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Cataract Surgery | Jul/Aug 2009

Marking the Axis for Toric IOL Implantation

Marks made with the Nd:YAG laser can be placed up to 24 hours before surgery.

Marking the axis during toric IOL implantation is a crucial step in accurately orienting the lens in the capsular bag. Current techniques identify the horizontal 0° to 180° meridian with different markers while the patient is seated at the slit lamp. However, use of a pen marker may constitute a possible infection source. Additionally, pen marks on the eye may fade or disappear during surgery due to corneal irrigation. Therefore, we have proposed a new method: marking the axis with the Nd:YAG laser at the slit lamp.

The major requirement for succes with toric IOLs is rotational stability. It has been estimated that approximately 1° of off-axis rotation results in a loss up to 3.3% of the lens cylindrical power of the lens.1 When the toric IOL rotates 30°, the cylinder power is completely lost.2

During toric IOL implantation, the IOL must be rotated to the desired axis, taking into account the previously identified 0° to 180° meridian. In our technique with the Nd:YAG laser, several marks are placed on the corneal meridian where the toric IOL is to be implanted. These marks can be placed immediately before surgery or up to 24 hours in advance. These marks appear as a small group of bubbles in the corneal epithelium, disappearing with time.

PROCEDURE
With the patient seated at the slit lamp and a coaxial thin slit turned to the meridian where the toric axis is to be implanted (Figure 1), we align the patient's head vertically and ask him to focus on the distance vision test. Using topical anesthesia, we place four aligned reference marks with 1.6 to 2 mJ of power. The first two marks are made in the limbus; the second two are made in the cornea at the level of Bowman's layer (Figures 2 and 3). Corneal marks should be placed in a centered diameter of approximately 6 to 7 mm so that they are visible when the pupil is dilated (Figure 4).

After the marks are made with the Nd:YAG laser, we perform cataract surgery and phacoemulsification without considering the astigmatism induced by our main incision. We place this incision on the same meridian habitually used. Finally, once the toric IOL has been implanted, we proceed to align the marks on the toric IOL with the corneal marks we made with the Nd:YAG laser. Once both marks (toric and corneal) are duly matched, we leave the IOL in this position and finish the procedure. Because the toric IOL should be rotated clockwise, it should be implanted counter-clockwise, 20° to 30° from its final position, to avoid a high degree of rotation.

CONCLUSION
There are two occasions for error that may induce deviation from the correct meridian in which the toric IOL should be implanted: (1) when marking the 0° to 180° meridian and (2) when trying to identify the final axis of implantation. With our novel Nd:YAG technique to mark the axis, we believe that these two errors are less common than when pen markers are used. Our technique allows us to make a direct marking on the implantation axis without adding intermediate steps. This technique prevents errors, and the marks clear over several days postoperatively.

Marceliano Crespo Bordonaba, MD, is an ophthalmologist at the Clínica Cirugía Ocular, Madrid, Spain. Dr. Crespo Bordonaba states that he has no financial interest in the products or companies mentioned. He may be reached at e-mail: crespo@cirugiaocular.com.

Laureano Álvarez-Rementería Fernández, MD, is an ophthalmologist at the Clínica Cirugía Ocular, Madrid, Spain. Dr. Álvarez-Rementería Fernández states that he has no financial interest in the products or companies mentioned. He may be reached at e-mail: rementeria@cirugiaocular.com.

  1. Ophthalmology Times Web site. Guttman C. Toric IOL rotational stability is demonstrated in analysis. Available at: http://ophthalmologytimes.modernmedicine.com/ophthalmologytimes/Modern+Medicine+Now/Toric-IOL-rotational-stability-is-demonstrated-in-/ArticleStandard/Article/detail/599635. Accessed: July 9, 2009.
  2. Lane SS. The Acrysof Toric IOL's FDA Trial Results. Cataract & Refractive Surgery Today. 2006;5:66-68.

Jul/Aug 2009