Intraocular lens power calculation in short eyes

To compare the accuracy of the Hoffer Q and SRK-T formulae in eyes below 22 mm in axial length, using biometry measured with partial coherence inferometry (PCI), without a customised ACD constant.

Data were retrospectively and prospectively collected by identifying eyes of axial length below 22 mm in the records of the intraocular lens (IOL) master and in preoperative notes. Biometry was performed using PCI and IOL power was calculated using both SRK-T and Hoffer Q formulae. Refractive outcome was measured and the accuracy of the two formulae compared.

Forty-one eyes of 41 patients were identified with an axial length <22 mm. Axial lengths ranged from 21.96 to 20.29 with a mean of 21.51 mm, and IOL power ranging from 23 dioptres (D) to 29 D. The Hoffer Q formula showed a mean prediction error of 0.61 D (SD 0.80) compared with the SRK-T, which showed a mean prediction error of 0.87 D (SD 0.829). A paired t-test found that the Hoffer Q was significantly more accurate than the SRK-T formula (P<0.001).

Hoffer Q was found to be more accurate than the SRK-T formula in this series of eyes <22 mm axial length when customised ACD constants are not used. Royal College of Ophthalmologists guidelines may need to be adjusted in accordance with these findings. This study underlines the importance of monitoring outcomes, and suggests different customisations are needed for different formulae, with a higher correction if the SRK-T formula is used for short eyes.