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Anthony J. Bron, Norihiko Yokoi, Georgi A. Georgiev, John M. Tifffany; The Lipid Layer Forms A Semi-rigid Carapace Over The Tear Film, Following Spreading In The Interblink. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2096.
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© ARVO (1962-2015); The Authors (2016-present)
To examine the transmission of force from the aqueous layer of the tear film to the tear film lipid layer (TFLL) following a horizontal saccade.
The interference pattern of the TFLL was studied in one eye of 6 normal subjects, using the DR-1TM videomeniscometer. Images were recorded continuously within a single interblink, to capture: i. the interference pattern with the eye in the primary position. The pattern was captured from the stable TFLL, after the spreading phase, at least 1 s after the upstroke of a blink. ii. -after a smooth pursuit movement to the temporal side - the change in patternwas recorded, immediately following a return saccade to the primary position
In all subjects the TFLL interference pattern failed to show substantial change comparing the first and second sequence in the primary position. At least 3 sequences were captured in each subject.
During the upstroke of a normal blink, the TFLL is spread over the aqueous subphase by surface tension forces. After about one second, spreading ceases and the pattern remains stable for the remainder of the interblink. We interpret this stability to be due to cooling of the TFLL in the interblink, resulting in increased viscosity or stiffness of TFLL. We have proposed that this stiffness explains the relative constancy of the interference pattern in the normal eye, over several cycles of consecutive blinks, prior to a mixing event with the meibomian reservoir. After this, the cycle begins again. In the present study it appears that the force transmitted to the TFLL in the saccade is insufficient to displace it, depite imparting an additional stress during the eye movements, when the cornea rotates about an axis centred at the centre of the globe. We conclude that the TFLL forms a thin, semi-rigid, viscoelastic carapace over the aqueous phase of the tear film, which is sufficiently stiff to resist forces transmitted to it in the saccade. We predict that changes in aqueous layer thickness or the fluidity of the TFLL will alter this response and may be of diagnostic use in the presence of an aqueous deficient dry eye or TFLL deficiency.
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