Effect of corneal hydration on ultrasound velocity and backscatter.
The cornea's acoustic properties (speed-of-sound, backscatter, attenuation) are related to its state of hydration. Our aim was to determine these properties as a function of corneal hydration using high-frequency ultrasound. Bovine corneas were suspended in a Dexsol-equivalent corneal preservation medium at 33 degrees C and then immersed successively in 75%, 50% and 25% medium and distilled water. Using a 38-MHz focused ultrasound transducer, we measured speed-of-sound and corneal thickness (n = 8) and stromal backscatter (n = 6) after 45-min immersion in each medium. Corneal speed-of-sound was modeled as a function of corneal thickness. We found the mean speed-of-sound to be 1605.4 +/- 2.9 m/s in normotensive medium. The maximum observed speed-of-sound was 1616 m/s. As we decreased medium tonicity, the cornea swelled and the speed-of-sound decreased, reaching 1563.0 +/- 2.2 m/s in water. Average corneal thickness increased from 969 +/- 93 microm in 100% medium to 1579 +/- 104 microm in water. Going from 100% medium to water, stromal backscatter (midband-fit) increased from -60.0 +/- 0.8 dBr to -52.5 +/- 3.5 dBr, spectral slope increased from -0.119 +/- 0.021 to -0.005 +/- 0.030 dB/MHz and attenuation coefficient decreased from 0.927 +/- 0.434 to 0.010 +/- 0.581 dB/cm-MHz. The observed correlation between acoustic backscatter and attenuation with the speed-of-sound offers a potential means for more accurate determination of speed-of-sound and, hence, thickness in edematous corneas.
Silverman
Ronald H
RH
Department of Ophthalmology, Weill Medical College of Cornell University, New York, NY 10065, USA. ros2012@med.cornell.edu
Patel
Monica S
MS
Gal
Omer
O
Sarup
Aman
A
Deobhakta
Avnish
A
Dababneh
Haitham
H
Reinstein
Dan Z
DZ
Feleppa
Ernest J
EJ
Coleman
D Jackson
DJ
D000818:Animals; D001834:Body Water; D002417:Cattle; D003315:Cornea / Q000000981:diagnostic imaging* / Q000473:pathology; D015715:Corneal Edema / Q000000981:diagnostic imaging* / Q000473:pathology; D012029:Refraction, Ocular; D012815:Signal Processing, Computer-Assisted; D046509:Tissue Culture Techniques; D014463:Ultrasonography