Medical laser application : international journal for laser treatment and research最新文献

Purpose

To evaluate the effectiveness of transpupillary thermotherapy (TTT) for the closure of classic and occult subfoveal choroidal neovascularization (CNV) and to discuss whether TTT is a useful treatment modality for age-related macular degeneration (AMD).

Materials and methods

The present paper is a retrospective review of the clinical results from a patient group which was treated with TTT in the University Eye Clinic in Mainz. From January 2000 to December 2002, a total of 20 eyes of 20 patients with subfoveal CNV (due to AMD in 16 eyes, due to pathologic myopia in 4 eyes) received TTT. The procedure was delivered using an infrared diode laser at 810 nm, equipped with a modified slit-lamp adapter with an adjustable beam width of 1.2, 2.0 and 3.0 mm. The spot size was selected so that the treatment beam entirely encompassed the lesion. For a 3 mm spot size, up to 800 mW was delivered to the treatment area using a wide-field contact lens. Power was adjusted in such a way that a barely detectable, light-gray appearance of the lesion was seen after 60 s. Patients were seen in follow-up at 6–8 weeks and re-treatment was considered at 12 weeks postoperatively, if persistence or worsening in the leakage of the lesion was observed.

Results

Twenty eyes with subfoveal CNV were treated with TTT and the healing process was followed for at least 6 months. After an average of 2.5 treatment sessions in 14/20 eyes, a rapid decline of CNV activity was observed with resolution of subretinal fluid accompanied by reduction of central scotoma and a significant relief of metamorphopsia. Four eyes with classic subfoveal CNV, due to pathologic myopia, showed closure of the CNV and no visual loss (more than 2 lines) in all cases. In the 16 eyes with occult subfoveal CNV in AMD, closure of the neovascular membrane was achieved in 10/16 eyes leading to a visual stabilization (within 2 lines) during the 6 months follow-up. Six of 16 eyes with AMD became legally blind despite repeated TTT treatment sessions (mean: 4.6 sessions; range: 3–6 sessions). A loss of central vision was due to persistence of macular leakage accompanied by choroidal bleeding, atrophy of the retinal pigment epithelium or progressive subfoveal fibrosis.

Conclusion

The results from this retrospective study demonstrate that occlusion of the neovascular membranes could be observed after TTT for subfoveal CNVs in AMD, as well for highly myopic eyes. Review of the literature shows that the success rate of TTT in AMD (60% after 6 months) is in accordance with the natural progression of occult CNVs in AMD.

Ultrafast lasers, such as the femtosecond (fs) laser, are being increasingly used in ophthalmology, thus allowing a wide variety of applications in refractive surgery. In the future, their use may also be further extended to include cataract, glaucoma, and retinal surgery. The fs laser first appeared in ophthalmology in 2001 and it continues to grow in popularity. Its main uses include LASIK, penetrating keratoplasty, and presbyopia correction all of which will be discussed in this paper.

A method for the fabrication of phantoms is described based on an epoxy resin system that simulates the optical properties of tissue in the wavelength range 500–700 nm. The absorption of the phantoms is determined by two dyes (Epolight 5411 and Epolight 5457; Epolin Inc., Newark, New Jersey) with absorption gradients in the same spectral region as hemoglobin, and the scattering is provided by titanium dioxide particles (Aldrich Chemical, Milwaukee, Wisconsin). The reduced scattering and absorption coefficients were measured using a steady-state spatially resolved reflectance system. The absorption coefficients of phantoms made with both dyes are linear with dye concentration over the entire spectral range. The diffuse reflectance spectra of the phantoms are qualitatively similar to those measured on Caucasian skin in vivo. Both dyes were found to fade during the first three weeks after fabrication, and their long-term stability requires further investigation.

The spatial dependence of the optical properties of the female breast was investigated in the wavelength range 600–1000 nm using a fully automated system for time-resolved reflectance spectroscopy. Both absorption and reduced scattering spectra of the breast of two healthy volunteers, having different ages (24 and 44 years), were measured at eight different angular positions (0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°), and age-related changes in the optical properties of breast were investigated. Both absorption and scattering properties change remarkably as a function of position. They also differ for the two subjects of different age. The best-fit of breast spectra with the combination of the absorption spectra of water, lipid, oxy-, and deoxyhemoglobin related the observed changes to the heterogeneous distribution of the main tissue constituents in the breast. The reduced scattering spectra were interpreted based on approximate Mie theory, which provides structural information about the tissue.

Objective

A cancer diagnostics method is proposed using the 3D reconstruction of luminescence-based optical imaging data.

Material and methods

The diffusion equation solution for a cube was used to tackle the forward problem. The forward solution for two-layered media is also applied in the reconstruction method. The inverse problem was solved using a linear reconstruction technique based on the approximation that the light source needing reconstruction can be decomposed into a weighted sum of unit light sources positioned at each node in the search volume. The calculation for the light propagation in the forward problem was done using values cited in literature for the optical properties of the involved tissue.

Results

The system was tested with numerical simulations that assumed correct as well as erroneous values of the optical coefficients for canine prostate at 810 nm. The quantitative accuracy of reconstructed sources diminished from 100% to approximately 50% with an increase from 0 to 50% in the error for the values of the absorption coefficient, and from 0 to 20% in the error for the values of the reduced scattering coefficient, respectively.

Conclusion

The absolute determination of the tumor locations is dependent on the information gathered by the recorded data by the detectors monitoring the light propagation through the tissue under investigation. For a determined or an over-determined system, the locations have been extracted accurately, and partially determined for an under-determined system.

The influence of the configuration of the optodes on the images of diffuse optical tomography (DOT) was investigated using 3D numerical simulations. 3D distributions of the absorption coefficients in a spherical object were reconstructed from the numerically simulated measurement data for various configurations of the optodes. When the optodes were placed in a plane containing a target which strongly absorbs light, the target could be reconstructed with good localization. For good reconstruction of the target, it was found to be very important that the optode configuration was optimized in order to detect light propagating through the target effectively. The simulations also showed that the optode configuration affects the quality of the reconstructed images and that some prior information about the measured object improved the DOT images. Finally the simulation results were verified by a phantom experiment.