Eyeworld

EW CATARACT 36 October 2016 Even optical biometry could not measure to the retina in this 40.59 mm globe A cataract case brought before Kevin M. Miller, MD, professor of clinical ophthalmology, Univer- sity of California, Los Angeles, a few years ago "may be the most myopic eye ever operated on in the world," he said. Speaking recently about this complicated case, which involved a patient whose eyes were of unusual- ly long axial lengths—40.59 mm in the right eye and 38.29 in the left— Dr. Miller said a quick literature search didn't yield any published cases where the globe was longer than 40 mm. He also asked the fore- most experts on lens power calcula- tions—Jack Holladay, MD, Douglas Koch, MD, and Warren Hill, MD— about their longest eyes at the time this case was presented to him and found none of them recalled oper- ating on an eye with an axial length longer than 37.5 mm. Dr. Koch said his longest axial length was 34 mm. Cataract surgery on long eyes presents some specific challenges, especially with regard to accurate IOL power calculations but also surgically. "The bottom line is you need to target myopia using the most accurate formulas to achieve em- metropia," Dr. Miller said. "In most of these eyes, you want to go even further than that because the last thing you want is a highly myopic eye ending up hyperopic. Patients will be utterly miserable if they're hyperopic." The reason myopia should be targeted in lens power calculations is due to the inaccuracy of axial length measurements using ultrasound or even optical biometry. This 41-year-old patient, who had Crouzon syndrome, had a staphyloma of her posterior seg- ment, meaning it was misshapen, Dr. Miller said. One cannot assume that the farthest point back in the eye is her locus of best vision, which is where axial length is usually measured. "The functional axial length is going to be where on the retina she's looking from, the locus of best eccentric fixation. It's not going to machines have gates on them and they expect to see the retina in a certain area; if it's too far out of the window, they just can't see it." He said even after the cata- ract was taken out and a clear lens placed, the optical biometers still couldn't find her retinas. Even if optical biometry is used in cases of long eyes, Dr. Miller said the lens power calculations are still not exactly accurate. He recom- mended physicians use something like the Wang-Koch adjustment, de- veloped by Li Wang, MD, PhD, and Dr. Koch to compensate for this. "The reason is that the machine makes an assumption about the average speed of light through the eye," Dr. Miller said. "When light goes through the cornea and lens, it be the point farthest back in the eye because that's totally ectatic and probably has no rods and cones," Dr. Miller said. "You have to assume the functional axial length is short- er, therefore, you have to go with a higher power lens." As such, Dr. Miller recommends using optical biometry in long eyes because it allows physicians to identify the locus of best eccentric fixation by having the patient look at the machine's fixation target. He tried to do this with the IOLMaster (Carl Zeiss Meditec, Jena, Germany) and the LENSTAR LS 900 (Haag- Streit, Koniz, Switzerland) with this patient but could not get readings. "The machines simply couldn't see the back of her eye," Dr. Miller said. "I think it was too far back. The Cataract surgery on what could be "the most myopic eye ever operated on" by Liz Hillman EyeWorld Staff Writer T here are many challenges we encounter in cataract surgery. Many times we can anticipate them beforehand and try to plan appropriately. Some are preop, some intraop, and some postop. In this "Cataract editor's corner of the world," we get an up-close view of the challenges we face with a highly myopic eye. This one is incredible. Most "highly" myopic eyes will have an axial length in the low- to mid-30s, but this is a case of a 40+ mm axial length eye. Intraoperative challenges of high myopes are daunting, but I think sometimes our biggest chal- lenges are with IOL calculations in such a long eye. Kevin Miller, MD, discusses IOL cal- culations and formulae he used to help get the best visual outcome for this incredible patient. He had discussed aspects of the case with Jack Holladay, MD, Doug Koch, MD, and Warren Hill, MD, who are some of the greatest thought leaders in this field, and came up with the best solution to this daunting issue. Read on and see what he decided to do given all the challenges and what the final outcome was for this patient. Rosa Braga-Mele, MD, MEd, FRCSC, Cataract editor A complicated cataract surgery case involved a patient with extremely long eyes. Her right eye had an axial length of 40.59 mm, her left 38.29 mm. Source: Kevin M. Miller, MD Cataract editor's corner of the world

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