Physical Properties of Stimulated and Unstimulated Tears

Pandit, Jyotin C.; Nagyová, B; Bron, Anthony J.; Tiffany, John M.

doi:10.1006/exer.1998.0600

Cited by 83 publications

(51 citation statements)

References 13 publications

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“…The lack of dependence of the efficiency of mixing on the presence of surfactants is important for two reasons: (i) most physiological samples contain surface-active ingredients that might, in principle, influence the operation of the mixer, and (ii) specific diagnostic applications might require the use of surfactants to prevent adsorption of proteins to the gas/liquid interface, 15 or require their absence to prevent denaturation of proteins. 40 The mixer is compatible with viscosities corresponding to those of biological fluids that are of potential interest: the viscosity of human blood serum (y2 mPa s), 41 whole blood, which has a viscosity of approximately 5-6 mPa s at low rates of shear, 41 urine (y1 mPa s), 42 tears (2 to 9 mPa s), 43 and saliva (2 to 9 mPa s). 44 …”

Section: Efficiency Of Mixingmentioning

confidence: 99%

Mixing with bubbles: a practical technology for use with portable microfluidic devices

et al. 2006

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This paper demonstrates a methodology for micromixing that is sufficiently simple that it can be used in portable microfluidic devices. It illustrates the use of the micromixer by incorporating it into an elementary, portable microfluidic system that includes sample introduction, sample filtration, and valving. This system has the following characteristics: (i) it is powered with a single hand-operated source of vacuum, (ii) it allows samples to be loaded easily by depositing them into prefabricated wells, (iii) the samples are filtered in situ to prevent clogging of the microchannels, (iv) the structure of the channels ensure mixing of the laminar streams by interaction with bubbles of gas introduced into the channels, (v) the device is prepared in a single-step soft-lithographic process, and (vi) the device can be prepared to be resistant to the adsorption of proteins, and can be used with or without surface-active agents.We fabricated the device (Figs. 1a) in a polydimethylsiloxane (PDMS) slab sealed to a PDMS substrate. We chose to use PDMS because it is the most useful material for testing concepts in microfluidics, and because it is easily coupled with

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Section: Efficiency Of Mixingmentioning

confidence: 99%

Mixing with bubbles: a practical technology for use with portable microfluidic devices

et al. 2006

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“…The properties of tear are chosen to be σ = 0.045N/m and η ∞ = 10 −3 Pa s after [17] and [16]. These values give ∂h /∂t (0, 0) = −0.072 µm/ min; experimental values from King-Smith et al [48] are, on the average about −4 µm/ min.…”

Section: Central Cornea Thinningmentioning

confidence: 99%

“…The precorneal tear film is a few microns thick in the center of the cornea after a blink (e.g., [10][11][12]) and has a considerably larger meniscus around the eye lid margins [13][14][15]. Tear fluid (a sample combining all components of tears) is mildly shear thinning [16] but weakly elastic [17]; recent measurements of meibomian lipids alone show that they may have significant elasticity [18], but its contribution to the overall rheology and properties of tears is yet to be understood. Other interfacial properties, such as the apparent surface tension of the tear-air interface, are definitely affected by polar lipids that are attracted to the lipid-aqueous interface [19,20], and those lipids can cause upward motion of the tear fluid after a blink [21,22].…”

Section: Introductionmentioning

confidence: 99%

Thin film dynamics on a prolate spheroid with application to the cornea

et al. 2011

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The tear film on the front of the eye is critical to proper eyesight; in many mathematical models of the tear film, the tear film is assumed to be on a flat substrate. We re-examine this assumption by studying the effect of a substrate which is representative of the human cornea. We study the flow of a thin fluid film on a prolate spheroid which is a good approximation to the shape of the human cornea. Two lubrication models for the dynamics of the film are studied in prolate spheroidal coordinates which are appropriate for this situation. One is a self-consistent leading-order hyperbolic partial differential equation (PDE) valid for relatively large substrate curvature; the other retains the next higher-order terms resulting in a fourth-order parabolic PDE for the film dynamics. The former is studied for both Newtonian and Ellis (shear thinning) fluids; for typical tear film parameter values, the shear thinning is too small to be significant in this model. For larger shear thinning, we find a significant effect on finite-time singularities. The second model is studied for a Newtonian fluid and allows for a meniscus at one end of the domain. We do not find a strong effect on the thinning rate at the center of the cornea. We conclude that the corneal shape does not have a significant effect on the thinning rate of the tear film for typical conditions.

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“…Direct Sampling Glass microcapillary tubes are directly used to sample tear fluid by capillarity [5,6,23,25,26,29,30,31,33,34,40,43,50,51,52,54,61,63]. The sampling procedure has been very precisely described (specifying position and corresponding gestures of the operator) and must respect strict supervisions in order to avoid any direct contact with ocular tissue or accidental puncture [62].…”

Section: Sampling Supportmentioning

confidence: 99%

Lachrymal Determinations: Methods and Updates on Biopharmaceutical and Clinical Applications

Dumortier

Chaumeil²

2004

Ophthalmic Res

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This article displays different procedures used to collect lachrymal fluid and describes some of its applications. Sampling tears represents the main difficulty to produce precise and reproducible results. The direct sampling procedure consists in collecting tears with capillary tubes and has the drawback of demanding previous stimulation that induces major dilution. The indirect method does not require preliminary stimulation but has been held responsible for altering epithelium and promoting leakage from plasma. Schirmer strips and sponges are classically required. Applications are numerous in biopharmaceutical and clinical fields. The determination of endogenous components has great potentiality as a diagnostic tool, but the use of tear as a substitute of plasma does not present clinical relevance. Levels of drugs like immunosuppressive or antibiotic agents are determined in tears to verify that pharmacological concentrations are reached and frequency of administration is deduced from kinetic fitting.

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Physical Properties of Stimulated and Unstimulated Tears

Cited by 83 publications

References 13 publications

Mixing with bubbles: a practical technology for use with portable microfluidic devices

Mixing with bubbles: a practical technology for use with portable microfluidic devices

Thin film dynamics on a prolate spheroid with application to the cornea

Lachrymal Determinations: Methods and Updates on Biopharmaceutical and Clinical Applications

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