[IOL calculation for high ametropia]

Long and short eyes are connected with high ametropia and constitute special problems for biometry and IOL calculations. Ultrasound measurements on these eyes, which often have altered geometries, are frequently more difficult than in normal eyes. This holds especially for long eyes, which significantly benefit from optical biometry. Measurement errors, IOL manufacturing tolerances and uncertainties regarding the effective lens position affect short eyes much more than normal eyes. The selection of a suitable IOL formula is of special importance for the refractive outcome. For short eyes, Holladay-2, HofferQ and Haigis are recommended, for long eyes Holladay-1, Holladay-2 and Haigis. In each case, optimized IOL constants must be used. If minus lenses for extremely long eyes are calculated with the same constants as plus lenses, a hyperopic refractive error is created, which can be avoided by a separate set of constants for minus lenses. For extremely short eyes the commonly used approximation of thinner lenses fails necessitating a thick lens calculation or raytracing.