Date: 25 Sep 2009

Dynamic changes in the air–tear film interface modulation transfer function

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To determine objectively the changes in the optical quality of the air–tear film interface by measuring the modulation transfer function (MTF) of the anterior surface of the film.


Air–tear film interface MTF was determined from the wavefront aberration obtained from corneal elevation maps and custom software. MTF and Strehl ratio were derived for 3 (photopic) and 7 (mesopic) mm pupils, in 14 healthy young subjects at various intervals after a blink (1 second up to 15 seconds). Fluorescein tear break-up times (TBUT) measured by a standard method were determined for clinical correlation purposes


The MTF profile varies as a function of the time post-blink, showing the highest values at 6–7 seconds. Strehl ratio showed a similar dynamic pattern reaching its maximum level, on average, at 6.2 ± 0.4 seconds after a blink. Minimum levels occur from 10 seconds after a blink, worsening with larger times. Strehl ratio values were correlated with clinical TBUT: minimum values were found to occur earlier for those subjects with shorter TBUT and vice versa.


Air–tear film interface MTF and Strehl ratio estimation are useful metrics for optical quality analysis of tear film changes.

The authors have no proprietary interest in any of the materials mentioned in this article.