Read more from Priya Narang, MS.
Toric IOLs comprise a very important part of cataract surgery and are the most preferred method to meet the dual demands of correcting astigmatism with cataract and providing the potential for better uncorrected visual acuity. Constantly meeting the demands of patients is often taxing to the surgeon and accentuated when a surgeon detects postoperative rotation of the toric IOL. Surgical realignment is often needed to realign the IOL in the correct meridian.
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. Although useful, these methods are subjective. Digital retroillumination photography, which is more accurate, involves a customized image analysis software tool to objectively compare the position of the pupil/limbal margin with the center of the IOL to assess centration. It can also assess rotation, comparing the toric IOL axis markers with consistently identifiable conjunctival blood vessels or iris features (to normalize for any ocular rotations). 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.
High-frequency endodiathermy capsulorrhexis, in which heat energy is used to incise the anterior capsule, was first proposed by Kloti in 1984. Creating a mark on the anterior capsule with thermal energy can serve as a permanent landmark, which can help detect any postoperative rotation of the IOL. Dr. Harshul Tak uses a high-frequency capsulotomy probe to create a hole in the anterior capsule along the astigmatic axis, and he has named it a “porthole” technique. In our practice, we incorporate the use of endodiathermy probe-assisted marks on the anterior capsule, which serve as an indicator of astigmatic axis in cases of misalignment or rotation of the toric IOL postoperatively.
After phacoemulsification, the capsular bag is inflated with viscoelastic. An endodiathermy probe with a 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, 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 when the capsule is touched, but they do not usually interfere with visualization of the capsulorrhexis edge. The marks are oriented 180° opposite to each other. Often, creation of even one mark on the anterior capsule is enough to serve as an indicator of the astigmatic meridian.
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.
In the porthole technique, after intraoperative alignment of the toric IOL, portholes are fashioned in the anterior capsule over the outermost toric IOL marks at each side of the IOL optic. Viscoelastic is removed from the anterior chamber, and wounds are hydro-stitched. Postoperatively, in a fully dilated pupil, the portholes in the anterior capsule are seen over the toric IOL mark, signifying accurate alignment of the toric IOL. Rotation of the toric IOL can be easily picked up by its deviation from portholes made in the anterior capsule.
The advantage of framing anterior capsular marks is that this method is accurate and fast, doesn’t rely on sophisticated software, and is free from observer’s bias and independent of cyclorotation of the eye and head position of the patient.