Kumar Sambhav

Optical coherence tomography angiography in retinal diseases

Optical coherence tomography angiography (OCTA) is a new, non-invasive imaging system that generates volumetric data of retinal and choroidal layers. It has the ability to show both structural and blood flow information. Split-spectrum amplitude-decorrelation angiography (SSADA) algorithm (a vital component of OCTA software) helps to decrease the signal to noise ratio of flow detection thus enhancing visualization of retinal vasculature using motion contrast. Published studies describe potential efficacy for OCTA in the evaluation of common ophthalmologic diseases such as diabetic retinopathy, age related macular degeneration (AMD), retinal vascular occlusions and sickle cell disease. OCTA provides a detailed view of the retinal vasculature, which allows accurate delineation of microvascular abnormalities in diabetic eyes and vascular occlusions. It helps quantify vascular compromise depending upon the severity of diabetic retinopathy. OCTA can also elucidate the presence of choroidal neovascularization (CNV) in wet AMD. In this paper, we review the knowledge, available in English language publications regarding OCTA, and compare it with the conventional angiographic standard, fluorescein angiography (FA). Finally, we summarize its potential applications to retinal vascular diseases. Its current limitations include a relatively small field of view, inability to show leakage, and tendency for image artifacts. Further larger studies will define OCTAs utility in clinical settings and establish if the technology may offer a non-invasive option of visualizing the retinal vasculature, enabling us to decrease morbidity through early detection and intervention in retinal diseases.

The application of optical coherence tomography angiography in retinal diseases

Optical coherence tomography angiography (OCTA) is a new, noninvasive imaging technique that generates real-time volumetric data on chorioretinal vasculature and its flow pattern. With the advent of high-speed optical coherence tomography, established enface chorioretinal segmentation, and efficient algorithms, OCTA generates images that resemble an angiogram. The principle of OCTA involves determining the change in backscattering between consecutive B-scans and then attributing the differences to the flow of erythrocytes through retinal blood vessels. OCTA has shown promise in the evaluation of common ophthalmologic diseases such as diabetic retinopathy, age-related macular degeneration, and retinal vascular occlusions. It quantifies vascular compromise reflecting the severity of diabetic retinopathy. OCTA detects the presence of choroidal neovascularization in exudative age-related macular degeneration and maps loss of choriocapillaris in nonexudative age-related macular degeneration. We describe principles of OCTA and findings in common and some uncommon retinal pathologies. Finally, we summarize its potential future applications. Its current limitations include a relatively small field of view, inability to show leakage, and a tendency for image artifacts. Further larger studies will define OCTAs utility in clinical settings and establish if the technology may offer its utility in decreasing morbidity through early detection and guide therapeutic interventions in retinal diseases.

Comparison of central corneal thickness: ultrasound pachymetry versus slit-lamp optical coherence tomography, specular microscopy, and Orbscan

Background Central corneal thickness (CCT) can be measured by using contact and non-contact methods. Ultrasound pachymetry (US pachymetry) is a contact method for measuring CCT and is perhaps the most commonly used method. However, non-contact methods like scanning slit topography (Orbscan II), slit-lamp optical coherence tomography (SL-OCT), and specular microscopy are also used. Not many studies have correlated the measurement of CCT with all four modalities. The purpose of this study was to compare and correlate the CCT measurements obtained by US pachymetry with SL-OCT, specular microscopy, and Orbscan. Method This is a prospective, comparative study done in an institutional setting. Thirty-two eyes of 32 subjects with no known ocular disease and best-corrected visual acuity of 20/20 were enrolled. CCT measurements were obtained using SL-OCT, specular microscopy, scanning slit topography (Orbscan), and US pachymetry. Three measurements were made with each instrument by the same operator. Mean, standard deviation, and coefficient of variation were calculated for CCT measurements acquired by the four measurement devices. Bland–Altman plot was constructed to determine the agreements between the CCT measurements obtained by different equipment. Results The mean CCT was 548.16±48.68 μm by US pachymetry. In comparison, CCT averaged 546.36±44.17 μm by SL-OCT, 557.61±49.92 μm by specular microscopy, and 551.03±48.96 μm by Orbscan for all subjects. Measurements by the various modalities were strongly correlated. Correlations (r2) of CCT, as measured by US pachymetry compared with other modalities, were: SL-OCT (r2=0.98, P<0.0001), specular microscopy (r2=0.98, P<0.0001), and Orbscan (r2=0.96, P<0.0001). All modalities had a linear correlation with US pachymetry measurements. Conclusion In subjects with healthy corneas, SL-OCT, specular microscopy, and Orbscan (with correction factor) can be used interchangeably with US pachymetry in certain clinical settings. The four modalities showed significant linear correlations with one another.

Aqueous Interleukin-6 Levels Are Superior to Vascular Endothelial Growth Factor in Predicting Therapeutic Response to Bevacizumab in Age-Related Macular Degeneration

Objective. To prospectively evaluate the effect of intravitreal bevacizumab on aqueous levels of interleukin-6 (IL-6) and vascular endothelial growth factor (VEGF) in patients with exudative age-related macular degeneration (AMD) and correlate clinical outcomes with cytokine levels. Methods. 30 eyes of 30 patients with exudative AMD underwent intravitreal injection of bevacizumab three times at monthly intervals. The aqueous samples prior to the 1st injection (baseline) and 3rd injection were analyzed for VEGF and IL-6 levels. Subjects were subgrouped based upon change in the central subfield (CSF) macular thickness on SD-OCT at 8 weeks. Group 1 included patients (n = 14) with a decrease in CSF thickness greater than 10% from the baseline (improved group). Group 2 included patients (n = 16) who had a decrease in CSF thickness 10% or less (treatment-resistant). Results. In subgroup analysis, in both groups 1 and 2 patients, compared to aqueous VEGF, aqueous IL-6 levels showed a better correlation with CSF thickness on SD-OCT (r = 0.72 and 0.71, resp.). Conclusions. Aqueous IL-6 may be an important marker of treatment response or resistance in wet macular degeneration. Future therapeutic strategies may include targeted treatment against both VEGF and IL-6, in patients who do not respond to anti-VEGF treatment alone.

Clinical applications of spectral domain optical coherence tomography in retinal diseases

Optical coherence tomography (OCT) was introduced about two decades ago and has revolutionized ophthalmic practice in recent years. It is a noninvasive noncontact imaging modality that provides a high-resolution cross-sectional image of the cornea, retina, choroid and optic nerve head, analogous to that of the histological section. Advances in OCT technology in signal detection technique from time-domain (TD) to spectral-domain (SD) detection have given us the potential to study various retinal layers more precisely and in less time. SD-OCT better delineates structural changes and fine lesions in the individual retinal layers. Thus, we have gained substantial information about the pathologic and structural changes in ocular conditions with primary or secondary retinal involvement. This review we discuss the clinical application of currently available SD-OCT in various retinal pathologies. Furthermore, highlights the benefits of SD-OCT over TD. With the introduction of enhanced depth imaging and swept – source OCT visualization of the choroid and choriocapillaris has become possible. Therefore, OCT has become an indispensable ancillary test in the diagnosis and management of diseases involving the retina and/or the choroid. As OCT technology continues to develop further it will provide new insights into the retinal and choroidal structure and the pathogenesis of posterior segment of the eye.

Capillary nonperfusion by novel technology of OCT angiography in a patient with sickle cell disease with normal fluorescein angiogram

Purpose Retinal ischemia is a pathophysiologic feature of sickle cell retinopathy. Inner retinal thinning of retina temporal to the fovea has been reported on spectral-domain optical coherence tomography (SD-OCT) even though clinical examination is normal and fluorescein angiography (FA) does not show any capillary dropout. In a patient with sickle cell disease with temporal inner retinal thinning on SD-OCT and normal FA, the new technology of OCT angiography (OCTA) showed a corresponding area of nonperfusion. Methods The patient with sickle cell disease underwent visual acuity testing, refraction, slit-lamp biomicroscopy, and dilated fundus examination. The patient also underwent SD-OCT, digital FA, and OCTA. The findings are described in this case report. Results In this patient with sickle cell disease, although clinical examination was normal and FA did not show any capillary dropout, the SD-OCT showed inner retinal thinning temporal to the fovea. Corresponding to this area, OCTA showed an area of nonperfusion. Conclusions Optical coherence tomography angiography technology may be more sensitive than the gold standard FA in identifying retinal ischemia in patients with sickle cell disease.

Deep capillary macular perfusion indices obtained with OCT angiography correlate with degree of nonproliferative diabetic retinopathy

Purpose To evaluate the integrity of macular and temporomacular vasculature in nonproliferative diabetic retinopathy (NPDR) with noninvasive optical coherence tomography angiography (OCTA) and correlate perfusion indices with degree of NPDR. Methods In this prospective observational cross-sectional study, 102 eyes with newly diagnosed NPDR (mild NPDR, 36; moderate NPDR, 21; severe NPDR, 13; NPDR with diabetic macular edema [DME], 32) underwent OCTA. Sixty eyes of normal subjects served as control. Degree of NPDR (based on Early Treatment Diabetic Retinopathy Study criteria) was confirmed with fluorescein angiography. Automated OCTA/split-spectrum amplitude decorrelation angiography software generated perfusion indices (vessel density and flow index) from images of the retina. The perfusion index of superficial and deep retinal plexuses was obtained in both perifoveal (central 1-3 mm) and parafoveal (3-6 mm) areas. Results Deep plexus parafoveal vessel density was 25.23% (±6.1) in mild NPDR, 20.16% (±6.16) in moderate NPDR, 11.16% (±4.16) in severe NPDR, and 17.91% (±4.42) in NPDR + DME compared to normal subjects (36.93% [±8.1]; (p<0.01). Spearman correlation coefficient (rs) between vessel density and level of NPDR severity in the parafoveal region showed inverse correlation for both superficial (rs -0.87; p = 0.083) and deep (rs -0.96; p = 0.017) plexus. Similarly, when vessel density of the perifoveal region was compared with level of NPDR severity, inverse correlation was noted in both superficial (rs -0.85; p = 0.08) and deep (rs -0.98; p = 0.011) plexus. Conclusions Optical coherence tomography angiography clearly delineated the retinal microcirculation and allowed quantification of vascular perfusion of each layer. As diabetic retinopathy progressed, a decrease in perfusion index is more pronounced in the deep retinal plexus and precedes changes in superficial plexus.

Evaluation of the iPad as a low vision aid for improving reading ability

Purpose To evaluate the effect of the iPad as a low vision aid in improving the reading ability of low vision patients (LVPs). Methods In this study, 228 consecutive patients that came for their routine eye care examination at the University of Florida, Jacksonville eye clinic, were enrolled. Patients met inclusion criteria if they had best-corrected visual acuity (BCVA) of 20/100 or worse in the best corrected eye and were willing to participate in the study. The patient’s reading ability was assessed both with the patient’s own spectacles and an iPad. Patients were encouraged to enlarge the reading material as well as change the contrast until they could read comfortably. The number of patients able to read the text comfortably was recorded. Results Out of the total 228 participants who qualified, 103 (45%) were male and 125 (55%) were female. Only 22% could read standard newsprint-sized text (N8) without the help of an iPad. With the help of an iPad, 94% participants with impaired vision were able to read standard newsprint-sized text (N8) or smaller text (P<0.01). Conclusion The iPad, a new portable electronic media device, can be adapted by LVPs to improve their reading ability.

Bilateral isolated concurrent superior ophthalmic vein thrombosis in systemic lupus erythematosus.

We describe a case of bilateral consecutive superior ophthalmic vein thrombosis as a presenting feature in a patient previously not known to have systemic lupus erythematosus (SLE). A 68-year-old African–American female presented with decreased vision in right eye, mild right orbital tenderness, and frontotemporal headache of 3 days duration. MRI of the orbits confirmed thrombosis of the right superior ophthalmic vein without extension into the cavernous sinus. Sequential MRI at 1 month showed interval improvement of the right superior ophthalmic vein thrombosis and a new thrombosis in the left superior ophthalmic vein. Renal biopsy revealed granular membranous and mesangial deposits of IgG, IgA, IgM, C3, and C1q and confirmed the diagnosis of SLE.

SWEPT SOURCE OPTICAL COHERENCE TOMOGRAPHY VALIDATES LAMINA CRIBROSA ANOMALY IN OPTIC DISK PIT.

Purpose: Swept Source Optical Coherence Tomography validates lamina cribrosa anomaly in optic disk pit. Method: Observational case report. Results: A 25-year-old African American male presented with decreased vision in right eye of 4 days duration. Best corrected visual acuity (BCVA) for distance in right eye was 20/200 and in left eye was 20/20. Dilated fundus examination of right eye showed serous macular detachment of entire posterior pole along with an optic pit on temporal margin of optic disk. En—face image of the optic disk on Swept source OCT (SS-OCT) confirmed defect in the lamina cribrosa in the right eye. Conclusion: Congenital optic disk pit a birth defect in lamina cribrosa is a rare, visually impairing disorder. Spectral domain optical coherence tomography (SD-OCT) scan showed neurosensory detachment, however, lamina cribrosa defects are not delineated with it. SS-OCT a recent advance in scanning technology allows superior resolution of optic disk and confirms the anomaly of lamina cribrosa.