Measuring Nominal Power Of Hemidissected Intraocular Lenses

Various reasons for a postoperative refractive surprise after uneventful cataract surgery have been identified, such as inaccurate biometry or A-constant optimization. In rare situations, the incorrectly labeled power may also be to blame, which can only be confirmed by the laboratory examination of an explanted intraocular lens (IOL). However, the lens must often be cut during the explantation procedure to remove the failed implant without enlarging the incision size. Although there is a general expectation that optical assessment can no longer provide reliable results, this study aimed to test this assumption.

David J. Apple Center for Vision Research, Department of Ophthalmology, University of Heidelberg, Germany.

In this study, 8 monofocal, 2 (mono) extended-depth-of-focus (EDoF) and 2 diffractive-trifocal IOLs were hemidissected. The optical metrology of the IOLs pre and post-cutting was performed using an optical-bench system. Measurements were performed in monochromatic (546 nm) light at room temperature. The magnification method described in the ISO 11979-2 standard was followed to determine the diopter power of an intact IOL. Then, following hemidissection, one measurement was taken with two halves adjacent to each other, and then one piece was tested separately. 

The mean (±standard deviation) diopter power of the studied lenses was 20.28 ±0.30 D for the intact IOLs. After cutting the lenses, the measurements of two adjacent halves resulted in 20.34 ±0.31D. Confirming the nominal power using only one-half yielded comparable results (20.37 ±0.31D). Of the 12 IOLs, the maximum deviation from the pre-cut power was 0.62D (one half) and 0.46D (two halves). Statistical testing confirmed the lack of significant differences between the powers of the whole IOL and with one- and two-piece measurement (ANOVA, P =.77). The difference in the lens power before and after hemidissection was, on average, 0.15 ±0.17D for monofocal, 0.10 ±0.07D for (mono)EDoF and 0.02 ±0.01D for trifocal IOLs. 

We confirmed that the nominal power of explanted lenses after hemidissection could be measured reliably in various IOL types. Our results showed that measuring only half yields comparable results to two halves tested together. Thus, in the event of a refractive surprise, confirming the labeled power of an explanted lens is a viable option despite the physical damage to the IOL caused by the explanation procedure.