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Daniel Hockaday Pamplin, Luis A V Carvalho, Holly Butler Hindman, Geunyoung Yoon, James Zavislan, James Aquavella; Novel Multi-Colored Placido Disk Based Videokeratoscopy. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1983. doi: https://doi.org/.
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Conventional monochromatic placido disk experiments which measure tear film break-up struggle to collect meaningful data once the tear surface becomes too irregular. The rings reflected from the placido mire eventually become indistinguishable from one another. The purpose of this experiment is to evaluate the performance of a three-color channel placido mire videokeratoscope in objectively detecting non-invasive tear film break-up.
A placido disk with sequential transparent red, green, and blue rings separated by opaque black rings was evenly illuminated by a bank of narrow band LEDs attached to the disk along the periphery. There are 10 red (645 nm), 10 green (515 nm), and 10 blue (460 nm) LEDs attached to three switches which allowed individual control. The light from the LEDs was scattered off of a diffuse housing to uniformly illuminate the back of the placido disk. A color camera that can record up to 20 frames per second captures the tear film break up. The images were separated into the individual RGB channels where they were registered, processed and compared to the combined (traditional) data. To assess the performance of the system, a contact lens was attached to a cornea-shaped dome. The structure containing the dome was flooded with artificial tears and drained. Afterwards, the tears on the contact lens evaporated. This process simulated tear film evaporation from a real eye. The evaporating tear film imaged the disk to a color video camera which recorded for over 6 minutes per trial.
In each single-color channel, spacing between the adjacent rings increased by a factor of 5. The greater area in the nulls allowed meaningful data over longer timespans: the individual RGB patterns did not spread into one another over the entire 6 minutes due to the increased spacing between the rings. However, conventional placido disk system’s data becomes unreliable once the tear film breaks up into one another. This occurred at 5.8 ± 2.6 seconds for the traditional illumination pattern.
The multichannel videokeratoscope had all of the benefits of a conventional monochromatic system. The ability to look at the images in individual channels allowed the data to be reliable when considerable tear break-up occurred. This tear-imaging system provided a reliable tool to better quantify tear film topography measurements as well as to improve our understanding of tear film break-up mechanisms.
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