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Cataract Surgery | May 2011

TriMic: An Astigmatically Neutral Variation on MICS

This technique virtually eliminates surgically induced astigmatism and promotes rapid visual rehabilitation.

Taking advantage of various technological advances such as enhanced phaco tools and premium IOL designs, rapid development in cataract surgery has been marked by the introduction of new techniques that improve surgeons’ comfort and patients’ optical quality. Modern cataract surgery is safe, accurate, and—in large part due to the variety of IOLs— provides postoperative outcomes that meet increasing patient demands.

Perhaps the most frequent barrier to patient satisfaction after cataract surgery is residual astigmatism. The importance of controlling astigmatism has increased in recent years due to the growing use of multifocal and toric multifocal IOLs.

The first step in astigmatism correction is to control surgically induced astigmatism. Conventional microincision cataract surgery (MICS) techniques do not provide sufficiently accurate prediction of surgically induced astigmatism, and therefore we have developed a hybrid of MICS, dubbed TriMic, which eliminates the induction of astigmatism during cataract surgery. As the name indicates, three incisions are created for this MICS technique (Figure 1). It is the next step beyond bimanual or coaxial MICS.


A demonstration of TriMic may be viewed at http://eyetube. net/?v=zeven. This MICS technique promotes rapid visual rehabilitation because the incisions induce minimal trauma and fully respect the anatomy of the cornea. Complete rehabilitation is usually attained 1 to 2 days after surgery. During TriMic, bimanual cataract removal is done through two clear corneal microincisions of 1.1 mm (Figure 2). I use a knife calibrated to 1.1, 1.8, or 2.2 mm to create simple paracenteses. A third incision, a scleral tunnel incision, is then created to facilitate IOL implantation (Figure 3). The size of this incision varies from 1.8 to 2.8 mm depending on the type of the implant.


The choice of IOL depends on the type of correction and the patient’s preference. If the patient wants an aspheric lens, I use the Akreos Advanced Optics IOL (Akreos AO; Bausch + Lomb, Rochester, New York); however, if he or she wants a multifocal IOL and has more than 1.00 D of astigmatism, I recommend the AcrySof IQ Restor Multifocal Toric (Alcon Laboratories, Inc., Fort Worth, Texas). This lens corrects the existing astigmatism and provides the best image focus and contrast sensitivity.

Insertion of the IOL through a clear corneal incision in coaxial or biaxial MICS induces minimal astigmatism. By deploying the IOL through a corneoscleral incision (Figure 4), TriMic limits the amount of induced astigmatism. This incision site does not distort corneal curvature and therefore reduces induction of corneal astigmatism.

Using the TriMic technique, we have seen that surgically induced astigmatism tends toward neutrality. In our first 100 consecutive cases, the average amount of surgically induced astigmatism at 1-month follow-up was 0.20 D (Figure 5). Study in a larger patient population with longer follow-up is under way.


It is extremely important to correct astigmatism during cataract surgery, especially when implanting a multifocal IOL. Once surgically induced astigmatism is controlled, as we have found possible with TriMic, any remaining astigmatism can be corrected with toric implants.

Jérôme Bovet, MD, practices at Clinique de l’Oeil, Onex, Switzerland, and is a Visiting Professor at the J.J. Hospital, Mumbai, India. Dr. Bovet states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +41 792020771; e-mail: jbovet@vision.tv.



  • The TriMic technique relies on three incisions to eliminate the induction of astigmatism.
  • Two 1.1-mm clear corneal incisions facilitate bimanual phaco, and a corneoscleral tunnel that varies in size depending on the IOL is used only for IOL insertion.