Dr. Kohnen classified irregular astigmatism into ocular pathologies (keratoconus, pellucid marginal degeneration (PMD), and dry eye syndrome), postoperative (such as keratoplasty), and trauma.
Patients can have corneal astigmatism because of dry eye syndrome (DES). "(This has) to be treated before surgery,” Dr. Kohnen said. “This helps the outcome particularly in premium IOL lenses when we go to presbyopia corrections."
Post-penetrating keratoplasty astigmatism is particularly significant and difficult to treat because the irregularities are all over the cornea, he said. Conservative treatments for irregular astigmatism include spectacles and contact lenses.
Corneal procedures include ablative approaches (LASIK and photorefractive keratectomy [PRK]), limbal-relaxing incision (LRI), and add-ons such as intrastromal corneal ring segments (e.g., Intacs, Addition Technology).
Phakic IOLs for irregular astigmatism include monofocal toric IOLs with small apertures and multifocal toric IOLs. There are also add-on pseudophakic IOLs.
Which patients might benefit most from a toric IOL and which might need a surgical procedure is "a question which is asked worldwide," said Dr. Kohnen.
"Maybe for toric, we start with 1.5 D and above and for limbal relaxing, 0.75 D and above," Dr. Kohnen said. "But for the future, I still see a trend that goes more in the direction of toric lenses because they are more stable."