Dynamic changes in the air-tear film interface modulation transfer function.

PURPOSE

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.

METHODS

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

RESULTS

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.

CONCLUSION

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