Optimising Outcomes of Cataract Surgery in Challenging Cases

Using a ray tracing power calculation provides favourable outcomes. Cheryl Guttman Krader reports

Good biometry, optimisation of the ocular surface, and use of a ray tracing IOL power calculation will help to achieve good outcomes after cataract surgery in the challenging and demanding population of patients with a history of keratorefractive surgery, Kjell Gunnar Gundersen MD, PhD told delegates.

“We found that at 5 to 15 years postLASIK, our cohort of patients had a significantly higher prevalence of dry eye disease compared to normal individuals and those who underwent phakic IOL implantation. Optimising the ocular surface preoperatively will reward surgeons with improved refractive accuracy and stability and will also result in improved patient comfort,” Dr Gundersen said.

He explained that due to the altered corneal profile after laser vision correction (LVC), the traditional formulae used for IOL power calculations resulted in errors and outliers. Post-LVC formulae have been developed, but they are based on mathematical averaging and modelling. Ray tracing power calculations are exact calculations, and they are independent of patient history. Instead, they use available data to calculate the best focus for single rays at varying radial distances from the optical axis through the different refractive media of the eye.

A study conducted by Dr Gundersen and colleagues demonstrated the accuracy of ray tracing IOL calculations in post-LVC eyes. The study included 37 eyes of 20 post-myopic LASIK patients and evaluated the refractive predictive error (RPE) resulting from ray tracing calculations (Okulix, Tomey Corporation) done with biometric data from two OCT devices (Anterion®, Heidelberg Engineering, and Casia SS-1000, Tomey Corporation) and traditional post-LVC IOL formulae (Barrett True-K and Haigis-L) incorporating reflectometry data (Lenstar 900, Haag-Streit Diagnostics).

Using the ray tracing program with the Anterion data resulted in the lowest mean absolute RPE and mean arithmetic RPE and the highest percentages of eyes with prediction errors of ±0.25 D (60%), ±0.50 D (88%), and ±0.75 D (100%).

“These outcomes compare favourably with those achieved in virgin eyes,” Dr Gundersen noted.

“Accurate toric correction remains a challenge in these eyes that have asymmetric astigmatism. Nevertheless, implanting a toric IOL is still worthwhile considering the clinical effect.”

EYES WITH KERATOCONUS Discussing cataract surgery in keratoconic eyes, Dr Gundersen said ray tracing power calculations can also be used in these cases. In addition, available evidence shows implantation of a toric IOL in eyes with stable keratoconus is associated with good long-term refractive outcomes and excellent improvement in uncorrected visual acuity.

“Accurate toric correction remains a challenge in these eyes that have asymmetric astigmatism. Nevertheless, implanting a toric IOL is still worthwhile considering the clinical effect,” Dr Gundersen said.

He suggested that the “safe” IOL choices for post-LVC eyes and those with keratoconus are monofocal spherical or toric IOLs. Presbyopia-correcting IOLs might be considered for post-LVC patients especially interested in spectacle independence, but these individuals must be informed about the optical compromises.

An alternative for the latter group would be to implant a monofocal spherical or toric IOL in the bag with a sulcus-placed, add-on presbyopia-correcting IOL that offers ease of removal if the patient is dissatisfied. Eyes with keratoconus can also be managed with a two-step strategy using a monofocal spherical or toric IOL in the bag and a spherical or toric IOL in the sulcus to fine-tune the refractive error, he noted.

This presentation was made at the ESCRS Virtual Winter Meeting 2022.

Kjell Gunnar Gundersen MD, PhD, is in private practice at the IFocus Eye Clinic AS, Haugesund, Norway. KGg@Ifocus.no

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