Michael K. Smolek PhD, FARVO Director of Research

 

 

 

Some Images of Tear Film Lipid Layer Dynamics

 

A confocal microscopy view of the anterior surface of the normal, healthy human tear film is shown here. The image was acquired after a series of blinks to mix the tear film thoroughly. The typical appearance tends to have a grainy texture somewhat similar to tapioca pudding. The natural tendency is for lipid to pool on the surface of the aqueous layer, so when the lipid is well-mixed, it has the appearance of numerous small bright blobs of lipid on the surface. The pure lipid surface is more reflective than the aqueous tear surface, so lipid will appear brighter than aqueous in these photographs. The width of these images is the full frame width of the Nidek Technologies CS4 microscope.

This image is of another normal tear film. It was acquired after the eye has remained open for many seconds after a blink. You can begin to see the coalescing and pooling of the lipid near the bottom of the frame, and the lipid begins to lose some of the granular texture seen immediately after a series of blinks. Flow patterns are also beginning to emerge near the center and top of the image, indicative of gravity and evaporation at work. In general, horizontal layered patterns tend to be caused by gravity (lack of blinking), while vertical patterns tend to be due to blinking.

This is not a view of the tear film surface, but rather the view of the surface of a lipid/aqeuous emulsion created in a laboratory. The scale is approximately the same as the confocal images. Note that the granular appearance of the laboratory emulsion is very similar to that of the normal tear film that has not been recently disturbed by a blink.

In this view, the Meibomian glands have been stimulated by warmth and massage to secrete more lipid. With each blink, strands of lipid are pulled vertically from the gland opening and across the aqueous tear layer. After a few blinks, this pattern emerges in which you see a vertical curtain-like structure of lipid strands across the aqueous. Again, thicker lipid appears brighter, while the background aqueous layer alone would appear dark. The variation in brightness is probably indicative of a variation of the lipid density (thickness), with medium gray areas indicating thinner lipid coverage than the brigher white areas. If this eye is blinked so as to mix the lipid, the pattern would tend to become similar to the one seen in the first image.

This view shows a normal tear film, but with many inclusions that are most likely due to dust (specifically building construction dust). The larger inclusions are possibly eczema from the eyelids or maybe even sloughed off corneal epithelial cells. These particles are most likely coated with mucin, which creates a barrier around them composed of aqueous. Note that the lipid is repelled away from these particles. This action creates numerous open pores (fenestrations) through which aqueous can more readily evaporate. Therefore, this is a form of dry eye that in environmental in nature. Elimination of the particles that enter the eye would in turn eliminate the fenestrations in the lipid layer and reduce evaporation.

 

 

A magnified view of fenestrations in the lipid layer.

 

 

This is a case of moderate dry eye. Note that the lipid layer is not well-mixed and much of the surface is dark gray indicating little lipid coverage over the aqueous tear layer.

 

 

Another case of moderate dry eye caused by poor lipid coverage. Lipid is present as indicated by the bright regions, but it is poorly distributed. It is not entirely clear because of the complexity of the pattern, but some of the dark banding may be due to optical interference fringes that are very broad.

 

 

A very dramatic image of severe dry eye due to meibomian gland disease. Note that most of the surface is devoid of lipid and has a dark gray appearance. This large expanse of aqueous tears can rapidly evaporate without a lipid layer to protect it. The lipid that is seen occurs in isolated clumps, indicating that the lipid is turbid and does not disperse evenly into a thin layer as the normal lipid oil would do. Some of the lipid clumps have thin interference fringes suggesting that the accumulated lipid is very thick.

 

Do you have a need for the type of tear film analysis shown above? We are available for general consulting or collaborative research efforts.