Barrie Soloway, MD; Y. Ralph Chu, MD; and Jessica Heckman, OD
While Von Hemholtz’s1 lenticular-based theory from 1855 of accommodation and presbyopia continues as the mainstay of ophthalmic training, over the past 40 years or so, numerous investigators have found that accommodation and presbyopia involve a delicate interaction of the varied contraction of the ciliary muscles in the anterior, equatorial, posterior, and vitreous zonules, along with the growth of the ectodermal lens. In 1987, Coleman2 presented his zonular theory of accommodation, attributing the changes in the lens shape to the zonular fibers and lens capsule forming a diaphragm, which is held in a catenary shape due to the pressure differential between the aqueous and vitreous on either side of the lens. Newer work by researchers Daniel Goldberg3 and Mary Ann Croft et al4 provides further insight into the mechanism of accommodation and the development of presbyopia from a zonular approach.
In these newer theories of accommodation, the ciliary body moves anteriorly and centripetally, and there is movement of the vitreous interface. These movements affect the zonules, which, in turn, produce steepening of the anterior and posterior surfaces of the crystalline lens. These theories provide the basis for a scleral solution to restore dynamic accommodation.
The VisAbility Micro-Insert System (Refocus Group) is a binocular presbyopia correction procedure performed outside the visual axis. Unlike static corrections such as corneal inlay technologies, monovision or multifocal laser vision correction, and lens replacement, this procedure provides a full-range improvement in intermediate to near vision without compromising distance vision. The micro-insert system places 4 small locking micro-inserts into precise scleral tunnels without removing any ocular tissue. As there is no surgery or change along the visual axis, patients undergoing VisAbility surgery require no adjustments in future cataract implant measurements and the procedure allows for the possibility of future refractive corrections. Earlier studies of manually positioned micro-inserts have reported 93% of patients reading 20/40 or better at near at up to 2 years postoperatively.5 Preliminary data from surgery using the VisAbility Micro-Insert System including the docking station and scleratome are even better, with 100% of this cohort having binocular uncorrected near visual acuity of 20/32 (J2 [Jaeger]) and 90% reading 20/25 (J1).6 This procedure has CE mark for Europe and other countries. It is in Food and Drug Administration–monitored clinical trials in the United States.
The system uses 4 micro-inserts made of biocompatible polymethyl methacrylate, positioned in precisely cut scleral tunnels over the oblique quadrants 4.0 mm posterior to the limbus. Integral to the systematic reproducibility of the procedure is the novel docking station. The docking station (Figure 13-1) provides for fixation of the eye position, which minimizes surgical trauma; a reference template for accurate and reproducible tunnel positioning with the scleratome (Figure 13-2); and stabilization with appropriate tension during tunnel creation and main body segment insertion. The docking station is held firmly in place with 4 twist tines in the scleral limbus.
Each micro-insert is comprised of 2 pieces that lock together for stability on the eye (Figure 13-3): the main body segment (Figure 13-4) and the locking insert segment. The main body segments are implanted in the scleral tunnels created with the docking station and scleratome. Due to the position of the anterior ciliary arteries, careful positioning of the micro-inserts in the oblique quadrants is imperative to the success and safety of the procedure. Despite extensive collateral circulation, rotated placement of the docking station will cause compression of multiple anterior ciliary arteries and increase the risk of anterior segment ischemia. Unlike strabismus surgery, however, where vessels are cut, in the unlikely event that the anterior ciliary vessels are compressed, they can be reopened to restore circulation by removal of the compressing implants.
Prior to surgery, the 6- and 12-o’clock conjunctival limbal positions are marked with the patient in the upright position. A drop of brimonidine is placed in the patient’s eye to reduce subconjunctival bleeding. It is imperative to maintain normal pupillary reaction during and after surgery, so dilating drops and epinephrine should be avoided preoperatively and during surgery. At the surgical microscope, direct visual identification of the rectus muscles provides for the best precision in marking their insertion centers radially extended to the limbal cornea. This is crucial to the placement of the docking station and subsequent micro-insert positions. Figure 13-5 shows the position of the rectus muscles and their accompanying anterior ciliary arteries to exemplify this point. Once these landmarks are identified, the barrel marker (Figure 13-6) is used to mark the position where the docking station should be placed.
Under topical anesthesia, a 4.0-mm circumferential peritomy is made in 2 places centered on the 3- and 9-o’clock positions. These are then buttonholed through Tenon’s capsule to bare sclera posteriorly, avoiding the horizontal recti muscles. A blunt, large gauge cannula is then used to hydrodissect between Tenon’s capsule and the anterior sclera with an injection of 1% lidocaine (without epinephrine) to anesthetize the eye in a sweeping motion 360 degrees. Approximately 0.25 cc is used in each quadrant for a total of 1.0 cc, which is typically adequate for the entire procedure. A 360-degree conjunctival peritomy including Tenon’s capsule is then performed, taking care to ensure that the conjunctival limbus is not torn or stretched.