Analysis of the healthy rabbit lens surface using MAC Mode atomic force microscopy

In this investigation healthy rabbit crystalline lenses were characterized by atomic force microscopy (AFM). The lenses were cut in slices with thickness with 1mm and thus, put after cortex distinct regions of nucleus and cortex for AFM examination. AFM analysis were carried out using a PicoSPM I operating in Mac Mode. We obtained topographic images of rabbit lenses and a quantitative analysis of the width and height of fibers for nucleus and cortex regions. The longitudinal section analysis of fibers in the nucleus region indicated structures with an average width of 200nm and average height of 200nm. The intershells distance was determined as 4microm. Fiber cell cross-section dimensions, longitudinal and transverse widths, could be estimated in these regions from the AFM images. Structures with average widths as small as 1.0microm are observed in the nucleus; the intershell distance is 4.0microm. In cortical regions, hexagonal structures with average longitudinal and transverse widths of 5.0mum and 3.0mum, respectively, were identified. Three-dimensional images of tissue sections with resolution on a nanometer scale were obtained. The potential of AFM analysis for characterizing healthy and pathologic lens tissues is discussed.

Predicted light scattering from particles observed in human age-related nuclear cataracts using mie scattering theory

PURPOSE

To employ Mie scattering theory to predict the light-scattering from micrometer-sized particles surrounded by lipid shells, called multilamellar bodies (MLBs), reported in human age-related nuclear cataracts.

METHODS

Mie scattering theory is applicable to randomly distributed spherical and globular particles separated by distances much greater than the wavelength of incident light. With an assumed refractive index of 1.40 for nuclear cytoplasm, particle refractive indices from 1.33 to 1.58 were used to calculate scattering efficiencies for particle radii 0.05 to 3 microm and incident light with wavelengths (in vacuo) of 400, 550, and 700 nm.

RESULTS

Surface plots of scattering efficiency versus particle radius and refractive index were calculated for coated spherical particles. Pronounced peaks and valleys identified combinations of particle parameters that produce high and low scattering efficiencies. Small particles (<0.3 microm radius) had low scattering efficiency over a wide range of particle refractive indices. Particles with radii 0.6 to 3 microm and refractive indices 0.08 to 0.10 greater (or less) than the surrounding cytoplasm had very high scattering efficiencies. This size range corresponds well to MLBs in cataractous nuclei (average MLB radius, 1.4 microm) and, at an estimated 4000 particles/mm(3) of tissue, up to 18% of the incident light was scattered primarily within a 20 degrees forward cone.

CONCLUSIONS

The calculated size of spherical particles that scatter efficiently was close to the observed dimensions of MLBs in cataractous nuclei. Particle refractive indices only 0.02 units different from the surrounding cytoplasm scatter a significant amount of light. These results suggest that the MLBs observed in human age-related nuclear cataracts may be major sources of forward light scattering that reduces contrast of fine details, particularly under dim light.

Identification of retained nucleus fragment in the posterior chamber using ultrasound biomicroscopy

PURPOSE

To describe the use of ultrasound biomicroscopy (UBM) to image retained nuclear fragments posterior to the iris plane after uncomplicated phacoemulsification with posterior chamber intraocular lens (PCIOL) implantation in two patients.

DESIGN

Interventional case report.

METHODS

Two patients presented with an iris elevation after uncomplicated phacoemulsification and lens implantation.

RESULTS

Visual acuity was 20/20 in the first patient and 20/30 in the second. There was no anterior chamber inflammation in either eye. UBM revealed a small, retained nuclear fragment between the iris pigment epithelium and the anterior lens capsule, causing localized anterior iris displacement in both patients. The PCIOL was within the capsular bag, and the iris root and ciliary body were normal in both patients.

CONCLUSION

UBM can demonstrate retained lens fragments within the posterior chamber.

Distribution, spherical structure and predicted Mie scattering of multilamellar bodies in human age-related nuclear cataracts

PURPOSE

To characterize multilamellar bodies (MLBs), determine their distribution along the optic axis and predict their potential Mie scattering within human age-related nuclear cataracts. Previous studies restricted to the equatorial plane have shown that MLBs are rare spherical objects that are 1-4 microm in diameter and covered by multiple layers of thin lipid-rich membranes.

METHODS

Eight human aged transparent lenses were obtained from eye bank donors and eight human age-related nuclear cataracts were obtained immediately after extracapsular extraction. Each sample was Vibratome sectioned fresh into 200 microm thick sections that were fixed and embedded for light or electron microscopy. Light micrograph montages of the optic axis containing the juvenile, fetal and embryonic nuclei were examined. Mie scattering for random coated spherical particles was calculated based on assumed and measured particle parameters.

RESULTS

Cells along the optic axis of the cataract contained approximately 7.5 times more MLBs as similar regions of the aged transparent lens, although these MLBs occurred with extremely low frequency. Cells of the aged transparent lens contained 1.3 MLBs mm(-2), while those of the cataract contained 9.6 MLBs mm(-2), which are equivalent to calculated densities of 5.6 x 10(2) and 4.1 x 10(3)mm(-3), respectively. While some MLBs were located within the cytoplasm near cell membranes, others were found away from membranes. The MLBs are distinct from circular profiles resulting from finger-like projections between adjacent cells. MLBs displayed varying geometries and cytoplasmic textures, although predominately spherical with interiors similar to adjacent fiber cell cytoplasm. These results are in agreement with previous theoretical analysis of light scattering from human lenses and with previous morphological studies examining the equatorial plane of the lens. Potential Mie scattering of spherical particles with the average properties of the observed MLBs and assumed refractive index properties was calculated to be forward scattering of as much as 20% of the incident light.

CONCLUSIONS

The observed low frequency and absence of clustering of MLBs in the equatorial plane and along the optic axis suggests that MLBs are most likely uniformly distributed throughout the embryonic, fetal and juvenile nuclei of age-related cataracts. Because of their size, distribution, textured cytoplasm and calculated Mie scattering, MLBs probably cause local fluctuations in refractive index in human lens nuclei and, therefore, are potential sources of low-angle, forward light scattering that could impair image formation.

[Morphological and functional characteristics of the lens histamine-containing structures at the early stages of chemical irritation of the eye]

The purpose of the present study was to determine, using the methods of light, fluorescence microscopy and cytospectrofluorometry, the morpho-functional changes in histaminergic structures of the lens as influenced by extrinsic chemical irritation of the eye (exposure to ether vapors). The experiments were conducted on 74 outbred male albino rats. Extremely fast simultaneous changes (demonstrated in all lens structures already 3 minutes after an irritation) were found in histamine content of the lens cells. According to the results of luminescence analysis, maximal increase in histamine content (by 53.3%) took place in the area of lens nucleus. In the cytoplasm of lens epitheliocytes, histamine content was increased by 22%, while in the cytoplasm of equatorial epithelial cells it was increased by 36.1%, and in the nuclei of central epithelial cells--by 26.4%. The data obtained suggests an existence of diffuse neurotransmission in the lens, that is not associated with neurons.

[A study of human lens epithelial cells by light and electron microscopy and by immunohistochemistry in different types of cataracts]

PURPOSE

To evaluate the characteristics of cataract changes in lens epithelial cells (LECs), in different types of human cataract.

MATERIAL AND METHODS

Anterior capsules for the study were obtained from patients with different types of cataracts during extracapsular cataract extraction, or phacoemulsification using continuous curvilinear capsulorhexis. LECs attached to the anterior capsules were analyzed for morphological changes by light and electron microscopy, and for cellular characteristics by immunohistochemistry. The reactivity to cytokeratins 5,6,8,17 and 19 (arker for epithelial cells) and to vimentin (arker for mesenchymal cells) was determined.

RESULTS

The consecutive degenerative changes were observed in most of the cells: multilayered cells, nuclei of abnormal diameters and shapes, vacuolation of nuclei and cytoplasm. LECs were immunohistochemically positive for cytokeratin and vimentin, or only for vimentin in all types of cataract. Some of LECs showed morphological and immunohistochemical characteristics of mesenchymal cells.

CONCLUSIONS

Lens epithelial cells show similar degenerative changes in different types of cataract and may have the ability to transdifferentiate into mesenchymal cells.

Analysis of nuclear fiber cell compaction in transparent and cataractous diabetic human lenses by scanning electron microscopy

BACKGROUND

Compaction of human ocular lens fiber cells as a function of both aging and cataractogenesis has been demonstrated previously using scanning electron microscopy. The purpose of this investigation is to quantify morphological differences in the inner nuclear regions of cataractous and non-cataractous human lenses from individuals with diabetes. The hypothesis is that, even in the presence of the osmotic stress caused by diabetes, compaction rather than swelling occurs in the nucleus of diabetic lenses.

METHODS

Transparent and nuclear cataractous lenses from diabetic patients were examined by scanning electron microscopy (SEM). Measurements of the fetal nuclear (FN) elliptical angles (anterior and posterior), embryonic nuclear (EN) anterior-posterior (A-P) axial thickness, and the number of EN fiber cell membrane folds over 20 microns were compared.

RESULTS

Diabetic lenses with nuclear cataract exhibited smaller FN elliptical angles, smaller EN axial thicknesses, and larger numbers of EN compaction folds than their non-cataractous diabetic counterparts.

CONCLUSION

As in non-diabetic lenses, the inner nuclei of cataractous lenses from diabetics were significantly more compacted than those of non-cataractous diabetics. Little difference between diabetic and non-diabetic compaction levels was found, suggesting that diabetes does not affect the degree of compaction. However, consistent with previous proposals, diabetes does appear to accelerate the formation of cataracts that are similar to age-related nuclear cataracts in non-diabetics. We conclude that as scattering increases in the diabetic lens with cataract formation, fiber cell compaction is significant.

Fourier analysis of cytoplasmic texture in nuclear fiber cells from transparent and cataractous human and animal lenses

Comparisons were made of the cytoplasmic textures in electron microscope images of nuclear fiber cells from a variety of human and animal lenses. The goals were to establish the optimal conditions for quantifying the textural features and for relating the extent of roughness with the observed extent of nuclear opacification. Freshly cut Vibratome sections were fixed and processed for thin-section electron microscopy. Normal human donor lenses, human age-related cataracts from surgery, and rat, guinea pig, and canine lenses were analyzed using density linescans, Fourier transforms, and autocorrelation analysis. Normal and control lenses were compared to lenses with varying degrees of scattering including fully opaque nuclear cataract. Images were recorded at 21,000 x, giving structural information in the critical range of 2-300 nm. Human normal and nuclear cataractous lens cytoplasm produce Fourier transforms with relatively high intensity in the range 10-50 nm (equivalent spacing) and relatively low intensity greater than 100 nm. This is consistent with the smooth image appearance, linescans with small fluctuations and autocorrelation functions indicating that the images are nearly homogeneous. Images of the transparent animal lenses were very smooth and produced Fourier transforms that showed less intensity in the range 10-50 nm and less intensity greater than 100 nm compared to the human lenses. Animal lenses with progressively enhanced light scattering showed a strong correlation between increased textural roughness and increased Fourier intensity greater than 100 nm. These analytical image analysis techniques readily documented the wide range of cytoplasmic textural variations in human and animal lenses and cataracts. Consistent comparisons were possible only when well-preserved tissues were examined with high-resolution images. The cytoplasm with the greatest roughness correlated with the greatest light scattering suggests that redistribution and/or loss of cytoplasmic proteins contribute to cataract formation.

Multilamellar bodies as potential scattering particles in human age-related nuclear cataracts

PURPOSE

To characterize within human age-related nuclear cataracts rare spherical objects covered by multiple membranes, termed multilamellar bodies (MLBs).

METHODS

Adult human normal, transparent lenses were obtained from eye bank donors and age-related nuclear cataracts were obtained immediately after extracapsular extraction. Each sample was Vibratome sectioned fresh into 200 microm thick sections that were fixed and embedded for light or electron microscopy. Confocal images were recorded from sections stained with the lipid soluble dye, DiI.

RESULTS

Light micrograph montages of the equatorial plane containing the fetal and embryonic nuclei were examined. Rare, but distinct, circular 1-3 microm diameter objects were observed consistently in the cataracts. These objects did not appear to be components of the complex intercellular interfaces. Serial sections indicated that the objects were spherical, or contained a spherical component. For about 20,000 fiber cell cross-sections in each lens, the frequency of MLBs was 10 times higher in cataracts than in the normal lens nuclei. Although extensive searching with the electron microscope was necessary, the size, circular profile and multiple layers of thin (5 nm) membranes easily identified the MLBs. Interiors of the MLBs displayed variable textures. Confocal images indicated that the coverings were enriched in lipid compared to the adjacent plasma membranes. The calculated density of the MLBs in the cataractous nuclei was about 3800/mm3, which represents a volume fraction of 0.00003.

CONCLUSIONS

Because the MLBs are large compared to the wavelength of light, display interiors with variable staining textures and have lipid-rich coverings, they appear to be ideal candidates for large scattering particles that may contribute to the forward light scattering in nuclear cataracts.

Confocal microscopy of cataracts from animal model systems: relevance to human nuclear cataract

A recent study demonstrated that cytosolic lipid membrane structures, independent of the plasma membrane, preferentially occurred in human cataractous lenses. Animal model systems of cataractogenesis (selenite treated rats: galactose fed rats; buthionine-sulfoxime treated mice; Emory mice) were screened for possible relevant structures using the lipid membrane probe DiI and confocal microscopy. Well delineated plasma membranes of lens fiber cells with independent cytosolic staining structures were only observed in the selenite model system. These cytosolic structures were not observed in aged matched control lenses or within the transparent cortical regions of selenite treated animals with intense nuclear opacification. These results suggested that the morphological changes in DiI staining structures seen in the nucleus of the human cataractous lens were best approximated by those seen in the selenite model system.

Morphology of the normal human lens

PURPOSE

To provide a quantitative, morphologic description of differentiated lens fiber cells in all regions of aged normal human lenses.

METHODS

Transparent normal human lenses (age range, 44 to 71 years) were examined with correlative transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Vibratome sections allowed examination of internal structures, whereas dissected whole lenses revealed surface characteristics. Additionally, image analysis was used to measure cross-sectional areas of fiber cells.

RESULTS

Approximate regional dimensions (percentage of diameter and thickness, respectively) were determined for whole lenses: cortex 16%, 17%; adult nucleus 24%, 21%; juvenile nucleus 12%, 9%; fetal nucleus 45%, 49%; and embryonic nucleus 3%, 4%. Cortical cells were irregularly hexagonal, and the average cross-sectional area measured 24 +/- 9 microns2. Adult nuclear cells were flattened with intricate membranous interdigitations and an area of 7 +/- 2 microns2. Juvenile nuclear cells had an area of 14 +/- 5 microns2. Fetal nuclear cells were rounded with an area of 35 +/- 22 microns2. Embryonic nuclear cells also were rounded and had a variable area of 80 +/- 68 microns2. Fiber cell cytoplasm in all lens regions appeared smooth in texture and homogeneous in staining density.

CONCLUSIONS

Both TEM and SEM are necessary to obtain a complete description of fiber cells. Cross-sections of fibers give new insights into the lamellar organization of the lens, indicating that each region has characteristic cell shapes and sizes. Furthermore, average dimensions were used to demonstrate that the number of cells and approximate growth rates vary significantly between adjacent regions.

Fiber cell morphology and cytoplasmic texture in cataractous and normal human lens nuclei

PURPOSE

The goal of this study was to compare the ultrastructure of the oldest cells in opaque and transparent human lenses.

METHODS

Age-related nuclear cataracts, late-onset diabetic nuclear cataracts and normal aged lenses were examined by transmission electron microscopy. Cross-sectional profiles of fiber cells in the embryonic, fetal and juvenile nuclear regions were obtained to facilitate direct comparisons between lens regions and between sample groups. Image analysis was performed to determine cross-sectional areas of fiber cells in each region.

RESULTS

The average cross-sectional area increased approximately sixfold from the outer to the inner nuclear regions in all lenses measured. In each nuclear region, fiber cells displayed a characteristic size, shape, arrangement and type of interdigitations which were consistently seen in all the lenses examined. Some lenses had more complex interdigitations than others. Gap junctions were identified as pentalamellar structures having 16 nm width and appeared identical throughout the nuclei of both normal and cataractous lenses. The cytoplasm of all lenses was smooth and free of large density variations. However, the cytoplasm of some cataractous lenses appeared more granular in texture than noncataractous lenses. Cellular degeneration, debris or large cellular defects were not seen in the cores of cataractous lens nuclei.

CONCLUSIONS

These results indicate that only minor ultrastructural differences exist between the oldest fiber cells in normal and cataractous lenses, and that the presence of extensive cellular damage and disruptions is not necessary for the generation of nuclear opacities in aged lenses. Our observations suggest that light scattering sufficient for vision impairment may involve structural alterations much smaller than previously proposed.

Nuclear light scattering, disulfide formation and membrane damage in lenses of older guinea pigs treated with hyperbaric oxygen

Nuclear cataract, a major cause of loss of lens transparency in the aging human, has long been thought to be associated with oxidative damage, particularly at the site of the nuclear plasma membrane. However, few animal models have been available to study the mechanism of the opacity. Hyperbaric oxygen (HBO) has been shown to produce increased nuclear light scattering (NLS) and nuclear cataract in lenses of mice and human patients. In the present study, older guinea pigs (Initially 17-18 months of age) were treated with 2.5 atmospheres of 100% O2 for 2-2.5-hr periods, three times per week, for up to 100 times. Examination by slit-lamp biomicroscopy showed that exposure to HBO led to increased NLS in the lenses of the animals after as few as 19 treatments, compared to lenses of age-matched untreated and hyperbaric air-treated controls. The degree of NLS and enlargement of the lens nucleus continued to increase until 65 O2-treatments, and then remained constant until the end of the study. Exposure to O2 for 2.5 instead of 2 hr accelerated the increase in NLS; however, distinct nuclear cataract was not observed in the animals during the period of investigation. A number of morphological changes in the experimental lens nuclei, as analysed by transmission electron microscopy, were similar to those recently reported for human immature nuclear cataracts (Costello, Oliver and Cobo, 1992). O2-induced damage to membranes probably acted as scattering centers and caused the observed increased NLS. A general state of oxidative stress existed in the lens nucleus of the O2-treated animals, prior to the first appearance of increased NLS, as evidenced by increased levels of protein-thiol mixed disulfides and protein disulfide. The levels of mixed disulfides in the experimental nucleus were remarkably high, nearly equal to the normal level of nuclear GSH. The level of GSH in the normal guinea pig lens decreased with age in the nucleus but not in the cortex; at 30 months of age the nuclear level of GSH was only 4% of the cortical value. HBO-induced changes in the lens nucleus included loss of soluble protein, increase in urea-insoluble protein and slight decreases in levels of GSH and ascorbate; however, there was no accumulation of oxidized glutathione. Intermolecular protein disulfide in the experimental nucleus consisted mainly of gamma-crystallin, but crosslinked alpha-, beta- and zeta-crystallins were also present.(ABSTRACT TRUNCATED AT 400 WORDS)

UV-B and early cortical and nuclear changes in the human lens

Experimental studies in mice and rats have shown that UV (B) irradiation leads to specific lens changes, viz. yellowing of the nucleus and a multilayered epithelium in the anterior pole with disrupted cortical fibres underneath. Biomicroscopic and ultrastructural studies on ageing human lenses revealed yellowing of the lens nucleus and locally ruptured membranes and small opacities in the equatorial cortex. No changes in the anterior pole were ever observed. This discrepancy between the human and animal lens, contraindicating UV as an important risk factor for human cataract, is discussed and may be due to several factors: (1) a difference between the high level acute and low level chronic irradiation; (2) species differences: nocturnal animals may be unable to cope with bright light exposure; (3) differences in scavenger and other defense mechanisms between humans and animals.

Morphological study on glucocorticoid-induced cataract in developing chick embryo

Nishigori et al. reported a transient cataract model after administering glucocorticoid to a 15-day-old chick. Biochemically, the mechanism of onset of this cataract was though to be related to damage caused by the formation of oxidative stresses and by a protein-water phase separation. There appear to be no reports on changes in the fine structure. After hydrocortisone succinate sodium was administered to 15-day-old chick embryos, the lenses were removed at 12, 24, 30, 48, 72 and 96 h and put in 4% glutaraldehyde. The specimens were examined by light, transmission and scanning electron microscopy. Twelve to 24 h after administration to chick embryos, lens fibers containing electron-dense cytoplasm began to appear in the bow area of the equator and were still present thereafter. Thirty to 48 h after administration, numerous vacuoles of varying sizes began to appear in the lens in sites corresponding to the opaque region. These vacuoles, ranging from 2 to 8 microns in diameter, were distributed in the intercellular spaces between the lens fibers. The vacuoles had disappeared by 96 h after administration, but during that period, the height of the epithelial cells in the equatorial region and the elongation of the equatorial lens fibers had become irregular. Transient opacity was due to the presence of vacuoles of various sizes, occurring in the intercellular space between the lens fibers around the lens nucleus. Moreover, the effect of glucocorticoid administration was noted in the lens epithelium and the lens fibers in the equatorial region.

[Scanning electron microscopic observation of hydrodissected human lens nucleus]

Using a scanning electron microscope, we studied the surface structure of 5 different central nuclei, isolated by repeated hydrodissection during extracapsular cataract extraction. Aside from the damage induced by surgical maneuvers, the surfaces were very smooth, and there was no major disruption of the lamellar structure of the lens. Our studies have shown that hydrodissection, which allows atraumatic separation of the lens fiber layers, can be used to analyze the lamellar structure of the lens. Some of the evaluated specimens showed a distinct suture line and the lens fibers were approximately at right angles to it. These observations were different from those reported previously.

Morphological changes in human nuclear cataracts of late-onset diabetics

The ultrastructure of human diabetic lens nuclei is described for the first time. Two cataractous lenses from late-onset diabetics were examined using transmission electron microscopy to determine the type and distribution of cellular disruptions. The diabetic lens nuclei were compared to a transparent nucleus from a normal human lens. Cellular damage to the exterior region of the diabetic lens nuclei was extensive, especially at the cortical-nuclear interface. Areas of lens fiber condensation as well as areas of cytoplasmic loss were observed in the outer nucleus. Morphological defects commonly seen in this region included: multilamellar membrane aggregates, voids where cytoplasmic material was lost, deposits in the extracellular spaces, density variations between adjacent fiber cells, and heterogeneously staining globules. The opaque central regions of the nuclei displayed relatively little cell damage, but fiber cells were very irregular in shape and packing. The ultrastructure of inner nuclear fiber cells was comparable to that seen in the normal lens and in age-related nuclear cataracts in non-diabetics. It appears that the effect of hyperglycemia on lens fiber cells is dependent on their age and stage of differentiation.

Ultrastructure of fiber cells and multilamellar inclusions in experimental diabetes

PURPOSE

The goal of this ultrastructural study was to examine fiber cell shape and intercellular junctions during the early stages of fiber cell breakdown and edema in diabetic rabbit lenses.

METHODS

Lens abnormalities were recorded with a slit lamp. Between 6-10 mo after drug treatment, diabetic lenses and untreated control lenses were freshly enucleated and sectioned with a vibrating knife microtome. The thick tissue sections were chemically fixed and processed for thin-section electron microscopy.

RESULTS

Alloxan-induced diabetes in albino rabbits produced clinically apparent cataracts as soon as 1 mo after the animals became hyperglycemic. The cataracts displayed cortical fluid-filled vacuoles in the equatorial region and at the cortex-nucleus interface, white specks scattered throughout the cortex, and posterior subcapsular cataracts. Fiber cells just deeper than the large cortical vacuoles had oval or spindle-shaped cross sections. Multilamellar inclusions, not reported previously for diabetic lenses, were observed at or near the fiber cell interfaces and were composed of concentric or spiral rings of plasma membrane-bound cytoplasmic processes. Undulating membranes were present throughout most of the multilamellar inclusions. Transparent lenses from untreated controls did not have such multilamellar bodies or extensive membrane undulations in cells at the same distance from the lens surface.

CONCLUSIONS

Fiber cells respond to the diabetic insult differently depending on their stage of differentiation and age. The observed changes are consistent with the hypothesis that hyperglycemia accelerates the formation of age-related changes in fiber cells.

The altricial pigeon is born blind with a transient glycogen cataract

The lens nucleus of altricial birds contains a large amount of glycogen. It is not known why glycogen in such concentration does not cause a trace of lens opalescence. Here we report that the altricial pigeon is born with a dense nuclear opacity; this opacity has practically disappeared by 4 weeks of age. Thin-section electron microscopy revealed that the opacity was specifically associated with an enormous number of large glycogen aggregates in nuclear fiber cells. These aggregates of various sizes (up to approximately 5 microns) were composed of smaller individual 35-nm beta glycogen particles. In contrast, glycogen aggregates were not seen in nuclear fiber cells of all transparent older lenses. The glycogen aggregates have gradually dissociated into a homogeneous distribution of individual beta particles in the entire cytoplasm of nuclear fibers which accompanies the development of lens transparency. This study suggests that an extensive accumulation of glycogen aggregates in the lens nucleus is the cause of light scattering and opacification. The transparency of the altricial pigeon lens during normal development is therefore regulated by two different forms of glycogen. Precocial birds such as chick have no lens glycogen, therefore never develop a glycogen cataract and have excellent visual acuity upon hatching.

Selenite nuclear cataractogenesis: a scanning electron microscope study

The sequential changes during selenite nuclear cataractogenesis were examined with a scanning electron microscope (SEM) and correlated with slit lamp observations. A posterior opacity, visible with the slit lamp 1-2 days after injection of sodium selenite, was found to consist of masses of vacuoles in the superficial posterior cortex by SEM. 2-3 days post injection, a biomicroscopic refractile ring around the nucleus was represented by SEM abnormalities suggesting membrane damage and possible loss of cytosol in the perinuclear region. All normal structure in this region was lost by 5 days after injection when the central nucleus had become opaque. SEM also showed evidence for damage in areas which were still clear by slit lamp examination. Changes, characteristic of aging, were found near selenite induced damage in peripheral (younger) fibers.

Cellular architecture in age-related human nuclear cataracts

Age-related or senile human nuclear cataracts were examined using electron microscopy of thin sections prepared from thick vibrating-knife microtome sections of nuclei extracted by extracapsular surgery. The use of extended aldehyde-tannic acid fixation of 80-120-microns thick vibrating-knife microtome sections overcame the difficult problem of preserving the hardened nuclear core of aged lenses. Comparisons were made between a typical nuclear cataract, containing a central opacity and a transparent rim, and a more advanced, or mature, completely opaque nuclear cataract. The typical nuclear cataract contained no obvious cell disruption, cellular debris, or objects that readily could explain the central opacity. The fiber cells had intact uniformly stained cytoplasms with well-defined plasma membrane borders and gap junctions. The transparent rim and the nuclear core appeared similar, except that fiber cells in the nucleus were more condensed with more elaborate intercellular interdigitations. The mature cataract showed various types of cell disruption in the perimeter but not in the core of the nucleus. These disruptions were globules, vacuoles, multilamellar membranes, and clusters of highly undulating membranes. Because these potential scattering centers were not found in the nuclear core, they probably were not the sole cause of the observed opacity. Other potential scattering centers found throughout the mature cataract nucleus included variations in staining density between adjacent cells, enlarged extracellular spaces between undulating membrane pairs, and protein-like deposits in the extracellular space. Similar features, although less pronounced, were present in the typical nuclear cataract. It was concluded that massive cell disruption is not essential to the formation of a central nuclear opacity. Subtle structural changes, especially small fluctuations in protein density between adjacent cells and alterations of the membranes and the extracellular space, probably contribute significantly to the central opacities in human nuclear cataracts.

A comparison of excimer laser (308 nm) ablation of the human lens nucleus in air and saline with a fiber optic delivery system

BACKGROUND

Photoablation with excimer lasers has demonstrated precise tissue cutting and minimal thermal damage. Potential ophthalmic applications of these lasers include remodelling of the corneal surface, glaucoma treatment, and phacoablation. Ablation of human lens with a 308 nm XeCl excimer laser light delivered through a fiber has been demonstrated in preliminary experiments. Intraocular delivery of laser light must be done in a fluid medium to preserve the integrity of ocular structures. However, little information is available on the effect of the fluid media on the ablation process. Therefore, a series of experiments was conducted to determine whether the ablation of human lens nucleus at 308 nm via a fiber differs in air and saline media.

METHODS

Ablation of human lens nuclei (n = 30) was conducted with a XeCI excimer laser (308 nm) coupled to a 600 microns core size fiber. Irradiation was performed at 2.8 mJ/cm2 energy density and 20 Hz. The fiberoptic was brought to contact with the lens nucleus and remained fixed for the duration of irradiation. Variables consisted of the medium (air or saline) and number of pulses delivered (100 to 10,000). Following establishment of the tissue shrinkage ratio, the depth of each crater and the tissue volume removed were measured histologically. The histological features of nucleus ablation in air and in saline were also examined with both light and scanning electron microscopy.

RESULTS

Light microscopy revealed that the average zone of thermal damage adjacent to the crater is thinner in the presence of saline (60 microns, SD = 6 microns) than it is in air (90 microns, SD = 12 microns). In both media, the thickness of the zone of thermal damage is greater at the surface than it is at its base. Following irradiation in air, deep sharpedged craters with smooth walls are formed. Craters formed by irradiation in saline are characterized by reduced depth and irregular walls. For the same number of pulses applied (500, 1000, and 2000), the mean depth of ablation per pulse in air (8.6 to 2.7 microns/pulse) was greater by approximately a factor of two than that in saline (4.10 to 1.30 microns/pulse) at P < .01. However, the mean ablated volume removed per pulse was greater in saline (0.00250 to 0.00150 mm3/pulse) than in air (0.00120 to 0.00080 mm3/pulse), for the same number of pulses (1000, 2000) at P < .01.

CONCLUSIONS

In comparing the data for the same number of pulses applied in air and in saline, it appears that the depth of crater formed by irradiation in air is deeper than that in fluid. The overall volume ablated is greater in fluid than it is in air at 1000 and 2000 pulses. Additionally, the zone of thermal damage is thinner in the presence of saline than it is in air. Smoother crater shapes were observed following irradiation in air than in saline. These results suggest that under this specific experimental setup, the ablation in saline is different from that in air.

Study of the substructure of the Morgagni and Brunescens cataract with the TAO non-coating technique. Part 2: Brunescens cataract

Lens tissue from a Brunescens cataract was prepared for SEM study by prefixation with glutaraldehyde and postfixation with the tannic acid/arginine/OsO4 combination; for TEM study the material was prefixed with glutaraldehyde, postfixed with OsO4/K4Fe(CN)6 and poststained with uranyl acetate/lead citrate. At low magnification, in contrast to the Morgagni cataract, no difference could be seen between the lens fibres in the cortical and nuclear areas. Morphologically, the destruction of the ball and socket system and the development of holes and spherical structures was striking. The latter appeared to have a thin coating and, after fracture, were either empty or showed remnants of material resembling membranes. In sections of the cataractous material, larger vacuoles containing smaller spheres were indistinctly visible.

Ultrastructural observations of typical gap junctions in human foetal lens nucleus

The ultrastructure of gap junctions throughout the human foetal lens was observed. By freeze-fracture analysis, we observed numerous gap junctions in both lens cortex and lens nucleus. Comparison between lens cortex and lens nucleus showed that the gap junctions of lens nucleus are characterized by extreme mosaics of closely apposed P- and E-faces in junctional areas, though no significant difference in the area of gap junctions was observed between lens cortex and lens nucleus. In addition, some morphological variations, such as the smooth domains without particles or pits in junctional areas and the reticulated figures of gap junctions, were observed only in the lens nucleus. We also observed by thin-section electron microscopy that cell membranes of human foetal lens nucleus, as observed in the lens cortex, are mainly composed of continuous lipid bilayer and junctional structures. We concluded that characteristic morphology of lens gap junctions, as observed in the cortex of human foetal lens, is mostly preserved in the human foetal lens nucleus, although some depth-dependent alterations were also observed.

Scanning EM studies of normal human lens fibres and fibres from nuclear cataracts

Normal human lenses obtained from an eye bank, and the central nuclear regions from nuclear sclerotic cataracts, were examined using scanning electron microscopy. Lens fibres were found to possess a varied array of well defined interlocking processes. Fibres from brunescent nuclear cataracts showed complete preservation of membrane architecture in contrast to the extensive membrane disruption that has been seen in cortical cataracts.

[Crystalline lenses of newborn infants in scanning electron microscope. Preliminary report]

Results of examination of 6 transparent infant lenses in a scanning microscope are presented. Discussed is the structure of the termination of the zonula on the lens capsule and the appearance of lenticular fibres in the cortical and nuclear layers.

Square arrays and their role in ridge formation in human lens fibers

Square arrays in human lens fibers were studied with freeze-fracture and thin-section TEM. In superficial fibers a number of patches of square array particles in the P face and pits in the E face are found in the smooth membrane. In the deeper cortex and the nucleus, fiber cells have undulating membranes and many ridges. Numerous patches of the particles (P face) are distributed in the concave regions, and the pits (E face) in the convex areas of the bumpy membrane. In most ridges, patches of the particles occur at regular intervals in the "valley" portion, while the pits are on the "crest" portion of ridges. Also, continuous square arrays having the same "valley" location as the regularly arranged patches are found in areas with extensive ridge patterns. The overlapping of the outer portions of two adjacent square arrays is found on the sides between the "crest" and the "valley" of the ridges. Structurally, square arrays are located in a nonjunctional part of the membrane; in an orthogonal crystalline arrangement; and with a particle size of about 6 nm and center-center spacing about 6.4 nm. They are structurally different from gap junctions found in the lens fibers. Thin-section studies reveal two types of cellular contacts: thin pentalamellar structures (about 12-13 nm in overall thickness) associated with the ridge patterns are believed to be square arrays; thick heptalamellar structures (about 16-17 nm in overall thickness) with a narrow gap in between the two central laminae are believed to be gap junctions. This study strongly suggests that square arrays are specifically involved in ridge formation in human lens fibers.

An improved fixation technique for maintaining the fine structure of the nuclear zone of neonatal mouse lens

The fine structure of the nuclear zone of neonatal mouse lenses can vary considerably according to the fixation used. When normal neonatal mouse lenses are fixed in a commonly used chilled glutaraldehyde solution, the nuclear zone develops a grossly visible opacity, and irregular sized protein granules appear in the subsequent sections. Similar artifacts of aggregated irregular sized protein granules appear when cataractous mouse lens are conventionally processed. These artifacts can be avoided by soaking the lens in 0.15 M reduced glutathione solution for 10-15 min before fixation in a phosphate buffered 2% glutaraldehyde solution (pH 7.4) at 27-35 C. Normal lenses treated in this manner maintain translucency in the nuclear zone throughout the fixation-embedding procedure, and the resulting sections show finely uniform granularity with the cell membrane well preserved. Similarly processed nuclear portions of cataractous lenses of Nakano mice show uniformly aggregated protein granules, measuring about 350A in diameter. The cell membranes in the cataractous zone are also not interrupted.