In vivo, real-time confocal imaging

Objective Analysis of Corneal Nerves and Dendritic Cells

Corneal nerves and dendritic cells are increasingly being visualised to serve as clinical parameters in the diagnosis of ocular surface diseases using intravital confocal microscopy. In this review, different methods of image analysis are presented. The use of deep learning algorithms, which enable automated pattern recognition, is explained in detail using our own developments and compared with other established methods.

MondoA regulates gene expression in cholesterol biosynthesis-associated pathways required for zebrafish epiboly

The glucose-sensing Mondo pathway regulates expression of metabolic genes in mammals. Here, we characterized its function in the zebrafish and revealed an unexpected role of this pathway in vertebrate embryonic development. We showed that knockdown of mondoa impaired the early morphogenetic movement of epiboly in zebrafish embryos and caused microtubule defects. Expression of genes in the terpenoid backbone and sterol biosynthesis pathways upstream of pregnenolone synthesis was coordinately downregulated in these embryos, including the most downregulated gene nsdhl. Loss of Nsdhl function likewise impaired epiboly, similar to MondoA loss of function. Both epiboly and microtubule defects were partially restored by pregnenolone treatment. Maternal-zygotic mutants of mondoa showed perturbed epiboly with low penetrance and compensatory changes in the expression of terpenoid/sterol/steroid metabolism genes. Collectively, our results show a novel role for MondoA in the regulation of early vertebrate development, connecting glucose, cholesterol and steroid hormone metabolism with early embryonic cell movements.

Quantification of confocal fluorescence microscopy for the detection of cervical intraepithelial neoplasia

BACKGROUND

Cervical cancer remains a major health problem, especially in developing countries. Colposcopic examination is used to detect high-grade lesions in patients with a history of abnormal pap smears. New technologies are needed to improve the sensitivity and specificity of this technique. We propose to test the potential of fluorescence confocal microscopy to identify high-grade lesions.

METHODS

We examined the quantification of ex vivo confocal fluorescence microscopy to differentiate among normal cervical tissue, low-grade Cervical Intraepithelial Neoplasia (CIN), and high-grade CIN. We sought to (1) quantify nuclear morphology and tissue architecture features by analyzing images of cervical biopsies; and (2) determine the accuracy of high-grade CIN detection via confocal microscopy relative to the accuracy of detection by colposcopic impression. Forty-six biopsies obtained from colposcopically normal and abnormal cervical sites were evaluated. Confocal images were acquired at different depths from the epithelial surface and histological images were analyzed using in-house software.

RESULTS

The features calculated from the confocal images compared well with those features obtained from the histological images and histopathological reviews of the specimens (obtained by a gynecologic pathologist). The correlations between two of these features (the nuclear-cytoplasmic ratio and the average of three nearest Delaunay-neighbors distance) and the grade of dysplasia were higher than that of colposcopic impression. The sensitivity of detecting high-grade dysplasia by analysing images collected at the surface of the epithelium, and at 15 and 30 μm below the epithelial surface were respectively 100, 100, and 92 %.

CONCLUSIONS

Quantitative analysis of confocal fluorescence images showed its capacity for discriminating high-grade CIN lesions vs. low-grade CIN lesions and normal tissues, at different depth of imaging. This approach could be used to help clinicians identify high-grade CIN in clinical settings.

Imaging cell biology in live animals: ready for prime time

Time-lapse fluorescence microscopy is one of the main tools used to image subcellular structures in living cells. Yet for decades it has been applied primarily to in vitro model systems. Thanks to the most recent advancements in intravital microscopy, this approach has finally been extended to live rodents. This represents a major breakthrough that will provide unprecedented new opportunities to study mammalian cell biology in vivo and has already provided new insight in the fields of neurobiology, immunology, and cancer biology.

Confocal endomicroscopy: instrumentation and medical applications

Advances in fiber optic technology and miniaturized optics and mechanics have propelled confocal endomicroscopy into the clinical realm. This high resolution, non-invasive imaging technology provides the ability to microscopically evaluate cellular and sub-cellular features in tissue in vivo by optical sectioning. Because many cancers originate in epithelial tissues accessible by endoscopes, confocal endomicroscopy has been explored to detect regions of possible neoplasia at an earlier stage by imaging morphological features in vivo that are significant in histopathologic evaluation. This technique allows real-time assessment of tissue which may improve diagnostic yield by guiding biopsy. Research and development continues to reduce the overall size of the imaging probe, increase the image acquisition speed, and improve resolution and field of view of confocal endomicroscopes. Technical advances will continue to enable application to less accessible organs and more complex systems in the body. Lateral and axial resolutions down to 0.5 and 3 μm, respectively, field of view as large as 800 × 450 μm, and objective lens and total probe outer diameters down to 0.35 and 1.25 mm, respectively, have been achieved. We provide a review of the historical developments of confocal imaging in vivo, the evolution of endomicroscope instrumentation, and the medical applications of confocal endomicroscopy.

In vivo non-linear optical (NLO) imaging in live rabbit eyes using the Heidelberg Two-Photon Laser Ophthalmoscope

Imaging of non-linear optical (NLO) signals generated from the eye using ultrafast pulsed lasers has been limited to the study of ex vivo tissues because of the use of conventional microscopes with slow scan speeds. The purpose of this study was to evaluate the ability of a novel, high scan rate ophthalmoscope to generate NLO signals using an attached femtosecond laser. NLO signals were generated and imaged in live, anesthetized albino rabbits using a newly designed Heidelberg Two-Photon Laser Ophthalmoscope with attached 25 mW fs laser having a central wavelength of 780 nm, pulsewidth of 75 fs, and a repetition rate of 50 MHz. To assess two-photon excited fluorescent (TPEF) signal generation, cultured rabbit corneal fibroblasts (RCF) were first labeled by Blue-green fluorescent FluoSpheres (1 mum diameter) and then cells were micro-injected into the central cornea. Clumps of RCF cells could be detected by both reflectance and TPEF imaging at 6 h after injection. By 6 days, RCF containing fluorescent microspheres confirmed by TPEF showed a more spread morphology and had migrated from the original injection site. Overall, this study demonstrates the potential of using NLO microscopy to sequentially detect TPEF signals from live, intact corneas. We conclude that further refinement of the Two-photon laser Ophthalmoscope should lead to the development of an important, new clinical instrument capable of detecting NLO signals from patient corneas.

Single-wavelength reflected confocal and multiphoton microscopy for tissue imaging

Both reflected confocal and multiphoton microscopy can have clinical diagnostic applications. The successful combination of both modalities in tissue imaging enables unique image contrast to be achieved, especially if a single laser excitation wavelength is used. We apply this approach for skin and corneal imaging using the 780-nm output of a femtosecond, titanium-sapphire laser. We find that the near-IR, reflected confocal (RC) signal is useful in characterizing refractive index varying boundaries in bovine cornea and porcine skin, while the multiphoton autofluorescence (MAF) and second-harmonic generation (SHG) intensities can be used to image cytoplasm and connective tissues (collagen), respectively. In addition, quantitative analysis shows that we are able to detect MAF from greater imaging depths than with the near-IR RC signal. Furthermore, by performing RC imaging at 488, 543, and 633 nm, we find that a longer wavelength leads to better image contrast for deeper imaging of the bovine cornea and porcine skin tissue. Finally, by varying power of the 780-nm source, we find that comparable RC image quality was achieved in the 2.7 to 10.7-mW range.

Extent of Corneal Injury as a Biomarker for Hazard Assessment and the Development of Alternative Models to the Draize Rabbit Eye Test

We have characterized 22 ocular irritants differing in type (surfactants, acid, alkali, bleaches, alcohol, aldehyde, acetone) and severity (slight to severe) by using the low-volume rabbit eye test. Ocular irritation was evaluated by 1) light microscopy to assess pathological changes, 2) in vivo confocal microscopy (CM) to quantify 4-dimensionally (x, y, z, and t) initial corneal injury and later responses in the same eye, and 3) laser scanning CM to quantify initial cell death. These studies revealed that regardless of the processes leading to injury, slight irritants injure the corneal epithelium, mild irritants injure the corneal epithelium and the superficial stroma, and moderate/severe irritants injure the epithelium, deep stroma, and at times the corneal endothelium. Furthermore, extent of initial corneal injury was shown to predict subsequent responses and final outcomes. These findings suggest that extent of corneal injury may be used as a basis for the development of alternative ocular irritation tests. To test the validity of this approach, we have used an ex vivo, rabbit cornea culture model to measure extent of corneal injury following exposure to ocular irritants. Data indicate that the extent of ex vivo corneal injury significantly correlate with the extent of initial injury measured previously in live animals. Overall, these findings indicate that extent of initial corneal injury can be used as a new "gold standard" for the continued refinement and ultimate replacement of the Draize rabbit eye Ocular Irritation Test.

Skin imaging with reflectance confocal microscopy

Confocal microscopy is a new imaging modality for noninvasive real-time tissue imaging with high resolution and contrast comparable with conventional histology. Application of this technology to skin imaging during the last decade has been an exciting advance in dermatology, allowing a virtual widow into living skin without the need for a conventional biopsy or histologic processing of tissue. High-resolution noninvasive skin imaging with confocal microscopy has potential broad applications in the clinical and research arenas, including differentiating between benign and malignant skin lesions, tumor margin mapping, monitoring response to medical or surgical treatments, and pathophysiologic study of inflammatory processes.

Cartilage viability after trochleoplasty

Trochleoplasty is an established and accepted technique for the treatment of patellar instability because of a missing trochlear groove. In this technique, a flap of cartilage over the trochlea is carefully removed and a new trochlear groove is created in the underlying bone before the cartilaginous flap is reattached with sutures. The mid-term clinical and radiological results of this operation are promising but no information about the viability of the reattached cartilage has been reported. To evaluate cartilage viability and quality after trochleoplasty and to verify the healing process, two osteochondral biopsies were harvested from three patients 6, 8, and 9 months after trochleoplasty. One cylinder was evaluated histologically to assess cartilage, calcified cartilage (cc), and subchondral bone quality, while the other one was examined by confocal microscopy to evaluate cell viability. The histological examination showed a normal matrix and cell distribution of the cartilage, while the cc showed lacunae ingrowing from the underlying bone. The subchondral bone showed normal lamellae and histology, and the healing of the flap. Confocal microscopy showed almost exclusively viable chondrocytes. This demonstration of non-injured cartilage at short-term follow-up together with promising clinical and radiological 2- and 5-year follow-up results indicate a potential promising outlook for the long term, as further chondral damage is not expected. So trochleoplasty can be seen as a primary intervention for patellar instability because of trochlear dysplasia as the risk for cartilage damage is low.

Low-power laser stimulation of tissue engineered cartilage tissue formed on a porous calcium polyphosphate scaffold

BACKGROUND AND OBJECTIVE

Forming cartilage tissue in vitro that resembles native tissue is one of the challenges of cartilage tissue engineering. The aim of this study was to determine whether low-power laser stimulation would improve the formation of cartilage tissue in vitro.

STUDY DESIGN/MATERIALS AND METHODS

Bovine articular chondrocytes were seeded on the top surface of porous calcium polyphosphate substrates. After 2 days, laser stimulation was applied daily at a wavelength of 650 nm using a laser diode with energy densities of either 1.75 or 3 J/cm(2) for 4 weeks. Proteoglycan and collagen synthesis and matrix content were determined. Cartilage tissue morphology was evaluated histologically.

RESULTS

Histologically, there was no difference in the appearance or cellularity of the tissues that formed in the presence or absence of laser stimulation at either dosage. There were no differences in DNA content between treated and untreated constructs and live-dead assay confirmed that this treatment was not toxic to the cells. Laser stimulation at 3 J/cm(2) enhanced matrix synthesis resulting in significantly more tissue formation than laser stimulation at 1.75 J/cm(2) or untreated cultures.

CONCLUSION

Short exposures to low-power laser stimulation using a laser diode with 3 J/cm(2) dose improves cartilage tissue formation.

Monopolar radiofrequency treatment of partial-thickness cartilage defects in the sheep knee joint leads to extended cartilage injury

BACKGROUND

The application of radiofrequency energy to smooth and stabilize the cartilage surface has become increasingly controversial. There is little knowledge on extended-term effects, such as cartilage viability.

PURPOSE

To analyze the effect of radiofrequency treatment on artificially created partial-thickness defects in the femoral cartilage of sheep knee joints 24 weeks after surgery.

STUDY DESIGN

Controlled laboratory study.

METHODS

Grade II cartilage surface defects on the medial and lateral femoral condyles were artificially created in sheep for in vivo analysis. The cartilage lesions were treated alternately on the lateral or the medial condyle using a monopolar radiofrequency probe. Radiofrequency treatment was performed in a freehand technique until surface smoothing without change of cartilage color was seen. At 24 weeks after surgery, cartilage samples were harvested and were processed for macroscopic and histological evaluation. To analyze the effect of radiofrequency at time zero, samples of sheep femoral condyle cartilage with and without artificially created clefts were treated in vitro with radiofrequency. Evaluation was performed by scanning electron and confocal microscopy.

RESULTS

At 24 weeks after surgery, grade IV cartilage defects were detected in all radiofrequency-treated samples. The histological findings showed a central ulcer and dead chondrocytes in the radiofrequency-treated regions. The radiofrequency-treated cartilage revealed partial surface irregularities with partial-defect repair. After radiofrequency treatment in vitro, samples at time zero showed smoothing of the artificially created clefts, as seen by scanning electron microscopy. Confocal microscopy showed necrosis of chondrocytes over approximately one fourth of the upper cartilage thickness.

CONCLUSION

Even if chondrocyte death is seen only in approximately one fourth of the upper cartilage layers in the sheep femur after in vitro application, radiofrequency treatment can cause damage to cartilage 24 weeks after application.

CLINICAL RELEVANCE

Caution is recommended in the application of monopolar radiofrequency energy by visual control to partial-thickness cartilage defects. Irregular fronds of chondromalacia may be unattractive but represent viable articular cartilage. Using radiofrequency to obtain a more visually pleasing smooth surface may be counterproductive.

Changing paradigms in dermatology: confocal microscopy in clinical and surgical dermatology

The current practice of pathology and dermatopathology depends upon the evaluation of tissue in some manner extirpated from the patient and then processed and stained. While high resolution of detail can be accomplished by this method, there are certain risks and disadvantages. Recent imaging techniques now allow for a potential of achieving noninvasive high-resolution analysis of lesions in situ in the patient. Of these, Reflectance mode confocal microscopy offers the highest resolution imaging comparable to routine histology. Being entirely non invasive, skin can be observed in its native, dynamic state. This chapter will review the fundamentals of in vivo confocal imaging and the clinical applications in general and surgical dermatology.

Surface analysis methods for characterizing polymeric biomaterials

Surface properties have an enormous effect on the success or failure of a biomaterial device, thus signifying the considerable importance of and the need for adequate characterization of the biomaterial surface. Microscopy techniques used in the analysis of biomaterial surfaces include scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and confocal microscopy. Spectroscopic techniques include X-ray photoelectron spectroscopy, Fourier Transform infrared attenuated total reflection and secondary ion mass spectrometry. The measurement of contact angles, although one of the earlier techniques developed remains a very useful tool in the evaluation of surface hydrophobicity/hydrophilicity. This paper provides a brief, easy to understand synopsis of these and other techniques including emerging techniques, which are proving useful in the analysis of the surface properties of polymeric biomaterials. Cautionary statements have been made, numerous authors referenced and examples used to show the specific type of information that can be acquired from the different techniques used in the characterization of polymeric biomaterials surfaces.

Near real-time confocal microscopy of amelanotic tissue: detection of dysplasia in ex vivo cervical tissue

RATIONALE AND OBJECTIVES

The authors performed this study to determine whether images of ex vivo tissue obtained with a near real-time confocal microscope can be used to differentiate between normal and dysplastic tissue.

MATERIALS AND METHODS

Biopsy specimens of colposcopically normal and abnormal cervical tissue were obtained from 19 patients and imaged at various depths with a confocal microscope. Nuclear morphologic features were extracted from the confocal images; in addition, a group of reviewers examined the images and attempted to identify whether the specimen contained high-grade dysplasia. Results of both analyses were compared with the histopathologic findings of the same specimens provided by a board-certified pathologist with expertise in gynecologic pathology.

RESULTS

The morphologic feature measurements compared well with the findings at pathologic examination. The use of the nuclear-cytoplasmic ratio to determine the presence of dysplasia resulted in a sensitivity of 100% and a specificity of 91%. The untrained reviewers had an average sensitivity of 95% and an average specificity of 69% in the determination of dysplasia.

CONCLUSION

The results indicate the clinical potential of in vivo confocal imaging in the detection of dysplasia.

Articular cartilage repair using a tissue-engineered cartilage-like implant: an animal study

OBJECTIVE

Because articular cartilage has limited ability to repair itself, treatment of (osteo)chondral lesions remains a clinical challenge. We aimed to evaluate how well a tissue-engineered cartilage-like implant, derived from chondrocytes cultured in a novel patented, scaffold-free bioreactor system, would perform in minipig knees with chondral, superficial osteochondral, and full-thickness articular defects.

DESIGN

For in vitro implant preparation, we used full-thickness porcine articular cartilage and digested chondrocytes. Bioreactors were seeded with 20x10(6) cells and incubated for 3 weeks. Subsequent to culture, tissue cartilage-like implants were divided for assessment of viability, formaldehyde-fixed and processed by standard histological methods. Some samples were also prepared for electron microscopy (TEM). Proteoglycans and collagens were identified and quantified by SDS-PAGE gels. For in vivo studies in adult minipigs, medial parapatellar arthrotomy was performed unilaterally. Three types of defects were created mechanically in the patellar groove of the femoral condyle. Tissue-engineered cartilage-like implants were placed using press-fit fixation, without supplementary fixation devices. Control defects were not grafted. Animals could bear full weight with an unlimited range of motion. At 4 and 24 weeks postsurgery, explanted knees were assessed using the modified ICRS classification for cartilage repair.

RESULTS

After 3-4 weeks of bioreactor incubation, cultured chondrocytes developed a 700-microm- to 1-mm-thick cartilage-like tissue. Cell density was similar to that of fetal cartilage, and cells stained strongly for Alcian blue and safranin O. The percentage of viable cells remained nearly constant (approximately 90%). Collagen content was similar to that of articular cartilage, as shown by SDS-PAGE. At explantation, the gross morphological appearance of grafted defects appeared like normal cartilage, whereas controls showed irregular fibrous tissue covering the defect. Improved histologic appearance was maintained for 6 months postoperatively. Although defects were not always perfectly level upon implantation at explanation the implant level matched native cartilage levels with no tissue hypertrophy. Once in place, implants remodelled to tissues with decreased cell density and a columnar organization.

CONCLUSIONS

Repair of cartilage defects with a tissue-engineered implant yielded a consistent gross cartilage repair with a matrix predominantly composed of type II collagen up to 6 months after implantation. This initial result holds promise for the use of this unique bioreactor/tissue-engineered implant in humans.

Measurement of corneal sublayer thickness and transparency in transgenic mice with altered corneal clarity using in vivo confocal microscopy

Measurement of sublayer thickness and transparency at cellular level in the living animal are critical to understanding the role of specific transgenes and transgene products in controlling corneal development and maintenance of transparency. Using two different transgenic mouse strains having altered corneal clarity, we have evaluated the ability of in vivo confocal microscopy to measure corneal haze and localize light scattering structures. Projection of 2-D and 3-D image information identified the nature and location of light scattering within the cornea and allowed correlation of unique structural differences to transgene expression. Our findings suggest that in vivo confocal microscopy can be used to identify the effects of transgene expression on mouse corneal transparency.

Morphology of corneal nerves using confocal microscopy

PURPOSE

The aim of the current study was to evaluate the distribution and morphology of corneal nerves as seen by means of white light confocal microscopy.

METHODS

This study analyzed images of corneal nerves that were obtained using the Tomey Confoscan slit scanning confocal microscope (40x/0.75 objective lens). The images were classified according to their location within the cornea. The objective and subjective evaluation of the images involved measuring, grading, or judging a number of parameters from both individual pictures and from each single nerve fiber within any image.

RESULTS

The in vivo observations made in this work are in agreement with those of previous histologic studies. The general scheme of corneal innervation is described as originating from thick and straight stromal nerve trunks that extend lateral and anteriorly and give rise to plexiform arrangements of progressively thinner nerve fibers at several levels within the stroma. From there, nerve fibers perforate Bowman's layer and eventually form a dense neural plexus just beneath the basal epithelial cell layer, which is characterized by tortuous and thin beaded nerve fibers interconnected by numerous nerve elements; nerve fibers from this plexus are known to be responsible for the innervation of the epithelium.

CONCLUSION

This study provides convincing evidence of the suitability of confocal microscopy to image corneal nerves, the only drawback being the limited resolution in terms of the differentiation of the ultrastructure of nerve bundles.

Quantification of laser-induced cartilage injury by confocal microscopy in an ex vivo model

BACKGROUND

The application of lasers in orthopaedic surgery is increasing. However, some investigators have reported that osteonecrosis may occur after laser meniscectomy. The objective of the present study was to evaluate the effect of laser wavelength and energy on cartilage injury in an ex vivo model.

METHODS

Fresh bovine articular cartilage was exposed to either holmium:yttrium-aluminum-garnet (Ho:YAG) or erbium:YAG-laser (Er:YAG) irradiation. Both lasers were operated in a free-running mode and at a pulse-repetition rate of 8 Hz. The effect of laser treatment at several energy levels (Er:YAG at 100 and 150 mJ and Ho:YAG at 500 and 800 mJ) was examined. For each light source and energy level, ten cartilage samples were assessed by conventional histological analysis and by confocal microscopy. Thermal damage was assessed by determining cell viability.

RESULTS

The extent of thermal damage demonstrated by confocal microscopy was much greater than that demonstrated by histological analysis. The extent of thermal injury after Ho:YAG-laser irradiation was much greater than that after Er:YAG-laser irradiation, which was associated with almost no damage. In addition, the ablation depth was greater after treatment with the Er:YAG laser than after treatment with the Ho:YAG laser.

CONCLUSIONS

In the present study, histological analysis underestimated thermal damage after laser irradiation. In addition, our findings highlighted problems associated with use of high-power settings of Ho:YAG lasers during arthroscopic surgery.

Methods for imaging the structure and function of living tissues and cells: 3. Confocal microscopy and micro-radiology

This review article looks at the development of confocal imaging technology, with emphasis on its abilities to overcome some of the problems of imaging life processes, particularly in the intact organ or animal. A brief summary of three promising micro-imaging modalities is provided (which are microscopical analogues of conventional radiological techniques) with a bibliography for the interested reader to pursue.

Near real time confocal microscopy of amelanotic tissue: dynamics of aceto-whitening enable nuclear segmentation

High resolution, in vivo confocal imaging of amelanotic epithelial tissue may offer a clinically useful adjunct to standard histopathologic techniques. Application of acetic acid has been shown to enhance contrast in confocal images of these tissues. In this study, we record the time course of aceto-whitening at the cellular level and determine whether the contrast provided enables quantitative feature analysis. Confocal images and videos of cervical specimens were obtained throughout the epithelium before, during and post-acetic acid after the application of 6% acetic acid. Aceto-whitening occurs within seconds after the application. The confocal imaging system resolved sub-cellular detail throughout the entire epithelial thickness and provided sufficient contrast to enable quantitative feature analysis.

Near-infrared confocal laser scanning microscopy of bladder tissue in vivo

OBJECTIVES

To assess the potential of a near-infrared confocal laser scanning microscope (CLSM) for imaging bladder tissue in vivo.

METHODS

Confocal images of the exposed bladder of male Sprague-Dawley rats were obtained with a CLSM. To minimize tissue motion, the bladder was placed in light contact under an objective lens housing, and the top surface was lightly flattened with a coverslip. Images were obtained from the outer and inner layers of the bladder wall with a lateral resolution of 0.5 to 1 microm and an axial resolution (section thickness) of 3 to 5 microm. The confocal images were later correlated with routine histologic studies.

RESULTS

The CLSM allows imaging of the urothelium, the superficial and deep portions of the lamina propria, the muscularis propria, and the serosa of the bladder wall in vivo. Urothelial cells, collagen bundles and fibers, muscle, and circulating blood cells in capillaries and larger blood vessels are easily visualized. The confocal images correlated well with the histologic studies.

CONCLUSIONS

Confocal microscopy allows real-time, high-resolution, high-contrast imaging of cellular and structural morphologic features to a maximal depth of 300 microm within the bladder wall in vivo. Artifacts caused by tissue motion can be minimized with a bladder-objective lens contact housing.

Video-rate confocal scanning laser microscope for imaging human tissues in vivo

We have built a video-rate confocal scanning laser microscope for reflectance imaging of human skin and oral mucosa in vivo. Design and imaging parameters were determined for optimum resolution and contrast. Mechanical skin-holding fixtures and oral tissue clamps were made for stable objective lens-to-tissue contact such that gross tissue motion relative to the microscope was minimized. Confocal imaging was possible to maximum depths of 350 microm in human skin and 450 microm in oral mucosa, with measured lateral resolution of 0.5-1 microm and axial resolution (section thickness) of 3-5 microm at the 1064-nm wavelength. This resolution is comparable with that of conventional microscopy of excised biopsies (histology). Normal and abnormal tissue morphology and dynamic processes were observed.

Use of in vivo confocal microscopy to understand the pathology of accidental ocular irritation

In vivo confocal microscopy (CM) provides a unique ability to section optically through living, intact tissues and organs to characterize qualitatively and quantitatively pathological changes in 4 dimensions (x, y, and z, and time). It involves the capture of real-time images without the need for excision, fixation and processing. In vivo CM principally has been used for evaluation of eyes in patients and laboratory animals but has potential application to studies of other tissues/organs. In vivo CM is being used in human ophthalmology clinics. It has been used as a research tool for quantitative, in situ measurement of corneal wound contraction, fibroblast migration, corneal endothelial cell migration, corneal epithelial cell size and desquamation following contact lens wear and surgery, and the assessment of corneal surface toxicity following application of commonly used ophthalmic preservatives. In vivo CM allows us to (a) characterize changes to a light microscopic (i.e., cellular) level; (b) quantify changes objectively: (c) conduct studies of injury and repair in the same animal and directly correlate microscopic changes to clinical observations over time as this technique is used in the living animal; and (d) conduct comparative studies in humans. Here we present a brief overview of in vivo CM and how we are using it to provide noninvasive, in situ qualitative and quantitative histopathologic characterization of accidental ocular irritation. Our intent is to provide an awareness of this relatively new methodology and one practical application of its use in research. The goal of our work is to provide objective, quantitative data for use in developing and validating mechanistically based in vitro replacement tests.

Spectrally encoded confocal microscopy

An endoscope-compatible, submicrometer-resolution scanning confocal microscopy imaging system is presented. This approach, spectrally encoded confocal microscopy (SECM), uses a quasi-monochromatic light source and a transmission diffraction grating to detect the reflectivity simultaneously at multiple points along a transverse line within the sample. Since this method does not require fast spatial scanning within the probe, the equipment can be miniaturized and incorporated into a catheter or endoscope. Confocal images of an electron microscope grid were acquired with SECM to demonstrate the feasibility of this technique.

Experimental hypercholesterolemia induces ultrastructural changes in the internal elastic lamina of porcine coronary arteries

The internal elastic lamina (IEL) serves as a barrier for cells and macromolecules migration between the intima and the media in the vascular wall. Several investigators have reported internal elastic lamina ultrastructural changes in elastic arteries with atherosclerosis. However, no quantitative and qualitative assessment of the internal elastic lamina architecture in muscular arteries such as the coronary circulation during early atherosclerosis have been performed yet. In this study, we therefore evaluated the ultrastructural morphological changes of the IEL in the coronary circulation of pigs fed with high cholesterol diet. Animals were sacrificed after being fed either a high cholesterol diet for 10-12 weeks (n = 5, 12 coronary segments) or a control diet (n = 4, 15 coronary segments). Coronary arteries were analyzed by transmission and scanning electron microscopy. In addition, computerized digital analysis of the images obtained by confocal scanning microscopy was performed for the quantitation of the morphologic changes in the internal elastic lamina. Confocal microscopy and scanning electron microscopy revealed an altered pattern characterized by large oval fenestration formation in the internal elastic lamina of hypercholesterolemic animals. Computerized morphometric analysis of confocal microscopy images demonstrated that compared to controls, the IEL of cholesterol-fed animals was characterized by an increase in the minor diameter of the fenestrae (2.16 +/- 0.04 microm versus 3.32 +/- 0.06 microm, P = 0.003) and a decrease in the fenestrae density (22333 +/- 1334/mm2 versus 17552 +/- 931/mm2, P = 0.015) of the internal elastic lamina. The percentage of the IEL area covered by the fenestrae correlated with the intimal thickness (r = 0.79, P = 0.004). This study demonstrates that experimental hypercholesterolemia is characterized by ultrastructural changes of the internal elastic lamina in the coronary circulation. This study suggests that the IEL may play an important role in the development of structural changes which characterize the early phase of coronary atherosclerosis.

In vivo fibre optic confocal imaging of microvasculature and nerves in the rat vas deferens and colon

A fluorescence confocal microscopy technique was employed to obtain subsurface images of nerve and microvascular structure in the vas deferens and colon of the living rat. The use of dual labelling with vital dyes and 2-channel confocal acquisition allowed differentiation of microscopic structure at both low and higher magnification. Characteristic staining patterns of nerves and blood vessels were repeatedly obtained in each tissue, suggesting the potential of this technique for studying morphological changes associated with surgical procedures and/or models of neuronal or vascular pathology.

Penetration depth limits of in vivo confocal reflectance imaging

We present experiments to predict the maximum penetration depth atwhich typical biological structures in amelanotic tissue can bedetected with confocal microscopy. The detected signal is examinedas the signal source strength (index of refraction mismatch), thesource depth, and the medium scattering coefficient are varied. Thedetected background produced by scattering outside the focal volume isexamined as the medium scattering coefficient, the depth in the medium, the dimensionless pinhole radius, nu(p), and theshape of the scattering phase function are varied. When the systemapproaches ideal confocal performance (nu(p) ? 3), the penetration depth is limited by the signal-to-noiseratio to approximately 3-4 optical depths (OD's) for a 0.05 indexmismatch. As nu(p) increases to 8, thepenetration depth is limited by the signal-to-background ratio and isdependent on the scattering coefficient. At mu(s) = 100 cm(-1) (l(s) = 100 mum) and an index mismatch of 0.05, the maximum penetrationdepth is approximately 2 OD.

Confocal microscopy as a tool for the investigation of the anterior part of the eye

In recent years, confocal microscopy has become a powerful tool for examining microscopic structures in the living eye. The decisive advantage of this technique is that it permits the investigation of optical sections of relatively thick (> 10 microns) specimens. Because confocal microscopy suppresses the out-of-focus blur, sharp three-dimensional images with excellent resolution can be obtained. Confocal microscopy is therefore able to provide more information than the classic methods--i.e., specular microscopy and slit-lamp biomicroscopy. This paper reviews recent applications of confocal microscopy in three fields of ophthalmology: the observation of the anatomy of the anterior parts of the eye, the investigation of these structures after local administration of drugs and, finally, the use of this technique for the diagnosis of infectious ocular diseases.

Confocal microscopic characterization of initial corneal changes of surfactant-induced eye irritation in the rabbit

We have previously demonstrated with slightly and severely irritating surfactants that the new technology of noninvasive, in vivo confocal microscopy (CM) can be a useful approach to a better understanding of the pathobiology of ocular irritation in situ. In this study, in vivo CM was used to qualitatively and quantitatively characterize the initial microscopic corneal changes occurring with surfactants of slight, mild, moderate, and severe irritation. Surfactants were directly applied to the corneas of rabbits (6/group) at a dose of 10 microl. Eyes and eyelids were examined macroscopically and scored for irritation beginning at 3 hr after dosing and periodically through Day 35. Concurrently, the corneas were evaluated by in vivo CM; 3D data sets extending from the surface epithelium to the endothelium were assessed for surface epithelial cell size, epithelial layer thickness, total corneal thickness, and depth of keratocyte necrosis. The average macroscopic scores at 3 hr for the slight, mild, moderate, and severe irritants were 6.0, 39.3, 48.5, and 68.7, respectively, of a possible 110. At 3 hr, in vivo CM revealed corneal injury with the slight irritant limited to the epithelium, resulting in reductions in epithelial cell size and thickness to 59.0 and 82.4% of controls (p < 0.001 and p < 0.01, respectively). These parameters returned to normal by Day 3. For the mild irritant, at 3 hr the epithelium was absent, corneal thickness was increased to 157.6% of controls (p < 0.001), and necrosis of keratocytes extended to an average depth of 4.3 microm (0.8% of the corneal thickness); these parameters were essentially normal by Day 14. For the moderate irritant, at 3 hr the epithelium was markedly attenuated, corneal thickness was increased to 155.8% of controls (p < 0.001), and keratocyte necrosis extended to an average depth of 19.0 microm (3.6% of corneal thickness; statistically greater than with the mild irritant, p < 0.001); these parameters were essentially normal by Day 14. For the severe irritant, at 3 hr the epithelium was significantly thinned, corneal thickness was increased to 165.9% of controls (p < 0.001), and keratocyte necrosis occurred to an average depth of 391.1 microm (70.1% of corneal thickness). These findings demonstrate that significant differences in area and depth of injury occur with surfactants of differing irritancy. The data suggest that differences at 3 hr can be used to distinguish different levels of ocular irritation. Data such as these will be important in the development and evaluation of future mechanistically based in vitro alternatives for ocular irritancy testing.

In vivo visualization of hippocampal cells and dynamics of Ca2+ concentration during anoxia: feasibility of a fiber-optic plate microscope system for in vivo experiments

The feasibility of a fiber-optic plate (FOP) microscope system employing a bundle of optical fibers and videomicroscopy for in vivo experiments was investigated. The FOP used here consisted of optical fibers 3 microns in diameter. By inserting the FOP into an animal, optical signals from the deep-lying tissue invisible from the surface could be obtained as two-dimensional images. Using this system, hippocampal cells stained with a fluorescent dye in an anesthetized rat were visualized. Elevation of intracellular free calcium concentration ([Ca2+]i) in the hippocampus of the rat during anoxic exposure was also detected with a fluorescent indicator dye. These results showed that the FOP microscope system was sufficiently applicable to in vivo experiments for studying tissue structure and physiological activity even in the deep regions with fluorometric techniques.

Scanning electron microscopic observation of basal cells following corneal epithelial abrasion

By desquamating single layers of corneal epithelial cells by digitonin, we attempted to observe the basal cell layer of corneal epithelium during wound healing by scanning electron microscopy. Central corneal deepithelisation (diameter 7.0 mm) was performed on rabbit eyes. Animals were killed following healing periods of up to 14 days. Half the eyes were treated with digitonin to expose the basal cell layer, and the other half were left untreated to preserve the superficial layer. In non-wounded controls, basal cells were observed as small and columnar-shaped cells. In experimental animals, on day 3 the superficial cells as well as the underlying basal cells were elongated and enlarged. On day 7, the basal cells became columnar in shape, but remained large. Both superficial cells and basal cells returned to normal on day 14. This technique allowed us to observe the morphological reconstruction process of basal cells by scanning electron microscopy.

Application of in vivo confocal microscopy to the understanding of surfactant-induced ocular irritation

The purpose of this study was to assess the ability of in vivo confocal microscopy (CM) to provide noninvasively derived histopathologic correlates of surfactant-induced eye irritation from which specific pathologic mechanisms can be identified and later evaluated in alternative in vitro models. Rats and rabbits, divided into groups of 5, received 10 microliters of an anionic or cationic surfactant in one eye with the other eye used as a control. At specified times, eyes were examined and scored for ocular irritancy using a penlight and slit-lamp. Subsequently, corneas were evaluated by in vivo CM to evaluate epithelial layer thickness and surface epithelial cell area, corneal thickness, depth of necrosis, inflammation, fibrosis, and endothelial injury. At 3 hr, the anionic surfactant produced slight irritation with peak scores of 12.4 and 8.0 out of a possible 110 in the rats and rabbits, respectively. In vivo CM revealed changes limited to the corneal epithelium that decreased in thickness to 78% in rats and 81% in rabbits at 3 hr. This decrease in the thickness correlated with a significant decrease in surface epithelial cell area from 2,061 +/- 395 microns2 to 567 +/- 330 microns2 in the rats and 1,523 +/- 185 microns2 to 934 +/- 71 microns2 in the rabbits (p < 0.005 and 0.005, respectively). The cationic surfactant produced severe irritation in both the rats and rabbits with peak scores of 85.4 and 80.2 occurring at day 2, respectively. In vivo CM in the rats showed complete loss of corneal epithelium, lysis of keratocytes, and loss of corneal endothelium. In the rabbits, injury appeared limited to the anterior cornea with complete loss of epithelium and loss of keratocytes extending to 52% of the corneal thickness. These findings establish the application of noninvasive, in vivo CM to qualitatively and quantitatively characterize the pathobiology of ocular irritation in situ. This information will be important in the development and evaluation of mechanistically based in vitro alternatives for ocular irritancy testing.

Quantitative three-dimensional confocal imaging of the cornea in situ and in vivo: system design and calibration

A new depth encoding system (DES) is presented, which makes it possible to calculate, display, and record the z-axis position continuously during in vivo imaging using tandem scanning confocal microscopy (TSCM). In order to verify the accuracy of the DES for calculating the position of the focal plane in the cornea both in vitro and in vivo, we compared TSCM measurements of corneal thickness to measurements made using an ultrasonic pachymeter (UP, a standard clinical instrument) in both enucleated rabbit, cat, and human eyes (n = 15), and in both human patients (n = 7). Very close agreement was found between the UP and TSCM measurements in enucleated eyes; the mean percent difference was 0.50 +/- 2.58% (mean +/- SD, not significant). A significant correlation (R = 0.995, n = 15, p < 0.01) was found between UP and TSCM measurements. These results verify that the theoretical equation for calculating focal depth provided by the TSCM manufacturer is accurate for corneal imaging. Similarly, close agreement was found between the in vivo UP and TSCM measurements; the mean percent differences was 1.67 +/- 1.38% (not significant), confirming that z-axis drift can be minimized with proper applanation of the objective. These results confirm the accuracy of the DES for imaging of the cornea both ex vivo and in vivo. This system should be of great utility for applications where quantitation of the three-dimensional location of cellular structures is needed.

In vivo human corneal confocal microscopy of identical fields of subepithelial nerve plexus, basal epithelial, and wing cells at different times

A technique is described to obtain time-lapse reflected light confocal images of cells in the basal epithelium and adjacent wing cell layer from the in vivo human cornea. The technique is based on the sequential relocation of the unique patterns of the subepithelial nerve plexuses immediately posterior to Bowman's membrane. The patterns of individual subepithelial nerve plexuses, as well as perforation points where nerves traverse Bowman's membrane, serve as fixed landmarks. A real-time, scanning slit, confocal microscope is used to obtain reflected light images of a subepithelial nerve plexus, and the anterior and adjacent fields of basal and wing cells in the in vivo human cornea. All of the photographs are obtained from single video frames without the necessity of frame averaging or digital image processing. The instrument and relocation technique are prerequisites for applying a time-lapse observation technique to investigate the dynamics of basal cell proliferation and differentiation in the living eye.

Potential vascular damage from radiation in the space environment

Cultured endothelial cells of blood vessels have a Do of 2 Gy for X-rays. A dose of 0.5 Gy of X-rays has an acute effect on vessel diameter. The vessels may show other acute effects such as change in permeability including a change in the blood brain barrier. Changes occurring from late effects of chronic exposure in vascular architecture include telangiectasia and decrease in vascular density. Changes in the perivascular connective tissue particularly collagen may play a role in these changes. After charged particle exposure of 15 and 30 Gy, radiation changes in the blood brain barrier and vascular changes are noted in the nervous system. These long term changes are recorded by PET, MRI, and CT imaging. Chronic exposure to alpha particles causes vascular damage in compact bone resulting in bone infarcts. Using tandem scanning confocal microscopy in-situ imaging of the capillaries and collagen of the papillary dermis provides a non-invasive method of serial recording of changes in irradiated microvasculature.

The use of confocal microscopy in evaluating corneal wound healing after excimer laser keratectomy

Corneal wound healing following excimer laser keratectomy is the major cause of regression of treatment results. The amount of anterior stromal haze that develops may be influenced by topical medications. Over a period of 6 months, we followed 15 New Zealand white rabbit eyes that underwent excimer laser keratectomy with the VISX 193-nm ArF laser at a fluence of 150 mJ/cm2 for a depth of 130 microns. Eyes were randomized to treatment with prednisolone acetate, diclofenac sodium (Voltaren), a combination of both, and a control group. Drops were administered four times a day for 1 week, two times a day for 3 weeks, and the drops were then tapered. All eyes were reepithelialized by 5 to 7 days. The tandem scanning confocal microscope (TSCM) was used to evaluate the corneal wound in vivo weekly for a month and monthly for 6 months. During the early postoperative period, the TSCM revealed significant anterior stromal keratocyte activation with cell elongation and the spindle-shaped appearance of fibroblasts in all groups. Collagenous stromal scarring was evident initially, then slowly decreased in all treatment groups. This study shows that TSCM is clinically useful for successive in vivo examinations of corneal wounds after excimer laser keratectomy and for comparing the effects of various topical medications.

Limitations in tandem scanning confocal microscopy as a diagnostic tool for microbial keratitis

One potential application of tandem scanning confocal microscopy is the detection of in vivo pathogens. Our study of an experimental model of Acanthamoeba keratitis demonstrates that while this technology can successfully detect certain organisms, there are currently limitations. These limitations relate to instrument configuration, movement of either the tissue or the microscope, difficulty in reproducibly returning to the area of interest for serial examination, the lack of a distinctive morphology of some pathogens, and limited resolution of the microscope.

In vivo spatio-temporal visualization of the human skin by real-time confocal microscopy

A modified tandem scanning confocal microscope is used to obtain in vivo images of the human skin in real time. Three-dimensional and temporal visualizations are demonstrated with volume reconstruction and blood flow images. Two image processing methods based on Fourier transform and logarithmic processing are presented. Their applications in noise removal of the scanning disk lines and of the heterogeneity of light are illustrated.

The application of confocal microscopy to the study of living systems

A unique tandem confocal microscope (TSCM) has been developed that permits noninvasive imaging in vivo of the eye and many other organ systems in real time in situ. The application to the study of microphysiological processes in vivo is described and illustrated for the cornea, kidney, liver, epididymis, muscle, and adipose tissue. Novel applications are shown for studying the healing of wounds in four dimensions (x, y, z, t) in single animals over time at the cellular level. Application to clinical diagnostic use in humans is also demonstrated. When combined with Laser Scanning Confocal fluorescence microscopy, the TSCM offers a unique new imaging paradigm for experimental biology and medicine with great potential for use in neuroscience and many other disciplines.

Morphometry of human epidermis in vivo by real-time confocal microscopy

Real-time confocal microscopy has brought substantial improvements to the imaging of the human skin in vivo. On early images, the stratum corneum could be distinguished from the living epidermis and the circulatory network of the superficial dermis. We have adapted the Tandem Scanning Microscope to obtain images of the living skin, showing thinner structures such as the stratum lucidum and the dermo-epidermal junction, both of which are essential markers for micron-order measurements of the thickness of the stratum corneum and living epidermis. The measurements were corrected for the differences in the refractive index of the various cutaneous layers, and the undulation of the dermo-epidermal junction. Furthermore, nucleus size and number could be assessed from horizontal optical sections. To illustrate the sensitivity of the thickness measurements, changes in the thickness of the epidermis were recorded during and after stripping of the horny layers. This non-invasive methodology is a very promising tool for morphometric studies of the living human skin at the cellular level.

Clinical and diagnostic use of in vivo confocal microscopy in patients with corneal disease

BACKGROUND

The purpose of this article is to introduce the practicing ophthalmologist to the optical principles and images produced by a tandem scanning confocal microscope (recently approved by the Food and Drug Administration for general clinical use). The tandem scanning confocal microscope allows real-time viewing of structures in the living cornea at the cellular level in four dimensions (x, y, z, and time).

METHODS

Nine patients (2 males, 7 females), ranging in age from 7 to 52 years, were examined. Images were recorded on super VHS videotape, digitized and processed on a computer workstation, and photographed for presentation.

RESULTS

Two-dimensional (x, y) 400 x 400-microns images (9-microns z-axis thickness) are presented for normal corneal structures and for the clinical conditions of herpetic keratitis, wound healing after myopic excimer ablation, Acanthamoeba infection, corneal dystrophies (granular, Reis-Buckler), contact lens abrasion, and the irido-corneal endothelial syndrome.

CONCLUSION

Clinical confocal microscopy has the unique potential of providing noninvasive assessment of corneal injury and disease at the cellular level that is not available currently from other technologies.

Three-dimensional imaging of corneal cells using in vivo confocal microscopy

Confocal microscopy is a unique and powerful imaging paradigm which allows optical sectioning through intact tissue. Real-time tandem scanning confocal microscopy has previously been used to generate high-magnification two-dimensional (2-D) images of cells in living organ systems. Inherent problems with movement, however, have prevented the in vivo acquisition of complete 3-D datasets. The development of a new objective lens, used in combination with specialized real-time image acquisition procedures, has allowed sequential serial sections to be obtained in vivo from the rabbit cornea for the first time. These sections can be digitally registered and stacked on the computer to provide a 3-D reconstruction of the corneal cells. This technique should serve as a useful method for studying 3-D structures and analysing 4-D phenomena at the cellular level in living animals. Three-dimensional images of a stromal nerve in normal rabbit cornea and of fibroblasts within a rabbit corneal wound are presented as examples of current capabilities.