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Intraocular Lens Calculation after Implantation of Phacic Posterior Chamber Lenses (ICL)

Speicher L., Philipp W.,
Universitätsklinik für Augenheilkunde und Optometrie (Innsbruck)

Purpose: While difficulties in intraocular lens (IOL) calculation after keratorefractive procedures are primarily due to problems with exact corneal power determination of the treated cornea, inaccurate axial length measurements by ultrasound biometry may be expected after implantation of phakic intraocular lenses. The aim of the present study was to compare the pre- and postoperative results of axial length measurements and their implication on IOL power calculation in patients with phakic posterior chamber lenses (ICL).
Method: In five patients with high myopia (range -11 to -16 D) ultrasound biometry and IOL calculation were performed prior to and after ICL implantation.
Results: Although in some cases values of postoperative axial length measurements were found to be minimally smaller than the preoperative values, these differences were not statistically significant. However, significant differences in postoperative anterior chamber depth values were found, which were 0.45 to 1.0 mm smaller than the corresponding preoperative values, primarily depending on the degree of ICL vaulting. Nevertheless, preoperative values of IOL power calculation corresponded well with the postoperative values and differed only between ±0.5 and ±1.0 D.
Conclusions: In the present study we were able to show that only minimal differences exist between the preoperative and postoperative axial length measurements in high myopic patients with ICL implantation. One reason for this may be the material of the ICL, which is made of Collamer, and another may be the low thickness at the middle of the lens in myopic ICLs. Difficulties in axial length measurement may occur with hyperopic phakic IOLs due to the higher central thickness of the lens and the fact that an error in the measurement of axial length in hyperopic eyes may have more effect than in myopic eyes. Depending on the lens material different results are expected in phakic PMMA lenses. In contrast to corneal refractive patients, in whom the IOL power prediction cannot be based solely on the preoperative values, for patients in whom ICL implantation is planned, the complete IOL calculation can already be performed before this refractive procedure and given to the patient for later use.