Scleritis and temporal arteritis. (1/822)

Thirty consecutive patients with severe scleritis or episcleritis were admitted as in-patients to the Medical Ophthalmology Unit and assessed for systemic disease. There were seventeen women and thirteen men. The mean age was 53 with a median of 57 (range 23-83). Eighteen of the patients had scleritis: eleven of these had evidence of connective tissue disease and three of them had temporal arteritis. Twelve patients had episcleritis: six of them had a collagen disease and one of them developed temporal arteritis. This high incidence of temporal arteritis in association with scleritis has not been previously reported. It is important to diagnose and treat overt temporal arteritis early with parenteral steroids so that ischaemic papillopathy can be avoided. A higher incidence of collagen diseases than previously described is reported in episcleritis. It is thought that this is secondary to selection since patients with the usual self-limiting episcleritis are not normally referred for further in-patient investigation. In no patient was more than one significant diagnosis made. There was no significant medical illness in only 11% of patients with scleritis and 33% of patients with episcleritis. The majority of the non-collagen diseases (e.g. hypertension) were not previously recognized. In none of the patients with temporal arteritis was the diagnosis made before admission. It is concluded that full examination and investigation for underlying disease is indicated in both scleritis and severe episcleritis.  (+info)

Structural specializations of the eye in the vizcacha (Lagostomus maximus maximus). (2/822)

Vizcachas (Lagostomus maximus maximus, Chinchillidae) are nocturnal rodents living in burrows in many regions of Argentina, Bolivia, and Chile. We have studied the eye of the vizcacha using several light and electron microscopic procedures, with the purpose of understanding the role of vision in the behavior of this species. Our observations demonstrated an avascular, rod-rich retina, with a specialized region spanning through most of the equator of the eye. In this central band, all neural retinal layers exhibited a high cell density, whereas the photoreceptor layer was characterized by the presence of very long rods. In addition, the central region was associated with a distinct pigmentation pattern, including scarce granulation of the pigment epithelium, low pigmentation of the choroid, and the selective attachment of suprachoroidal cells to the inner scleral surface. These central modifications probably form the structural basis of a reflecting tapetum. The eye of the vizcacha received both long and short ciliary vessels, and a specialized cilio-sclero-choroidal vascular network appeared at the equatorial region. Our findings suggest that the equatorial region of the eye of the vizcacha could be a highly sensitive light detector related to foraging behaviors during crepuscular or nocturnal hours.  (+info)

Regulation of the mechanical properties of tree shrew sclera by the visual environment. (3/822)

Experiments in several species have shown that the axial elongation rate of the developing eye can be increased or decreased by manipulating the visual environment, indicating that a visually guided emmetropization mechanism controls the enlargement of the vertebrate eye during postnatal development. Previous studies in tree shrews (Tupaia glis belangeri) suggest that regulation of the mechanical properties of the sclera may be an important part of the mechanism that controls the axial elongation rate in this mammal. To learn whether the mechanical properties of the sclera change when the axial elongation rate is increased or decreased under visual control, uniaxial mechanical tests were performed on 3-mm wide strips of tree shrew sclera. The creep rate was measured under 1, 3, and 5 g of tension, maintained for 30 min at each level. The modulus of elasticity was calculated from the elastic extension that occurred when the force was increased from 0 to 1 g, 1 to 3 g, and 3 to 5 g. Both were measured in the sclera of both eyes from animals exposed to four experimental conditions: (1) Normal development, at intervals from the day of natural eyelid opening (day 1 of visual experience [VE]) to greater than 5 years of age; (2) Monocular form deprivation (MD), for varying lengths of time; (3) Recovery from MD; (4) Monocular -5 D lens treatment. The creep rate was low in normal animals (1-2% elongation/h), did not change significantly between day 1 and day 75 of VE, and was not significantly different between the two eyes. Four days of MD produced a 200-300% increase in creep rate in the sclera from deprived eyes. Creep rate remained similarly elevated after 11 and 21 days of MD. After 2 days of recovery, which followed 11 days of MD, the creep rate of sclera from the recovering eyes was below normal levels. In animals that wore a monocular -5 D lens for up to 21 days, creep rate increased, and then decreased, in concert with the increase, and decrease, in axial elongation rate as the eyes compensated for the lens. The modulus of elasticity of the sclera was not significantly affected by any manipulation. The temporal correspondence between changes in axial elongation rate and changes in creep rate support the hypothesis that regulation of the time-dependent mechanical properties of fibrous mammalian sclera plays a role in controlling axial elongation rate during both normal emmetropization and the development of refractive errors.  (+info)

Enthacrynic and acid effects on inner wall pores in living monkeys. (4/822)

PURPOSE: The influence of the inner wall of Schlemm's canal on aqueous outflow facility remains poorly understood. We examined the relationship between inner wall pore characteristics and outflow facility in living primate eyes in which facility had been pharmacologically increased by ethacrynic acid (ECA) infusion and in contralateral control eyes. METHODS: Outflow facility (two-level constant pressure perfusion) was measured in eight pairs of living monkey eyes before and after administration of a bolus dose of either 0.125 mM ECA or vehicle. After exsanguination, eyes were fixed in situ under constant-pressure conditions (mean fixation pressure approximately 19 mm Hg). The density and diameter of inner wall pores and the number and area of platelet aggregates on the inner wall of Schlemm's canal were measured by scanning electron microscopy. RESULTS: In ECA-treated eyes, outflow facility increased 63% (P < 0.0001), intracellular pore density decreased 46% (P = 0.0094), intracellular pore size increased 27% (P = 0.049), platelet aggregate density increased 158% (P < 0.0001), and area covered by platelets increased 210% (P = 0.012) relative to contralateral controls. Although the average density and size of intercellular pores were essentially unaffected by ECA, an increased density of large (> or = 1.90 microm) intercellular pores was seen in ECA-treated eyes. The density of intracellular pores increased with the duration of fixative perfusion. Other than a weak negative correlation between outflow facility and intracellular pore density in ECA-treated eyes (P = 0.052), facility was not correlated with inner wall pore features. CONCLUSIONS: Our data are most consistent with a scenario in which ECA promotes formation of large intercellular pores in the inner wall of Schlemm's canal, which are then masked by platelet aggregates. Masking of intercellular pores, combined with fixation-induced alteration of inner wall pore density, greatly complicates attempts to relate facility to inner wall structure and suggests that in vivo pore density is smaller than in fixed tissue. Additionally, facility-influencing effects of ECA on the juxtacanalicular tissue cannot be excluded.  (+info)

Effects of ethacrynic acid on Schlemm's canal inner wall and outflow facility in human eyes. (5/822)

PURPOSE: The role of the inner wall of Schlemm's canal in determining aqueous outflow facility is poorly understood. To quantify the relationship between inner wall pore characteristics and aqueous outflow facility in human eyes, both control eyes and eyes in which facility had been pharmacologically increased by ethacrynic acid (ECA) infusion were studied. METHODS: Outflow facility was measured in enucleated human eyes before and after delivery of 0.25 mM ECA (one eye of each of 6 pairs) or 2.5 mM ECA (one eye of each of 13 pairs). ECA, and vehicle in contralateral eyes, was delivered into Schlemm's canal by retroperfusion, thereby largely avoiding drug exposure to the trabecular meshwork. After facility measurement, eyes were fixed under conditions of either constant pressure (physiological intraocular pressure, 13 pairs) or "equal flow" (6 pairs) and were microdissected to expose the inner wall of Schlemm's canal. The density and diameter of intercellular and intracellular inner wall pores were measured using scanning electron microscopy. RESULTS: Retroperfusion with 2.5 mM ECA increased facility by 73% (P < 0.001), whereas 0.25 mM ECA increased facility by 19% (not statistically significant). The density of intercellular pores in the inner wall of Schlemm's canal was increased by 520% in 2.5 mM ECA-retroperfused eyes (P < 0.00004), whereas intracellular pore density remained approximately constant. Large pores (size > or = 1.1 microm) were particularly enhanced in ECA retroperfused eyes. The net change in facility due to ECA was not correlated with changes in pore density or other inner wall pore statistics. CONCLUSIONS: Our data are most consistent with a model in which pores in the inner wall of Schlemm's canal indirectly influence facility. However, measured changes in facility due to changes in inner wall properties did not agree with quantitative predictions of the pore funneling theory, suggesting that changes in facility may instead be due to gel leakage from the extracellular spaces of the juxtacanalicular tissue. More definitive experiments are required to confirm this hypothesis.  (+info)

Morphological variations of the peripapillary circle of Zinn-Haller by flat section. (6/822)

AIMS: To evaluate the morphometric and morphological variations of the circle of Zinn-Haller (CZH) in the human eye. METHODS: 42 human enucleated eyes were used in this study. After transverse flat thick sections were cut through the optic nerve and adjacent sclera, tissue sections were stained with haematoxylin and eosin or examined immediately by wet preparation under a light microscope. The average vessel diameter of the arterial circle and the average distance between the optic nerve head (ONH) and the arterial circle were determined. Various branching patterns of the CZH were also evaluated. RESULTS: The vessel diameter of the arterial circle was 123 (SD 75) microm (range 20-230 microm). The distance of the CZH from the ONH margin was 403 (352) microm (0-1050 microm). The CZH gave off branches to the optic nerve and to the peripapillary choroid (PPC) with various branching patterns especially at the entry point of paraoptic short posterior ciliary artery. CONCLUSIONS: The CZH exists within a variable distance from the ONH and its average diameter is similar to that of the central retinal vessels though it shows marked variation even in the same circle. The CZH also shows variable configurations in branching patterns. These variations may act as contributing factors that are responsible for the individual susceptibility of the anterior optic nerve and the PPC to circulatory disturbances.  (+info)

Excimer laser effects on outflow facility and outflow pathway morphology. (7/822)

PURPOSE: To determine the relative contributions to aqueous outflow resistance of the tissues distal to the inner wall of Schlemm's canal. METHODS: While performing constant pressure perfusion at 10 mm Hg, a 193-nm excimer laser (Questek) was used to precisely remove portions of sclera, unroofing Schlemm's canal while leaving the inner wall intact. The laser beam was masked to produce a beam 2 mm by 1 mm. The laser output was constant at a fluency of 75 mJ/cm2 and 20 Hz. The excimer laser at a frequency of 1 Hz was used as the aiming beam. Photoablation was performed on human cadaver eyes at the limbus at an angle of 0 degrees to 45 degrees from the optical axis. As the excimer photoablations progressed, Schlemm's canal was visualized by the fluorescence of the Barany's solution containing fluorescein dye. After perfusion fixation the eyes were immersion-fixed overnight. The facility of outflow before (Co) and after (Ce) the excimer ablation was measured in 7 eyes. RESULTS: The facility of outflow increased in all eyes after the excimer sinusotomy, from a mean of 0.29+/-0.02 before the sinusotomy to 0.37+/-0.03 microl/min per mm Hg after (P < 0.05). The mean ratio of outflow facility after and before ablation (Ce/Co) was 1.27+/-0.08 (range, 1.20-1.39), a reduction of outflow resistance of 21.3%. Using the formula of Ellingsen and Grant (1972), percentage of resistance to outflow eliminated = 100 [1 - alphaCo/Ce - (1 - alpha)Co], where alpha = fraction of the circumference dissected. Assuming that because of circumferential flow approximately 50% of Schlemm's canal is drained by the single opening made in the outer wall ablation studies, this results in resistance to outflow eliminated of 35%, which is consistent with the calculated eliminated resistance derived from the data of Rosenquist et al., 1989. Light and scanning electron microscopy confirmed the integrity of the inner wall Schlemm's canal underlying the area of ablation. CONCLUSIONS: The results provide direct evidence indicating that approximately one third of resistance to outflow in the human eye lies distal to the inner wall Schlemm's canal in an enucleated perfused human eye.  (+info)

Glucocorticoids regulate transendothelial fluid flow resistance and formation of intercellular junctions. (8/822)

The regulation of transendothelial fluid flow by glucocorticoids was studied in vitro with use of human endothelial cells cultured from Schlemm's canal (SCE) and the trabecular meshwork (TM) in conjunction with computer-linked flowmeters. After 2-7 wk of 500 nM dexamethasone (Dex) treatment, the following physiological, morphometric, and biochemical alterations were observed: a 3- to 5-fold increase in fluid flow resistance, a 2-fold increase in the representation of tight junctions, a 10- to 30-fold reduction in the mean area occupied by interendothelial "gaps" or preferential flow channels, and a 3- to 5-fold increase in the expression of the junction-associated protein ZO-1. The more resistive SCE cells expressed two isoforms of ZO-1; TM cells expressed only one. To investigate the role of ZO-1 in the aforementioned Dex effects, its expression was inhibited using antisense phosphorothioate oligonucleotides, and the response was compared with that observed with the use of sense and nonsense phosphorothioate oligonucleotides. Inhibition of ZO-1 expression abolished the Dex-induced increase in resistance and the accompanying alterations in cell junctions and gaps. These results support the hypothesis that intercellular junctions are necessary for the development and maintenance of transendothelial flow resistance in cultured SCE and TM cells and are likely involved in the mechanism of increased resistance associated with glucocorticoid exposure.  (+info)