Digital image acquisition in in vivo confocal microscopy

Confocal microscopy in ocular argyrosis

PURPOSE

To identify the presence of silver deposits in the cornea using a new-generation confocal microscopy technique.

METHODS

Case report.

RESULTS

A 70-year-old man, who had been a jeweler for many years, was referred to our center for assessment of corneal opacity and ocular pigmentation. Slit-lamp examination revealed grayish, dense confluent deposits in the central and peripheral cornea, deep stroma, and Descemet's membrane. On confocal microscopy, we observed typical images of hyperreflective keratocytes across the entire stromal surface and two hyperreflective plaques coinciding with areas of metal deposition, one at Descemet's membrane and the other at Bowman's membrane. This last deposition site has not been previously identified in vivo by confocal microscopy.

CONCLUSIONS

Confocal microscopy is a useful tool for the diagnosis of corneal argyrosis because it allows the in vivo visualization of silver deposits at different corneal levels.

Occupational corneal argyrosis in art silver solderers

PURPOSE

To determine the value of confocal and specular microscopy in the examination of corneal argyrosis in art silver solderers.

METHODS

Six patients with corneal argyrosis underwent a complete physical and ophthalmologic examination. Specular microscopy was performed in three cases, and in vivo confocal microscopy in four cases. Ultrasound biomicroscopy and corneal topography were performed in three cases. A conjunctival specimen of one patient was examined histologically in paraffin sections.

RESULTS

Slit-lamp examination showed gray, diffuse opacities in the deep corneal stroma. Confocal microscopy showed highly reflective deposits with a granular pattern anterior to the corneal endothelium and hypereflective keratocyte nuclei with visible cytoplasm in the anterior stroma. Specular microscopy demonstrated round white bodies anterior to the corneal endothelium. Silver deposits were not found histologically.

CONCLUSIONS

Silver solderers with long-term exposure to silver compounds are at high risk of developing corneal argyrosis. We conclude that specular microscopy and in vivo confocal microscopy provided important information for the diagnosis of corneal argyrosis.

In vivo confocal microscopy through-focusing to measure corneal flap thickness after laser in situ keratomileusis

PURPOSE

To measure flap thickness in laser in situ keratomileusis (LASIK) patients using in vivo confocal microscopy through-focusing (CMTF) and compare measured versus intended flap thickness achieved by 2 microkeratomes, the Automated Corneal Shaper(R) (ACS) (Chiron Bausch & Lomb) and the Hansatome (Bausch & Lomb).

SETTING

Department of Ophthalmology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, USA.

METHODS

Twenty-seven eyes of 27 patients were examined by in vivo CMTF 3 to 12 months after LASIK was performed with the ACS (12 patients) or Hansatome (15 patients) microkeratome. The central cornea was scanned, and the epithelium, flap, stroma, and total corneal thickness were measured. Normalized flap thickness (NFT) was also calculated to account for changes in epithelial thickness that may have occurred postoperatively.

RESULTS

The mean posterior stromal thickness was 341.1 microm +/- 53.9 (SD) (range 233 to 431 microm) in the ACS group and 320.3 +/- 42.3 microm (range 258 to 382 microm) in the Hansatome group. The mean nonnormalized flap thickness was 132.7 +/- 12.5 microm (range 11 to 151 microm) in the ACS group and 167.4 +/- 21.4 microm (range 141 to 209 microm) in the Hansatome group. The NFT was 129.6 +/- 9.5 microm and 158.4 +/- 22.1 microm, respectively. Both microkeratomes cut significantly less than intended (P <.05); however, the ACS cut a thinner-than-intended thickness in all cases, and the Hansatome cut thicker than intended in 13% of cases. The Hansatome also showed significantly greater variability in flap thickness than the ACS (P <.05).

CONCLUSIONS

A significant difference in precision was noted between the 2 microkeratomes. The findings emphasize the importance of performing thickness measurements and the usefulness of in vivo CMTF in making these determinations to ensure the safety and effectiveness of LASIK.

Pathology of ocular irritation with bleaching agents in the rabbit low-volume eye test

Despite differences in the processes leading to tissue damage, the ocular irritation response to various surfactants, two concentrations of an acid and an alkali, and an acetone, alcohol, aromatic amine, and aldehyde has been shown to depend on the extent of initial injury. The purpose of this study was to assess the extent to which this fundamental relationship exists for bleaching agents in the rabbit low-volume eye test. Ten microl of sodium perborate monohydrate (NaBO3), sodium hypochlorite (NaOCl), 10% hydrogen peroxide (H2O2), and 15% H2O2 was applied directly to the cornea of the right eye of each rabbit. Macroscopic assessments for irritation were made 3 hours after dosing and periodically until 35 days. Light microscopic examinations were conducted on tissues obtained at 3 hr and on 1, 3, and 35 days. In vivo confocal microscopy (CM) and measurements of dead corneal epithelial cells and keratocytes at 3 hours and 1 day were used to characterize quantitatively initial corneal injury, while in vivo CM performed at 3 hours and 1, 3, 7, 14, and 35 days was used to characterize quantitatively the corneal changes over time. The changes with NaBO3 and NaOCl were consistent with mild irritancy. For both, corneal injury was limited to the epithelium and superficial stroma. The changes with 10% H202 and 15% H2O2 were consistent with severe irritation. Both concentrations affected the epithelium and deep stroma, with 15% H2O2 also at times affecting the endothelium. However, unlike other irritants previously studied, with 10% H2O2 and 15% H2O2 there was an incongruity between the extent of epithelial and stromal injury, with stromal injury being more extensive than epithelial injury. A similar, although less dramatic, effect was observed with NaBO3. Additionally, there was still significant keratocyte loss at 35 days with 10% H2O2 and 15% H2O2 even though the eyes at times were considered to be macroscopically normal. These observations highlight the need to include both epithelial and stromal components in an ex vivo or in vitro alternative assay. In conclusion, these results continue to support and extend our hypothesis that ocular irritation is principally defined by the extent of initial injury despite clear differences in the means by which irritants cause tissue damage. Importantly, we have identified unique differences in the ocular injury and responses occurring with bleaching agents that are important to consider in the development and validation of alternative ocular irritation tests to characterize a broad range of materials differing in type and irritancy.

Pathology of ocular irritation with acetone, cyclohexanol, parafluoroaniline, and formaldehyde in the rabbit low-volume eye test

The ocular irritation responses to 11 different surfactants and two concentrations of acetic acid and sodium hydroxide have been shown to depend on the extent of initial injury, despite marked differences in the processes leading to tissue damage. The purpose of these studies was to determine the extent to which this fundamental relationship applies to other nonsurfactants. Ten microl of acetone (ACT). cyclohexanol (CY), parafluoroaniline (PF), or 37% formaldehyde (FA) was directly applied to the cornea of the right eye of each rabbit. Eyes and eyelids were macroscopically scored for signs of irritation beginning 3 hours after dosing and periodically until recovery or 35 days. Tissues were obtained for light microscopic examination after 3 hours and on days 1, 3, and 35. Initial corneal injury was characterized quantitatively at 3 hours and I day using in vivo confocal microscopy (CM) and by postmortem quantitation of dead corneal epithelial cells and keratocytes using a Live Dead Assay (L/D, Molecular Probes) and scanning laser CM. Corneal changes over time were characterized quantitatively using in vivo CM performed at 3 hours and 1, 3, 7, 14, and 35 days. The changes with ACT were consistent with mild irritation. Corneal injury was limited to the epithelium and superficial stroma, with the mean normalized depth of injury (NDI) being less than 10% with the majority of regions showing no stromal injury. Changes with CY and PF were consistent with moderate to severe irritation, and FA caused severe irritation. Specifically, corneal injury by CY and PF tended to involve the epithelium and anterior stroma, with the mean NDI being 10.4% to 23.8%, while injury with FA involved the epithelium, deep stroma, and at times the endothelium. Interestingly, with FA significantly less injury was observed at 3 hours with a dramatic increase in injury observed at 1 day and thereafter. In conclusion, these results continue to support and extend our hypothesis that ocular irritation is principally defined by the extent of initial injury despite clear differences in the means by which irritants cause tissue damage. We believe this approach can be applied to developing alternative assays based on injury to ex vivo eyes or injury to an in vitro corneal equivalent system.

Quantitative measurement of acute corneal injury in rabbits with surfactants of different type and irritancy

We have hypothesized that differences in ocular irritancy are related to differences in extent of initial injury and that, regardless of the processes leading to tissue damage, extent of injury is the primary factor that determines the final outcome of ocular irritation. In previous in vivo confocal microscopic (CM) studies we identified quantifiable differences in the extent of corneal injury occurring with four surfactants (three anionic, one cationic) known to cause different levels of ocular irritation and demonstrated that extent of initial corneal injury was related to the magnitude of cell death. The purpose of this study was to assess the applicability of this hypothesis to a broad sampling of surfactants. Specifically, initial corneal changes induced by seven different surfactants (one anionic, three cationic, three nonionic) were measured by in vivo CM and cell death was measured by an ex vivo live/dead assay. The right eye of each rabbit was treated by placing 10 microl of a surfactant directly on the cornea. Eyes were examined macroscopically and scored for irritation at 3 h and 1 day. At 3 h and 1 day, in vivo CM was used to examine the corneas and quantitate epithelial cell size, epithelial thickness, corneal thickness, and depth of stromal injury. At 3 h and/or at 1 day, corneas were removed and excised regions were placed in culture media containing 2 microM calcein AM and 4 microM ethidium homodimer. Using laser scanning CM, the number of dead epithelial and/or stromal cells in a 300 x 300 x 170-microm3 (xyz) volume of the cornea was determined. In vivo CM and live/dead assay findings revealed three surfactants to affect only the epithelium, three surfactants to affect the epithelium and superficial stroma, and one surfactant to affect the epithelium and deep stroma. Extent of initial corneal injury reflected level of ocular irritation, and magnitude of cell death was related to the extent of initial corneal injury. These findings are consistent with those for known slight, mild, and moderate to severe irritants, respectively. They suggest that our hypothesis is broadly applicable to surfactants. Additionally, we believe these surfactants should be included as part of a new "gold standard" for use in developing and validating in vitro tests to replace the use of animals in ocular irritancy testing.

Corneal stromal wound healing in refractive surgery: the role of myofibroblasts

While laser and incisional refractive surgery offer the promise to correct visual refractive errors permanently and predictably, variability and complications continue to hinder wide-spread acceptance. To explain variations, recent studies have focused on the role of corneal wound healing in modulating refractive outcomes. As our understanding of the corneal response to refractive surgery broadens, it has become apparent that the response of one cell, the corneal stromal keratocyte, plays a pivotal role in defining the results of refractive surgery. Studies reviewed herein demonstrate that injury-induced activation and transformation of keratocytes to myofibroblasts control the deposition and organization of extracellular matrix in corneal wounds. Myofibroblasts establish an interconnected meshwork of cells and extracellular matrix that deposits new matrix and contracts wounds using a novel and unexpected "shoe-string-like" mechanism. Transformation of keratocytes to myofibroblasts is induced in culture by transforming growth factor beta (TGFbeta) and blocked in vivo by antibodies to TGFbeta. Overall, myofibroblast appearance in corneal wounds is associated with wound contraction and regression following incisional keratotomy and the development of "haze" or increased scattered light following laser photorefractive keratectomy (PRK). By contrast, absence of myofibroblasts is associated with continued widening of wound gape and progressive corneal flattening after incisional procedures. Based on these studies, we have arrived at the inescapable conclusion that a better understanding of the cellular and molecular biology of this one cell is required if refractive surgery is ever to achieve predictable and safe refractive results.

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.

Real-time confocal microscopic observations on human corneal nerves and wound healing after excimer laser photorefractive keratectomy

PURPOSE

Corneal wound healing after excimer laser photorefractive keratectomy (PRK) passes through a series of characteristic stages which have earlier been defined by means of histological, histochemical, and biochemical approaches. We investigated the potential of confocal microscopy to verify morphological changes in human corneas in vivo after PRK.

METHODS

Ten corneas of eight patients that had earlier undergone PRK were examined at different postoperative time points (7 days-34 months). One of the PRK patients was examined sequentially three times. Three additional corneas, which had earlier undergone corneal grafting surgery and then were subjected to excimer laser photoastigmatic keratectomy (PARK), were studied as well. Seven healthy untreated corneas served as controls to define the normal morphology of human cornea. A tandem scanning confocal microscope (TSCM) was used to generate real-time images of the corneas on an S-VHS videotape. The images were either digitized and further processed or the individual video frames were produced with a video printer.

RESULTS

Seven days post-PRK in vivo confocal microscopy revealed the presence of morphologically immature surface epithelial cells. Delicate nerves, activated keratocytes and deposition of extracellular light-reflecting scar tissue were perceived. The epithelium appeared normal one month post-PRK. Ongoing activation of the anterior stromal keratocytes along with extracellular scar tissue were detected. We also observed increasing numbers of regenerating subepithelial nerve leashes with somewhat twisted pattern. Highly reflective, presumably activated keratocytes were no longer detected 6-7 months post-PRK. Hypercellularity with scar tissue could still be found up to 30 months post-PRK. Only one cornea examined 34 months post-PRK showed normal keratocyte morphology and recovery of the anterior stroma. However, the morphology of subepithelial nerves was still somewhat abnormal. The two corneal grafts examined 11 or 32 months post-PARK exhibited a normal-appearing epithelium but considerable stromal hypercellularity and extracellular scar deposition. The subepithelial nerves were poorly regenerated in one eye and fairly well detectable in the other. The third graft examined 15 months post-PARK revealed the presence of enlarged surface epithelial cells and dense stromal scarring but no nerves.

CONCLUSION

TSCM clinically confirms the earlier histological data on healing of excimer laser wounds. It offers a distinct improvement in the assessment of excimer laser-treated corneas, as it enables cellular details and nerves to be perceived in vivo. In addition the thickness of the stromal scar can be be measured for e.g. planning of phototherapeutic keratectomy.

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.

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.

Confocal microscopy of corneal penetration by tarantula hairs

In vivo identification of foreign bodies in the cornea may be impossible if the size and/or location precludes visualization by slit lamp biomicroscopy, which has an upper limit of magnification of 50x. These limitations became obvious when we attempted to identify the offending material in the inflamed eye of a patient who complained of foreign body sensation after contact with a pet tarantula. As a model of this clinical situation, we used a newly developed tandem scanning confocal microscope to observe and to photograph tarantula hairs as they penetrated the corneal stroma and endothelium and entered the anterior chamber in rabbit eyes. We found that, experimentally, the hairs penetrated the ocular tissues apparently without inciting inflammation or causing fibrosis. The instrument we used--a prototype with a Nipkow disk from Noran, Inc. (Middleton, Wis.) and a 25/0.8 na glycerin immersion lens (Plan-Neofluor, Zeiss)--provides magnifications of 100-500x, real-time viewing in vivo, optical sectioning, contrast control, high resolution, processing through image analysis systems, and video and hard copy output. We believe that confocal microscopy offers a new approach to the identification and localization of foreign bodies in the anterior segment, as well as to the visualization and diagnosis of ocular diseases, including bacterial, fungal, and other parasitic invasions, in the human eye.

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.

Applications of high-speed confocal imaging techniques in operative dentistry

All confocal scanning optical microscopes are suitable for making high-resolution images of many structures in teeth under near normal conditions. If the microscope can operate at high speed, then the number of applications widens considerably. The high-frame speed of the tandem scanning reflected light microscope (TSM) enables real-time examination of teeth in vivo, especially when the microscope is configured with a stabilising objective, featuring internal focusing elements. Experimental procedures examined microscopically on extracted teeth can include the cutting of the hard tissues, observation of fluid flow in dentine, the application of adhesives, and the fracturing of adhesive interfaces under load. Undertaking experiments where time is an important function has improved our knowledge of many of the materials/substrate interactions involved in dental operative procedures. Storing images on media other than video tape can be expensive, but reductions in the cost of computer memory is making digitisation and storage of images in real-time more widely available.

The relation between contact lens oxygen transmissibility and binding of Pseudomonas aeruginosa to the cornea after overnight wear

PURPOSE

To assess adverse effects of contact lens-induced hypoxia on the rabbit cornea in vivo and determine the relation between binding of Pseudomonas aeruginosa and oxygen transmissibility for rigid and hydrogel lenses.

METHODS

Six rigid lenses with Dk/Ltotal values between 0 and 97 x 10(-9) (cm/second) (ml O2/ml mmHg) and four hydrogel lenses (Dk/Ltotal 9, 20, 39, 51) were tested. All lenses had 14.0-mm diameters and a thickness (parallel) of 0.12 or 0.15 mm. Tear lactate dehydrogenase activity and tandem scanning confocal microscopy determinations were performed after the lens was worn for 24 hours. Binding of P. aeruginosa then was separately determined by the colony-forming unit method. Scanning electron microscopy was used to confirm in vivo tandem scanning confocal microscopy findings.

RESULTS

Lens oxygen transmissibility determines binding of P. aeruginosa to the cornea after the lens is worn for 24 hours; epithelial damage produced by lenses of lower Dk/Ltotal appears to be the dominant biologic factor for P. aeruginosa binding and not lens rigidity.

CONCLUSIONS

These results suggest that the risk of P. aeruginosa keratitis developing with overnight wear will be enhanced significantly for contact lenses with Dk/Ltotal values less than 50 x 10(-9) (cm/second) (ml O2/ml mmHg) (human equivalent oxygen percentage < or = 15%), and this risk will increase with further decreases in oxygen transmissibility. Because no hydrogel lenses approved by the Food and Drug Administration are available with oxygen transmission at this level, patients should be made aware of the increased risk of infectious keratitis associated with the overnight wear of current extended wear hydrogel lenses. Results of this study also demonstrate that quantitative clinical tandem scanning confocal microscopy imaging and tear lactate dehydrogenase activity measurements can provide prospective, noninvasive methods for assessing the ongoing interaction between contact lens and cornea in vivo.

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.

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.

Quantitative analysis of stress fiber orientation during corneal wound contraction

Previous studies of actin and actin-binding proteins in corneal myofibroblasts suggest the development of a contractile apparatus composed, in part, of F-actin micro-filament bundles, i.e. stress fibers. To better understand the mechanics of wound contraction and the relationship between microfilament bundles and wound closure, we have analyzed the spatial and temporal organization of stress fibers during the process of corneal wound healing. Rabbit corneas (26 eyes) received 6 mm full-thickness, central incisions and were studied at various times for F-actin organization using en bloc (whole cornea) staining with FITC-phalloidin, as well as conventional histological techniques. 3-D datasets (z-series of 40 en face optical sections, 1 micron steps) were collected using the Biorad MRC-600 laser scanning confocal microscope at various regions within the wound. At 7 days, 3-D analysis showed randomly oriented, interconnected F-actin filament bundles (stress fibers). Between 7 and 28 days, stress fibers appeared to organize gradually into planes parallel to the wound surface, with a large population achieving a final orientation nearly parallel to the long axis of the wound. Using Fourier Transform analysis techniques, an orientation index (OI) was calculated to quantitate global fiber orientation at each time point. Analysis of variance demonstrated a significant change (P &lt; 0.001) in overall stress fiber orientation from a random distribution at day 7 to an alignment more parallel to the lateral wound borders at day 28. Overall, these data suggest that stress fibers undergo temporal changes in spatial organization that correlate with wound closure, and that wound closure does not involve the development of previously described contractile or tractional forces aligned directly across the wound.

In vivo confocal microscopy in clinical dental research: an initial appraisal

Until recently, the in vivo microscopic investigation of intraoral tissues at high resolution has been virtually impossible. Confocal microscopy enables high-resolution imaging to be achieved below semitransparent surfaces in intact living specimens, but this may still be impractical for intraoral applications because of the need to stabilize the sample. The development of a steadying objective (x 240 overall mag.) which is held against the sample surface and is focused by moving internal elements, avoids the need for fine adjustment of the living sample under the microscope to achieve a change of focus. It is therefore more comfortable and also reduces the problems of movement due to the pulse. The objective was used with a tandem scanning microscope, with images recorded via a SIT video camera. Using this system internal tooth structure (e.g. enamel prisms/adhesive restoration interfaces) and the lining cells of the gingival crevice through to the junctional epithelium may be examined. It is also possible to image the oral mucous membrane, focusing to the capillary loops in the basal layers, where streaming red blood cells can be seen. Access is limited to the anterior regions as far back as the premolar teeth. Applications could include caries research, soft and hard tissue responses to biomaterials (e.g. implants), wound healing and monitoring the effect of periodontal treatment regimens. This new technique offers numerous exciting opportunities for the microscopic investigation of many clinical operative procedures in vivo, allowing the response of the tissues to be non-destructively monitored, over time, at high resolution.