Impact of optical coherence tomography scanning density on quantitative analyses in neovascular age-related macular degeneration.

PurposeTo assess the influence of varying B-scan frame-sampling densities on retinal thickness and volume measurements from spectral domain optical coherence tomography (OCT) in eyes with neovascular age-related macular degeneration (AMD).MethodsVolume OCT data (512 × 128 macular cube over 6 × 6 mm) were collected from 39 eyes with neovascular AMD. All 128 B-scans in each image set were manually segmented, allowing quantification of the neurosensory retina, subretinal fluid (SRF), subretinal hyperreflective material (SRHM), and pigment epithelium detachment (PED). Thickness maps were generated for less dense subsets of scans, ranging from every other (64 B-scans) to every 64th (2 B-scans). For each less dense subset, foveal central subfield thickness and total macular volume (TMV) were compared with values obtained using all 128 scans (considered the reference).ResultsFor each parameter, the mean absolute difference compared with the reference increased with reducing B-scan density. However, these differences did not reach statistical significance until frame-sampling density was reduced to every eighth scan (ie, 16 B-scans spaced 375 µm apart) for neurosensory retina, and every fourth scan (ie, 32 B-scans spaced 188 µm apart) for SRF, SRHM, and PED. For neurosensory retina, the mean (% error) and maximum (% error) absolute differences in TMV were 0.02 mm3 (0.24%) and 0.06 mm3 (0.79%), respectively. Similarly, at a density of 32 B-scans, mean and maximum differences for SRF were 0.004 mm3 (3.47%) and 0.02 mm3 (22.22%), respectively. The mean differences for SRHM and PED were 0.01 mm3 (8.03%) and 0.01 mm3 (4.04%), respectively.ConclusionsA minimum of 16 equally spaced B-scans, covering a 6 × 6 mm area, appears necessary to generate retinal thickness measurements similar to those obtained using all 128 B-scans in eyes with choroidal neovascularization (CNV). When considering other CNV lesion features, a minimum of 16 B-scans for SRF and PED, and 32 B-scans for SRHM are required to generate volume maps similar to ground-truth values. These findings may have implications for the design of acquisition and grading protocols for clinical trials using OCT in neovascular AMD.

Correlation between retinal sensitivity and cystoid space characteristics in diabetic macular edema.

PURPOSE: To evaluate the correlation between retinal sensitivity and cystoid space characteristics in eyes with diabetic macular edema (DME). MATERIALS AND METHODS: Prospective cross-sectional study of 22 subjects with DME (32 treatment-naïve eyes). All study subjects underwent complete ophthalmic examination, including slit-lamp biomicroscopy and dilated fundus examination. All subjects underwent spectral domain optical coherence tomography (SD-OCT) and microperimetry (MP). Intraretinal cystoid space (ICS) volume was generated after manual delineation of cystoid space boundaries using the three-dimensional-OCT software. Various SD-OCT parameters, including retinal thickness, retinal volume, cystoid space volume, cystoid space intensity, and outer retinal structure integrity, were correlated with MP parameters and best-corrected visual acuity (BCVA). RESULTS: Subject's mean age was 57 ± 9 years. The mean logarithm of minimum angle of resolution BCVA was 0.4 ± 0.2. The intraclass correlation coefficient for inter- and intra-grader assessment of cystoid space volume by manual delineation was 0.99 and 0.99, respectively. Mean total ICS volume was 0.4 ± 0.4 mm 3 and for the foveal center, subfield was 0.1 ± 0.1 mm 3 . Mean retinal sensitivity was 12.89 ± 10 dB; however, foveal retinal sensitivity was 12.3 ± 11.1 dB. We found no significant correlation between BCVA and total cystoid space volume (r = 0.33, P = 0.06). Correlation between total retinal sensitivity and total ICS was negative and nonsignificant (r = -0.17, P = 0.36). Correlation between foveal retinal sensitivity and foveal cystoid space intensity was moderate and marginally significant (r = -0.43, P = 0.05). CONCLUSION: Total cystoid space volume was not significantly correlated with BCVA or total retinal sensitivity in subjects with DME. Foveal cystoid space optical intensity was negatively correlated with foveal retinal sensitivity. These findings suggest further investigation of cystoid space characteristics in the setting of DME may be of value.

OCT angiography and sequential quantitative analysis of type 2 neovascularization after ranibizumab therapy.

PURPOSE: To study the precise structural aspects of a type 2 neovascular membrane in a patient with age-related macular degeneration (AMD) using optical coherence tomography (OCT) angiography and perform sequential quantitative analysis of the membrane after ranibizumab therapy. PATIENTS AND METHODS: Split-spectrum amplitude-decorrelation (SSADA) OCT angiography macular cubes (3 × 3 mm) were acquired with a light source centered at 840 nm, a bandwidth of 45 nm, and an A-scan-rate of 70 000 scans per second. Visible pathologic vessels were outlined manually on average intensity projection en face images, and the area of the lesion and the vessel density were measured at baseline and follow-up. RESULTS: At baseline, the neovascular lesion measured 4.12 mm(2) and the vessel density was 19.83 mm(-1). Four weeks after the first, and 2 and 4 weeks after the second ranibizumab injection, OCT angiography revealed a progressively smaller vascular lesion (2.32, 1.77 and 1.64 mm(2)), and vessel density (10.24, 8.52 and 7.57 mm(-1)), although the large central trunks of the lesion were unchanged. CONCLUSIONS: In this study, an obvious reduction in size and vessel density of the neovascular lesion was noted after treatment with ranibizumab using SSADA OCT angiography technology. Microvascular components can be delineated with precision, suggesting that this technique may be useful for the management of patients with neovascular AMD in a clinical setting as well as for future clinical trials.

Effect of OCT volume scan density on thickness measurements in diabetic macular edema.

PURPOSE: To evaluate the impact of reducing B-scan frame-sampling density on retinal thickness measurements using spectral domain optical coherence tomography (SD-OCT) in eyes with diabetic macular edema (DME). METHODS: We retrospectively collected OCT data for 64 eyes of 43 patients undergoing imaging for DME using the Cirrus HD-OCT 512 × 128 macular cube protocol. For each case, raw OCT data were imported into the 3D-OCTOR software, and retinal thickness maps were generated using all 128 B-scans and for lower densities of B-scans ranging from every other scan to only four scans (every 30-s B-scan). Maps were generated before and after manual correction of retinal boundary segmentation errors. The foveal central subfield (FCS) and total macular volume (TMV) values were used to compare thickness maps of varying densities. RESULTS: The mean difference in FCS retinal thickness and TMV increased as the B-scan density was reduced, particularly when the density was reduced to fewer than 16 B-scans over 6 mm. At a density of 16 B-scans, the mean absolute difference in FCS thickness was 2.43 µm (0.79%), with a maximum of 10.1 µm (4.09%). At this density, the mean difference in TMV was 0.012 mm(3) (0.13%), with a maximum difference of 0.04 mm(3) (0.47%). Manual correction of OCT segmentation errors resulted in a difference in FCS thickness of ≥ 10 µm in only 12.5% of cases, with a maximum difference of 115.7 µm. CONCLUSION: A minimum of 16 equally spaced B-scans appear necessary to generate retinal thickness measurements similar to those produced using all 128 B-scans in eyes with DME. Manual correction of segmentation errors appeared to have a clinically meaningful effect in a small minority of cases. These results may have implications for the design of SD-OCT imaging and grading protocols in clinical trials of DME, particularly when using multiple SD-OCT instruments that acquire varying numbers of B-scans.

Visual restoration and transplant connectivity in degenerate rats implanted with retinal progenitor sheets.

The aim of this study was to determine whether retinal progenitor layer transplants form synaptic connections with the host and restore vision. Donor retinal sheets, isolated from embryonic day 19 rat fetuses expressing human placental alkaline phosphatase (hPAP), were transplanted to the subretinal space of 18 S334ter-3 rats with fast retinal degeneration at the age of 0.8-1.3 months. Recipients were killed at the age of 1.6-11.8 months. Frozen sections were analysed by confocal immunohistochemistry for the donor cell label hPAP and synaptic markers. Vibratome slices were stained for hPAP, and processed for electron microscopy. Visual responses were recorded by electrophysiology from the superior colliculus (SC) in 12 rats at the age of 5.3-11.8 months. All recorded transplanted rats had restored or preserved visual responses in the SC corresponding to the transplant location in the retina, with thresholds between -2.8 and -3.4 log cd/m(2). No such responses were found in age-matched S334ter-3 rats without transplants, or in those with sham surgery. Donor cells and processes were identified in the host by light and electron microscopy. Transplant processes penetrated the inner host retina in spite of occasional glial barriers between transplant and host. Labeled neuronal processes were found in the host inner plexiform layer, and formed apparent synapses with unlabeled cells, presumably of host origin. In conclusion, synaptic connections between graft and host cells, together with visual responses from corresponding locations in the brain, support the hypothesis that functional connections develop following transplantation of retinal layers into rodent models of retinal degeneration.

Imaging chorioretinal vascular disease.

Since its first description more than 40 years ago, fluorescein angiography had a crucial role in the diagnosis and management of chorioretinal vascular disorders such as neovascular age-related macular degeneration. Although fluorescein angiography permits visualization of the retinal microcirculation in exquisite detail, visualization of the choroidal circulation is more limited. Moreover, fluorescein angiography provides only minimal information regarding the functional consequences of vascular disease and allows, at best, only semi-quantitative assessment of retinal thickness. In recent years, the development of other chorioretinal imaging modalities, such as indocyanine green angiography, fundus autofluorescence, and optical coherence tomography (OCT), has addressed many of these issues. In particular, OCT has become an integral tool for vitreoretinal specialists as it allows high-resolution cross-sectional images of the neurosensory retina to be obtained in a non-invasive manner. The latest generation of commercial OCT technology-spectral domain OCT-offers high-speed scanning that allows complete coverage of the macular area, generation of three-dimensional retinal reconstructions, and precise image registration for inter-visit comparisons. The high speed of spectral domain OCT also facilitates B-scan averaging, which reduces speckle noise artefact and allows unparalleled visualization of the outer retina and choroid. In the near future, further advances in OCT technology (eg Doppler OCT) are likely to dramatically enhance the diagnosis and management of patients with chorioretinal vascular disease.

Accuracy of retinal thickness measurements obtained with Cirrus optical coherence tomography.

AIM: To report the frequency and severity of retinal thickness measurement errors in a Fourier domain optical coherence tomography (FDOCT) device, Cirrus OCT. METHODS: Data from 209 eyes undergoing Cirrus OCT imaging with the Macular Cube protocol were collected. For each eye, the position of the automated retinal boundary lines used by the Cirrus OCT software for thickness calculations was assessed using a 6-point categorical scale. The presence of errors was correlated with various parameters including: retinal morphological features and disease diagnosis. RESULTS: Errors of retinal boundary detection were observed in 57.5% of eyes but were severe in only 9.6% of eyes. The identification of subretinal fluid, subretinal tissue, pigment epithelium detachment or a diagnosis of choroidal neovascularisation was associated with more severe errors. Retinal cysts or a diagnosis of retinal vascular disease were less likely to be associated with significant error. CONCLUSIONS: Retinal thickness measurement errors appear to occur less frequently with Fourier domain OCT (Cirrus OCT), but segmentation errors remain a concern, particularly in assessment of eyes with structurally complex retinal disease. With the recent release of multiple FDOCT systems, assessment of segmentation error may be an important factor in determining the relative merits of these systems.

Comparison of the optical coherence tomographic features of choroidal neovascular membranes in pathological myopia versus age-related macular degeneration, using quantitative subanalysis.

AIM: To compare the retinal morphological characteristics of eyes with choroidal neovascularisation (CNV) secondary to pathological myopia versus eyes with CNV secondary to age-related macular degeneration (AMD), using quantitative optical coherence tomography (OCT) subanalysis. METHODS: Twenty-one eyes of 21 patients newly diagnosed as having CNV secondary to pathological myopia, and 43 consecutive cases of eyes with newly diagnosed subfoveal CNV secondary to AMD were retrospectively collected. In all patients, StratusOCT images and fluorescein angiograms (FA) were available for analysis. StratusOCT images were analysed using custom software (termed "OCTOR"), which allowed calculation of the thickness/volume of the neurosensory retina, subretinal fluid (SRF), subretinal tissue (SRT) and pigment epithelial detachments (PEDs). FA images were used to calculate CNV leakage area and CNV lesion size for each eye. RESULTS: The total volume of neurosensory retina in the pathological myopia group was significantly less than in the AMD group (7.10 (SD 0.50) mm3 vs 7.76 (0.93) mm3, p = 0.004). The total volume of SRF in the pathological myopia group was less than in the AMD group, but the difference was not statistically significant (0.33 (1.38) mm3 vs 0.55 (0.82) mm3, p = 0.434). The total volume of SRT in the pathological myopia group was less than in the AMD group, but the difference was not statistically significant (0.16 (0.15) mm3 vs 0.36 (0.60) mm3, p = 0.144). The total volume of PED in the pathological myopia group was markedly less than in the AMD group (0.01 (0.03) mm3 vs 1.09 (1.89) mm3, p<0.001). On FA, the total leakage of CNV in the AMD group was significantly greater than in the pathological myopia group (4.17 (3.29) DAs vs 0.53 (0.58) DAs, p<0.001). CONCLUSIONS: CNV lesions in pathological myopia were associated with considerably less retinal oedema, SRF and SRT compared with CNV associated with AMD. PEDs were almost negligible in myopic lesions compared with AMD. These findings are consistent with previous clinical and angiographic descriptions of myopic CNV as relatively small lesions with modest exudation.

Restoration of visual responses following transplantation of intact retinal sheets in rd mice.

PURPOSE: To correlate the functional outcomes with histologic findings following transplantation of fetal retinal sheets in rd mice, and to investigate the mechanisms of visual function restoration. METHODS: Twenty-one postnatal day 31-38 rd/rd (C3H/HeJ) mice were transplanted in one eye with retinal sheets (1.0 x 0.4 mm) obtained from embryonic day (E) 17 enhanced-green-fluorescent protein (eGFP) mice. Five mice underwent sham surgery without insertion of tissue. Four to five weeks after transplantation, visual responses to a light flash were recorded across the superior colliculus (SC) in seven eyes of seven transplanted mice that had clear corneas and lenses, and in all five sham surgery mice. Following the SC recording, the eyes were enucleated and processed for immunohistochemistry and examined using confocal microscopy. RESULTS: In three out of the seven eyes (43%), positive responses were recorded in the SC in an area topographically corresponding to the placement of the transplant in the host retina. No responses were recorded in the untreated eyes of 5-week-old and 9-week-old rd/rd mice, and in the 9-week-old sham surgery mice. In contrast, visual responses were recorded over the entire SC in normal eyes. The response onset latencies of the 3 transplanted mice with responses were similar to those of normal control mice. The organization of the graft did not appear to correlate as expected with the electrophysiology results, as eyes with well-organized, laminated grafts showed no response whereas the three light-responsive eyes had rosetted or disorganized grafts. All three light-responsive eyes demonstrated much higher levels of recoverin immunoreactivity in the host retina overlying the graft compared with untreated age-matched rd/rd mice. CONCLUSION: Restoration of the SC visual response does not appear to depend on a well-organized transplant in the rd mouse. Increased recoverin-staining in the host retina in light-responsive animals suggested that host cone rescue was the likely mechanism of vision restoration in this transplant model.

Alternative culture conditions for isolation and expansion of retinal progenitor cells.

PURPOSE: To investigate different in vitro model systems for retinal progenitor cell (RPC) isolation and expansion. METHODS: RPCs were isolated from embryonic day (E) 17 Long Evans rat retinas. Three different culture media: (1) modified serum free defined media (2) serum-containing media and (3) embryonic stem cell (ES)-conditioned media were used for RPC isolation and long term expansion. Expression of various cellular markers and cell morphologies were compared among the three culture systems at different passages by immunostaining and confocal microscopy. RESULTS: All three culture systems could maintain RPCs as nestin-positive cells (78-87%) after long-term in vitro expansion. However, RPCs appeared to proliferate faster in the serum-free culture system. The ES-conditioned media provided the best RPC survival. Cells appeared smaller at early passages compared with later passages. This morphology change occurred at P9-P10 in the serum-free medium, and at P5-P6 in the other two culture systems. CONCLUSIONS: The serum-free medium may be superior for preventing RPC differentiation during expansion.

Clinical spectrum of posterior ischemic optic neuropathy.

PURPOSE: To describe the systemic and visual characteristics and prognosis in patients with posterior ischemic optic neuropathy (PION). DESIGN: Observational case series. METHODS: Retrospective chart review in a multicenter setting. Seventy-two patients (98 eyes) with a clinical diagnosis of PION. Co-morbid systemic diseases and visual function were recorded at both initial presentation and after mean visual follow-up of 4.1 years and systemic follow-up of 5.4 years. RESULTS: PION occurred in three main settings: in the perioperative period following a variety of surgical procedures (28 patients), associated with giant cell (temporal) arteritis (6 patients), and associated with nonarteritic systemic vascular disease (38 patients). Patients with perioperative and arteritic PION were more likely to have severe, bilateral visual loss that did not improve. Among eyes with nonarteritic PION, 34% experienced improvement in vision, 28% remained stable, and 38% worsened. Among patients with nonarteritic PION, carotid artery disease and a history of stroke (with or without carotid artery disease) were both associated with a statistically significant increased risk of poor final visual outcome. CONCLUSIONS: There are three distinct subtypes of PION: perioperative, arteritic, and nonarteritic. Patients with PION that is unassociated with surgery should undergo an evaluation for systemic vascular diseases, including giant cell arteritis, that may or may not be apparent at the time of vision loss. The visual prognosis for patients with perioperative or arteritic PION is poor, whereas that for nonarteritic PION is similar to that for patients with nonarteritic AION.

Light-driven retinal ganglion cell responses in blind rd mice after neural retinal transplantation.

PURPOSE: Light-elicited retinal ganglion cell (RGC) responses after fetal neural retinal transplantation have not been demonstrated in animal or human subjects blind from outer retinal degeneration, despite apparent morphologic success. This study was designed to test the hypothesis that the functional success of retinal transplantation may be enhanced by using a young host retina (13 days old). METHODS: At postnatal day (P)13 C3H/HeJ (rd/rd) retinal degenerate mice received a subretinal transplant, in one eye only, of neural retinal tissue isolated from newborn normal C57/BL6J mice. Between 33 and 35 days after transplantation, local electroretinograms (ERGs) and ganglion cell responses were recorded directly from the retinal surface using a differential bipolar surface electrode. Measurements were performed both with and without light stimulation. Similar recordings were also performed in age-matched eyes subjected to sham transplantation, in control eyes that were not subjected to surgery, and in animals eyes that underwent transplantation at 8 weeks of age. After the recordings, the eyes were processed for light and transmission electron microscopy. RESULTS: Three of 10 mice showed bursts of ganglion cell action potentials (ON response only) as well as recordable intraocular ERGs over the transplant in response to 1-second and 200-msec light stimuli. Light-driven ganglion cell responses could not be recorded in areas outside the transplant in all transplant-recipient eyes, age-matched control eyes, and sham-transplantation eyes. Light responses also could not be recorded in animal eyes that received transplants at an older age (8 weeks). Electron microscopic examination confirmed the presence of photoreceptor outer segments in the areas affected by transplantation. CONCLUSIONS: This study demonstrates the presence of light-driven ganglion cell responses after subretinal transplantation in a retinal degenerate model. This finding may reflect functional integration of the transplant with the host, but a rescue effect on remaining host photoreceptors cannot be ruled out. The findings suggest, however, that modification of host parameters, such as host age, may be important approaches for improving the functional success of retinal transplantation.

Human neural retinal transplantation.

PURPOSE: A pilot study of human neural retinal transplantation was undertaken to investigate three major issues: whether a safe surgical procedure could be devised for transplantation of neural retinal tissue into the subretinal space, whether the transplant would be accepted in the subretinal space, and whether an improvement in vision could be achieved. METHODS: Eight patients with bare light perception (LP) vision due to retinitis pigmentosa (RP) and one patient with bare LP vision due to advanced neovascular age-related macular degeneration (AMD) received subretinal transplants of human fetal retinal microaggregate suspensions without postoperative systemic immunosuppression. The patient with AMD also received a fetal retinal sheet transplant. The ages of the patients ranged from 31 to 94 years (median, 55 years). The pre- and postoperative evaluations included visual function testing, detailed fundus examinations, fundus photography, fluorescein angiography, macular perimetry using a scanning laser ophthalmoscope (SLO), and full field and focal electroretinograms (ERGs). RESULTS: Three of the eight RP patients demonstrated possible improved light sensitivity during the initial months of follow-up. However, visual improvement disappeared between 3 and 13 months of follow-up. After transplantation, no subject showed any changes in the ERG recordings or SLO macular perimetry relative to their preoperative baseline. No patient experienced a retinal detachment, infection, or extensive bleeding. None of the patients developed retinal vasculitis or intraocular inflammation. In one RP patient, fluorescein angiography and fundus photography documented the formation and maturation of new host retinal vessels in the area of the transplant. CONCLUSIONS: Transplantation of fetal retinal photoreceptor suspensions into the subretinal space was achieved safely in nine subjects. Although a definite positive effect on visual function could not be demonstrated, the apparent high tolerance for graft tissue is promising for future efforts in the field of neural retinal transplantation.

Histologic correlation of human neural retinal transplantation.

PURPOSE: To describe the histologic findings of the transplanted eye of a 94-year-old man with neovascular age-related macular degeneration, who 3 years earlier underwent subretinal transplantation of both a fetal neural retinal sheet and a retinal microaggregrate suspension. METHODS: Serial sections of the posterior segment of the eye and the transplanted areas were processed and studied by routine histologic techniques, including both light and transmission electron microscopy (TEM). Transplanted areas were also examined for the presence of glial, neuronal, and photoreceptor cell markers by standard immunohistochemical methods. RESULTS: After transplantation in this patient, there was no visual improvement. Light microscopic examination disclosed survival of the transplanted cells in the subretinal space with no evidence of inflammation or rejection. The neural retinal sheet transplant developed a layered configuration. The retinal pigment epithelium (RPE) was absent over much of the posterior pole, including the area of transplantation. TEM examination and immunohistochemical analysis disclosed the presence of neuronal and glial cells within the transplant. A few transplant neuronal cell processes overlying a focus of residual RPE cells were positive for S-antigen, but well-developed photoreceptor outer segments were not present. CONCLUSIONS: Long-term survival of transplanted neural retinal tissue can be achieved in human patients without immunosuppression. The lack of photoreceptor development in this patient may be the result of absent or dysfunctional RPE. Nonetheless, the long-term survival of grafted tissue in the human subretinal space in the absence of immunosuppressive treatment is promising for future efforts in the field of neural retinal transplantation.

Anomalous optic disc elevation associated with ultrasonographic evidence of increased subarachnoid fluid.

The presence of increased subarachnoid fluid around the optic nerve as measured by ultrasound has been shown to be associated with elevated intracranial pressure, as well as a number of other conditions. This finding has proved useful for distinguishing optic disc elevation secondary to papilledema from disc elevation attributable to other causes. This report describes a patient with anomalous optic disc elevation and increased subarachnoid fluid around the optic nerve.