Evaluation of acoustic wave propagation velocities in the ocular lens and vitreous tissues of pigs, dogs, and rabbits

Objective - To evaluate propagation velocity of acoustic waves through the lens and vitreous body of pigs, dogs, and rabbits and determine whether there were associations between acoustic wave speed and age, temperature, and time after enucleation. Sample population - 9 pig, 40 dog, and 20 rabbit lenses and 16 pig, 17 dog, and 23 rabbit vitreous bodies. Procedure - Acoustic wave velocities through the ocular structures were measured by use of the substitution technique. Results - Mean sound wave velocities in lenses of pigs, dogs, and rabbits were 1,681, 1,707, and 1,731 m/s, respectively, at 36°C. Mean sound wave velocities in the vitreous body of pigs, dogs, and rabbits were 1,535, 1,535, and 1,534 m/s, respectively, at 38°C. The sound wave speed through the vitreous humor, but not the lens, increased linearly with temperature. An association between wave speed and age was observed in the rabbit tissues. Time after enucleation did not affect the velocity of sound in the lens or vitreous body. The sound wave speed conversion factors for lenses, calculated with respect to human ocular tissue at 36°C, were 1.024, 1.040, and 1.055 for pig, dog, and rabbit lenses, respectively. Conclusions and clinical relevance - Conversion factors for the speed of sound through lens tissues are needed to avoid underestimation of the thickness of the lens and axial length of the eye in dogs during comparative A-mode ultrasound examinations. These findings are important for accurate calculation of intraocular lens power required to achieve emmetropia in veterinary patients after surgical lens extraction.