Effect of Fluorescein dye staining of the tear film on Scheimpflug measurements of central corneal t...
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Oliver Findl 1,2, Nino Hirnschall 1,2, Alja Crnej 2 1 VIROS Vienna Institute for Research in Ocular Surgery, Hanusch - PowerPoint PPT Presentation


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Effect of Fluorescein dye staining of the tear film on Scheimpflug measurements of central corneal thickness. Oliver Findl 1,2 , Nino Hirnschall 1,2 , Alja Crnej 2 1 VIROS Vienna Institute for Research in Ocular Surgery, Hanusch Hospital, Vienna, Austria

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Effect of Fluorescein dye staining of the tear film on Scheimpflug measurements of central corneal thickness

Oliver Findl 1,2, Nino Hirnschall 1,2, Alja Crnej 2

1 VIROS Vienna Institute for Research in Ocular Surgery, Hanusch Hospital, Vienna, Austria

2 Moorfields Eye Hospital, London, UK

Financial interest: none

OF is scientific advisor to Alcon, AMO, Croma & Carl Zeiss Meditec AG


Background
Background Scheimpflug measurements of central corneal thickness

  • Fluorescein dye is commonly used in routine ophthalmic examination

    • staining epithelial defects of the cornea

    • break up time of the tear film

    • Goldmann applanation tonometry

  • Correct CCT measurement needed for:

    • corneal refractive surgery

    • diagnosis of corneal diseases (keratoconus)

    • to correct for systematic errors of IOP measurements using Goldmann applanation.


Cct measurement devices
CCT measurement devices Scheimpflug measurements of central corneal thickness

  • Pentacam: rotating Scheimpflug photographic

    • measures the thickness from the image, which is created from the back-scattered light from the corneal tissue

      => Influenced by fluorescein eye drops?

  • ACMaster: partial coherence interferometry (PCI)

    • gold standard for CCT measurement

    • measures distances between surface interfaces with a different refractive index


Methods
Methods Scheimpflug measurements of central corneal thickness

  • Prospective randomised controlled study

  • 30 eyes of 15 patients (8 female, 7 male)


Methods1
Methods Scheimpflug measurements of central corneal thickness

3 x rotating Scheimpflug imaging + 3 x PCI measurement

Instilling 0.25% fluorescein +

0.5% proxymetacaine hydrochloride

Rotating Scheimpflug imaging + PCI measurement

Irrigation with 2ml BSS

Rotating Scheimpflug imaging + PCI

after 5min, 10min, 20min, 40min, 60min, (120min)

Rotating Scheimpflug imaging + PCI


With Fluorescein Scheimpflug measurements of central corneal thickness

Without Fluorescein


Results
Results Scheimpflug measurements of central corneal thickness

Rotating Scheimpflug: 46.6µm difference

PCI: 1.6µm difference


Results1
Results Scheimpflug measurements of central corneal thickness

CCT difference (PCI) in µm

CCT difference (Scheimpflug) in µm


Results2
Results Scheimpflug measurements of central corneal thickness

Number of patients (%) with a fluorescein layer +5µm compared to baseline

Subjects with Fluorescein layer (%)

time after applying Fluorescein (min)

Fluorescein layer -> more than 5µm difference to the baseline measurement


Results3
Results Scheimpflug measurements of central corneal thickness

Schirmer 2 results (sec)

time after applying Fluorescein (min)


Conclusion
Conclusion Scheimpflug measurements of central corneal thickness

  • Scheimpflug imaging

    • Fluorescein dye causes intense back-scatter of light resulting in a measurement error

    • Irrigating the eye reduces this effect only insignificantly

  • PCI: is not influenced by altered or higher reflectivity

  • => Fluorescein eye drops MUST NOT be used prior to Scheimpflug imaging measurements


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