Lipid Layer Structure Research Articles

The Novel Myosin Motor, Myosin VC, Facilitates Stimulated Exocytosis in Rabbit Lacrimal Acinar Cells

The aim of this study was to establish the relationship between OST, tear film stability as assessed by NIBUT and subjective evaluation of the lipid layer thickness in a young, asymptomatic, sample group (N = 29). Non-invasive tear break-up time (NIBUT) and tear lipid layer structure were evaluated through a slit-lamp mounted Tearscope Plus. A self-calibrating infrared thermography camera was used to record two OST values (one immediately post-blink and one immediately pre the subsequent blink). The most common lipid layer pattern observed was the amorphous pattern (48.3%). Differences between post- and pre-blink OST values were observed (paired t-test; p < 0.001). Significant differences of pre-blink OST values were observed between the closed marmoreal group with that from the amorphous and flow groups (Tukey post hoc test, p < 0.05). There were no differences of NIBUT values between each lipid layer thickness (Kruskal–Wallis test; p = 0.152). A no significant tendency for higher OST in eyes with increased NIBUT was observed. This study suggests that higher OST values could be associated with thicker tear lipid layer in normal subjects. The lack of significant results in relation with tear film stability may be due to only normal subjects were included.

Corneal sensitivity and some properties of the tear film after laser in situ keratomileusis.

To investigate central corneal sensitivity, lipid layer structure of the precorneal tear film, and tear volume after laser in situ keratomileusis (LASIK). Central corneal sensitivity was measured using the Non-Contact Corneal Aesthesiometer. The aesthesiometer was mounted on a slit lamp and an airpulse of controlled pressure was directed onto the cornea. When central corneal sensitivity was reduced, a higher air pulse pressure was required to stimulate the cornea. The final central corneal sensitivity threshold measured was recorded in millibars. Tear lipid layer structure was assessed by optical interferometry and classified according to appearance using the Keeler Tearscope. Tear volume was measured using the phenol red cotton thread test. Subjects were recruited from a group of patients after LASIK who had experienced no complications (n=22). The average postoperative time was 14 weeks and measurements were taken on one eye. In bilateral cases, measurements were recorded from the right eye only. Average attempted correction was -6.30 D (range, -2 to -11 D). Age-matched controls were later recruited for central corneal sensitivity threshold (n=24). A second group of age-matched controls were recruited for tear volume and lipid layer structure (n=24). The median (range) was 1.1 mbars (0.2 to 4.3 mbars) after LASIK and 0.58 mbars (0.20 to 1.3 mbars) in the controls; the difference was statistically significant (P = .043). The lipid layer of the tear film tended to be thinner in eyes after LASIK compared with controls (P = .032). The mean (+/- SD) tear volume was 16.9 +/- 8.3 mm after LASIK and 19.8 +/- 7.1 mm in controls. This difference was not statistically significant (P = .492). At 14 weeks postoperatively, central corneal sensitivity was below normal levels and the tear lipid layer was thinner. The poorer quality lipid layer may predispose to symptoms of dry eye after LASIK.

The role of tear physiology in ocular surface temperature.

To determine whether the more rapid cooling of the tear film in dry eyes is related to other tear film parameters, a battery of tear physiology tests was performed on dry eye patients and control subjects. Tear evaporation rate was measured with a modified Servomed (vapour pressure) evaporimeter and ocular temperature with an NEC San-ei 6T62 Thermo Tracer in 9 patients diagnosed as having dry eye and in 13 healthy control subjects. Variability in temperature across the ocular surface was described by the temperature variation factor (TVF). Lipid layer structure and tear film stability were assessed with the Keeler Tearscope and tear osmolality was measured by freezing point depression nanolitre osmometry. The data were explored by principal component analysis. The subjects with and without dry eye could be separated into two distinct groups entirely on the basis of their tear physiology. Dry eye patients exhibited higher tear evaporation rates, osmolalities and TVF, lower tear film stabilities and poorer-quality lipid layers than the control subjects. A significant linear relationship was found to exist between tear evaporation rate and TVF for all subjects (R2 = 0.242, p = 0.024). Rapid cooling of the tear film in dry eyes appears to be related to the reduced stability of the tears and the increased rate of evaporation. The higher latent heat of vaporisation, associated with the increased evaporation in dry eyes, may account for the increased rate of cooling of the tear film in this condition.

Self-assembly of soluble proteins on functionalized lipid layers: a tentative correlation between the fluidity properties of the lipid film and protein ordering

New series of amphiphilic structures are designed to exhibit various fluidity properties when spread at the air–water interface. The influence of the molecular structure of these lipids on the process of two-dimensional (2D) crystallization of the B subunit of DNA gyrase, a soluble protein, is investigated in terms of size of the crystals produced, protein ordering, and crystallization kinetics. Whereas no difference is observed concerning the mean size of the protein 2D crystals obtained on the different lipid supports, the ultimate protein ordering observable by electron microscopy using the negative-staining technique is more regularly attained with some of these new lipids. The most interesting point results from large discrepancies in crystallization kinetics as highly-ordered protein 2D crystals form within 6–24 h depending on the lipid layer structure. Thus, these new lipids reveal of special interest when studying proteins that suffer from extended incubation time at 4°C or higher temperature and lose their functionality.

Tear lipid layer structure and stability following expression of the meibomian glands

SummaryIn a masked investigation, tear lipid layer structure and non‐invasive break‐up time (NIBUT) of both eyes of 40 normal subjects were assessed with the Keeler Tearscope® after unilateral manual expression of meibomian fluid from the lower lid. The HIRCAL grid (modified keratometer mire) provided the additional measure of tear thinning time (TTT). Twenty untreated normal subjects formed the control group. No difference in lipid layer structure or stability was observed between the right and left eyes of the controls. The NIBUT of the treated eyes was significantly higher than that of the untreated contralateral eyes which was, in turn, greater than that of the control eyes. Lipid layer thickness in the treated eyes was significantly higher than that in the untreated contralateral eyes and the controls but did not differ between the latter two groups. The TTT of the treated eyes was not significantly different from that of the untreated contralateral eyes but both were significantly higher than that of the controls. Unilateral meibomian gland expression results in increased lipid layer thickness and tear stability. A possible reason for the slight increase in tear stability in the untreated contralateral eyes is a complimentary reflex lacrimation induced by mechanical stimulation of the treated eye. Differences between the results of the Tearscope® and HIRCAL grid are attributed to differences in the techniques of tear stability measurement.

Tear lipid layer structure and stability following expression of the meibomian glands

In a masked investigation, tear lipid layer structure and non-invasive break-up time (NIBUT) of both eyes of 40 normal subjects were assessed with the Keeler Tearscope after unilateral manual expression of meibomian fluid from the lower lid. The HIRCAL grid (modified keratometer mire) provided the additional measure of tear thinning time (TTT). Twenty untreated normal subjects formed the control group. No difference in lipid layer structure or stability was observed between the right and left eyes of the controls. The NIBUT of the treated eyes was significantly higher than that of the untreated contralateral eyes which was, in turn, greater than that of the control eyes. Lipid layer thickness in the treated eyes was significantly higher than that in the untreated contralateral eyes and the controls but did not differ between the latter two groups. The TTT of the treated eyes was not significantly different from that of the untreated contralateral eyes but both were significantly higher than that of the controls. Unilateral meibomian gland expression results in increased lipid layer thickness and tear stability. A possible reason for the slight increase in tear stability in the untreated contralateral eyes is a complimentary reflex lacrimation induced by mechanical stimulation of the treated eye. Differences between the results of the Tearscope and HIRCAL grid are attributed to differences in the techniques of tear stability measurement.

Laser Raman spectroscopy of lipid-protein systems Differences in the effect of intrinsic and extrinsic proteins on the phosphatidylcholine Raman spectrum

Laser Raman spectroscopy is used to examine the interactions of intrinsic and extrinsic proteins with the lipid layer structure. The interactions of cytochrome c and cytochrome c oxidase with lipids have been well established by others using a variety of techniques. Cytochrome c is thought to act as an extrinsic membrane protein while cytochrome c oxidase is thought to act as an intrinsic membrane protein. The lipid-cytochrome c and lipid cytochrome c oxidase systems are used to assist in interpreting the spectral changes due to extrinsic and intrinsic protein interactions. The two types of proteins examined produced differential changes in the lipid hydrocarbon CH stretch Raman modes for both dimyristoyl and dipalmitoyl phosphatidylcholine. The plasma proteins albumin and fibrinogen were also found to differentially affect the lipid hydrocarbon CH stretch Raman modes. These proteins appear to interact with lipids in an extrinsic manner different from that of cytochrome c.

Laser Raman spectroscopy of lipid-protein systems differences in the effect of intrinsic and extrinsic proteins on the phosphatidylcholine Raman spectrum

Laser Raman spectroscopy is used to examine the interactions of intrinsic and extrinsic proteins with the lipid layer structure. The interactions of cytochrome c and cytochrome c oxidase with lipids have been well established by others using a variety of techniques. Cytochrome c is thought to act as an extrinsic membrane protein while cytochrome c oxidase is thought to act as an intrinsic membrane protein. The lipid-cytochrome c and lipid cytochrome c oxidase systems are used to assist in interpreting the spectral changes due to extrinsic and intrinsic protein interactions. The two types of proteins examined produced differential changes in the lipid hydrocarbon C-H stretch Raman modes for both dimyristoyl and dipalmitoyl phosphatidylcholine. The plasma proteins albumin and fibrinogen were also found to differentially affect the lipid hydrocarbon C-H stretch Raman modes. These proteins appear to interact with lipids in an extrinsic manner different from that of cytochrome c.