Comparison of the Concordance Between Digital Marking and Manual Marking for Toric Intraocular Lens Positioning

Patients with visually significant cataract and regular corneal astigmatism who were scheduled for phacoemulsification were screened for eligibility. Inclusion criteria were adults (18 -90 years of age) that were candidates for uncomplicated cataract surgery. The exclusion criteria were irregular corneal astigmatism, lens subluxation, uveitis, glaucoma, trauma, history of retinal disease or optic neuropathy, previous intraocular or corneal surgery and corneal disease that could not be evaluated by the ARGOS or VERION systems.

Preoperative assessment included best-corrected visual acuity (BCVA), which were determined by Snellen's chart and converted to logMAR. Spherical equivalent (SE) and astigmatic refraction (AR) were examined by Full Auto Ref-Keratometer (RK-F2, Canon). Evaluation for corneal astigmatism and axial length with ARGOS® Biometer. Slit lamp examination (BP 900®, Hagg-Streit) intraocular pressure measurement (Canon TX-20P), and dilated retinal examination was performed on all of the patients.

For manual technique a slit-lamp was used. Patients were seated with their head fixed with the horizontal supporting band and their chin placed in the center of the chinrest. A thin horizontal slit beam is projected onto the cornea and moved vertically (up and down) until the area of maximum light concentration (brightest reflection) on the corneal surface is identified. For each eye, after identifying the point of maximum light reflex, under topical anesthesia with 0.5% proparacaine hydrochloride eye drops, the corneal limbus was marked at the 0° and 180° meridian (3 and 9 o'clock) positions using a blunt tip of the Sinskey hook coated with sterile gentian violet ink, using light pressure as a single touch of approximately one second, in order to standardize ink deposition and minimize ink spread. The marking was maintained horizontally without any movement during the marking. The thickness of marks was routinely less than 0.25 mm

For the digital technique, preoperative biometry data obtained from the ARGOS Biometer were entered into the Alcon Vision Planner v1.6, which was paired with the VERION Image-Guided System (Alcon Laboratories, Inc., Fort Worth, Texas, USA) to project the digital overlays directly into the operating microscope. This module captures a high-resolution preoperative reference image of the eye which can be used to document the center of the undilated pupil, corneal reflex position or eccentricity of the visual axis, scleral vessels and iris structures. All marking was performed by the same experienced surgeon (W. Tattiyakul) who was experienced with using all techniques, performed all procedures and measurements. No complications had occurred.

With both the manual and digital marks visible intraoperatively, the angular deviation along the horizontal meridian (in degrees) between the manual mark and the digital reference was recorded from the operating-microscope display for each eye by two trained observers independently, each blinded to the other's readings, using the same standardized display. The mean of the two observers' readings was used for all subsequent analyses, and inter-observer agreement was assessed using the intraclass correlation coefficient (ICC) and Bland-Altman analysis