Intraocular lens power requirements for humanitarian missions

Purpose

To develop a generalized method to determine an optimum set of intraocular lens (IOL) powers for humanitarian missions.

Setting

Humanitarian missions to Central America, South America, and Southeast Asia.

Methods

Biometric data of adults who had cataract surgery on 2 humanitarian missions were reviewed, and the ideal emmetropic IOL power for each eye was calculated. Using statistical modeling, the number of extra IOLs required at each power to account for natural variation inherent in random population samples was calculated. To limit the total number of IOLs and maximize availability of suitable IOLs for each patient, a tolerance strategy for choosing IOL powers was developed and the ideal proportion of extra IOLs required at each power was empirically determined.

Results

Data of 103 patients were reviewed. The mean IOL power was 20.38 diopters (D) ± 2.32 (SD). Applying a tolerance strategy to accept IOLs with powers 0.5 D below or 1.0 D above the emmetropic IOL power, the number of extra IOLs required at each power was decreased to a fraction of the fourth root of the number of eyes anticipated to require that IOL power. The model predicted that with this strategy, fewer than 2% of all patients would be rejected due to lack of an IOL with a suitable power.

Conclusions

The spreadsheet-based IOL power prediction model calculated an ideal distribution of IOLs to order for humanitarian cataract surgery. It is generalizable to missions of any size and should help planners minimize costs while ensuring excellent refractive outcomes.