EyeWorld Asia-Pacific September 2016 Issue

51 EWAP CATARACT/IOL September 2016 There’s residual- from page 49 Views from Asia-Pacific Michael LAWLESS Clinical Associate Professor, Sydney Medical School and Vision Eye Institute 4/720 Victoria Ave. Chatswood, NSW Australia Tel. no. +61-2-9424-9999 Fax no. +61-2-9410-3000 michael.lawless@visioneyeinstitute.com.au W ith modern intraocular lens formulae, improvements in biometry with swept-source OCT and the ability to diagnose and improve tear quality perioperatively, the value patients get from toric intraocular lenses has increased dramatically. Particularly the use of low powered toric IOLs, as much of the “noise” in the system that limited their use has now been dealt with. In my hands, toric lenses are now used in 80% of patients. They are superior to any form of corneal incisions, whether it be laser or manual, and they are simply a product whose time has come and should be widely used. Placing the lens in the right position has been improved with digital alignment systems, particularly where the image of the patient has been measured preoperatively in a sitting position so that cyclotorsion is taken into account at the time of surgery. With all of these improvements, it is unusual to have a less than ideal outcome. If there is residual astigmatism postoperatively I tend to wait six weeks for refractive stability, and sometimes more if there is progressive change. As the authors have noted, if the spherical equivalent is close to plano then simply rotating the axis using the astigmatism fix website to guide you is a logical first step. The iPhone app Axis Assistant is very helpful in determining what axis the toric intraocular lens has ended up at, as this information is essential when deciding whether rotation is sensible. I think these lenses can be rotated a few months postoperatively and there is no hurry to do it in the first 1–2 weeks, and the time taken to wait a few more weeks for refractive accuracy is helpful in my view. I agree with Dr. Harden that, if possible, it is best to rotate the IOL without opening the primary incision or making a new primary incision, in case this influences the refractive outcome. There are particular patients at risk of spontaneous rotation: highly myopic eyes and those with oblique axes, these are the cases I am most concerned that I will see a rotation from the desired position postoperatively. I have no evidence to support this, but in high myopes and those with oblique axes, I will place a capsular tension ring in an attempt to provide an environment which allows the toric IOL to stay in the desired position. Anecdotally it seems to be helpful in my hands. It is rare that I will go to an intraocular lens exchange. If rotation of the lens will not be sufficient to get me to where I need to be, then I would normally perform surface laser (PRK). Tiding up small residual errors is easy with PRK. There are no aberrations induced because of the small amount of correction mostly required, and generally it is only in one eye and it is tolerated very well and is extremely accurate. I would always prefer to avoid an intraocular lens exchange when there are other methods that are helpful. Editors’ note: Dr. Lawless declared no relevant financial interests. YEO Tun Kuan Consultant, Department of Ophthalmology Tan Tock Seng Hospital 11, Jalan Tan Tock Seng, Singapore 308433 Tel. no. +65-97242020 tun_kuan_yeo@ttsh.com.sg T he presence of significant residual astigmatism after toric IOL can be quite disheartening for both the surgeon and patient. The problem is further compounded for a multifocal toric IOL, where the patient is unable to see clearly for both distance and near despite forking out a large sum to be spectacle-free. Before jumping to any conclusion, we need to identify the source of the residual astigmatism; whether it is due to IOL misalignment, surgically induced astigmatism (SIA), inaccurate preoperative keratometry or inappropriate IOL selection. IOL selection issues can include using formulae that ignores posterior corneal astigmatism. First of all, I would repeat the keratometry of the patient and then dilate the pupil to determine if the IOL was positioned in the intended axis. Performing postoperative keratometry enables you to calculate your SIA, as well as compare with your preoperative values to see if they are significantly different. You may be surprised that in some cases preoperative and postoperative K values differ greatly. This may suggest inaccuracy in the preoperative keratometry performed. Corneal topography, if not done preoperatively, can also determine the presence of any irregular astigmatism. If the IOL is not at its intended axis, IOL rotation is likely warranted. My preferred calculator for this is the Barrett Rx formula, which not only advises on IOL rotation but also piggyback IOL or IOL exchange. The Rx formula utilizes the post-operative refraction, keratometry and IOL position to recalculate the actual effective lens position (ELP) and determine the required axis of rotation. This is more technically sound, as it does not assume the original predicted IOL axis to be correct nor rely on a predicted or fixed ELP. At the same time, it can also again incorporate your SIA, since rotating the IOL would be another procedure that can induce astigmatism. When the calculator is unable to reduce the astigmatism to a low level despite rotation, it suggests that an IOL of inappropriate toricity may have been implanted, either due to errors in measurement or calculation. In that case, laser refractive surgery, piggyback IOL or IOL exchange is advisable. While toric IOLs are wonderful in reducing or eliminating astigmatism, counseling the patient of the possibility of a second procedure remains important, no matter how low the likelihood. Editors’ note: Dr. Yeo declared no relevant financial interests. continued on page 52 assessment for astigmatism correction at the time of cataract surgery” and “Managing astigmatism at the intraoperative stage” in the May and June 2016 issues of the U.S.-based EyeWorld magazine – ed.], but Drs. Kieval, Berdahl, and Hardten reiterated some advice to help avoid pitfalls in the end as well. At the preop stage, Dr. Kieval said making sure all corneal astigmatism measurements are consistent and taking into account posterior corneal astigmatism are key, not to mention treating any ocular surface disease that could skew measurements. Intraoperatively, Dr. Kieval said he uses a “bubble level marker” to mark patients while they’re seated upright with the head straight. After insertion, he’ll leave the IOL 10 degrees shy of its intended axis, remove all of the viscoelastic, and rotate the lens into its final position. Dr. Berdahl had similar advice, noting that using stable IOLs in the first place can help prevent rotation. In addition to making sure you remove all the viscoelastic and give the lens adequate time to unfold completely, he suggested surgeons tamp on the lens, making sure it comes into solid contact with the posterior capsule. Dr. Hardten said one of the most common preoperative pitfalls is using a toric IOL in a patient with irregular astigmatism. “Toric IOLs are designed to treat regular astigmatism, so if the patient has irregular astigmatism from