Eyeworld

EW SECONDARY FEATURE 92 September 2016 by Ellen Stodola EyeWorld Senior Staff Writer can be drastically improved in some of these cases," Dr. Lee said. Disad- vantages include the inability to use an RGP or hybrid contact lens down the road if a toric IOL is present, and keratoconus is typically a progressive disorder that worsens with time. Also, the toric IOL will be null and void if keratoplasty is needed in the future, Dr. Lee said. Best imaging device for astigmatism "For me, there's no perfect device," Dr. Harvey said, although he wishes there was one perfect device for determining central corneal pow- er because that is one of the most important aspects. "When you take average K, it's not really any better than the actual topography-derived keratometry," he said. Dr. Harvey tends to use a Placi- do-based topographer. "For me, it is fine to use optical biometry Ks with an intentional minus target," he said. There are also a variety of formulas that can be used. Formu- las often undercorrect because the cornea will read higher than the patient is actually using, he said. The patient may have steepening below the central optical zone, but that tricks the devices, Dr. Harvey recommendation is to try to correct astigmatism on the cornea as much as possible preoperatively, and AK can be done for large astigmatism. If the astigmatism is irregular, topog- raphy-guided minimal PRK can be used, he said, and if there is regular astigmatism, that can be corrected with a toric lens. Using a toric IOL post-kerato- plasty can be tricky, Dr. Lee said. "While you may get excellent short- term results in post-keratoplasty patients, the corneal astigmatism will change as the graft ages and the graft-host junction becomes altered over time," he said. Great short-term results can be achieved in post-ker- atoplasty cases with topography/to- mography maps showing "bow tie" astigmatism, Dr. Lee added, but long term, all of these grafts will even- tually have a change in the corneal astigmatism, making the toric lens implant less ideal. Advantages of a toric IOL in ker- atoconus are that high amounts of astigmatism can be neutralized eas- ily during cataract surgery, and col- lagen crosslinking is now available and can stabilize and even improve some cases of keratoconus, making use of a toric IOL more beneficial, he said. "Uncorrected visual acuity implant. "Older patients who likely have stiffer corneas make better toric lens candidates," he said. "But if the corneal imaging shows irregular astigmatism without the classic 'bow tie' pattern and they have recently worn RGP or hybrid contact lenses, I would stick to a monofocal lens implant and leave them myopic with the IOL calculations so the spherical equivalent can account for the astigmatism." Implanting a toric IOL after keratoplasty It's possible to implant a toric IOL after keratoplasty, Dr. Harvey said, but the surgeon may want to consid- er several points. He suggested wait- ing a year if it was a full thickness transplant and correcting the re- mainder of astigmatism with a toric implant. However, Dr. Harvey noted that the patient could still regress. When that happens, the patient is usually better with a toric implant. "Some of my happiest patients are those who have undergone kerato- plasty and then we've put in a toric implant," he said. When surgeons implant a toric IOL post-keratoplasty, they need to be confident that the pa- tient is stable, Dr. Barsam said. His T oric lenses can be a valu- able tool for surgeons, but it's important to be sure they are implanted in the correct candidates. Thomas Harvey, MD, Chippewa Valley Eye Clinic, Eau Claire, Wisconsin; W. Barry Lee, MD, Eye Consultants of Atlanta; and Allon Barsam, MD, London, discussed when they use toric IOLs, particularly relating to patients with irregular corneas. Indications for a toric IOL Most commonly, toric IOLs are indi- cated when the patient is planning to never wear a contact and the astigmatic features are mildly irregu- lar, Dr. Harvey said. This means that there is lower magnitude of astigma- tism and relative regularity, with not too much skewing of the axes. If it's more than 15 degrees from its imag- inary linear axis in each direction, that could be too much, he said. Dr. Harvey said that if the patient's cornea is very warped, a toric implant could be challenging. The surgeon also has to be sure that the information from the readings is accurate. Dr. Barsam said that he rarely uses a toric lens in keratoconus patients. Instead, he uses them more frequently in patients with pellucid marginal degeneration because these patients often have and tolerate an astigmatic correction in their glasses. If they are not using that in either condition, then he doesn't use a toric IOL, he said. If the patient is using astigmatic correction in glasses and is old enough and stable enough that he doesn't think the cornea will change, then that patient could be a candidate for a toric IOL. Dr. Barsam said he is careful to make sure the axis of placement corresponds with topographic features and also with what the patient has in refractive correction in his or her glasses. He is quite cautious when implanting these lenses. When using a toric intraocular lens implant in keratoconus, Dr. Lee said if the patient is young, has worn rigid gas permeable (RGP) lens- es, and liked them prior to cataract surgery, or if the corneal imaging does not show regular bow tie astigmatism, he would avoid a toric Using toric lenses in patients with irregular corneas A toric implant being positioned in an eye with stable keratoconus post-keratoplasty Source: Thomas Harvey, MD

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