Imaging Vitreomacular Interface Abnormalities in the Coronal Plane by Simultaneous Combined Scanning Laser and Optical Coherence Tomography

Imaging Vitreomacular Interface Abnormalities in the Coronal Plane by Simultaneous Combined Scanning Laser and Optical Coherence Tomography A. M. Tammewar; D-U Bartsch; I. Kozak; R. Rosen; I. A. Falkenstein; P. Garcia; W. R. Freeman Published: 04/14/2009Abstract Aim: To describe vitreoretinal imaging of eyes with vitreomacular abnormalities using high-resolution coronal-plane optical coherence tomography (OCT) scanning combined with simultaneous scanning laser ophthalmoscope (SLO) imaging. Methods: A SLO-OCT (OTI, Canada) was used to scan 835 eyes in 736 patients with vitreomacular interface abnormalities including epiretinal membranes, macular hole, incomplete posterior vitreous detachment, vitreomacular traction syndromes and diabetic and cystoid macular oedema in a retrospective study. The longitudinal-B scan images and the transverse -C scan images in the coronal plane were used to describe vitreomacular interface abnormalities. The SLO-OCT simultaneously produces a confocal image of the retina. Results: The longitudinal "B" scan and en-face "C" scan images allowed identification of tractive forces of epiretinal membrane, contour of the hyaloid membrane and changes in inner retinal surface. A simultaneously obtained OCT scan and SLO image of the fundus offered exact co-localisation of retinal structures and vitreomacular interface abnormalities. Conclusion: Scanning the vitreomacular interface by using combined OCT and SLO enables the visualisation and better understanding of various vitreomacular interface abnormalities, due to the ability to colocalise pathology on OCT with retinal vascular landmarks and the ability to visualise pathology from a new perspective, coronal plane parallel to retinal surface. Introduction Optical coherence tomography (OCT) is now a widely used imaging technique in ophthalmology to diagnose various macular and optic nerve conditions since its first report in 1991.[1] Optical coherence tomography achieves two-dimensional cross-sectional imaging of tissue by measuring the echo delay and intensity of back-reflected infrared light from internal tissue structures.[2] Optical coherence tomography enables the direct real-time imaging of retinal pathology that could not previously be visualised in vivo, and so it is described as a non-invasive optical biopsy of the retina.[3] Since the introduction of commercial OCT in 1996, OCT technology has undergone multiple generations of improvement. OCT has been largely used to create longitudinal images of the eye (analogous to ultrasound B-scan images), which are in-depth measurement through the retina,[4] "i.e. images in the plane (X, Z) or (Y, Z) with the "Z" axis normal to the patient's face." Podoleanu et al, reported an OCT system capable of producing both transverse (en-face) and longitudinal images from the retina in living eye. They developed the combined system of confocal scanning laser ophthalmoscopy to obtain the high-resolution transverse image of retina (fundus view) and OCT to obtain cross-sectional transverse and longitudinal scans.[5,6] This system produces en-face OCT images and a pixel-to-pixel corresponding transverse image of retina provided by the confocal channel simultaneously to compare them directly.[7,8] This is achieved by selective capture of different orientations of OCT images at precise points on the confocal image. The optical source used in this combined system of OCT and confocal scanning laser ophthalmoscopy is similar to that in conventional high-resolution longitudinal OCT (Stratus OCT, Carl Zeiss Meditec, Dublin, California), so the depth resolution obtained is also the same, that is 10-15 µm.[9,10] The recent introduction of several commercial spectral-domain OCT devices has allowed ophthalmologists to obtain three-dimensional high-resolution OCT data.[11-13]  In this pilot study, we present the clinical evaluation of various vitreomacular (VM) interface abnormalities by using this novel system of combined scanning laser ophthalmoscope and optical coherence tomography. Our purpose is to show examples of visualisation of VM interface pathology in eyes with epiretinal membrane (ERM), VM traction syndrome, macular hole, incomplete posterior vitreous detachment (PVD) and cystoid macular oedema due to VM interface abnormalities like ERM and diabetic macular oedema in the coronal plane (en-face view). Patients and Methods We used scanning laser ophthalmoscope optical coherence tomography (SLO-OCT; OTI, Toronto, Ontario, Canada) to scan patients with VM interface abnormalities including epiretinal membrane, macular hole, incomplete (shallow) posterior vitreous detachment, VM traction syndrome, diabetic macular oedema (DME) and cystoid macular oedema (CMO). The SLO-OCT combines optical coherence tomography and confocal ophthalmoscopy. The system uses a super-luminescent diode emitting at a central wavelength of 820 nm with a bandwidth of 20 nm. The light beam is split, directing one part to the patient's eye (sample arm) and the other part to the reference arm (mirror). The returning light beams both from the patient's eye and the reference arm are collected through an interferometer to produce an OCT signal. A fraction of the light returning from the patient's eye is also directed towards another detector to produce a confocal signal, so that both images in the confocal and OCT channels correspond strictly in a pixel-to-pixel manner. The OCT ophthalmoscope produces both transverse and longitudinal scans. The transverse scans or "C" scans are produced in the X-Y plane at a fixed "Z" coordinate. The system produces OCT "C" scans (ie, coronal scans) parallel to the retinal surface by changing the "Z" coordinate. The SLO-OCT also produces longitudinal "B" scan images by making en-face "A" scans along a fixed axis in the X-Y plane and continuously moving the "Z" coordinate. In the current system, both "C" and "B" scans are acquired at a speed of two frames per second. Each scan covers an area of 30 × 20°. Both OCT and confocal images are displayed on a monitor simultaneously as a grey scale image. Within this system, both the depth ("Z" axis) and transverse (X-Y plane) resolutions are 10-15 µm. Both transverse ("C") and longitudinal ("B") scans were obtained through the macular area of all patients with VM interface abnormalities. In the longitudinal "B" scan mode, the images were obtained in both vertical and horizontal lines in the X-Y plane. A total of 835 eyes in 736 patients of various VM interface abnormalities were scanned with the combined SLO-OCT from September 2005 through June 2006 at two university-based retinal practices (Jacobs Retina Center at the Shiley Eye Center, University of California San Diego and New York Eye and Ear Infirmary). Of these patients, 362 were males, and 374 were females. Incomplete PVD patients formed the major group (with 308) followed by diabetic macular oedema, ERM, macular hole, ERM with cystoid macular oedema and VM traction (see Table 1 ). We received approval from the University of California San Diego Human Research Protection Program for the retrospective analysis of these data.   Results The following features of each type of VM interface abnormality were identified and are illustrated here. Epiretinal Membrane In all eyes with epiretinal membrane (113 eyes), "B" scan images showed a hyper-reflective membranous structure (band) on the surface of retina with a serrated or folded internal retinal surface. At some places, it showed points of cleavage with the internal retinal surface (see fig 1A arrow and fig 1B). The en-face "C" scan of ERM showed a radiating pattern with retinal folds and the membrane's extensions (see fig 1C,D). The surface of the membrane was visible when the plane of the "C" scan was superficial at the level of vitreous-retina interface. As the plane of the "C" scan had travelled deeper (changing the "Z" coordinate), the ERM appeared less visible, and the retinal layers started appearing as concentric rings in en-face imaging. The en-face imaging of ERM showed the complete structure of the membrane along with the traction's epicentre. Figure 1.  (A,B) Epiretinal membrane with the traditional transverse B-scan image on top of both images. The position of the B-scan in correspondence to the scanning laser ophthalmoscope (SLO) fundus image (bottom right of A and B) is indicated by the grey line. The B-scan is located at the macula showing a hyper-reflective membrane on the retinal surface with folds of internal limiting membrane (arrow). The small image on the bottom left of A and B allows us to judge eye movement during the B-scan. (C,D) Image pair showing the SLO fundus view (left) and the en-face "C" scan (right) of the same patient's macular area showing the epicentre of the membrane with its radiating transverse extensions.   VM Traction Syndrome VM Traction with Retinal Surface Abnormalities. Figure 2A,B shows the longitudinal scan ("B" scan) showing vitreous attachment to the retinal surface and elevated areas of it indicating the transverse as well as axial traction on the retina. The firm adherence of the posterior hyaloid to the retina is seen clearly (fig 2B, arrow). The en-face scan ("C" scan) showed the vitreous as a moderate hyper-reflective circular structure surrounded by concentric layers of retina when the "C" scan depth was anterior to the retinal surface. Figure 2C shows a circular hyper-reflective structure indicating the posterior hyaloid (arrow). Since the scan is slightly tilted, the bottom of this circular structure shows its point of adhesion to the retinal surface (arrow head) with different retinal layers seen within the same scan. The bottom of the scan showing the retinal layers is scanning deeper in the retina than the top of the scan, which shows the ERM (curved arrow). Figure 2D is a "C" scan of the same eye at a deeper level in the retina showing ERM (arrow).    Figure 2.  Vitreomacular traction with retinal surface abnormality. (A) Scanning laser ophthalmoscope image (bottom right) and transverse "B" scan of macular area showing epiretinal membrane (ERM) (arrowhead) with vitreomacular traction (arrow). (B) "B" scan of the same eye nasal to fovea. Note the attachment of posterior hyaloid to the retina with traction induced retinal oedema (arrow). (C) En-face "C" scan of the same patient's epiretinal membrane with vitreomacular traction showing circular hyper-reflective posterior hyaloid (arrow) with its attachment with retinal surface at the base (arrowhead). The curved arrow shows the ERM in the same scan. (D) "C" scan of the same eye at a deeper level than in C, showing the ERM (arrow). Diabetic Macular Oedema with VM Traction. The second category of the patients with VM traction were diabetic macular oedema with axial traction on the macula. Figure 3A depicts horizontal cross-sectional high-resolution OCT image (longitudinal "B" scan) through the foveal region of right eye showing an attachment of a hyper-reflective membranous shadow in the vitreous (posterior hyaloid) with the fovea (arrow). The inner retinal layer at the attachment is elevated indicating the VM traction at the fovea. The foveal region shows a large hypo-reflective area below the elevated superficial retinal layers indicating the traction induced cystoid macular oedema and disrupted photoreceptor layer below it (arrowhead). Figure 3B is an image of the same eye by conventional (stratus) OCT, which did not show posterior hyaloid and its traction on fovea. The StratusOCT image appears horizontally stretched due to the difference in lateral scan length between both instruments. We do not know why the SLO-OCT has a better visualisation of the VM traction. We speculate that differences in wavelength or detector design may contribute to the better visualisation.    Figure 3.  Vitreomacular traction in diabetic macular oedema. (A) Horizontal cross-sectional high resolution optical coherence tomography (OCT) image (longitudinal "B" scan) through the foveal region of the right eye with scanning laser ophthalmoscope (SLO) image of the fundus in a 63-year-old diabetic male, showing an attachment of a hyper-reflective membranous shadow in the vitreous (posterior hyaloid) with the fovea (arrow). Note the cystoid change in the fovea and disrupted photoreceptor layer (inner and outer segment junction) (arrowhead) due to axial vitreofoveal traction. (B) Image of the same eye (on the same day and same location) with conventional OCT showing vitreomacular traction (arrowhead) less clearly compared with that seen in A with SLO-OCT. (C) En-face "C" scan of the same eye anterior to retinal surface showing a hyper-reflective ring shadow (arrow) of vitreous cone (coronal cut) anterior to the fovea with concentric retinal layers seen at the periphery. (D) En-face "C" scan of the same eye very close to the fovea, showing a small ring of the shadow of the posterior hyaloid in continuation with the retinal layers (short arrow). Figure 3C,Ddepicts the en-face "C" scan (transverse scan) of the same eye in the macular region at different depths. When the "Z" axis coordinate was superficial, that is, anterior to the retinal surface, the posterior hyaloid was seen as a hyper-reflective ring shadow in the centre (fig 3C, arrow), and when the "Z" axis coordinate was deeper, that is, very close to the retinal surface, the "C" scan showed a small hyper-reflective ring in continuation with concentric shadows of retinal layers (fig 3D short arrow) indicating the adherent posterior hyaloid in the foveal area. Macular Hole The longitudinal "B" scan of the full-thickness macular hole (fig 4A) showed typical OCT features in the form of a full-thickness gap in retinal layers with the exception of the hyper-reflective RPE layer with cystic spaces at the edges of the hole (fig 4A, arrow). The "C" scan (fig 4B) images showed a unique feature. When the depth of the "C" scan was at the level of vitreoretinal interface and superficial retinal layers, the hole was seen as a black central circular area surrounded by small circular hyper-reflective cystic images (fig 4B, arrow). As the scan travelled deeper at the level of RPE, the floor of the macular hole appeared as a white hyper-reflective circular area surrounded by a dense reflective shadow of RPE (fig 4C, black arrowhead). The "B" scan (fig 4D) of lamellar macular hole showed a gap in the superficial layers of retina. The absence of cystic changes surrounding the hole is notable in the "C" scan (fig 4E). The visualisation of PVD, gap or discontinuity in the retinal layers on "B" scan differentiates it from the pseudo-hole.    Figure 4.  Macular hole. (A) Scanning laser ophthalmoscope image and longitudinal "B" scan of the macular area showing the full- thickness macular hole with cystic spaces in the retina at the edges (arrow). (B) En-face "C" scan of the macular hole from the same patient showing centrally the hole (circular black area within the retinal layer mage) with radially arranged cystic spaces (flower petal appearance) (arrow). (C) "C" scan of the same patient of the macular hole for a deeper layer of the retina showing the floor of the hole as a white (hyper-reflective) circular shadow (black arrowhead). (D) Longitudinal "B" scan of the macula showing a lamellar macular hole and hyper-reflective posterior hyaloid. (E) En-face view ("C" scan) of the same lamellar macular hole. Shallow Posterior Vitreous Detachment In the longitudinal "B" scan done at the level of the superior arcade, a linear hyper-reflective shadow was seen anterior to the surface of the retina with its attachment to the retinal surface in the macular area indicating incomplete PVD (fig 5A, arrow). The "C" scan showed the posterior hyaloid as a hazy white concentric shadow when the depth of the "C" scan was anterior to the retinal surface, that is, prior to the appearance of image of the retinal layers (fig 5B, arrows). Retinal layers were seen at the periphery of the scan, since the depth of the "C" scan was more tangential due to the normal curvature of the eye (fig 5B).   Figure 5.  Shallow posterior vitreous detachment. (A) Longitudinal "B" scan showing posterior hyaloid (arrow) separated from retina with its attachments at two places (incomplete posterior vitreous detachment). (B) En-face "C" scan with corresponding scanning laser ophthalmoscope image showing posterior hyaloid in the optically translucent space anterior to retinal layers as concentric hazy white shadow (arrowheads). The shape is curved because the "C" scan is tangential to the curved retinal surface. CMO with VM Interface Abnormality The imaging of CMO secondary to the VM interface abnormalities in 59 patients showed a classic appearance on the "C" scan. The longitudinal scan ("B" scan) showed vertical cystic spaces involving retinal layers in macular area (fig 6A). It also showed the disrupted photoreceptor outer segment band due to oedema and traction (arrow in fig 6A). Figure 6B,C shows an en-face image of typical CMO in the form of multiple circular hyper-reflective shadows, variable in size, representing the intra-retinal cysts (arrow in fig 6C). The macular image appeared anterior to the rest of retinal layers due to its swelling (fig 6B).    Figure 6.  Cystoid macular oedema with VM interface abnormality. (A) Longitudinal "B" scan of macular area showing cystic spaces (axial view) in the retinal layers with the epiretinal membrane. Note the disrupted photoreceptor outer segment band anterior to the retinal pigment epithelial layer (arrow) due to oedema. (B) En-face "C" scan of elevated macula of same patient showing cystic spaces and oedema. Note that the macular image appears anterior to the rest of the retinal layers due to its elevated position (oedema). (C) "C" scan of same patient at a deeper retinal level showing an en-face view of cystoid macular oedema with multiple cysts of variable sizes arranged radially (arrow). Diabetic Macular Oedema In patients with diabetic macular oedema, SLO-OCT images of macula not only showed typical cystoid or non-cystoid oedema but also revealed the VM interface relations. Figure 7A depicts the vertical cross-sectional longitudinal "B" scan image with SLO-OCT in an eye with diabetic macular oedema showing partial vitreous detachment with attachment of posterior hyaloid to the macula (arrow) and cystoid oedema of retinal layers in the macular region. Figure 7B shows a vertical cross-sectional image of the macular region of the same eye with conventional (stratus OCT, Carl Zeiss) OCT, which is not showing the posterior hyaloid and its attachment at the macular region. Figure 7C shows the enface "C" scan image of the macular area of the same eye showing small bubble-like clear areas with hyper-reflective margins in the retinal tissue, which was a coronal section of multiple cystic spaces in the retinal layers (white arrowhead). In all these eyes, the "B" scan showed a very clear, thin, hyper-reflective band in front of the hyper-reflective RPE band representing the junction of the outer and inner segments of the photoreceptors.    Figure 7.  Diabetic macular oedema with incomplete posterior vitreous detachment. (A) Vertical cross-sectional longitudinal "B" scan image with scanning laser ophthalmoscope-optical coherence tomography (SLO-OCT) in an eye with diabetic macular oedema in a 62-year-old male showing partial vitreous detachment with attachment of posterior hyaloid to the macula (arrow) and cystoid oedema of retinal layers in the macular region. (B) Vertical cross-sectional image of the macular region of the same eye with conventional (stratus) OCT in the location (close to the location in A), not showing the posterior hyaloid and its attachment to the macular area. Multiple stratus images were obtained which did not show this attachment. None of the six StratusOCT images corresponded exactly with the SLO-OCT image. (C) En-face "C" scan image of macular area of the same eye showing the coronal section of multiple cystic spaces in the retinal layers (arrowhead). Discussion Interpretation of images obtained by scanning the retina in the coronal plane by combined scanning laser and optical coherence tomography is different from the conventional longitudinal "B" scan. En-face imaging gives a top (surface) view of retinal layers obtained at different depths by changing the "Z" axis coordinate. This gives images the appearance as if one is slicing the retina parallel to its surface or histological sections taken through the retina perpendicular to the optical axis. The images are cross-sectional cuts through the retinal tissue. However, since the optical axis of the OCT scanner and the optical axis of the eye do not always coincide, different parts of one image can be recorded from different optical depths. Thus, several structures of different depths are simultaneously imaged. In en-face "C" scans, retinal layers are seen as concentric rings. The deeper structures appear further away from the centre of the rings. The exact position of each of these concentric rings within the image depends on the depth of the scan along the "Z" axis. Although the precise location of the scan along "Z" axis (depth) cannot be predicted accurately, it can be judged by the appearance of the retinal vessels in the "C" scan. As the "C" scan depth progresses deeper into the retinal layers, the retinal vessels appear as dark lines, due to the shadow cast on the deeper layers. As the "C" scan images are obtained at a superficial level (near the retinal surface), the retinal vessels appear as white lines (fig 3A, red arrowhead), and as the depth of "C" scan increases, the retinal blood vessels appear as black lines (green arrowhead in fig 3A). Van Velthoven et al [14] documented a similar observation. We describe this new imaging device, combined coronal OCT and SLO. This imaging technique involves en-face scanning in the X-Y plane and combines the high-resolution tomographic images with the surface imaging ability of the scanning laser ophthalmoscope. It has two advantages. The first advantage is that the "C" scan of the retina shows pathology parallel to RPE and shows tractional forces, retinal surface and inner retina in a way not usually seen with a commercially available OCT system. Second, combined SLO gives a simultaneous fundus image with OCT. The fundus image is taken simultaneously with the OCT that allows co-localisation of the structures and pathology visible with conventional imaging or ophthalmoscopy with the OCT image of the exact same area of the fundus. Thus, the confocal image is used for general orientation and localisation of the pathology on the retina. It is also used for better and more reliable positioning of the OCT "B" scan and to detect the eye movements so that images with eye movements can be discarded. This freedom of imaging and precise co-localisation of retinal pathology with the fundus image were not available previously with the StratusOCT (OCT-3), since OCT-3 uses a scan orientation fundus photograph taken after completion of all of the OCT "B" scans. Another advantage of the simultaneous confocal image is that, given that the images in confocal and OCT channel are correspond pixel-to-pixel, transformed angiographic images can be directly superimposed over the OCT image, since angiography images are also displayed in the transverse plane.[15]  The rapid technological advances in spectral-domain (SD) or Fourier-domain OCT have allowed ophthalmologists to choose from seven different vendors with seven different types of instruments in addition to several laboratory devices with advanced capabilities. A recent review by Drexler and Fujimoto gives an excellent overview of the advances in this field.[13] SD-OCT technology has achieved an improvement of axial scan rates from 400 A-scans per second in the time-domain OCT technology to 236 000 A-scans per second in laboratory devices, while commercially available devices top out at 40 000 A-scans per second.[16] However, even at the highest scan rate of 236 000/s, it takes more than 1 s to image an area of 512 by 512 pixels. In contrast, simultaneous acquisition of the SLO image as demonstrated in this device allows the co-localisation of the OCT B-scan with the SLO fundus image. Coronal scans or C-scans can be calculated from SD-OCT image stacks by projection of the data into the coronal plane. However, in the absence of eye-motion correction,[17] the coronal scan calculation can be complicated, or incomplete. OCT images have been proved to be very helpful in evaluating VM interface abnormalities. VM interface abnormality may exert traction in the axial direction and as well as in the transverse direction, and lead to the distortion of retinal layers and loss of the foveal depression, also exemplified here in the images of ERM and VM traction syndromes. Delineation of all these transverse tractional forces is much clearer by scanning the retina in the coronal plane and obtaining the en-face "C" scan images with this combined SLO-OCT. In this report, we have documented the en-face "C" scan (coronal scan) and the longitudinal "B" scan features of VM interface abnormalities including ERM, macular hole, VM traction syndrome and incomplete or shallow PVD by combined scanning laser ophthalmoscope and optical coherence tomography. The "C" scan of ERM showed the complete structure of the membrane in the form of radial lines extending from the traction's epicentre with all its extensions in a radiating pattern along with retinal folds; this was not possible with the conventional "B" scan mode of OCT. ERM in the longitudinal "B" scan mode showed several points of cleavage with the internal retinal surface. It indicates that traction is formed between the hyper-reflective band (epiretinal membrane) and the surface of the retina (transverse traction forces). Since there is pixel-to-pixel correspondence between the OCT image and confocal image, a particular area can be localised within the X-Y plane of the confocal image of the retina, and a parallel can be directly drawn with its location on the OCT image. Thus, one can determine the areas of ERM where there is some space between it and the retinal surface. This may aid in the planning of dissection sites for surgical removal of ERM. On "C" scan imaging of macular holes, we found similar features to those reported by van Velthoven et al.[14] In full-thickness macular holes, the "C" scan showed a typical central black space surrounded by small circles of adjacent retinal oedema. In the cases of CMO en-face "C" scanning, small intraretinal cysts were found in the form of circular structures arranged in radial pattern around the fovea. The coronal view of the macular hole provides a unique opportunity to assess the state of the tissue around the hole and to determine the dimensions of the hole more precisely. Combining the vertical diameter calculated from "B" scan images, it is possible to get the exact dimensions of the macular hole. Various studies have reported the size of the hole as one of the strong prognostic factors for surgical outcome of the macular hole.[18-21] In VM traction syndrome, the "B" scan showed points of adhesion and traction at the retinal surface very distinctly, these areas of vitreoretinal traction could be colocalised with simultaneously produced confocal image of the retina as previously described. Specifically, imaging the macular area in suspected VM traction cases on SLO-OCT with en-face scanning mode is very useful to identify the VM traction areas which are otherwise missed by conventional OCT imaging systems, as exemplified in fig 3A,B in a diabetic macular oedema case. This can be useful in managing the cases of VM traction syndromes. In incomplete PVD cases, the "B" scan showed the posterior hyaloid distinctly as a highly reflective band at a distance from the retina within the vitreous cavity. This enables ophthalmologists to identify the contour of the hyaloid membrane. This band was absent in vitrectomised eyes and eyes with no clinical signs of PVD. Identification of this perifoveal vitreous detachment, as probably the important pathogenic event in idiopathic macular hole formation,[22] is reported as stage 0 macular hole. The presence of a stage 0 hole was associated with an almost sixfold increase in risk of macular hole formation.[23]  In all cases, while imaging on the combined scanning laser ophthalmoscope and OCT system, the double structure of the "outer retinal band" is generally seen quite clearly. The interior of the two represents the photoreceptor inner and outer segment junction, and the outer represents the retinal pigment epithelium. By documenting these features of VM interface abnormalities on a combined scanning laser and OCT system, we report that it can provide additional information, which is not possible by conventional OCT. An excellent understanding of these VM interface abnormalities can be acquired by mentally combining the several "C" scans obtained at different depths and "B" scans at different positions along the X-Y axis with simultaneously obtained confocal images of the retina. This technique can be applied to a variety of clinical conditions in the macular area and enables us to understand them in a broader sense within the confines of a non-invasive modality of imaging. Further work with image-processing algorithms to "flatten" the images and therefore allow "C" scans in the plane parallel to the retinal surface, will allow coronal sections of the tissue and aid in three-dimensional reconstruction, retinal topography and thickness analysis. Newer spectral OCT technology using high-resolution and high-speed spectral scan technology is under way to improve the resolution by a factor of three to five. 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