OCT-based IOL formula shows promise in eyes without previous refractive surgery

J Refract Surg. 2010;26(6):430-437.

An IOL power calculation formula based on optical coherence tomography equaled conventional methods in cataract patients without previous laser vision correction, a study showed.

"This new formula is based on direct OCT assessment of the posterior curvature and avoids the calculation errors inherent in conventional IOL formulae," the study authors said. "The new OCT-based IOL formula might be a promising solution for cataract patients with prior laser vision correction because OCT measures the actual posterior corneal curvature instead of assuming a fixed value or a fixed relationship with the anterior curvature."

The prospective study included 27 eyes of 27 patients without previous laser vision correction who underwent phacoemulsification and IOL implantation; 24 eyes received the AcrySof SN60AT and three eyes received the SA60AT (both Alcon).

The IOLMaster (Carl Zeiss Meditec) was used to measure anterior corneal power and axial length. A high-speed anterior segment OCT prototype (Zeiss) was used to measure anterior chamber depth and crystalline lens thickness and map corneal thickness.

Posterior corneal curvature was calculated by combining IOLMaster keratometry with OCT corneal thickness mapping. A new IOL formula based on those measures was compared with three existing formulae: SRK/T, Hoffer Q and Holladay II.

Study data showed that at 1 month after surgery, the mean prediction error in postoperative manifest refraction spherical equivalent was 0.04 D for the OCT formula and –0.35 D for the SRK/T.

Eighteen eyes using the SRK/T formula and 21 eyes using the OCT formula were within 0.5 D of targeted refraction. Differences between formulae were statistically insignificant, the authors said.

Further study is warranted to ensure surgical and refractive accuracy, they said.

Follow OSNSuperSite.com on Twitter.