CCD-based projectional imaging of fluorescent probes in tissue-like media: experimental setup and characterization.

In this article, a non-contact imaging setup for the acquisition of multiple 2D projections of fluorescent probes in tissue-like phantoms is described. The setup basically consists of a high-sensitivity CCD camera for the detection of fluorescence and a rotating broad-beam light source for the continuous illumination of a rotatable phantom located in the rotation center. This allows for imaging of various projections in a full angular projection range of 360°. Beside the detailed description of the system layout, important key characteristics of the setup are outlined. The setup is demonstrated with projectional measurements of a tissue-like phantom and the results are verified by comparison of the projection-dependent fluorescence intensity distributions with corresponding 2D simulations. It is shown that the instrument is suitable for the sensitive detection of fluorescence emanating from fluorescent objects in tissue-like phantoms. Such setup could facilitate the collection of large projection data sets as they are used in optical fluorescence tomography of small animals.

Linear method of fluorescent source reconstruction in a diffusion medium.

A new method is described for obtaining a 2D reconstruction of a fluorescent source distribution inside a diffusion medium from planar measurements of the emission light at the surface after excitation by a plane wave. Point sources are implanted at known locations of a rectangular phantom. The forward model of the photon transport is based on the diffusion approximation of the radiative transport equation (RTE) for homogeneous media. This can be described by a hierarchical system of two time-independent RTE's, one for the excitation plane wave originating from the external light source to the medium and another one for the fluorescence emission originating from the fluorophore marker to the detector. A linear inverse source problem was solved for image reconstruction. The applicability of the theoretical method is demonstrated in some representative working examples. For an optimization of the problem we used least squares minimization technique.

Computerized calculation scheme for retinal image size after implantation of toric intraocular lenses.

PURPOSE: To describe a paraxial computing scheme for tracing an axial pencil of rays through the 'optical system eye' containing astigmatic surfaces with their axes at random. METHODS: Two rays (-10 prism diopters from vertical and horizontal) are traced through the uncorrected and corrected eye. In the uncorrected eye one specific ray is selected from the pencil of rays, which passes through the pupil center. In the corrected eye any ray can be traced through the eye. From the slope angle, the intersection of the ray with the refractive surface and the refraction the slope angle of the exiting ray is determined and the ray is traced to the subsequent surface. From both rays traced through the eye an ellipse is fitted to the image to characterize the image distortion of an circular object. EXAMPLE: Assumptions: target refraction -0.5-1.0D/A = 90 degrees at 14 mm, corneal refraction 42.5 + 3.5D/A = 15 degrees, axial length 23.6 mm, IOL position 4.6 mm, central lens thickness 0.8 mm, refractive index 1.42, front/back surface of the toric IOL 10.0 D/7.14 + 6.47D/A = 101.8 degrees. The vertical incident ray was imaged to (x, y) = (0.0055 mm, -1.6470 mm)/(0.0067 mm, -1.6531 mm) in the uncorrected/corrected eye. The horizontal incident ray was imaged to (x, y) = (1.6266 mm, -0.0055 mm)/(1.6001 mm, -0.0067 mm) in the uncorrected/corrected eye. The ellipse (semi-major/semi-minor meridian) fitted to the conjugate image of a circle sized 1.648 mm/1.625 mm in an orientation 14.2 degrees in the uncorrected and 1.654 mm/1.599 mm in an orientation 7.1 degrees in the corrected eye. CONCLUSION: This concept may be relevant for the assessment of aniseikonia after implantation of toric intraocular lenses for correction of high corneal astigmatism.

Ray tracing through a schematic eye containing second-order (quadric) surfaces using 4 x 4 matrix notation.

Ray tracing is used in ophthalmology for evaluation of the optical properties of the eye. We demonstrate an algebraic method for tracing a bundle of rays through the optical system of an eye containing aspheric surfaces. Restricting to second-order surfaces (quadric surfaces) such as ellipsoids, paraboloids or hyperboloids, a surface is described by a 4 x 4 matrix. In this case, the normal vector can be derived analytically and the ray-surface intersection is calculated by solving a quadratic equation. We applied this straightforward matrix-based strategy to the spherical 4-surface Le Grand schematic eye, and the Le Grand eye modified by Kooijman containing four aspheric surfaces. We calculated the spot diagram for the focal plane as well as a pre- and post-focal plane for both model eyes, and found that the optical quality of the aspheric model characterized by the ray scatter in the spot diagram at the focal plane is much better than that of the spherical model. This calculation strategy may be helpful for evaluating the image distortion of decentred or tilted spherical or aspheric artificial intra-ocular lenses.

Inverse mushroom-shaped nonmechanical penetrating keratoplasty using a femtosecond laser.

PURPOSE: To demonstrate the feasibility of an inverse mushroom-shaped nonmechanical corneal trephination using a femtosecond laser in a noncontact manner. DESIGN: Experimental study. METHODS: In this laboratory study, 10 polymethylmethacrylate (PMMA) blocks and 20 porcine corneas were treated with an industrial femtosecond laser source. The trephination profile consisted of (1) a 7- or 6-mm diameter cylinder from the anterior chamber, (2) an intermediate horizontal connecting plane, and (3) a concentric 5- or 4-mm diameter cylinder upwards. RESULTS: Applying appropriate combinations of pulse energy and spacing, trephination took less than 60 seconds. In porcine eyes, light microscopy displayed trephination edges delineated by partly confluent gas bubbles (10-40 mum) with tissue bridges in between. By TEM, the cut edges were lined by a delicate, electron-dense layer (5-40 nm). CONCLUSIONS: Femtosecond laser technology seems to offer a promising approach towards minimally invasive self-sealing "no-stitch keratoplasty."