REFRACTIVE OUTCOME, LENS POWER CALCULATION AND SURGICAL INDUCED ASTIGMATISM AFTER 4 FLANGED INTRASCLERAL INTRAOCULAR LENS FIXATION

To evaluate the refractive prediction error of common intraocular lens (IOL) power calculation formulae in patients who underwent intrascleral IOL fixation using the 4-flanged technique.

Department for Ophthalmology and Optometry, Medical University of Vienna, Austria

Prospective, longitudinal, single-site, single-surgeon study

Patients who received intraocular lens implantation via the 4-flanged technique were followed up three months after the operation. Refraction was measured using the best-corrected visual acuity test at four metres (ETDRS chart). Lens decentration, tilt, and effective lens position (ELP) were evaluated using an anterior segment optical coherence tomography (AS-OCT). The SRK/T, Holladay1, and Hoffer Q formulas were used to assess prediction error (PE) and absolute error (AE). Correlations between axial length, keratometry, and white-to-white distance were subsequently evaluated.

A total of 28 eyes of 28 patients were examined in this study. The application of all formulae resulted in a hyperopic PE, with SRKT: 0.35±0.86D, Holladay1: 0.36±0.78D and HofferQ: 0.37±0.73D. There was no variation between the PE of different formulae discovered (p>0.05). The AE was within 0.5 D in 54% to 61%

and within 1D in 79% of eyes, depending on the formula used. Furthermore, Cochranes Q test detected no significant distinctions between formulae (p>0.05). The PE of each formula demonstrated a significant correlation to the axial length of the eyes (p<0.05). The correlation estimates ranged from -0.25D/mm to -0.39D/mm, subject to the applied formula.

Our study demonstrates that the four-flanged technique for scleral intraocular lens (IOL) fixation yields reliable outcomes. PE was closest to zero using the Hoffer Q formula, although there was no statistically significant difference compared to the other formulae. AL emerged as the most pertinent factor for PE. Short eyes resulted in a more hyperopic outcome, while longer eyes resulted in a more myopic outcome, than intended. The underlying reason for this myopic and hyperopic shift is due to the standardized surgical technique with a externalization of the haptics 2.5mm behind the limbus resulting in a consistent ELP across all eye lengths, coupled with a reduction or increase in the distance from the IOL to the macula, which is dependent on the length of the eye.