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Endodiathermy marks useful in cases of postoperative toric IOL rotation
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Imperative to the efficacy of all toric IOLs is the position of the IOL with regards to the intended alignment axis because every degree of misalignment leads to residual astigmatism. Misalignment of the IOL may be caused by either inaccurate placement or rotation of the IOL.
Toric IOLs represent a significant advance in achieving optimal cylindrical and spherical refractions after IOL surgery and are the preferred method for correcting pre-existing astigmatism during cataract surgery. Accurate rotational stability and axial alignment of toric IOLs are critical to the efficacy of surgery. Each degree of rotation causes an average loss of cylinder power of approximately 3%; subsequently, when an IOL rotates 30°, there is a complete change of axis with no astigmatic correction. Several studies have evaluated the rotation of toric IOLs using methods such as slit lamp estimation and digital photography, but not all of them take head tilt and cyclorotation into consideration.
High-frequency endodiathermy capsulorrhexis was proposed first by Klöti in 1984, in which heat energy was used to incise the anterior capsule. Harshul Tak from India uses high-frequency capsulotomy probe to create “portholes” in the anterior capsule to serve as a landmark for toric IOL rotation. We describe a technique that incorporates the use of 25-gauge endodiathermy probe, which creates marks on the anterior capsule and serves as an indicator of the astigmatic axis in cases of misalignment or rotation of the toric IOL both intra- and postoperatively.
Surgical technique
Preoperatively, initial markings are made with the patient sitting up to avoid cyclorotation. The eye is marked at 0° and 180° using an instrument such as a Bakewell bubble level (Mastel). A 5-mm continuous curvilinear capsulorrhexis is created in all cases. After completion of phacoemulsification, the capsular bag is inflated with viscoelastic (Figures 1 and 2). To mark the desired axis of IOL orientation intraoperatively, instruments such as a Bores meridian marker (Axis) with a Gimbel Mendez ring (Mastel) or a Mendez ring with a Nuijts toric axis (American Surgical Instruments) are used, and the reference marks made preoperatively are taken into consideration (Figure 3). An endodiathermy probe with 25-gauge tip is introduced, and a mark is made about 1 mm to 1.5 mm away from the capsulorrhexis margin along the astigmatic meridian to be corrected (Figure 4) with an endodiathermy unit in continuous mode with the power setting at 1. A low mean energy is delivered, which minimizes the cutting energy and decreases heat generation. The base of the needle tip is placed in contact with the anterior capsule as the tip is activated by pressing the foot pedal. Small gas bubbles form as the capsule is cut, but they do not usually interfere with visualization of the capsulorrhexis edge. The marks are oriented 180° opposite to each other.
Figure 1. Completion of nucleus emulsification. Note an adequate capsulorrhexis size of approximately 5 mm.
Images: Narang P, Agarwal A
Figure 2. The capsular bag inflated with adequate viscoelastic.
Figure 3. Intraoperative toric axis marking in relation to preoperative reference marks.
Figure 4. Twenty-five-gauge endodiathermy probe employed to create a mark on the anterior capsule along the toric meridian.
Figure 5. Toric IOL placed in the capsular bag. Alignment of the toric marks of the IOL with the anterior capsular marks is confirmed.
The IOL is placed in the capsular bag, and gross alignment (within 20° to 30° of the desired axis) is performed by rotating the IOL clockwise while it is unfolding. The ophthalmic viscosurgical device is gently removed from behind the IOL before the toric IOL is moved clockwise into final axis alignment. The marks on the IOL are made to correspond to the marks on the anterior capsule (Figure 5).
Discussion
The most commonly employed method to assess postoperative toric IOL alignment (both orientation and position) involves evaluation through slit lamp biomicroscopy using an axis graticule integrated eye piece or the slit beam protractor. Because this measuring reticule on the slit lamp uses 5° steps, it is not a very accurate method to determine postoperative IOL rotation. Although useful, these methods are dependent on the patient maintaining a stable and erect head position against the slit lamp at each assessment. Moreover, this method is subjective, which may lead to inconsistencies among different practitioners. Digital retroillumination photography, which is more accurate, involves customized image-analysis software tools to objectively compare the position of the pupil/limbal margin with the center of the IOL to assess centration and rotation, comparing the toric IOL axis markers with consistently identifiable conjunctival blood vessels or iris features (to normalize for any ocular rotations). Because the IOL marks are located at the periphery of the IOL optic, full mydriasis of the pupil is required. Objective methods such as wavefront aberrometry, combined wavefront aberrometers and corneal topographers directly determine the orientation of the toric IOL and do not necessitate pupil dilation.
Realignment of a rotated toric IOL should ideally be performed as soon as possible and preferably before 2 weeks postoperatively because of the formation of adhesions between the capsular bag and IOL optics. Radiofrequency diathermy-assisted capsulotomy has been used as an alternative to manual capsulorrhexis for cataract surgery in children as well as for intumescent adult cataracts. The probe tip is heated to about 160°C and produces a thermal capsulotomy. Endodiathermy probes are available with tip variants of 20 gauge, 23 gauge and 25 gauge. Utilization of a 25-gauge tip ensures the creation of a mark that is apt for serving the purpose of localization of the alignment of the axis. Because the mark is created about 1.5 mm away from the edge of the capsulorrhexis, it does not compromise on the strength of the edge of the capsulorrhexis. Inflation of the capsular bag with viscoelastic helps to push the posterior capsule behind, allowing a safe margin to make a mark or burn holes in the anterior capsulorrhexis. A short burst of heat energy at minimal power suffices the need to create a scar in the anterior capsulorrhexis. Gentle pressure is maintained on the capsule as the tip touches the surface of the capsule. Small gas bubbles are formed while the tip is active.
Intraoperative placement of endodiathermy marks on the anterior capsulorrhexis has advantages in cases of postoperative toric IOL rotation. Creation of a mark along the alignment axis on either side provides a guideline as to the alignment of the toric marks of the IOL intraoperatively and postoperatively. This technique delimits the use of various sophisticated software employed for determining postoperative rotation and helps to serve as a permanent landmark for realignment.