Background and Objective:A method to increase light transport deeply into target areas of tissue would enhance both therapeutic and diagnostic laser applications. The effects of a hyperosmotic agent on the scattering properties of rat and hamster skin were investigated. Study Design/Materials and Methods: A hyperosmotic agent, glycerol, was applied in vitro and in vivo to rat and hamster skin to assess the changes in tissue optical properties. Changes in the reduced scattering coefficient after application of the agent in vitro to rat skin and after the skin has been rehydrated were assessed to evaluate the effect of the agent on tissue. Results: Experimental results showed a transient change in the optical properties of in vitro rat skin. A 50% increase in transmittance and decrease in diffuse reflectance occurred within 5-10 min after the introduction of anhydrous glycerol. In addition, reduction of light scattering with this technique increased depth of visibility with optical coherence tomography. Injection of glycerol under the skin allowed in vivo visualization of blood vessels. Conclusions:The application of the agent reduces the amount of refractive mismatch found in the tissue and markedly reduces random scattering, thereby making the skin less turbid for visible wavelengths for a controlled period of time.

Background and Objective:A method to increase light transport deeply into target areas of tissue would enhance both therapeutic and diagnostic laser applications. The effects of a hyperosmotic agent on the scattering properties of rat and hamster skin were investigated. Study Design/Materials and Methods: A hyperosmotic agent, glycerol, was applied in vitro and in vivo to rat and hamster skin to assess the changes in tissue optical properties. Changes in the reduced scattering coefficient after application of the agent in vitro to rat skin and after the skin has been rehydrated were assessed to evaluate the effect of the agent on tissue. Results: Experimental results showed a transient change in the optical properties of in vitro rat skin. A 50% increase in transmittance and decrease in diffuse reflectance occurred within 5-10 min after the introduction of anhydrous glycerol. In addition, reduction of light scattering with this technique increased depth of visibility with optical coherence tomography. Injection of glycerol under the skin allowed in vivo visualization of blood vessels. Conclusions:The application of the agent reduces the amount of refractive mismatch found in the tissue and markedly reduces random scattering, thereby making the skin less turbid for visible wavelengths for a controlled period of time.

Form-biattenuance ( chi) in biological tissue arises from anisotropic light scattering by regularly oriented cylindrical fibers and results in a differential attenuation (diattenuation) of light amplitudes polarized parallel and perpendicular to the fiber axis (eigenpolarizations). Form-biattenuance is complimentary to form-birefringence (n) which results in a differential delay (phase retardation) between eigenpolarizations. We justify the terminology and motivate the theoretical basis for form-biattenuance in depth-resolved polarimetry. A technique to noninvasively and accurately quantify form-biattenuance which employs a polarization-sensitive optical coherence tomography (PS-OCT) instrument in combination with an enhanced sensitivity algorithm is demonstrated on ex vivo rat tail tendon (mean chi = 5.3.10-4, N = 111), rat Achilles tendon ( chi = 1.3.10-4, N = 45), chicken drumstick tendon ( chi = 2.1.10-4, N = 57), and in vivo primate retinal nerve fiber layer ( chi = 0.18.10-4, N = 6). A physical model is formulated to calculate the contributions of chi and n to polarimetric transformations in anisotropic media.

We demonstrate non-contact sub-nanometer optical measurement of neural surface displacement associated with action potential propagation. Experimental results are recorded from nerve bundles dissected from crayfish walking leg using a phase-sensitive optical low coherence reflectometer. No exogenous chemicals or reflection coatings are applied. Transient neural surface displacement is less than 1 nm in amplitude, 1 ms in duration and is coincident with action potential arrival to the optical measurement site. Because the technique uses back-reflected light, noninvasive detection of various neuropathies may be possible.

PURPOSE. We identified candidate optical coherence tomography (OCT) markers for early glaucoma diagnosis. Time variation of retinal nerve fiber layer (RNFL) thickness, phase retardation, birefringence, and reflectance using polarization sensitive optical coherence tomography (PS-OCT) were measured in three non-human primates with induced glaucoma in one eye. We characterized time variation of RNFL thickness, phase retardation, birefringence, and reflectance with elevated intraocular pressure (IOP). METHODS.One eye of each of three non-human primates was laser treated to increase IOP. Each primate was followed for a 30-week period. PS-OCT measurements were recorded at weekly intervals. Reflectance index (RI) is introduced to characterize RNFL reflectance. Associations between elevated IOP and RNFL thickness, phase retardation, birefringence, and reflectance were characterized in seven regions (entire retina, inner and outer rings, and nasal, temporal, superior and inferior quadrants) by linear and non-linear mixed-effects models.RESULTS. Elevated IOP was achieved in three non-human primate eyes with an average increase of 13 mm Hg over the study period. Elevated IOP was associated with decreased RNFL thickness in the nasal region (P ¼ 0.0002), decreased RNFL phase retardation in the superior (P ¼ 0.046) and inferior (P ¼ 0.021) regions, decreased RNFL birefringence in the nasal (P ¼ 0.002) and inferior (P ¼ 0.029) regions, and loss of RNFL reflectance in the outer rings (P ¼ 0.018). When averaged over the entire retinal area, only RNFL reflectance showed a significant decrease (P ¼ 0.028).CONCLUSIONS. Of the measured parameters, decreased RNFL reflectance was the most robust correlate with glaucomatous damage. Candidate cellular mechanisms are considered for decreased RNFL reflectance, including mitochondrial dysfunction and retinal ganglion cell apoptosis. (Invest Ophthalmol Vis Sci. 2012;53:4380-4395) DOI:10.1167/iovs.11-9130 G laucoma is an optic neuropathy characterized by the progressive death of retinal ganglion cells and loss of associated axons in the retinal nerve fiber layer (RNFL). Without early diagnosis and therapeutic intervention, glaucoma eventually results in visual field abnormalities and vision loss. Studies indicate that as many as 40% of the axons may die before the visual field is affected, 1 suggesting an opportunity for the development of diagnostic tools that can prevent visual field loss in conjunction with application of neuroprotective strategies. As axons in the RNFL are lost, an associated RNFL thinning is observed. 2-4Optical coherence tomography (OCT) is an imaging modality that provides high-resolution (2-15 lm) cross-sectional images of the retina at video rate, and can quantify macroscopic changes in the optic nerve head (ONH) and RNFL. Inasmuch as previous studies have demonstrated a link between decreased RNFL thickness measured with OCT and glaucoma, 3 OCT measurements of RNFL thickness have become a routine component of glaucoma screening, diagnosis, and monitoring protocols...