<sec><title>Introduction</title> The ability to reduce illumination levels is generally accepted as one of the main benefits of a three-dimensional heads-up system (3D system: Ngenuity®; Alcon, CA, USA). Some studies have focused on illumination reduction in vitreoretinal procedures; however, information regarding illumination reduction in cataract surgery has not been published.

</sec><sec><title>Purpose</title> This study aimed to compare the illumination of the operational field with a 3D system and a standard microscope eyepiece during cataract surgery.

</sec><sec><title>Subject and methods</title> We retrospectively evaluated 91 eyes of 84 consecutive patients who were undergoing cataract surgery at our hospital. We used the 3D system and the eyepiece on alternative days. We determined the minimum light intensity required for safe surgery using the foot switch of the microscope (OMS800; Topcon, Tokyo, Japan). Illuminance on the ocular surface and the minimum illuminance required for the operation were calculated from the minimum light intensity.

</sec><sec><title>Results</title> The 3D system was used in 45 eyes (3D group), and the eyepiece was used in 46 eyes (eyepiece group). The values of minimum illuminance in the 3D group were significantly lower than those in the eyepiece group (3D: 5500 ± 2000 lux, eyepiece: 11,900 ± 1800 lux; p &lt; 0.001*). In addition, the illuminance of the operational field was reduced by 60.4% on average using the 3D system.

</sec><sec><title>Conclusion</title> With real-time digital processing and automated brightness control, the 3D system reduced ocular surface illumination by 50% or more. Hence, the 3D system may contribute to reducing the risk of retinal phototoxicity and patient photophobia.

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