Comprehensive Ophthalmology Free Papers - aioseducation

Comprehensive Ophthalmology Free Papers
6.0.3) using the corneal reflectivity profile. The central cornea was identified
from the peak of the reflectivity profile on the horizontal axis. The calipers were
then aligned on the peak reflections at the anterior and posterior boundaries
of the cornea, in the axis of the corneal apex. The two measurements were
averaged for right eye only to avoid any bias. Ultrasound testing was also
performed twice for right eye only. The cornea was first anesthetized with one
drop of pro-paracaine hydrochloride 0.5% (Paracain, Sunways, India). It would
be very difficult to assess whether the two instruments took measurements
at the same exact location. However, to ensure that ultrasound CCT was
measured at the center of the cornea, we placed the probe tip at the very center
of the cornea and kept the pachymeter horizontal. If the patient moved and
the probe decentered, then the measurements were repeated. Ultrasound
pachymetry was performed in each case by one of two authors (Dr. MJ and Dr.
AJ) to measure the inter individual variability. Ten sequential measurements
were obtained from the center of the cornea and averaged. Values with standard
deviation (SD) of 5 micron or less were considered suitable for inclusion.
Statistical Analysis. Pearson correlation was used to assess the strength of
correlation of the two measurements. The measurements were also compared
with the paired t-test. Since AS-OCT measurements involved caliper
measurements made by the observer all eyes were remeasured by a second
observer to study inter observer agreement.
RESULTS
Mean age was 32.9 +/- 16.1 years with 41 male and 49 female patients. Mean CCT
with ultrasonic pachymetry for observer 1 and 2 were 523.2 +/- 28.6 microns
and 522.5 +/- 30.9 respectively. Mean CCT with AS-OCT for observer 1 and 2
were 526.6 +/- 26.7 and 525.8 +/- 26 microns respectively. The value with AS
OCT is slightly higher than with ultrasonic pachymetry but the P value is not
significant. The P value was 0.405 and 0.436 between ultrasonic pachymetry
and AS OCT for observer 1 and 2 respectively which is not significant.
Correlation coefficient between ultrasonic pachymetry and AS-OCT was 0.95
(observer 1) and 0.93 (observer 2). Correlation between the two observers, to
assess the inter individual variability for ultrasonic pachymetry and AS-OCT
was 0.96 and 0.97 respectively.
DISCUSSION
Doughty and Zaman 2 (300 patients) found that mean normal CCT was
530 microns for slit-lamp-based optical pachymetry and 544 microns for
ultrasonography. Subsequent reports using retinal OCT adapted for the
anterior segment 3–5 suggest a similar effect; other authors have reported no
significant difference 6 or even thicker measurements of CCT by OCT. 7
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