BACKGROUND: Zonular weakness caused by pseudoexfoliative syndrome is very common among residents of Northwest Russia. Along with the increasing risk of intraoperative complications, zonular weakness may worsen refractive outcomes of phacoemulsification, as it affects the effective lens position. AIM: The work aimed to assess the effect of zonular weakness on refractive outcomes of phacoemulsification. METHODS: The study included data from 282 patients (282 eyes) divided into the following three groups: patients with healthy zonules (n=109; group 1, control), patients with pseudoexfoliative syndrome (n=100; group 2), and patients with grade I lens subluxation caused by pseudoexfoliative syndrome and required capsular tension ring implantation (n=73; group 3). Intraocular lens power was calculated using the SRK/T formula. Optical biometry was performed using IOL-Master 500 device (Carl Zeiss, Germany). The criteria for accuracy of intraocular lens power calculations were the mean calculation error and modulus of the mean calculation error. RESULTS: The mean calculation errors were 0.00±0.39 D (control), 0.12±0.50 D (group 2), and 0.26±0.59 D (group 3) (p=0.003), indicating a hyperopic shift in groups 2 and 3. The moduli of the mean calculation error were 0.32±0.30, 0.37±0.28, and 0.52±0.45 D, respectively (p 0.001), suggesting lower predictability of refractive outcomes of phacoemulsification in patients with zonular instability. CONCLUSION: Patients with zonular weakness showed a hyperopic shift caused by a deeper lens position after surgery. To achieve optimal refractive outcomes in this population, A-constant for an intraocular lens should be further optimized.