Deviation from the planned axis of three toric intraocular lenses

The medical charts of 190 eyes with a TIOL implantation during cataract surgery, operated by two surgeons using two different manual marking techniques, were retrospectively reviewed. The study adhered to the tenets of the Declaration of Helsinki, and all methods were carried out following the relevant guidelines and regulations. The Meir Medical Center Ethics Committee approved all experimental protocols. The IRB of the Meir Medical Center Ethics Committee waived the requirement for informed consent from the study subjects.

Lenses

Three types of TIOLs were compared: SN6AT (Alcon Laboratories, Inc., Fort Worth, TX, USA), POD FT (PhysIOL, Liège, Belgium), and Symfony ZXT (Johnson & Johnson Vision, Santa Ana, CA, USA). The SN6AT AcrySof IQ Toric is monofocal toric, hydrophobic acrylic IOL. It has a 6.0 mm optic diameter, and its overall length is 13.0 mm. The FineVision POD FT is a trifocal toric hydrophilic IOL with an optic body diameter of 6.00 mm and an overall diameter of 11.40 mm. The ZXT Symfony Toric lens is an extended depth of focus, toric, foldable, hydrophobic acrylic 1-piece lens, with an optic diameter of 6 mm and an overall diameter of 13 mm.

Lens selection

Preoperatively, all patients underwent measurements by the Lenstar LS 900, IOLMaster 500, Pentacam, and the Atlas topographer.

All biometric measurements were compatible with the strict validation criteria described by Warren Hill (Hill-RBF Calculator Version 2.0 https://rbfcalculator.com/online/index.html). The surgeon chose the implanted TIOL using the Barrett online toric calculator (https://ascrs.org/barrett-toric-calculator) and the IOL manufactures’ online calculators, (https://www.acrysoftoriccalculator.com/, https:/ /www.physioltoric.eu/, https://www.tecnistoriccalc.com/). The TIOL power and placement axis were calculated using the Lenstar measurement when agreement between all devices was achieved. When no agreement was achieved between Lenstar and the IOL Master, the measurements that were closer to the axis of the topographer and tomographer were chosen for the IOL calculation. When no agreement was achieved between all devices, the toric IOL was not implanted. Additional adjustments were made according to the surgeon’s experience and preferences (eg, surgical main incision site, posterior corneal astigmatism and astigmatism orientation).

Surgical technique

Two experienced surgeons (EIA, GK) performed all the surgeries at Ein-Tal Eye Center, Tel-Aviv.

Ink marks were placed, preoperatively, at the limbus, while the patient’s head was positioned behind the Haag-Streit (Köniz, Switzerland) slit lamps. The two surgeons used different manual marking techniques. One surgeon (EIA), marked the planned axis of the TIOL lens (Primary IOL marking) directly. The second surgeon (GK) marked 0, 180- and 270-degrees (Reference axis marking). The incision and the IOL axis were marked as the first step of the surgery using the Mendez ring or other similar ring.

All surgical procedures performed through a small clear corneal incision (2.2–2.4 mm), using the phacoemulsification technique. After removing the cataract, the IOL was implanted into the capsular bag under an anterior chamber maintainer (ACM) and without an ophthalmic viscoelastic device (OVD). The IOL dialed into the planned axis and pushed gently back against the posterior capsule.

Follow-up

Follow-up visits were 1 day, 1 week, and 1 month after the surgery. On the 1 month postoperative visits, a complete dilated examination and manifest refraction were performed. The TIOL position was detected, and retroillumination pictures were taken with a slit lamp digital color camera (CSO Elite Mega Digital Vision camera). The Goniotrans software (Eventos Médicos y Sociales, SL) was used to determine the TIOL axis. This software integrates virtual protractor over an eye picture, by dragging the radial line to the position of the toric lens axis marks on the angles pattern (Fig. 1)7.

Figure 1

Example of a Retroillumination photo documentation of a TIOL position, using the Goniotrans software (Eventos Médicos y Sociales, SL). By dragging the radial line to the position of the TIOL axis mark on the angles pattern the position of the TIOL is determined.

Data analysis

For the study outcome, we evaluated and compared the effect of the IOL type (cylinder and spherical power), surgeon’s marking techniques, and other eye characteristics such as corneal astigmatism (direction and power) axial length, and anterior chamber depth, on the IOL deviation and its direction. TIOL deviation was defined as the difference between the TIOL planned axis and the actual alignment axis measured at least 1 month after surgery.

Statistical analysis

Statistical analyzes were performed using SPSS (version 21.0, SPSS, Inc., Chicago, IL). Between-subjects design was applied, as specified in the editorial of the Journal of Cataract and Refractive Surgery on IOL studies4. Continuous variables were compared using a one-way analysis of variance (ANOVA) or the Kruskal–Wallis test, followed by post-hock tests, as indicated by a normality test (Shapiro–Wilk). Categorical variables were compared using the Pearson’s chi-square test. Pearson correlation was used to evaluate the correlation between axial length, anterior chamber depth, preoperative astigmatism, TIOL cylinder power and TIOL spherical power to the degree of rotation. A P value of less than 0.05 was considered statistically significant.

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