Examiner Awareness Of Surgical Axis Affects Toric Intraocular Lens Misalignment Assessment: A Prospective Study

To investigate whether prior knowledge of the intended surgical axis affects postoperative Toric intraocular lens (IOL) misalignment measurements and to evaluate potential observer bias in clinical practice.

Department of Ophthalmology, Shamir Medical Center, Be’er Ya’akov, Israel.

In this prospective study, 82 eyes of 82 patients undergoing cataract surgery with Toric IOL implantation were included. Each postoperative evaluation involved two Ophthalmologists: one aware of the intended surgical axis (non-blinded) and one unaware (blinded). Several examiners took part in total, and each examiner could serve in either role (blinded or non-blinded) for different patients. At 1–4 weeks postoperatively, both examiners measured the IOL axis alignment by aligning the slit-lamp beam with the lens markings. Digital image analysis (ImageJ) was employed in most cases for an objective assessment. Misalignment was defined as the difference between the postoperative IOL axis and the target axis recorded at the end of surgery.

The blinded group exhibited significantly greater misalignment than the non-blinded group (p = 0.0003). The overall mean difference in misalignment between these two groups, accounting for lens rotation direction, was 3.33° (95% CI: 2.73–3.92, p < 0.0001). Bland-Altman analysis showed wide limits of agreement between examiners' IOL axis assessments, ranging from -9.05° to +7.56°, while discrepancies were especially pronounced at higher and lower alignment axes. Subgroup analysis by astigmatism type (with the rule, against the rule, and oblique) demonstrated relatively consistent findings, with examiners aware of the surgical axis reporting smaller deviations.

Examiner awareness of the intended surgical axis can significantly influence the measurement of postoperative Toric IOL misalignment, potentially introducing systematic bias. These findings underscore the importance of using blinded or objective measurement strategies to ensure accurate postoperative IOL axis assessment and optimize patient outcomes.