Artificial tear fluid

Figure 26.24 Wilhelmy force loops of (CH4 + air) plasma treated glass plates in (W) DDI water and (T) artificial tear fluid at varying second immersion velocities (1) 2mm/min, (2) 5mm/min, (3) lOmm/min, and (4) 20mm/min. Plasma discharge conditions were 38W, SOmTorr, 1 seem CH4, 2 seem air, 20 min first and second emersion and first immersion velocities were fixed at 20mm/min, the use of water and tear fluid 4elded advancing contact angles, 0D,a,i means, and standard deviations of 47° 1 and 48° 3, respectively.

Figure 26.25 The effect of Wilhelmy plate second immersion velocity (Adv. 2) on the fluid holding time of water and artificial tear fluid on CH4 + air plasma treated glass slides.

Figure 26.31 depicts the same measuring procedure applied to a contact lens material sheet (A) untreated, (B) (CH4 + air) plasma treated, and (C) (CH4 + air) plasma treated and then O2 plasma treated. Characterizing aqueous film stability on untreated and plasma-modified contact lens materials using artificial tear fluid by... 

The surface chemistry of the eye is probably better understood than that of the ear. The cornea is covered with a thin, fluid film the so-called tear film, which is believed to consist of an aqueous phase, approximately 10" cm thick, with an adsorbed lipid and mucin layer at the air-water interface and an adsorbed mucin layer on the corneal side. The latter renders the cornea hydrophilic and enables the tear film to spread. In dry eye syndrome local areas of dewetting occur due to increased contact angle. Dry eye is sometimes precipitated by drug therapy, and there is a search for adequate artificial tear fluids. The surface chemistry of tear film components has been discussed by Holly [331]. Adsorption of cationic surfactants present in eye drops as preservatives can lead to the production of a hydrophobic surface due to electrostatic adsorption of the cations with the hydrocarbon chains oriented towards the tear film. Such a process can itself result in dewetting and thus cationics should be excluded from artificial tear fluids. 

Artificial tear fluid (ATF) containing a mixture of proteins (lysozyme, albumin, and mucin) and lipids (triolein, cholesteryl linoleate, etc.) was prepared following the procedure published previously 7a), The total protein concentration of the ATF was 3.2 mg/mL as determined using the Pierce BCA protein assay. Hydrogel pieces (1x1 cm in area and --1 mm in thickness) were immersed and incubated with gentle shaking, for a period of 24h in ATF solution (2 mL per hydrogel piece) in a water bath maintained at 36 C. After incubation,... 

Protein deposition on materials surface is dependent on chemical nature of the surface (hydrophilicity, hydrophobicity, charge density) and also on the size and chemical composition of the proteins exposed to the synthetic surface (2). Since different biological media are composed of rather different types of proteins, materials designed for specific in lant applications must be tested using those proteins most likely encoimtered in vivo. Materials used in contact leiis applications are generally tested for in vitro protein adsorption using an artificial tear fluid (ATF) containing mixtures of proteins and lipids that are commonly found in hximan tear fluid and in contact lens deposits (15, 16). A... 

When mixed hydrogels of HEMA-1 (10-40 wt%) were incubated in artificial tear fluid solution for a period of 24h, the amounts of total polymer-bound protein were found to be about the same as that was bound to pure HEMA... 

Secondary effects of irrigation fluids ex vivo eye irritation assay with four scratches on the cornea, incubated for 2 days and treated with artificial tears containing CaCl in 0.13 mmol/L concentration each 24 drops per day with 30 min of interval between phosphate and tear application. Second image is taken after 2 days with obvious comeal calcification. 

The ideal artificial tear would reproduce the metabolic, optical, and physical characteristics of natmal tears. Additionally, it would have a long ocular residence time and would contain therapeutic additives to treat primary and secondary damage to the eye. Supplementation of natural tears with a substance that prolongs residence time generally improves tear film breakup time (TBUT) and is superior to tear replacement fluids of low retention time. 

Because they are not produced constantly, as are natural tears, tear substitutes should have properties to enhance their retention time in the tear film. The addition of various types of polymers to artificial tears not only improves retention of added fluid but also increases corneal surface wettability, decreases blink friction, and minimizes surfece tension. Natural tears contain glycoproteins and other surfectant macromolecules to decrease surface tension. Although polymers may enhance tear film stability without enhancing viscosity, there appears to be no correlation between retention time and viscosity. Polysaccharides, including mucilages, dextrans, and... 

The device is generally comfortable and well accepted by many patients, but its use does have certain disadvantages. Some patients have problems with discomfort (foreign body sensation) or expulsion of the Lacrisert.The insert can be wetted with saline before insertion to improve comfort, but this can make even more difficult the insert s placement into the lower cul-de-sac, which requires a moderate amount of dexterity. Supplementation with artificial tears after insertion may improve comfort. The most common patient complaint is blurred vision associated with the intense release of polymer during the first 4 to 6 hours after instillation, from a thickened tear film.Adding such fluid as drops of NaCl 0.9% or artificial tear solution can reduce the tear film viscosity and minimize the visual complaints. As the insert dissolves it releases debris that can blur vision and cause irritation. Most patients with mild signs and symptoms of dry eye do not experience improvement with use of the insert, as compared with the use of conventional tear solutions. Because some tear secretion is necessary to dissolve the Lacrisert, KCS patients with low basal tear secretion may not benefit from or tolerate its use. 

Dry eye symptoms and significant ocular surface disease frequently occur in patients taking isotretinoin.The associated symptoms may be accompanied by blepharocon-jimctivitis. The presence of isotretinoin in tear fluid decreases stability (and tear break-up time) of the lipid layer of the tear film but may also cause a decrease in aqueous production, leading to ocular surface dryness. These effects could be responsible for the dry eye symptoms, contact lens intolerance, superficial punctate keratitis, and conjunctival irritation accompanying isotretinoin therapy. Use of artificial tear preparations may help to alleviate the associated discomfort. 

Figure 26.30 Wilhelmy force loops of (A) nylon-6, (B) PMMA, and (C) PTFE plates in artificial tear solution. At the end of the first emersion, the plates were held out of the solution for (1) Omin, (2) 5 min, and (3) 40 min at a depth of 5 mm the use of tear fluid on nylon-6, PMMA, and PTFE, yielded advancing contact angles, 0D,a,i. means, and standard deviations of 68° 3, 91° 3, and 130° 1, respectively.

Lens hazing and protein deposition are common problems for wearers of soft contact lenses. Previous experiments with hydrophobic-hydrophilic copolymers exposed to plasma showed protein adsorption to be minimal at intermediate copolymer compositions. Adsorption of proteins from artificial tear solutions to a series of polymers and copolymers ranging in composition from 100% poly (methyl methacrylate) (PMMA) to 100% poly(2-hydroxyethyl methacrylate) (PH EM A) was measured. The total protein adsorption due to the three major proteins in tear fluid (lysozyme, albumin, and immunoglobulins) was at a minimum value at copolymer compositions containing 50% or less PH EM A. The elution of the adsorbed proteins from these polymers and copolymers with various solutions also was investigated to assess the binding mechanism. 

---