In your eye / lecithin

ironjustice@aol.com · medicine forum Guru Joined: 28 Apr 2005 Posts: 1522

http://tinyurl.com/jz68z

<<snip>>
The lecithin-oil composition was found to significantly mimic the
physical properties that characterise the natural tear lipid film
<<snip>>

Invest Ophthalmol Vis Sci 2006;47: E-Abstract 5606.
© 2006 ARVO

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5606-B376

Biophysical Evaluation of Meibomian Layer and Lipid Analogues Is a Clue
for Tear Film Disorders Treatment
F. Miano1, M.G. Mazzone1, A.C. Scuderi1 and C.P. Winlove2
1 SIFI S.p.A., Catania, Italy
2 University of Exeter, Exeter, United Kingdom

Commercial Relationships: F. Miano, None; M.G. Mazzone, None; A.C.
Scuderi, None; C.P. Winlove, None.

Support: None

Abstract

Purpose: Tear film Meibomian lipid layer features were investigated and
compared to artificial analogues.

Methods: Grazing Incidence X-Ray Diffraction resolved the 2D spatial
organisation of the lipid layer. A pendant drop model measured
evaporation rate, dilatational rheology and protein insertion by means
of drop shape analysis. Neutron reflectivity produced an accurate
description of the mass density profile of the lipid/protein layer.

Results: Despite its complex composition, Meibomian lipid layer showed
an ordered 2D structure that is index of a remarkable molecular
organisation. The d-spacings of the Meibomian and of an analogue
comprising egg lecithin and soy bean oil systems are very close (4 Å).
In the presence of such layer the evaporative flux of the underlying
aqueous phase was significantly reduced.

The evaporative flux j follows a physical model in which the driving
force is the relative humidity and the total resistivity against
evaporation is the sum of Rw (water) and Rm (lipid layer). The Rm of
the Meibomian and lipid analogue are very close while DPPC was lower.

Rheological measurements showed that the meibomian film, weakly packed,
is prevalently elastic where the viscous component of the dilatational
modulus increases at high surface compression.

Another feature of meibomian layer is the ability to limit tear
proteins adsorption at the interface and their consequent interference.
The neutron reflectivity study showed that lactoferrin adsorbs at a
free air/aqueous interface not retaining its native globular structure.
A close packed lipid layer effectively prevented such event where a
non-uniform or weakly packed lipid layer allowed protein coadsorption
and the set up of a lipid protein mixed interface. The insertion of
proteins at the interface and their progressive loss of ternary
structure eventually impaired the stability of the whole interface.

Conclusions: The Meibomian layer is an effective evaporation
retardation agent and its dilatational rheology is ideal for efficient
respreading after a blink. Moreover, if densely packed, it prevents the
undesired insertion of proteins. The lecithin-oil composition was
found to significantly mimic the physical properties that characterise
the natural tear lipid film. This was not an obvious result since pure
phospholipids compositions and some commercial emulsions were found to
produce a substantially dissimilar interface. The therapeutic approach
of supplementing lipids to deficient tear films, may produce an
effective restructuring of the pre-existing lipid layer in the case
of lecithin-oil emulsions.

Key Words: extracellular matrix · lipids

© 2006, The Association for Research in Vision and Ophthalmology,
Inc., all rights reserved. For permission to reproduce any part of this
abstract, contact the ARVO Office at arvo@arvo.org.

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