Barrett True K formula provides accurate results in post-refractive surgery patient

[caption id="attachment_7411" align="alignnone" width="750"] Valentijn SC Webers[/caption] The Barrett True K intraocular lens (IOL) calculation formula provided better results than the ORA intraoperative aberrometer (Alcon) in a patient who had previously undergone radial keratotomy (RK), said Valentijn SC Webers MD, in a case study he presented at Cornea Day at the 21st ESCRS Winter Meeting in Maastricht, The Netherlands. The patient, a 50-year-old man, had a very unusual eye. Apart from undergoing previous RK with five cuts for high myopia, he had an axial length of 30mm and a very flat K-reading of 30D. He presented with a progressive cataract that had reduced his visual acuity to a decimal value of 0.4, noted Dr Webers, of University Eye Clinic Maastricht, The Netherlands. Dr Webers and his associates opted to perform femtosecond laser-assisted cataract surgery and also perform intraoperative IOL calculation with the ORA device. Preoperative IOL calculations performed with the Barrett True K IOL calculation formula suggested using a 12.5D IOL, however intraoperative measurements suggested using a 14.5D IOL. In the end the Maastricht team compromised and implanted a 13.0D monofocal IOL, which, according to the ORA should have yielded a postoperative spherical equivalent refraction of 0.00D, but according to the Barrett True K formula would result in a postoperative refraction of -1.5D. They found that at one day postoperative the spherical equivalent was 0.25D, very close to that predicted by the ORA. However, by six weeks the spherical equivalent was 1.5D, exactly as predicted by the Barrett True K formula.