Lifting the lid on tear film dynamics: tear film movement upon vertical gaze change

Purpose: When examining the ocular surface, patients are required to look straight ahead and the effects of vertical eye movement on tear film behavior are not considered despite it being natural and common to change gaze without blinking. This exposes parts of the bulbar conjunctiva previously covered by the eyelids and therefore not covered by the tear film during the preceding blink. This study investigates how the tear film behaves when presented with newly exposed areas of ocular surface due to vertical eye movements. Methods: The tear film dynamics of a sequence of vertical open-eye gaze maneuvers (upgaze-downgaze) were studied in 15 participants with no ocular surface related complaints (OSDI <13) using the TearView infrared camera system. TearView detects the tear film based on natural infrared radiation emitted from the ocular surface. Interferometry was used to examine lipid layer behavior. In a subgroup (n = 3), eyelids were mechanically lifted using a finger to reveal bulbar conjunctiva. Results: Vertical eye movements exposed bulbar conjunctiva not covered by the tear film during the preceding blink. The fully formed tear film reacted by spreading toward the newly uncovered ocular surface area, thereby recoating it. This also occurred when the eyelids were mechanically lifted to reveal ocular surface previously beneath the eyelids. No apparent flow occurred from the menisci onto the ocular surface. Conclusions: The fully formed tear film is isolated from the meniscal tear and meibum reservoirs (a completely perched tear film). This tear film spontaneously spreads to cover ocular surface area that is newly exposed during vertical eye movements.