Ultrasonographic measurement of induced myopia associated with capsular bag distention syndrome

Objective: To determine the causes of postoperative myopia associated with capsular bag distention syndrome (CBDS) and characterize the associated fin dings. Design: Prospective, multicenter, nonrandomized, comparative (self-controll ed) trial. Participants: Six eyes from six patients had CBDS develop after phacoemulsi fication and posterior chamber intraocular lens implantation. Methods: Keratometric values, axial length, visual acuity, and manifest ref raction were assessed in each eye. Using 20-MHz ((ISYSTEM)-S-3-ABD, Innovat ive Imaging Inc, Sacramento, CA) and 50-MHz (Ultrasound Biomicroscope, Zeis s Humphrey Systems, Dublin, CA) ultrasonographic probes, images and measure ments of the anterior segment were obtained. After neodymium:yttrium-alumin um-garnet (Nd:YAG) capsulotomy, these measures were repeated and correlated with predicted and actual refractive changes. Main Outcome Measures: Uncorrected visual acuity (UCVA), best-corrected vis ual acuity (BCVA), manifest refraction, and anterior chamber depth before a nd after treatment of CBDS. Results: Although intended postoperative refraction averaged -0.58 diopters (D) (range, -0.12 to -1.63 D), eyes with CBDS had an average spherical equ ivalent refraction of -2.35 D (range, +0.13 to -4.50 D), P < 0.05 (one-tail ed, paired t test). BCVA averaged 20/24 (range, 20/15-20/40-1), but UCVA av eraged 20/133 (range, 20/60 to 20/400). Average distance from the corneal s urface to the anterior intraocular lens (IOL) optic surface was 3.55 mm in eyes with CBDS, and 4.30 mm after Nd:YAG capsulotomy. Posterior movement of theIOL optic after capsulotomy accounted for 1.23 D of hyperopic shift or 82% of the CBDS-induced myopia. Treatment of CBDS resulted in both improved UCVA and BCVA. Nd:YAG capsulotomy also released the colloidal suspension w ithin the capsular bag posterior to theIOL optic. The incidence of CBDS was 0.3% in one of the practices reviewed. Conclusions: Capsular bag distention syndrome includes unexpected myopia an d poor UCVA after cataract surgery with lens implantation in cases involvin g a continuous capsulorhexis. A dramatic posterior distention of the poster ior capsule is observed, as well as anterior chamber shallowing, tight appo sition of the iris to the IOL, and anterior bowing of the iris. A slightly turbid colloidal suspension behind the IOL implant and late posterior capsu lar fibrosis are also observed. Timely treatment of CBDS can correct unwant ed myopia, improve UCVA and BCVA, and restore normal anatomic relationships in the eye. (C) 2000 by the American Academy of Ophthalmology.