Author Topic: Tear Film analysis - how to interpret the results?  (Read 448 times)

jonnynesbitt

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Tear Film analysis - how to interpret the results?
« on: December 30, 2016, 01:04:55 am »
Does anybody have any experience of understanding the results of the Tear Film Break-up areas and quality etc..
Thanks
Jon

Grant

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Re: Tear Film analysis - how to interpret the results?
« Reply #1 on: August 31, 2017, 09:41:48 am »
The Tear Film Quality map shows the tear film surface quality (TFSQ) over the surface of the eye at a given point in time.   This is basically a measurement at each point on the eye of local variability in the ring width.  Typically local tear film break down is characterized by a large variability in the ring width.

Mathematically the TFSQ at a point is calculated by finding the standard deviation (SD) in the widths of the surrounding rings 10 degrees either side of the point.  The TFSQ  at the point is then calculated as percentage of the square of the SD normalized by the average width (W) between the rings:

TFSQ = 100 * (SD / Average W)^2

A local TFSQ value of greater than 0.3 typically indicates that there is some tear film breakup going on in that area.

The TFSQ Area attribute (which is graphed over time in the bottom graph for Tear Film Exams) is the percentage of the eye, within a 7mm chord, that has a local TFSQ value greater than 0.3 (ie is in breakup).  So a value of 5 in the graph indicates that 5% of the eye surface has tear film breakup.

The Auto Tear Film Breakup Time (TBUT) is calculated by finding the first two consecutive frames where the TFSQ Area exceeds 5%.

The Tear Film Breakup map shows the time (in seconds) until the TFSQ exceeds 0.3 for each point on the cornea (ie the time till breakup).   It is useful for understanding how the tear film breakup progresses over time.