Comparison Of Energy Application Of Nano Laser And Ultrasound In Cataract Surgery

In cataract surgery, technologies are used that make it possible to shred the clouded and often no longer soft lens in the eye and then to suck it out of the eye through a small-lumen cannula. The gold standard most commonly used today is the ultrasound application in the so-called phacoemulsification. An alternative to this is photofragmentation using nano-laser technology. In the present consideration, the question of how large the energy input or the energy deposition in the eye is with the respective technology is to be investigated. The focus is on the, compared to phacoemulsification, still young and innovative laser technology.

Dr. Walker and Prof. Parasta will be speaking on behalf of Nano Laser and Ultrasound in Cataract Surgery

Literature used will be:

[1] H. Höh and A. Gamael; Der Ophthalmologe volume 99, pages 188–192 (2002)

[2] Physikalisch Technische Bundesanstalt – Annual report - Erstmalige Messung des Leistungseintrages eines Phakoemulsifikationsgerätes in das Auge; 19.06.2012 Jahresbericht 2012

[3] A. Vogel, S. Busch, U. Parlitz; J. Acoust. Soc. Am. 100 (1), July 1996

An ultrasonic handpiece moves the ultrasonic needle at high frequencies, usually between 27 and 45 kHz, i.e. 27,000 - 45,000 times per second. With most phacoemulsification systems based on ultrasound, it is possible to read out the electrical energy given off during the treatment to the handpiece. For example, values ​​of approx. 50 J with a maximum load on the oscillating crystals in the ultrasonic handpiece for 1 s are quite common. In a publication by Höh and Gamael [1], application times of 0.7; 9.6; 23.7; 39.3 and 68.9 seconds (core hardness divided into 0 to 4; 0, 1, 2, 3 and 4). The energy values ​​read out with the ultrasound device were: 7.2; 96.7; 237.3; 392.5 and 688.6 Joules.

Dimensions are: outer diameter: 1.0 mm, inner diameter 0.75 mm, diameter of the hole opening: 0.65 mm. The outlet opening has a cross section of 0.33 mm2. The spherical surface which is an ellipsoid, since the starting point of the plasma is a surface and not a point, cube or sphere. Therefore, the mean of 0.5 mm (distance) and 0.75 mm (distance) is used to take into account the fact that the source is extended (max. 1 mm x 1 mm). As a result, the surface is calculated as: 2.45 mm2 (4/2 x Pi x r2 with r = 0.625 mm). This is the complete area of ​​the shock wave front above the absorption area. The proportion of the shock wave that can exit through the opening (F = 0.33 mm2) is 13%. Result: energy portion of 0.4 mJ per pulse.

In the case of photo fragmentation using nano-laser technology, individual shock waves are generated. Energies used for the plasma ignition are from a min. of 3 mJ to approx. 5 mJ; Higher energy values are only used in few exceptions. This is comparable to the settings for ultrasonic phacoemulsification. Nano-laser technology limits the max. shock waves emitted to the eye to 1500. The resulting energy is at least 0.9 J to a max. of 2.5 J. The energy released from the application handpiece into the eye during photofragmentation with nano-laser is less than the energy delivered by the laser.

The energy actually emitted into the eye is approx. 8% of the laser energy, which can be set on the system and read off as total energy after surgery.