Anterior chamber depth predicts refractive errors after cataract surgery
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Patients who underwent cataract surgery showed increased anterior chamber depth postoperatively, which correlated with refractive error.
Additionally, study investigators found that changes in the anterior chamber depth (ACD) correlated with preoperative ACD and axial length.
“Our preliminary results suggested that the ACD played an important role in predicting postoperative [refractive error] after cataract surgery,” the researchers wrote. “A hyperopic shift would often occur when the change in the ACD was smaller, whereas a myopic shift was related to a larger change in the ACD, which determined the refraction status and visual quality. In addition, the regression formula of the ACD could provide a theoretical basis for predicting refractive errors in the clinic.”
The study involved 125 patients (145 eyes) who underwent phacoemulsification without complication. Fifty-five patients had lens thickness data available.
Postoperative ACD was different between 2 days and 2 weeks (4.16 mm vs. 4.31 mm; P = .016); however, there was no difference between 2 weeks and 1 month.
“This indicated that the ACD tended to stabilize gradually 2 weeks postoperatively,” the researchers noted.
They also found that a hyperopia shift of refractive errors would often occur when there was less change in ACD after cataract surgery, whereas a myopic shift correlated with more of a change in ACD.
The change in ACD was significantly larger in the shallow anterior chamber than the deep chamber. Similarly, the overall change in ACD, refractive errors and absolute refractive errors were different in the short axial length compared with normal axial length (P < .05) and the long axial length (P < .01).
The researchers proposed possible formulas to predict postoperative ACD: postoperative ACD = 3.524 + 0.294 × preoperative ACD; postoperative ACD = 3.361 + 0.228 × (preoperative
ACD + 1/2 lens thickness). As noted, postoperative ACD did not correlate with the lens thickness.
“The ACD is an index that reflects the effective position of the IOL, which means that the prediction errors of the postoperative ACD will lead to a myopia or hyperopia shift after cataract surgery,” the researchers wrote. “Therefore, ACD plays an important role in predicting postoperative refractive errors after cataract surgery.” – by Talitha Bennett
Disclosures: The authors report no relevant financial disclosures.
Perspective
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Donald Mutti, OD, PhD, FAAO
Cataract surgeons are always looking for the formula that will do the best job of calculating the IOL power to implant to hit a target postsurgical refractive error. These various formulas hit this target within ±1 D about 90% of the time using preoperative measurements of keratometry, axial length and anterior chamber depth. The performance of the more recent formulas all seemed very much the same. The wild card is where the IOL will eventually land within the eye. Due to effectivity, an IOL that is more anterior than predicted will result in a more myopic refractive error and vice versa if more posterior than predicted.
The data from Ning and colleagues do not add much to this prediction challenge. They find what most formulas already use, that preoperative anterior chamber depth helps to predict how deep the IOL will be located postoperatively. The eye is living tissue and it resists being totally predictable. New data will be needed to crack the mystery of the 10% with more significant postoperative refractive errors. Cataract surgeons may continue their search for a formula that hits the refractive error target more often, but correction of residual refractive error post-cataract surgery is still just a visit to the optometrist away.
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