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Astigmatism may be safely and effectively corrected with toric IOLs
The implantation of a PMMA toric IOL can be utilized to correct higher amounts of corneal astigmatism in cataract surgery, study says.
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VIENNA, Austria — Although the implantation of a toric IOL at the time of cataract surgery can safely reduce refractive astigmatism, the IOL can rotate postoperatively. The initial rotational stability of the haptics in the capsular bag has still to be improved and the corneal surgically-induced astigmatism has to be reduced by smaller incisions, according to the study’s presenter, Georg Gerten, MD. Three-piece foldable IOLs with a new haptic design are currently under development. “One can see that if there’s a rotation of more than 10°, approximately 25% of the intended cylindrical correction is lost,” Dr. Gerten said. “Therefore, a rotation of more than 10° may reduce the corrections.”
Round and round it goes
Astigmatism may be corrected during cataract surgery by altering the corneal curvature or by implantation of a toric IOL. With toric IOLs, the influence of rotational stability in the capsular bag is most important for the refractive result. However, if the toric IOL rotates too much, a portion of the intended cylindrical correction can be lost.
When considering the effects from the toric IOL, the position of the toric on the cornea is of great importance. The axis of the IOL has to be aligned precisely to the corresponding axis of the cornea. After proper alignment, the IOL should not rotate. But if rotation does occur, the two superimposed spherical cylindrical lenses cross. From this, a new aspheric cylindrical lens is created.
In the worst case, which is rotation of 90°, the power of the two cylinders increases, according to Dr. Gerten. If the rotation is more than 10°, approximately one-quarter of the correction is lost. That occurred in six cases, which required the surgeon to go back in and re-rotate the toric IOL back into the proper position. After this second intervention, all lenses remained stable with an average rotation of only 1° clockwise, according to Dr. Gerten. The cylinder induction to this minimal rotation was less than 0.5 D in most cases and not clinically significant.
Dr. Gerten concluded that the implantation of a toric IOL is a safe, effective procedure used to correct higher amounts of corneal astigmatism in cataract surgery. Dr. Gerten warns that special attention should be given 1 month postoperatively. This is when rotation of the IOL is most likely to occur. Early rotations of the haptic in the capsular bag have improved, and perhaps the corneal surgical induced astigmatism can be lessened by a smaller incision. Therefore, according to Dr. Gerten, a three-piece foldable IOL with a new haptic design needs to be developed.
Investigation protocol
The indication for implanting IOLs is in cataract patients who have corneal astigmatism of more than 2 D. In his study, which Dr. Gerten presented at the European Society of Cataract and Refractive Surgeons, 26 eyes of 24 patients were provided with toric IOLs. Two eyes had a high astigmatism after previous keratoplasty.
During phacoemulsification, the cloudy lens, astigmatism and the lens is removed. The cylindrical refraction remains due to corneal astigmatism. In order to correct the corneal astigmatism at the same time, a toric IOL may be used instead of a purely spherical one, according to Dr. Gerten.
Custom made, one-piece IOLs with cylindrical strengths between 1.5 D and a maximum of 12 D, manufactured by Dr. Schmidt Intraocularlinsen, Sankt Augustin, Germany, were implanted. The goal was to decrease the total refractive astigmatism from an average of 4.1 D before surgery to 1.6 D postoperatively.
“Something very critical was the fact that 20 out of 26 eyes had a total refractive astigmatism of less than 2 D postoperatively, which could easily be corrected with glasses,” Dr. Gerten said. “Even high astigmatisms of more than 10 D after keratoplasty can be lowered into the range between 2 D and 4 D.” In order to estimate how well the toric IOL corrected the corneal astigmatism, the effects of the incision and the toric IOL have to be taken into consideration separately.
At a mean follow-up of 12 months after the implantation of a toric IOL, all eyes showed a reduction of total astigmatism. The mean total refractive astigmatism could be reduced from 3.74 D ±2.44 D preoperatively to 1.64 ±1.21 D postoperatively. In six of 26 eyes, the toric IOL rotated more than 15° in the capsular bag, which was corrected and remained stable during the follow-up period.
For Your Information:
- Georg Gerten, MD, can be reached at Laserforum Koln C.V., Neumarket 4, Cologne, Germany 50667; (49) 2212776470; fax: (49) 2212776471; e-mail: info@laserforum.de. Dr. Gerten has no direct financial interest in any product mentioned in this article, nor is he a paid consultant for any company mentioned.