Cataract extractions and corneal measurements

October 5, 2013

Review of the first day of ESCRS 2013

Nano-laser phaco successful in cataract extraction


Nano-laser phacoemulsification with Nano Laser Phaco (A.R.C. Laser; Nürnberg, Germany) can be used successfully to remove mild to moderate cataracts alone or in combination with femtosecond fragmentation of the crystalline lens, announced Dr Gangolf Sauder (University Eye Hospital, Mannheim, Germany) during his free paper presentation this morning. However, he noted that the duration of surgery is longer than with standard phacoemulsification techniques, and its clinical significance with regard to surgical trauma, endothelial cell loss and visual recovery is yet to be determined by further study.
The Nano Laser Phaco is a nanosecond pulsed Nd:YAG laser that creates a plasma-induced emulsification of the cataract, using either a coaxial or a bimanual handpiece. In this prospective, non-comparative clinical trial, Dr Sauder performed nano-laser phacoemulsification on 20 patients with mild to moderate cortical cataract under topical anaesthesia. Although Dr Sauder reported that both coaxial and bimanual chop techniques were successful for removing up to moderate cortical cataracts, the surgery took 9.5±1.2 minutes (range: 5–12 minutes) to perform, and average endothelial cell count had decreased by 4% at the 3-month follow-up.
"Nano-laser phacoemulsification is a technique without severe ultrasound shock waves, which creates very distinct circumscript cavitation around the laser tip, but further investigation has yet to prove its clinical significance," said Dr Sauder.

High vacuums are safe with a new cataract removal system


A new cataract removal system that uses innovative fluidics has shown that 600 and 350 mmHg vacuums are safe and efficient in removing cataracts, resulting in good anterior chamber stability with both 2.2 mm and 2.0 mm incisions, according to a free paper delivered today.
Professor David Allen (Sunderland Eye Infirmary, Sunderland, UK) reported the results of his tests with the pre-release version of the new removal system at the dedicated cataract surgery centre at Sunderland Eye Infirmary, during which he examined the safety and efficacy of the system's high and low vacuum settings with different incision sizes. To use the system, Professor Allen sculpted a central trench and removed each hemi-nucleus using either the high (600 mmHg) or low (350 mmHg) vacuum; with the exception of the vacuum, the phacoemulsification and fluidics parameters were the same for all eyes tested.
For each hemi-nucleus, Professor Allen compared the phaco power (cumulative dissipated energy; CDE), estimated balanced salt solution (BSS) used and procedure time; the anterior chamber was also monitored throughout the procedure and was – as judged subjectively by the investigator – reported to be stable.
"Analysis of the surgical video confirms very good anterior chamber stability with the higher vacuum, even with 2.0 mm incisions," Professor Allen confirmed, noting that the stability of the anterior chamber was 'unprecedented'.
The study demonstrated a favourable parameter profile was associated with the 600 mmHg vacuum setting, and concluded that the system was safe and efficient for the removal of cataracts, even with the higher vacuum setting.

New measure of corneal astigmatism is more accurate


CorT (corneal topographic astigmatism), a vector analysis algorithm used to determine corneal astigmatism, is more accurate than other methods currently available, announced Dr Noel Alpins (NewVision Clinics, Melbourne, Australia), who presented a free paper during the 'Assessment of Astigmatism' session this morning.
Dr Alpins and his team conducted a retrospective analysis, reviewing data obtained by the Humphrey ATLAS 9000 (Carl Zeiss Meditec; Jena, Germany) on 504 eyes assessed for laser vision correction over a 2-year period; the corneal power at 100 points on 22 topography Placido rings and Zernike coefficients from simulated corneal wavefront was obtained using the "Export for research" function; corneal measurement parameters were calculated using the summated vector mean of topographic rings with adequate data. The accuracy of the various measurement parameters was then compared.
When evaluated, the data showed that the CorT had a high correlation with manifest refractive cylinder, with ocular residual astigmatism magnitude (ORA) 0.62±0.33 D; this was a closer correlation than those associated with manual keratometry (ORA 0.68±0.38 D), simulated keratometry (ORA 0.70±0.35 D), corneal wavefront (ORA 0.74±0.36 D) and paraxial curvature matching (ORA 0.85±0.48 D). Additionally, CorT was associated with significantly less variability of ORA (ORAsd) than the other measures of astigmatism (p"CorT corresponds better to manifest refractive cylinder than other commonly used measures, for regular and irregular corneas," said Dr Alpins. "The flat meridian of the CorT can also be used to conceptually divide the cornea into two hemidivisions and a CorT value subsequently calculated for each hemidivision of the cornea."
The researchers are now programming the CorT parameter into iASSORT ophthalmic surgical analysis system software, which interfaces with a number of brands of topographers; the Humphrey Atlas, Pentacam (Oculus, Germany), the Sirius Corneal Topographer (CSO, Italy) and the Galilei (Ziemer Ophthalmic Systems, Switzerland) are anticipated to be the first systems that will incorporate the CorT parameter.

Impact of posterior corneal measurements on toric IOL calculation


"Although the impact of posterior cornea on the outcome of toric IOL calculation is clinically not very high on average, the measurement is nevertheless particularly helpful to identify outliers, i.e., candidates for unhappy patients," announced Dr Paul-Rolf Preussner (University Eye Hospital, Mainz, Germany), while discussing his study to quantify the impact of posterior corneal data on the eye’s total astigmatism to be corrected in IOL plane.
Dr Preussner used the TMS-5 (Tomey; Nagoya, Japan) to measure the corneal tomography (anterior Placido topography plus rotating slit Scheimpflug imaging) of 438 eyes before they underwent cataract surgery, using the OKULIX tracing software on the measured data to determine the astigmatism of the anterior corneal surface and of the whole cornea, as well as assessing the vector difference between the two.
The biggest difference between anterior and total astigmatism recorded was 2.72 D, which was in the corneal plane; 8/438 eyes (1.8%) had a difference >1.0 D in the corneal plane, although the average vector difference between total and anterior corneal astigmatism was 0.22 D (median 0.18 D) in the corneal plane, corresponding to 0.32 D (median 0.26 D) in the IOL plane.
"The centroids are -0.32 D/7 degrees (anterior), -0.26 D/4 degrees (total) – meaning they are both with-the-rule - and -0.07 D/18 degrees for the vector difference, so we can see that the impact of posterior cornea on the outcome of toric IOL calculation is clinically not very high on average," said Dr Preussner.