Optical Coherence Tomography Ophthalmoscopy Research Articles

OPTICAL COHERENCE TOMOGRAPHY- MACULA IN DIABETIC MACULAR EDEMA

Diabetic Retinopathy (DR) was the fifth most prevalent cause of preventable blindness and thefifth most common cause of moderate to severe vision impairment between 1990 ̶̶ 2010. [1] Over one-third of the worlds 285 million diabetics have indications of DR, and a third of these have vision-threatening diabetic retinopathy (VTDR), which is defined as severe non-proliferative DR or proliferative DR (PDR) or the presence of diabetic macular edema (DME)[2]. DME is becoming more common in the world, owing to increase in type 2 diabetes. DME can be assessed using intravenous fluorescein angiography (FA) and optical coherence tomography (OCT)- noninvasive imaging technique [3]. OCT is important for early diagnosis in asymptomatic patients, as well as controlling and monitoring DME, depending on which the treatment method can be changed. Spectral domain optical coherence tomography (SD-OCT), which produces high-resolution retinal pictures, has a good reproducibility in measuring retinal thickness [7]. Longitudinal retinal B-scans and coronal C-scans are produced using the OCT ophthalmoscope. As a result, it delivers information that traditional imaging techniques or fundus inspection cannot.

Structural and functional human retinal imaging with a fiber-based visible light OCT ophthalmoscope.

The design of a multi-functional fiber-based Optical Coherence Tomography (OCT) system for human retinal imaging with < 2 micron axial resolution in tissue is described. A detailed noise characterization of two supercontinuum light sources with different pulse repetition rates is presented. The higher repetition rate and lower noise source is found to enable a sensitivity of 96 dB with 0.15 mW light power at the cornea and a 98 microsecond exposure time. Using a broadband (560 ± 50 nm), 90/10, fused single-mode fiber coupler designed for visible wavelengths, the sample arm is integrated into an ophthalmoscope platform, similar to current clinical OCT systems. To demonstrate the instrument's range of operation, in vivo structural retinal imaging is also shown at 0.15 mW exposure with 10,000 and 70,000 axial scans per second (the latter comparable to commercial OCT systems), and at 0.03 mW exposure and 10,000 axial scans per second (below maximum permissible continuous exposure levels). Lastly, in vivo spectroscopic imaging of anatomy, saturation, and hemoglobin content in the human retina is also demonstrated.

Morphological study of acute zonal occult outer retinopathy (AZOOR) by multiplanar optical coherence tomography

We set out to determine whether morphological retinal changes occur in patients with acute zonal occult outer retinopathy (AZOOR). Five patients diagnosed with AZOOR were studied. They included two men and three women, with an age range of 23-51 years. Symptoms and findings were retrospectively and prospectively collected. The three-dimensional multiplanar optical coherence tomography (OCT) Ophthalmoscope was used to examine the morphology of the retina in patients who were examined between April 2000 to December 2004. Standardized full-field electroretinograms (ERGs) and multifocal ERGs (mfERGs) were recorded. All the patients reported an acute onset of visual disturbances including a decrease of central vision and photopsia. The a- and b-waves of full-field ERGs were decreased, and the mfERGs in the central area were reduced. Ophthalmoscopic examination showed no obvious fundus abnormalities. OCT Ophthalmoscopic images of a cross-sectional plane revealed hyporeflection at the level of the photoreceptor layer in the macular region in three of five patients, and presence of one or two layers in which the inner/outer segment junction of the photoreceptor layer was absent in the other two patients. En-face, constant depth C-scans, which present the image parallel to the retina, revealed an abnormal, patchy hyper-reflection in the affected eyes of two patients and in the non-affected eye in one of these two patients. The changes in OCT Ophthalmoscope B-scan images indicate morphological damage to the photoreceptors, which probably accounts for the functional alterations. The alterations in the C-scan image in the normal fellow eye of one patient suggest that morphological changes may precede symptomatic changes.

Technical Note: Method for estimating volume of subretinal fluid in cases of localized retinal detachment by OCT ophthalmoscopy

The volume of the subretinal fluid can be used to assess the condition of different types of retinal and macular disorders. The purpose of this report is to introduce a method to measure the volume of the subretinal fluid with the images of the optical coherence tomography (OCT) Ophthalmoscope in three cases of central serous chorioretinopathy and one case of retinal pigment epithelial detachment. We used the topography-mode program of the OCT Ophthalmoscope and measured the average height of the retinal detachment. By multiplying the size of the area of the retinal detachment and the average height of the retinal detachment, the volume of subretinal fluid could be determined. Examples are given to show the results of volume measurement of subretinal fluid in cases of localized retinal detachments.

Simultaneous structural and functional imaging of the macula using combined optical coherence tomography ophthalmoscope and multifocal electroretinogram

Multimodal imaging (MMI) is a new imaging technique that combines an electrophysiological test (multifocal electroretinogram) with an optical coherence tomography ophthalmoscope. MMI allows the two technologies to operate simultaneously yet independently to provide accurate correlation of macular structure and function at multiple sites. Preliminary work with MMI in patients with macular holes showed that functional deficits existed beyond the geographical area of structural alterations and that macular hole size did not always correlate with the severity of functional loss. Functional information may therefore be important when assessing prognosis in these patients. We envisage that MMI may prove a useful new tool in the assessment of many macular pathologies.

Measurement of retinal thickness from three‐dimensional images obtained from C scan images from the optical coherence tomography ophthalmoscope

One of the unique features of the optical coherence tomography (OCT) ophthalmoscope is that it can record C scan images of the retina. The purpose of this study was to determine the best recording time to measure the retinal thickness with the OCT ophthalmoscope. In addition, the accuracy of the measurements was examined by comparing the values obtained by the OCT ophthalmoscope with those obtained with the Stratus OCT Model 3000 (OCT III) assuming that the OCT III gives an accurate measurement of retinal thickness. The topography mode of the OCT ophthalmoscope was used. First, the average retinal thickness recorded with 2-s scans was compared with that recorded with 4-s scans for a recording area of 15 degreesx15 degrees. Next, the average retinal thickness recorded by the OCT ophthalmoscope was compared with that obtained by the Fast Macular Thickness program of the OCT III in patients with macular oedema. The mean retinal thickness of the central area was 208.1 microm for both 2 and 4 s recording times. The average retinal thickness obtained by the OCT ophthalmoscope was highly correlated and not significantly different from the values obtained by the OCT III. The largest differences obtained by the two instruments were seen in the parts of the retina with accumulation of hard exudates. Accurate measurements of retinal thickness can be obtained with the OCT ophthalmoscope by 2-s scans, and thus, the OCT ophthalmoscope can be a valuable instrument for clinical assessments of retinal thickness.

Hyperreflective Sign in Resolved Cotton Wool Spots Using High-Resolution Optical Coherence Tomography and Optical Coherence Tomography Ophthalmoscopy

To characterize retinal changes in areas of cotton wool spots (CWSs) using optical coherence tomography (OCT) and to determine the optical density changes of the retina after CWSs have disappeared clinically. Prospective, noninterventional, observational study. Thirty-one patients with CWSs who underwent imaging studies. The study groups included patients with CWSs resulting from diabetic retinopathy (n = 12), human immunodeficiency virus (HIV) retinopathy (n = 10), hypertensive retinopathy (n = 3), branch retinal vein occlusion (n = 3), uveitis (n = 2), and radiation retinopathy (n = 1). The single line scan mode of the StratusOCT Model 3000 (Carl Zeiss Meditec, Dublin, CA) was used for imaging of acute CWSs, CWSs 3 months after their resolution, and adjacent normal retina. A fundus photograph served as a template for localization of OCT scanning of CWSs. Retinal tissue reflectivity images were compared across lesion types and time. Additional imaging in 14 patients was performed to localize lesions better and to provide coronal OCT sections using the combined OCT and scanning laser ophthalmoscope. Changes in retinal reflectivity in areas of normal retina and retina with acute and resolved CWSs. The average reflectivity of normal retina was 58.4+/-2.1 dB, the average reflectivity in the area of active CWSs was 62.6+/-2.5 dB, and the average reflectivity in the same area after CWSs resolved was 61.0+/-2.4 dB. A significant difference (P<0.05) exists between reflectivity of normal retina and acute CWSs as well as normal retina and resolved CWSs. Acute CWSs show a hyperreflective pattern on OCT. As they become ophthalmoscopically invisible, the OCT still shows signs of hyperreflectivity in the areas of previous CWSs (hyperreflective sign). The authors observed the same phenomenon using 2 imaging machines.

Three-dimensional Imaging of Macular Holes with High-speed Optical Coherence Tomography

To demonstrate the advantages of 3-dimensional imaging of macular hole pathology using new-generation high-speed optical coherence tomography (OCT). Prospective observational case series. Twenty-one eyes from 20 consecutive patients diagnosed with a macular hole. A prototype high-speed OCT system was built based on a Fourier-domain OCT (FD OCT) technology for patient examination. The system has achieved sensitivity of approximately 98 decibels, axial resolution of approximately 4.3 mum in tissue, and an acquisition rate of approximately 18,700 axial scans per second. Three-dimensional imaging of macular hole pathology was performed based on a raster scan protocol consisting of 256x256 axial scans. All patients were imaged with 3-dimensional OCT, Stratus OCT, and OCT Ophthalmoscope C7. Images of macular hole pathologies obtained by 3-dimensional OCT and standard OCT instruments. The 3-dimensional OCT imaging successfully generated realistic 3-dimensional images of the vitreofoveal interface and intraretinal microstructures associated with a macular hole. The 3-dimensional overview of the vitreofoveal interface was helpful in gaining an immediate understanding of the dynamic interactions of the vitreous and fovea. Observations of consecutive en face images in combination with conventional longitudinal images and of cross-sectional images in combination with sectioned volume images enabled identification of intraretinal microstructures and their 3-dimensional extension associated with a macular hole, such as subfoveal structural changes after vitreous traction, connection of the flap to intraretinal structures, the external limiting membrane (ELM) and its disruption, and elevated photoreceptor inner and outer segments delineated by the ELM. The appearance of inner-wall images of a macular hole produced by photoreceptor inner and outer segment backreflection varied throughout macular hole stages. Three-dimensional imaging of macular holes with high-speed OCT based on FD OCT technology offers 3-dimensional overviews that facilitate understanding of the abnormalities in the vitreofoveal interface. It also provides consecutive orthogonal images that allow much more precise and minute observation of 3-dimensionally extending intraretinal structural changes associated with a macular hole than conventional OCT imaging, especially in the photoreceptor inner and outer segments.

Morphologic Features of Group 2A Idiopathic Juxtafoveolar Retinal Telangiectasis in Three-Dimensional Optical Coherence Tomography

To investigate morphologic features of group 2A idiopathic juxtafoveolar retinal telangiectasis (IJRT) with three-dimensional optical coherence tomography (OCT). Observational case series. We performed OCT ophthalmoscopy on six eyes of three consecutive patients with group 2A IJRT. Thin cystic low-intensity space within inner and outer retinal layers was detected with the longitudinal B-scan through the fovea in five eyes. Partial loss of highly reflective line considered as the boundary between photoreceptor inner segments and outer segments was also detected. The transverse C-scan provided en-face images of the low-intensity space shown with the B-scan, if not entirely. These morphologic alterations appeared not to correspond with the staining observed in the late phases of fluorescein angiography. The OCT ophthalmoscope could visualize morphologic alterations indicating degeneration or atrophy of neurosensory retina, including photoreceptor layers. These alterations may play a role in the pathogenesis of group 2A IJRT.

IMAGING THE RETINA BY EN FACE OPTICAL COHERENCE TOMOGRAPHY

To present the possibilities of a new system that combines optical coherence tomography (OCT) and confocal ophthalmoscopy, producing en face OCT images in patients with retinal diseases. A prototype OCT Ophthalmoscope (OTI, Toronto, Canada) was used to scan patients with retinal conditions. The system uses a super luminescent diode (lambda = 820 nm; Deltalambda = 20 nm) and currently scans at a rate of 2 frames per second. In each frame, the OCT Ophthalmoscope simultaneously produces a transversal OCT scan and a confocal image in the X/Y plane. Both images correspond pixel to pixel. Between January 2002 and August 2003, >800 patients with various retinal diseases were scanned with the OCT Ophthalmoscope. Illustrative cases with regularly seen macular diseases are presented, such as macular hole and central serous retinopathy. Current difficulties as well as future possibilities of this new en face OCT ophthalmoscope are discussed. By presenting normal and pathologic transversal OCT images made by a prototype OCT Ophthalmoscope, we show that it can provide information not available using conventional OCT imaging.

Ophthalmic fundus imaging: today and beyond

PurposeTo review and update techniques of posterior segment ophthalmic fundus imaging. DesignLiterature review and collective experience of the authors. MethodsThis perspective includes sections on digital imaging, fundus autofluorescence, ultrasonography, angiography, and optical coherence tomography (OCT) -ophthalmoscopy written by leading clinicians and researchers in these areas. ResultsDigital angiography has become the new standard in the ophthalmic community based upon improved technology which has enhanced resolution, processing time, and ease of image duplication, manipulation, and transmission. A relatively new imaging technique, fundus autofluorescence, highlights lipofuscin deposits and improves our understanding of the metabolic status of the retinal pigment epithelium. Diagnostic ultrasonography continues to be a major adjunct to ocular evaluation where advances now allow for exceptional versatility and portability. High speed angiographic techniques provide detailed visualization of choroidal perfusion which improves our understanding of both normal and pathologic vascular phenomenon. Advances in high-resolution OCT currently under development promise an even more detailed fundus representation. The integration of the scanning laser ophthalmoscope and OCT has produced a dynamic new instrument, the OCT ophthalmoscope, which simultaneously images the fundus in numerous ways with point to point correlation. ConclusionsOphthalmic imaging technology has revolutionized fundus examination. Currently available systems have contributed significantly to our understanding of the pathophysiology and treatment of various retinal diseases. Future advances promise near histologic resolution of retinal structures as well as real-time image manipulation and instantaneous transmission world-wide.