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Laser capsulotomy optimizes effective lens position, refractive outcomes
A large patient group, single surgeon and controlled clinical environment afford a detailed statistical analysis showing the laser method’s predictability.
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 Warren E. Hill |
ORLANDO, Fla. — Femtosecond laser anterior capsulotomy yielded more predictable refractive outcomes than manual capsulorrhexis methods, a surgeon said here.
Capsulotomy technique and other factors influence effective lens position, a key determinant of refractive outcomes, Warren E. Hill, MD, FACS, said at the American Academy of Ophthalmology meeting.
“The effective lens position is influenced by a number of factors,” he said. “The main surgical influence is the configuration of the capsulorrhexis. It should be round, centered and slightly smaller than the optic of the IOL. The wonderful accuracy of femtosecond laser capsulotomy provides an incremental improvement in refractive outcomes. We can predict what this will be if we have numbers that are large enough and a controlled surgical situation.”
The measurement of axial length, central corneal power and the IOL power calculation formula used also have a significant influence on refractive outcomes, Dr. Hill said.
“It’s important to keep in mind that the capsulorrhexis is only one part of a multi-part process. So, the accuracy of all of the other components enter into the process,” he said.
Small patient group
“We have assumed that a perfect capsulorrhexis improves refractive outcomes. But up until now we haven’t had enough data to know exactly how much,” Dr. Hill said. “So, I’m going to talk about how effective lens position influences the refractive outcomes with some numbers that actually make sense.”
The first data set included 44 patients who underwent laser capsulotomy and 62 patients who underwent manual continuous curvilinear capsulorrhexis (CCC). Mean patient age was 67 years in the laser capsulotomy group and 66.4 years in the manual capsulorrhexis group.
Mean anterior chamber depth was 3.27 mm in the laser capsulotomy group and 3.35 mm in the manual CCC group. Mean axial length was 23.64 mm in the laser capsulotomy group and 23.48 mm in the manual CCC group.
All patients underwent standard phacoemulsification performed by a single surgeon using a single technique. All patients received an AcrySof SA60AT IOL (Alcon). The same IOL power calculation formula was used in all cases. The IOLMaster (Carl Zeiss Meditec) was used to measure axial length and keratometry values.
Study data showed that 81% of patients in the laser group and 74.6% of patients in the manual capsulorrhexis group had manifest refraction spherical equivalent within 0.5 D of the targeted result at 6 months, Dr. Hill said.
Enhanced predictability
A larger data set included 249 patients in the laser capsulotomy group and 123 patients in the manual CCC group.
The mean standard deviation from the targeted manifest refraction spherical equivalent was 0.39 D in the laser capsulotomy group and 0.41 D in the manual capsulorrhexis group, Dr. Hill said.
“When we do error analysis … what we do is calculate the mean absolute error for each individual component part that influences the refractive outcome,” he said. “Then, we identify the individual parts. We take the mean absolute error of each individual component, square them, sum them and take the square root of the sum of the squares. That gives you the absolute error for a series of patients.”
Mean absolute error for optical biometry, a 0.5 D-step high-quality IOL, small-zone autokeratometry, SRK/T formula at schematic eye parameters, and variable capsulorrhexis size, shape and position yielded a mean absolute error of 0.58 D.
Excluding variable capsulorrhexis size, shape and position, the square root of the sum of the squares predicted a mean absolute error of 0.4 D, he said.
The absolute deviation from the targeted manifest refraction spherical equivalent was 0.42 D in the laser capsulotomy group and 0.59 D in the manual CCC group.
“The outcomes that we predict and what we’re beginning to see with large enough numbers with a single surgeon in a highly controlled setting look very good and very close,” Dr. Hill said. – by Matt Hasson
- Warren E. Hill, MD, FACS, can be reached at East Valley Ophthalmology, 5620 E. Broadway Road, Mesa, AZ 85206; 480-981-6111; fax: 480-985-2426; email: hill@doctor-hill.com; website: www.doctor-hill.com.
- Disclosure: Dr. Hill is a consultant for LensAR and is a member of the company’s medical advisory board.