OSNAPAO: Refractive outcomes of cataract surgery increasingly important, but results remain suboptimal

The accuracy of postoperative refractive outcomes is key to a successful cataract surgery, especially when more and more refractive lensectomies are being performed. Increasingly, patients are demanding complete postoperative spectacle independence.

Recent advances in biometry have increased the accuracy of refractive outcomes. Unfortunately, outliers exist, and in general, postoperative refractions are still largely suboptimal. Measurement errors affect the spherical equivalent while ignoring pre-existing astigmatism, and surgically induced astigmatism increases the chances of having significant postoperative astigmatism. The cover story in this issue talks about recent advances in biometry, including intraoperative biometry, and ways to reduce postoperative astigmatism.

The latest developments in optical biometry have contributed to improving accuracy in spherical prediction. The new optical biometry equipment can measure not only axial length but also other associated parameters for more precise spherical equivalent prediction. These advanced measurements consistently help achieve more successful scans and accurate results in our practice. Even in difficult cases such as dense cataract, the results are reported to be reliable. However, extremely dense cataracts are still an exception in which we resort to ultrasonic biometry. Post-LASIK cases can also be a challenge because the Zeiss IOLMaster’s keratometry readings are often underestimated, resulting in curvature underestimation and myopic shift when estimating IOL power. These are problems that still need to be addressed.

Simultaneous correction of astigmatism in cataract surgery is an important component in achieving good refractive outcomes. The three commonly used techniques and technologies are astigmatic keratotomy, surgically induced astigmatism and toric IOL implantation.

As a small amount of misalignment from the intended axis in the placement of a toric IOL translates exponentially into significant deviation, we need accurate preoperative axis measurements and precise intraoperative placement. Intraoperative biometry claims to be able to improve the accuracy of the postoperative IOL position. Its ability to intraoperatively measure anterior chamber depth can also help in IOL selection. However, how accurately intraoperative parameters reflect postoperative IOL position is still unknown. Additionally, the effects of wound healing over time on postoperative refraction would compromise the value of intraoperative refractive measurement.

In our experience, a phaco corneal wound takes up to 6 weeks to heal, while IOL position and anterior chamber depth have been reported to take up to 6 months to stabilize. In other words, even with accurate intraoperative measurements, refraction is still expected to evolve for months postoperatively. Although this new intraoperative technology may be appealing, the cost-effectiveness of employing an expensive technology with confounding factors that affect the final results is questionable. We need more clinical studies and data to further evaluate the claims of this new technology.

Modern cataract surgery is demanding better refractive accuracy. Advances in technology and comprehensive working protocols help achieve high accuracy with fewer refractive surprises. Still, continuous refinement is needed and expected.

References:

Iwase T, et al. Br J Ophthalmol. 2006;doi:10.1136/bjo.2006.097766.

Koeppl C, et al. J Cataract Refract Surg. 2003;doi:10.1016/S0886-3350(02)02049-7.

Wong CW, et al. J Cataract Refract Surg. 2015;doi:10.1016/j.jcrs.2014.06.034.

For more information:

Dennis S.C. Lam, MD, FRCOphth, can be reached at State Key Laboratory in Ophthalmology, Sun Yat-Yen University, 54 South Xianlie Road, Guangzhou 510060, People’s Republic of China; email: dennislam.gm@gmail.com.

Disclosure: The authors report no relevant financial disclosures.

Click here to read the full commentary published in Ocular Surgery News APAO Edition, July/August 2015.