Study on IOL Power Calculation in Elderly Patients

A study conducted by researchers from Shiley Eye Institute, University of California San Diego, USA has shown that elderly patients undergoing cataract surgery are likely to have the most predictable refractive outcome when IOL power calculation is done using the Kane or the Barrett Universal II formula.

The study has been published in the Journal of Cataract and Refractive Surgery.

Cataract surgery has now become almost a refractive procedure due to increasing patient demand for spectacle independence post-surgery. Accurate biometry and IOL power calculation formula are essential to achieve the same. Extensive research has been going on in the field of IOL power calculation formulae but predictability of refractive outcome over a wide range of axial length and keratometry still remains a challenge.

The latest formula being studied is the Kane formula. Developed in 2017, this formula is based on theoretical optics and incorporates both regression and artificial intelligence components. The main focus of the formula is to reduce the errors seen at the extremes of the various ocular dimensions. It incorporates multiple variables like axial length, keratometry, anterior chamber depth, lens thickness, central corneal thickness, and patient gender.

A retrospective cohort study was conducted by the researchers with data collected from 90 eyes of 90 patients who had undergone uneventful cataract surgery with SN60WF intraocular lens implantation. All patients were elderly, aged 75 years or above. The first operated eyes of the patients having uncorrected distance visual acuity of 20/30 or better were included in the study. All eyes had axial length between 22-26mm. Prediction errors were calculated for Barrett Universal (BU) II, Haigis, Hoffer Q, Holladay 1, SRK/T, and Kane formulae. Two subgroups were formed based on the age: Subgroup I (75-84 years) and Subgroup II (>85 years) and a separate analysis was also done for each group.

Results

• The predictive accuracy within ±0.5D was significantly higher with the Kane and the Barrett Universal II formulae as compared to Hoffer Q, Holladay 1, and SRK/T.
• Percentage of eyes with prediction errors within ±0.50 D was 72% with each of the two formulae.
• Rate of predictability within ±1.00 D was 87% to 92% with no significant differences between the different formulas.
• Rate of predictability within ±0.25 D was 31% to 38% with no significant differences between the different formulae.
• Subgroup analysis showed better predictability of all formulae in the younger age group.

According to the authors, there is no available literature evaluating the Kane formula exclusively in the elderly population. In this study, the Kane formula was found to be of equal accuracy to the Barrett Universal II and superior to the Hoffer Q, Holladay 1, and SRK/T formulas.

"Elderly patients undergoing cataract extraction might have less predictable refractive outcomes. This group could benefit from IOL calculations with the Kane and the Barrett Universal II formulas." conclude the authors.

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