Morphologic Changes in Patients with Geographic Atrophy Assessed with a Novel Spectral OCT–SLO Combination

Ten-year follow-up of eyes treated with stereotactic fractionated external beam radiation for neovascular age-related macular degeneration

PURPOSE

To determine the long-term effects of stereotactic fractionated external beam radiation on eyes treated for neovascular age-related macular degeneration.

METHODS

A retrospective review of all eyes treated with stereotactic fractionated external beam radiation (20-40 Gy, 2-Gy fractions) between 1997 and 2000 was performed to identify eyes with ≥ 2-year follow-up for analysis. A subset was imaged prospectively using a high-resolution Fourier-domain optical coherence tomography.

RESULTS

Among 94 eyes treated, 33 eyes (32 subjects) had ≥ 2-year follow-up information (mean follow-up, 6.2 years; range, 2-10 years). Final visual acuity ranged from 20/50 to no light perception. Final macular findings included central geographic atrophy (49%), disciform scar (30%), and active choroidal neovascular membrane (9%). Fourier-domain optical coherence tomography images of three eyes with geographic atrophy revealed photoreceptor layer loss within areas of geographic atrophy with intact retinal morphology in areas of radiation exposure outside geographic atrophy. Radiation retinopathy was suspected in 18% and confirmed by fluorescein angiography in 15%, ranging from mild to neovascular glaucoma/phthisis bulbi (2 eyes). Mean time from stereotactic fractionated external beam radiation to development of radiation retinopathy was 5.4 years (range, 1-10 years).

CONCLUSION

A moderate rate of delayed radiation retinopathy was noted in eyes with neovascular age-related macular degeneration treated with stereotactic fractionated external beam radiation. Geographic atrophy was a common finding.

New grading criteria allow for earlier detection of geographic atrophy in clinical trials

PURPOSE

To evaluate new grading criteria for geographic atrophy (GA), as detected by annual stereoscopic color fundus photographs and fluorescein angiograms, and to assess whether application of the revised criteria provides earlier identification of GA than previous criteria involving only color fundus photography.

METHODS

Annual fundus image sets from 114 CAPT patients who developed GA in the untreated eye during 5 to 6 years of follow-up were reassessed for the presence of GA, using revised grading criteria, in which GA was defined by (1) the presence of hyperfluorescence on fluorescein angiography; and (2) at least one other characteristic indicative of involution of the retinal pigment epithelium (i.e., sharp edges, excavation of the retina, or visible choroidal vessels on either color images or fluorescein angiograms). Reliability and time of initial detection of GA using the revised criteria were assessed.

RESULTS

The revised criteria are reliable (97.8% intragrader, 93.3% intergrader agreement) and accurate (false-positive rate, 0.8%) for detecting individual early GA lesions. Using this revised method, individual GA lesions were identified 1-year earlier on average than was possible with criteria used in previous CFP studies. The use of two imaging modalities was more sensitive in detecting GA and its features than either imaging modality alone (P ≤ 0.0001).

CONCLUSIONS

Early GA areas can be reliably identified when defining criteria are based on both color photographs and fluorescein angiograms. These methods can be used to investigate the natural history of GA earlier in the course of disease than previously possible and to facilitate the design of future clinical trials of treatments for GA. (ClinicalTrials.gov number, NCT00000167).

Polarization sensitive optical coherence tomography in the human eye

Optical coherence tomography (OCT) has become a well established imaging tool in ophthalmology. The unprecedented depth resolution that is provided by this technique yields valuable information on different ocular tissues ranging from the anterior to the posterior eye segment. Polarization sensitive OCT (PS-OCT) extends the concept of OCT and utilizes the information that is carried by polarized light to obtain additional information on the tissue. Several structures in the eye (e.g. cornea, retinal nerve fiber layer, retinal pigment epithelium) alter the polarization state of the light and show therefore a tissue specific contrast in PS-OCT images. First this review outlines the basic concepts of polarization changing light-tissue interactions and gives a short introduction in PS-OCT instruments for ophthalmic imaging. In a second part a variety of different applications of this technique are presented in ocular imaging that are ranging from the anterior to the posterior eye segment. Finally the benefits of the method for imaging different diseases as, e.g., age related macula degeneration (AMD) or glaucoma is demonstrated.

Simultaneous confocal scanning laser ophthalmoscopy combined with high-resolution spectral-domain optical coherence tomography: a review

We aimed to evaluate technical aspects and the clinical relevance of a simultaneous confocal scanning laser ophthalmoscope and a high-speed, high-resolution, spectral-domain optical coherence tomography (SDOCT) device for retinal imaging. The principle of confocal scanning laser imaging provides a high resolution of retinal and choroidal vasculature with low light exposure. Enhanced contrast, details, and image sharpness are generated using confocality. The real-time SDOCT provides a new level of accuracy for assessment of the angiographic and morphological correlation. The combined system allows for simultaneous recordings of topographic and tomographic images with accurate correlation between them. Also it can provide simultaneous multimodal imaging of retinal pathologies, such as fluorescein and indocyanine green angiographies, infrared and blue reflectance (red-free) images, fundus autofluorescence images, and OCT scans (Spectralis HRA + OCT; Heidelberg Engineering, Heidelberg, Germany). The combination of various macular diagnostic tools can lead to a better understanding and improved knowledge of macular diseases.

Imaging geographic atrophy in age-related macular degeneration

Advances in retinal imaging technology have largely contributed to the understanding of the natural history, prognostic markers and disease mechanisms of geographic atrophy (GA) due to age-related macular degeneration. There is still no therapy available to halt or slow the disease process. In order to evaluate potential therapeutic effects in interventional trials, there is a need for precise quantification of the GA progression rate. Fundus autofluorescence imaging allows for accurate identification and segmentation of atrophic areas and currently represents the gold standard for evaluating progressive GA enlargement. By means of high-resolution spectral-domain optical coherence tomography, distinct microstructural alterations related to GA can be visualized.

Drusen characteristics revealed by spectral-domain optical coherence tomography and their corresponding fundus autofluorescence appearance in dry age-related macular degeneration

PURPOSE

To analyze the relationship between drusen morphology revealed by spectral-domain optical coherence tomography (SD-OCT) and corresponding fundus autofluorescence (FAF) features of the same drusen using the Heidelberg Retina Angiograph 2 (HRA2), in patients with dry age-related macular degeneration (AMD).

METHODS

Dry AMD patients were imaged with SD-OCT and HRA2 on the same day. SD-OCT B scans were then precisely overlaid onto the HRA2 images, and the SD-OCT morphological characteristics of the drusen were correlated with the corresponding FAF appearance. The analyzed morphological features of the drusen included: size, status of the inner segment/outer segment (IS-OS) junctional layer above the drusen, shape of the drusen, internal reflectivity, homogeneity and presence of overlaying hyperreflective foci. The FAF characteristics of each druse were rated as hyperautofluorescent, hypoautofluorescent or normally autofluorescent. Spearman's correlation coefficient was used to analyze the correlation between the 2 primary outcomes: SD-OCT morphology of the drusen and their autofluorescent appearance.

RESULTS

431 drusen in 32 eyes of 16 dry AMD patients were evaluated. Of the 7 morphological characteristics assessed by SD-OCT, only drusen size and the status of the IS-OS layer above the drusen were strongly correlated with the autofluorescent appearance (r = 0.78, p < 0.001, and r = 0.58, p < 0.001, respectively). The strength of correlation with other features appeared less robust: homogeneity (r = 0.38; p = 0.001), shape (r = 0.29; p = 0.004), reflectivity (r = 0.28; p = 0.004) and presence of overlaying foci (r = 0.25; p = 0.12).

CONCLUSIONS

Autofluorescent changes most strongly correlate with drusen size and disruption of the IS-OS layer and may be useful as an additional functional-morphological feature by which drusen and their impact upon overlying photoreceptors may be judged.

Human chorioretinal layer thicknesses measured in macula-wide, high-resolution histologic sections

PURPOSE

To provide a comprehensive description of chorioretinal layer thicknesses in the normal human macula, including two-layer pairs that can produce a combined signal in some optical coherence tomography (OCT) devices (ganglion cell [GCL] and inner plexiform [IPL] layers and outer plexiform [OPL] and outer nuclear [ONL] layers).

METHODS

In 0.8-μm-thick, macula-wide sections through the foveola of 18 donors (age range, 40-92 years), 21 layers were measured at 25 locations by a trained observer and validated by a second observer. Tissue volume changes were assessed by comparing total retinal thickness in ex vivo OCT and in sections.

RESULTS

Median tissue shrinkage was 14.5% overall and 29% in the fovea. Histologic laminar boundaries resembled those in SD-OCT scans, but the shapes of the foveolar OPL and ONL differed. Histologic GCL, IPL, and OPLHenle were thickest at 0.8. to 1, 1.5, and 0.4 mm eccentricity, respectively. ONL was thickest in an inward bulge at the foveal center. At 1 mm eccentricity, GCL, INL, and OPLHenle represented 17.3% to 21.1%, 18.0% to 18.5%, and 14.2% to 16.6% of total retinal thickness, respectively. In donors ≥ 70 years of age, the RPE and choroid were 17.1% and 29.6% thinner and OPLHenle was 20.8% thicker than in donors <70 years.

CONCLUSIONS

In this study, the first graphic representation and thickness database of chorioretinal layers in normal macula were generated. Newer OCT systems can separate GCL from IPL and OPLHenle from ONL, with good agreement for the proportion of retinal thickness occupied by OPLHenle in OCT and histology. The thickening of OPLHenle in older eyes may reflect Müller cell hypertrophy associated with rod loss.

Fundus autofluorescence and spectral-domain optical coherence tomography characteristics in a rapidly progressing form of geographic atrophy

PURPOSE

To further characterize a previously described phenotypic variant of geographic atrophy (GA) associated with rapid progression and a diffuse-trickling appearance on fundus autofluorescence (FAF).

METHODS

Thirty-six patients (60 eyes; 72.2% women; mean age, 69.4 ± 10.7 years) with this distinct phenotype were examined by simultaneous confocal scanning laser ophthalmoscopy (cSLO) and spectral-domain optical coherence tomography (SD-OCT) imaging. Images were qualitatively and quantitatively analyzed and compared with 60 eyes (38 patients) with non diffuse-trickling GA.

RESULTS

The atrophic area in the diffuse-trickling phenotype showed a grayish FAF signal and characteristic coalescent lobular configuration at the lesion boundaries. SD-OCT revealed a marked splitting of band 4 (the presumptive retinal pigment epithelium (RPE)/Bruch's membrane (BM) complex) in all 240 analyzed border sections of diffuse-trickling GA eyes (four borders/eye) with a mean distance between the inner and outer parts of band 4 of 23.2 ± 7.5 μm. This finding was present in only 13.8% (33/240) of analyzed border sections in non diffuse-trickling GA.

CONCLUSIONS

Patients with the rapidly progressing diffuse-trickling GA phenotype exhibited a characteristic marked separation within the RPE/BM complex on SD-OCT-imaging. The presumed histopathologic correlates are basal laminar deposits. Such deposits may promote RPE cell death and, thus, contribute to rapid GA progression. The persistence of these deposits within the atrophic lesion may account for the distinct grayish FAF appearance, which differs from the markedly reduced signal in other forms of GA. Identification of such alterations based on FAF and SD-OCT imaging may be helpful in future interventional trials directed toward slowing GA progression. (ClinicalTrials.gov number, NCT00393692.).

Performance of OCT segmentation procedures to assess morphology and extension in geographic atrophy

PURPOSE

Investigating segmentation procedures and morphological findings in time domain (TD) and current spectral domain (SD) optical coherence tomography (OCT) devices in patients with geographic atrophy (GA).

METHODS

Fifty eyes of 46 patients with GA secondary to AMD and 15 control eyes were examined in this prospective noninterventional comparative case series. All patients underwent Stratus (model 3000), Cirrus (Carl Zeiss Meditec), Spectralis (Spectralis HRA+OCT; Heidelberg Engineering) and 3D-OCT-1000 (Topcon). Automated segmentation analyses were compared. An overlay of scanning laser ophthalmoscope (SLO) and three-dimensional retinal thickness (RT) maps were used to investigate whether areas of retinal thinning correspond to areas of retinal pigment epithelium (RPE) atrophy.

RESULTS

Geographic atrophy areas identified in SLO scans were significantly larger than areas of retinal thinning in RT maps. No convincing topographic correlation could be found between areas of retinal thinning and actual GA size as identified in SLO and fundus photography. Spectralis OCT showed significantly more mild and severe segmentation errors than 3D and Cirrus OCT.

CONCLUSION

This study showed substantial limitations in identifying zones of GA reliably when using automatic segmentation procedures in current SD-OCT devices. This limitation should be addressed to visualize and document RPE loss realistically in a frequent disease like GA.

Association of pathomorphology, photoreceptor status, and retinal thickness with visual acuity in diabetic retinopathy

PURPOSE

To evaluate whether visual acuity (VA) is associated with pathologic changes in morphology (pathomorphology), macular thickness, and the status of external limiting membrane (ELM) in diabetic retinopathy (DR).

DESIGN

Retrospective, observational case series.

METHODS

One hundred twenty-five consecutive eyes of 73 patients with DR were analyzed retrospectively. No patients had been treated for diabetic macular edema, and all had Spectralis optical coherence tomography (OCT) images. We evaluated the pathomorphology, qualitatively evaluated the status of ELM and cystic changes, and measured the retinal thickness. The correlation with logarithm of the minimal angle of resolution (logMAR) was investigated.

RESULTS

We classified 3 types of pathomorphology at the presumed fovea: cystoid macular edema (CME type, n = 20), serous retinal detachment (SRD type, n = 21), and the absence of either cystoid macular edema or serous retinal detachment (diffuse type, n = 84). The mean logMAR VA with the CME type (0.460 ± 0.301) was significantly worse than with the SRD type (0.222 ± 0.178; P = .004) or diffuse type (0.149 ± 0.260; P < .001). With CME type and diffuse type, a disrupted ELM or parafoveal thickening was significantly correlated with poor VA; these correlations were not found with the SRD type. Seventy-nine of 104 eyes with CME type or diffuse type presented intact ELM and showed the significant correlation between logMAR and the parafoveal thickness or cystic changes, although these parameters were not associated with logMAR VA in 25 eyes with disrupted ELM.

CONCLUSIONS

The pathomorphology and photoreceptor status at the fovea and retinal edema in the parafovea are correlated with the VA in DR.

Predicting visual outcomes for macular disease using optical coherence tomography

In recent years, the management of macular disease has undergone radical changes, in part because of new therapeutic approaches, but also due to the introduction of a new imaging modality - optical coherence tomography (OCT). The application of OCT imaging has clarified many aspects of chorioretinal disease pathophysiology and elucidated many hitherto unrecognized disease characteristics. From an early stage in its development, OCT has also been revolutionary in attempting to extract clinically useful measurements from image data in an automated fashion. As a result, OCT-derived measurements of retinal thickness have been rapidly embraced in clinical and research settings. However, as knowledge of OCT image analysis has developed, it has become increasingly clear that even accurate measurements of retinal thickness may fail to predict visual outcomes for many diseases. As a result, the focus of much current clinical imaging research is on the identification of other OCT-derived anatomic biomarkers predictive of visual outcomes - such biomarkers could serve as surrogate endpoints in clinical trials and provide prognostic information in clinical practice. In this review, we begin by highlighting the importance of accurate visual function assessment and describing the fundamentals of OCT image evaluation, before describing the current state-of-the-art with regard to predicting visual outcomes, for a variety of macular diseases, using OCT.

Fourier-domain optical coherence tomography and microperimetry findings in retinitis pigmentosa

PURPOSE

To investigate the relation between the optical coherence tomography (OCT) findings and retinal sensitivity in patients with retinitis pigmentosa (RP) by assessing the retinal thickness and retinal function using Fourier-domain OCT (FD-OCT) and microperimetry, respectively.

DESIGN

Observational case series.

METHODS

Fifty-nine patients (118 eyes) were enrolled, mean age 47 ± 14.8 years. Thirty-two healthy subjects (HS) were enrolled as a control group. Patients were assessed by means of FD-OCT and microperimetry. We analyzed the average foveal thickness (diameter of 1 mm centered on the point of fixation), the value of the retinal sensitivities corresponding to the 4 degrees centered on the fixation point, and logMAR visual acuity for regression analysis converted from Snellen chart.

RESULTS

We distinguished 4 groups of RP patients according to the macular pattern seen on OCT images. The first group of 36 eyes, mean age of 33.5 ± 7.4 years, had no macular changes, mean best-corrected visual acuity (BCVA) of 0.95 ± 0.07, mean foveal thickness of 256.3 ± 9.14 μm, and mean retinal sensitivities inside the central 4 degrees of 19.27 ± 0.87 dB (P > .05 for all the values). The second group of 28 eyes, mean age 35.4 ± 6.3 years, showed clinical macular edema (CME) on OCT images with mean BCVA of 0.72 ± 0.22, mean foveal thickness of 363.5 ± 93.45 μm, and mean retinal sensitivity inside the central 4 degrees of 15.94 ± 3.6 dB (P < .01 for all the values). The third group of 26 eyes, mean age 50.8 ± 8.7 years, showed macular vitreoretinal traction on OCT images with a mean BCVA of 0.5 ± 0.2, mean foveal thickness of 337.1 ± 71.7 μm, and mean retinal sensitivity inside the central 4 degrees of 11.78 ± 3.09 dB (P < .01 for all the values). The last group of 28 eyes, mean age 52.1 ± 13.6 years, showed macular retinal thinning on OCT images with mean BCVA of 0.36 ± 0.15, mean foveal thickness of 174.2 ± 24.40 μm, and mean retinal sensitivity inside the central 4 degrees of 10.22 ± 3.82 dB (P < .01 for all the values).

CONCLUSIONS

MP-1 and FD-OCT showed high sensitivity for identifying functional and structural macular abnormalities, respectively. Future studies should investigate the relationships among photoreceptor cell loss, retinal sensitivity, and fixation in patients with RP.

Spatial correlation of mouse photoreceptor-RPE thickness between SD-OCT and histology

Spectral Domain Optical Coherence Tomography (SD-OCT) applied to the mouse retina has been limited due to inherent movement artifacts and lack of resolution. Recently, SD-OCT scans from a commercially available imaging system have yielded retinal thickness values comparable to histology. However, these measurements are based on single point analysis of images. Here we report that using the Spectralis HRA + OCT Spectral Domain OCT and Fluorescein Angiography system (Heidelberg Engineering, Heidelberg, Germany), retinal thickness of linear expanses from SD-OCT data can be accurately assessed. This is possible by the development of a Spectralis-compatible ImageJ plug-in that imports 8-bit SLO and 32-bit OCT B-scan images, retaining scale and segmentation data and enabling analysis and 3D reconstruction. Moreover, mouse retinal layer thickness values obtained with this plug-in exhibit a high correlation to thickness measurements from histology of the same retinas. Thus, use of this ImageJ plug-in results in reliable quantification of long retinal expanses from in vivo SD-OCT images.

Induction of STAT3-related genes in fast degenerating cone photoreceptors of cpfl1 mice

Cone dystrophies are genetic diseases characterized by loss of cone photoreceptor function and severe impairment of daylight vision. Loss of function is accompanied by a progressive degeneration of cones limiting potential therapeutic interventions. In this study we combined microarray-based gene-expression analysis with electroretinography and immunohistochemistry to characterize the pathological processes in the cone photoreceptor function loss 1 (cpfl1) mouse model. The cpfl1-mouse is a naturally arising mouse mutant with a loss-of-function mutation in the cone-specific Pde6c gene. Cpfl1-mice displayed normal rod-specific light responses while cone-specific responses were strongly diminished. Despite the lack of a general retinal degeneration, the cone-specific functional defect resulted in a marked activation of GFAP, a hallmark of Müller-cell gliosis. Microarray-based network-analysis confirmed activation of Müller-glia-specific transcripts. Unexpectedly, we found up-regulation of the cytokine LIF and the anti-apoptotic transcription factor STAT3 in cpfl1 cone photoreceptors. We postulate that STAT3-related pathways are induced in cpfl1 cone photoreceptors to counteract degeneration.

Therapeutic targets in age-related macular disease

Age-related macular disease (AMD) accounts for more than 50% of blind registration in Western society. Patients with AMD are classified as having early disease, in which visual function is well preserved, or late disease, in which central vision is lost. Until recently, there was no therapy available by which the course of the disorder could be modified. Now, the most common form of late-stage AMD - choroidal neovascularization - responds to treatment with anti-VEGF therapies; although visual loss is modified in a portion of these cases, no therapeutic approach exists that alters the evolution from early to late disease. However, as discussed in this Review, research over the last few years has demonstrated several features of AMD that are likely to be amenable to treatment. Potential targets for treatment are described, and possible therapeutic approaches are discussed.

Retinal pseudocysts in age-related geographic atrophy

PURPOSE

To report the presence of pseudocysts in retinal layers of eyes with geographic atrophy (GA) attributable to age-related macular degeneration (AMD) and to estimate their prevalence.

DESIGN

Retrospective study.

METHODS

setting: Clinical practice. patients: Consecutive patients with GA, assessed by spectral-domain optical coherence tomography (OCT). main outcome measures: Assessment of pseudocyst prevalence in retinal layers. Statistical analysis by the chi(2) test, Fisher exact test, Mann-Whitney U test, and Cramer test, performed to explore links between the presence of pseudocysts and demographic features and/or pattern of atrophy, ie, horseshoe, homogeneous area, homogeneous area or patchy atrophy with foveal sparing, and patchy atrophy.

RESULTS

Eighty-eight eyes of 68 GA patients aged between 61 and 94 years (mean: 79.8) were examined. In 20 patients, GA was bilateral. Twenty-four eyes (27.2%) exhibited pseudocysts corresponding to small cystoid spaces frequently located in the inner nuclear layer of the retina. There was no macular edema. Fluorescein angiography, performed in 71 eyes (80%), ruled out possible choroidal neovascularization. No correlation was found between 1) patients' age (P = .7) or gender (P > .99) and the presence of pseudocysts or 2) patterns of atrophy (Cramer test: V = 0.183) and the presence of pseudocysts.

CONCLUSIONS

Pseudocysts seemed to be frequent in atrophic AMD. They might correspond to Müller cell degeneration, as suspected in other degenerative retinal disorders like tamoxifen retinopathy or group 2A idiopathic juxtafoveolar retinal telangiectasis. The present results indicate that pseudocysts are frequently seen on OCT in eyes with atrophic AMD and their presence should not be considered as a manifestation of neovascular AMD that requires prompt treatment.

Relationship between retinal sensitivity and morphologic changes in eyes with confluent soft drusen

PURPOSE

To examine the relationship between retinal sensitivity and morphologic changes in the macular area of eyes with confluent soft drusen.

METHODS

We retrospectively reviewed the medical records of the 21 consecutive patients (22 eyes) who had confluent soft drusen in the macular area. Using spectral-domain optical coherence tomography, a 6 x 6-mm area of each macula was examined with 256 sequential horizontal scans. Microperimetry in the macular area was carried out using the Micro Perimeter 1.

RESULTS

Spectral-domain optical coherence tomography images showed that protrusion of the retinal pigment epithelium (RPE) corresponded to the site of the confluent soft drusen. In addition, irregularities of the reflective line of the junction between inner and outer segments (IS/OS) of the photoreceptors were noted in 17 (77.3%) eyes. These irregularities were seen in the area with the protrusion of RPE. At 510 (68.1%) of 748 points with an intact retina, retinal sensitivity was 14 decibels or better. However, a retinal sensitivity of 14 decibels or better was obtained at 38.9% of points in irregular RPE with an intact IS/OS line, but at only 15.2% of points with an irregular IS/OS line. The mean retinal sensitivities within the area of irregular RPE with an intact IS/OS line, or in areas with an irregular IS/OS line, respectively, were significantly lower than that of intact retina (P < 0.0001).

CONCLUSION

Eyes with confluent soft drusen often show focal areas with reduced retinal function, areas that are consistent with irregularity of the RPE or of the IS/OS line.

Cone loss is delayed relative to rod loss during induced retinal degeneration in the diurnal cone-rich rodent Arvicanthis ansorgei

Cone photoreceptor breakdown underlies functional vision loss in many blinding diseases. Cone loss is often secondary to that of rods, but little experimental data are available on the relationship between the two populations. Because of its high cone numbers, we used the diurnal rodent Arvicanthis ansorgei to explore changes in rod and cone survival and function during chemically-induced retinal degeneration. Adult animals received intraperitoneal injections of N-methyl-N-nitrosourea (MNU), and changes in retinal fundus appearance, histology, phenotype, apoptosis (TUNEL staining) and functionality (scotopic and photopic electroretinography) were monitored as a function of post-treatment time and retinal topography. Relative to control animals injected with vehicle only, MNU-injected animals showed time-, region- and population-specific changes as measured by morphological and immunochemical criteria. Histological (gradual thinning of photoreceptor layer) and phenotypical (reduced immunostaining of rhodopsin and rod transducin, and mid wavelength cone opsin and cone arrestin) modifications were first observed in superior central retina at 11 days post-injection. These degenerative changes spread into the superior peripheral and inferior hemisphere during the following 10 days. Rod loss preceded that of cones as visualized by differential immunolabelling and presence of apoptotic cells in rod but not cone cells. By 3 months post-injection, degeneration of the photoreceptor layer was complete in the superior hemisphere, but only partial in the inferior hemisphere. Despite the persistence of cone photoreceptors, scotopic and photopic electroretinography performed at 90 days post-treatment showed that both rod and cone function were severely compromised. In conclusion, MNU-induced retinal degeneration in Arvicanthis follows a predictable spatial and temporal pattern allowing clear separation of rod- and cone-specific pathogenic mechanisms. Compared to other rodents in which MNU has been used, Arvicanthis ansorgei demonstrates pronounced resistance to photoreceptor cell loss.

Three dimensional optical coherence tomography imaging: advantages and advances

Three dimensional (3D) ophthalmic imaging using optical coherence tomography (OCT) has revolutionized assessment of the eye, the retina in particular. Recent technological improvements have made the acquisition of 3D-OCT datasets feasible. However, while volumetric data can improve disease diagnosis and follow-up, novel image analysis techniques are now necessary in order to process the dense 3D-OCT dataset. Fundamental software improvements include methods for correcting subject eye motion, segmenting structures or volumes of interest, extracting relevant data post hoc and signal averaging to improve delineation of retinal layers. In addition, innovative methods for image display, such as C-mode sectioning, provide a unique viewing perspective and may improve interpretation of OCT images of pathologic structures. While all of these methods are being developed, most remain in an immature state. This review describes the current status of 3D-OCT scanning and interpretation, and discusses the need for standardization of clinical protocols as well as the potential benefits of 3D-OCT scanning that could come when software methods for fully exploiting these rich datasets are available clinically. The implications of new image analysis approaches include improved reproducibility of measurements garnered from 3D-OCT, which may then help improve disease discrimination and progression detection. In addition, 3D-OCT offers the potential for preoperative surgical planning and intraoperative surgical guidance.

Noninvasive, in vivo assessment of mouse retinal structure using optical coherence tomography

Background

Optical coherence tomography (OCT) is a novel method of retinal in vivo imaging. In this study, we assessed the potential of OCT to yield histology-analogue sections in mouse models of retinal degeneration.

Methodology/Principal Findings

We achieved to adapt a commercial 3^rd generation OCT system to obtain and quantify high-resolution morphological sections of the mouse retina which so far required in vitro histology. OCT and histology were compared in models with developmental defects, light damage, and inherited retinal degenerations. In conditional knockout mice deficient in retinal retinoblastoma protein Rb, the gradient of Cre expression from center to periphery, leading to a gradual reduction of retinal thickness, was clearly visible and well topographically quantifiable. In Nrl knockout mice, the layer involvement in the formation of rosette-like structures was similarly clear as in histology. OCT examination of focal light damage, well demarcated by the autofluorescence pattern, revealed a practically complete loss of photoreceptors with preservation of inner retinal layers, but also more subtle changes like edema formation. In Crb1 knockout mice (a model for Leber's congenital amaurosis), retinal vessels slipping through the outer nuclear layer towards the retinal pigment epithelium (RPE) due to the lack of adhesion in the subapical region of the photoreceptor inner segments could be well identified.

Conclusions/Significance

We found that with the OCT we were able to detect and analyze a wide range of mouse retinal pathology, and the results compared well to histological sections. In addition, the technique allows to follow individual animals over time, thereby reducing the numbers of study animals needed, and to assess dynamic processes like edema formation. The results clearly indicate that OCT has the potential to revolutionize the future design of respective short- and long-term studies, as well as the preclinical assessment of therapeutic strategies.

Correlation between spectral-domain optical coherence tomography and fundus autofluorescence at the margins of geographic atrophy

PURPOSE

To study the appearance of margins of geographic atrophy in high-resolution optical coherence tomography (OCT) images and to correlate those changes with fundus autofluorescence (FAF) imaging.

DESIGN

Retrospective, observational case study.

METHODS

Patients with geographic atrophy secondary to dry age-related macular degeneration were assessed by means of spectral-domain OCT (Spectralis Heidelberg Retinal Angiograph/OCT; Heidelberg Engineering, Heidelberg, Germany; or OTI Inc, Toronto, Canada) as well as autofluorescence imaging (Heidelberg Retinal Angiograph or Spectralis; Heidelberg Engineering). The outer retinal layer alterations were analyzed in the junctional zone between normal retina and atrophic retina and were correlated with corresponding FAF.

RESULTS

Twenty-three eyes of 16 patients between 62 and 96 years of age were examined. There was a significant association between OCT findings and the FAF findings (r = 0.67; P < .0001). Severe alterations of the outer retinal layers at margins on spectral-domain OCT correspond significantly to increased autofluorescence; smooth margins on OCT correspond significantly to normal FAF (kappa, 0.7348; P < .0001).

CONCLUSIONS

Spectral-domain OCT provides in vivo insight into the pathogenesis of geographic atrophy and its progression. Visualization of reactive changes in the retinal pigment epithelial cells at the junctional zone and correlation with increased FAF; secondary to increased lipofuscin, together these methods may serve as determinants of progression of geographic atrophy.

Spectral domain optical coherence tomography in mouse models of retinal degeneration

PURPOSE

Spectral domain optical coherence tomography (SD-OCT) allows cross-sectional visualization of retinal structures in vivo. Here, the authors report the efficacy of a commercially available SD-OCT device to study mouse models of retinal degeneration.

METHODS

C57BL/6 and BALB/c wild-type mice and three different mouse models of hereditary retinal degeneration (Rho(-/-), rd1, RPE65(-/-)) were investigated using confocal scanning laser ophthalmoscopy (cSLO) for en face visualization and SD-OCT for cross-sectional imaging of retinal structures. Histology was performed to correlate structural findings in SD-OCT with light microscopic data.

RESULTS

In C57BL/6 and BALB/c mice, cSLO and SD-OCT imaging provided structural details of frequently used control animals (central retinal thickness, CRT(C57BL/6) = 237 +/- 2 microm and CRT(BALB/c) = 211 +/- 10 microm). RPE65(-/-) mice at 11 months of age showed a significant reduction of retinal thickness (CRT(RPE65) = 193 +/- 2 microm) with thinning of the outer nuclear layer. Rho(-/-) mice at P28 demonstrated degenerative changes mainly in the outer retinal layers (CRT(Rho) = 193 +/- 2 microm). Examining rd1 animals before and after the onset of retinal degeneration allowed monitoring of disease progression (CRT(rd1 P11) = 246 +/- 4 microm, CRT(rd1 P28) = 143 +/- 4 microm). Correlation of CRT assessed by histology and SD-OCT was high (r(2) = 0.897).

CONCLUSIONS

The authors demonstrated cross-sectional visualization of retinal structures in wild-type mice and mouse models for retinal degeneration in vivo using a commercially available SD-OCT device. This method will help to reduce numbers of animals needed per study by allowing longitudinal study designs and will facilitate characterization of disease dynamics and evaluation of putative therapeutic effects after experimental interventions.

Clinical use and research applications of Heidelberg retinal angiography and spectral-domain optical coherence tomography - a review

Fluorescein angiography (FA) was discovered by Nowotny and Alvis in the 1960s of the 20th century and has evolved to become the 'Gold standard' for macular diagnostics. Scanning laser imaging technology achieved enhancement of contrast and resolution. The combined Heidelberg retina angiograph (HRA2) adds novel innovative features to established fundus cameras. The principle of confocal scanning laser imaging provides a high resolution of retinal and choroidal vasculature with low light exposure providing comfort and safety for the patient. Enhanced contrast, details and image sharpness image are generated using confocality. For the visualization of the choroid an indocyanine green angiography (ICGA) is the most suitable application. The main indications for ICGA are age-related macular degeneration, choroidal polypoidal vasculopathy and choroidal haemangiomas. Simultaneous digital FA and ICGA images with three-dimensional resolution offer improved diagnosis of retinal and choroidal pathologies. High-speed ICGA dynamic imaging can identify feeder vessels and retinal choroidal anastomoses, ensuring safer treatment of choroidal neovascularization. Autofluorescence imaging and fundus reflectance imaging with blue and infrared light offer new follow-up parameters for retinal diseases. Finally, the real-time optical coherence tomography provides a new level of accuracy for assessment of the angiographic and morphological correlation. The combination of various macular diagnostic tools, such as infrared, blue reflectance, fundus autofluorescence, FA, ICGA and also spectral domain optical coherence tomography, lead to a better understanding and improved knowledge of macular diseases.

Three-dimensional high resolution OCT imaging of macular pathology

Raster scanning spectral domain optical coherence tomography (SD-OCT) enables realistic three-dimensional (3D) imaging of macular disease. This approach allows the clinician to investigate the diagnostic situation in detail before and during pharmacological or surgical intervention. This study demonstrates the clinical potential of SD-OCT in chorioretinal disease. Selected datasets are presented to visualize typical morphologic findings, which are identified in more than 2700 patients. Scans are presented as online assessable 3D-models. Clinically relevant structures are visualized in macular disease and highlight the importance of precise imaging, which clearly is a clinical necessity to plan and indicate modern therapeutic strategies for our patients.

Spectral domain-optical coherence tomography to detect localized retinal nerve fiber layer defects in glaucomatous eyes

This study examines the ability of RTVue, Cirrus and Spectralis OCT Spectral domain-optical coherence tomographs (SD-OCT) to detect localized retinal nerve fiber layer defects in glaucomatous eyes. In this observational case series, four glaucoma patients (8 eyes) were selected from the University of California, San Diego Shiley Eye Center and the Diagnostic Innovations in Glaucoma Study (DIGS) based on the presence of documented localized RNFL defects in at least one eye confirmed by masked stereophotograph assessment. One RTVue 3D Disc scan, one RTVue NHM4 scan, one Cirrus Optic Disk Cube 200x200 scan and one Spectralis scan centered on the optic disc (15x15 scan angle, 768 A-scans x 73 B-scans) were obtained on all undilated eyes within a single session. Results were compared with those obtained from stereophotographs. In 6 eyes the presence of localized RNFL defects was detected by stereophotography. In general, by qualitatively evaluating the retinal thickness maps generated, all SD-OCT instruments examined were able to confirm the presence of localized glaucomatous structural damage seen on stereophotographs. This study confirms SD-OCT is a promising technology for glaucoma detection as it may assist clinicians identify the presence of localized glaucomatous structural damage.

Reproducibility of retinal thickness measurements in healthy subjects using spectralis optical coherence tomography

PURPOSE

To test the reproducibility of retinal thickness measurements in healthy volunteers of a new Frequency-domain optical coherence tomography (OCT) device (Spectralis OCT; Heidelberg Engineering, Heidelberg, Germany).

DESIGN

Prospective, observational study.

METHODS

Forty-one eyes of 41 healthy subjects were included into the study. Intraobserver reproducibility was tested with 20 x 15 degree raster scans consisting of 37 high-resolution line scans that were repeated three times by one examiner (M.N.M.). Mean retinal thickness was calculated for nine areas corresponding to the Early Treatment Diabetic Retinopathy Study (ETDRS) areas. Coefficients of variation (COV) were calculated.

RESULTS

Retinal thickness measurements were highly reproducible for all ETDRS areas. Mean total retinal thickness was 342 +/- 15 microm. Mean foveal thickness was 286 +/- 17 microm. COVs ranged from 0.38% to 0.86%. Lowest COV was found for the temporal outer ETDRS area (area 7; COV, 0.38%). Highest COV was found for the temporal inner ETDRS area (area 3; COV, 0.86%). Mean difference between measurement 1 and 2, measurement 1 and 3, and measurement 2 and 3 for all ETDRS areas was 1.01 microm, 0.98 microm, and 0.99 microm, respectively.

CONCLUSION

Spectralis OCT retinal thickness measurements in healthy volunteers showed excellent intraobserver reproducibility with virtually identical results between retinal thickness measurements performed by one operator.