Brett Schroeder

Variable optical activation of human cone photoreceptors visualized using a short coherence light source

It has been shown that after a visible stimulus, optical oscillations of nearly all cone photoreceptors can be observed using long coherence length light and in a few cones using short coherence length light. Here, we show that after exposure to a visible stimulus, a short coherence length imaging source reveals light-evoked oscillation signals in a large number of cones. More than 80% of cones in a given retinal area are activated (modulation in the reflectance signal) after stimulation, and the pattern of their activation can be subjectively classified into one of four categories. The application of light-evoked signal detection techniques for in vivo retinal imaging may prove useful for assessing the functional status of cones in normal and diseased retinae.

Neurotrophin-3- and norepinephrine-mediated adrenergic differentiation and the inhibitory action of desipramine and cocaine

In the presence of neurotrophin-3 (NT-3), high-affinity norepinephrine (NE) uptake by quail neural crest cells was significantly increased as judged by in vitro colony assay of adrenergic differentiation. In the presence of the related neurotrophins nerve growth factor (NGF) or brain-derived neurotrophic (BDNF) factor, or of basic fibroblast growth factor (bFGF), there were no significant changes. When NE was added to the culture medium in addition to NT-3, more colonies contained dopamine-beta-hydroxylase (DBH)-immunoreactive cells, an enzyme that is characteristic for adrenergic cells. The NE-mediated increase in the portion of colonies that contained DBH-immunoreactive cells was prevented by the tricyclic antidepressant desipramine (DMI) and by cocaine, two types of drug that block cellular transport of NE. To further examine whether NE acts via uptake, colony assays were performed in the presence and absence of adrenergic antagonists and agonists. These would be expected to mimic the DMI and NE effects, respectively, if the mechanism of action involved activation of adrenergic autoreceptors. Neither class of drug showed a detectable effect within a wide range of concentrations. Immunocytochemistry using antibodies against beta 1 and beta 2 adrenergic receptors further supported the notion that DMI action and beta-receptor expression are not causally related. Ratio imaging was subsequently used in an attempt to elucidate the mechanism of NE action. Within a few minutes of addition of NE to the culture medium, there was an increase in intracellular free calcium in a subset of neural crest cells. Taken together, our data indicate that NT-3 is involved in the appearance of the NE transporter (NET) during embryonic development; internalized NE directly or indirectly increases adrenergic differentiation as measured by immunoreactivity of the adrenergic biosynthetic enzyme DBH; and norepinephrine uptake inhibitors have treatogenic potential.

Spectral Domain Optical Coherence Tomography and Adaptive Optics: Imaging Photoreceptor Layer Morphology to Interpret Preclinical Phenotypes

Recent years have seen the emergence of advances in imaging technology that enable in vivo evaluation of the living retina. Two of the more promising techniques, spectral domain optical coherence tomography (SD-OCT) and adaptive optics (AO) fundus imaging provide complementary views of the retinal tissue. SD-OCT devices have high axial resolution, allowing assessment of retinal lamination, while the high lateral resolution of AO allows visualization of individual cells. The potential exists to use one modality to interpret results from the other. As a proof of concept, we examined the retina of a 32 year-old male, previously diagnosed with a red-green color vision defect. Previous AO imaging revealed numerous gaps throughout his cone mosaic, indicating that the structure of a subset of cones had been compromised. Whether the affected cells had completely degenerated or were simply morphologically deviant was not clear. Here an AO fundus camera was used to re-examine the retina (~6 years after initial exam) and SD-OCT to examine retinal lamination. The static nature of the cone mosaic disruption combined with the normal lamination on SD-OCT suggests that the affected cones are likely still present.

Adaptive Optics and SD-OCT Imaging of Human Photoreceptor Structure After Short Duration (20 ms) Pascal™ Macular Grid and Panretinal Laser Photocoagulation

To the Editor: To understand the effect of therapeutic doses of laser application on the neurosensory retina, detailed histologic1-3 and optical coherence tomographic4-10 evaluations have been employed in both animal models and in the human eye. We sought to evaluate photoreceptor structure associated with laser photocoagulation lesions using two high-resolution retinal imaging tools (adaptive optics (AO) and SD-OCT).

Adaptive optics and spectral- domain optical coherence tomography of human photoreceptor structure after short-duration [corrected] pascal macular grid and panretinal laser photocoagulation.

To the Editor: To understand the effect of therapeutic doses of laser application on the neurosensory retina, detailed histologic1-3 and optical coherence tomographic4-10 evaluations have been employed in both animal models and in the human eye. We sought to evaluate photoreceptor structure associated with laser photocoagulation lesions using two high-resolution retinal imaging tools (adaptive optics (AO) and SD-OCT).

Adaptive Optics and Spectral-Domain Optical Coherence Tomography of Human Photoreceptor Structure After Short Pascal Macular Grid and Panretinal Laser Photocoagulation

To the Editor: To understand the effect of therapeutic doses of laser application on the neurosensory retina, detailed histologic1-3 and optical coherence tomographic4-10 evaluations have been employed in both animal models and in the human eye. We sought to evaluate photoreceptor structure associated with laser photocoagulation lesions using two high-resolution retinal imaging tools (adaptive optics (AO) and SD-OCT).