Scheimpflug Principle Research Articles

Evaluation of system models for an endoscopic fringe projection system

To be able to perform inline inspection of complex geometries, which exhibit for example undercuts or internal structures, a new endoscopic micro fringe projection system has been developed. It is designed to perform areal measurements for tool inspection inside the limited space of metal forming presses by employing flexible image fibers to couple the measurement system’s camera and projector to a compact sensor head. The projector features a laser light source and a digital micro-mirror device to generate high-contrast fringe patterns. To increase the depth of field of the sensor heads, custom gradient-index lenses have been designed as an approximation to the Scheimpflug principle. Challenges arise for both calibration and phase measuring algorithms from the optics, as well as from the reduction in resolution introduced by the fiber bundles. This paper presents an evaluation of two different system models for the endoscopic fringe projection system, which are based on the pinhole camera model and a black box model. An automated calibration process, which gathers the calibration data for two calibration algorithms that are robust to artifacts introduced by the optical path, is demonstrated. Based on a comparison of measurements, differences between the two modeling approaches are discussed. Finally, results of measurements of a demonstrational metal forming tool are shown as an application example.

Fringe projection 3D microscopy with the general imaging model.

Three-dimensional (3D) imaging and metrology of microstructures is a critical task for the design, fabrication, and inspection of microelements. Newly developed fringe projection 3D microscopy is presented in this paper. The system is configured according to camera-projector layout and long working distance lenses. The Scheimpflug principle is employed to make full use of the limited depth of field. For such a specific system, the general imaging model is introduced to reach a full 3D reconstruction. A dedicated calibration procedure is developed to realize quantitative 3D imaging. Experiments with a prototype demonstrate the accessibility of the proposed configuration, model, and calibration approach.

SUPER RESOLUTION LASER RADAR WITH BLINKING ATMOSPHERIC PARTICLES ---- APPLICATION TO INTERACTING FLYING INSECTS (Invited Paper)

Assessment of biodiversity of pollinators on the landscape scale or estimation of fluxes of disease-transmitting biting midges constitutes a major technical challenge today. We have developed a laser-radar system for field entomology based on the so called Scheimpflug principle and a continuouswave laser. The sample-rate of this method is unconstrained by the round-trip time of the light, and the method allows assessment of the fast oscillatory insect wing-beats and harmonics over kilometers range, e.g., for species identification and relating abundances to the topography. Whereas range resolution in conventional lidars is limited by the pulse duration, systems of the Scheimpflug type are limited by the diffraction of the telescopes. However, in the case of sparse occurrence of the atmospheric insects, where the optical cross-section oscillates, estimation of the range and spacing between individuals with a precision beyond the diffraction limit is now demonstrated. This enables studies of insect interaction processes in-situ.

Parabasal theory for plane-symmetric systems including freeform surfaces

An extension of paraxial theory to systems with a single plane of symmetry is provided. This parabasal model is based on the evaluation of a differential region around the reference ray that is defined by the center of the object and the center of the stop. To include freeform surfaces in this model, the local curvatures at the intersection point of the reference ray and the surface are evaluated. As an application, a generalized Scheimpflug principle is presented. The validity of the derived formulas is tested for highly tilted surfaces and is in good agreement with the exact ray tracing results. The analytical expressions are used to provide a first-order layout design of a planar imaging system.

Development and evaluation of a petal thickness measuring device based on the dual laser triangulation method

The growth and health status of plants can be evaluated by their petal or leaf thickness. However, the thickness of these sections is difficult to measure because of the irregular curvature of petal and leaf surfaces and their soft nature. The petal surface is easily damaged when traditional contact mechanical apparatus is used to measure it. In this research, we developed a novel noncontact measuring device that uses dual laser triangulation based on the Scheimpflug principle to measure petal thickness. A cubic spline method is employed to curve fit the multipoints of the petal surface after dual laser triangulation module measurement. The actual petal thickness can be calculated precisely from the normal equations of curvatures of the petal surface. The measuring range and the resolution of the petal thickness measuring device are ±2mm and 2μm/pixel, respectively. The total measurement uncertainty (comprising measurement repeatability, different surface slopes, and colors) of the dual laser triangulation system is less than 16μm. Using Phalaenopsis as a sample case, we make various compensations according to the different surface curvatures of its petal.

Clinical applications of Scheimpflug imaging in cataract surgery

Since the Scheimpflug principle was first described over a century ago, there has been a great interest among ophthalmologists for the use of Scheimpflug camera in anterior segment imaging. Scheimpflug imaging has since advanced significantly and modern day instruments provide comprehensive imaging and topographic data of the anterior segment. In this article the clinical applications and limitations of Scheimpflug imaging in modern cataract surgery patients are discussed. This article reviews recent work on assessment of lens transparency for cataract grading and integrity, using preoperative lens density measurements to help predict phacoemulsification parameters, its utility in challenging situations like capsular bag distension syndrome and traumatic cataract and assessment of density of the posterior capsule for objectively quantifying posterior-capsule opacification.

Clinical applications of Scheimpflug imaging

Since the Scheimpflug principle was first described more than a century ago, there has been great interest among ophthalmologists in the use of Scheimpflug cameras in anterior-segment imaging. Scheimpflug cameras have advanced significantly and modern-day instruments provide comprehensive imaging and topographic data of the anterior segment. The clinical applications and limitations of Scheimpflug imaging in corneal, cataract and refractive surgery patients are discussed. This article also covers an assessment of anterior chamber biometry for precataract surgery calculations and glaucoma screening, corneal topography of the anterior and posterior corneal surfaces using elevation data for early detection of keratoconus and post-laser in situ keratomileusis ectasia, lens changes with accommodation, lens transparency for cataract grading, and integrity and density of the posterior capsule for posterior-capsule opacification grading using the currently commercially available Scheimpflug cameras.

Development of a novel scattered triangulation laser probe with six linear charge-coupled devices (CCDs)

Abstract The objective of this paper is to develop an inexpensive, robust, and precise scattered-type triangulation laser probe system with six linear charge-coupled devices (CCDs), that can be used to measure simultaneously the distance and inclination angle of a workpiece surface. The developed system has been configured and assembled based on Scheimpflug's principle. Through the specific arrangement of the six linear CCDs, four different measurement modules for the developed system were possible, namely the standard triangulation probe module, the double triangulation probe module, the pentagon-like triangulation probe module, and an approximately circular triangulation probe module. Angular measurements of an inclined surface were possible using the double triangulation probe module. The measuring range of the developed laser probe was ±2 mm and the resolution was 2 μm/pixel. The performance tests among the different measurement modules of the developed probe and the commercial circular triangulation laser probe OTM3-03 have been carried out. The measurement uncertainty of the developed laser probe system, with respect to different surface roughness and slope, was generally smaller than ±20 μm within the measuring range using the pentagon-like triangulation probe module with the statistical methodology of skewness (Sk) and kurtosis (Ku) analysis by setting the appropriate threshold values for Sk and Ku, respectively. The developed probe has been integrated with a PC-based 3-axis micro-positioning stage to construct an automatic non-contact 3D measurement system and to digitize the 3D profile of a small complex object.

Quantification of light scattering and cataract development using the Scheimpflug’s principle

Abstract Purpose: Light entering the eye is scattered in a forward and backward direction in the cornea and lens due to their cellular architecture and the high protein content. Short wave optical radiation, UV, ionizing radiation, other internal and external risk factors and ageing increase light scattering especially in the lens finally leading to cataract development. Methods: Back scattered light can be reproducibly measured with the Scheimpflug principle generating time and space resolved lens density data. Scheimpflug’s principle minimalises imaging distortion, but cornea and lens themselves distort the images, so that mathematical corrections are needed for true biometrical data. Quantification of scattering data requires standardization and correction. Standardization is necessary because each recording medium has non linear components. External standards have been evaluated, e.g. Ulbricht spheres and a diacepam solution. Correction is necessary because scattering changes in any layer of the transparent tissues in the anterior eye segment affects the data from underlying tissues, meaning that an internal standard is necessary as well. Results: Based on these correction procedures the actual amount of data is depending on the number of optical sections recorded per eye. For evaluation of normal age‐related changes in light scattering and homogenous opacities like nuclear cataracts about 4 meridians are sufficient whereas asymmetric opacities like most cortical cataracts require a higher number of meridians. Conclusions: Densitometric analysis of a large number of images including all the corrections mentioned above should be performed with custom‐designed image analytical software in order to maximize the information output from the Scheimpflug recording.

Influence of a Tilt of Mirror Surface on the Measurement Accuracy of Laser Triangulation Rangefinder

Results of investigation of influence of tilt of mirror surface on the measurement accuracy of laser triangulation rangefinder are represented. Optical system of sensor satisfying to Scheimpflug's principle is considered. The measuring errors produced by asymmetry of light distribution in photorecording plane at sensing a surface by anisotropic Gaussian light beam are analyzed. The example of measuring a melt level in the crucible during the Czochralski pulling is considered at which the tilt of a melt surface depends on angular velocity of crucible rotation.

Évaluation de l’échographie 20 MHz CineScan ® dans les mesures intra-oculaires

Evaluation of the Quantel Medical 20-MHz Ultrasound Cinescan using a closed transducer in intraocular measurements and its reproducibility. We measured sulcus-to-sulcus distance of 40 control eyes using the20-MHz Cinescan. Then we compared the sonography to the Oculus Pentacam based on the Scheimpflug principle in the measurements of anterior chamber depth, cornea-to-implant distance, and implant-to-crystallin lens distance in patients who underwent phakic implantation (56 eyes). With this technique, the sulcus-to-sulcus distance can be measured with a reproducibility of 86%-88% (p<0.05). The authors show that the corneal diameter is not correlated with the sulcus measurement (R=24%, p<0.05). Several techniques are used to quantify anterior segment biometry. Some of these methods, such as White-to-White, are too empirical and others, such as the Scheimpflug camera - for example the EAS-1000 (Nidek) - or high-frequency ultrasound - Ultrasound BioMicroscopy UBM P45 (Paradigm) - are too expensive. The 20-MHz Cinescan has good reproducibility and provides easier access to anterior segment biometry. The 20-MHz Cinescan appears to be an accessible technique that may become a useful tool in the refractive surgery of the phakic intraocular lens.

Intra-observer and inter-observer repeatability of anterior eye segment analysis system (EAS-1000) in anterior chamber configuration.

Anterior chamber configuration can be assessed via optical or ultrasonic techniques. Scheimpflug photography is a non-invasive method measuring the anterior segment. The Anterior Eye Segment analysis system, EAS-1000, utilises the Scheimpflug principle and was found to have good repeatability. Previous repeatability studies, however, have had limitations in their design. The current study investigated the intra-observer and interobserver repeatability of the EAS-1000. Twenty-five healthy young subjects were recruited. The anterior chamber angles in different quadrants were measured by two examiners for interobserver analysis. The first examiner repeated the measurement at another session for intra-observer analysis. The 95% limits of agreement and intra-class correlation coefficient (ICC) were calculated. The anterior chamber depth was also measured and compared with ultrasound biometry. The anterior chamber angle assessment demonstrated good intra-observer (ICC ranging from 0.77 to 0.90 for different quadrants) and interobserver (ICC ranging from 0.68 to 0.81 for different quadrants) repeatability. The 95% intra-observer limits of agreement were within +/-5 degrees. The 95% interobserver limits of agreement were within +/-6 degrees. There was no significant difference between male and female subjects or among angles at different quadrants. The anterior chamber depth was found to be repeatable (ICC > 0.90) with 95% limits of agreement +/-0.1 mm. The anterior chamber depth was shallower than that obtained from ultrasound biometry. The EAS-100 is a non-invasive instrument which is repeatable for measuring the anterior chamber angle and depth. It provides quick results and is good for screening purposes. There is an under-estimation of anterior chamber depth, as previously reported.

Glycemic control and lens transparency in patients with type 1 diabetes mellitus

PURPOSE: To assess quantitatively the cumulative effect of hyperglycemia on lens transparency in patients with juvenile type 1 diabetes mellitus. METHODS: Subjects were 30 patients (30 eyes) with type 1 diabetes mellitus who had well-documented records on the duration of diabetes mellitus and condition of glycemic control from the onset. They were 35 years of age or younger (mean, 26.0 years), had a history of type 1 diabetes mellitus at least 5 years (mean, 8.4 years), had corrected visual acuity of 20/20 or better, and showed no clinically apparent cataract on slit-lamp examination. Twenty-one eyes of 21 subjects served as age-matched normal controls. They were 35 years of age or younger (mean, 25.7 years), had no diabetes mellitus, had corrected visual acuity of 20/20 or better, and showed no signs of cataract on slit-lamp examination. The degree of lens opacity was quantified using the anterior eye segment analysis system based on the Scheimpflug principle. An index was created to represent the cumulative effect of long-term glycemic control (hyperglycemic accumulation) by multiplying the average hemoglobin A 1c value and the number of months from the onset. RESULTS: The patients with diabetes mellitus exhibited significantly greater degree of lens opacity than the normal controls ( P = .017, Mann-Whitney U-test). Among the patients with diabetes mellitus, the lens opacity was greater in eyes with retinopathy than those without retinopathy ( P = .011). Multiple regression analysis revealed that only the index of hyperglycemic accumulation significantly correlated with the degree of lens opacity ( P = .042). CONCLUSION: Accumulated effect of hyperglycemia is related to the lens transparency in patients with diabetes.

Image analysis and Sheimpflug photography of anterior segment of the eye--a review

Light scattering properties of the cornea and lens change in relation to age. This process is influenced by noxious factors which may induce the formation of cataracts. Four different camera types based on the Scheimpflug principle have been developed for documentation and evaluation of light scattering in the eye. Topcon SL-45. Zeiss SLC, Oxford CASE 2000, Nidek EAS 1000. Only the SL-45 and EAS 1000, however, have found a wider application in clinical and experimental studies. Documentation of the eye with a Scheimpflug system is performed in a dark room after mydriasis induction. The rotating axis of the camera is aligned to the optical axis of the eye with fixation devices. Four meridians have been found appropriate for routine documentation. Image analysis is based on peak height and distance evaluation of 2 layers in the cornea and 10 layers in the lens. Standardization devices allow correction of technical differences in the recording process. Evaluation of the ageing properties of the lens has evidenced typical density developments for each individual layer, the cortex increasing in density earlier than the nucleus. Cataract classification using a Scheimpflug camera provides an objective characterization of cataract type and progression. The outcome of surgical procedures changing the refractive power of the eye can be evaluated with a Scheimpflug camera as well. Its application in studies dealing with the ocular effects of Quinolones and HMG-CoA-reductase inhibitors, has demonstrated that Scheimpflug photography is the method of choice for establishment of a safety profile for a new drug. Scheimpflug photography has proven to be ideal for objective documentation of the anterior eye segment in human and animal eyes, although both documentation and image analysis demand technical expertise to be reproducible.

Examination of UPL Rats by EAS1000, a Photographic System with the Scheimpflug Principle

Examination of UPL Rats by EAS1000, a Photographic System with the Scheimpflug Principle

Scheimpflug Records without Distortion – A Mythos?

The Scheimpflug principle was recommended as allowing distortion-free imaging; however, a detailed analysis reveals geometrical errors as well as distortions arising from absorption of light along the optical pathway. Correction formulas and factors will be presented and applied to the biometry of the eye.

Cataract classification.

Opacifications of the eye lens--generally defined as cataracts--develop in various different parts of the lens. Therefore, one has to differentiate the types of opacities. For epidemiological studies it is prerequisite to classify the cataracts according to their localization within the lens as well as to the size and intensity of the opacified area. Two approaches have been used in the past: 1) subjective methods of lens observation (based on slit lamp microscopy) and 2) objective methods with measurements of lens transparency or lens opacity respectively based on slit image documentation according to the Scheimpflug principle combined with the retroillumination technique. With ageing, the light transparency of the lens is subjected to considerable changes. Even without the formation of an opacity the transmission of the wavelengths in the UV-B/UV-A and the visible range is diminished. The single lens layers are affected by this phenomenon to different degrees. These changes which might also indicate an early stage of 'cataract formation' cannot be discerned by subjective methods. The densitometric image analysis of Scheimpflug slit images, however, allows the exact measurement of the light scatter in the single lens layers and enables the early recognition of disturbances in transparency which is of crucial importance particularly in cataract epidemiology. In view of our present knowledge the evaluation of risk factors which might be of importance in multifactorial cataract processes will hardly be possible by carrying out prevalence and/or incidence studies involving a single examination of the population. In this case follow-up studies (cohort studies) with repeated examinations are prerequisite. The 'objective methods' for classification alone are able to ensure the necessary reproducibility and the possibility to measure transparency changes in the lens before visible (and therefore subjectively recognizable) opacifications occurred. The methodical procedure with respect to an epidemiological study on the involvement of UV-B radiation in the processes of cataract formation in man requires the application of objective methods for cataract classification.

Effect of pilocarpine on anterior chamber angles.

Pilocarpine is widely used in the treatment of glaucoma, especially for the acute form of angle-closure glaucoma. Previous studies have shown that pilocarpine decreases central anterior chamber depth. In the present study, a quantitative measurement method, applying Scheimpflug photography, was used to report whether pilocarpine also affected the anterior chamber angles. Twenty-nine normal Chinese subjects, 17 female and 12 male with an age range from 11 to 63 years old, were enrolled. One eye of each subject was treated with one drop of 2% pilocarpine. Photographs of each of four quadrants were taken prior to, and after, pilocarpine treatment in both eyes, using a rotating slit-lamp video camera based on the Scheimpflug principle. The slit beams were set at 0 degrees and 90 degrees. The eyes which did not receive pilocarpine treatment served as control. The angles of the four quadrants were calculated for both eyes both prior to, and after, pilocarpine treatment, and results were compared by Student's paired t-test. The comparison of angles between the eyes prior to, and after, pilocarpine treatment indicated that there is a significant narrowing of angles in all quadrants. The complex factors involved in the change of anterior chamber angle are reviewed in the light of muscarinic action of pilocarpine.

Theodor Scheimpflug

Today, Scheimpflug’s principle is used for technical photography, even in slitlamp photography of the anterior eye segment. Little is known about the young Austrian marine captain, who sacrificed his military career to proceed in the uncertain future of aerial photogrammetry. His adolescence, a character study during military service and his obsession to use the newly developed photographic technique for land surveying, reveal a highly intelligent, sometimes difficult and always unwavering personality. Even though he died at an early age, he succeeded in developing the Scheimpflug principle for practical use.

Scheimpflug photography in clinical ophthalmology. A review.

The development of a slitlamp camera system based on the Scheimpflug principle with image analysis has been a major improvement in lens and cataract research. Since its introduction into ophthalmology by Brown and Niesel in the sixties of this century and further technical amelioration by Hockwin, Dragomirescu and Sasaki it has been applied in various experimental and clinical investigations. The purpose of this paper is to summarize and review the application of Scheimpflug photography in clinical ophthalmology and to show possibilities and indications for the use of the Scheimpflug technique in clinical studies.