Search

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. [ABSTRACT FROM AUTHOR]

Hydrogel (HEMA) contact lenses of increased thickness were worn by owl monkeys (Aotus tivergatus) under open and closed eye conditions to study ultrastructurally the corneal epithelial response to increased stress. The 0.07 mm thick lens with a calculated Dk/L of 4.2-2.2 caused an epithelial thinning without oedema. This thinning was due to a loss of superficial cells and a flattening of the remaining ones. Factors in the mechanism of epithelial thinning without oedema may include anoxia, trauma, lid pressure, and lens weight. The 0.4 mm thick lens offers negligible gas transmission in the closed eye, and after 48 hours much of the epithelium was stripped, while oedema and degenerative cytoplasmic changes were prominent in areas of surviving cells. In such areas the thickness of the epithelium was reduced to one or two layers of cells. The basement membrane was in all experiments unharmed by hydrogel contact lens wear. The epithelial innervation was maintained in all corneas except those of the closed eye, and finding correlates well with the good corneal touch threshold in soft contact lens wearers. [ABSTRACT FROM PUBLISHER]

One lens each from 2 separate patients suffering from pseudoexfoliation and one lens from a normal eye were examined ultrastructurally. The normal lens capsule was internally lamellar in places and externally of a somewhat reduced electron density but otherwise of a homogeneous appearance and free of inclusions. Observations on the abnormal lenses revealed an electron dense and mainly granular but sometimes fibrillar material along the surface of the peripheral one-third of the capsule. Material of similar ultrastructural appearance was also found deeper in the capsule and in the immediately underlying epithelium. Since the capsule close to the pole of the lens was completely free of these abnormal inclusions and the underlying epithelium also lacked this material, it is concluded that the lens epithelium is a source of the surface debris in pseudoexfoliation. These findings therefore support previous authors who proposed a lenticular involvement in this disease. The present study does, however, not rule out the possibility of a uveal contribution of abnormal material but disputes its exclusive involvement in this disease, as has previously been postulated. Build-up of exfoliated material close to the capsular surface caused an apparent peeling of the lens capsule. It is therefore concluded that the anomalous lenses suffered from a true exfoliative process that may be more correctly termed 'exfoliation of the lens capsule.' [ABSTRACT FROM PUBLISHER]

Three adult rhesus monkeys were subjected to 2 and 24 hours of polymethylmethacrylate (PMMA) contact lens wear. The induced corneal changes were examined with the electron microscope. Mild epithelial oedema as well as early degenerative cell changes was present already after 2 hours' wear. Rigid lens wear for 24 hours produced more severe oedema and cell alterations together with premature cell loss and ultimately, in areas of lens bearing, corneal denuding. Only the monkeys wearing contact lenses for 24 hours had significant stromal swelling, which was primarily evident in the posterior region, while the anterior limiting lamina remained unaffected. The stromal swelling was patchy and mainly around keratocytes and between lamellae, while fluid within the lamellae was evident only occasionally in posterior stroma. Changes among keratocytes were evident, especially posteriorly, where reaction was frequently severe. Endothelial reaction was restricted to a limited fluid uptake in the 24-hour-wear experiment. In addition there was in these monkeys an apparent loosening of the endothelial adhesion to the posterior limiting lamina. It is concluded that the oedematous epithelium undergoes cell shrinkage and flattening, which is compensated for by an uptake of fluid. The uptake of fluid maintains the overall normal thickness of the epithelium. The conclusion is supported by other studies, where the normal thickness of oedematous epithelium has been shown by pachometry. The results in the present study further suggest that stromal oedema in the contact lens wearer is a result of a relative loss of endothelial function, leading to a swelling that moves in a posterior to anterior direction. [ABSTRACT FROM PUBLISHER]

The feasibility of the American Optical Non-Contact Tonometer as an instrument for tonography was assessed. It was found that after 20 measurements in quick succession, there was a statistically insignificant change in IOP. Multiple intraocular pressure (IOP) readings with this instrument are helpful in determining an abnormally high IOP from an aberrant recording. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the anterior chamber angle in keratoconus eyes by use of the Visante™ OCT and Orbscan™ II., Methods: Anterior chamber angle was measured with the Visante™ OCT and Orbscan™ II in 52 subjects, 26 KC subjects and 26 age and control subjects., Results: When comparing the nasal and temporal angles obtained with the two techniques no correlation was found (R(2) always below 0.01) in either the control subjects or in the KC subjects. Despite this, there was an overall statistically significant difference in mean anterior chamber angles (p<0.001) between Visante™ OCT and Orbscan™ II. There was no statistical difference (p>0.05) between nasal and temporal anterior chamber angles when comparing controls and KC subjects with either of the two instruments. In general, the Visante™ OCT gave a smaller estimate of the anterior chamber angle., Conclusion: The values from the Visante™ OCT and Orbscan™ II cannot be interchanged since the difference in measurement of the anterior chamber angle was significantly different between the two instruments., (Copyright © 2015 British Contact Lens Association. All rights reserved.)

A fibre optic spectrophotometer front-end system for measuring corneas to overcome shortcomings associated with existing instruments was tested. The system allowed prompt measurement postmortem, minimizing beam pathlength to reduce the effects of scatter and unwanted refraction and eliminated optical interfaces and cuvette media. Rabbit corneas were excised immediately postmortem and placed on a detecting fibre optic coupled to an Ocean Optics spectrophotometer and illuminated by a deuterium-halogen source. The compact instrument with its small beam size allowed tissue profiling at test points across the corneal surface and efficient interchange for comparison of different tissues. This simplified system operation allowed rapid tissue altering to study induced changes on transmittance. The corneal transmittance data showed a consistent sharp cut-off at 320 nm in the ultraviolet radiation (UVR) spectrum, which decayed rapidly from postmortem swelling. Inter- and intra-corneal consistency was demonstrated by comparing data from different regions of the same cornea and those from opposite eyes. Changes to the spectra, particularly in the UVB below 300 nm, were evident when the corneal epithelium was removed, indicating that this layer is not the only corneal UVR filter. The new system reduced much of the variability associated with previous methods, as it rapidly measured corneal transmittance postmortem. Data are in broad agreement with published transmittance curves. The removal of the corneal epithelium revealed a substantial stromal contribution to the overall corneal UVR absorption, suggesting that corneas with pathologically or iatrogenically thinned stromas are less effective UVR blockers.

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.

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.

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.

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.

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., (Copyright 1999 Academic Press.)

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.

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.

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.

The purpose of this study was to examine the impact of a low osmolality glutaraldehyde fixative and a high osmolality glutaraldehyde-formaldehyde fixative on the structural organization of a tissue that could be exposed to low and high osmolality environments. The corneas of freshwater trout were prepared for transmission and scanning electron microscopy using either a fixative of 2% glutaraldehyde in 60 mM cacodylate buffer (pH 7.8, 260 mOsm/l) or a fixative prepared by adding 2.5% glutaraldehyde to a solution of 1% formaldehyde and buffering the solution with 0.1 M cacodylate (pH 7.6, 850 mOsm/l; Karnovsky-type fixative). The corneal epithelial cell layer thickness was greater after glutaraldehyde compared to glutaraldehyde-formaldehyde fixation (67 vs 55 microm), as was the thickness of the superficial cells (5.1 vs 3.4 microm) and basal cells (43 vs 38 microm). The intermediate (wing) cells of the epithelium were, however, less thick after glutaraldehyde fixation (15 vs 18 microm). The width of the squamous, intermediate and basal cells was greater following glutaraldehyde fixation with the effect being greatest in the superficial layers and insignificant at the level of the basal cells. The results show that chemical fixatives with extremes of osmolality cannot only produce different cell sizes in a tissue but also determine the overall organization of the cells in a positional-dependent fashion.

Background: To determine the corticosteroid effect on the activity and repopulation of keratocytes after photorefractive keratectomy (PRK)., Methods: A 193-nm excimer laser (VISX Twenty/Twenty) created a central ablation depth of 22 microns (diameter:5 nm) on 22 corneas of 16 albino rabbits. Two ablated eyes were examined 6 hours following PRK. Twelve eyes received no postoperative corticosteroids and eight were treated with topical fluoromethalone for 3 months. Corneas were examined 1, 3, 6, and 12 months after PRK by immunofluorescence and transmission electron microscopy., Results: Corticosteroids reduced haze (p=0.02), but all corneas (treated or untreated) cleared 6 months after PRK. Keratocytes were absent from the anterior 100 microns of the stroma 6 hours after PRK. However, the number and activity of keratocytes were significantly greater in this area in untreated corneas at 1 month and then gradually decreased. By 6 and 12 months, the number of keratocytes approached controls. Treated corneas had fewer keratocytes than either controls or untreated eyes (p<0.01) and by 3 months, a subepithelial acellular zone of 30 to 50 microns thickness appeared and persisted until at last 12 months after PRK., Conclusions: Corticosteroids have a transient effect in reducing haze and seem to inhibit keratocyte movement, leading to an acellular subepithelial region beneath the ablated area.

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.

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.

Background: In patients who are free of pathology, automatic refractions have shown close agreement with the subjective refractions. Clinical experience indicated that the normally strong relationship between objective and subjective refraction is significantly weakened as a result of radial keratotomy., Methods: Seventy-two patients were refracted before and after surgery, objectively with a Humphrey Model #510 autorefractor and subjectively using a binocular refraction procedure without cycloplegia. All patients were free of ocular disease and had preoperative myopia ranging from -1.00 to -9.00 diopters as determined by the subjective spherical equivalent., Results: The results indicated that the preoperative difference between the mean spherical automatic and subjective refractions was a clinically acceptable 0.25 diopter. However, postoperatively, there was a statistically significant difference of 1.25 D with the automatic refractor determining more myopic refractions. Subsequent analysis revealed that the age of the patient had a direct bearing on this finding with patients less than 40 years of age showing more minus in the automatic refraction than patients 40 years and older., Conclusions: The postoperative discrepancy between the two refractions may be explained by induced optical aberrations and may contribute towards the visual fluctuations experienced by radial keratotomy patients. It is postulated that the inconsistency in refractive determination is due to optical distortion since the age dependence of this effect may be related to the reduction of pupil size that occurs with aging. In the radial keratotomy patient, the practitioner is faced with a more complex and uncertain refraction that may vary according to refractive procedures used and other factors such as pupil size.

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.

The morphology of the filtration angle and pathway of aqueous outflow was studied in 10 pigmented rabbits using light and electron microscopic techniques. The following conclusions were arrived at: Numerous pectinate ligaments were found to cross the rabbit filtration angle. However, large spaces between these ligaments allows aqueous access to the peripheral portion of the angle and then to the trabeculum. The drainage of aqueous filtered through the meshwork is served by a plexus of 1 to 4 channels, which contain giant vacuoles along their internal and external walls. A single layer of endothelial cells was found covering all meridians of the entire trabeculum from the termination of the cornea to the filtration angle recess. This layer, here termed the trabecular endothelial layer, is a continuation of the corneal endothelium, and it is accompanied by the posterior limiting lamina (Descemet's membrane) for its full length. The aqueous passes through the trabecular endothelial layer by an intracellular route that possibly requires energy. The presence of the trabecular endothelial layer in the rabbit may explain the variation that is known to exist between human and rabbit in responses to pharmaceutical agents. The physiology of the rabbit trabecular endothelial layer needs to be investigated to determine the suitability of this species as an animal model for the human glaucomatous conditions caused by the presence of such a layer.

Complications from contact lens wear are seldom examined histopathologically. Understanding of the epithelial reactions in response to contact lens wear would help early diagnosis and direct treatment action. Therefore, this study examines the histopathology of abrasion, epithelial edema, epithelial thinning and superficial punctate staining. Important factors in the etiology of these conditions are various definable lens and tear characteristics as well as mechanical effects from the lens. Observations on corneal innervation that have not been previously reported are used to help explain the reduced corneal sensitivity in the contact lens wearer. It is concluded that the breakdown of the epithelial surface prevents the epithelium from fulfilling its fluid and microorganism barrier functions. In addition, disturbance of the normal epithelial structure interferes with its ability to withstand further trauma and to convey the injury to the brain via the neural pathways.

Two F40CW fluorescent lamps mounted in an EYS-2404 fixture and 300 nm, 5 nm waveband UV radiation were used to expose pigmented rabbit eyes. The results of the exposures to the eye were evaluated with the biomicroscope, ophthalmoscope, light microscope and electron microscope. The following conclusions were reached: The adverse ocular responses to fluorescent radiation exposure were due to long-duration, broadband radiation. These reactions were more generalized for fluorescent exposures when the cornea and lens are compared to UV exposures. The differences between the levels of threshold exposure needed to cause damage for the fluorescent source and UV radiation were attributed to exposure duration and the rate of delivery of the radiation. Corneal and lenticular damage was mild when compared with UV 300 nm exposures, and the threshold occurred after 8 h to 12 h of exposure. The effect of the radiation was to interfere with the normal functions of the cell while changes to the inert materials in the tissues was secondary to injury to the cell. The damage was mild in the corneal epithelium, somewhat more severe in the corneal endothelium, but minimal in the corneal stroma. Early retinal changes were found after 8 h of exposure to the fluorescent source. These induced changes were evident in the neural retina as spaces and were assumed to represent oedema. The retinal oedema was initially found only in the receptor cell, outer nuclear and nerve fibre layers. Many vacuoles or spaces were located in the junctional area between the ganglion cell and nerve fibre layers while smaller spacing occurred also within the nerve fibre layer. Twelve h of exposure to the fluorescent source produced a further increase in the oedema in the retina. The outer segments of the receptor cells appear to disintegrate and significant open spaces are evident among the inner and outer segments of the receptors. The inner plexiform layer shows an increased number of spaces within and among the neural elements, and the mitochondria appeared to be undergoing changes. The 20-h and longer exposure induced severe changes affecting all layers of the retina. These changes include massive retinal oedema with degenerative signs in all retinal neurons. A sympathetic reaction of the unexposed, contralateral eye occurred as the result of the damage to the exposed eye. Minimal sympathetic responses to the cornea and the lens began at exposure durations at or above 12 h, while the retina showed the sympathetic reaction beginning at 8 h.(ABSTRACT TRUNCATED AT 400 WORDS)

Premature onset of presbyopia may be an early sign of cataractous lenticular changes. For many years ultraviolet radiation (UVR) has been suspected as a major factor in the degradation of the crystalline lens. Controlled laboratory studies have demonstrated that UVR does cause opacities that closely resemble those naturally occurring in the aging process. Is it true that environmental UVR is also the prime contributor in the deleterious lenticular changes that may begin with premature presbyopia, as has been postulated? This review examines the evidence supporting this and other suggested causes of early presbyopia, including genetics, nutrition, toxins, and environmental temperature. Of all factors reported to affect the onset of presbyopia, UVR has the most scientific support, but further research is necessary to conclusively establish this link.

The comparative corneal epithelial effects of rigid gas permeable and soft contact lenses are reported in the present preliminary study using two bush baby monkeys (Galago senegalensis). Both types of lenses produced early cell death among the surface squamous cells while internally the epithelium and its nerve fibers remained normal. Sporadically small abnormal groups of cells involving two to three of the surface layers were observed in both the hard and soft lens wearing corneas. It was concluded that this represented superficial punctate keratitis (SPK). Small superficial intracellular epithelial cysts with membranous contents were infrequently noted in the gas permeable lens wearing cornea and it is suggested here that they were mild forms or precursors of those seen clinically in human corneas. Since the gas permeable lens met the corneal oxygen requirement it is postulated that the traumatic effect of the rigidity of the lens caused the cystic formation to occur. The relative hypoxia induced by the soft contact lens resulted in a mild superficial epithelial edema.

Recent studies have indicated that sensory terminals can be recognized by the presence of an accumulation of mitochondria. By inducing changes in uveal ophthalmic nerve fibers it was shown that an accumulation of mitochondria also occurs in autonomic terminals. Although an aggregation of mitochondria may occur in sensory terminals, it is not a feature unique to them. The ophthalmic fibers in the iris and the ciliary body appeared to terminate as free nerve endings without characteristics peculiar to them.

The optometric educator needs insurance against malpractice suits. A survey was made of the policies available at twelve schools and colleges of optometry in the United States. The object of this survey was to compare the various protections offered by the optometric institutions and also to inform the educators of what is available to them. It was found that coverage and premiums vary considerably between the institutions. At only one of the twelve schools and colleges of optometry responding to this survey were faculty members required to pay for their own policies, but to avoid undue risk, two other colleges highly recommended that their faculty purchase their own coverage. Implications of the low number of claims brought against optometric teaching facilities and other factors are discussed in light of the "malpractice insurance crisis."

Recently, it has been shown that UV keratitis is more serious than previously thought because it is not limited to the corneal epithelium but also involves the stroma and the endothelium. It is, therefore, very important to avoid ultraviolet radiation (UVR) damage, and the purpose of the present study was to examine the ability of a UV absorbing hydrogel lens to filter such wavelengths. Ultrastructural observations of rabbit corneas showed that a regular soft (Vistamarc normal) contact lens offered no protection, and since wearing one adds stress to the cornea it seems possible that the cornea may be more vulnerable to UVR trauma. A UV absorbing soft contact lens (Vistakon UV-BLOC) provided complete protection to all corneal layers. Subepithelial nerve fibres in the traumatized corneas were mostly of normal morphology and may explain why UV keratitis is a very painful experience. It was concluded that a UV absorbing soft contact lenses with acceptable clinical performance may be prescribed on a routine basis.

Rigid contact lenses were fitted on primates to study the subsequent corneal epithelial injury. This trauma was compared to corneal abrasions produced by a blunt object. The traumatic abrasion caused a rupture of the basal cells, which were identified as the most vulnerable part of the corneal epithelium for such an injury. The internal plasmalemma of the basal cell remained adherent to the epithelial basement membrane due to the strong hemidesmosomes along the cell membrane. Contact lenses were capable of producing similar injuries which did not penetrate the basement membrane and therefore did not involve the anterior limiting lamina (Bowman's membrane). We concluded that contact lenses produce a self-limiting trauma and even a severe case of contact lens overwear, although it causes deep corneal abrasions, seldom results in permanent scar formation.