• Predicting Refractive Outcomes of Cataract Surgery

    By Lynda Seminara
    Selected By: Stephen D. McLeod, MD

    Journal Highlights

    Ophthalmology, July 2018

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    Accurate measurement of axial length (AL) and corneal power (K) is essential for achieving good visual outcomes from cataract surgery. Surgeons often compare biometry between the 2 eyes to check for discrep­ancies. However, data are lacking to describe the rela­tionship between the degree of discrepancy and the refractive outcomes. Kansal et al. aimed to determine whether interocular differ­ences in AL or K are predictive of refrac­tive outcomes. They found that an AL difference of just 0.2 mm is linked to greater likelihood of refractive errors exceeding 0.5 D from the target value and to poorer uncorrected visual acuity (UCVA). An interocular difference in K correlated with poorer UCVA but not with substantial refractive error.

    This retrospective study included 729 patients (1,458 eyes) who under­went bilateral phacoemulsification at a laser eye center in Canada. The primary outcome was the incidence of biometry prediction error, defined as a difference of >0.5 D between the target and postoperative refractive power. Secondary outcomes included postoperative UCVA >0.3 logMAR and differences of >0.25 D and >1.0 D between target and postoperative refractive powers. The primary predictors were the absolute value of the interocular AL difference and absolute values of interocular K differences (steep, flat, and average).

    Results showed that approximately 79% of eyes had outcomes within 0.5 D of target values, 47% were within 0.25 D, and 97% were within 1.0 D. The odds ratios for a refractive out­come >0.5 D from target for the 0.2-mm, 0.3-mm, and 0.4-mm cutoffs for interocular AL difference were 1.4 (95% confidence interval [CI], 1.1-1.8), 1.6 (CI, 1.2-2.1), and 1.8 (CI, 1.3-2.5), respectively. This translates to 70.0% being within target for interocular AL difference >0.4 mm versus 80.7% for that of <0.4 mm. For eyes that fell out­side the target threshold, twice as many were below 0.5 D as above 0.5 D.

    Interocular differences in K generally were not associated with prediction errors, but increasing steepness or flatness was linked to greater odds of UCVA >0.3 logMAR.

    The authors suggested that these cutoff points be considered in preop­erative planning, including discussions with patients. Further research is war­ranted to determine whether certain methods could reduce refractive error, such as repeating measurements, using adjunct measuring tools, or attempting to separate true differences from arti­fact based on preoperative refractive characteristics.

    The original article can be found here.