A comparative evaluation of three different ultrasound frequencies for phacoemulsification of hard cataract

Phacoemulsification is the most commonly used procedure in the cataract surgery.1 It uses high intensity ultrasound energy for fragmentation and emulsification of the lens. With advancement of  surgical devices and techniques the safety and efficacy index of the procedure has increased dramatically.

However, higher grades of cataract require higher ultrasound energy resulting in more effective phaco time (EPT) and greater corneal endothelial cell density loss (ECDL). The aim is to remove cataract efficiently with highest safety to the eye i.e. lowest incidence of per-op and post-op complications.

For per-op evaluation of any phaco modality the amount of energy used is assessed. Effective Phaco Time is defined as total time taken to surgically remove the cataract using continuous 100% phaco power.

Higher effective phaco time thus leads to many other complications of phacoemulsification, most common of which is endothelial cell density loss.2,3 Therefore using optimal frequencies for hard cataract is most important.

The thickness and corneal transparency are maintained by a barrier function and active fluid pump action of endothelial cells.4Intraocular manipulations during phacoemulsification and fluid and lens fragment turbulence may lead to endothelial cell damage.5

An evaluation of ECDL is an important parameter to assess corneal endothelial insult during the procedure.

Basically, phacoemulsification is ultrasound based dissolution of lens matter. The piezoelectric crystal imparts a specific frequency vibratory motion to the phaco tip which when interacts with the lens matter in a fluid based environment leads to disintegration and dissolution of the cataractous lens. It is in accordance with the principles of physics that subjecting a solid to a frequency matching its internal resonant frequency would lead to disintegration of intermolecular bonds and make it easily aspirable. Biological experiments have shown supporting evidence in other human tissue.6

As the hardness of lens increases, the physical and chemical properties of lens also change and thus require change in frequency. However different machines though in range of 22-55 KHz use same ultrasonic frequency for higher grades of cataract hence increasing the effective phaco time of phacoemulsification.1,7,8

In a pilot study, conducted at this institution we found lower effective phaco time with use of higher frequency ultrasound.3

Based on the results of the same, a registered trial was conducted which proved that use of 42 KHz frequency lowered the EPT and protected the endothelium more than 28 KHz in moderate and hard cataract.9

Another study evaluating the use of 28 KHz, 42 KHz, 53 KHz has shown lower EPT with 53 KHz.

The ultrasound energy and time needed in hard cataract is more as compared to soft cataract thus leading to more risk of surgical induced trauma and more corneal endothelial dysfunction. Lower energy is delivered in the eye if effective phaco time is less thus leading to clearer cornea with better visual rehabilitation.10

Hence, this study is being conducted in Hard cataract (LOCS III Grade 5.6-6.9) comparing the effect of  higher frequency on per-op and post-op parameters esp. EPT and ECDL to enable us to choose ideal frequency for these cases.

RESEARCH QUESTION

 Is there any difference in effective phacoemulsification time and endothelial cell density loss between three different ultrasound frequencies in Hard Cataract (LOCS III Grade 5.6-6.9)?