October 2016

 

CATARACT

 

Cataract editor’s corner of the world

Cataract surgery on what could be “the most myopic eye ever operated on”


by Liz Hillman EyeWorld Staff Writer

 
 

Rosa Braga-Mele, MD
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 challenges are with IOL calculations in such a long eye. Kevin Miller, MD, discusses IOL calculations 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

 
Eye

Patient with long eyes
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

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, University 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 unusually 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 foremost experts on lens power calculations—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 operating 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 emmetropia,” 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 segment, 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 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 shorter, 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 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 cataract 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 recommended physicians use something like the Wang-Koch adjustment, developed 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 travels slower. When it goes through the aqueous and vitreous, it travels faster. Unfortunately, optical biometers make an assumption about the average speed of light through the whole eye so that you can calculate the distance from the front to the back based on the average speed. The extremely myopic eye is going to have a bigger vitreous cavity, so the amount of time light is going to spend traveling in the vitreous is much greater. However, the assumption is that the lens and cornea comprise a certain percentage of the overall length of the eye, which is totally off when you have a myopic eye. So the speed of light calculation is off; it doesn’t measure the actual axial length of the eye. You have to compensate.” Based on ultrasound measurements, the SRK-T formula, and his own compensation, Dr. Miller chose a –7 D lens for this patient. Calculations using SRK-T alone recommended a –10 D lens. While the main challenge in these eyes is lens power calculation, this case specifically held some other complications as well. This patient had an irregular cornea showing 44 D in some spots and 33 D in others. This irregularity was due in part to the patient’s eye being exposed more than normal and drying due to the fact that she had small orbits, which are associated with Crouzon syndrome. She had previous tarsorrhaphy to allow her to fully close her eyelids, which Dr. Miller noted were extremely thin. She also had strabismus, where when her eyes were relaxed they pointed toward her nose. As such, Dr. Miller couldn’t have her head turned straight toward the microscope for the operation. Rather, he had her turn her head to the opposite side so her eye was in the proper orientation with respect to the microscope. Surgically, Dr. Miller said long eyes also demonstrate more trampolining of the lens-iris diaphragm. “When you go into such an eye, you have to lower the bottle height big time—I mean, really close to the eye,” he said, adding that if your machine has pressurized infusion, the IOP setting should be set very low. Another issue is that lens implants for highly myopic eyes come only in three-piece designs. The haptics of these lenses are generally too short for the capsular bag, leading many of these cases to develop capsular striae. “We prepare patients for this, and they get a laser capsulotomy to make the starburst symptoms go away somewhere down the road,” Dr. Miller said. “They also develop posterior capsule opacification fast because the capsule doesn’t shrink wrap to the lens very well because it’s big and floppy. Lens cells get behind the optic really fast.” Finally, Dr. Miller said that patients with long eyes, like this woman, need to be counseled and prepared for their likely visual outcomes. “These patients have cataract surgery expecting they’ll be like their friends—20/20 perfect vision without correction afterward—and that’s not the way it is,” Dr. Miller said. In the end, Dr. Miller said this cataract surgery was “a total life changer.” The patient’s visual acuity with correction was 20/80 in the right eye and 20/25 –2 in the left. Her manifest refraction produced 20/70 in her right eye and 20/25 +2 in her left. Even with a mild residual refractive error, Dr. Miller said, for this patient, “it was amazing.” “Never argue with success—what a great result!” Dr. Koch said, reviewing Dr. Miller’s case. “It appears as if he made an estimate of how much to increase the IOL power to avoid postoperative hyperopia.” Dr. Koch offered an example of the Wang-Koch adjustment for the Holladay 1 formula, which suggested that the optimized axial length in this case was 37.91 mm. Plugging this figure into the LENSTAR calculation, selecting the IOL closest to plano on the minus side, would recommend –7.0 D—the same IOL Dr. Miller inserted with the excellent refractive outcome.

Editors’ note: Drs. Miller and Koch have no financial interests related to their comments.

Contact information

Koch
: dkoch@bcm.edu
Miller: kmiller@ucla.edu

Related articles:

Management of capsule rupture at cataract surgery by Steve Charles, MD

Double trouble: Diplopia following cataract or refractive surgery by Maxine Lipner Senior EyeWorld Contributing Editor

ASA classifications correlate with cataract surgery outcomes by Vanessa Caceres EyeWorld Contributing Writer

Cataract surgery varies by race, state, even latitude by Matt Young and Gloria Gamat EyeWorld Contributing Writers

Gender inequality in some pediatric cataract surgery cases by Liz Hillman EyeWorld Staff Writer

How are we performing nucleus division during cataract surgery? by Mitchell Gossman, MD

Uveitis: Posterior synechiae, lens deposits, CME, prolonged post-op inflammation, and secondary glaucoma by James P. Dunn, M.D.

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