Enhanced aspheric optic: the ideal compromise for intermediate visual acuity.

Abstract

We read with interest the study by Mencucci et al. in which the visual outcome, optical quality, and patient satisfaction of the TECNIS Eyhance ICB00 IOL were analyzed and compared with those of the TECNIS ZCB00 IOL.1 The authors concluded that the Eyhance ICB00 IOL provided better uncorrected intermediate visual acuity (UIVA) and higher intermediate spectacle independence without impairment of far vision and visual quality, compared with the ZCB00 IOL.1 In general, the study is well designed. On the other hand, the article has some weaknesses. First, the depth of focus of an optical system might be influenced by appropriate modification of spherical aberration (SA).2 In a young human eye, SA is a combination of the positive SA of the cornea and the negative SA of the crystalline lens.3 The SA of the cornea is highly variable between 0.0 and +0.64 μm with an average of +0.22 to +0.33 μm, according to different authors.3,4 Patients included in the study by Mencucci et al. had a comprehensive preoperative ophthalmological examination but not evaluation of the corneal SA. Because of the relatively small sample size, there is no guarantee that the average corneal SA was the same in the 2 groups of patients. Second, the authors compared the newly developed Eyhance ICB00 IOL with the ZCB00 IOL (both with −0.27 μm SA at 6.0 mm pupil), and they found a significantly higher UIVA in the Eyhance IOL group. The aspheric IOLs with negative SA have presumably decreased depth of focus. For that reason, it would be better to compare the visual performance of the Eyhance ICB00 IOL also with an SA-free monofocal aspheric IOL, where one can expect a wider depth of focus and, theoretically, a better intermediate visual acuity (VA). Third, mesopic contrast sensitivity is a sensitive measure of visual performance of IOLs. The authors evaluated contrast sensitivity under photopic conditions at different spatial frequencies, but they did not examine it under mesopic conditions. There are data in the literature that the only difference between TECNIS ZCB00 IOL and another monofocal aspheric IOL was the better mesopic contrast sensitivity with TECNIS ZCB00 IOL.5 Fourth, the optical quality parameters were analyzed correctly with the same pupil diameter, but there were no data in the article whether the subjective VA (especially intermediate) was assessed with the same pupil size. Of course, it is technically hard to measure these data during VA testing, but different pupil sizes alone can result in different depth of focus, that is, without taking into account the type of the implanted IOL. Pupil size measurement before VA testing might partially help to solve this obvious problem. We do believe that it is possible to construct a monofocal IOL with an ideal compromise between relatively wide depth of focus and satisfactory optical quality. However, the data obtained about TECNIS Eyhance ICB00 IOL are not sufficient to declare that this type of IOL would be the ideal compromise. Further investigations are necessary.