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Biomedical subjects

J P Bergmanson

Publications and source records attributed to J P Bergmanson.

At least 19 recordsLinked to original sources
PubMed2005

A novel sensor array for field based ocular ultraviolet radiation measurements.

The intensification of terrestrial solar ultraviolet radiation (UVR) due to the diminution of the ozone layer has promoted a variety of research into establishing the impact of this elevated potential dose of UVR on biological tissues. Certain anterior ocular tissues have been found to be susceptible to damage by incident UVR and potentially blinding diseases such as pterygium are thought to be a direct result of absorbed UVR at the nasal limbus. There is a need for more accurate quantification and localisation of incident UVR at the anterior ocular surface. A novel solar blind photodiode sensor array system has been designed, constructed and tested for this purpose. Initial measurements to quantify the irradiance across the anterior ocular surface within the latitudes known as the 'pterygium belt' provide us with a set of core data for different head orientations and tilt angles and indicate the accuracy and stability of the system.

Equipment Design↗
PubMed2001

A descriptive and quantitative study of the keratocytes of the corneal stroma of albino rabbits using transmission electron microscopy.

The present morphometric study was designed to assess the dimensions and shape of keratocytes and their nuclei by transmission electron microscopy, and to assess these features in relation to the stromal lamellae. Corneas from 10 albino rabbits were fixed in 2% glutaraldehyde in cacodylate buffer (pH 7.4, 300 mOsm/kg) and embedded in Spurr's epoxy resin. Both transverse and coronal thin sections through the corneal stroma were prepared. The stromal lamellae had an average thickness of 2.45+/-1.15 microm. The average cell thickness of the keratocytes was 1.34+/-0.46 microm (range 0.49-4.76 microm), with the apparent cell thickness being related to the average anterior-posterior thickness of the adjacent lamellae (r = 0.424, P = 0.001)). The relative length and thickness of the cell nucleus, in transverse section, was measured to be 0.65+/-0.13 and 0.76+/-0.10 of the cell body section respectively. As assessed by planimetry, the area of the keratocyte cell body viewed in coronal section was 292+/-118 microm2, with a nucleus-to-cytoplasm ratio of 0.437+/-0.295. The electron micrographs confirmed the presence of gap junctions between keratocyte cell processes, and the occasional presence of centrioles in the cells. Some keratocyte processes were observed to extend from one face of the lamellae to the other, suggesting anterior-to-posterior cell communication. These studies indicate that the keratocyte cell thickness is influenced by the physical pressure exerted by adjacent stromal lamellae. The cell nucleus, while a dominant feature in transverse section, has a normal size in relation to the cell cytoplasm when viewed in coronal section.

Albinism↗
PubMed2001

Quantification of the ultraviolet radiation (UVR) field in the human eye in vivo using novel instrumentation and the potential benefits of UVR blocking hydrogel contact lens.

BACKGROUND/AIMS: Certain degenerative eye conditions occur predominantly nasally, at the limbal region, and are associated with solar ultraviolet radiation (UVR) induced damage. The relative contribution to the in vivo ocular flux of (a) the reflection of UVR incident on the skin of the nose onto the nasal limbus, and (b) the focusing of UVR incident on the temporal side of the cornea onto the nasal limbus were examined. METHODS: A novel photodiode sensor array was used to measure the UVR field across the eye. In addition, a novel spectrometer set-up was used to measure the spectrum of radiation refracted across the cornea. The efficacy of UVR blocking hydrogel contact lenses in filtering incident UVR was assessed in vivo. RESULTS: Qualitative and quantitative data indicated an increase nasally of UVR. Photodiode readings showed a net UVR increase from the temporal to the nasal side. Transmission curves showed that most UVR incident on the limbal region is either absorbed by, or transmitted through, the ocular tissues. This radiation is filtered by UVR blocking soft contact lens. CONCLUSIONS: An increased UVR flux on the nasal side of the eye, due to reflection off the nasal skin, was identified in vivo. Any UVR passing through the cornea is either absorbed by the conjunctiva and/or transmitted through it onto the sclera where it is absorbed. UVR blocking hydrogel contact lenses can eliminate these sources of UVR.

Contact Lenses, Hydrophilic↗
PubMed2001

Proliferation rate of rabbit corneal epithelium during overnight rigid contact lens wear.

PURPOSE: To examine cell proliferation of the normal corneal epithelium and during extended rigid gas-permeable (RGP) lens wear. METHODS: Twenty-three New Zealand White rabbits were fitted unilaterally with either a low oxygen transmissible (Dk/t) or hyper-Dk/t RGP lens, with the other eye serving as a control. The rabbits were injected with 5-bromo-2-deoxyuridine (BrdU) 24-hours later and killed at three time points: 1, 3, and 7 days after injection. Corneas were processed for immunocytochemistry, and sequential digital images were taken from the superior limbus to the central epithelium with an epifluorescence microscope. The total number of BrdU-labeled cell pairs was quantified. RESULTS: The limbus in normal corneas was significantly less populated with BrdU-labeled cells than the central and peripheral epithelium (P < 0.05). The peripheral epithelium adjacent to the limbus was marked by a peak of labeled cells (P < 0.05). Both types of RGP lenses produced an increase in BrdU labeling in the limbus and a dramatic decrease in the central epithelium (80% for low Dk/t, 37% for hyper Dk/t). At day 3 and 7 after BrdU injection, the low-Dk/t lens continued to show decreased BrdU labeling centrally, whereas the limbus remained increased. Hyper-Dk/t lens wear however, showed persistent limbal elevation but equivalent numbers of BrdU-labeled cells centrally at days 3 and 7, compared with control corneas. Keratocytes unexpectedly showed BrdU labeling during RGP lens wear. CONCLUSIONS: Limbus, peripheral, and central epithelium were characterized by different proliferation rates in the normal rabbit cornea. RGP lens wear significantly altered the homeostatic proliferation pattern of the epithelium with the low-Dk/t lens having the most dramatic effect. RGP contact lens wear appears to stimulate proliferation of keratocytes.

Animals↗
PubMed1999

The acinar and ductal organisation of the tarsal accessory lacrimal gland of Wolfring in rabbit eyelid.

The purpose of this study was to objectively assess the tarsal accessory lacrimal gland of Wolfring and its excretory duct by transmission electron microscopy (TEM). The upper eyelid of 6 female grey rabbits (2 kg) was fixed in the fully extended configuration with buffered glutaraldehyde. At the tarsal/orbital portion of the palpebral conjunctiva, a series of prominent acinar glands were located by both light microscopy and TEM. Cells within the acini were characterised by apical tight junctions and desmosomal connections as well as abundant intra-cytoplasmic osmophillic (secretory) granules. The apical surfaces were profusely decorated with microvilli-like extensions. In the vicinity of the acini, and traversing over several millimetres of adjacent sub-epithelial parenchyma and epithelium, was an extensive system of duct-like spaces lined with secretory cells decorated with microvilli. These ducts run a tortuous course within the palpebral conjunctival epithelium leading to crypt-like termination's along the eyelid inner surface. The tarsal accessory lacrimal gland of Wolfring thus has an acinar structure similar to the main lacrimal glands, and its ducts are lined by secretory cells along the entire tortuous course towards the palpebral conjunctival surface, where the ducts emerge at multiple points at the tarsal/orbital portion of the surface.

Animals↗
PubMed1999

A return to primitive practice? Radial keratotomy revisited.

Recently, a refractive surgeon was quoted in the national and professional press as proposing that radial keratotomy (RK) is to be preferred over laser procedures, such as photorefractive keratectomy (PRK) and laser assisted in situ keratomileusis (LASIK). The rationale for this public recommendation was that the RK procedure achieves better visual results and fewer complications than the laser procedures. Peer reviewed literature on these refractive procedures was surveyed to establish the validity of such a statement and it was found that current data do not support the notion that RK results in better visual outcomes than PRK and LASIK The true incidence of complications is difficult to establish. However, when the post procedure chronic effects are compared between RK, PRK and LA SIK, it becomes apparent that the post-RK patient pays the highest price, by a large margin, in visual quality impairment and corneal health. Although the visual acuity outcomes for low to moderate myopes, when corrected by any of the three refractive procedures considered here, are not dramatically different, we concluded that RK is not the preferred methodology because of its associated chronic visual and corneal health complications.

Editorial↗
PubMed1999

Fuchs' endothelial dystrophy: a fresh look at an aging disease.

The increasing number or corneal and intraocular surgeries performed together with longer life expectancy, elevates the risk for developing symptomatic Fuchs' endothelial dystrophy (FED). This article reviews the current understanding of FED, and, in addition, a case of early FED is presented clinically and histopathologically. Two FED corneas from one patient were examined histopathologically using an established histological protocol for light and electron microscopy. FED is an inherited autosomal dominant corneal endothelial disorder with incomplete penetrance that is up to 3 times less likely to develop in men. Treatment options are primarily palliative while surgical intervention routinely involves a penetrating keratoplasty. In this disease process the endothelium produces excessive amounts of basement membrane material of an abnormal composition resulting in the formation of a posterior collagenous layer. Extreme accumulations of this material created mushroom-like formations, guttae, projecting into the anterior chamber. The endothelial cells were extremely thinned over the guttae, to the point where the cells may provide little more than barrier function. Despite a presumably compromised endothelial pump the corneas appeared relatively free of edema clinically and histopathologically. However, some edematous pockets deep in the basal epithelial layer were present suggesting that epithelial involvement occurs at an early stage in the disease. An early diagnosis of FED will help patients and surgeons to better elect optimal surgical timing and procedures. The current trend is to intervene surgically before the patient reaches the painful end-stage. Interestingly, in the case examined, the endothelium presumably provided only a barrier function over large areas with an apparently reduced contribution from the endothelial fluid pump and yet the corneas remained relatively clear. Future research may confirm that decompensation occurs only when complete endothelial coverage is lost. If the endothelial barrier function is more important to corneal transparency than the endothelial pump function in FED, then the relative combination of these two functions in the normal cornea should also be reassessed.

Aged↗
PubMed1998

Keratocytes: no more the quiet cells.

BACKGROUND: In the past, the keratocytes of the adult cornea have been characterized as quiescent cells populating the stroma. Recent research and the introduction of laser refractive procedures have forced us to reassess this notion. METHODS: By reviewing recent, pertinent papers, an attempt was made to give an overview of the new information the scientific community is learning about keratocytes. This overview assesses the heightened interest in the keratocytes, while maintaining a clinical perspective. Where applicable, this information was tied in with our own laboratory observations. RESULTS: It is becoming increasingly clear that keratocytes may play a vital role in regulating the stromal constituents, while also providing structural stability in maintaining the interlamellar organization and, thus, promote corneal transparency. Keratocytes form a communicating network of cells linked in a anterior-posterior fashion, as well as laterally. This ability to communicate appears instrumental in triggering and orchestrating the corneal response in wound healing. External corneal injury, such as epithelial debridement and excimer laser exposure, can cause profound anterior keratocyte loss. These cells are replaced by aggressive stromal cells, which may play an important role in the formation of scar tissue and corneal haze. CONCLUSION: Keratocytes play an important role in both the healthy and the injured cornea. It appears that the improved outcomes of laser refractive procedures will--to a large extent--depend on our ability to maintain keratocyte health, while also controlling the negative effects of cells replacing injured or dead keratocytes.

Animals↗
PubMed1997

Shrinkage and distortion of the rabbit corneal endothelial cell mosaic caused by a high osmolality glutaraldehyde-formaldehyde fixative compared to glutaraldehyde.

The purpose of this study was to quantitatively compare cell dimensions and cell layer organization of the corneal endothelium after chemical fixation. Rabbit corneas (9-10 weeks of age) were prepared immediately postmortem for transmission electron microscopy (TEM) and scanning electron microscopy (SEM) using either a widely used high osmolality fixative (glutaraldehyde-formaldehyde, after Karnovsky; 1% formaldehyde, 2.5% glutaraldehyde, 0.1 M cacodylate, pH 7.6, 850 mOsm/kg) or a glutaraldehyde fixative (2% glutaraldehyde in 80 mM cacodylate, pH 7.4, 330 mOsm/kg). With the glutaraldehyde-formaldehyde fixative, TEM revealed gross shrinkage (up to 40%) and distortion of the cytoplasm and organelles, while the regions of the cell-cell junctions were not attenuated but included dilated extracellular space. With the glutaraldehyde fixative, TEM also revealed shrinkage but the cytoplasm was less compact than with the high osmolality fixative. The overall cell shrinkage and relative accentuation of the cell-cell borders was confirmed by SEM, which also revealed that the 11 to 20% area shrinkage was also related to the number of cell sides.

Animals↗
PubMed1997

Ultraviolet radiation revisited.

PURPOSE AND METHODS: It is likely that we currently receive a greater lifetime exposure to ultraviolet radiation (UVR) than earlier generations due to increased UVR reaching the earth's surface, our longer life expectancy, and increased activities in UV intense environments. This elevated UVR exposure is likely to lead to a higher incidence of acute and chronic ocular and skin radiation trauma. We reviewed the evidence in the current literature supporting these assertions as well as reports of preventive strategies for blocking UVR. RESULTS: Hawaii is the most UV-intense location on earth as it has the lowest ozone thickness values ever recorded outside the Antarctic zone. It is anticipated that the overall ozone depletion will continue into the next millennium. Significant evidence suggests a correlation between UVR exposure and conjunctival pterygium, photokeratitis, climatic droplet keratopathy and cataracts. The incidence of skin cancer is also on the rise as a result of the increased amount of UVR reaching the earth secondary to the thinning ozone. CONCLUSIONS: There are compelling reasons to counsel our patients on the adverse effects of UVR and to offer them the various options available for UV protection. Sunglasses and UV blocking ophthalmic lenses traditionally have been the most commonly selected forms of UVR protection. The UV blocking hydrogel contact lens, a recent addition to our armamentarium, is a means of blocking UVR.

Animals↗
PubMed1995

The significance of ultraviolet radiation for eye diseases. A review with comments on the efficacy of UV-blocking contact lenses.

Acute and cumulative ultraviolet radiation (UVR) exposure has been proposed as an important causative factor in the development of a whole spectrum of eye diseases. The present review examines the scientific evidence for and against such an association, with special emphasis on recent additions to the literature. The sun is the main UVR source on earth, and it is beyond scientific doubt that the cornea can be harmed by both acute and cumulative ambient exposures. There is also powerful epidemiological support for an association between chronic UVR exposure and the formation of cataracts and pterygia. The evidence in support of UVR linkage to pinguecula, ocular neoplasms and retinal changes is weaker--in part because there are fewer studies reported in the literature. It is concluded that UVR-blocking hydrogel contact lenses and spectacles are two equally effective preventive measures in minimizing unnecessary suffering and health costs, especially for people who spend a significant time outdoors and for those who live in more UV intense environments. UVR-blocking contact lenses and spectacles must not, however, be substitutes in situations that require UVR-blocking safety goggles.

Contact Lenses↗
PubMed1995

Clinical assessment of ocular response to a multipurpose contact lens care solution.

The issue of possible adverse effects of contact lens care solutions on ocular health has been raised in the literature. Possible effects of a multipurpose contact lens care solution (Bausch & Lomb ReNu) on eight measures of ocular function were evaluated relative to the effects of physiological saline (Bausch & Lomb Sensitive Eyes). In a randomized, two-treatment, crossover design, all subjects were treated with each of the two solutions on successive weeks. In 73 subjects, comprised of contact lens and non-lens wearers, tear break-up time was measured using the keratometer mire and fluorescein techniques. Measures of autonomic function were vertical palpebral aperture size, amplitude of accommodation, intraocular pressure, pupil size, conjunctival injection, and pupil reactivity. The results indicated that this multipurpose solution provoked no adverse ocular response as determined by the tear break-up time and autonomic functions, and the multipurpose solution was clinically equivalent to physiological saline. These results apply to both contact lens wearers and non-lens wearers. Additional findings speak of the unreliability of the fluorescein method for measuring tear break-up time.

Accommodation, Ocular↗
PubMed1993

A masked quantitative cytologic study of the safety of a multipurpose contact lens solution applied to the in vivo rabbit eye.

The purpose of this study was to challenge the cornea in vivo with a lens care solution (ReNu Multi-Purpose Solution, Bausch & Lomb) formulated with polyaminopropyl biguanide at a higher than standard concentration of 1.0 ppm (1.0 x 10(-6) percent) rather than the marketed 0.5 ppm (0.5 x 10(-6) percent) and to evaluate any cytotoxic epithelial response. Test solutions included the modified formulation of Bausch & Lomb ReNu Multi-Purpose Solution (poloxamine, EDTA, borate buffer, and polyaminopropyl biguanide) and Bausch & Lomb Hypo-Clear unpreserved, isotonic saline. A dose of 50 microL of each solution was administered to the superior limbus of 10 pigmented rabbits free of anterior segment disease. Neither the unpreserved saline solution nor the more highly concentrated multipurpose solution produced significant toxic effects on the corneal epithelial cells and compared favorably with previously reported incidences of desquamating cells in the normal corneal epithelium.

Animals↗
PubMed1992

Histopathological analysis of corneal endothelial polymegethism.

The corneal endothelium from six humans (three contact lens wearers and three non-contact lens wearers) was examined. Scanning electron microscopy confirmed endothelial polymegethism. Observations with the transmission electron microscope showed that an oblique reorientation of the lateral walls of the endothelial cells had occurred in the contact-lens-wearing group of corneas. The endothelium of the contact lens wearers also showed some inter- and intracellular edema but were otherwise of a healthy appearance containing normal organelles. The oblique reorientation of the lateral wall of the endothelial cell allows for the possibility that a cell with a large anterior surface area may have a small posterior surface area or vice versa. Thus, polymegethous cells may not vary in cell volume. This hypothetical alternative to current theories of contact lens-induced polymegethism should be explored in future research.

Adult↗
PubMed1992

Explanation.

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Basement Membrane↗
PubMed1990

Corneal damage in photokeratitis--why is it so painful?

The primate cornea was examined ultrastructurally subsequent to ultraviolet radiation (UVR) (300 nm) exposures of 0.08 and 0.225 J/cm2. The lower exposure caused significant, but incomplete, destruction of the epithelium and mild edema of the posterior stroma. The higher exposure resulted in complete destruction of the epithelium, significant stromal swelling, and some decomposition of endothelial cells. Widespread intracellular edema of the endothelium was also noted with the higher exposure. The ultrastructural examination subsequent to these UVR exposures also helps to explain why UV-induced keratitis is so painful. The 0.08 J/cm2 exposure left the epithelial and subepithelial-stromal nerve plexuses intact, whereas the 0.225 J/cm2 exposure destroyed the epithelial axons but spared the subepithelial ones. These results suggest that the pain associated with UV keratitis results from the combined effect of epithelial cell loss and sparing of the subepithelial axons.

Animals↗