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Case report

Eccentric capsulorhexis and postoperative dysphotopsia following phacoemulsification

Birchall, Wayne FRCOphth*; Brahma, Arun K FRCOphth, MD

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Journal of Cataract & Refractive Surgery: June 2004 - Volume 30 - Issue 6 - p 1378-1381
doi: 10.1016/j.jcrs.2003.11.029
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Abstract

Alarge proportion of cataract surgeons favor use of foldable hydrophilic acrylic intraocular lenses (IOLs), in particular the AcrySof® (Alcon) models.1 The square, sharp-edged design is likely responsible for the low rate of posterior capsule opacification (PCO) associated with this IOL2 but may contribute to undesirable optical effects described as dysphotopsia3 and may be sufficiently troublesome to require IOL exchange.4,5 Provided the capsulorhexis is smaller than the IOL optic, postoperative opacification or whitening of residual anterior capsule overlying the optic edge may reduce the risk of such optical edge effects.3,6 We report a case in which an eccentric capsulorhexis likely contributed to unpleasant dysphotopsia by leaving part of the optic edge and 1 haptic insertion uncovered by anterior capsule.

Case Report

A 68-year-old myopic female patient presented with a complaint of gradual onset of blurred vision in the right eye. There was no significant past ophthalmic or medical history. Best corrected visual acuity (BCVA) measured 6/18 in the right eye and 6/9 in the left eye with distance correction of −9.75 +1.00 × 80 in the right eye and −6.25 +0.50 × 130 in the left eye. Examination revealed early lens opacities with bilateral nuclear sclerosis (grade 1+) and early posterior subcapsular changes more pronounced in the right eye. On fundoscopy, bilateral peripapillary atrophy consistent with myopia was noted, but no evidence of posterior staphyloma or other retinal pathology or degeneration was found. The ocular examination was otherwise normal.

After counseling about the risks and benefits, the patient decided to proceed with right eye cataract surgery. In view of the relatively mild cataract and good visual acuity in the left eye, a target postoperative refraction of −3 diopters (D) was chosen to minimize postoperative anisometropia. Preoperative biometry confirmed axial lengths of 27.27 mm in the right eye and 25.89 mm in the left eye consistent with the anisometropia. She underwent uneventful right phacoemulsification via a superior on axis clear corneal incision. A continuous circular anterior capsulorhexis was performed followed by hydro-dissection and phacoemulsification of the lens using a divide and conquer technique. A 12 D 3-piece foldable AcrySof MA60BM was placed in the capsular bag for a target postoperative refraction of −3.18 D based on the SRK-T formula.

The postoperative course was initially uneventful, and BCVA had improved to 6/9 with a correction of −4.50 +1.00 × 25 in the right eye 4 weeks after surgery. The operated eye was quiet with normal intraocular pressure and a well-centered IOL. Three months after surgery, the patient complained of unpleasant visual phenomena at night in the form of multiple rays of light that radiated toward the left from artificial light sources. She found reading difficult with her usual reading light placed on her right side. She did not drive but found glare from car headlights unpleasant and disliked traveling as a passenger after dark.

No subjective glare or photic phenomena could be elicited from the right eye at the slitlamp with the pupil undilated. After pharmacological dilation of the pupil, the IOL appeared well-centered. Early anterior capsule whitening was noted, and the anterior capsulorhexis was eccentric and displaced nasally such that the anterior capsule overlaid the temporal edge of the lens optic but not the nasal edge (Figure 1). There was no PCO. At the slitlamp, a vertical slit beam of light was directed from the temporal side toward the nasal edge of the optic and elicited subjective flare in the form of lines radiating out from a single point, identical to that previously experienced. No flare was elicited with the slit beam directed at the temporal edge of the optic from the nasal side or from either direction with the pupil undilated.

Figure 1.
Figure 1.:
(Birchall) Retroillumination slit lamp photograph of the right eye presenting an Acrysof MA60BM intraocular lens well centered within the capsular bag. The capsulorhexis is eccentric and the nasal haptic insertion and optic edge uncovered by the anterior capsule.

The patient was counseled about positioning of incident light while reading but remained troubled by the visual phenomena and disliked being out of doors after dark. A trial of miotic therapy at dusk was suggested, but pilocarpine 1% drops and gel and brominidine 0.2% drops were all poorly tolerated, caused headache and ocular irritation, and did not reduce the photic phenomena though none was used for more than 48 hours. Intraocular lens exchange was offered but declined by the patient after discussion of the risks and potential benefits.

Discussion

The term dysphotopsia has been used to describe troublesome visual symptoms experienced by patients after intraocular lens implantation.3 Such symptoms are often worse at night and can be sufficiently debilitating to prevent night driving.

Arnold7 defined various photic phenomena experienced by pseudophakic patients and listed potential causes: Glare (reduced vision in bright conditions) is caused by PCO, macular degeneration, and dry eye/blepharitis; halos (circular or large arcuate rings of light occurring around a point source of light which may be colored by diffraction and which persist for the duration of observation) also seem to be caused by PCO or tear-film debris; flashes (very brief nondescript streaks, spots, or splashes of light) may represent internal reflection from the IOL optic; flare (a streak or tail of light seen when a point source of light is viewed with the streak extending perpendicular to the optic edge) most commonly seen with postoperative mydriasis, a decentered lens optic, or iatrogenic corectopia.

Photic phenomena have been reported with IOLs of various materials and design3,4 but the AcrySof IOL appears to be particularly prone to such phenomena. In a 1998 questionnaire survey of 5000 members of the American Society of Cataract and Refractive Surgery,5 glare phenomena were the commonest reason for an AcrySof lens to be explanted and exchanged.

Farbowitz et al.4 report several cases in which patients experiencing troublesome AcrySof-related dysphotopsia benefited from IOL exchange and replacement with a silicone or poly(methyl methacrylate) (PMMA) IOL. These phenomena included starbursts (similar to that described by our patient), glare, halos around point sources of light, and peripheral arcs described as “seeing the lens edge”.

Ray-tracing studies have elucidated some of the characteristics of the AcrySof lens that may contribute to unwanted photic phenomena. Holladay and coauthors8 demonstrated that IOLs with a flat circumference with sharp peripheral edges produce relatively bright glare images appearing as a thin crescent or partial ring in the periphery of the retina. In contrast, rounded edges distribute reflected rays over a much wider area, producing a less bright, more diffuse image that is less likely to be perceived.

Erie and coauthors9 suggest that not all subjective photic phenomena can be explained by the edge effect, and that second-order images produced by internal reflection within the IOL optic may also account for unwanted optical images. They demonstrated that the unequal biconvex design (less curvature of the anterior optic surface) of the AcrySof lens and its relatively high refractive index (1.55) increase the potential for such reflections, which are likely to be small, relatively bright, and focused close to the retina. In contrast, secondary images produced by equiconvex lenses are larger, more defocused, and less likely to be perceived.

These problems have been addressed in the design of the newer generation, single-piece AcrySof MA60AC lens. Like its predecessor the MA60BM, this is a hydrophobic acrylic lens maintaining the square-edged design important in reducing PCO. Various modifications should reduce the risk for dysphotopsia—The MA60AC has a nonreflective edge that should reduce or eliminate the edge effect and a more convex anterior surface reducing the likelihood of troublesome internal reflection discussed above.

Apart from IOL design, a number of factors may contribute to symptomatic dysphotopsia in individual patients—scotopic pupil diameter, degree of overlap of the optic edge by the capsulorhexis, the degree of anterior capsule whitening because of fibrosis, and lifestyle, including driving habits and psychological factors. It is likely that a relatively opaque anterior capsule with good overlap of the optic edge will prevent incident light from peripheral light sources from reaching the optic edge and protect against edge-related dysphotopsia.

This point is illustrated by a case reported by Schugar,10 in which glare symptoms disappeared over 2 years as the anterior capsule overlying the optic edge became opaque, and by another reported by Dick and Pfeiffer10 of glare while reading in dim light conditions in which the capsulorhexis edge did not cover an AcrySof optic edge. In the latter case, symptoms resolved after the patient was advised to alter the incident light angle while reading.

Our patient described multiple streaks of light radiating in a horizontal direction closely resembling Arnold's description of flare. That they only occurred in dim-light conditions with a more dilated pupil and could be reproduced by shining a slit beam at the nasal edge of the optic not covered by opacified anterior capsule suggest that these were edge effects rather than these second-order images. It is also possible that the streaks were produced by the site of insertion into the optic of the nasal PMMA haptic, which was also uncovered by the anterior capsule. The opaque anterior capsule overlying the temporal optic edge was likely protective, but its deficiency on the nasal side allowed light rays from a temporal light source to strike the optic edge and nasal haptic insertion and produce flare images.

It is generally accepted that the diameter of the capsulorhexis should be slightly smaller than that of the IOL optic so that a thin band of anterior capsule overlies the optic edge. This may help to reduce PCO, particularly with PMMA lenses, by reducing the incidence of posterior capsule wrinkling.11 This benefit may be less pronounced with the AcrySof lens, which prevents such wrinkling even with a capsulorhexis larger than the optic.12

This case suggests that an additional important benefit of a smaller capsulorhexis may be that whitening resulting from fibrosis of the anterior capsule overlying the optic edge may help prevent edge related dysphotopsia.

Arshinoff13 listed oval or irregular shape and decentration as a capsulorhexis complication,13 and this case illustrates that leaving part of the optic edge uncovered may result in unpleasant dyphotopsia and may warrant IOL exchange. The importance of creating a central and roughly spherical capsulorhexis of the correct size that overlies the IOL optic edge should be stressed to all trainee cataract surgeons.

References

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© 2004 by Lippincott Williams & Wilkins, Inc.