Ocular Media (ocular + media)

Distribution by Scientific Domains

Selected Abstracts

Non-invasive monitoring of commonly used intraocular drugs against endophthalmitis by raman spectroscopy

K. Hosseini MD
Abstract Purpose To develop a non-contact and non-invasive method for quantification of the local concentration of certain antibiotic and antifungal drugs in the eye. Study Design/Materials and Methods An integrated CCD-based Raman spectroscopic system designed specifically for ophthalmic applications was used to non-invasively detect the presence of ceftazidime and amphotericin B in ocular media. Specific Raman signatures of the above named drugs were determined for various concentrations that were injected through a needle in the aqueous humor of rabbit eyes in vivo. Raman spectra were subsequently acquired by focusing an argon laser beam within the anterior chamber of the eye. Results Compared to ocular tissue, unique spectral features of ceftazidime appeared near 1,028, 1,506, 1,586, and 1,641 cm,1. Amphotericin B exhibited its characteristic peaks at 1,156.5 and 1,556 cm,1. The amplitude of the spectral peak corresponding to these drugs (acquired by 1 second exposure time and 25 mW of laser power) were determined to be linearly dependent on their local concentration in the anterior chamber of the eye. Conclusions Raman spectroscopy may offer an effective tool to non-invasively assess the local concentration of the delivered drugs within the ocular media. This technique potentially could be used to investigate the pharmacokinetics of intraocular drugs in vivo either from a releasing implant or a direct injection. Lasers Surg. Med. 32:265,270, 2003. 2003 Wiley-Liss, Inc. [source]

Towards metabolic mapping of the human retina

D. Schweitzer
Abstract Functional alterations are first signs of a starting pathological process. A device that measures parameter for the characterization of the metabolism at the human eye-ground would be a helpful tool for early diagnostics in stages when alterations are yet reversible. Measurements of blood flow and of oxygen saturation are necessary but not sufficient. The new technique of auto-fluorescence lifetime measurement (FLIM) opens in combination with selected excitation and emission ranges the possibility for metabolic mapping. FLIM not only adds an additional discrimination parameter to distinguish different fluorophores but also resolves different quenching states of the same fluorophore. Because of its high sensitivity and high temporal resolution, its capability to resolve multi-exponential decay functions, and its easy combination with laser scanner ophthalmoscopy, multi-dimensional time-correlated single photon counting was used for fundus imaging. An optimized set up for in vivo lifetime measurements at the human eye-ground will be explained. In this, the fundus fluorescence is excited at 446 or 468 nm and the time-resolved autofluorescence is detected in two spectral ranges between 510 and 560 nm as well as between 560 and 700 nm simultaneously. Exciting the fundus at 446 nm, several fluorescence maxima of lifetime t1 were detected between 100 and 220 ps in lifetime histograms of 40 fundus images. In contrast, excitation at 468 nm results in a single maximum of lifetime t1 = 190 16 ps. Several fundus layers contribute to the fluorescence intensity in the short-wave emission range 510,560 nm. In contrast, the fluorescence intensity in the long-wave emission range between 560 and 700 nm is dominated by the fluorescence of lipofuscin in the retinal pigment epithelium. Comparing the lateral distribution of parameters of a tri-exponential model function in lifetime images of the fundus with the layered anatomical fundus structure, the shortest component (t1 = 190 ps) originates from the retinal pigment epithelium and the second lifetime (t2 = 1,000 ps) from the neural retina. The lifetime t3 , 5.5 ns might be influenced by the long decay of the fluorescence in the crystalline lens. In vitro analysis of the spectral properties of expected fluorophores under the condition of the living eye lightens the interpretation of in vivo measurements. Taking into account the transmission of the ocular media, the excitation of NADH is unlikely at the fundus. Microsc. Res. Tech., 2007. 2007 Wiley-Liss, Inc. [source]

The effect of light scattering on multifocal electroretinography

H. L. Chan
Purpose:,Unclear ocular media is a very common condition of older eyes characterized by significant light scattering and image degradation. The multifocal electroretinography (MERG) is a useful objective technique to measure retinal activity but its validity in the presence of cloudy ocular media remains unclear. We tested the MERG under controlled light scattering conditions using a liquid crystal diffuser (LCD) that simulated different degrees of image degradation. Methods:,The MERG were taken from 13 normal young subjects seated behind a LCD set under two conditions: scatter (visual acuity ,6/18) and non-scatter (visual acuity ,6/6). The pupils had been dilated and the eyes were optically corrected for the working distance. The first-order kernel MERG response was analysed. Three subjects underwent MERG measurement with two additional intermediate light scattering levels (i.e. visual acuity ,6/9 and 6/12). Results:,The macular MERG response density was reduced (p < 0.001), but the peripheral MERG response densities were increased (p < 0.001) under the scattering condition. A similar trend was also observed with intermediate degrees of light scattering. Comparing the MERG waveforms without light scattering, a new retinal response was identified with a characteristic latency of about 60 ms (P60), but it was diminished in size under the scattering conditions. Conclusions:,The veiling luminance might have caused the reduction in the macular MERG response and an elevation in the peripheral retina with light scatter. The functional suppression of P60 observed under the influence of light scatter may be related to retinal adaptation. Unclear optical media will affect the interpretation of MERG results. [source]

3124: Algorithms and instrumentation for quantified retinal oximetry in a snapshot

Purpose To develop an instrument and techniques for useful absolute and relative clinical oximetry of the retina. Methods A novel snapshot multispectral imaging system has been optimised for retinal oximetry. Eight monochromatic images of the retina are recorded with a field of view of 24 degrees. Algorithms calculate the absorption of light at each point along delineated blood vessels and for each of the eight wavebands. Data inversion using an analytical model for light propagation enables oximetry at along the blood vessels. Spectral inversion has been refined using ray tracing and Monte Carlo modelling of light propagation using a realistic phantom eye. Results A comparison of Monte Carlo modelling of light propagation in the phantom retina with recorded images for blood of various oxygenations indicates the influence of several unknowns, including scatter from optical surfaces within the ophthalmoscope and eye, the geometry of the blood vessels and eye, the optical constants of the ocular media and the complexity of light propagation in the retinal structure. Relative oximetry within the retina is possible with repeatability of about 1% in the phantom and 5% in a real eye but the influence of various systematic effects can introduce systematic differences between actual and calculated oxygenation that can significantly exceed these values. Conclusion Although oximetry using only a very small number of spectral bands is possible, this is prone to systematic errors that can effect both absolute and relative oximetry. The ability to record eight spectral images in a single snapshot offers promise to provide an enhanced clinically useful and validated oximetry technique. [source]

Non-viral strategies of intra-ocular gene delivery

Purpose Systemic anti TNF strategies are efficient to treat intraocular inflammation but require repeated injections and are associated to severe systemic side effects. Our aim was to develop a non viral gene transfer method to produce locally anti-inflammatory proteins in a sustained and minimally invasive manner in the ocular media. For this purpose, we have transformed the ciliary muscle into a bioreactor, using an electrically assisted gene transfer technique. Methods Electrotransfer (ET) of plasmids, encoding for different variants of TNF alpha soluble receptors, was performed in the ciliary muscle cells. Using toptimized conditions, soluble receptors were dosed in the ocular media up to 8 months after a single treatment. The technique has been applied in two models of intraocular inflammation: Endotoxin-Induced Uveitis (EIU) and auto immune experimental uveitis (EAU) in rats. Results When performed 8 days or 3 months before the LPS challenge, ET significantly reduced both clinical and histological signs of EIU. Particularly, iNOS, IL6 and TNF were down regulated while IL10 was upregulated. Importantly, systemic TNF alpha was not decreased demonstrating a local effect of the treatment. In EAU, ET significantly delayed the onset of EAU and deceased its severity. Similarly, a switch towards a Th2 cytokines profile was observed in the ocular media without any effect on systemic TNF alpha. Conclusion - ET is a safe and efficient non viral method to produce locally TNF alpha soluble receptors. - Local anti TNF allows for a local intraocular immunomodulation, without affecting systemic TNF. ET could therefore be used to reduce systemic side effects of anti TNF and prevent repeated injections. [source]