Optical coherence photoacoustic microscopy for in vivo multimodal retinal imaging.

We developed an optical coherence photoacoustic microscopy (OC-PAM) system, which can accomplish optical coherence tomography (OCT) and photoacoustic microscopy (PAM) simultaneously by using a single pulsed broadband light source. With a center wavelength of 800 nm and a bandwidth of 30 nm, the system is suitable for imaging the retina. Generated from the same group of photons, the OCT and PAM images are intrinsically registered in the lateral directions. To test the capabilities of the system on multimodal ophthalmic imaging, we imaged the retina of pigmented rats. The OCT images showed the retinal structures with quality similar to conventional OCT, while the PAM images revealed the distribution of absorbers in the retina. Since the absorption of hemoglobin is relatively weak at around 800 nm, the NIR PAM signals are generated mainly from melanin in the posterior segment of the eye, thus providing melanin-specific imaging of the retina.

OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY OF RETINAL VENOUS OCCLUSION.

PURPOSE: To noninvasively evaluate the retinal microvasculature in human subjects with retinal venous occlusions using optical coherence tomography angiography and assess potential clinical applications. METHODS: This was a prospective, observational study of adult human subjects with clinical and imaging findings demonstrating retinal venous occlusion. Subjects underwent complete ophthalmic examination and fluorescein angiography as appropriate for their standard of care. Optical coherence tomography angiography was performed on a prototype spectral domain-OCTA system in 3 mm × 3 mm and 6 mm × 6 mm regions centered on the fovea and parafoveal areas. Retinal vasculature was assessed within three horizontal slabs consisting of the superficial, middle, and deep retina. The vasculature within each slab was reconstructed using intensity contrast-based algorithms and visualized as en-face images. Optical coherence tomography angiograms were manually segmented to verify the accuracy of the automated segmentation algorithms. RESULTS: Optical coherence tomography angiography was able to demonstrate almost all of the clinically relevant findings in 25 subjects with acute and chronic retinal venous occlusion. These findings were consistent with clinical, anatomic, and fluorescein angiographic findings including areas of impaired vascular perfusion, retinal atrophy, vascular dilation, shunt vessels, and some forms of intraretinal edema. CONCLUSION: Optical coherence tomography angiography is an investigational method that generates high-resolution, noninvasive angiograms that qualitatively illustrate most of clinically relevant findings in retinal venous occlusion. Optical coherence tomography angiography corresponds well with fluorescein angiograms and in many cases provides more detailed anatomic and blood flow information. Optical coherence tomography angiography, in conjunction with standard spectral domain-OCT, is at least equally as effective as fluorescein angiography for evaluation and management of the macular complications of retinal venous occlusions.

Spectral domain optical coherence tomography imaging of drusen in nonexudative age-related macular degeneration.

PURPOSE: To measure drusen area and volume in eyes with nonexudative age-related macular degeneration (AMD) using spectral domain optical coherence tomography imaging (SD-OCT). DESIGN: Evaluation of diagnostic technology. PARTICIPANTS: One hundred three eyes from 74 patients with drusen. METHODS: Patients with drusen secondary to nonexudative AMD were enrolled in this study. Five separate SD-OCT scans, each consisting of 40 000 uniformly spaced A-scans organized as 200 A-scans in each B-scan and 200 horizontal B-scans, were performed on each eye. Each scan covered a retinal area of 6×6 mm centered on the fovea. A novel algorithm was used to quantitatively assess drusen area and volume. Measurements from the entire scans, as well as in regions contained within 3- and 5-mm circles centered on the fovea, were analyzed. Test-retest standard deviations of drusen area and volume measurements were calculated for each eye. MAIN OUTCOME MEASURES: Drusen area and volume. RESULTS: The algorithm created drusen maps that permitted both qualitative and quantitative assessment of drusen area and volume. Both the qualitative appearance and the quantitative measurements of drusen area and volume were highly reproducible over the 5 different datasets. The intraclass correlation coefficient was >0.99 for both area and volume measurements on the entire dataset as well as the 3- and 5-mm circles. The correlation between lesion size and the test-retest standard deviations can be eliminated by performing a square root transformation of the area measurements and a cube root transformation of the volume measurements. These transformed data allowed for the inclusion of all drusen sizes in the calculation of an estimated single pooled test-retest standard deviation, which will be useful for longitudinal studies of drusen natural history. CONCLUSIONS: A novel algorithm for the qualitative and quantitative assessment of drusen imaged using SD-OCT was shown to be highly reproducible. The ability to assess drusen volume reliably represents a new quantitative parameter to measure in AMD and may be useful when assessing disease progression, particularly in trials for treatments of nonexudative AMD.

Dual-band spectral-domain optical coherence tomography for in vivo imaging the spectral contrasts of the retinal nerve fiber layer.

The ultimate goal of the study is to provide an imaging tool to detect the earliest signs of glaucoma before clinically visible damage occurs to the retinal nerve fiber layer (RNFL). Studies have shown that the optical reflectance of the damaged RNFL at short wavelength (<560 nm) is reduced much more than that at long wavelength, which provides spectral contrast for imaging the earliest damage to the RNFL. To image the spectral contrast we built a dual-band spectral-domain optical coherence tomography (SD-OCT) centered at 808 nm (NIR) and 415 nm (VIS). The light at the two bands was provided by the fundamental and frequency-doubled outputs of a broadband Ti:Sapphire laser. The depth resolution of the NIR and VIS OCT systems are 4.7 µm and 12.2 µm in the air, respectively. The system was applied to imaging the rat retina in vivo. Significantly different appearances between the OCT cross sectional images at the two bands were observed. The ratio of the light reflected from the RNFL over that reflected from the entire retina at the two bands were quantitatively compared. The experimental results showed that the dual-band OCT system is feasible for imaging the spectral contrasts of the RNFL.

Endophthalmitis after intravitreal vascular [corrected] endothelial growth factor antagonists: a six-year experience at a university referral center.

PURPOSE: To assess the rate of infectious endophthalmitis and to describe the clinical and microbiological features of eyes that develop clinically suspected endophthalmitis after an intravitreal injection of vascular endothelial growth factor antagonists. METHODS: The medical records of patients undergoing intravitreal injections of anti-vascular endothelial growth factor agents from January 1, 2005, through December 31, 2010, at a single university referral center and associated satellite clinics were retrospectively analyzed to determine the rate of infectious endophthalmitis after intravitreal anti-vascular endothelial growth factor injections. RESULTS: Twelve cases (11 patients) of clinically suspected endophthalmitis were identified after a total of 60,322 injections (0.02%; 95% confidence interval, 0.0114%-0.0348%). Of the 12 cases, 11 presented within 3 days of the injection. Of the 7 culture-positive cases, 5 were because of Streptococcus species. In 4 of the 5 Streptococcus cases, final visual acuity was hand motions or worse. The rate of clinically suspected endophthalmitis was 0.018% after bevacizumab and 0.027% after ranibizumab injections. CONCLUSION: A very low rate of endophthalmitis after intravitreal injections of anti-vascular endothelial growth factor agents was observed. Patients typically presented within 3 days of injection. Streptococcus species was the most common bacteria isolated, and it was generally associated with poor visual outcomes.

Adaptive optics photoacoustic microscopy.

We have developed an adaptive optics photoacoustic microscope (AO-PAM) for high-resolution imaging of biological tissues, especially the retina. To demonstrate the feasibility of AO-PAM we first designed the AO system to correct the wavefront errors of the illuminating light of PAM. The aberrations of the optical system delivering the illuminating light to the sample in PAM was corrected with a close-loop AO system consisting of a 141-element MEMS-based deformable mirror (DM) and a Shack-Hartmann (SH) wavefront sensor operating at 15 Hz. The photoacoustic signal induced by the illuminating laser beam was detected by a custom-built needle ultrasonic transducer. When the wavefront errors were corrected by the AO system, the lateral resolution of PAM was measured to be better than 2.5 µm using a low NA objective lens. We tested the system on imaging ex vivo ocular samples, e.g., the ciliary body and retinal pigment epithelium (RPE) of a pig eye. The AO-PAM images showed significant quality improvement. For the first time we were able to resolve single RPE cells with PAM.

Collecting back-reflected photons in photoacoustic microscopy.

Since the photoacoustic effect relies only on the absorbed optical energy, the back-reflected photons from samples in optical-resolution photoacoustic microscopy are usually discarded. By employing a 2 x 2 single-mode fiber optical coupler in a laser-scanning optical-resolution photoacoustic microscope for delivering the illuminating laser light and collecting the back reflected photons, a fiber-optic confocal microscope is integrated with the photoacoustic microscope. Thus, simultaneous multimodal imaging can be achieved with a single light source and images from the two modalities are intrinsically registered. Such capabilities are demonstrated in imaging both phantoms and small animals in vivo.

Photoacoustic ophthalmoscopy for in vivo retinal imaging.

We have developed a non-invasive photoacoustic ophthalmoscopy (PAOM) for in vivo retinal imaging. PAOM detects the photoacoustic signal induced by pulsed laser light shined onto the retina. By using a stationary ultrasonic transducer in contact with the eyelids and scanning only the laser light across the retina, PAOM provides volumetric imaging of the retinal micro-vasculature and retinal pigment epithelium at a high speed. For B-scan frames containing 256 A-lines, the current PAOM has a frame rate of 93 Hz, which is comparable with state-of-the-art commercial spectral-domain optical coherence tomography (SD-OCT). By integrating PAOM with SD-OCT, we further achieved OCT-guided PAOM, which can provide multi-modal retinal imaging simultaneously. The capabilities of this novel technology were demonstrated by imaging both the microanatomy and microvasculature of the rat retina in vivo.

Simultaneous dual molecular contrasts provided by the absorbed photons in photoacoustic microscopy.

We investigated the feasibility of simultaneously imaging two distinctive molecular contrasts provided by the absorbed photons in biological tissues with a single light source. The molecular contrasts are based on two physical effects induced by the absorbed photons: photoacoustics (PA) and autofluorescence (AF). In an integrated multimodal imaging system, the PA and AF signals were detected by a high-sensitivity ultrasonic transducer and an avalanche photodetector, respectively. The system was tested by imaging ocular tissue samples, including the retinal pigment epithelium and the ciliary body. The acquired images provided information on the spatial distributions of melanin and lipofuscin in these samples.

Optical coherence tomography: a new tool for intraoperative decision making.

Optical coherence tomography (OCT) has traditionally been used in the outpatient environment as an important diagnostic tool for retinal clinical decision making. Recent advances in OCT technology have made intraoperative use of OCT feasible.

Surgical management of vitreofoveal traction syndrome: optical coherence tomographic evaluation and clinical outcomes.

BACKGROUND AND OBJECTIVE: To characterize vitreofoveal traction syndrome and to correlate clinical observations, optical coherence tomography features, and surgical results. PATIENTS AND METHODS: A retrospective, consecutive, interventional case series of 36 patients. Clinical and optical coherence tomography features taken from patient charts were compared preoperatively and postoperatively and correlated with visual outcomes. RESULTS: Preoperatively, visual acuity ranged from 20/40 to 20/400 and improved more than 2 lines in 50% of eyes. A macular hole developed in 2 eyes. The optical coherence tomography appearance of traction resolved in all eyes; cystic change improved markedly or resolved in 86% of eyes. Preoperative optical coherence tomography features did not correlate with visual acuity. Patients with symptoms for less than a 6-month duration (P = .048) were more likely to obtain a visual acuity of 20/40 or better postoperatively. Presence or resolution of macular cystic changes and subretinal fluid did not correlate with visual acuity or change (P > .05). CONCLUSION: Patients with vitreofoveal traction syndrome usually achieve favorable visual optical coherence tomography outcomes after pars plana vitrectomy.

New Frontiers in Retina: highlights of the 2020 angiogenesis, exudation and degeneration symposium.

We summarize the most important findings presented at the 2020 angiogenesis, exudation and degeneration symposium in five topic areas: (1) epidemiology of retinal vascular disease and macular degeneration; (2) dry AMD and geographic atrophy; (3) neovascular age-related macular degeneration; (4) drug delivery and devices and (5) diabetic retinopathy.

Retinal tumor imaging and volume quantification in mouse model using spectral-domain optical coherence tomography.

We have successfully imaged the retinal tumor in a mouse model using an ultra-high resolution spectral-domain optical coherence tomography (SD-OCT) designed for small animal retinal imaging. For segmentation of the tumor boundaries and calculation of the tumor volume, we developed a novel segmentation algorithm. The algorithm is based on parametric deformable models (active contours) and is driven by machine learning-based region classification, namely a Conditional Random Field. With this algorithm we are able to obtain the tumor boundaries automatically, while the user can specify additional constraints (points on the boundary) to correct the segmentation result, if needed. The system and algorithm were successfully applied to studies on retinal tumor progression and monitoring treatment effects quantitatively in a mouse model of retinoblastoma.

Simultaneous multimodal imaging with integrated photoacoustic microscopy and optical coherence tomography.

We have developed a multimodal imaging technique by integrating photoacoustic microscopy and spectral-domain optical coherence tomography to provide simultaneous volumetric microscopic imaging of both optical absorption and scattering contrasts in biological tissues. In the integrated system, the two imaging modalities share the same optical scanning and delivery mechanisms after their probing and illumination light beams are combined. By further synchronizing the image acquisitions, the images from the two modalities are intrinsically registered. The capabilities of this novel technique were demonstrated by imaging both the microanatomy and microvasculature in mouse ears in vivo.

Spectral domain optical coherence tomography characteristics of cuticular drusen.

PURPOSE: To evaluate the appearance of cuticular drusen with spectral domain optical coherence tomography. METHODS: Eyes of patients with cuticular drusen were imaged using a prototype spectral domain optical coherence tomography instrument with 5-microm axial resolution. Thickness maps were obtained after automated segmentation of the internal limiting membrane and retinal pigment epithelium layers using a proprietary algorithm. The volume of subretinal fluid (SRF) was calculated using a manual segmentation technique that involved drawing boundaries around the SRF. The repeatability of these measurements was tested by comparing the volume measurements from multiple scans performed on the same day in four eyes of three patients. RESULTS: Sixteen eyes from eight patients with cuticular drusen were scanned. Areas of decreased retinal thickness overlying drusen were best visualized using the three-dimensional retinal thickness map. The distribution and sawtooth pattern of cuticular drusen were best visualized using three-dimensional retinal pigment epithelium segmentation. Of the 16 eyes, 13 had SRF within the macula. In the eyes with macular SRF, characteristic excrescences were present along the outer retina and attenuation of the photoreceptor inner and outer segment boundary were observed in many areas. In areas where the retina was detached, the retinal pigment epithelium-Bruch's membrane complex appeared nodular or attenuated. The volumetric measurements of the SRF were performed using a manual segmentation with a 1.11% mean difference between repeated measurements on the same day (range, 0.47-1.68%; standard deviation, 0.55%). CONCLUSION: The sawtooth pattern of drusen and the presence of excrescences along the detached outer retina are characteristic features of cuticular drusen that should be helpful in confirming the diagnosis of this condition. The volumetric analysis of the SRF is repeatable and may be useful in following the clinical course of these patients.

Comparison of intravitreal bevacizumab followed by ranibizumab for the treatment of neovascular age-related macular degeneration.

PURPOSE: To compare outcomes after switching from intravitreal bevacizumab (Avastin) to ranibizumab (Lucentis) in patients with neovascular age-related macular degeneration (AMD). METHODS: A retrospective review was performed of patients with neovascular AMD who were switched from treatment with intravitreal bevacizumab to intravitreal ranibizumab once ranibizumab became commercially available. All reviewed patients had at least three bevacizumab injections before being switched to ranibizumab. The treatment outcomes included comparisons of visual acuity and dosing frequency while receiving both drugs. RESULTS: Eighty-four eyes met the inclusion criteria. Mean baseline visual acuity was 20/100. Mean duration of bevacizumab treatment was 7.1 months followed by 7.3 months with ranibizumab (P = 0.68). Best-obtained visual acuity during treatment was 20/63 with bevacizumab and 20/63 with ranibizumab (P = 0.5). Last mean visual acuity after receiving bevacizumab at the time of the first ranibizumab injection was 20/80. Mean visual acuity at the last ranibizumab follow-up visit was 20/80 (P = 0.49). Mean injection rates per month while receiving bevacizumab and ranibizumab were 0.66 (P = 0.98). CONCLUSION: In this subset of patients with neovascular AMD switched from bevacizumab to ranibizumab therapy, there were no apparent differences in visual acuity outcomes or injection rates. Larger prospective studies are under way to directly compare these drugs for the treatment of neovascular AMD.

Safety and efficacy of intravitreal bevacizumab (avastin) for the management of branch and hemiretinal vein occlusion.

PURPOSE: To evaluate the safety and efficacy of intravitreal bevacizumab (Avastin, Genentech) for the treatment of macular edema (ME) secondary to branch retinal vein occlusion (BRVO) and hemiretinal vein occlusion (HRVO). METHODS: A retrospective review was performed of consecutive patients treated with intravitreal bevacizumab (1.25 mg) for ME secondary to BRVO/HRVO from May 2005 to August 2006 with follow-up through February 2007. Re-treatment was performed at monthly or longer intervals at the discretion of the treating physician. RESULTS: Fifty-two eyes with a BRVO and 13 eyes with an HRVO received intravitreal bevacizumab at baseline. Visual acuity improved by a mean of 12 letters at 1 month (n = 51; P < 0.001), 13 letters at 3 months (n = 61; P < 0.001), 13 letters at 6 months (n = 42; P < 0.001), 14 letters at 9 months (n = 27; P < 0.001), and 15 letters at 12 months (n = 17; P = 0.015). The mean optical coherence tomography (OCT) thickness decreased by 184 microm (P < 0.001), 131 microm (P < 0.001), 161 microm (P < 0.001), 158 microm (P = 0.002), and 205 microm (P = 0.002) at 1 month, 3 months, 6 months, 9 months, and 12 months, respectively. The mean number of injections was 1.4, 2.1, 2.7, and 3.1, and 3.3 at 1 month, 3 months, 6 months, 9 months, and 12 months, respectively. No ocular or systemic adverse events were observed. CONCLUSION: Improvements in visual acuity and OCT outcomes were observed during the first year after intravitreal bevacizumab in patients with ME secondary to BRVO and HRVO.

A brief history of optical coherence tomography: a personal perspective.

The historical highlights of the development of optical coherence tomography (OCT) are reviewed.

Thirty-two month follow-up of successful treatment of choroidal neovascularization from angioid streaks with intravitreal bevacizumab.

A patient presented with subfoveal choroidal neovascularization associated with angioid streaks and was treated with three intravitreal injections of off-label bevacizumab (1.25 mg) in the right eye. Visual acuity improved from 20/70 to 20/20 and remained at this level for 32 months. In certain patients with choroidal neovascularization from angioid streaks, intravitreal bevacizumab may produce normalization of visual acuity and macular anatomy for an extended period of time.

Spectral domain optical coherence tomographic imaging of geographic atrophy.

BACKGROUND AND OBJECTIVE: To compare images of geographic atrophy (GA) obtained using spectral domain optical coherence tomography (SD-OCT) with images obtained using fundus autofluorescence (FAF). PATIENTS AND METHODS: Five eyes from patients with dry AMD were imaged using SD-OCT and FAF, and the size and shape of the GA were compared. RESULTS: GA appears bright on SD-OCT compared with the surrounding areas with an intact retinal pigment epithelium because of increased reflectivity from the underlying choroid. SD-OCT and FAF both identified GA reproducibly, and measurement of the area of GA is comparable between the two methods with a mean difference of 2.7% of the total area. CONCLUSION: SD-OCT can identify and quantitate areas of GA. The size and shape of these areas correlate well to the areas of GA seen on autofluorescence images; however, SD-OCT imaging also provides important cross-sectional anatomic information.