Julie C. Tsai

Removal of viscoelastic materials after experimental cataract surgery in vitro

ABSTRACT The one significant complication of viscoelastic materials is that they may cause postoperative intraocular pressure rise. We investigated the rate and ease of removal of various viscoelastics using the Miyake video technique. Five viscoelastics were investigated: sodium hyaluronate (Healon®), Healon GV®, chondroitin sulfate‐sodium hyaluronate (Viscoat®), hydroxypropylmethylcellulose (Occucoat®), and polyacrylamide (Orcolon®). The viscoelastics were dyed with fluorescein and, after filling the capsular bag with a viscoelastic material, a posterior chamber intraocular lens (IOL) was implanted. The viscoelastic was then aspirated using an automated irrigation/aspiration device. Healon and Healon GV were completely removed within 20 to 25 seconds. Viscoat adhered to the lens capsule and to the posterior surface of the IOL and cooplete removal required approximately 3.5 minutes. Most Occucoat and Orcolon was aspirated within one minute; however, removal was completed only after three minutes. Removal of Healon and Healon GV was faster and more complete than removal of the other viscoelastics. Whether a small amount of viscoelastic left in the eye or trapped behind the IOL optic has any clinical significance has to be studied.

The Elastic Properties of the Lens Capsule in Capsulorhexis

We investigated the ability of the anterior lens capsule to stretch and allow removal of lens substance and intraocular lens implantation through a continuous circular capsulorhexis. Capsulorhexis of various sizes (2.5 to 7.5 mm) were performed in 50 eyes obtained post mortem from 31 patients. The nucleus and cortex were removed by either phacoemulsification (35 eyes) or manual extracapsular cataract extraction (15 eyes). The opening of the capsule was then gradually enlarged, using a modified caliper with two pins attached to its tips, until the margins were torn. The capsule was torn when the circumference at the time of rupture was 1.6 times larger than the circumference of the original circular capsulectomy or 5.0 times larger than the diameter of the capsulectomy. Manual extraction of a lens nucleus with profile circumference (sagittal or anteroposterior) of 18.0 to 22.0 mm can be performed through a 5.5-mm opening and a 6.0- to 7.0-mm optic intraocular lens (profile circumference of 13.0 to 17.0 mm) can be implanted through a 4.5-mm capsulectomy.

MECHANISM OF RADIAL TEAR FORMATION AND EXTENSION AFTER ANTERIOR CAPSULECTOMY

The mechanisms of anterior capsular radial tear formation and extension around the equator onto the posterior capsule were investigated in 57 eyes obtained postmortem. Experimental radial tears were created by gradual opening of a caliper. In 95% of cases, the tear immediately reached the equator but none extended to the posterior capsule. The elastic forces of the zonules attached to or crossing the edges of the tear resisted a widening of the gap between the edges and thus limited the radial progression of the rupture. A significantly stronger force and severing of the zonules were necessary for a tear to extend around the equator. The authors have determined that radial tears in the anterior capsule seldom extend around the equator, providing the zonules bridging the tear are intact. There is a diminution of the tearing force when the flaps are widely open. Careful surgery with preservation of the integrity of the capsular-zonular apparatus is a major factor in preventing major complications such as posterior capsular ruptures.

Posterior Continuous Curvilinear Capsulorhexis: An Experimental Study with Clinical Applications

The posterior continuous curvilinear capsulorhexis technique has been advocated in cases of posterior capsule rupture during extracapsular cataract extraction. The authors compared posterior continuous curvilinear capsulorhexis with posterior capsular sharp-edged tears. Two different types of forces were experimentally created on the posterior capsule of 30 human eyes obtained after death: (1) implantation and dialing of posterior chamber intraocular lenses (PC IOLs) and (2) increased intravitreal pressure by injection of balanced salt solution. All posterior capsular tears extended toward the equator, causing major capsular defects. In contrast, the posterior continuous curvilinear capsulorhexis remained intact in all cases. This experimental study proves that in cases where an inadvertent posterior capsular tear occurs, a posterior continuous curvilinear capsulorhexis is useful in preventing further capsular damage. Also, in cases where a posterior capsulotomy is indicated, a smooth edge created by a posterior continuous curvilinear capsulorhexis may be useful to maintain the integrity of the capsular bag for PC IOL capsular implantation.

Scanning electron microscopic study of modern silicone intraocular lenses

ABSTRACT Silicone, as manufactured today, appears to be a biocompatible material. The safety and efficacy of silicone lenses are primarily related to the intraocular lens (IOL) design. We compared the edge finish of two three‐piece polypropylene loop foldable silicone IOL designs (Allergan Medical Optics) and three one‐piece designs (Staar Surgical Co., CooperVision‐Cilco). Except for an early Staar one‐piece design, all lenses including the more recent Staar lenses had acceptably smooth edges with minimal molding flash.