Instability and Breakup of Model Tear Films

Bhamla, M. Saad; Chai, Chew; Rabiah, Noelle I.; Frostad, John M.; Fuller, Gerald G.

doi:10.1167/iovs.15-18064

Cited by 37 publications

(27 citation statements)

References 44 publications

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“…2) (Green-Church et al, 2011) (Butovich, 2011a). Between the blinks, the normal tear film preserves its integrity for up to 10–20 seconds, after which it starts to disintegrate due to collapsing of the lipid sublayer, accompanied by evaporation of the aqueous sublayer and its thinning (Bhamla et al, 2016). In dry eye patients, the integrity of the tear film is severely compromised, which results in desiccation of the ocular surface, its irritation, and inflammation.…”

Section: Introductionmentioning

confidence: 99%

Meibomian glands, meibum, and meibogenesis

Butovich

2017

Experimental Eye Research

106

118

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Meibum is a lipid-rich secretion that is produced by fully differentiated meibocytes in the holocrine Meibomian glands (MG) of humans and most mammals. The secretion is a part of a defense mechanism that protects the ocular surface from hazardous environmental factors, and from desiccation. Meibomian lipids that have been identified in meibum are very diverse and unique in nature. The lipid composition of meibum is different from virtually any other lipid pool found in the human body. In fact, meibum is quite different from sebum, which is the closest secretion that is produced by anatomically, physiologically, and biochemically related sebaceous glands. However, meibum of mice have been shown to closely resemble that of humans, implying similar biosynthetic mechanisms in MG of both species. By analyzing available genomic, immunohistochemical, and lipidomic data, we have envisioned a unifying network of enzymatic reactions that are responsible for biosynthesis of meibum, which we call meibogenesis. Our current theory is based on an assumption that most of the biosynthetic reactions of meibogenesis are catalyzed by known enzymes. However, the main features that make meibum unique – the ratio of identified classes of lipids, the extreme length of its components, extensive ω-hydroxylation of fatty acids and alcohols, iso- and anteiso-branching of meibomian lipids (e.g. waxes), and the presence of rather unique complex lipids with several ester bonds – make it possible that either the activity of known enzymes is altered in MG, or some unknown enzymes contribute to the processes of meibogenesis, or both. Studies are in progress to elucidate meibogenesis on molecular level.

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Section: Introductionmentioning

confidence: 99%

Meibomian glands, meibum, and meibogenesis

Butovich

2017

Experimental Eye Research

106

118

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“…In vitro when bovine 39 or human meibum 37,38 was layered on top of saline, it did not inhibit R evap or inhibited it much less (6–8%) 4 than conventionally attributed to the TFLL. One may speculate that the reason for lack of evaporative resistance by lipids in some studies is that the films did not spread across the entire surface leaving exposed regions for water to evaporate.…”

Section: Discussionmentioning

confidence: 76%

“…67 The multilamellar sheets are likely to be joined by interdigitated lipid hydrocarbon chains. One would expect that large ‘islands’ of tightly packed lipids, 70 times thicker than the TFLL, might decrease the rate of evaporation as it has been estimated that “…in some areas where the meibum is thicker, it acts as a better barrier to evaporation,” 39 although the total rate of evaporation was unchanged with meibum.…”

Section: Discussionmentioning

confidence: 99%

“…The rheology of meibum on artificial tears is different for meibum on buffer. 39 The interaction of meibum with tears results in the exclusion of water at the TFLL-aqueous tear interface and it was suggested this interaction could inhibit R evap . 61 In this study we tested the idea that components in human tears such as proteins interact with human meibum placed on the surface of human reflex tears and together they inhibit R evap .…”

Section: Discussionmentioning

confidence: 99%

“…Surprisingly, three studies showed that a film of human 4,37,38 and bovine 39 meibum does not inhibit the evaporation of buffer in vitro, as the rheology of meibum on artificial tears is different than for meibum on buffer. 39 …”

Section: Introductionmentioning

confidence: 99%

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Evaporation and Hydrocarbon Chain Conformation of Surface Lipid Films

et al. 2016

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Purpose The inhibition of the rate of evaporation (Revap) by surface lipids is relevant to reservoirs and dry eye. Our aim was to test the idea that lipid surface films inhibit Revap. Methods Revap were determined gravimetrically. Hydrocarbon chain conformation and structure were measured using a Raman microscope. Six 1-hydroxyl hydrocarbons (11–24 carbons in length) and human meibum were studied. Reflex tears were obtained from a 62-year-old male. Results The Raman scattering intensity of the lipid film deviated by about 7 % for hydroxyl lipids and varied by 21 % for meibum films across the entire film at a resolution of 5 µm2. All of the surface lipids were ordered. Revap of the shorter chain hydroxyl lipids were slightly (7%) but significantly lower compared with the longer chain hydroxyl lipids. Revap of both groups was essentially similar to that of buffer. A hydroxyl lipid film did not influence Revap over an estimated average thickness range of 0.69 to >6.9 µm. Revap of human tears and buffer with and without human meibum (34.4 µm thick) was not significantly different. Revap of human tears was not significantly different from buffer. Conclusions Human meibum and hydroxyl lipids, regardless of their fluidity, chain length, or thickness did not inhibit Revap of buffer or tears even though they completely covered the surface. It is unlikely that hydroxyl lipids can be used to inhibit Revap of reservoirs. Our data do not support the widely accepted (yet unconfirmed) idea that the tear film lipid layer inhibits Revap of tears.

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