TEAR FILM TOPOGRAPHY MEASURED WITH TWO NOVEL TECHNIQUES: SHACK-HARTMANN WAVEFRONT TOPOGRAPHY AND VIRTUAL RETRO-ILLUMINATION

Title TEAR FILM TOPOGRAPHY MEASURED WITH TWO NOVEL TECHNIQUES: SHACK-HARTMANN WAVEFRONT TOPOGRAPHY AND VIRTUAL RETRO-ILLUMINATION
Author, Co-Author Fan Zhou, Larry Thibos, Donald Miller, Arthur Bradley
Topic
Year
2003
Day
Thursday
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Affiliation
Abstract PURPOSE: Real-time monitoring of tear film topography provides a valuable tool for understanding tear break-up (TBU), the impact of TBU on the optical and visual performance of the eye, and for testing the efficacy of dry eye medications.

METHODS: High-resolution Shack-Hartmann (SH) sensing technology was adapted to measure corneal topography and surface aberrations (Zhou, ARVO 2003). The tear film was sampled every 130 micron (about 1400 samples across a 5.5 mm pupil) and topography determined with sub-micron accuracy. In our novel virtual retro-illumination (VRI) technique, we imaged the corneal reflection that is typically used to generate Purkinje I, but in this application we image the tear film plane. Thus instead of distorting the Purkinje image, TBU generates high contrast intensity fluctuations in a high resolution (about 50,000 samples) tear film image. Subjects were instructed to blink normally or suppress blinking while wavefront topography and VRI images were taken simultaneously in real-time.

RESULTS: Displacement of the SH point images was used to quantify changes in the wavefront reflected from the tear film. From this the tear film surface topography was reconstructed. The high resolution high sensitivity of the VRI technique allowed us to visualize the tear surface dynamics and resolve even small (< 30 micron) lipid deposits on/near the tear surface. The tear structure illustrated by VRI correlated well with the displacement/blur of SH dots in wavefront topography. In general, the tear integrity degraded during blink suppression. In worst cases, the tear film broke into a honey-comb pattern and its corresponding wave aberrations demonstrated drastic increase of higher order aberrations. The sensation of tear drying was not well correlated with the optical assessments.

CONCLUSIONS: We have developed two novel high resolution methods for examining the topography of the pre-corneal tear film surface. Both methods are highly sensitive to surface changes that accompany TBU.

ADDITIONAL COMMENTS: STTR EY 013888; NIH EY 05109
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