ASTIGMATISM

Correcting the regular component of an eye with irregular astigmatism with toric intraocular lenses can often result in a satisfactory visual outcome, said Jose Guell MD, director of the Cornea and Refractive Surgery Unit at IMO Autonomous University of Barcelona, Barcelona, Spain. “When you're able to compensate the regular component in eyes with irregular astigmatism, visual improvement is so significant in a large number of cases that the patient does not regard the irregularity as significant,†said Dr Guell at the 16th ESCRS Winter Meeting.

Toric IOLs provide an alternative to rigid gas-permeable contact lenses, which is the standard treatment for irregular astigmatism, whether the condition results from keratoconus or corneal grafting, he said. The lenses that have been used with success include pseudophakic, phakic and piggyback IOLs. Customised IOLs, specifically designed for an individual’s corneal optics, are another option that has recently become available, and the future will hopefully see light-adjustable IOLs employed in a similar manner, he predicted.

Patients with irregular astigmatism often require a highly individualised treatment. Therefore, the peer-reviewed literature regarding specific lenticular approaches is fairly sparse, Dr Guell noted. However, several case-studies derived from his own experience show that those approaches can be of considerable benefit to some patients. As an example, he cited the case of a woman in her mid-50s with irregular astigmatism from congenital corneal lesions and coloboma. She wanted refractive surgery but was an unsuitable candidate for refractive laser ablation.

Following clear lens extraction and implantation of an AcrySof pseudophakic IOL she had significant improvements in her vision, despite some residual irregular astigmatism, Dr Guell said. Another patient who achieved a good result with a pseudophakic IOL had irregular astigmatism as well as cataract. The irregularity of the cornea was a result of keratoplasty, itself performed to correct irregularities after radial keratotomy, Dr Guell said. “One of the advantages of using these phakic IOLs (Toric Artiflex) is that they can be introduced through a 3.1mm incision and, especially, when you use this posteriorly located limbal incision the amount of astigmatism induced is clinically insignificant,†he explained. Toric phakic IOLs are also a useful option in some cases.

Dr Guell reported that implantation of phakic IOLs has produced good results at his centre in eyes with keratoconus, after he and his associates first stabilise the ectasia by stiffening the corneal collagen through collagen cross-linking. Another option is to use piggyback IOLs. He noted that Rayner produces a type of IOL that is specifically designed for sulcus implantation, including a model with an astigmatism-correcting component. He noted that such IOLs are particularly useful in cases where the cornea is best left untouched, such as in eyes with forme fruste keratoconus Occasionally a patient who has undergone piggy-back IOL implantation may require further correction, Dr Guell said. He described the case of a man with irregular astigmatism who had undergone a radial keratotomy many years previously.

The patient had since undergone implantation of two IOLs, one in the capsular bag and the other in the sulcus. To correct the residual ametropia, Dr Guell and his associates implanted a third lens in the anterior chamber, an iris-fixated Artisan/Verisyse lens (AMO) to correct the still residual sphere and cylinder. “Once this was done, visual acuity improved to 0.8 in spite of the residual irregular astigmatism, which was not as significant,†Dr Guell said. He noted that the ophthalmic device company, Topcon, has introduced a service that could bode well for the treatment of astigmatism in general. It produces a madeto- order toric IOL, the Lentis T Plus, which provides individual astigmatism correction. Surgeons using the IOL can use an online calculator to specify the IOL’s dimensions.

“You can send this data and they can prepare a customised lens for you, not only to correct sphere and cylinder, but also higher order aberrations. Although only with preliminary experience, we have found vision can be improved significantly when we've corrected higher order aberrations, even when the corneal irregular astigmatism remains unchanged,†Dr Guell said. Another development along similar lines is the light-adjustable lens, which allows postoperative correction of residual sphere and cylinder and could theoretically be used to correct irregular astigmatism and higher order aberrations as well. “Today we can only theoretically correct irregular astigmatism with IOLs experimentally but it will happen in the near future because we already have this technology available,†he concluded.