Optimising patient outcomes post cataract surgery was the focus of a Zeiss event hosted in Sydney in August. The event was planned around the launch of ‘Total Keratometry’, a software update for the Zeiss IOLMaster 700. It was simulcast live to ophthalmologists at events in Brisbane and Melbourne.
The Zeiss IOLMaster 700 with SWEPT Source OCT technology allows ophthalmologists to directly measure the posterior corneal surface. It combines telecentric keratometry measurement of the anterior corneal surface with measurement of the posterior corneal surface in order to calculate Total Keratometry (TK). Two new formulas – Barrett TK Universal II and Barrett TK Toric – were developed exclusively for the IOLMaster 700 by Prof. Graham Barrett, developer of the globally used Barrett formulas for calculating intraocular lenses (IOL).
Patients assume safety and precision… and they’re getting safety, but not the precision…
Speaking at the event, Prof. Barrett said, “The benefit of TK within the IOLMaster 700 is real – it will be a significant advance in predictable refractive outcomes after cataract surgery”.
Prof. Barrett said his studies had shown that by using the Barrett toric calculator, in combination with the measured posterior corneal astigmatism provided by the IOLMaster 700, the area of prediction when determining the appropriate IOL for a patient, within half a dioptre, is within 82.2 per cent – which is very close to the traditional theoretical model.
“Early analysis suggests the potential for incorporating TK is not only useful for toric IOLs, but also for spherical outcomes and I think the benefit will be in the diminishing surprises,” he said.
LONG AWAITED AND CRITICAL TO MATRIX
A/Prof. Michael Lawless described TK as “a long awaited and critical part of a long matrix” used to determine which IOL will achieve the optimum outcomes for each patient.
“Patients assume safety and precision when undergoing cataract surgery and they’re getting safety, but not the precision in the way they would think they are,” said A/Prof. Lawless.
He described strategies he uses to achieve best outcomes, which included pre-operative planning to optimise the tear film, corneal aberrometry, use of the right formula to determine the most appropriate IOL and, “a realistic conversation with the patient – I tell them the IOL formulation is an estimation not a calculation”, said A/Prof. Lawless.
Speaking of IOL stability, he said one study showed that 82–90 per cent of toric IOLs will remain within five degrees of the intended axis. A rotation of 5 degrees means the patient is losing 17 per cent of the toric effect. He said, “IOL rotation will happen within the first 60 minutes of surgery – this is unequivocal. Minimising the risk of misalignment significantly comes down to completely removing the ocular viscoelastic, making sure haptics are fully unfolded and ensuring there is anterior chamber stability.”
IOL TRADE OFFS
Dr. Fam Han Bor, deputy director of NHG Eye Institute and head of cataract, implant and anterior segment and eye operating theatre services at Tan Tock Seng Hospital Singapore, discussed the trade-offs associated with different IOLs. He said selecting the most appropriate IOL will depend on what the patient wants and ahead of a cataract operation he always asks patients questions to determine their habits, typical reading distances and whether they usually read from paper or digital devices.
He said if a patient reads Chinese characters, which are very difficult to read, he definitely recommends bifocals. For high myopes he also recommends bifocals because “it gives the near back”.
He said Trifocal IOLs have good distance vision acuity, with a sweet spot at near which is easier for them to find post operatively than multi-focals. Glare and haloes are less problematic.
“For general purpose, trifocal IOLs are good, as long as the patient is not holding the reading material too close,” said Dr. Fam.
Dr. Fam said musicians particularly, benefit from extended depth of focus (EDOF) IOLs because manuscripts are held at a distance. “EDOF has very good intermediate all the way to distance vision, and glare and haloes are not so bad,” he said.
Monofocal IOLs offer very good distance vision, very good contrast, minimum glare and haloes, however he said, “not all patients can tolerate them because of postoperative anisomyopia”.
The evening concluded with a lively panel discussion fuelled by questions from the audience.