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Surgical technique and pearls for toric IOL implantation
With the addition of toricity to an IOL, it is important for the surgeon to understand how to achieve proper orientation of the lens during implantation.
IOL model
The first step for consistent, proper implantation is to determine the model of IOL needed to correct a patient’s degree of astigmatism.
AcrySof toric IOL
The AcrySof toric IOL (Alcon, Fort Worth, Texas) is manufactured in three toric powers, and the proper toric power is chosen using the online AcrySof Toric Calculator based on the patient’s preexisting corneal astigmatism and the estimated amount of astigmatism that will be induced by the planned surgical incision. The amount of surgically induced astigmatism varies depending on the surgeon. For example, in my hands, a 3-mm incision will induce approximately 0.5 D of astigmatism perpendicular to the incision, and a 2.2-mm incision will induce less than 0.25 D.
The axis for the surgical incision is chosen by the surgeon and entered into the AcrySof Toric Calculator, and the axis for alignment of the recommended toric IOL is then determined by the AcrySof Toric Calculator.
The AcrySof Toric Calculator is a powerful tool for use with this lens. I would advise for the surgeon to “experiment” with the calculator to learn how changing the input data affects the surgical outcome. By adjusting the incision location and size (and thus the amount of induced astigmatism), preexisting astigmatism can be reduced to nearly zero in most cases.
Surgical marking
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On the day of surgery, prior to prepping the eye, reference marks to identify the horizontal and vertical meridia are made on the limbus with the patient sitting or standing. Both ASICO (Westmont, Ill.) and Duckworth & Kent (Hertfordshire, England) have toric pre-markers designed for marking the reference axes preoperatively. Another alternative is “eyeballing” the horizontal and vertical meridia and creating the marks freehand using a marking pen. The freehand method was used during the clinical study of the AcrySof toric IOL. It is perhaps not as accurate as using the toric marking kits but works well in patients who are less cooperative.
After the patient has been prepped and is supine under the operating microscope, two more marks are made on the limbus: the axis of the incision and axis of the desired IOL alignment. To do so, the toric axis marker is dialed to the desired axis for the incision or IOL placement, inked and aligned with the reference marks that were made preoperatively. The marker is then lowered to the ocular surface to mark the desired axis.
It is important to ensure that the limbus is dry before making these marks. If the tissue is wet, then the ink can blot and cover a span of approximately 10°, making it difficult to identify the proper axis. If this occurs, then the limbus should be dried off and re-marked.
A Mendez ring can also be used to make these orientation marks. The Mendez ring is lined up with the previously made reference marks on the principal meridia, and the axes for the incision and IOL alignment are identified by choosing corresponding landmarks such as limbal vessels. An ink pen is then used to clearly mark the desired axes.
After these axes are marked, a printout of the output page from the AcrySof Toric Calculator should be hung on the microscope showing the surgeon’s view, should the surgeon be implanting an AcrySof toric IOL. The proper orientation of the calculator will depend on whether the surgeon is operating from the top of the bed or temporally. The aim is to have the diagrams on the printout showing the same view that the surgeon is seeing through the microscope to eliminate confusion and the need for the surgeon to convert to a different orientation than what is shown in the diagram. This will decrease confusion and make it more likely that the lens will be oriented in the proper position.
Considerations during surgery
The cataract surgery is routine except that the entrance incision must be made on the axis, which was determined and marked preoperatively. In addition, a temporal clear corneal incision can be used to achieve an astigmatically neutral incision.1
The capsulorrhexis size should be slightly smaller than the optic diameter to ensure good stability. Removal of the nucleus and cortex is routine. After nucleus and cortex removal, the capsular bag is filled with viscoelastic and the IOL is inserted. If the surgeon uses a microincisional technique, then the toric IOL can be inserted through an incision as small as 2.2 mm.
The IOL is rotated until it is 5° or 10° shy of the final desired axis of orientation. With the bag full of viscoelastic, flexible haptics aid in rotation. The viscoelastic is then removed from the eye while the IOL is held in position with the second instrument so that it does not rotate away from the desired axis.
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Once the viscoelastic is removed, the final orientation is achieved. The silicone-tipped irrigation and aspiration instrument is a good tool for performing this final rotation of the IOL without scratching it. The three dots on the IOL must be perfectly aligned with the marks on the limbus. The microscope can be zoomed in to better see the dots for this step. Final orientation can also be achieved by aligning the IOL axis with a Mendez ring degree gauge and double-checking it against preoperative notes or a chart.1
Finally, the last traces of viscoelastic are removed from the angles, the incision is hydrated and checked to ensure watertightness, and the chamber is deepened with saline solution. Even at this point, the IOL’s orientation can be fine-tuned with saline solution and a 30-gauge cannula.
In my experience, once the IOL is on axis, it does not rotate. If the reference marks are made properly and the IOL is aligned properly, then it stays in the correct position.
It is critically important to follow these steps during implantation to ensure proper orientation. In an early case at our center, the toric calculator was hung in the wrong orientation and, as a result, the lens was implanted 90° off axis. This patient’s astigmatism was doubled from 2 D to 4 D rather than reduced to 0 D.
In this case, the orientation was revised. The patient was brought back to the operating room, viscoelastic was injected through the original incision, the bag was deepened and the lens was rotated to the proper orientation. The final steps of the revision were the same as in a primary cataract surgery; the lens was rotated to within a few degrees of the desired orientation, the viscoelastic was removed and the orientation was fine-tuned with a cannula while a small amount of saline solution was injected.
Conclusion
Successful patient outcomes require proper implantation of a toric IOL, and a few surgical pearls exist to ensure proper implantation (Table). The first step is for proper determination of which lens should be implanted in the patient. The correct axis should be determined and reference marks should be placed with the patient sitting upright or standing. To ensure proper placement, final alignment of the IOL should be achieved after removing the viscoelastic. Following these steps ensures success. The surgery must be planned properly and performed with the described techniques. Correct alignment is essential. Attention to these steps will lead to successful outcomes.
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