ABSTRACT Purpose. To study a position of the posterior chamber phakic intraocular lens (PIOL) with a total size selection using ultrasound bio-microscopy (UBM) and a new algorithm based on anterior segment optical coherence tomography (AS OCT) in patients with high myopia. Material and methods. Retrospective analysis of data from patients who underwent surgical correction of high myopia with posterior chamber PIOL ICM V4 (STAAR Surgical) in the period from July 2005 to May 2011 was performed. The sulcus ciliaris diameter was used to select the PIOL size and was assessed with either UBM (straight measurement on 3 scans) or AS OCT (using the new algorithm). Two study groups were formed: UBM group (15 patients, 29 eyes) and AS OCT group (16 patients, 29 eyes). In each case the PIOL vault was analyzed in the center by the AS OCT method. Results. Preoperative spherical equivalent (SE) values in UBM and AS OCT groups were 12.05±4.22 D and -16.55±3.65 D respectively (P0.05). Mean PIOL vault values demonstrated statistical insignificant decrease trend in the UBM group 0.36±0.28mm in comparison with 0.53±0.18mm in the AS OCT group. Optimal PIOL vault range (0.35 to 0.7mm) was found in 8 eyes of 4 patients and in 16 eyes of 8 patients in the UBM and AS OCT groups, respectively. Excessive PIOL vault (over 0.7mm) — in 5 eyes of 3 patients and in 7 eyes of 5 patients, respectively. Poor vault (under 0.35mm) — in 16 eyes of 8 patients and in 6 eyes of 3 patients, respectively (P<0.01). We observed constant central or paracentral contact between PIOL and the natural lens in 8 eyes of 5 patients in the UBM poor vault cohort only. Conclusion. PIOL sizing based on the new algorithm of sulcus ciliaris diameter assessment using AS-OCT allows to achieve a safe PIOL vault and demonstrates its clinical effectiveness.