Approximately 20% to 30% of patients undergoing cataract surgery have at least 0.75 D of corneal astigmatism.1-5 Left uncorrected, this condition can lead to spectacle dependence and patient dissatisfaction, especially in patients implanted with presbyopia-correcting IOLs. The standard methods for correcting corneal astigmatism during cataract surgery include (1) adjusting wound size and location, (2) placing relaxing incisions at the steepest meridian, and (3) implanting a toric IOL.2,3
Toric IOLs can correct up to 4.00 D of corneal astigmatism, but their accurate alignment and precise placement in the capsular bag are essential to achieving the targeted refractive outcome. Every 3º of toric IOL misalignment causes a 10% reduction in intended astigmatism correction; a rotation of 30º can negate the IOL’s entire cylindrical effect.2-5
Manual marking has been considered the gold-standard technique to ensure accurate alignment for years.5 In the past few years, several new approaches have been introduced. These include the following:
- Image-guided systems, such as the »Verion Reference Unit (Alcon), »TrueVision Smart 3D visualization system (TrueVision), and »Callisto Eye (Carl Zeiss Meditec)1,2,5,6;
- Femtosecond laser intrastromal marking with the IntelliAxis-L System (»Lensar) or »Catalys femtosecond laser (Johnson & Johnson)1,2,7,8; and
- Intraoperative aberrometry systems, such as Optiwave Refractive Analysis with VerifEye+ (»ORA; Alcon)1,2,9 and Holos IntraOp (Clarity Medical Systems).
Studies have been conducted to compare these new technologies with traditional manual marking. However, none revealed superiority of one technique over another.5,6,9 Looking at the image-guided systems, Webers et al5 found a higher rate of toric IOL misalignment in the manual-marking group compared with the Verion group. Montes de Oca et al,6 however, found slightly more misalignment errors with digital marking using the TrueVision 3D system. Neither study’s findings were statistically significant for differences in residual astigmatism or distance UCVA.
"Every 3º of toric IOL misalignment causes a 10% reduction in intended astigmatism correction."
Studies evaluating intraoperative aberrometry have also demonstrated mixed results.9 Although the ORA is able to determine the magnitude and axis of a toric IOL, concerns exist about the influence of external variables, such as the eyelid speculum, dry eye, intraocular pressure, and corneal hydration, on the intraoperative measurements.1,2,9
With manual markers, on the other hand, it has been suggested that the pendulum can damage the corneal epithelium if the patient moves when it is approaching the eye.8 The ink can also lead to allergic reactions or corneal toxicity7 or can be dissolved by the tear film,7,8 making alignment more difficult during surgery.
Femtosecond laser intrastromal marks 10º to 15º in length can be created at the steepest axis with any available laser. These marks can theoretically help to ensure correct alignment of a toric IOL, as they are permanent and can be well visualized during surgery. Postoperatively, this method enables correlation to the positioning of the IOL intraoperatively and to the IOL’s rotational stability.7,8
Image-guided systems and aberrometry enable the visualization of an image overlay to facilitate IOL placement and alignment. Femtosecond laser intrastromal marks are visualized directly under the microscope, allowing direct comparison of the intrastromal marks with the IOL axis.5-9
Postoperatively, most surgeons use dilated slit-lamp photos to evaluate IOL stability. Ray-tracing technology such as the »iTrace (Tracey Technologies) can be used to evaluate corneal and internal toricity axes without dilation. We are using the iTrace device to confirm accurate postoperative toric IOL positioning in a study we are currently conducting.
CONCLUSION
Because no method has been found to be more effective than any other, many surgeons continue to use the manual marking technique, especially due to fear and insecurity over patient dissatisfaction. Nevertheless, new technologies may serve to increase OR efficiency, reduce complications, and improve refractive outcomes.
With further advances in intraoperative marking systems, we hope to see a new technology that combines the best features of the available techniques, including axial length measurement, corneal mapping, and iris registration, and that can take refractive outcomes into consideration to allow adjustment of postoperative individual outcomes without the need for preoperative marks.
1. Thulasi, P, Khandelwal SS, Randleman JB. Intraocular lens alignment methods. Curr Opin Ophthalmol. 2016;27(1):65-75.
2. Ventura BV, Wang L, Weikert MP, Robinson SB, Koch DD. Surgical management of astigmatism with toric intraocular lenses. Arq Bras Oftalmol. 2014;77(2):125-131.
3. Kessel L, Andresen J, Tendal B, Erngaard D, Flesner P, Hjortdal J. Toric intraocular lenses in the correction of astigmatism during cataract surgery. Ophthalmology. 2016;123(2):275-286.
4. Popp N, Hirnschall N, Maedel S, Findl O. Evaluation of 4 corneal astigmatic marking methods. J Cataract Refract Surg. 2012;38:2094-2099.
5. Webers VSC, Bauer NJC, Visser N, Berendschot TTJM, van den Biggelaar FJHM, Nuijts RMMA. Image-guided system versus manual marking for toric intraocular lens alignment in cataract surgery. J Cataract Refract Surg. 2017;43(6):781-788.
6. Montes de Oca I, Kim EJ, Weikert MP, Khandelwal SS, Al-Mohtaseb Z, Koch DD. Accuracy of toric intraocular lens axis alignment using a 3-dimensional computer-guided visualization system. J Cataract Refract Surg. 2016;42(4):550-555.
7. Fadlallah A, Chelala E, Robinson S, Melki S. Femtosecond laser intrastromal incisions as fiducial marks for alignment of toric IOLs. Acta Ophthalmol. 2016;94(7):e673-e674.
8. Dick HB, Schultz T. Laser-assisted marking for toric intraocular lens alignment. J Cataract Refract Surg. 2016;42:7-10.
9. Woodcock MG, Lehmann R, Cionni RJ, Breen M, Scott MC. Intraoperative aberrometry versus standard preoperative biometry and a toric IOL calculator for bilateral toric IOL implantation with a femtosecond laser: one month results. J Cataract Refract Surg. 2016;42(6):817-825.
