Cornea

Graefe's Archive for Clinical and Experimental Ophthalmology

, Volume 248, Issue 1, pp 127-132

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

  • Teresa Ferrer-BlascoAffiliated withOptometry Research Group, Optics Department, Faculty of Physics, University of Valencia
  • , Santiago García-LázaroAffiliated withOptometry Research Group, Optics Department, Faculty of Physics, University of Valencia
  • , Robert Montés-MicóAffiliated withOptometry Research Group, Optics Department, Faculty of Physics, University of Valencia Email author 
  • , Alejandro CerviñoAffiliated withOptometry Research Group, Optics Department, Faculty of Physics, University of Valencia
  • , Jose M. González-MéijomeAffiliated withClinical & Experimental Optometry Research Lab, School of Sciences, Universidade do Minho

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Abstract

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.

Keywords

Tear Optical quality Ocular surface