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Effect of Fluorescein dye staining of the
tear film on Scheimpflug measurements of
central corneal thickness
Oliver Findl
1
2
1,2,
Nino Hirnschall
1,2,
Alja Crnej
2
VIROS Vienna Institute for Research in Ocular Surgery,
Hanusch Hospital, Vienna, Austria
Moorfields Eye Hospital, London, UK
Financial interest: none
OF is scientific advisor to Alcon, AMO, Croma & Carl Zeiss Meditec AG
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.
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
Methods
• Prospective randomised controlled study
• 30 eyes of 15 patients (8 female, 7 male)
Methods
3 x rotating Scheimpflug imaging + 3 x PCI measurement
Instilling 0.25% fluorescein +
0.5% proxymetacaine hydrochloride
Rotating Scheimpflug imaging + PCI measurement
Rotating Scheimpflug
imaging + PCI
after 5min, 10min, 20min,
40min, 60min, (120min)
Irrigation with 2ml BSS
Rotating Scheimpflug imaging +
PCI
Without Fluorescein
With Fluorescein
Results
Continuous measurement group
CCTScheimpflug
(SD) in µm
CCTPCI (SD) in
µm
Baseline
539.1 (32.2)
519.0 (33.1)
1min
585.7 (29.7)
520.6 (33.2)
5min
570.1 (31.6)
519.7 (33.0)
10min
560.8 (35.0)
519.8 (32.8)
20min
550.1 (33.4)
520.0 (32.7)
40min (10
patients)
545.0 (33.8)
523.2 (38.7)
Irrigation group
CCTScheimpflug
(SD) in µm
CCTPCI (SD)
in µm
Baseline
536.5 (34.7)
519.4 (33.9)
1min
586.5 (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
Results
CCT difference (PCI) in µm
70
60
50
40
30
20
10
0
0
10
20
30
40
50
60
CCT difference (Scheimpflug) in µm
70
Results
Number of patients (%) with a fluorescein
layer +5µm compared to baseline
Subjects with Fluorescein layer (%)
100
80
60
40
20
0
0
20
40
60
80
100
120
140
160
time after applying Fluorescein (min)
Fluorescein layer -> more than 5µm difference to the baseline measurement
Results
Schirmer 2 results (sec)
20
18
16
14
Pearson= 0.72
12
10
8
0
20
40
60
80
100
120
time after applying Fluorescein (min)
140
160
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