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Case report

Visual aberrations in a multifocal intraocular lens with injection-related scratches

Cole, Scott C. MD, MS; Werner, Liliana MD, PhD*; Schwiegerling, Jim PhD; Crandall, Alan MD

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Journal of Cataract & Refractive Surgery: November 2014 - Volume 40 - Issue 11 - p 1913-1918
doi: 10.1016/j.jcrs.2014.08.028
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Abstract

Phacoemulsification is among the most common surgeries performed in the United States, and developments in pseudoaccommodating intraocular lenses (IOLs) offer patients greater potential to be spectacle free postoperatively than monofocal IOLs.1 Kohnen et al.2 report that 88.0% and 84.6% of patients implanted with the Acrysof Restor (Alcon Laboratories, Inc.) IOL achieved spectacle independence with distance vision and near vision, respectively. Multifocality in this IOL is achieved by a 9-step apodized diffractive pattern that occupies the central 3.6 mm of the anterior surface. The progressively decreasing step height distributes an increasing amount of light energy to the distance power as the pupil aperture increases. According to the manufacturer, this apodization improves the visual properties of the IOL and reduces unwanted visual aberrations commonly associated with multifocal IOLs.3

Multiple studies have shown that multifocal IOLs have a higher incidence of visual aberrations such as halos and glare as well as reduced contrast sensitivity than their monofocal counterparts.1–4 Studies have also demonstrated that factors such as decentration, tilt, and astigmatism have the potential to produce greater visual impairments in multifocal IOLs than in monofocal IOLs.5–8 Intraocular straylight levels are significantly less reduced after cataract surgery with implantation of multifocal IOLs than of monofocal IOLs.9 We describe a case in which the patient had cataract surgery with implantation of a multifocal IOL that was remarkable for multiple large scratches predominantly located in the central portion of the optic. The patient reported continuous visual disturbances for approximately 2 years until the IOL was successfully exchanged. The explanted IOL then underwent thorough laboratory evaluation.

Case report

The patient was a 70-year-old woman who had a history of bilateral age-related cataracts and no other associated ocular pathology. On December 6, 2011, phacoemulsification with implantation of a 1-piece hydrophobic acrylic apodized diffractive posterior chamber IOL (PC IOL) (model SN6AD1 Acrysof Restor) was performed in her left eye at another facility. The corrected distance visual acuity (CDVA) prior to surgery was unknown. Immediately following surgery, the patient reported blurring with distance and near vision, positive dysphotopsia, impaired night vision, and glare. She was informed that these symptoms would improve with time. Brimonidine (Alphagan) was used to improve the symptoms but provided no relief.

After almost 2 years of progressive symptoms, the patient sought a second opinion and was referred to one of us (A.C.). The clinical examination revealed multiple large scratches located primarily on the central portion of the anterior surface of the optic (Figure 1), likely corresponding to damage related to the IOL injection procedure. The CDVA at this point was 20/30.

Figure 1
Figure 1:
Clinical photograph taken intraoperatively prior to making the clear corneal incision. Multiple scratches and defects can be seen on the IOL, the largest of which are located on the central portion of the optic.

On November 25, 2013, a PC IOL exchange was performed successfully. The PC IOL was viscodissected from the capsular bag with an ophthalmic viscosurgical device (OVD) and brought into the anterior chamber. The IOL was then folded and removed whole (Video 1, available at: http://jcrsjournal.org). A PC IOL of the same design was implanted in the capsular bag, and the incision was closed with stromal irrigation. The post-exchange CDVA was 20/20, and the patient reported no further positive dysphotopsia, decreased night vision, glare, or blurring.

Laboratory Analysis

The explanted IOL was sent to the Intermountain Ocular Research Center immersed in fixative by the explanting surgeon. Gross examination was performed, and gross pictures were taken using a digital camera (D40 with a 55 mm lens, Nikon Corp.). Macroscopically, the single-piece hydrophobic acrylic multifocal blue light–filtering IOL with haptics was intact overall. The anterior surface of the optic was, however, notable for a large central defect and a few peripheral scratches. The specimen was then evaluated and photographed under a light microscope (Olympus Optical Co. Ltd.). This revealed 3 large linear parallel scratches (approximately 2.0 mm long) in the central part of the optic, as well as thinner linear scratches and defects in the paracentral and peripheral areas of the optic and corresponding haptic. The scratches and defects appeared mostly on the anterior surface of the IOL (optic and 1 haptic). The anterior surface showed an apodized diffractive pattern consistent with a multifocal PC IOL (Figure 2).

Figure 2
Figure 2:
Light photomicrographs of the explanted PC IOL after it was rinsed with distilled water. A: Multiple scratches on the anterior surface of the IOL optic. The anterior apodized diffractive rings can also be seen (original magnification ×20). B: Large central scratches on the anterior optic surface (original magnification ×200). C: One of the haptics showing surface scratches (original magnification ×100). D: The opposite haptic, which was generally unremarkable (original magnification ×100).

Scheimpflug photography with densitometry analysis was performed to measure the amount of backlight scatter on the anterior surface of the IOL. A 3-piece dark-eye model with a poly(methyl methacrylate) cornea was used to hold the IOL under immersion in balanced salt solution. The solution–filled model containing the IOL was placed in front of an EAS-1000 Scheimpflug camera (Nidek Co., Ltd.) (cornea facing the device), and the room lights were turned off. A cross-sectional image of the IOL inside the model was obtained (settings: flash level 200 W, slit length 10.0 mm, meridian angle 0) and analyzed using the densitometry peak function. Results were expressed in computer-compatible tape (CCT) units. This is a measure of brightness or intensity of reflected (backscattered) light on a scale from 0 (black) to 255 (white). Backlight scatter was extremely high (measured as 227 CCT units) on the anterior surface of the explanted IOL within the area corresponding to the scratches (Figure 3, A). This was in contrast to 28 CCT units and 18 CCT units on the anterior surface and posterior surface, respectively, in areas without scratches (Figure 3, B).

Figure 3
Figure 3:
Scheimpflug photography of the explanted IOL. A: Photograph showing the significant light scattering of 227 CCT units at the area of the large central scratches on the anterior optic surface of the IOL. B: Same photograph demonstrating the light scattering measurements performed in areas of the anterior surface (28 CCT units) and the posterior surface (18 CCT units) without scratches.

Modulation transfer function (MTF) of the explanted IOL as well as of a new control IOL of the same design was obtained in the hydrated state using an optical bench and a model eye. The MTF values were obtained with 3.0 mm and 5.0 mm pupils. Badal images were also obtained using a letter chart object. The MTF plots and Badal images shown in Figure 4 and Figure 5, respectively, demonstrate that the IOLs performed similarly. The differences in MTF values were within the margin of measurement error.

Figure 4
Figure 4:
The MTF curves for the explanted IOL (blue lines) and the control IOL (red lines) obtained at a single spatial frequency (50 cycles/mm) and variable object distance (left side: MTF through focus) and for the distance focus (right side).
Figure 5
Figure 5:
Badal images with explanted and control IOLs obtained with different pupillary apertures.

Discussion

It is well-established in the peer-reviewed literature that multifocal IOLs historically have a higher incidence of visual aberrations and reduced contrast sensitivity than monofocal IOLs. These complications are often worse under mesopic conditions in which the pupil aperture is enlarged and the defocused near image is projected concomitantly with the distance image. According to the manufacturer, the apodized diffractive surface of the Acrysof Restor IOL was designed to compensate for this by ensuring that the redirection of light energy from near to distance vision is gradual. Since the diffractive surface occupies only the central 3.6 mm of the optic, the amount of defocused near-light energy under mesopic conditions is reduced compared with IOLs in which the diffractive surface is larger.3 Diffractive multifocal IOLs are known to have a lower contrast image and higher amount of light scatter than their monofocal counterpart. Increased light scatter from scratches, further reducing contrast, would be expected to have a greater impact on visual performance.

Various studies have shown that factors such as decentration, tilt, or astigmatism may have a more negative impact on the functionality of multifocal IOLs.5–8 A study done in an artificial model eye (3.0 mm pupil aperture) has shown that the near MTF of the diffractive Acrysof Restor decreased with increasing decentration and decreased the most at a decentration of 1.0 mm. Conversely, the far MTF increased, 0.45 at 0 mm and 0.52 at 1.0 mm.6 This is likely explained by a greater amount of light energy passing through the periphery of the optic that is dedicated to distance vision and less light energy passing through the near focused central 3.6 mm of the optic. It can be hypothesized that a similar decentration in a monofocal IOL would not yield as great a change in MTF because it has only 1 focal point. Another in vitro optical performance study done in an artificial model eye also showed the potential deleterious effects of decentration and tilt on different types of presbyopia-correcting IOLs, including the Acrysof Restor SN6AD1 aspheric IOL.7 Astigmatism has also been shown to negatively affect visual acuity in patients with multifocal IOLs to a greater extent than it affects patients with monofocal IOLs. Hayashi et al.8 showed that distance visual acuity in conditions with 0.5, 1.0, and 1.5 diopters (D) of astigmatism was significantly worse in patients with multifocal IOLs than in their monofocal counterparts. With 2.0 and 2.5 D of astigmatism, intermediate visual acuity also became significantly worse.

Another variable that may affect the functionality of multifocal IOLs to a greater extent than that of monofocal IOLs is intraocular straylight. Intraocular straylight, or the forward scattering of light as it transmits through the optic media, may reduce the contrast of the retinal image (depending on the amount of forward light scattering) and therefore the contrast sensitivity. This is a particular problem in cataractous patients. Phacoemulsification and IOL implantation with a monofocal or a multifocal IOL will reduce straylight related to the cataract.9 A prospective observational case series objectively compared the mean level of intraocular straylight 6 months postoperatively in patients implanted with an Acrysof Restor SA60D3 multifocal PC IOL or an Acrysof SA60AT monofocal PC IOL. The study found that the mean level of intraocular straylight was lower in the cataract surgery patients than in age-matched noncataractous subjects, as determined by the C-Quant straylight meter. After compensation for differences in mean age, the mean levels of intraocular straylight were slightly lower in the monofocal group than in the multifocal group.9 As described earlier, the apodized diffractive pattern on the anterior surface of the Acrysof Restor IOL was designed to decrease the visual aberrations commonly associated with multifocal IOLs. A multicenter study of the Acrysof Restor IOL in Europe reported that severe halos and glare were reported by 4.2% and 8.5% of patients, respectively.2 This compares with a study of the Tecnis ZM900 diffractive multifocal IOL (Abbott Medical Optics, Inc.) in which halos and glare were reported in 14% of eyes and 10% of eyes, respectively.10

The levels of straylight associated with a multifocal IOL might be increased by the presence of significant surface abnormalities/damage. We did not have means to measure the forward light scattering through the explanted scratched IOL in our case, but we measured the backlight scattering by using Scheimpflug photography and found extremely high values at the level of the optic damage. In previous studies by our center, we evaluated backlight scattering in IOLs explanted because of clinically significant opacification using the same device and method used in the current study.11,12 Poly(methyl methacrylate) IOLs with snowflake degeneration, hydrophilic acrylic IOLs with different patterns of calcification, and a calcified silicone IOL explanted from an eye with asteroid hyalosis were evaluated. Symptoms leading to IOL explantation in those cases included decrease in contrast sensitivity and, sometimes, visual acuity and glare. All IOLs were monofocal. Backlight scattering measured at the level of the snowflake lesions or the calcified deposits was generally high (more than 200 CCT units). Although the pathology of those IOLs was very different from that in our current case (optic opacification versus optic scratches), we found it interesting that in our case, backlight scattering measured at the level of the central optic scratches on the anterior surface was 227 CCT units. It is therefore reasonable to hypothesize that the effect of large optic scratches located in the central part of the optic on the functionality of a multifocal IOL would be clinically significant. It is interesting that MTF and Badal images obtained from the explanted IOL and a control IOL of the same design did not differ significantly. Forward light scattering is likely the cause of the patient’s symptoms. Forward light scatter tends to be at large angles, so when a simple target such as a slit in the case of the MTF measurements or the letter chart in the Badal measurements is used, the forward-scattered light will spread and tend not to be captured by the measurement system. Consequently, the MTF and Badal images for the damaged IOL and the control IOL are almost identical. The deleterious effects seen by the patient such as positive dysphotopsia and glare are likely due to light from peripheral glare sources being scattered by the scratches on the foveal region. This effect was not captured by the measurement system used in our study.

The presence of linear surface abnormalities on the surface of IOLs related to the injection procedure is a possibility; it has been described in the literature with different IOLs.13 The frequency of scratches found on Acrysof IOLs after their injection is unknown. In a study by Milazzo et al.,14 a monofocal Acrysof IOL was implanted in 4 eyes using a McDonald-Livernois forceps; 50 other sterile monofocal Acrysof IOLs were experimentally folded under a surgical microscope by 1 person using 2 other forceps. Three IOLs implanted clinically had scratches, marks, or both. The scratches and marks were noted during surgery but were not significant enough to justify explantation. They had no effect on the recovery of vision. Of the 50 IOLs studied microscopically, 18 showed no defects; 32 had alterations that were difficult to assess because they were minimal or because more than 1 alteration appeared on the same IOL.14 The alterations described in the Milazzo et al. study were, however, much less prominent than the damage described in our current case.

It is noteworthy that the Acrysof material was shown to exhibit adhesive properties, forming stronger attachment to the capsule than other IOL materials, which is mostly mediated by fibronectin.15 Fortunately, in our case, the Restor IOL could be appropriately viscodissected with OVD and removed from the eye without compromising the integrity of the capsular bag, even 2 years after implantation. However, there are reports of in-the-bag explantation of an Acrysof IOL due to strong attachment to the capsule, which was fibrotic and contracted.16 A case such as the one we report warrants consideration of immediate explantation/exchange of an IOL damaged after injection, based on the extent and location of the damage, as well as the characteristics of the optic.

References

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Supplementary data

Video 1 Explantation procedure for the 1-piece hydrophobic acrylic apodized diffractive IOL implanted in the left eye of the patient (surgery performed by Alan Crandall, MD).

Figure
Figure:
No Caption available.
© 2014 by Lippincott Williams & Wilkins, Inc.