Purpose:
Mechanisms of tear film breakup are not well understood andcontroversial. A method of simultaneous imaging of fluoresceinbreakup and the lipid layer is described, providing unique informationon the role of the lipid layer.
Methods:
After instillation of 5ul of 2% fluorescein solution, a central,4.5 mm diameter, area of the cornea is illuminated at normalincidence with blue light. Light from the tear film is separatedusing beam splitters into blue reflected and green fluorescentcomponents and recombined on a video camera recording at 10Hz. Blue and green interference filters were used to eliminateblue reflected light from the green fluorescent image.
Results:
Illustrative images from the 20 non contact lens wearing subjectsare shown in Figures 1 and 2. Fluorescein and (contrast-enhanced)lipid images are shown at left and right respectively. Correspondencebetween the fluorescein and lipid images can be observed inthese images. Structures in the lipid layer are visible beforeany corresponding breakup occurs, indicating that these structuresare a cause rather than a consequence of breakup. The dark lipidspecks in Figure 1 probably represent thin lipid rather thandebris, as they did not cause darkening of the fluorescenceat early times after the blink. Evaporation through these thinlipid specks may have caused tear thinning and breakup.
Figure 1
Figure 2
Conclusions:
This imaging system provides novel information about mechanismsof tear film breakup. It also provides insights into other featuresof the tear film, such as possible mucus strands and burstingbubbles.
Keywords: cornea: tears/tear film/dry eye • microscopy: light/fluorescence/immunohistochemistry • imaging/image analysis: non-clinical