Hyporeflective Band Research Articles

Multimodal imaging of the retina and choroid in healthy Macaca fascicularis at different ages

PurposeThe aim of this study was to identify the morphological features of the retina and choroid in Macaca fascicularis of different ages using multimodal imaging.MethodsA total of 27 Macaca fascicularis with no ocular diseases were studied (mean age, 104.2 months; range, 1.2–223.6 months). Multimodal imaging was obtained from each subject. The morphological features were compared within four subgroups according to age.ResultsOn spectrum-domain optical coherence tomography (SD-OCT), four hyper-reflective bands could be observed in the outer retina in non-infant macaques (21/21, 100%), while the interdigitation zone could not be observed in the six infant macaques. A narrow hypo-reflective band just posterior to the retinal pigment epithelium (RPE) was noted in most eyes (25/27, 92.6%). The choroidal–scleral junction (CSJ) was visible in 83.3% of infants but only in 12.5% of adults and 14.3% of the geriatric population, and it could not be seen in juveniles. There was a significant difference in CSJ visibility between the infant group and the other three groups (P < 0.001). Tessellated fundus, in which the choroidal vessels are visible through the retina, could be observed clearly with near-infrared reflectance imaging (NIR). Some granular spots were noted in juveniles, and they accumulated dramatically with age, but were absent in infants.ConclusionNotable morphological features can be observed in the Macaca fascicularis subjects using multimodal imaging, and these features vary distinctly according to their age. It is important to note that infant macaques had no interdigitation zone, while the other macaques had no visible CSJ but did have well-defined choroidal capillaries. Age and the features should be considered seriously in future animal studies.

Mitochondrial Respiration in Outer Retina Contributes to Light-Evoked Increase in Hydration In Vivo.

PurposeTo test the hypothesis that mitochondrial respiration contributes to local changes in hydration involved in phototransduction-driven expansion of outer retina, as measured by structural responses on optical coherence tomography (OCT) and diffusion magnetic resonance imaging (MRI).MethodsOxygen consumption rate and mitochondrial reserve capacity of freshly isolated C57BL/6 and 129S6/SvEvTac mouse retina were measured using a Seahorse Extracellular Flux Analyzer. Light-stimulated outer retina layer water content was determined by proton density MRI, structure and thickness by ultrahigh-resolution OCT, and water mobility by diffusion MRI.ResultsCompared with C57BL/6 mice, 129S6/SvEvTac retina demonstrated a less robust mitochondrial respiratory basal level, with a higher reserve capacity and lower oxygen consumption in the light, suggesting a relatively lower production of water. C57BL/6 mice showed a light-triggered surge in water content of outer retina in vivo as well as an increase in hyporeflective bands, thickness, and water mobility. In contrast, light did not evoke augmented hydration in this region or an increase in hyporeflective bands or water mobility in the 129S6/SvEvTac outer retina. Nonetheless, we observed a significant but small increase in outer retinal thickness.ConclusionsThese studies suggest that respiratory-controlled hydration in healthy retina is linked with a localized light-evoked expansion of the posterior retina in vivo and may serve as a useful biomarker of the function of photoreceptor/retinal pigment epithelium complex.

Correlation of spectral domain optical coherence tomography with histology and electron microscopy in the porcine retina

Spectral domain optical coherence tomography (SD-OCT) is used as a non-invasive tool for retinal morphological assessment in vivo. Information on the correlation of SD-OCT with retinal histology in the porcine retina, a model resembling the human retina, is limited. Herein, we correlated the hypo- and hyper-reflective bands on SD-OCT with histology of the lamellar architecture and cellular constituents of the porcine retina. SD-OCT images were acquired with the Heidelberg Spectralis HRA + OCT. Histological analysis was performed using epoxy resin embedded tissue and transmission electron microscopy. Photomicrographs from the histologic sections were linearly scaled to correct for tissue shrinkage and correlated with SD-OCT images. SD-OCT images correlated well with histomorphometric data. A hyper-reflective band in the mid-to-outer inner nuclear layer correlated with the presence of abundant mitochondria in horizontal cell processes and adjacent bipolar cells. A concentration of cone nuclei corresponded to a relative hypo-reflective band in the outer portion of the outer nuclear layer. The presence of 3 hyper-reflective bands in the outer retina corresponded to: 1) the external limiting membrane; 2) the cone and rod ellipsoid zones; and 3) the interdigitation zone of photoreceptor outer segments/retinal pigment epithelium (RPE) apical cell processes and the RPE. These correlative and normative SD-OCT data may be employed to characterize and assess the in vivo histologic changes in retinal vascular and degenerative diseases and the responses to novel therapeutic interventions in this large animal model.

Cellular Characterization of OCT and Outer Retinal Bands Using Specific Immunohistochemistry Markers and Clinical Implications

OCT has been a technological breakthrough in the diagnosis, treatment, and follow-up of many ocular diseases, especially retinal and neuro-ophthalmologic pathologic conditions. Until now, several controversies have arisen over the specific cell types that the bands observed in the OCT represent, especially over the 4 outer retinal bands. To correlate the 4 outer hyperreflective bands observed in the OCT with the histologic structures using human retinal sections and immunocytochemistry at the fovea level. Eyes from human donors. Vertical cryosections of human retinas were immunostained with antibodies specific for cones photoreceptors, bipolar cells, mitochondria, Müller cells, and retinal pigment epithelium (RPE) cells and were visualized using confocal microscopy. Morphological correlation between histology and OCT at the fovea level. Triple immunolabeling allowed distinguishing between cells types and different cell compartments. Immunostaining with guanine nucleotide-binding protein β 3 (GNB3) and cellular retinaldehyde-binding protein (CRALBP) antibodies showed all retinal layers at the foveola, especially the separation between the outer nuclear layer and the Henle fiber layer. CRALBP and cytochrome C (Cyt C) immunolabeling revealed that hyperreflective bands 1 and 2, observed in the OCT, correspond to the outer limiting membrane and the cone ellipsoids, respectively, separated by the cone myoids. CRALBP, cytochrome C, and GNB3 showed that the RPE interdigitations extend along the entire external segment of the cones, we do not believe them to be the structure responsible for forming the third band. However, the identification of small fragments of cone outer segments within the RPE led us to characterize the third band as the cone phagosomes located in the top of the RPE. Finally, we propose that the fourth band corresponds to the accumulation of mitochondria at the basal portion of the RPE, as identified by cytochrome C immunoreactivity, and that the hyporeflective band between bands 3 and 4 corresponds to the RPE nuclei and melanosomes zone. This study proposes a new interpretation of the outer retinal bands that leads to a moreaccurate interpretation of OCT images, providing information about the health of cones and their relationshipwiththe RPE, and could help to form a better understanding of retinal disease diagnosis and prognosis.

Light-Induced Thickening of Photoreceptor Outer Segment Layer Detected by Ultra-High Resolution OCT Imaging.

PurposeWe examined if light induces changes in the retinal structure that can be observed using optical coherence tomography (OCT).MethodsNormal C57BL/6J mice (age 3–6 months) adapted to either room light (15 minutes to ∼5 hours, 50–500 lux) or darkness (overnight) were imaged using a Bioptigen UHR-OCT system. Confocal histologic images were obtained from mice killed under light- or dark-adapted conditions.ResultsThe OCT image of eyes adapted to room light exhibited significant increases (6.1 ± 0.8 μm, n = 13) in total retina thickness compared to the same eyes after overnight dark adaptation. These light-adapted retinal thickness changes occurred mainly in the outer retina, with the development of a hyporeflective band between the RPE and photoreceptor-tip layers. Histologic analysis revealed a light-evoked elongation between the outer limiting membrane and Bruch's membrane from 45.8 ± 1.7 μm in the dark (n = 5) to 52.1 ± 3.7 μm (n = 5) in the light. Light-adapted retinas showed an increase of actin staining in RPE apical microvilli at the same location as the hyporeflective band observed in OCT images. Elongation of the outer retina could be detected even with brief light exposures, increasing 2.1 ± 0.3 μm after 15 minutes (n = 9), and 4.1 ± 1.0 μm after 2 hours (n = 6). Conversely, dark-adaptation caused outer retinal shortening of 1.4 ± 0.4 μm (n = 7) and 3.0 ± 0.5 μm (n = 8) after 15 minutes and 2 hours, respectively.ConclusionsLight-adaption induces an increase in the thickness of the outer retina and the appearance of a hyporeflective band in the OCT image. This is consistent with previous reports of light-induced fluid accumulation in the subretinal space.

Swept Source optical coherence tomography of choroidal nevi

ObjectiveThe aim of this article is to report on retinal and choroidal morphology in choroidal nevi documented with Swept Source optical coherence tomography (SS-OCT). DesignThis is a retrospective, observational study. ParticipantsWe included 27 consecutive patients with choroidal nevi. Mean age was 66.3 years (21–95 years). MethodsThe SS-OCT scanning protocol consisted of a single line scan through the centre of the nevi with a resolution of 3 µm, built from 1024 A-scans, with a length of 12 mm. We attempted to visualize the outer choroidoscleral boundary and suprachoroidal layer (SCL) below the choroidal nevus and to observe any other defects of retinal or choroidal morphology. ResultsIn all cases, we observed that the inner margin of benign tumours was separated from the retinal pigment epithelium with a hyporeflective band. Melanotic nevi cast partial (41%) or complete shadow (41%) on the underlying structures. The outer choroidoscleral boundary was visible under the tumour in 8 eyes (25%). SCL and suprachoroidal space were noted in 40% of eyes in close proximity to the lesion, but in no case were these lines visible directly below the lesion. Thinning of the choriocapillaries was observed in 8 eyes (25%) and thinning of the choroid in 5 eyes (15.6%). ConclusionsUsing SS-OCT, we observed that the inner border of benign choroidal lesions was always situated below a hyporeflective band, possibly corresponding to the choriocapillaries. A new finding was that we observed the SCL in 40% of cases. This was always visible in close proximity to the nevus, never directly below it.

Correlation of Type 1 Neovascularization Associated With Acquired Vitelliform Lesion in the Setting of Age-Related Macular Degeneration

To correlate postmortem histology with previously recorded multimodal imaging from a patient with type 1 neovascularization (NV) associated with an acquired vitelliform lesion in the setting of age-related macular degeneration (AMD). Case study. Multimodal imaging that was obtained antemortem was matched with exvivo and high-resolution histologic images of the preserved donor macula. Anatomic correlates for multimodal imaging findings were then defined. Spectral-domain optical coherence tomography (OCT) revealed a split in the retinal pigment epithelium-Bruch membrane band. Type 1 NV in this case was composed of 6 layered components: (1) retinal pigment epithelium, (2) basal laminar deposits, (3) fibrovascular membrane, (4) fibrocellular scar, (5) hemorrhage, and (6) Bruch membrane. The anatomic correlates for the hyporeflective band on spectral-domain OCT included a thick basal laminar deposit. Not all structures could be readily separated on the basis of their reflectivity patterns. This is an important clinicopathologic correlation of NV secondary to AMD in the spectral-domain OCT era. Our findings of 6 layers include and extend the anatomic framework encapsulated by the double-layer and triple-layer signs. The resolution of current devices does not always permit distinction of the different layers of NV tissue. Thick basal laminar deposits may appear hyporeflective on spectral-domain OCT and may be confused with fluid from a neovascular process. It will be important to perform a larger clinicopathologic series to aid our anatomic interpretation of spectral-domain OCT images.

Prevalence and characteristics of hyporeflective preretinal tissue in vitreomacular interface disorders

AimsTo assess prevalence and characteristics of hyporeflective preretinal tissue on spectral domain optical coherence tomography (SDOCT) in eyes with vitreomacular interface disorders.Methods4037 eyes (3195 patients) with diagnosis of lamellar macular...

Suprachoroidal layer and suprachoroidal space delineating the outer margin of the choroid in swept-source optical coherence tomography.

To define the morphology of outer choroidal margins in swept-source optical coherence tomography. This is a prospective observational study of 180 eyes: 20 eyes of healthy volunteers, 20 eyes of myopic patients, and 20 eyes from each of the following groups: macular hole, lamellar macular hole, epiretinal membranes, drusen, dry age-related macular degeneration (AMD), neovascular AMD, and vitreomacular traction. A single 12-mm wide swept-source optical coherence tomography image for each of the examined eyes consisting of 1,024 A-scans has been created. The main outcome measure selected was to estimate the presence of suprachoroidal layer, as well as to estimate the ability to delineate the outer choroidoscleral boundary using the software available (DRI-OCT) and to determine its shape. Suprachoroidal layer was observed in 5% of healthy emmetropic eyes, in 50% of eyes with full-thickness macular holes, and in 60% of eyes with vitreomacular traction syndrome. It was also present in 50% of eyes with dry AMD and in 20% of eyes with neovascular AMD. The outer margin of the choroid in all eyes of the healthy volunteers and in eyes with macular diseases has been delineated correctly. In all healthy and myopic eyes, we recognized the outer choroidoscleral boundary as having a regular shape following the natural oval contour of the globe. In eyes with epiretinal membranes, macular hole, vitreomacular traction, and AMD, the outer choroidoscleral boundary was irregular; the choroid varied in thickness from point to point. Swept-source optical coherence tomography enables exact visualization of the outer choroidoscleral boundary. Suprachoroidal layer consisting of two bands has been recognized, the upper of which is hyperreflective and the lower of which is hyporeflective. It may be supposed that the lower hyporeflective band corresponds to suprachoroidal space, which was not earlier visualized in vivo in eyes without choroidal effusion. Suprachoroidal layer in myopic and emmetropic healthy subjects has been rarely observed. We observed it more frequently in different macular diseases.

Optical coherence tomogram and demographic profile in central retinal artery occlusion: A South Indian study

Aim: To describe the demographic profile and optical coherence tomography (OCT) findings in patients with central retinal artery occlusion (CRAO). Materials and Methods: Thirty-eight patients with CRAO who presented to Vitreo Retina Department at Minto Ophthalmic Hospital between January 2009 and December 2013 were studied. All the patients underwent detailed ophthalmic examination including OCT and routine laboratory investigations. All patients were subjected to cardiac evaluation. Results: In our study, 27 (71%) were males and 11 (29%) were females. The average age of our patients was 44.8 years (range 25-65 years). Seven patients had diabetes, and six had hypertension. Seven (18%) patients had CRAO with sparing of the cilioretinal artery. History of smoking was present in 15 (56%) of males with an average duration of 16.9 years. OCT showed average central macular thickness of 288.2 mm in acute stage and 163.75 mm in chronic stage. Conclusion: CRAO had varying etiologies but had similar clinical findings and OCT features. In our study, smoking was found to be the most common association in males. CRAO was also seen in younger age groups too. In all cases, OCT in acute stage shows increased reflectivity of inner retina and a hyporeflective band and in chronic stage thinning of sensory retinal layer. OCT findings were similar irrespective of the etiology.

Optical Coherence Tomography–Defined Changes Preceding the Development of Drusen-Associated Atrophy in Age-Related Macular Degeneration

To characterize the pathological changes preceding the development of drusen-associated atrophy in eyes with age-related macular degeneration (AMD) using spectral-domain optical coherence tomography (SD-OCT). Longitudinal and cross-sectional retrospective observational study. A total of 181 participants with intermediate AMD in at least 1 eye (141 unilateral, 40 bilateral) were assessed longitudinally. A total of 230 participants with bilateral intermediate AMD (40 longitudinalparticipants with an additional 190 participants) were analyzed cross-sectionally. Spectral-domain OCT, color fundus photography (CFP), near-infrared reflectance, and fundus autofluorescence imaging were performed in all participants at cross-section and every 3 months for up to 30 months in the longitudinal study. Spectral-domain OCT volume scans were examined for features that portend the development of drusen-associated atrophy, and the topography, prevalence, and risk factors of these features were determined through cross-sectional analysis. The pathological features on SD-OCT preceding the development of drusen-associated atrophy and the characteristics of these features. Twenty areas from 16 eyes of 16 participants developed drusen-associated atrophy after an average of 20 months (range, 8-30 months). Spectral-domain OCT features unique in these areas included: subsidence of the outer plexiform layer (OPL) and inner nuclear layer (INL), and development of a hyporeflective wedge-shaped band within the limits of the OPL. These characteristics were termed "nascent geographic atrophy" (nGA), describing features that portend the development of drusen-associated atrophy. Cross-sectional examination of participants with bilateral intermediate AMD revealed that independent risk factors for the presence of nGA included the presence of pigmentary changes (odds ratio [OR], 16.84; 95% confidence interval [CI], 2.42-117.24) and nGA in the fellow eye (OR, 4.15; 95% CI, 1.12-15.34); nGA was present in 21.9% ofparticipants with drusen >125 μm and pigmentary changes in both eyes. This study identified pathological changes occurring before the development of drusen-associated atrophy using SD-OCT, which we defined as nGA. Although nGA is undetectable on CFP, it is important for determining the risk of future vision loss in AMD and could be used as an earlier surrogate end point in interventional trials targeting the early stages of AMD.

Characterization of the Choroid-Scleral Junction and Suprachoroidal Layer in Healthy Individuals on Enhanced-Depth Imaging Optical Coherence Tomography

Accurate measurements of choroidal thickness (CT) using enhanced-depth imaging optical coherence tomography (EDI-OCT) require a well-defined choroid-scleral junction (CSJ), which may appear in some eyes as a hyporeflective band corresponding to the suprachoroidal layer (SCL). To identify factors associated with the presence and thickness of the SCL in healthy participants and determine how different CSJ boundary definitions impact CT measurements. Secondary analysis of EDI-OCT images obtained prospectively from 74 eyes of 74 controls (mean age, 68.6 years) from the Age-Related Eye Disease Study 2 Ancillary SDOCT Study. The CSJ appearances were categorized as either having no visible SCL or a hyporeflective band corresponding to the SCL. Ocular parameters associated with the presence and thickness of the SCL were identified. Subfoveal CT was measured using 3 different posterior boundaries: (1) the posterior vessel border (vascular CT [VCT]), (2) inner border of the SCL (stromal CT [StCT]), and (3) inner border of the sclera (total CT [TCT]). Manual segmentation using custom software was used to compare VCT, StCT, and TCT across the macula. RESULTS The SCL was visible in 33 eyes (44.6%). Factors associated with SCL presence and thickness included hyperopic refractive error (R2 = 0.123; P = .045) and increased TCT (R2 = 0.215; P = .004), but not age, visual acuity, intraocular pressure, retinal foveal thickness, VCT, or StCT. In eyes where the SCL was not visible, mean [SD] subfoveal VCT was 222.3 [101.5] μm and StCT and TCT were 240.0 [99.0] μm, with a difference of 17.7 [16.0] μm (P < .001). In eyes where the SCL was visible, mean [SD] subfoveal VCT, StCT, and TCT were 221.9 [83.1] μm, 257.7 [97.3] μm, and 294.1 [104.8] μm, respectively, with the greatest difference of 72.2 [30.4] μm between VCT and TCT (P < .001). All 3 CT measurements were significantly different along all points up to 3.0 mm nasal and temporal to the fovea. A hyporeflective SCL is visible at the CSJ on EDI-OCT in nearly half of healthy individuals, and its presence correlates with hyperopia. Different posterior boundary definitions may result in significant differences in CT measurements and should be explicitly identified in future choroidal studies and segmentation algorithms.

Hyperautofluorescence in outer retinal layers thinning.

Purpose. To evaluate if paracentral hyperautofluorescence (HAF) retinal regions, which can be occasionally found and analyzed by optical coherence tomography (OCT), were related to retinal layer changes and to detect which layer was involved. Methods. This is a cross-sectional and retrospective study. 648 OCT files were revised. OCTs that showed a paracentral HAF area by using the fundus autofluorescence imaging in Heidelberg Spectralis (Heidelberg Engineering, Germany) were selected. Then retinal layer morphology was analyzed observing OCT scans and a retinal thickness was measured. Results. 31 patients were selected: 20 patients had chronic serous epitheliopathy (CSE), 8 patients had resolved central serous chorioretinopathy (CSC), and 3 patients wet age related macular degeneration (ARMD). The HAF zones corresponded to areas of thickness reduction of the external hyporeflective band. In all these areas the retinal pigment epithelium was not atrophic and the neuroepithelium was more or less dystrophic. In particular the retinal thickness was 264 um, 232 um, and 243 um in wet ARMD, CSE, and CSC, respectively; the reduction was significant (P < 0.01) compared to the same area of the other eye. Discussion. The presence of HAF imaging might be mostly due to a “window effect” rather than an accumulation of lipofuscin.

Hyporeflective Wedge-Shaped Band in Geographic Atrophy Secondary to Age-related Macular Degeneration: An Underreported Finding

To describe and interpret the frequently observed spectral-domain optical coherence tomography (SD-OCT) finding of a marked hyporeflective wedge-shaped structure at the boundaries of the areas of atrophy. A prospective, longitudinal follow-up study. Consecutive patients (n = 71) 50 years of age and older with geographic atrophy (GA) secondary to age-related macular degeneration (AMD) were examined between January 2010 and June 2011. Patients were evaluated with the use of imaging techniques that included 35° fundus photography, infrared, fundus autofluorescence (FAF), and SD-OCT. Visualization of the fundus with FAF was done simultaneously with OCT. Two acquisition protocols were followed: a macular cube for coverage (19 horizontal B-scans centered on the fovea) and high-resolution horizontal B-scan for qualitative foveal detail. Estimation of the prevalence of a hyporeflective wedge-shaped band among patients with GA. A marked hyporeflective wedge-shaped structure, with its base on Bruch's membrane and its apex pointing toward the inner limit of the outer plexiform layer (OPL) adjacent to the margin between the atrophied area and the preserved retina, was observed in 72.9% of eyes (70/96; 95% confidence interval, 63.9-82.0). This hyporeflective band appeared to be within the OPL. Using eccentric SD-OCT acquisition, the boundaries between the outer nuclear layer (ONL) and Henle's fiber layer (HFL) were well defined, showing that the ONL ends before the margin of atrophy of the retinal pigment epithelium (RPE). A narrow hyperreflective band separated the margin of the ONL and RPE from the hyporeflective band, already within the atrophic area. A hyporeflective wedge-shaped structure appears frequently within the boundaries of the OPL in patients with GA secondary to AMD, corresponding to an increase in the width of the HFL, presumably because of axonal swelling or interaxonal edema. This finding may improve the interpretation of SD-OCT images of the outer layers, may help in understanding better the interactions between photoreceptor cells and the RPE, and may help in the development of monitoring techniques and therapies for GA secondary to AMD.

Novel Corneal Phenotype in a Patient With Alport Syndrome

To report the clinical and histopathologic findings of an unusual keratopathy, which may represent a new corneal dystrophy in a patient with Alport syndrome (ATS). A 59-year-old woman with longstanding diagnosis of autosomal recessive ATS was evaluated for progressively decreasing vision in the left eye. She had anterior lenticonus and cataract and central corneal stromal opacification with significant thinning and flattening bilaterally. She underwent penetrating keratoplasty and cataract extraction with posterior chamber intraocular lens implantation. We describe the light microscopic and ultrastructural findings from the cornea. Histopathology of the corneal button revealed marked stromal thinning with decreased keratocytes. The endothelial cells were attenuated and focally lost. Immunohistochemical stains for cytokeratin were positive, findings consistent with posterior polymorphous dystrophy (PPMD). Transmission electron microscopy showed necrosis and a marked loss of keratocytes. Multilayering of the endothelium was consistent with PPMD, but mature desmosomes and microvilli were absent. In vivo confocal microscopy on the fellow eye showed linear hyporeflective bands at the level of Descemet's membrane consistent with PPMD. In addition, there were fine linear changes in the deep stroma and diffuse hyperreflectivity of the mid and superficial stroma with lack of identifiable keratocytes throughout. We believe this to be the first reported case to demonstrate some histopathologic features of PPMD in ATS. However, the clinical, histopathologic, and ultrastructural characteristics are not typical of PPMD. This may represent a new phenotypic expression of PPMD or may be a distinct clinicopathologic dystrophy associated with ATS.

Tomografía óptica de coherencia en oclusión de arteria central de la retina

Three eyes with central retinal artery occlusion (CRAO) have been studied. Optical coherence tomography (OCT) was performed in each of them. Ophthalmoscopic signs of CRAO were equivocal in the three eyes. However, the presence of a hyporeflective signal in the OCT scan could be seen clearly in each of them. The presence of a hyporeflective band between the neurosensory retina and the retinal pigment epithelium in OCT images, that persist for several months after a CRAO episode, is useful in establishing the diagnosis in these patients.

Correlation of endoscopic optical coherence tomography with histology in the lower-GI tract

Optical coherence tomography (OCT), a noninvasive optical imaging technique, provides high-resolution cross-sectional images of tissue microstructure. We developed a system for real-time endoscopic OCT (EOCT) of the human GI tract. During clinical trials, the structure of mucosa and submucosa, glands, blood vessels, pits, villi, and crypts was observed in a range of GI organs. Although EOCT images are thought to accurately depict actual histologic features, there are few data to support this assumption. Therefore, the present study correlated images acquired with an EOCT imaging system in vitro to corresponding histologic sections. EOCT images were obtained of fresh specimens of ileum, colon, and rectum that then were fixed in formalin and were processed for microscopic evaluation by using standard methods. The thickness of mucosa and of submucosa was determined for both EOCT images and histologic slides. The first hyper-reflective layer in the EOCT images was identified as mucosa. A close correlation (R 2=0.84) was observed between EOCT and histology. Furthermore, the submucosa and the muscularis propria could be identified as the next deepest hyporeflective band and a hyper-reflective layer, respectively, in EOCT images. The submucosa was found to be more compressible than mucosa, and its EOCT appearance was dependent on its content of adipose tissue. EOCT provides images that precisely correlate with the histologic structure of the mucosa and the submucosa of the GI tract.