1. 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 Effect of Fluorescein dye staining of the tear film on Scheimpflug measurements of central corneal thickness Financial interest: none OF is scientific advisor to Alcon, AMO, Croma & Carl Zeiss Meditec AG

2. Background 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.

3. CCT measurement devices 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

4. Methods Prospective randomised controlled study 30 eyes of 15 patients (8 female, 7 male)

5. Methods 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)

6. Without Fluorescein With Fluorescein

7. Results Continuous measurement group CCT Scheimpflug (SD) in µm CCT PCI (SD) in µm Baseline 539.1 (32.2)519.0 (33.1) 1min 585.7 (29.7)520.6 (33.2) 5min570.1 (31.6)519.7 (33.0) 10min560.8 (35.0)519.8 (32.8) 20min550.1 (33.4)520.0 (32.7) 40min (10 patients) 545.0 (33.8)523.2 (38.7) Irrigation group CCT Scheimpflug (SD) in µm CCT PCI (SD) in µm Baseline 536.5 (34.7)519.4 (33.9) 1min586.5 (44.3)521.7 (33.8) After irrigating 561.7 (39.5)520.7 (34.0) Rotating Scheimpflug: 46.6µm difference PCI: 1.6µm difference

8. Results CCT difference (PCI) in µm CCT difference (Scheimpflug) in µm

9. Results time after applying Fluorescein (min) Subjects with Fluorescein layer (%) Fluorescein layer -> more than 5µm difference to the baseline measurement Number of patients (%) with a fluorescein layer +5µm compared to baseline

10. Results time after applying Fluorescein (min) Schirmer 2 results (sec)

11. Conclusion 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