Using the intraocular lens refraction factor to improve refractive prediction accuracy

In 1984, I reported that the refraction constant used in the SRK formula was too high and should have a value of 1.0 or less. The term refraction factor (RF) was adopted to replace the refraction constant which was under scrutiny. The current study was done in four phases. Phase 1 showed improved refraction prediction accuracy for sulcus-fixated intraocular lenses (IOLs) when an RF of less than or equal to 1.0 was used instead of a fixed RF of 1.25. The anterior chamber IOLs had worse results under the same conditions. Phase 2 retrospectively determined computer optimized and matched A constant and RF pairs for anterior chamber, sulcus-fixated, and bag-fixated IOLs for all axial lengths (AL), short (AL less than or equal to 21.5 mm), long (AL greater than or equal to 24.5 mm), and mid-range (21.5 mm less than AL less than 24.5 mm). Phase 3 demonstrated a dramatic improvement in the refraction prediction accuracy when the matched pairs according to AL were used in 61 consecutive patients receiving Jaffe, bag-fixated IOLs. Phase 4 demonstrated good results in 15 consecutive patients, using the RF found for Jaffe IOLs in calculations for a meniscus-type, bag-fixated IOL, with which I had no experience. I determined that the longer the eye, the smaller the RF, for any given IOL position in the eye. The data indicated that different RFs should be used for different IOL locations within the eye. The more forward the IOL, the larger the RF.(ABSTRACT TRUNCATED AT 250 WORDS)