Comparison of corneal thickness measurements using ultrasound pachymetry, ultrasound biomicroscopy, and digital caliper in frozen canine corneas

Abstract

The purpose of this study was to evaluate the clinical efficacy among ultrasound pachymetry (UP), ultrasound biomicroscopy (UBM), and manual measurement (MM) with digital caliper by comparing corneal thickness (COT) values obtained on frozen canine corneas ex vivo. The COT was measured using UP, UBM, and MM in 8 enucleated normal canine eyes frozen at -20℃ for 4 weeks. After thawing at room temperature for 2 hrs, the COT values were obtained from five sites in each cornea: central corneal thickness (CCOT), thickness at the 3, 6, 9, and 12 o'clock positions ii (3COT, 6COT, 9COT, and 12COT, respectively). For each device, measurements were performed three times at each designated site by one operator. The mean CCOT was 839.0 ± 138.2, 857.6 ± 127.9, and 849.1 ± 132.8 μm for UP, UBM, and MM, respectively. There was no statistically significant difference among the measurements by all three devices. The statistical agreement among these devices was also shown to be good according to Bland-Altman plots. In addition, the values measured on the peripheral sites of the cornea (3COT, 6COT, 9COT, and 12COT) also revealed no significant differences among the three devices. The difference between CCOT and peripheral corneal thickness (PCOT) was also statistically insignificant. Based on the results of the present study, the UP, UBM, and MM measurements showed statistically similar COT values. The UBM and UP provided accurate and reliable measurements comparable to MM, and could be used effectively for clinical COT measurements. LL Limbus to limbus LoA Limits of agreement MM Manual measurement PCOT Peripheral corneal thickness SD Standard deviation UBM Ultrasound biomicroscopy UP Ultrasound pachymetry 3COT

Corneal thickness and anterior chamber depth of the normal adult horse as measured by ultrasound biomicroscopy

“…This differs from a recent report in dogs in which the two techniques were found to produce similar central corneal thickness measurements with strong agreement between methods 21 . Another study that compared ultrasonic pachymetry to UBM in the assessment of corneal thickness of frozen canine corneas indicated that UBM consistently resulted in greater corneal thickness measurements 22 . As previously discussed, the accuracy of ultrasonic pachymetry in determination of corneal thickness is dependent upon the set velocity of the instrument being consistent with the speed of sound through the measured tissue 23 …”

“…21 Another study that compared ultrasonic pachymetry to UBM in the assessment of corneal thickness of frozen canine corneas indicated that UBM consistently resulted in greater corneal thickness measurements. 22 As previously discussed, the accuracy of ultrasonic pachymetry in determination of corneal thickness is dependent upon the set velocity of the instrument being consistent with the speed of sound through the measured tissue. 23 The widely used velocity of 1640 m/s for ultrasonic pachymetry is appropriate for the human cornea, though the speed of sound in both the canine and bovine cornea has been demonstrated to be less than this, and it is likely that the same is true for the horse.…”

The effect of central corneal thickness on intraocular pressure values using various tonometers in the dog

“…Ultrasonic pachymeters calculate CCT by measuring the length of time for an ultrasonic wave to pass through the cornea and reflect back to the transducer. Ultrasound pachymetry produces similar accuracy to optical coherence tomography (OCT) and is commonly used in veterinary ophthalmology due to affordability and ease of use 16–19 . Optical coherence tomography, although the most accurate means of gathering CCT data, is rarely used outside of an academic or research setting in veterinary medicine 20–22 .…”