Concurrent birefringence and forward light-scattering measurements of flash-bleached rod outer segments

Functional intrinsic optical signal imaging for objective optoretinography of human photoreceptors

Functional mapping of photoreceptor physiology is important for better disease diagnosis and treatment assessment. Fast intrinsic optical signal (IOS), which arises before light-evoked pupillary response, promises a unique biomarker of photoreceptor physiology for objective optoretinography with high resolution. This study is to test the feasibility of non-mydriatic IOS mapping of retinal photoreceptors in awake human. Depth-resolved optical coherence tomography verified outer segment (OS) as the anatomic origin of fast photoreceptor-IOS. Dynamic IOS changes are primarily confined at OS boundaries connected with inner segment and retinal pigment epithelium, supporting transient OS shrinkage due to phototransduction process as the mechanism of the fast photoreceptor-IOS response.

Functional optical coherence tomography enables in vivo optoretinography of photoreceptor dysfunction due to retinal degeneration

Stimulus-evoked intrinsic optical signal (IOS), which occurs almost immediately after the onset of retinal stimulus has been observed in retinal photoreceptors, promises to be a unique biomarker for objective optoretinography (ORG) of photoreceptor function. We report here the first-time in vivo ORG detection of photoreceptor dysfunction due to retinal degeneration. A custom-designed optical coherence tomography (OCT) was employed for longitudinal ORG monitoring of photoreceptor-IOS distortions in retinal degeneration mice. Depth-resolved OCT analysis confirmed the outer segment (OS) as the physical source of the photoreceptor-IOS. Comparative ERG measurement verified the phototransduction activation as the physiological correlator of the photoreceptor-IOS. Histological examination revealed disorganized OS discs, i.e. the pathological origin of the photoreceptor-IOS distortion.

Fast intrinsic optical signal correlates with activation phase of phototransduction in retinal photoreceptors

IMPACT STATEMENT

As the center of phototransduction, retinal photoreceptors are responsible for capturing and converting photon energy to bioelectric signals for following visual information processing in the retina. This article summarizes experimental observation and discusses biophysical mechanism of fast photoreceptor-intrinsic optical signal (IOS) correlated with early phase of phototransduction. Quantitative imaging of fast photoreceptor-IOS may provide objective optoretinography to advance the study and diagnosis of age-related macular degeneration, retinitis pigmentosa, diabetic retinopathy, and other eye diseases that can cause photoreceptor dysfunctions.

Intrinsic optical signal imaging of retinal physiology: a review

Intrinsic optical signal (IOS) imaging promises to be a noninvasive method for high-resolution examination of retinal physiology, which can advance the study and diagnosis of eye diseases. While specialized optical instruments are desirable for functional IOS imaging of retinal physiology, in depth understanding of multiple IOS sources in the complex retinal neural network is essential for optimizing instrument designs. We provide a brief overview of IOS studies and relationships in rod outer segment suspensions, isolated retinas, and intact eyes. Recent developments of line-scan confocal and functional optical coherence tomography (OCT) instruments have allowed in vivo IOS mapping of photoreceptor physiology. Further improvements of the line-scan confocal and functional OCT systems may provide a feasible solution to pursue functional IOS mapping of human photoreceptors. Some interesting IOSs have already been detected in inner retinal layers, but better development of the IOS instruments and software algorithms is required to achieve optimal physiological assessment of inner retinal neurons.

Regulation of rhodopsin-eGFP distribution in transgenic xenopus rod outer segments by light

The rod outer segment (OS), comprised of tightly stacked disk membranes packed with rhodopsin, is in a dynamic equilibrium governed by a diurnal rhythm with newly synthesized membrane inserted at the OS base balancing membrane loss from the distal tip via disk shedding. Using transgenic Xenopus and live cell confocal imaging, we found OS axial variation of fluorescence intensity in cells expressing a fluorescently tagged rhodopsin transgene. There was a light synchronized fluctuation in intensity, with higher intensity in disks formed at night and lower intensity for those formed during the day. This fluctuation was absent in constant light or dark conditions. There was also a slow modulation of the overall expression level that was not synchronized with the lighting cycle or between cells in the same retina. The axial variations of other membrane-associated fluorescent proteins, eGFP-containing two geranylgeranyl acceptor sites and eGFP fused to the transmembrane domain of syntaxin, were greatly reduced or not detectable, respectively. In acutely light-adapted rods, an arrestin-eGFP fusion protein also exhibited axial variation. Both the light-sensitive Rho-eGFP and arrestin-eGFP banding were in phase with the previously characterized birefringence banding (Kaplan, Invest. Ophthalmol. Vis. Sci. 21, 395–402 1981). In contrast, endogenous rhodopsin did not exhibit such axial variation. Thus, there is an axial inhomogeneity in membrane composition or structure, detectable by the rhodopsin transgene density distribution and regulated by the light cycle, implying a light-regulated step for disk assembly in the OS. The impact of these results on the use of chimeric proteins with rhodopsin fused to fluorescent proteins at the carboxyl terminus is discussed.

Reflection of a Gaussian beam at a nonlinear interface

By numerical simulations of the reflection of a (2-D) Gaussian beam from a nonlinear interface, we show several new features of the behavior of such an interface and resolve the difference between the results of two previous studies of this type. Newly reported features include a very large nonlinear Goos-Hanchen shift and large variations of the angle of an output beam for small changes in the input intensity. The latter phenomenon has potential applications for a light-controlled angular scanning element. The differences between prior studies of this type are shown to be an artifact of the numerical procedures used.

Modeling the rod outer segment birefringence change correlated with metarhodopsin II formation

A rapid birefringence loss associated with metarhodopsin II formation, delta (delta n) MII, is produced when frog rod outer segments are exposed to a bleaching light flash. To analyze the nature of the underlying structure change, measurements of delta (delta n) MII were made in rod outer segments perfused with glycerol solutions to increase the refractive index of the cytoplasmic and intradisk spaces. Comparisons of experimental results with computed changes in the form birefringence component using two- and three-dielectric outer segment models for several putative structure changes were made. It is concluded that delta (delta n) MII can be due to either a change in the intrinsic birefringence component caused by the reorientation of anisotropic molecules, or to a change in the form birefringence component caused by small changes in the cytoplasmic and/or intradisk volumes.