Warren E Hill MD
An intraocular lens (IOL) power selection formula derived from patient data using artificial intelligence (AI) may more accurately predict patient refractive needs than existing formulae, particularly for eyes with short axial length, Warren E Hill MD told the 2019 ASCRS ASOA Annual Meeting in San Diego, USA.
The best current IOL power formulae are based largely on theoretical relationships among biometric measures and yield about 80 percent of patients within 0.5 dioptre of target refraction – far lower performance than laser refractive surgery. AI approaches the task differently, said Dr Warren, of Case Western Reserve University, Cleveland, USA.
Based entirely on data using pattern recognition, AI can create an independent representation of data that unravels complex, non-linear relationships and is free from calculation bias. This makes AI well suited to solving real-world problems where ideal models are not available, such as optics in the human eye, Dr Warren explained.
Using a process known as evolutionary modeling, Dr Warren developed and tested several AI models based on various factors, such as axial length, anterior chamber depth and postoperative spherical equivalent. These models were iteratively altered and modified. Those that best fit the original data set and a validation data set with the fewest cases excluded due to insufficient data were refined further. Several ultimately exceeded 90 percent predictive power.
The first version of the resulting formula, based on 459 cases, yielded 92 percent within 0.5 dioptre. A second version based on more than 12,000 cases greatly expanded the range of cases included, improving accuracy for hyperopes up to +30 dioptres. The model is being further refined to account for unusual variations in central cornea thickness and white-to-white measures. Versions optimised for Asian ocular anatomy are also in development. “90 percent within 0,5 doptre is achievable,” Dr Warren said.
What to do when the posterior capsule tears
Posterior capsule tears can occur at any stage of cataract surgery, Thomas Kohnen MD, PhD, told the 2019 ASCRS Annual Meeting in San Diego, USA. He gave tips for avoiding and managing them.
When creating the capsulorhexis, avoid radial tears, which can spread from the anterior to the posterior. When a capsulorhexis veers peripherally, bring it back toward the centre as you end it to minimize risk of a posterior tear, advised Dr Kohnen, of Goethe University, Frankfurt, Germany.
For capsule rupture during lens extraction, the first goal is keeping the nucleus from diving into the vitreous. Deepen the bottle and apply viscoelastic in front of and behind the core to avoid posterior dislocation and protect the endothelium.
How an IOL should be implanted after a capsule rupture depends on the condition of the capsular bag. If the rhexis is not torn, an optic capture in the capsulorhexis with haptics in the sulcus may be possible. In cases of lost zonules, open the sulcus ciliaris with viscoelastic, retract the iris and position hapitcs away from the foramen in case of rhexis rupture. Avoid placing single-piece IOLs in the sulcus to avoid future iris chafe and pigment dispersion.
