EyeWorld Asia-Pacific September 2011 Issue

35 EW CATARACT/IOL September 2011 For Stephen S. Lane, MD, adjunct clinical professor, University of Minnesota, Minneapolis, Minn., USA, the fundamental question is even more basic: “Is this a person who is going to have cataract surgery in both eyes? That determination FAM Han Bor, MD Senior Consultant & Head, Cataract & Implant Service The Eye Institute @ Tan Tock Seng Hospital 11 Jalan Tan Tock Seng, Singapore 308433 Tel. no. +65-6357-7726 Fax no. +65-6357-7718 famhb@singnet.com.sg C ataracts in keratoconus pose certain issues to ophthalmologist. Keratometry is a challenge. Measuring corneal curvature and interpreting its readings can be confusing. Manual keratometry may improve reliability but is operator- dependent. Corneal topography is useful in evaluating the extent of irregularity of the cornea. IOL power calculation is another issue. The relationship between corneal curvature and anterior chamber depth may be abnormal. This may mislead some IOL formulas into mistakenly estimating the position of the IOL and consequently creating errors in the calculated IOL power. Toric IOLs should benefit mild keratoconus with fairly symmetric and regular astigmatism. As a rule of thumb, keratoconus patients who achieve good corrected vision with glasses before developing significant cataracts should benefit from toric IOL. For advanced cone that requires the use of rigid or hard contact lenses, the outcome is less predictable. Due to the excessive prolateness of the cornea, keratoconus may exhibit negative spherical aberration. In this case, a conventional IOL with a positive spherical aberration neutral IOL should be used to reduce the overall spherical aberration. Evaluation of the cornea’s spherical aberration should be done preoperatively before deciding on the IOL with the appropriate asphericity. Multifocal IOLs are best avoided in keratoconus. The stability of the keratoconus is also a factor to be considered. In young keratoconus with cataract, the stability of the cone needs to be assessed. The cone may progress and the refractive outcome may shift. If progressive, the cone should be stabilized by lamellar keratoplasty, Intacs, crosslinking or even penetrating keratoplasty before the cataract procedure. Bear in mind that some keratoconus cases may have associated conditions, e.g., Marfan, that may complicate cataract surgery. In Marfan, the zonules may be lax and the cataract subluxated. In these cases, the IOL may have to be stabilized with capsular-tension rings or segments. Unless centration and rotational stability can be ascertained, toric IOL should be avoided. Finally, counseling is of utmost importance for cataracts in keratoconus. As the outcomes cannot be predicted consistently, residual refractive errors can be expected and should be emphasized to these patients. For those who require rigid or hard contact lenses preoperatively, they would most likely still be dependent on contact lenses but with changes in power. Editors’ note: Dr. Fam is a consultant for Alcon, AMO, Allergan and Zeiss, but has no direct financial interests in his comments. alone will make a difference in how you approach treatment.” Noting there are “several discussion points” in patients like these, Eric D. Donnenfeld, MD, clinical professor of ophthalmology, New York University Medical School, New York, NY, USA, said determining what the true K value is and how to manage the patient’s astigmatism have to be the primary concerns. “In this example, the Ks aren’t too irregular—they’re both below 50. In patients with more severe keratoconus, it can create a problem,” he said. Dr. Devgan said if the patient can be refracted to good vision with a phoropter and “the central cornea is relatively symmetric and regular, the patient will likely do well with the toric IOL. But if the patient doesn’t see well with glasses and requires hard contact lenses for best vision, then be very careful—these patients can have unpredictable results from a toric IOL.” Another pearl for clinicians—if the cornea’s irregularity is on the periphery but the central cornea is symmetric and normal, likely the patient will do well in toric lenses, Dr. Devgan said. “Another way to look at it is, when patients are out of contacts, can they see sharply with glasses? Glasses can only fix regular, symmetric astigmatism, which is the same as with a toric IOL. The only thing that can fix irregular or asymmetric astigmatism is hard contact lenses,” he said. If both eyes are likely to undergo cataract surgery in the near future, Dr. Lane suggested “trying to shoot for the best uncorrected visual acuity you can get, a lot of which will depend on the state of the keratoconus.” If keratoconus is advanced, surgeons should consider deep anterior lamellar keratoplasty or a full corneal replacement before the cataract removal. Dr. Lane advised considering a toric IOL only if the keratoconus/topography has been stable over several years. “The problem with using a toric IOL is that when you correct corneal astigmatism with a lenticular solution, if the cornea changes, you’re trying to correct the corneal and lenticular astigmatism that you’ve induced with a toric lens. You’ll need a bitoric contact lens to correct and compensate for this,” he said. A conservative approach would be to treat with a monofocal IOL and correct any residual cylinder with a contact lens, he said. Determining the axis and other pearls With K values that can “vary widely over a small area of the cornea”, Dr. Donnenfeld tells patients their refractive results may be suboptimal. He does, however, recommend using the ORange (WaveTec, Aliso Viejo, Calif., USA), an intraoperative aberrometer that’s been on the market for about a year. “The ORange takes an intraoperative reading in the patient’s aphakic state and will tell you what IOL power is best,” Dr. Donnenfeld said. For patients who previously underwent LASIK or who have keratoconus, “an intraoperative reading is particularly helpful.” He said some surgeons advocate performing an aphakic refraction on the day of surgery and then taking the patient back to the OR to place the IOL. Limbal relaxing incisions are contraindicated in patients with keratoconus, making toric lenses a “reasonable alternative,” Dr. Donnenfeld said. “Under no circumstances would I implant a multifocal lens in these patients,” Dr. Lane said. Also, patients with keratoconus may end up developing cataracts earlier than normal, Dr. Devgan said. “PSC [posterior subcapsular continued on page 36