With the continuing improvement in outcomes after refractive surgery for most of the subjects, it becomes more and more important to gain a better understanding in the origin of the complaints of that small percentage of pseudophakic subjects that are not satisfied with their vision. One of the main causes of these complaints is dysphotopsia, of which two distinct types, negative and positive, can be distinguished [1]. Positive dysphotopsia (PD) is described by patients as glare, light streaks, light arcs, flashes of light, and starbursts produced by an external light source, whereas negative dysphotopsia (ND) is a dark temporal peripheral arc-shaped shadow or line [1].

Although ray tracing studies have unveiled the most likely optical origins of these conditions [1, 2], the understanding of why specific patients perceive these complaints and others do not is still a topic of continuing research and debate. The study by Fernández et al. [3] highlights two important elements, which are essential to understand the visual performance on the single subject.

The first element is the assessment of the alignment of the different optical elements of the eye, such as the pupil and IOL, in a real patient population. In contrast to textbook eye models, where all elements are conveniently centered along an optical axis, in real eyes, these elements are tilted and shifted with respect to each other. Although multiple ray tracing studies show how specific deviations from such an eye model can result in a lower quality of vision, experimental validation that these deviations are present in patients with vision complaints is often missing. For example, in ND, multiple optical origins of patients’ complaints have been proposed. However, the lack of data in real patients hindered the validation of the theoretical studies. In 2020, van Vught et al. performed quantitative measurements, similar to those of Fernández et al., in a cohort of ND patients and showed that they have larger deviations from a textbook eye model than controls [4]. Later studies subsequently confirmed that these anatomical differences have a direct relation with the shadow perceived by these subjects [2]. The study of Fernández provides a similar first set of clues for PD by showing that the amount of light distortion is related to the temporal centration of the IOL.

The second valuable element is use of objective measurements, such as the light distortion index, to quantify the potentially disturbing visual phenomena. Although the relation between these physical quantities and the subjective experience of the subject warrants further study, obtaining these types of measurements is critical in advancing the field of refractive surgery. As these types of complaints disturb the peripheral vision, conventional ophthalmic measures such as visual acuity or refraction do not characterize these phenomena as they are designed for the central vision. Accurate and quantitative measures of these complaints in a relevant patient population are, however, essential to validate the findings of laboratory or ray tracing studies, especially as these studies sometimes have contradicting conclusion. These quantitative measures are furthermore indispensable for future clinical studies on the efficacy of a potential treatment, as relying on the subjective experience of the patient as the only outcome parameter can be subject to various biases, including placebo effect and response bias [5].

As the study of Fernández combines quantitative measurements of the anterior chamber anatomy of pseudophakic subjects with an objective assessment of the potentially disturbing visual phenomena, the study provides to a valuable direction for future studies. The reported discrepancy in outcomes between this and other studies, however, also shows that there is still much research that needs to be performed before definite conclusions can be drawn on the relation between IOL location and PD. In this context, a validation of these results with multifocal IOLs from other manufacturers will be an indispensable next step. Additionally, a better understanding of how the measured optical quantities, such as the ocular scatter index, relate the patient’s perception of the complaints will be of great value as it will aid in translating these results to clinical practice.