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Anterior chamber depth measurement of fellow eye reduces refractive error
A subgroup of 36 eyes with prediction error of more than 0.5 D had shorter axial lengths and shallower anterior chambers than other eyes.
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Fellow-eye postoperative anterior chamber depth measurements taken 1 month after cataract surgery predicted refractive outcomes better than measurements taken at 1 day, according to a study.
Anterior chamber depth prediction error is the primary source of error in IOL power calculations with the availability of modern biometry, the study authors said, quoting Norrby.
“The most significant finding is that we now have very powerful means of measuring where the lens is sitting after surgery,” Irene C. Kuo, MD, the corresponding author, told Ocular Surgery News. “We can try to use the fellow eye information before we possibly plan timing of the second eye operation or plan the IOL power. That has always been a concern, when patients or surgeons want to wait a month or a week between surgeries or, in some parts of the country, perform simultaneous bilateral cataract surgery.”
Methods and measures
The consecutive case series, published in the Journal of Cataract and Refractive Surgery, included 130 eyes of 65 patients who underwent phacoemulsification and implantation of an SA60AT IOL (Alcon) by one surgeon. Most patients had second-eye surgery 2 weeks or less after first-eye surgery.
The authors compared refractive outcomes using fellow-eye postoperative anterior chamber depth in IOL power calculations with outcomes obtained without fellow-eye data and assessed postoperative anterior chamber depth stability.
The Lenstar LS 900 (Haag-Streit) with optical low-coherence reflectometry was used to measure axial length, corneal pachymetry, preoperative and postoperative anterior chamber depth, keratometry, lens thickness and IOL thickness. Anterior chamber depth was measured 1 day and 1 month postoperatively. Manifest refraction was evaluated at 1 month.
A program that input the operative eye’s actual measurements in the Olsen IOL power formula was used to predict postoperative anterior chamber depth and refractive outcomes. The program was also used to calculate theoretical refractive outcomes of inputting fellow-eye anterior chamber depth at 1 day and 1 month. Theoretical results were subtracted from the manifest refraction and optimized. Calculations were done for each eye.
“We were trying to see if we could retrospectively plug in postoperative data from the one eye into the fellow eye and compare these refractive outcomes to the outcomes we actually obtained,” Kuo said.
Primary outcome measures were the optimized median absolute error (MedAE) and anterior chamber depth at 1 day and 1 month after surgery as measured by optical biometry.
Results and conclusions
MedAE was 0.32 D with the Olsen formula without fellow-eye data, 0.33 D with fellow-eye postoperative day 1 anterior chamber depth, and 0.28 D with fellow-eye postoperative month 1 anterior chamber depth; the difference between the latter two MedAE values was statistically significant (P < .0005).
According to Kuo, Olsen said that by improving mean absolute error from 0.4 D to 0.32 D, the percentage of cases with refractive error less than 0.5 D increased from 68% to 78%.
“Over 2.5 million cases, the number of cataract cases done in the U.S. per year, a decrease in median absolute error from 0.33 to 0.28 is likely quite sizeable in increasing the number of patients who will be within 0.5 D of their target refraction,” Kuo said.
The difference between the optimized postoperative day 1 MedAE and postoperative month 1 MedAE using fellow-eye anterior chamber depth was statistically significant (P < .001). Conversely, differences between the optimized postoperative day 1 MedAE and optimized Olsen MedAE and between the optimized postoperative month 1 MedAE and optimized Olsen MedAE were not significant.
A subset of 36 eyes in which the optimized Olsen absolute error exceeded 0.5 D had a shorter axial length and shallower anterior chamber than the other eyes, Kuo said.
“You probably don’t want to do the two eyes of such patients on the same day or even a week apart. You want to wait about a month and see how the first eye does and then plan the second eye,” she said. “You might want to counsel these patients.”
In the eyes with an Olsen prediction error exceeding 0.5 D, use of either 1-day or 1-month anterior chamber depth in the fellow eye yielded significantly lower prediction errors (P .01).
Anterior chamber depth decreased by a mean of 148 µm, the authors reported.
Postoperative shallowing of the anterior chamber can be attributed to fibrosis, Kuo said.
“I think a lot of it is there is fibrosis that occurs as the eye is healing,” she said. “The bag that once held a large cataract is now holding a much smaller lens implant. The bag is contracting, so the lens is moving forward.”
There are few reports of the refractive outcome of using final postoperative anterior chamber depth in IOL calculations and none using postoperative day 1 measurements.
Further study may improve IOL power selection in routine cases and complicated cases, such as those involving previous refractive surgery, the authors said. – by Matt Hasson
- References:
- Muthappan V, et al. J Cataract Refract Surg. 2015;doi:10.1016/j.jcrs.2014.08.034.
- Norrby S. J Cataract Refract Surg. 2008;doi:10.1016/j.jcrs.20doi:7.10.031.
- Olsen T. Ophthalmology. 2011;doi:10.1016/j.ophtha.2011.04.030.
- For more information:
- Irene C. Kuo, MD, can be reached at Wilmer Eye Institute, 4924 Campbell Blvd., Suite 100, Baltimore, MD 21236; email: ickuo@jhmi.edu.
Disclosure: Kuo reports no relevant financial disclosures.