Compression forces of haptics of selected posterior chamber lenses

To compare the compressive forces of the haptics of different intraocular lens (IOL) models and analyze the observed differences.

Central Hospital of Central Finland and University of Jyväskylä, Jyväskylä, Finland.

The haptics of 28 IOL models were compressed to a diameter of 9.0 mm. The compression forces were measured at 0.5 mm intervals. The conclusions were verified by numerical simulations of mechanical models of the lenses.

The measured forces varied between 100 and 601 mg at a diameter of 11.0 mm, 206 and 1057 mg at a diameter of 10.0 mm, and 315 and 2094 mg at a diameter of 9.0 mm. The slopes of the force curves of the three-piece lenses were fairly linear. In general, the three-piece models were less rigid than one-piece models and underwent plastic deformations after repeated compressions. For most one-piece models, compression force increased progressively with increasing compression. The overall IOL diameter and differences in haptic thickness and length and the angle between optic at the point of haptic insertion were the main causes of the observed differences in the compression forces. The variation in forces between individual specimens of the same model, which occurred with almost all models, were mainly the result of variations in haptic thickness.

Great variations in the compression forces of the IOL haptics were found. Compression behaviors should be taken into account when selecting a lens to implant.