P. Cho et Sw. Cheung, Central and peripheral corneal thickness measured with the TOPCON specularmicroscope SP-2000P, CURR EYE R, 21(4), 2000, pp. 799-807
Purpose. Modern refractive surgery and follow up relies on a knowledge of c
orneal thickness (CT) and shape, and the reliability of modern instrumentat
ion providing such data is important. This study sought to determine the pe
rformance of the TOPCON SP-2000P specular microscope in measuring CT. The a
ims of this study were: (a) to determine if there is any difference between
the CT results obtained from the first image, the clearest of three images
and the mean of measurements from three images; (b) to determine the corre
lation between central and peripheral CT and (c) to investigate the reliabi
lity (repeatability and reproducibility) of the SP-2000P in the determinati
on of central and peripheral CT.
Methods. The central and peripheral CT measurements shown on the first (f),
the clearest (c) of three images and the mean (m) CT shown in three images
captured with the SP-2000P of 43 subjects were compared. All images were c
aptured by the same examiner. Nineteen of the subjects (male) returned on a
nother day and measurements were taken by two examiners.
Results. fCT, cCT and mCT were not significantly different from each other.
The intraclass correlation coefficients (ICC) between the three values wer
e > 0.9 for all corneal locations measured. However, the variability in the
differences between fCT and cCT was relatively greater for peripheral CT (
except temporal). The peripheral CT values obtained were all significantly
greater than the central CT, and statistically significant correlations wer
e found between the central and each of the peripheral thickness. There was
no statistically significant between-visit or between-examiner differences
in the central or peripheral CT. The ICC values for between-visit differen
ces for central and temporal measurements were > 0.9 but for the other corn
eal locations, the ICC values were 0.81 to 0.88. For between-examiner diffe
rences, the ICC value was 0.82 for inferior CT and > 0.9 for the other four
CT.
Conclusions. Differences in CT measurements obtained from the first and cle
arest images captured by the SP-2000P were not statistically significant bu
t can be clinically significant for peripheral CT. We therefore suggest the
use of the CT value obtained from the clearest of three images. For every
unit change in central CT, there is an approximately equivalent change in p
eripheral CT. Based on the ICC values, the SP-2000P showed very good repeat
ability and reproducibility in the determination of central CT. For the det
ermination of peripheral CT, the repeatability and reproducibility of the S
P-2000P were good and reasonably good respectively. These findings have rel
evance to the measurement of the cornea before and after refractive surgery
.