Frank J. Holly

Kinetics of lacrimal secretion in normal human subjects

A novel technique was used to study the time course of lacrimation in normal human subjects with and without the use of topical anesthetic. The Schirmer technique was modified to eliminate evaporation, to improve absorption capacity, and to allow the determination of the length of paper strip wetted as a function of time. By the use of a theoretical model, the wetting curve thus obtained could be analyzed and basic secretion parameters characteristic of lacrimation kinetics were obtained. Fourteen adult females and six adult males between the ages of 21 and 47 years were included in the study.All the eyes examined exhibited essentially the same type of tear secretion kinetics. Initially, the lacrimation occurred at a high rate which then exponentially diminished to a final, lower value. This exponential cycle of secretion pattern could occur repeatedly during the time of measurement and was not qualitatively altered by the use of topical anesthesia. In addition to the time dependence of wetted length, we ...

Protease activities in human tears

Several protease activities were measured in human tears by six specific substrates. The specific activity of cathepsin B-like enzyme was 7-fold higher in Orientals than in Caucasians. The trypsin-like and cathepsin C-like enzyme activities also showed 3 to 4-fold higher in Orientals than in Caucasians. However, the deviation in the activities of these two enzymes was high in both Orientals and Caucasians. Similar results were obtained when comparing the protease activities of tear collected by glass capillary and a filter-paper strip method. Since a surface-active small molecular weight fraction can be produced by incubation of freshly collected tears for 4 hours at 37 degrees C, the low molecular weight surfactant may be a proteolytic product.

Basic aspects of contact lens biocompatibility

Abstract Practically all tissue interfaces that have to be kept moist in the body, such as the mucous membranes, are internal, with the exception of the part of the ocular globe delineated by the palpebral fissure, which is intermittently exposed to the atmosphere between consecutive blinks. This exposed surface, the conjunctival and corneal epithelia have to be coated with a thin fluid layer, the so-called tear film, in order to provide a high optical quality refractive surface and to preserve the well-being of the underlying tissues. An elaborate system exists in the body which ensures the formation and the maintenance of a continuous tear film over the exposed ocular surface. When a contact lens is placed on the eye, two conditions have to be fulfilled to ensure the biocompatibility of the lens. First, the lens should be coated at all times by a continuous tear film complete with the superficial lipid layer. Second, there should be a continuous aqueous tear layer underneath the lens. The oxygen permeability of the lens, a much-stressed requirement, is actually of secondary importance. The thickness of the tear film and that of the pre-lens and the post-lens tear layers fall between 1–10 μm. Thus, the thickness is large as compared to molecular forces, so that the direct interaction between the boundary interfaces can probably be neglected. On the other hand, the film is not thick enough to maintain continuity when the tear—solid interfacial tension is appreciable, so that the tear-film-free energy becomes larger than the surface-free energy of the solid. Under lipid-laden ocular conditions, it is difficult to maintain a low interfacial tension even in the absence of a contact lens. It is thought that the low interfacial tension is maintained in the eye by the presence of a loosely-bound hydrophilic macromolecular layer that can mask lipid contaminants and can be readily removed once it becomes non-functional. The understanding of natural processes which maintain tear film stability over the ocular surface between blinks may enable us to develop better contact-lens materials and contact-lens-wetting solutions that will be more compatible with the ocular environment and will assist rather than hinder the natural processes in maintaining the stability of the pre-lens and post-lens aqueous tear layers and thus improve contact lens biocompatibility.

Kinetics of capillary tear flow in the Schirmer strip

The popular Schirmer test of tearing ability heretofore has never been analyzed kinetically and the interpretation of the results is usually based on implicit, often erroneous assumptions. We have analyzed the capillary flow of fluids in filter paper strips in vitro systems for the cases of unlimited supply and limited supply at constant rates, and in vivo using human subjects, who kinetically corresponded to limited supply having variable rates. The effects of evaporation, surface tension, viscosity, paper pore-size, and the wettability of the cellulose fibers in the paper were also studied. The results show that in the case of unlimited supply, the fluid absorption is kinetically identical to fluid uptake by a horizontal capillary. This implies that the paper strip can absorb fluids only at a certain maximum rate which decreases with time. At lower secretion rates, the rate of wetting length increase is linearly proportional to the secretion rate provided that evaporation is prevented. Evaporation increases with increased wetting length until a steady state is reached where the length of wetting remains constant in time. As long as the secretion rate remains below the maximum uptake rate of the paper strip, the paper and fluid characteristics have a negligible influence on the wetting rate thus the rate of wetting can provide quantitative information on the secretion rate. Wetting length versus time curves obtained in vivo can be best described mathematically by assuming that the initially high secretion rate exponentially decays to a lower, final value. From the data, the magnitude of the initial and final tear secretion rates as well as the secretion rate decay coefficient can be calculated. These physiologically relevant values quantitatively characterize the functioning of the lacrimal system and may have diagnostic value in detecting marginal lacrimal deficiencies and predicting poor contact lens tolerance.

Changes in lysosomal enzyme activities of eye tissues in endotoxin-induced inflammation

Lysosomal enzyme activities in rabbit ocular tissues were examined at various times after the intravitreal injection of endotoxin. Lysosomal enzyme activities in the aqueous, vitreous, and pigment epithelium-choroid were elevated 3 h after injection. It is deduced from the fluorescein-labeled dextran and SDS-polyacrylamide gel electrophoresis analysis of the aqueous, vitreous, and pigment epithelium-choroid from endotoxin injected rabbits that the elevation of lysosomal enzyme activities are probably due to a breakdown in blood-ocular barriers.

Decrease of lactoferrin concentration in the tears of myotonic muscular dystrophy patients

Tears from myotonic muscular dystrophy (MMD) patients and normal controls were analyzed for their tear proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Lactoferrin comprised about 18% of the total tear protein in MMD patients as opposed to about 27% in normals. The albumin content relative to total protein in MMD tears was about 25% while the same value for normals is 13%. The lactoferrin/albumin ratio, was about 0.8 for MMD patients and about 2.1 for normals.

Comparison of lacrimation kinetics in dry eye patients and normals

A 100 mm long and 5 mm wide filter paper strip enclosed in a transparent plastic sheath to prevent evaporation was used to determine the time dependence of wetting of the strip in the anesthetized eyes of dry eye patients and age-matched normals. Prior to the measurements, the paper strips were extracted by lipid solvents and marked at every millimeter length. Wetted length data were plotted against time and the resulting wetting curves were analyzed to obtain the time dependence of the tear secretion rate during lacrimation. Every eye studied exhibited an exponentially decaying tear secretion rate that could be characterized by three kinetic parameters per cycle: the initial and final tear secretion rates and the secretion decay coefficient. The eyes of the sicca patients showed a much simpler lacrimation pattern than did the controls: 60% of the dry eyes exhibited a one-cycle lacrimation pattern while only 5% of the normal group did so. The tear secretion kinetic parameters characterizing the lacrimation pattern reduced to one-cycle were compared. Both the dry eyes and the control eyes started to lacrimate at about the same high initial secretion rate. However, the lacrimation rate was found to decrease faster and to a lower final rate in dry eye patients as opposed to normal controls.

Intracellular distribution and properties of cathepsin B in the rat retina and its inhibition by a cytosolic fraction

The intracellular distribution and properties of cathepsin B in the rat retina are similar to those of cathepsin B in other mammalian tissues. The specific activity of cathepsin B was highest in the mitochondrial-lysosomal fraction [1650 +/- 450 pmole mg-1 protein hr-1 (mean +/- S.D.)]. Inhibition of cathepsin B activity by a cytosol fraction of retina is also described.

Novel Methods of Studying Polymer Surfaces by Employing Contact Angle Goniometry

Highly sophisticated instrumentations are available today for studying solid polymeric surfaces. Nevertheless, the relatively modest technique of contact angle goniometry has a disproportionately high potential for providing information on surface energetics and surface transformation that are largely unexploited. Such techniques employing one- and twocondensed-phase contact angle measurements are especially useful for studying the interfacial properties of polymeric surfaces, both electrically charged and neutral, that exhibit variability in surface composition and thus in surface properties, due to segmental mobility. Plasma-treated polymer surfaces, hydrogel surfaces, tissue and cellular interfaces are ordinarily prone to rapid and drastic surface changes depending on the polarity of the adjacent fluid phase or solid surface. Relations that have proven to be useful include adhesion tension and the relative contact angle hysteresis both as a function of the advancing contact angle. Hence, information can be obtained on surface hydrophilicity, thin film stability as related to disjoining pressure, and water-solid interfacial tension, all which play an important role in such widely diverse phenomena as the biocompatibility of contact lenses and other biomaterials, surgical trauma, tear film stability, cellular interaction, and bioadhesion.