Predicting Refractive Outcomes of Cataract Surgery
Ophthalmology, July 2018
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.