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A three-dimensional (3-D) imaging system based on Gray-code projection is described; it is thought to be used as an integration to the already developed profilometer based on the projection of multifrequency gratings. The Gray-code method allows us to evaluate the 3-D profile of objects that present even marked discontinuities of the surface, thus increasing the flexibility of the measuring system as to the topology of the objects that can be measured. The basic aspects of Gray-code projection for 3-D imaging and profiling are discussed, with particular emphasis devoted to the study of the resolution of the method and to the analysis of the systematic errors. The results of this study allow us to determine the optimal setting of the parameters of the measurement and to develop a suitable calibration procedure. The procedures for implementing the Gray-code method are presented, and some interesting experimental results are reported. Calibration of the system reveals an accuracy of 0.2 mm, corresponding to 0.1% of the field of view.

3D imaging sensors for the acquisition of three dimensional (3D) shapes have created, in recent years, a considerable degree of interest for a number of applications. The miniaturization and integration of the optical and electronic components used to build them have played a crucial role in the achievement of compactness, robustness and flexibility of the sensors. Today, several 3D sensors are available on the market, even in combination with other sensors in a "sensor fusion" approach. An importance equal to that of physical miniaturization has the portability of the measurements, via suitable interfaces, into software environments designed for their elaboration, e.g., CAD-CAM systems, virtual renders, and rapid prototyping tools. In this paper, following an overview of the state-of-art of 3D imaging sensors, a number of significant examples of their use are presented, with particular reference to industry, heritage, medicine, and criminal investigation applications.

An overview of the fluorophores of the eye, the methods used to measure ocular fluorescence, and the existing or ready-to-market instrumentation for the early diagnosis and monitoring of ophthalmic pathologies is presented. Emphasis is given to the impact that a more detailed knowledge of the fluorophores of the eye, their age and pathology relationship, and the considerable technology-driven progress in optical devices and components has had on the development of new compact yet powerful instruments for population screening and for patient follow-ups, using fluorometry alone or in combination with other optical techniques such as light scattering., ((c) 2004 Society of Photo-Optical Instrumentation Engineers.)

A simple, low-cost, portable instrument for measurement of the autofluorescence of the human cornea is presented. Corneal autofluorescence has proved to be strongly correlated with the grade of retinopathy in diabetic patients. It is therefore a reliable parameter for detection of different levels of diabetic retinopathy, thus permitting timely intervention by ophthalmologists. The instrument contains custom optics and electronics and exhibits excellent linearity and repeatability both in vitro and in vivo. Preliminary tests on volunteers show promise for its use in clinical practice.

Autofluorescence of the cornea within specific wavelength region and dynamic light scattering measurements of ocular tissue have both been used for early-stage detection of the presence of diabetic retinopathy. In the present study, autofluorescence of the cornea and dynamic light scattering in the cornea and vitreous have been measured and compared using two innovative research instruments in twenty-two insulin-dependent diabetes mellitus patients, for the diagnosis of diabetic retinopathy. Corneal autofluorescence mean values in each diabetic retinopathy grade significantly correlated with dynamic light scattering measurements in the vitreous, and in the cornea, thus confirming that changes in the natural fluorescence is strictly correlated with molecular changes of ocular tissues. © 1998 Society of Photo-Optical Instrumentation Engineers.

The damage that Nd:YAG laser radiation can cause to plastic (PMMA) IOLs during pseudophakic capsulotomy is well documented in the literature. This damage is the result of direct plasma action on the lens material. We report here another form of damage to PMMA IOLs which is more subtle and does not result from plasma action in the plastic. Even when the irradiance within the IOL is well below the threshold for optical breakdown, the PMMA can be damaged if irradiated by many laser pulses. This subthreshold damage is therefore cumulative. Its importance, likelihood of occurrence and ways to minimise this are considered.

Shielding of laser pulses by plasmas generated in ocular media has been experimentally investigated using single Nd:YAG laser pulses of different durations, ranging from several nanoseconds (ns) to a few tens of picoseconds (ps), both in saline solution and extracted calf vitreous. At the respective threshold radiant exposures for breakdown in saline (259 mJ/cm2 for 7 ns, 20.5 mJ/cm2 for 220 ps and 4.7 mJ/cm2 for 30 ps pulses) the single pulse energy transmission is found to be about 74% for 7 ns, 55% for 220 ps and 50% for 30 ps, thus showing that shielding of laser-induced plasmas is more effective for shorter pulses than for longer pulses. Moreover, the decrease in transmission with increasing radiant exposure is faster in the picosecond case than in the nanosecond case. These results show that direct irradiation of the retina is, to some extent, present especially near threshold. In the case of picosecond pulses, a comparison with published results indicates that shielding between subsequent pulses in a train is likely to occur only to a very limited extent.

We describe and analyze the temporally and spatially resolved luminescence and attenuation characteristics of plasmas induced in liquids commonly accepted as models for ocular media by high-irradiance Nd:YAG laser pulses of nanosecond duration. Measurements of plasma generated in different irradiation conditions, performed with the aid of a streak camera, show that, when expansion of the plasma column toward the incoming beam occurs, it coincides with quenching of the luminescence exhibited by plasma regions located closer to the focus, where breakdown has first occurred. Evidence for this effect is given both with impurityfree media, where plasma expansion occurs in a continuous and regular way, and with impurity-rich media, where plasma columns are composed either of unevenly distributed plasma regions or of single plasmas with irregular breakdown starting patterns. Experimental findings have been analyzed using a model of spatially distributed plasma shielding, in combination with a previously developed model of moving breakdown, that well interprets, in liquids, the spatially dependent breakdown starting times.

We report on a theoretical and experimental study of the temporal and spatial dynamics of plasmas produced in liquids by single Nd:YAG laser pulses of nanosecond duration. This study was motivated by the increasing attention paid to the phenomenon of optical breakdown and to its related effects on tissues and media in connection with microsurgical techniques developed for ophthalmology and urology. Streak camera recordings of the emission from laser-induced plasmas were taken in distilled and tap water in controlled irradiation conditions. From streak recordings, plasma starting times as a function of the axial distance from focus, the overall length of the plasma column, plasma lifetimes, and plasma absorption were derived and analyzed. In this first paper we analyze the curves of plasma starting time, as a function of the irradiation parameters and of the properties of the medium. We show that a model obtained by upgrading the theory of the moving breakdown allows accurate interpretation of the experimental observations.