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Novel endocapsular continuous-loop ring helps achieve good vision in cataract surgery
Ring includes features such as an interior-facing u-section and square outer edges.
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In an effort to reshape a normally flat capsular bag, my colleagues and I have designed the SALring, an endocapsular continuous-loop ring. Innovative features of the ring include the u-section facing the interior, which allows it to accommodate the haptics of IOLs; square outer edges with a sharp edge, which creates a barrier against the opacification of the posterior capsule; the thickness of the ring, which prevents contact between the anterior and posterior capsule; and use of standard IOL injectors for implantation.
Traditional ring characteristics include capsular tension rings, capsular banding rings and equatorial endocapsular rings. The SALring has characteristics in between the capsular banding and the equatorial endocapsular rings.
Capsular tension rings are used to maintain the stretched capsular bag after phacoemulsification. The main function of the new SALring is to stabilize the capsular bag to facilitate the centering of the IOL.
New design
We have found a significant loss of quality of vision in cataract patients caused by the fibrotic changes of the capsular bag.
To improve the performance of the IOLs, in particular the new diffractive bifocal or multifocal lenses, drastically reduce the posterior capsular opacification and facilitate minimal pseudo-accommodation, the new model of capsular ring was created using different dimensions and a new material compared to currently available rings.
We used an innovative design, with the ring calibrated to provide a stable manner to occupy the equator of the lens without leaving any residual elastic forces in the ring itself. The ring reaches its final dimensions immediately upon implantation into the capsular bag.
The ring is hosted in the capsular bag with a continuous outer edge and two margins, one lower and one upper, which create a slot that accommodates the haptics of an IOL. The upper and lower edges have four holes to promote adhesion of the capsule and allow maneuvers during surgical implantation.
The ring is sized to keep separate the anterior and posterior capsules and to prevent the migration of lens epithelial cells from the anterior capsule to the posterior. The hollow ring is a natural place for the spontaneous slippage of the IOL haptics, becoming an appropriate place to maintain the centered positioning. A solid anchor is needed to avoid tilting of the IOL with respect to an ideal plane, perpendicular to the optical axis within the capsular bag.
We used a material other than PMMA or silicone, creating the ring totally in acrylic material, the same material that is used in many IOLs. The acrylic material allows for easy implantation through the tunnel, and we can use the same injectors used for acrylic IOLs. The safety and biocompatibility of the material is assumed by decades of experience with the same material used for IOLs. IOLs that are normally housed in the capsular bag play, through their haptic, a similar but incomplete role with respect to the role performed by this new ring.
The squeezed ring is injected into the capsular bag and opens gently, respecting the intraocular structure and the rhexis. The ring is compressed enough to be injected into the capsular bag with injectors ranging from 2.25 mm to 1.8 mm. The outside diameter ranges from 10.6 mm to 11 mm. The internal system of the ring allows the insertion of most IOLs. The anteroposterior thickness is 1 mm.
Sizing of the SALring
The sizing of the ring was evaluated both theoretically and by conducting experimental tests on various sized pig eye models.
We derived that the average size of the human capsular bag is between 9.2 mm and 10.5 mm. This value is attributed to the equatorial diameter of the lens and not to the empty capsular bag. We recalculated simplistically, using only the theorem of Pythagoras, that the empty capsular bag reaches a maximum diameter that theoretically ranges from 10.2 mm to 11.5 mm (±1.5 mm). This theory was supported by a number of checks carried out during the surgical practice of the author.
The sizing of the capsular bag is mandatory for this surgery. We implanted 11-mm rings in 60% of patients and 10.8-mm rings in about 30% of patients. We do not recommend implanting the ring in small eyes or small bags.
Clinical results
Results at 2 years were encouraging. In 70 implants, we noted no PCO after a mean period of 12 months. We performed YAG laser capsulotomy in two cases because of pre-existing fibrosis of the capsule and in one case because of bad positioning of the ring.
Visual acuity, postoperative refraction and follow-up results were similar to those in cataract surgery cases without the ring.
Most of the treated cases were fitted with multifocal lenses. Our main observation was the importance of peripheral anterior chamber depth for IOL calculation. Additionally, the surgeon must take care to avoid undercorrection, particularly in low A constant IOLs (117 to 118). We most often use a peripheral anterior chamber depth of 5.84 mm or the A constant of 119.5 for the AcrySof SW60 lens (Alcon).