Optical coherence tomography (OCT) is a medical imaging technology that can perform high resolution, cross-sectional imaging of tissue morphology in situ and in real time.1 It can provide detailed images and quantitative information about retinal structure and has therefore become a standard diagnostic technique in ophthalmology.2,3 The StratusOCT system (Carl Zeiss Meditec, Inc., Dublin, CA), with an 8- to 10-μm axial image resolution, can provide detailed cross-sectional images of retinal disease and quantitative measurements, including macular thickness, nerve fiber layer thickness, and optic nerve head topography. Normative databases for macular thickness and nerve fiber layer thickness are available to aid in the interpretation of quantitative measurements. Analysis of finer intraretinal structures has been difficult because of speed and resolution limitations. However, segmentation of the inner retinal complex, outer plexiform layer, and outer retinal complex in StratusOCT images has recently been demonstrated.4 Another study demonstrated foveal photoreceptor layer changes in central serous chorioretinopathy that correlate with visual acuity loss.5 Recently, a correlation between macular hole postoperative visual acuity and photoreceptor thickness measured manually from StratusOCT images has been shown.6

Ultrahigh-resolution (UHR) OCT imaging with axial resolutions of 2 to 3 μm was demonstrated to improve significantly the visualization of normal retinal morphology7,8 and retinal disease9–14 Although conventional UHR OCT systems that use time domain detection enable visualization of structural detail in the outer retina, quantitative mapping with conventional UHR OCT technology has been difficult, because of imaging speed limitations and consequent motion artifacts. Nevertheless, several studies have been performed in which photoreceptor thickness was measured manually on a small number of images. One study correlated photoreceptor loss and foveal thickness with visual acuity in Stargardt disease-fundus flavimaculatus.12 In another study, central foveal photoreceptor thickness measured by UHR OCT was correlated with visual acuity in retinitis pigmentosa and degenerative diseases.14 To date, comprehensive quantitative mapping of the photoreceptors and RPE has not been possible with conventional UHR OCT, due to motion artifacts and limited retinal coverage.

Recently, advances in OCT technology have enabled UHR OCT imaging with a ~50× increase in imaging speed over standard resolution OCT systems and a ~100× increase in imaging speed over previous UHR OCT systems.15–17 These techniques are based on “spectral” or “Fourier domain” detection, where echo time delays of light are measured by acquiring the interference spectrum of the light signal and taking its Fourier transform.18,19 Since all the light echoes from different axial depths are measured simultaneously, sensitivity and imaging speed are dramatically increased.20–22 With increased imaging speed, individual images are acquired within a fraction of a second and depict the true retinal topography. Multiple images may be rapidly acquired at different locations or orientations, enabling three-dimensional imaging.23,24 The number of axial scans per image may be increased significantly, to obtain high-definition images.25 Adaptive optics has also been combined with high-speed OCT, to visualize the cone photoreceptors in three dimensions.26

In this study, high-speed UHR OCT was used for the visualization, measurement and mapping of outer retinal morphology in normal subjects. OCT imaging was performed with a 3.5-μm axial-resolution prototype instrument using a radial scan pattern, and scattering bands in the outer retina were measured and mapped in 43 normal subjects of various ages. Quantitative maps were used to assign these bands to specific outer retinal layers or features based on comparison with the known topographic distribution of cones and rods in the macula. The cross-sectional relationships between layer measurements and age were also investigated. In addition, high-definition imaging was performed with a 2.8-μm axial-resolution prototype instrument to visualize finer bands in the outer retina. Anatomic correlates for these more subtle outer retinal features were determined.

Characterization of Outer Retinal Morphology with High-Speed, Ultrahigh-Resolution Optical Coherence Tomography

Retinal assessment using optical coherence tomography

PURPOSE. To evaluate photoreceptor inner/outer segment (IS/ OS) defect parameters by using spectral domain-optical coherence tomography (SD-OCT) for correlation with visual outcomes in macular hole surgery (MHS). METHODS. This study was an interventional, retrospective case series. Twenty-three eyes (23 patients) were examined by SD-OCT before and after (median, 2.3 months) anatomically successful MHS. Two formats of OCT were analyzed: linear (raster) and composite (partial fundus image). Factors that may have confounded IS/OS measurements were controlled by using weighting and normalization of data. The main outcome measures were diameter and area of the IS/OS defect, weighted area of the IS/OS defect, macular density ratio (MDR), healing pattern of the macular hole, and preoperative and postoperative best corrected visual acuity (BCVA). RESULTS. Poorer preoperative BCVA correlated with larger preoperative diameter of the IS/OS defect (P 0.005). A greater improvement in BCVA correlated with a larger preoperative area of IS/OS defect (P 0.038) and smaller MDR (P 0.012). Poorer postoperative BCVA correlated with a larger postoperative diameter of the IS/OS defect (P 0.010), larger weighted postoperative area of IS/OS defect calculated by raster scan (P 0.013), larger postoperative area of IS/OS defect measured from the partial fundus image (P 0.003), and apparent glial sealing pattern on SD-OCT (P 0.0005). The shape of the IS/OS defect area was round and regular before surgery, but irregular afterward. CONCLUSIONS. BCVA after MHS correlates with objectively ascertainable SD-OCT measurements of IS/OS defects and other features. The postoperative area of the IS/OS defect, when directly measured, correlates more strongly with BCVA than do linear-based measurements, perhaps because of the irregular shape of the IS/OS defect after surgery. (Invest Ophthalmol Vis Sci. 2010;51:1651–1658) DOI:10.1167/iovs.09-4420

Photoreceptor inner/outer segment defect imaging by spectral domain OCT and visual prognosis after macular hole surgery.

https://escholarship.org/content/qt68b292hz/qt68b292hz.pdf?t=o2c3fi

Clinical application of rapid serial fourier-domain optical coherence tomography for macular imaging.

Background
To evaluate the ability of spectral-domain optical coherence tomography (SD-OCT) images of the inner/outer segment (IS/OS) junction to predict macular hole surgery outcomes.

Spectral-domain optical coherence tomography images of inner/outer segment junctions and macular hole surgery outcomes

Purpose: Study correlation between optical coherence tomography (OCT) findings and visual acuity (VA) outcomes after successful macular hole surgery (MHS).Design: Retrospective cross- sectional study. Methods: PostoperativeOCT scans were analyzed in 34 eyes of 30 patients. Raw files of horizontal and vertical OCT scans were exported to Adobe Photoshop 7.0. Measured parameters included central foveal thickness, photoreceptor thickness, photoreceptor reflectivity, and relative reflectivity of photoreceptor to retinal pigment epithelium in the foveal area. Foveal configuration was subjectively graded. Results: OCT scans were obtained at a median of 2 years (1 month to 10 years) postoperatively. The median visual acuity was 20/80 (20/50 to 8/200) preoperatively and 20/50 (20/20 to5/200) postoperatively. The median foveal thickness was 198.5 μ (148 to 283). The mean (SD) photoreceptor layer thickness was 16.5 (8) μ in the 500 μ area and 17.5 (8) μ in the 1000 μ area. Mean (SD) of relative reflectivity of the photoreceptor layer was 0.60 (0.10) in both 500 μ and 1000 μ area. Postoperative VA did not correlate with foveal thickness or foveal configuration. Central (500 μ and 1000 μ ) photoreceptor thicknesswas significantly correlated with final VA(r=.38, P=.026, each). Relative reflectivity of photoreceptors to retinal pigment epithelium in the 500 μ area was correlated with postoperative VA at a borderline significance (r=.32, P=.07). Relative reflectivity of photoreceptors to retinal pigment epithelium in the 1000 μ area was not significantly correlated with postoperative VA (r=.27, P=.12). Conclusion: Specific retinal features can be assessed from OCT images. Morphology and thickness of the foveal photoreceptor layer correlate well with macular function after successful MHS. Outer retinal features appear to be more important to determine postoperative visual function. Inner retinal features may be more relevant for the ophthalmoscopic appearance of anatomic closure.

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Photoreceptor layer features in eyes with closed macular holes: Optical coherence tomography findings and correlation with visual outcomes