While the a-wave of mouse electroretinogram (ERG) occurs within 50 milliseconds after exposure to light, the optoretinogram (ORG) slower than a 20Hz sampling rate could face limitations in observing immediate morphological changes from the retina. In this study, we develop a compact custom-built mouse ORG system based on spectral domain optical coherence tomography (SD-OCT) for 100Hz~1KHz B-scan rates comprised of 100 kHz A-scans. All the optics of the developed ORG system are designed on a 24 x 24 inches optical breadboard to move easily as well as to combine with the ERG system in a dark room. Without using a fundus camera, the OCT system provides en-face images from high-pass filtering and square of the OCT spectral signal for mouse retinal positioning in-vivo before acquiring ORG data. The 490nm LED for light stimulus is generated to make uniform illumination at the mouse retina using the Maxwellian view method. The common path of the OCT scanning light and the visible LED is built with achromatic doublet lens combinations based on optical simulation with Opticstudio® . The developed compact ORG system can not only observe light-evoked responses with 1~10 milliseconds but also be used for the studies of correlations between ORG and ERG in the mouse retina.
Observing micro-vessels in conjunctiva could be used not only for diagnosing conjunctival diseases including conjunctivitis and pterygium but also as biomarkers for circulatory diseases. Many research teams have developed compact imaging and auto-analysis systems to simplify the conventional slit lamp as well as enhance the analysis process. The imaging system, previously developed by our research team, corrects eye motion in imaging windows through image registration and template matching. The developed system quantifies blood flow velocity using the sequence of motion-corrected images. This study compares estimated flow velocity and the fluid's actual velocity using the experimental phantom comprising transparent hoses and fluid including beads corresponding to red blood cells. The flow velocities are calculated using the Hagen-Poiseuille equation, and the flow rates generated by the syringe pump. The pump applies three kinds of flow rates to generate flow velocity variations and the estimated velocities are linearly proportional to these variations. In addition, the phantom has a random motion to mimic the fixational eye movements within the range of the healthy subject's angular eye motion. Through these experiments, we verified the previously developed flow velocity measurement system having percent errors under 3% by comparing estimated flow velocities with actual flow velocities. The system's accuracy, especially under conditions without artificial motion, is over 98.5%. These experiments can provide the supporting background for feasibility and accuracy in a further clinical study in conjunctival microcirculation.
Adaptive optics(AO) compensates for aberration between light detector and imaging target, for example, air turbulence, misaligned optics, and eye lens. This technique, initially developed to improve the performance of astronomic imaging, is leading to advances in the ophthalmic imaging field through combination with various optical imaging systems. General hardware-based AO systems need additional optics and beam paths for adjusting the beam size at the deformable mirror(DM) as well as matching the image plane. Previous research has composed the system using spherical mirrors instead of the lens to reduce aberration. Additionally, previous papers have reported off-axis type AO imaging systems for eliminating astigmatism and more compact equipment than on-axis type. This study optimized an off-axis AO-region of the AO-scanning laser ophthalmoscope(SLO) through optical design by Opticstudio® and three-dimensional rendering by SOLIDWORKS®. The rendering process, including virtual mounting, allows checking whether block or pass of the beam by optomechanics and providing relative coordinate of mounted optics. The verification method for checking the alignment of the system is the comparison between simulation and practical beam wavefront at a specific beam path.
Microgravity, vacuum, and high-intensity ultraviolet waves are widely known characteristics of space. These different environments from the earth affect physical changes including ocular tissue changes while astronauts stay in the universe. The changes in ocular tissue in the space environment, also known as visual impairment intracranial pressure (VIIP) syndrome, including fundus optic disc edema, hyperopic drift, choroidal folds, cotton spots, and permanent fundus damage could influence astronauts’ vision system and ability of space operations. Especially, hyperopic drift by posterior flattening and folded retina by choroidal folds are reported to affect the retina's structures as a vision sensor directly. To investigate microgravity's effect on ocular tissues and vision, previous research on earth are used special facilities and various microgravity simulators, including head-down tilt bed-rest and random positioning machines. This study suggests that an experiment expose wild-type zebrafish to microgravity using a rotary cell culture system (RCCs) applied to experiments using cell and zebrafish's embryos in microgravity. Unlike previous research using zebrafish's embryos and larva, adult and growing zebrafish were employed in this study for observing ocular changes in simulated space environments. After exposing zebrafish to microgravity, in-vivo zebrafish's eye images were acquired by custom-built optical coherence tomography (OCT). This research for presenting the new method for small animal experiments in microgravity environments could be applied to investigate the influence of staying in the universe on an animal model with ophthalmic diseases.
KEYWORDS: Retina, 3D image processing, Stereoscopy, In vivo imaging, Optical coherence tomography, Injuries, Eye models, Eye, Animal model studies, Analytical research
The retina regeneration process has been observed in several animals including fish, birds, and amphibians, whereas the injured human retina cannot regenerate until today. The zebrafish is one of the animals which can regenerate their retina. Due to similarities between humans and the zebrafish in the morphology of the eye as well as the gene, the zebrafish has been chosen as a useful model for investigating retina regeneration. Previous studies have observed morphological changes in the zebrafish retina using optical coherence tomography during the retinal regeneration after light irradiation with a single beam power. However, these studies have limitations of demonstrating differences in regenerative abilities depending on degrees of retinal damages because they used only a single light irradiating condition. Through light-induced retinal injuries by various light irradiating conditions, investigation correlations between the time required for retina regeneration and grades of retinal damages were needed. To conduct these experiments, a custom-built OCT, which can acquire a cross-sectional and three-dimensional image of the zebrafish's eye, was developed based on OpticStudio simulations. The zebrafish's eye imaging can provide the ability to observe the damage and morphological changes after laser irradiation in the eye tissues including the cornea and retina.
Dermatologic patients have various skin characteristics such as skin tone and pigmentation color. However most studies on laser ablation and treatment only considered laser operating conditions like wavelength, output power and pulse duration. The laser ablation arises from photothermal effect by photon energy absorption. Chromophores like melanin exist as the absorber in the skin. In this study, we painted color to mimic chromophores on in-vivo and in-vitro skin models to demonstrate influence on the laser ablation by skin color. Water-based pens were used to paint color. Cross sectional images of the laser ablation were acquired by Fourier-domain optical coherence tomography (Fd-OCT). Light source to make ablation was a Q-switch diode-pumped Nd:YVO4 nanosecond laser (532nm central wavelength). Irradiated light energy dose of the laser could not make ablation craters in the control group. However experimental groups showed craters with same irradiation light energy dose. These results show painting on skin increased tissue damage by absorption in painted color without dyeing cells or tissues.
Laser-induced therapies include laser ablation to remove or cut target tissue by irradiating high-power focused laser beam. These laser treatments are widely used tools for minimally invasive surgery and retinal surgical procedures in clinical settings. In this study, we demonstrate laser tissue interaction images of various sample tissues using high resolution Fourier-domain optical coherence tomography (Fd-OCT). We use a Q-switch diode-pumped Nd:YVO4 nanosecond laser (532nm central wavelength) with a 4W maximum output power at a 20 kHz repetition rate to ablate in vitro and in vivo samples including chicken breast and mouse ear tissues. The Fd-OCT system acquires time-series Bscan images at the same location during the tissue ablation experiments with 532nm laser irradiation. The real-time series of OCT cross-sectional (B-scan) images compare structural changes of 532nm laser ablation using same and different laser output powers. Laser tissue ablation is demonstrated by the width and the depth of the tissue ablation from the B-scan images.
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