted using ridgelet transform to find the disc-edge point and cup-edge point in each B-scan. Finally, the ratio of summed areas of cups to summed areas of discs is calculated in corresponding local regions to find the local CDRs. Using this method, we can also introduce a new index called local volumetric CDR (VCDR) by dividing the volume of cup in a specific region to the corresponding volume of disc extracted from OCT images of ONH. Forty healthy OCT datasets of size 650 × 512 × 128 (acquired from Topcon 3D OCT-1000) and corresponding 1536 × 1612 fundus images were used in this study. In addition to point-by-point comparison of CDRs in equivalent B-scans of aligned OCTs, the CDRs in upper, middle and lower regions were calculated and the maximum symmetry is observed in middle region. In addition, using local VCDR, the symmetry of 3D OCTs of both eyes is analyzed in 24 volumetric sectors.

Effect of optic disc-fovea distance on the normative classifications of macular inner retinal layers as assessed with OCT in healthy subjects.

PurposeTo determine the influence of the optic disc–fovea distance (DFD) on the normative classifications based on thickness measurements of macular inner retinal layers with spectral-domain optical coherence tomography (OCT) in healthy subjects.MethodsA total of 182 eyes from 182 healthy subjects were included (mean (SD) spherical equivalent −0.8 (1.9) dioptres). We performed macula and optic disc imaging with the Topcon 3D OCT 2000. The thickness of the macular inner retinal layers (macular retinal nerve fibre layer (mRNFL), ganglion cell-inner plexiform layer (GCIPL) and both combined (ganglion cell complex; GCC)) and the corresponding classifications based on the built-in normative database were recorded. The occurrence of an abnormal normative classification (occurrence of any thickness variable below the fifth percentile) was related to the DFD and other factors (axial length/refraction, optic disc area, fovea–disc angle, age, gender, image quality, visual field mean deviation and peripapillary retinal nerve fibre layer thickness), using logistic regression.ResultsThe mean (SD) DFD was 4.90 (0.29) mm. A greater DFD was associated with a higher percentage of abnormal normative classification in the OCT parameters describing the thickness of the mRNFL (OR (95%CI) per 0.1 mm increase in DFD: 1.30 (1.13 to 1.50), p<0.001), GCIPL (1.18 (1.02 to 1.38), p=0.023) and GCC measurement (1.29 (1.08 to 1.55), p=0.006).ConclusionsEyes with a greater DFD are prone to false-positive classifications in the thickness assessment of the macular inner retinal layers. The thicknesses should always be interpreted in the context of DFD.

Исследование положения интраокулярной линзы с помощью оптической когерентной томографии и связанных с ним изменений рефракции после факоэмульсификации

Purpose. To reveal a variability of IOL position after phacoemulsification using the optical coherence tomography (OCT) and to determine associated changes in postoperative refraction. Material and methods . The study enrolled 187 patients (220 eyes) who underwent phacoemulsification with the AcrySof® IOL implantation. The preoperative examination included the «IOLMaster» and «Lenstar LS 900» biometry, and the «Pentacam HR» keratotopography. One month postoperatively all of the measurements were repeated. The «Topcon 3D OCT-2000» optical coherent tomography was used to detect an IOL tilt and its displacement. Results. Axial displacements of the IOL optical part revealed by the OCT data allowed to divide the patients into 2 groups. Patients with an IOL «deflection» had eyes with a bigger axial length and a wide corneal segment, a deeper pseudophakic anterior chamber with a larger volume. Also there was a shift of subjective refraction towards the hyperopia relative to values calculated by the Hoffer Q, Holladay I and Haigis formulas in the selected group. Constructed logistic regression equations included the «IOLMaster» and «Lenstar LS 900» biometry parameters, the calculated IOL power and had a high predictive quality. Conclusions. The OCT data allow to reveal axial «deflections» of the IOL in patients. This leads to a weakening of subjective refraction. The probability of displacements can be calculated with a high predictive quality according to the logistic regression model. So, it enables to assess a risk of such dislocations and to make adjustments in the calculation of IOL optical power.

The development of a reference database with the Topcon 3D OCT-1 Maestro.

ImportanceThe paper presents the range for measurements taken with a new spectral domain optical coherence tomography (OCT) device to establish a reference database for discrimination purposes.ObjectiveTo report the range of thickness values for the new Topcon Maestro 3D OCT device with 2 scan size settings: the 12×9 mm wide field and 6×6 mm scans.DesignProspective, multicenter cohort study conducted at 7 clinical sites across the USA.SettingPrimary eyecare clinics within academic, hospital, and private practice locations.ParticipantsHealthy volunteers; all enrolled participants underwent a complete ophthalmological examination to confirm healthy ocular status prior to being enrolled in the study.Main outcome measureAverage and 1st, 5th, 95th, and 99th percentile ranges for OCT parameters Early Treatment Diabetic Retinopathy Study macula full retinal thickness, ganglion cell + inner plexiform layer thickness (GCL + IPL), ganglion cell complex (GCC) thickness, circumpapillary retinal nerve fiber layer (cpRNFL) thickness.ResultsThree hundred and ninety-nine eyes of 399 subjects were included in the analysis. Mean (SD) age was 46.3 (16.3) years (range 18–88 years). Forty-three percent of the subjects were male. Mean (SD) measurements (in μm) for the 12×9 mm wide scan were as follows: foveal thickness=237.079 (20.899), GCL + IPL=71.363 (5.924), GCC=105.949 (8.533), cpRNFL=104.720 (11.829); measurements for the 6×6 mm scans were as follows: foveal thickness=234.000 (20.657), GCL + IPL=71.726 (5.880), GCC=106.698 (9.094), cpRNFL=104.036 (11.341).ConclusionThe overall normal thickness values reported with Topcon 3D OCT-1 Maestro were like those studies with OCT from different manufactures. The reference limits at the 1st, 5th, 95th, and 99th percentile points establish the thresholds for the quantitative comparison of the cpRNFL and the macula in the human retina to a database of known healthy subjects.

Evaluation of patients with keratoplasty in Tanta University Hospital using anterior segment optical coherence tomography

Purpose This study aimed to evaluate patients with keratoplasty in Tanta University Hospital using anterior segment optical coherence tomography (AS-OCT).Patients and methods This was a cross-sectional study that included 30 eyes of 22 patients who underwent keratoplasty in Tanta University Hospital from January 2016 till December 2016. The AS-OCT imaging using Topcon 3D optical coherence tomography; 3D OCT 2000(FA) was done. The preoperative pathology was corneal scarring in 16 (53.33%) eyes and advanced keratoconus in 14 (46.67%) eyes. Penetrating keratoplasty was done in 27 eyes, whereas deep anterior lamellar keratoplasty was performed in three eyes.Results Comparing the base line characteristics between the keratoconus and the corneal scar groups, statistically significant differences were detected in age (P<0.001), best corrected visual acuity (decimal) (P=0.001), spherical equivalent in diopters (D) (P=0.018), and thickness disparity at the wound interface (μm) (P=0.026). The keratoconus group was younger and had better best corrected visual acuity than the corneal scar group. The total number of graft–host interface images from 30 eyes obtained by the AS-OCT was 120 cross sections. Of these, 22 (18.33%) cross sections had well-apposed junction and 98 cross sections had malapposed junction (81.67%). Protrusion (50 cross sections; 41.67%) was the most frequent misalignment type. When classifying the eyes according to the most frequent alignment pattern among the four cross sections, five eyes had well-apposed junction state (16.67%) (all were keratoconus cases) and 25 eyes had the malapposed junction state (83.33%) (corneal scar: 16 eyes, keratoconus: nine eyes). Among the 25 eyes with malapposed junction state, 12 eyes had protrusion, seven eyes had gap, and six eyes had step.Conclusion The AS-OCT is a valuable tool for postoperative follow up of patients with keratoplasty. It helps in visualization of the internal surface of the graft–host interface. Thus, it can help in detecting the malapposition and so the cause of postoperative astigmatism can be recognized and can be managed early.

Correlations between local peripapillary choroidal thickness and axial length, optic disc tilt, and papillo-macular position in young healthy eyes.

Optical coherence tomography (OCT) has made it possible for clinicians to measure the peripapillary choroidal thickness (ppCT) noninvasively in various ocular diseases. However, the ocular factors associated with the ppCT have not been conclusively determined. The purpose of this study was to determine the relationship between the local ppCT and the axial length, optic disc tilt, and the angle of the papillo-macular position (PMP) in healthy eyes. This was a prospective, observational cross-sectional study of 119 right eyes of 119 healthy Japanese volunteers. The ppCT was manually measured at eight sectors around the optic disc using the B-scan images of the Topcon 3D OCT RNFL 3.4 mm circle scan. The trajectory of the retinal pigment epithelium in the B-scan image was fitted to a sine curve using ImageJ, and the amplitude of the sine curve was used to determine the degree of the optic disc tilt. The PMP angle was determined in the color fundus photographs. The relationships between the ppCT and the axial length, the optic disc tilt, and PMP angle were determined by Spearman and multiple correlation analyses. The mean age was 25.8 ± 3.9 years and the mean axial length was 25.5 ± 1.4 mm. The ppCT was significantly and negatively associated with the axial length (R = -0.43 to -0.24, P<0.01) and positively associated with the PMP angle (R = 0.28 to 0.37, P<0.01) in all eight circumpapillary sectors. The temporal and infratemporal ppCTs were significantly and negatively associated with the optic disc tilt (R = -0.31, -0.20, P<0.05). The results of multiple regression analyses were similar to that of Spearman correlation analysis. In conclusion, the axial length and PMP angle can affect the ppCT in all circumferential sectors, however the tilt of the optic disc is correlated with only some of the sectors. This should be remembered in interpreting the ppCT.

Structural neurodegeneration correlates with early diabetic retinopathy.

To examine differences in structural and functional neurodegenerative measurements between patients with no and early diabetic retinopathy (DR). In this cross-sectional study, we examined 103 patients with type 2 diabetes mellitus. In 7-field fundus photographs acquired with Topcon TRC-NW6S, a single, certified grader determined the presence of DR according to the Early Treatment Diabetic Retinopathy Study (ETDRS) scale. Retinal neurodegeneration was evaluated by Topcon 3D OCT-2000 spectral domain optical coherence tomography (OCT) and by a RETI-scan multifocal electroretinography (mf-ERG) system in rings 1-6. Median age and duration of diabetes were 63.6 and 10years, respectively, and 46% were men. Median HbA1c was 50mmol/mol (6.7%), and ETDRS levels were 10 (41.7%, n=43), 20 (35.0%, n=36), and 35 (23.3%, n=24). The duration of diabetes increased with higher levels of DR (p=0.04), but patients with different level of DR did not differ according to age, sex, blood pressure, HbA1c, and mf-ERG or OCT parameters. In a multiple logistic regression model, macular ganglion cell layer thickness was associated with the presence of DR (OR 1.73 per 5μm increase, 95% CI 1.06-2.85, p=0.03). Conversely, retinal nerve fibre layer thickness at optic disc was inversely related to DR (OR 0.69 per 5μm increase, 95% CI 0.51-0.95, p=0.02). There were no associations between DR and mf-ERG outcomes. In patients with type 2 diabetes, structural neurogenic characteristics were associated with DR. If confirmed by larger prospective studies, these results may indicate that a complex neurovascular interaction is an early event in the pathogenesis of DR.

Anterior lamina cribrosa surface depth in healthy Saudi females.

PurposeThis study was conducted to determine normative profile of anterior lamina cribrosa surface depth (ALCSD) in healthy Saudi females using Topcon Three-Dimensional (3D) Optical Coherence Tomography (OCT) 2000 – Spectral Domain (SD-OCT). In addition, the correlation between ALCSD and other clinical factors such as age, refractive error, intraocular pressure (IOP), central corneal thickness, anterior chamber depth, axial length, retinal nerve fiber layer thickness, and disk area was also assessed.DesignThis study was a prospective, nonrandomized, cross-sectional, observational, and quantitative study.MethodsThis study included 191 eyes of 191 healthy Saudi females from the College of Applied Medical Sciences of King Saud University. Stereoscopic disk photographs were reconstructed using Topcon 3D OCT-2000 for all subjects. ALCSD was measured at three planes (superior, middle, and inferior) and defined as the distance from Bruch’s membrane opening level (reference line) to anterior lamina cribrosa surface. Average of ALCSD at all planes was defined as mean ALCSD of the eye. Correlation between ALCSD and all the clinical factors was performed by linear regression analysis. Paired t-test was performed in order to compare ALCSD at all planes.ResultsIn this study, the average ALCSD was 371.88±114.62 μm (range, 155–647.6 μm). Paired t-test showed a significant difference between superior and middle planes (P=0.004) and middle and inferior planes (P=0.013). Using the same test, no significant difference between superior and inferior planes (P=0.820) was observed. Generally, the largest ALCSD was in the middle plane. In addition, linear regression analysis showed no significant correlation between ALCSD and associated clinical factors.ConclusionThis work is the first to provide the normative profile of ALCSD in Saudi females using Topcon 3D OCT-2000. Further studies are recommended for males, different ethnic populations, high myopic eyes, and different age groups using advanced imaging techniques such as enhanced depth imaging OCT.

Inter-visit Test-Retest Variability of OCT in Glaucoma.

To determine the inter-visit test-retest variability (TRV) of a spectral domain optical coherence tomograph, the Topcon 3D OCT-2000, in the measurement of optic nerve head topography, peripapillary retinal nerve fiber layer (pRNFL), and macular ganglion cell complex (GCC) parameters in glaucoma patients. We also examine whether TRV with this instrument varies with the extent of glaucomatous damage. Twenty-four subjects with varying degrees of glaucoma severity provided 41 eyes with usable results for the study. 3D Disc Retinal Nerve Fiber Layer Analysis and Macula V (GCC) scans were repeated 1 week apart, at the same time of day, to determine the inter-visit TRV. TRV was determined using Bland-Altman limits of agreement (LoA) and the resulting coefficients of repeatability (CR). The overall horizontal and vertical cup/disc ratio CRs were 0.05 and 0.07, respectively. The GCC CR was 2.9 μm. In contrast, average pRNFL TRV expanded with increasing damage, with the LoA being well fitted by ±(34.67 - 0.294(d)), where d is the pRNFL thickness. A more complex model, with constant LoA of ±5.61 μm at d >82 μm, and linearly expanding TRV below that, achieved marginal significance (P < .06). The repeatability of GCC measurements with this instrument was excellent. The determination of statistically significant change in average pRNFL should take into account average pRNFL thickness.

Correlations Between Retinal Nerve Fiber Layer Thickness and Axial Length, Peripapillary Retinal Tilt, Optic Disc Size, and Retinal Artery Position in Healthy Eyes

To determine the correlations between the retinal nerve fiber layer thickness (RNFLT) and the axial length, peripapillary retinal tilt (PRT), and optic disc size, and retinal artery position. A prospective, observational cross-sectional study of 119 healthy right eyes of 119 volunteers. All participants underwent comprehensive ophthalmologic examinations including peripapillary RNFLT imaging and measurements of the axial length. The RNFLT was determined by the TOPCON 3D OCT-1000, MARK II. The RNFLT in a 3.4 mm circular scan was divided into 12 clock-hour sectors and 4 quadrant sectors around the optic disc. The PRT was assessed using the RNFLT B-scan images. The angle between the supra-temporal and infra-temporal retinal arteries was determined in the color fundus photographs. The correlations between the sectorial RNFLTs and the axial length, PRT, optic disc size, and artery angles were determined by simple and multiple regression analyses. Multiple regression analyses showed that the nasal and inferior quadrants and the whole RNFLT were significantly and negatively correlated with the axial length (standardized coefficient (SC)=-0.39 to -0.30, P<0.05). The PRT was significantly and positively associated with all of the quadrants and the whole RNFLT (SC=0.22 to 0.45, P<0.05). The retinal artery angle was significantly and negatively associated with the temporal RNFLT and positively associated with inferior RNFLT (SC=-0.49 to 0.31, P<0.05). The optic disc size was significantly and positively associated with the superior and nasal quadrants, and the whole RNFLT (SC=0.20 to 0.27, P<0.05). The axial length, PRT, optic disc size, retinal artery angle can affect the peripapillary RNFLT. These variables should be considered when assessing the peripapillary RNFLT.

Comparison of choroidal thickness measurements between spectral-domain OCT and swept-source OCT in normal and diseased eyes.

PurposeSub-foveal choroidal thickness (SFCT) is affected in many ocular diseases. The aim of this study was to compare SFCT measurements between Topcon 3D 2000 spectral-domain optical coherence tomography (SD-OCT) and Topcon swept-source OCT (SS-OCT), with different laser wavelengths, in normal and diseased populations.Materials and methodsThis was a prospective, cross-sectional, noninterventional study including 27 normal volunteers and 27 participants with retinal disease. OCT scans were performed sequentially and under standardized conditions using both SD-OCT and SS-OCT. The OCT scans were evaluated by two independent graders. Paired t-tests and intraclass correlation coefficients (ICCs) were used to assess the statistically significant difference between SFCT measurements as measured by the two devices.ResultsMean SFCT measurements for all 54 participants were 264.9±103.1 μm using SD-OCT (range: 47–470 μm) and 278.5±110.5 μm using SS-OCT (range: 56–502 μm), with an inter-device ICC of 0.850. Greater variability was noted in the diseased eyes. Inter-device ICCs were 0.870 (95% CI; 0.760–0.924) and 0.840 (95% CI; 0.654–0.930) for normal and diseased eyes, respectively. However, the difference was not statistically significant (P=0.132).ConclusionBoth machines reliably measure SFCT. Larger studies are needed to confirm these findings.

Real-World Outcomes of Ranibizumab Treatment for Diabetic Macular Edema in a United Kingdom National Health Service Setting

To determine visual acuity (VA) and spectral-domain optical coherence tomography (OCT) outcomes with intravitreal ranibizumab for diabetic macular edema (DME) in a United Kingdom National Health Service clinical setting. Retrospective interventional case series. Consecutive patients with DME, treated with the first ranibizumab injection between August 2013 and March 2014 across 4 sites of Moorfields Eye Hospital, London. Two hundred eyes of 164 consecutive patients with center-involving DME and VA ≤79 ETDRS letters, central subfield macular thickness (CST) ≥350μm on Topcon 3D OCT 2000, initiated on a loading phase of 3 intravitreal ranibizumab injections and who had at least 6months follow-up were reviewed. Subsequent retreatment was guided by VA and OCT with the aim of treating to stability. VA, OCT CST, and macular volume (MV) were recorded at baseline and monthly to 12months. The mean VA, mean CST, and mean MV at baseline were 54.4 (± 15.26) letters, 490.16 (± 116.54) μm, and 10.46 (± 2.28) mm3. The mean VA change at 12months was+6.6 (± 13.35) letters (P= .0003). A total of 40.3% of patients (n= 77) gained ≥10 letters and 25.1% (n= 48) gained ≥15 letters; 8.9% (n= 17) lost ≥10 letters and 6.3% (n= 12) lost ≥15 letters. At 12months, the mean change in CST and MV were-133.9 (± 160.12) μm (P= .0001) and-1.5 (± 1.96) mm3 (P= .0001), respectively. An average of 7.2 (± 2.3) injections were given over 12months. Outcomes with 3 loading injections of 0.5mg ranibizumab given monthly followed by pro re nata retreatment in a clinical setting are comparable with outcomes from clinical trials.

Study of Macular Thickness Using Spectral Domain Optical Coherence Tomography in Healthy Indian Subjects

Purpose: To generate normative data for SD-OCT (Topcon 3D OCT 2000) estimated macular thickness in Indian eyes and establish its relation with age sex and refractive error. Materials and methods: In this cross sectional , observational, hospital based study 800 eyes of 400 healthy Indian individuals underwent a macula OCT scan using Topcon SD OCT. Macular thickness was measured in 9 ETDRS regions .The effect of age , sex , refractive error on foveal thickness was determined. Results: The mean central foveeal thickness was 226.4025 ±22.5063 μm. Males were found to have a significantly thicker macula (P< 0.05) than females with the central foveal thickness of 229.8153 ± 21.4222 vs 220.7748 ±23.14742 . Central foveal thickness was found to have very weak correlation with age which was not statistically significant. All other regions (the parafoveal and perifoveal thickness) showed statistically significant negative correlation with age. Conclusion: We provide the largest normative data for SD OCT Topcon 3D OCT 2000. We also suggest that demographic factor like gender should be considered while interpreting any OCT measurements. The normal range of central macular thickness for Indian population should be 181 µm to 270 µm for Topcon SD OCT. Age and refractive error do not show a significant correlation with central macular thickness.

Statistical Modeling of Retinal Optical Coherence Tomography.

In this paper, a new model for retinal Optical Coherence Tomography (OCT) images is proposed. This statistical model is based on introducing a nonlinear Gaussianization transform to convert the probability distribution function (pdf) of each OCT intra-retinal layer to a Gaussian distribution. The retina is a layered structure and in OCT each of these layers has a specific pdf which is corrupted by speckle noise, therefore a mixture model for statistical modeling of OCT images is proposed. A Normal-Laplace distribution, which is a convolution of a Laplace pdf and Gaussian noise, is proposed as the distribution of each component of this model. The reason for choosing Laplace pdf is the monotonically decaying behavior of OCT intensities in each layer for healthy cases. After fitting a mixture model to the data, each component is gaussianized and all of them are combined by Averaged Maximum A Posterior (AMAP) method. To demonstrate the ability of this method, a new contrast enhancement method based on this statistical model is proposed and tested on thirteen healthy 3D OCTs taken by the Topcon 3D OCT and five 3D OCTs from Age-related Macular Degeneration (AMD) patients, taken by Zeiss Cirrus HD-OCT. Comparing the results with two contending techniques, the prominence of the proposed method is demonstrated both visually and numerically. Furthermore, to prove the efficacy of the proposed method for a more direct and specific purpose, an improvement in the segmentation of intra-retinal layers using the proposed contrast enhancement method as a preprocessing step, is demonstrated.

Retinal Fibre Layer Thickness Measurement in Normal Paediatric Population in Sweden Using Optical Coherence Tomography.

Purpose. To evaluate the correlation between peripapillary retinal nerve fibre layer (RNFL) thickness and both age and refraction error in healthy children using optical coherence tomography (OCT). Patients and Methods. 80 healthy children with a mean age of 9.1 years (range 3.8 to 16.7 years) undergoing routine ocular examination at the orthoptic section of the Ophthalmology Department were recruited for this cross-sectional study. After applying cycloplegia, the peripapillary RNFL thickness was measured in both eyes using the Topcon 3D OCT 2000 device. Results. 138 eyes were included in the analysis. The average refractive error (SE) was +1.7 D (range −5.25 to +7.25 D). The mean total RNFL thickness was 105 μm ± 10.3, the mean superior RNFL thickness was 112.7 μm ± 16.5, and the mean inferior RNFL thickness was 132.6 μm ± 18.3. We found no statistically significant effect of age on RNFL thickness (ANOVA, f = 0.33, p = 0.56). Refraction was proven to have a statistically significant effect (ANOVA, f = 67.1, p < 0.05) in RNFL measurements. Conclusions. Data obtained from this study may assist in establishing a normative database for a paediatric population. Refraction error should be taken into consideration due to its statistically significant correlation with RNFL thickness.

Retinal Vascular Fractals Correlate With Early Neurodegeneration in Patients With Type 2 Diabetes Mellitus.

To investigate the correlation between the retinal vascular fractal dimension (Fd) and neurodegenerative changes in patients with no or mild diabetic retinopathy (DR). In this cross-sectional study we examined 103 patients with type 2 diabetes mellitus (T2DM) with no or mild DR. In a randomly selected eye of each patient, Fd was calculated using SIVA-Fractal, a specialized semiautomatic software. Retinal neurodegeneration was evaluated by Topcon 3D OCT-2000 spectral-domain optical coherence tomography (OCT) and by a RETI-scan multifocal ERG (mf-ERG) system in rings one to six. Level of DR was determined by a single trained grader in seven-field fundus photos according to the Early Treatment Diabetic Retinopathy Study (ETDRS) scale. Mean age and duration of T2DM were 62.3 and 11.6 years, respectively; 46.6% were men. Mean Fd was 1.413 (range, 1.278-1.509) and ETDRS levels were 10 (42.7%), 20 (35.0%), and 35 (22.3%), respectively. Fd correlated inversely with mf-ERG implicit time of ring one (r = -0.25, P = 0.01) and present diabetic neuropathy (P = 0.02), and positively with OCT ganglion cell layer (GCL) thickness (r = 0.20, P = 0.04). In a multivariable linear regression model, Fd was associated with mf-ERG implicit time of ring one (coefficient -0.0021/ms, P = 0.040) and the presence of diabetic neuropathy (coefficient -0.0209 for neuropathy present versus absent, P = 0.041). In patients with T2DM and no or minimal DR, independent correlations were found between early vascular and neurogenic changes. Thus, retinal vascular fractal analysis might be considered as a tool to identify patients with early neurodegenerative retinal changes.

Pigment epithelium central limit ‐ Inner limit of the retina, Minimal Distance, PIMD, a morphometrical variable for glaucoma follow‐up

PurposeTo establish the resolution of measurements of the minimal distance between the central limit of the pigment epithelium and the inner limit of the retina (PIMD) as measured with OCT.MethodsThe optic nerve head was topographically recorded with OCT (Topcon 3D, OCT‐2000, protocol: 6 × 6 mm 3D disc cube). The minimal distance between the inner limit of the retina and the central limit of the pigment epithelium was sampled 8 times resolved in 500 angles.ResultsThe angular minimal distance was longer in the upper and the lower meridian and averaged 0.21 mm. An analysis of the consequence of the resolution demonstrated that the minimal relevant significant average difference at α = 0.05 and aiming for β = 0.02 was 0.11 change (mm)/Average (mm). Thus, a change of 0.024 mm integrated over 2π is the detection limit at the selected statistical parameters. This corresponds to a local average change within one quadrant of 0.006 mm.ConclusionsPIMD has the potential to be a useful variable for follow‐up of nerve fiber loss in the optic nerve head.

Anatomical digital image analysis of the angle and optic nerve – a novel method for glaucoma imaging

PurposeTo devise a simple, fast and low‐cost method for glaucoma imaging using anatomical digital image analysis of the angle and optic nerve in human subjects.MethodsA pilot study included 10 open‐angle glaucoma patients attending the glaucoma services at the Department of Ophthalmology, University of Szeged, Hungary; colour photographs of the fundus, standard optic nerve images with OCT and additional digital slit lamp images of the angle where collected. Digital image conversion and analysis of the angle using Image J (NIH, USA) and adaptive histogram equalization Contrast Limited AHE (CLAHE) to prevent noise amplification. Angle and optic nerve images, were analyzed separately in the Red, Green and Blue (RGB) channels, then 3D volumetric analysis of the degrees of angle, cup volume of the optic nerve took place. Horizontal tomogram reconstitution and nerve fiber detection methods were developed and compared to a standard Topcon 3D OCT.ResultsAngle measurements from digital angle images by gonioscopy all fitted within one standard deviation of Anterior OCT measurements. Comparative analysis of RGB channels produced volumetric cup and Horizontal tomogram results closely resembling those of OCT 3D appearance and B‐scan of the cup, respectively. Similar RGB channel splitting and image subtraction produced a map closely resembling that of the thickness RNFL map on OCT.ConclusionsWhile spectral domain OCT is rapidly progressing in the area of optic disc and chamber angle assessment, rising health care costs and lack of availability of the technology, opens demand for alternative forms of image analysis of glaucoma. Volumetric, geometric and segmentational data obtained through digital image analysis correspond well to those obtained by high definition OCT imaging. A larger number of subjects is needed to further validate the method.