In situ measurements of attenuation coefficient for evaluating the hardness of cataract lens by a high frequency ultrasonic needle transducer

A cataract is a clouding of the lens in the eye that affects vision. Phacoemulsification is the mostly common surgical method for treating cataracts, and determining the optimal phacoemulsification energy is dependent on measuring the hardness of the lens. This study explored the use of an ultrasound needle transducer for in situ minimally invasive measurements of ultrasound attenuation coefficient to evaluate the hardness of cataract lens. A 47 MHz high frequency needle transducer with a diameter of 0.9 mm was fabricated by a polarized PMN-33%PT single crystal in the present study. The attenuation coefficients at different stages of artificial porcine cataract lens were measured using the spectral shift approach. The hardness of the cataract lens was also evaluated by mechanical measurement of its elastic properties. The results demonstrated that the ultrasonic attenuation coefficient was increased from 0.048±0.02 to 0.520±0.06 dB/mm-MHz corresponding to an increase of Young's modulus from 6 to 96 kPa as the cataract further developed. In order to evaluate the feasibility of combining needle transducer and phacoemulsification probe for real time measurement during cataract surgery, the needle transducer was mounted on the phacoemulsification probe for vibration test. The results indicated that there was no apparent damage to the tip of needle transducer and the pulse-echo test showed a good performance in sensitivity was maintained after the vibration test.