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Mark Alberti, Morten D De La Cour, Javier Cabrerizo; The effect of positioning on gas-endothelial contact in an ex-vivo model. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5685.
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Endothelial keratoplasty requires an adequate anterior chamber gas fill. The optimal gas bubble size is currently unknown and limited knowledge exists on how positioning affects the gas bubble configuration. We seek to understand this relationship by focusing on the gas-endothelial contact in relation to a central graft.
In an anterior chamber model with a human donor cornea we injected different gas bubble fills and tilted the model in varying positions. Main outcomes were gas-endothelial contact area and inferior contact angle measured by optical coherence tomography (OCT). Additionally, we measured the linear height of injected bubbles. The OCT instrument (Heidelberg Spectralis SD-OCT) was tilted to measure the anterior chamber model in positions ranging 90° to -15°. For improved visualization of the contact angle we added Triamcinalone (1 mg/50 ml) to the anterior chamber fluid.
With a 43% anterior chamber gas fill (linear bubble height) the total endothelial contact area measured 16.6, 18.3 and 14.3 mm2 with upward gaze at 0°, 45° and 90°, respectively. Increasing gas fill to 79% markedly enlarged the contact area to 57.7, 72.5 and 62.9 mm2 with upward gaze likewise at 0°, 45° and 90°. A 43% gas fill covered 18.3%, 24.5% and 28.4% of a centrally placed 8 mm endothelial graft with the model positioned at 0°, 45° and 90° whereas a 79% gas fill covered 79.4%, 98.4% and 100%. Additionally, we found a correlation between contact angles and gas bubble size with more acute angles seen in smaller gas bubbles.
Tilting the OCT instrument demonstrates how positioning influences the gas bubble configuration. Because of the more acute contact angles seen with smaller gas bubbles, smaller bubbles have less endothelial contact than suggested by linear bubble height. A bigger bubble is better if contact area and graft coverage is of paramount interest.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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