A quantitative analysis of sutural contributions to variability in back vertex distance and transmittance in rabbit lenses as a function of development, growth, and age

In vivo SS-OCT imaging of crystalline lens sutures

We demonstrate in vivo three-dimensional (3-D) visualization of crystalline lens sutures in healthy eyes using swept source optical coherence tomography (SS-OCT). Volumetric data sets of the crystalline lenses were acquired and processed to obtain enhanced contrast projection images and to extract suture patterns in both anterior and posterior lens. The results presented different types of the sutures including Y-sutures, simple and complex star sutures. Age-related changes in suture arrangement were characterized quantitatively. Crystalline lens suture imaging with SS-OCT might be a useful tool in fundamental studies on development and ageing of human lens.

A novel terminal web-like structure in cortical lens fibers: architecture and functional assessment

This study describes a novel cytoskeletal array in fiber cells of the ocular lens of the rat and shows its relationship to the classical terminal web of other epithelial tissues. Naive adult Sprague-Dawley rats (n = 28) were utilized. F-actin, fodrin, myosin IIA, and CP49 distribution was assessed in anterior and posterior polar sections. For functional analysis, lenses were cultured with or without cytochalasin-D for 3 hr, then processed for confocal microscopy or assessed by laser scan analysis along sutures. Phalloidin labeling demonstrated a dense mesh of F-actin adjacent to posterior sutural domains to a subcapsular depth of 400 μm. Anterior polar sections revealed a comparable actin structure adjacent to anterior suture branches however, it was not developed in superficial fibers. Fodrin and myosin were localized within the web-like actin apparatus. The data was used to construct a model showing that the cytoskeletal array is located within the blunt, variable-width fiber ends that abut at sutures such that the "terminal web" flanks the suture on either side. Treatment with cytochalasin-D resulted in partial disassembly of the "terminal web" and perturbed cellular organization. Laser scan analysis revealed that cytochalasin-D treated lenses had significantly greater focal variability than control lenses (P = 0.020). We conclude that cortical fibers of rat lenses contain a bipolar structure that is structurally and compositionally analogous to classical terminal webs. The results indicate that the lens "terminal web" functions to stabilize lens fiber ends at sutures thus minimizing structural disorder, which in turn, promotes the establishment and maintenance of lens transparency.

Structural function of MIP/aquaporin 0 in the eye lens; genetic defects lead to congenital inherited cataracts

Aquaporin 0 (AQP0) was originally characterized as a membrane intrinsic protein, specifically expressed in the lens fibers of the ocular lens and designated MIP, for major intrinsic protein of the lens. Once the gene was cloned, an internal repeat was identified, encoding for the amino acids Asp-Pro-Ala, the NPA repeat. Shortly, the MIP gene family was emerging, with members being characterized in mammals, insects, and plants. Once Peter Agre's laboratory developed a functional assay for water channels, the MIP family became the aquaporin family and MIP became known as aquaporin 0. Besides functioning as a water channel, aquaporin 0 also plays a structural role, being required for maintaining the transparency and optical accommodation of the ocular lens. Mutations in the AQP0 gene in human and mice result in genetic cataracts; deletion of the MIP/AQP0 gene in mice results in lack of suture formation required for maintenance of the lens fiber architecture, resulting in perturbed accommodation and focus properties of the ocular lens. Crystallography studies support the notion of the double function of aquaporin 0 as a water channel (open configuration) or adhesion molecule (closed configuration) in the ocular lens fibers. The functions of MIP/AQP0, both as a water channel and an adhesive molecule in the lens fibers, contribute to the narrow intercellular space of the lens fibers that is required for lens transparency and accommodation.

Age-related compaction of lens fibers affects the structure and optical properties of rabbit lenses

BACKGROUND

The goal of this investigation was to correlate particular age-related structural changes (compaction) to the amount of scatter in rabbit lenses and to determine if significant fiber compaction occurred in the nuclear and inner cortical regions.

METHODS

New Zealand White rabbits at 16-20 months old (adult; n = 10) and at 3.5-4 years old (aged; n = 10) were utilized for this study. Immediately after euthanising, scatter was assessed in fresh lenses by low power helium-neon laser scan analysis. Scatter data was analyzed both for whole lenses and regionally, to facilitate correlation with morphometric data. After functional analysis, lenses were fixed and processed for scanning electron microcopy (SEM; right eyes) and light microscopy (LM; left eyes). Morphometric analysis of SEM images was utilized to evaluate compaction of nuclear fibers. Similarly, measurements from LM images were used to assess compaction of inner cortical fibers.

RESULTS

Scatter was significantly greater in aged lenses as compared to adult lenses in all regions analyzed, however the difference in the mean was slightly more pronounced in the inner cortical region. The anterior and posterior elliptical angles at 1 mm (inner fetal nucleus) were significantly decreased in aged vs. adult lenses (anterior, p = 0.040; posterior, p = 0.036). However, the average elliptical angles at 2.5 mm (outer fetal nucleus) were not significantly different in adult and aged lenses since all lenses examined had comparable angles to inner fetal fibers of aged lenses, i.e. they were all compacted. In cortical fibers, measures of average cross-sectional fiber area were significantly different at diameters of both 6 and 7 mm as a function of age (p = 0.011 and p = 0.005, respectively). Accordingly, the estimated fiber volume was significantly decreased in aged as compared to adult lenses at both 6 mm diameter (p = 0.016) and 7 mm diameter (p = 0.010).

CONCLUSION

Morphometric data indicates that inner cortical fibers undergo a greater degree of age-related compaction than nuclear fibers. Increased scatter appears to be only tentatively correlated with regions of fiber compaction, suggesting that it is simply one of an array of factors that contribute to the overall decreased transparency in aged rabbit lenses.

Development and adult morphology of the eye lens in the zebrafish

The zebrafish has become an important vertebrate model organism to study the development of the visual system. Mutagenesis projects have resulted in the identification of hundreds of eye mutants. Analysis of the phenotypes of these mutants relies on in depth knowledge of the embryogenesis in wild-type animals. While the morphological events leading to the formation of the retina and its connections to the central nervous system have been described in great detail, the characterization of the development of the eye lens is still incomplete. In the present study, we provide a morphological description of embryonic and larval lens development as well as adult lens morphology in the zebrafish. Our analyses show that, in contrast to other vertebrate species, the zebrafish lens delaminates from the surface ectoderm as a solid cluster of cells. Detachment of the prospective lens from the surface ectoderm is facilitated by apoptosis. Primary fibre cell elongation occurs in a circular fashion resulting in an embryonic lens nucleus with concentric shells of fibres. After formation of a monolayer of lens epithelial cells, differentiation and elongation of secondary lens fibres result in a final lens morphology similar to that of other vertebrate species. As in other vertebrates, secondary fibre cell differentiation includes the programmed degradation of nuclei, the interconnection of adjacent fibres via protrusions at the fibre cells' edges and the establishment of gap junctions between lens fibre cells. The very close spacing of the nuclei of the differentiating secondary fibres in a narrow zone close to the equatorial epithelium, however, suggests that secondary fibre cell differentiation deviates from that described for mammalian or avian lenses. In summary, while there are similarities in the development and final morphology of the zebrafish lens with mammalian and avian lenses, there are also significant differences, suggesting caution when extrapolating findings on the zebrafish to, for example, human lens development or function.

Assessment of Airways with Three-dimensional Quantitative Thin-Section CT: In Vitro and in Vivo Validation

PURPOSE

To prospectively validate the ability of customized three-dimensional (3D) software to enable bronchial tree skeletonization, orthogonal reconstruction of the main bronchial axis, and measurement of cross-sectional wall area (WA) and lumen area (LA) of any visible bronchus on thin-section computed tomographic (CT) images.

MATERIALS AND METHODS

Institutional review board approval and patient agreement and informed consent were obtained. Software was validated in a phantom that consisted of seven tubes and an excised human lung obtained and used according to institutional guidelines. In vivo validation was performed with multi-detector row CT in six healthy subjects (mean age, 47 years; range, 20-55 years). Intra- and interobserver agreement and reproducibility over time for bronchial tree skeletonization were evaluated with Bland-Altman analysis. Concordance in identifying bronchial generation was assessed with the kappa statistic. WA and LA obtained with the manual method were compared with WA and LA obtained with validated software by means of the Wilcoxon test and Bland-Altman analysis.

RESULTS

WA and LA measurements in the phantom were reproducible over multiple sessions (P > .90) and were not significantly different from WA and LA assessed with the manual method (P > .62). WA and LA measurements in the excised lung and the subjects were not different from measurements obtained with the manual method (intraclass correlation coefficient > 0.99). All lobar bronchi and 80.8% of third generation bronchi, 72.5% of fourth generation bronchi, and 37.7% of fifth generation bronchi were identified in vivo. Intra- and interobserver agreement and reproducibility over time for airway skeletonization and concordance in identifying bronchial generation were good to excellent (intraclass correlation coefficient > 0.98, kappa > 0.54, respectively).

CONCLUSION

This method enables accurate and reproducible measurement of WA and LA on reformatted CT sections perpendicular to the main axis of bronchi visible on thin-section CT scans.

Desferrioxamine and zinc-desferrioxamine reduce lens oxidative damage

Our purpose was to investigate the quality and morphology of cultured bovine lenses after exposure to hyperbaric oxygen (HBO) in the presence or absence of desferrioxamine (DFO) or zinc-desferrioxamine (Zn-DFO). Intact bovine lenses were cultured and exposed to HBO of 100% oxygen at 2.5 ATA for 120 min. One hundred and fifty lenses were included in the present study. Lenses were divided into study groups of 25 lenses each: (1a) HBO-exposed lenses; (1b) control lenses extracted from the contralateral eyes of group 1a and exposed to normal room air. (2a) HBO-exposed lenses treated with DFO; (2b) control lenses extracted from the contralateral eyes of group 2a exposed to normal room air in the presence of DFO (3a) HBO-exposed lenses treated with Zn-DFO; (3b) control lenses extracted from the contralateral eyes of group 3a, exposed to normal room air in the presence of Zn-DFO. Lens optical quality and structural changes were assessed. Oxygen toxicity to lenses was demonstrated by decreased light transmission, increase in focal length variability and a decrease in morphological integrity. Light intensity measurements showed a distinct pattern in control lenses. A different pattern was noticed for hyperbaric oxygen-exposed lenses. Focal length variability values were stable in control lenses and increased significantly in oxygen-exposed lenses. Structural damage to lenses was demonstrated by the appearance of bubbles between lens' fibers possibly demonstrating failure of lens tissue to cope with oxygen load. All measured parameters showed that both Zn-DFO and DFO attenuated the oxidative damage. The effect of DFO was small whereas Zn-DFO demonstrated a significantly stronger effect. Treatment of hyperbaric oxygen-exposed lenses with DFO only marginally reduced the oxidative damage. Treatment with Zn-DFO was superior in reducing the oxidative damage to lenses. These results indicate a possible role for Zn-DFO in the prevention of cataracts.

First safety study of femtosecond laser photodisruption in animal lenses: Tissue morphology and cataractogenesis

PURPOSE

To determine through safety studies the tissue effects and potential cataractogenesis of laser modification of the crystalline lens (photophaco modulation).

SETTING

Laser Zentrum Hannover, Hannover, Germany.

METHODS

Six fresh porcine lenses and 6 living rabbit eyes (with the contralateral eye as a control) were radiated with a low-energy femtosecond laser to induce lens fiber disruption. After 3 months, the rabbit eyes were extracted and tested for light scatter and lens function and fixed for histology and ultrastructure.

RESULTS

After laser treatment, all lenses displayed a tightly packed array of intralenticular bubbles, which resolved with time. In the porcine eyes, the bubbles coalesced unless spacing of 9 mum or greater was applied at an energy of 2 microJ. In the rabbit eyes, an energy of 1 microJ and spacing of 10 microm was chosen for transcorneal delivery, showing minimum bubble coalescence. After 3 months, the rabbit lenses showed good transparency, with only 1 rabbit having cataract formation unrelated to the laser. Laser scanning studies show essentially identical values for the back focal length and sharpness of focus (variability of back focal length). Ultrastructurally, the rabbit eyes showed a 0.5 microm electron dense border layer with adjacent normal lens architecture.

CONCLUSIONS

Femtosecond laser photodisruption of the ocular lens yields a self-limited lesion with bubbles that resolve with time. In living animal eyes, no cataract formation was found with no loss of lens function or induced light scatter after 3 months. These results suggest that use of a low-energy femtosecond laser might be safe when modifying the lens for presbyopia correction.

Fibre cell organization in crystalline lenses

This review qualitatively and quantitatively compares the gross shape and size of lenses from different species as a function of their fibre cell organization. Grossly, all vertebrate lenses are asymmetrical, oblate spheroids with size and spheroidicity that varies considerably between species. Correlative LM and SEM analysis of the basic structural element of lenses, the fibre cell, shows that the average equatorial fibre width and thickness is relatively constant between most species. This indicates that inter-species differences in lens size is primarily a function of fibre number. Comparable analysis demonstrates that lens spheroidicity is due at least in part, to differences in the average anterior and posterior fibre end segment thickness in relation to that at the equator. In addition, the above analysis, supplemented by 3D-CAD reconstructions, illustrates how lifelong lens growth produces crescent fibres, that become arranged in age-related, concentric growth shells overlaid in slightly imprecise register. The reason for the non-exact registering of growth shells is that, while the vast majority of fibres are hexagonal in cross-section, a very small minority are pentagonal in cross-section and of inconstant width and thickness. Hexagonal and pentagonal fibres are required because the increase in the circumference of successive growth shells is frequently less than the widths of hexagonal fibres. Thus, lens growth is likely accomplished by a combination of the addition of successive growth shells containing more fibres, as well as by the addition of growth shells containing equal numbers of fibres that are incrementally wider as a function of radial location. Finally, SEM analysis, supplemented by 3D-CAD reconstructions, highlights the fact that the end-to-end arrangement of fibres within growth shells, the suture patterns, is not identical in all vertebrate lenses. This is important because lens optical quality is directly related to lens suture type and a negative influence of sutures on lens optical quality increases with age and as a result of some ocular surgeries (vitrectomy and trabeculectomy). These facts suggest that future research efforts should be directed at determining the factor or factors that influence or direct the differences in fibre shape, size and organization in branched and unbranched suture lenses.