Development of an anti-dysphotopic IOL

Dysphotopsia is the term commonly applied to patient reported undesired optical phenomena following cataract/ IOL surgery. Indeed, dysphotopsia is the chief cause of patient dissatisfaction after otherwise uncomplicated surgery [1,2]. Positive Dysphotopsia (PD) consists of light flashes and streaks in the temporal and central visual field and has been associated with square edge design, high index of refraction of the IOL material, high surface reflectivity, and low anterior radius of curvature of the optic [3–5]. IOL manufacturers have addressed these problems by design modification and have achieved some degree of success, although PD remains an important source of patient dissatisfaction. Negative Dysphotopsia (ND), on the other hand, is described as a temporal visual field arcuate dark area, similar to the effect of wearing ‘horse blinders. ’[6] Unlike PD, ND is not truly associated with particular IOL characteristics, although there aremisconceptions and the reality is that any ‘in the bag’ IOL can induce ND[7]. The manufacturing sector has not addressed ND as it has PD. While Goldmann visual field studies may show constriction in cases of ND, there is as yet no clear objective means for documenting subjective ND complaints[8]. As a result we rely primarily on patient reported outcomes (PROs). Moreover, non-clinical ray tracing studies have not been a close match to the clinical picture for ND[9]. Therefore, in order to address and hopefully prevent ND it is essential to pay close attention to patients’ experiences. That pathway helped lead to the development of an anti-dysphotopic IOL. While there is no consensus on the cause for ND, certain patterns have evolved to which there is a general agreement. Those include: In the susceptible patient ND is stimulated by light from the temporal side and generally improves if the temporal light source is blocked; ND symptoms are reduced with pupil dilation and worsened with pupil constriction; despite similar anatomy, etc., ND may not occur bilaterally; ND has not been reported with ciliary sulcus, anterior chamber, or scleral suture fixated IOLs; ND has only been reported with ‘in the bag’ IOLs with an overlying anterior capsulorrhexis, what is considered to be anatomically perfect surgery[10]. Also, ND tends to occur more commonly in the left eye[7]. Interestingly, our awareness of both PD and ND parallels the unrelated development of square edge IOLs and continuous circular anterior capsulotomy (capsulorrhexis). Although capsulorrhexis was described in 1985, it was not widely employed until the early to mid 1990s along with the advent of foldable and small incision IOLs. Prior to that time, rigid, single or multi-piece PMMA IOLs with round or knife-edge design predominated, and they were largely implanted into the ciliary sulcus entirely, or in part, as the can-opener anterior capsulotomy method employed at the time precluded secure fixation of the IOL haptics in the capsule bag. Neither PD nor ND existed or were recognized during that surgical era, whereas manifestations of PD were reported as early as 1993 with PMMA, truncated, square edge design, oval optic IOLs[3]. Given the near simultaneous deployment of square-edged, high Index of Refraction acrylic IOLs (SEAs) with the recognition of ND, early observers ‘incriminated’ that IOL type as causal[9]. Interestingly, and adding to the confusion is the fact that SEAs account for a significant majority of implanted IOLs. Moreover, despite reports to the contrary, some assumed that silicone IOLs, in particular those with round edge design do not induce ND[11]. However, in a series of 40 eyes requiring surgery for chronic ND, 23% of the IOLs were of silicone material, matching closely with US market share; additionally, 12.8% of the IOLs were of round edge design[7]. It now seems clear that an IOL of any design and material can induce ND if it is centered in the capsule bag underneath a continuous circular anterior capsulotomy [10,12]. A final misconception is that the increased depth and volume of the posterior chamber in the pseudophakic eye could be causal for ND[9]. Regarding the latter, a report from Vamosi disproved that concept and was revelatory, although not widely recognized[13]. The development of an anti-dysphotopic IOL followed observations of patient experiences regarding ND and in accord with certain literature contributions. The pivotal Vamosi, et al article dispelled the theory that the expanded posterior chamber in pseudophakia was causal of ND, and demonstrated that ND was associated with IOLs fixated in the capsule bag, but not if the same or putative IOL was elevated from the capsule bag to the ciliary sulcus[13]. This was later confirmed by Burke and Benjamin[14]. The Vamosi, et al study also demonstrated that there was no measurable difference in posterior chamber depth between a group of patients with ND and a control group. In approximately the same time frame (2010–2011) a patient was referred for management of ND after having an in-the bag-acrylic IOL exchanged for a larger silicone IOL with round edges;