Despite modifications in lens design, dysphotopsia may still occur in pseudophakic patients.
Pseudophakic dysphotopsia is one of the greatest sources of patient dissatisfaction following cataract surgery, and correlates strongly with visual function [1
dysphotopsia and its relation to IOL design have been explored in the literature. Bournas and colleagues reported that optic phenomena occurred more frequently in patients implanted with the square-edged AcrySof than with the AMO Clariflex® lens, which has a round anterior and posterior square edge [9
]. Data from a prospective randomized study of 61 patients also revealed that at 8 weeks postoperative, the incidence of positive and negative dysphotopsia was 31.3% in the group implanted with the SN60-AT® IOL (Alcon) and 20.7% in the group implanted with the Akreos Adapt® lens (Bausch & Lomb, Rochester, New York, USA). Although both are square-edged, single-piece acrylic lenses with the same optic diameter, the authors noted that the Akreos Adapt IOL has a lower radius of curvature and a lower refractive index design, which, in theory, makes it less prone to dysphotopsia than the SN60-AT® IOL. However, the authors also remark that the Akreos® IOL has a 50% greater edge thickness-a significant factor in a positive dysphotopsia edge effect [15
Shambhu et al. also compared the incidence of dysphotopsia associated with different lens types, comparing the AcrySof® MA30BA and MA60BM (Alcon) lenses with the Akreos Fit® single-piece lens [16
]. Data from this 111-patient study showed that there was significantly less dysphotopsia with the Akreos lens when compared to the Acrysof MA30 and MA60 lenses. The authors noted that aside from lens edge, other aspects of lens design also significantly reduce the incidence of moderate and severe grades of dysphotopic symptoms. For example, light reflected from the anterior surface of the lens decreases with decreasing refractive index; the AcrySof® refractive index is 1.56 as opposed to the Akreos, which is 1.46.
The present study used a questionnaire based on that used in the study by Tester and colleagues to determine the incidence of optical phenomena at 1 or 3 months post-C-flex® implantation [13
]. Although 55% patients reported optical disturbances, their symptoms were either ‘minimal’ or ‘annoying’, with 43% patients describing their symptoms as ‘minimal’.
In the original telephone questionnaire-based study by Tester et al, [13
] which included 302 patients who had received one of six commonly-used IOLs, patients who received an acrylic IOL with flattened edges were at increased risk of experiencing images associated with lens edge reflections [13
]. Specifically, 32.5% with AcrySof® lenses (5.5 mm and 6.0 mm), 24% with SI-40® lenses (Allergan, Inc, Irvine, California, USA), 18% with polymethylmethacrylate lenses and 4% with phakic controls reported a degree of unwanted imagery. Light glare or sensitivity was reported by over one-third of all patients including controls [13
]. As shown in Table 1, in the present study, the incidence of unwanted optical imagery with C-flex only was 17%-less than that with AcrySof® lens reported in the study by Tester et al [13
]. The incidence of dysphotopsia in the present study also compares favourably with that of the SI-40 silicone group in Tester’s report [13
]. Additionally, when compared with dysphotopsia associated with AcrySof® lenses reported in a similar questionnaire-based study by Wallin et al. [14
] no side light causing central flash was reported with the C-flex®, compared with 25% of patients implanted with three-piece and 7% with single piece AcrySof® lenses. Further, an arc of light in the side vision was reported by 2.5% of patients in the present study, compared with 47% with the three piece AcrySof® lens and 14% with the single piece AcrySof® lens in the study by Wallin and colleagues (Table 2) [14
There are several possible explanations associated with the lower incidence of dysphotopsia with the C-flex®, as compared with lenses evaluated by Tester et al [13
]. and Wallin and colleagues [14
]. Although previously published studies have given much credence to the relationship between lens edge design and the occurrence of dysphotopsia, other factors must also be considered. Of note, the C-flex® lens is made of hydrophilic acrylic biomaterial which could be a factor in reducing the risk of glare compared with hydrophobic acrylic biomaterials due to the absence of vacuoles or glistenings [10
]. In contrast, the Acrysof® lenses, used in the Tester and Wallins studies are composed of a hydrophobic acrylic material. As a consequence of its hydrophilic nature, the C-flex® also has a lower refractive index than the AcrySof® (1.46 versus 1.56). As a 2001 study by Erie et al. demonstrated, light reflected from the anterior surface of the lens increases with an increasing refractive index. Moreover, Erie’s study also showed that an unequal bi-convex design, as in the AcrySof® lens, produces internal reflections that focus on an area 60 times smaller than that of an equi-convex design such as that of C-flex® lens [8
Cases of unwanted imagery may also be due to entoptic phenomena, such as from posterior vitreous detachment (PVD). Tester’s study did not distinguish between the two but reported these symptoms in 4% of controls [13
]. In the present study, unwanted imagery occurred in 7 of 40 (17%) patients. However, clinical examination revealed that unwanted imagery was most likely unrelated to the C-flex® lens in 14.5% of these patients. Specifically, the first patient who reported ‘little black floaters’ had PVD. The second patient had an arc of light in the peripheral vision, which was mild in nature and not related to a source of light-this patient also had PVD. The third patient also noticed an arc of light in her side vision, but only when she switched on the light first thing in the morning; she was unable to replicate these symptoms later on in the day. On examination, she had a significant cluster of floaters in the periphery and centre of the vitreous. Therefore, her symptoms were most likely due posture-related changes in the vitreous. Moreover, at her 3-month follow-up visit, she reported these floaters to be less noticeable. The fourth patient had reported occasional nonspecific flashing lights, while the fifth and sixth patients had increased but mild light sensitivity. The final patient, however, described an arc of light in her side vision
in presence of a light source. She also saw similar arcs in the side when looking at streetlights. Although she reported these persistent symptoms to be annoying, she was very satisfied with her visual outcomes. The slit lamp examination showed a well-centred lens but with 360° overlap missing in a small area and the presence of a single fold on the posterior capsule
. Therefore, this patient’s positive dysphotopsia was likely related to the lens implant. When examined again at 3 months postoperative, she reported her symptoms to be less annoying.
Overall, the C-flex® monofocal IOL with 360° enhanced edge was associated with a high degree of patient satisfaction with postoperative visual outcomes in this study population. Unwanted imagery, which could be related to the lens implant, occurred in only one patient out of forty patients. The low incidence of dysphotopsia, as compared with previously-published studies that employed the same methodology to determine visual disturbances, is most likely related to the C-flex® lens design and material.