Challenges In Iol Power Calculation For Nanopthalmic Eyes

Cataract surgery in nanophthalmic eyes has been associated with a higher rate of complications and a higher degree of refractive predictability. Novel IOL formulas incorporated in the ESCRS calculator have revolutionized IOL calculation in patients with extreme axial lengths. However, within the group of very small eyes (axial length [AL] under 17mm), several challenges still arise. Formulas that perform well in short eyes, such as Pearl DGS, Kane and Hill RBF, no longer work. We reviewed our cohort of nanophthalmic eyes from 2009-2026, focusing on surgical techniques, biometric characteristics and refractive results. Furthermore, we attempted to analyse power calculation differences using the current ESCRS calculator. 

ULS Amadora-Sintra, Lisbon, Portugal. Surgical technique was as follows: general anaesthesia with prior vortex veins massage; anterior capsulorhexis performed through a 1mm side port before main incision; microcoaxial phacoemulsification (2.2mm) with active fluidic in most cases; bimanual irrigation/aspiration was performed carefully attending to floppy capsular bags followed by a single-piece hydrophilic acrylic intraocular lens (IOL) implantation. IOL implantation choice varied between 41-55D.

Eighteen eyes of nine patients with dense cataracts and nanophthalmos were included. Average AL was 16,76±1,37mm (range: 15,43 to 20,19mm), mean keratometry was 47.18±5.51D and ACD was 2.28±0.48mm. Only 4 eyes had AL>17mm. Biometric data were introduced in the ESCRS IOL calculator and refractive variability between formulas was analysed. In older cases biometry was performed with IOLMaster500, therefore lens thickness (LT) was ommitted. We calculated the agreement between formulas (difference between highest and lowest suggested IOL power). Good agreement was defined as a difference within 1D.

All surgeries achieved DCVA improvement and patient satisfaction. Intraoperative complications were iris prolapse (n=3); CTR insertion in the bag prior to IOL implantation (n=3); and iris retractors use (n=2). Cooke K6, EVO and HofferQST were calculated for most cases. Good agreement between formulas (±1D) was registered in all eyes with AL>17mm (n=4). In the other eyes (AL<17mm), IOL power variability averaged 3,15D. HofferQST consistently estimated lower IOL power, with a tendency towards hyperopia. EVO and Cooke K6 provided results closer to the final refraction. The highest IOL power differences of 4-4,5 D (n=3) occurred in patients with AL of 15,43, 15,64 and 16,1mm, suggesting that the lower the AL the highest the variability.

Although cataract surgery in nanophthalmic eyes is probably one of the most challenging procedures, in our experience, a careful surgical approach has good clinical outcomes. Our cohort of patients with an average AL of 16,73mm showcases challenges that still exist. Modern IOL calculator tools help achieve better results, yet below 17mm AL higher variability between formulas is apparent. Analysing our data, although limited by the retrospective nature, formulas such as Cooke K6 and EVO from the ESCRS calculator seem to provide good results in this cohort of patients, while HofferQST appears to show a tendency towards hyperopia. Larger databases in this niche population are needed to draw more robust results.