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This abstract is assigned to session BSCRS: Belgian Societies of Cataract and Refractive Surgery

Title

IOL calculation in vitrectomy patients that underwent previous refractive surgery

Purpose	Some vitrectomy patients underwent previous refractive surgery. In these cases, determining the correct implant lens can be difficult. Frequently, the preoperative K-values are not available, nor the pre-operative refraction. Moreover, the classical instruments to determine the actual keratometry may provide inaccurate K-values. In cases with retinal detachment, the retina is often detached at the macular area, which makes measurement of axial length also difficult. Finally, suturing an encircling band also influences the axial length of the patient.
Methods	In total, 15 patients had K-values measured using different measurement techniques: Javal keratometry, autokeratometer, IOLmaster and Pentacam. In some cases, the K-values measured before the refractive surgery were available, which could be used for calculation of the estimated K-power. Axial length was measured using IOLmaster or A-scan. Two IOL calculation formulas are compared: SRK/T and Holladay.
Results	Post-vitrectomy refractive outcome was used to determine which keratometry method or calculation was most accurate
Conclusion	-Pentacam “True Corneal Power” provided the most accurate K-power to be used for IOL calculation. If available, using a predictive formula with pre-refractive K-values also yielded a good estimation of the K-value. -If the retina is detached at the macular area, the fellow eye was used to determine axial length. If this in unavailable or there is a marked refraction difference between both eyes, A-scan measurement with manual placement of the markers is the best option. -An encircling band increases myopia by approximately 1.5 diopters. This difference is added to the target-refraction for IOL calculation when applicable.

Author 1

Last name	LEQUEU
Initials	I
Department	Afdeling Oogheelkunde UZLeuven
City	Leuven

Author 2

Last name	STALMANS
Initials	P
Department	Afdeling Oogheelkunde UZLeuven
City	Leuven