Rooting out surgical errors
Hunting high and low for accuracy in toric IOL implantations.
Bartlomiej Kaluzny MD, PhD
Outcomes after toric IOL implantation are influenced by numerous factors including preoperative patient selection, biometry, intraoperative alignment, surgical technique and postoperative care, according to Bartlomiej Kaluzny MD, PhD at the 25th Virtual ESCRS Winter Meeting.
Discussing the options of toric IOL implantation for patients at the extremes of low and high astigmatism, Dr Kaluzny, who is Professor of Ophthalmology and Head of Division of Ophthalmology and Optometry, Department of Ophthalmology, Collegium Medicum of Nicolaus Copernicus University, Bydgoszcz, Poland, said that while glasses or contact lenses are available to treat as little as 0.25D of astigmatism, no such option exists for toric lenses.
“We know that greater than 0.50D of astigmatism can degrade visual performance, including reading speed and contrast sensitivity. We also know that small amounts of residual or untreated astigmatism are a leading cause of patients’ dissatisfaction with multifocal IOLs and monovision. And yet, when we check what is available on the market, the lowest available cylinder power at the IOL plane is 1D, which corresponds to 0.67D at the corneal plane,” he said.
Several sources of error lie behind the difficulty in obtaining predictable and accurate outcomes with toric IOLs, especially low power, noted Dr Kaluzny.
“Keratometry readings from different devices are not always the same and integrated K is significantly more accurate than a value from a single device. Both the anterior and posterior corneal surfaces contribute to refractive power but are not always taken into account in preoperative measurements. Modern corneal tomographers have improved greatly in recent years but individual measurements may still be subject to significant variation,” he said.
Although the use of intraoperative aberrometry has helped to improve accuracy, the technology is still not widely available, said Dr Kaluzny.
Surgically induced astigmatism (SIA) remains the main source of error, he said.
“Even with small incisions and fixed meridians, the SIA is highly variable, especially in more curved corneas. Studies have shown not only a high standard deviation in SIA by different surgeons but also in the results produced by the same surgeon. So, we cannot perform reliable and reproducible SIA even if we use microincision cataract surgery,” he said.
Ensuring correct toric IOL alignment has improved in recent years with the introduction of digital markers, said Dr Kaluzny.
Nevertheless, it is important to remember that the eye evolves over time and that includes corneal astigmatism values.
“Even if we are on target immediately after the surgery and for weeks and months postoperatively, corneal astigmatism continues to change towards against-the-rule astigmatism over at least 20 years after cataract surgery. This change was found to be similar in eyes that did not have surgery, so our results may deteriorate in the future,” he said.
To sum up, “in my opinion industry people think that we are not ready for lower cylinder power IOL”.