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Anthony J Bron, Norihiko Yokoi, Yang Zhenghao, Georgi Asenov Georgiev; The Pre-Corneal Fluid Shell. What is the Effect of Drop Instillation?. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2496.
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© ARVO (1962-2015); The Authors (2016-present)
In an earlier study we found that the precorneal tear film (PTF), comprising its tear film lipid layer (TFLL) and mucoaqueous subphase (MAS), behaves as a “Fluid Shell”, integrated as one body and moving with the cornea during horizontal saccades (Yokoi et al. Ocul Surf. 2014). We further showed that the fluorescein-stained film is imprinted by meniscus-induced thinning (MIT) in pauses at the end of any saccade, made visible as dark arcs on return from horizontal saccades and dark bands after vertical saccades. Refractile, bright bands are revealed on return from a vertical saccade, resulting from corneal indentation by the lid margins. Here, we studied the effect of a saline drop on PTF behavior after horizontal or vertical saccades.
The effect of 25 μL drops of saline on PTF behavior was studied in the left eyes of 17 subjects without ocular surface disease, [8 males, 9 females, age: 31.4 ±8.4 (SD) years], The fluorescein-stained MAS and the TFLL were studied after vertical or horizontal saccades, using video-biomicroscopy and DR-1, video-interferometry, respectively.
In most instances the fluorescein-stained PTF and lower meniscus were visibly increased in volume. During blinking, the thickened MAS was dragged upwards by the upstroke of the blink but flowed back in the blink interval. When the eye was paused in upgaze or downgaze, a horizontal, dark band of PTF thinning, imprinted on the MAS, was revealed when the eye returned to the primary position. The PTF, expanded by drop instillation, was seen to flow following the return saccades, the dark bands sometimes forming a barrier to this flow. After drop instillation, video- interferometry demonstrated that the TFLL interference pattern after a horizontal and return saccade no longer resembled the primary pattern as it does in the untouched normal eye. Also, the return pattern continued to move, in the direction of the original saccade. This suggests a loss of cohesion between the TFLL and the MAS in this situation.
The mucoaqueous subphase of the tear film and its lipid layer are transiently dissociated after the instillation of a saline drop. Future studies will explore the behavior of tear substitutes on PTF integrity in normal subjects and in patients with ocular surface disease.
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