Prediction errors for the first (PE1) and second eyes (PE2) were obtained in the intra-ocular lens power calculation for 4 formulae (HofferQ, SRK II, SRK/T and Holladay 1). The optimal correction factor for each formula was determined as the one resulting in the lowest mean absolute error. A similar analysis was performed in the negative and positive PE1 subgroups.

Retrospective case series study. A retrospective chart review was conducted, which included demographics (age and gender) and several parameters for both the first and second eyes: surgery date, axial length, keratometric corneal power in 2 meridians, predicted intra-ocular lens (IOL) power recommended for plano target in each formulae (HofferQ, SRK II, SRK/T and Holladay 1), implanted IOL power, predicted post-operative refraction for the implanted IOL for the 4 formulae, observed post-operative refraction in spherical equivalent and post-operative best corrected visual acuity. The prediction error was calculated for the first eye (PE1) as the difference between the observed post-operative refraction in spherical equivalent and the predicted post-operative refraction by the IOL Master for the implanted IOL. This was obtained for the 4 formulae. The prediction error for the second eye (PE2) was obtained in a similar fashion. The optimal partial adjustment for second eye refinement was obtained subtracting a portion of the PE1 from the PE2 (PE2-xPE1, where 0≤x≤1) for the 4 formulae. The optimal correction factor was determined for all formulae by using an array of different proportions of PE1 that were applied to the second eye. The values ranged from 10% to 100%, with increments of 10% each.

Inclusion Criteria:

• Patients having performed bilateral cataract surgery between 1st October 2012 and 24th April 2014 in a single ophthalmological center (Centro Hospitalar Baixo Vouga, Portugal)

Exclusion Criteria:

• Inadequate follow-up
• Incomplete medical records
• Previous or combined ocular surgery
• Manual extracapsular cataract extraction and not phacoemulsification
• Corneal sutures
• Implantation of any other IOL type different from Abbott Tecnis® 1-piece IOL (Abbott Laboratories Inc., Illinois, USA), ZCB00
• IOL implanted in the sulcus
• Intra or postoperative complication
• Post-operative best corrected visual acuity worse than 5/10
• Corneal astigmatism>3.00 D

Patients from a single ophthalmological center (Centro Hospitalar Baixo Vouga, Portugal) admitted for bilateral consecutive cataract surgery