Mastering the Posterior Capsule and Optic Capture: Elimination of Secondary Cataract
Placing an intraocular lens (IOL) in the capsular bag potentially allows lens epithelial cells (LECs) to invade the retro-optical space and proliferate to form vision-disturbing posterior capsule opacification (PCO), frequently requiring YAG-laser capsulotomy. The barrier effect of a sharp posterior optic edge is often only transient in spite of proper circumferential rhexis-optic overlap: 3-5 years after surgery, Soemmering´s ring formation tends to reverse a previously formed capsular bend, thereby allowing dormant LECs to be reactivated and access the retro-optical space (“Delayed secondary barrier failure”). In an author’s own prospective comparison study of otherwise identical hydrophobic acrylic IOL models, the sharp-edged model, after 3-5 years of significantly lower PCO rates, demonstrated a continuously increasing PCO rate which finally caught up with the initially significantly better PCO rate of the round-edged model to finally end up with the same poor PCO score after 6.5 to 7 years. In another study, the 3-piece Acrysof IOL which provides optimum PCO inhibition characteristics exhibited a YAG capsulotomy rate of 42% after 10 years.
PCO is still a major problem of standard in-the-bag IOL implantation. The Medicare database reports several hundreds of thousands of Nd: YAG capsulotomy procedures performed for PCO every year in the United States alone. PCO and the necessity to perform YAG laser capsulotomy has again increased over the last decade because of the introduction of single-piece hydrophobic IOLs with broad haptic-optic junctions, but also because more of the newer hydrophobic IOL models have rounder edges than 10 years ago.
Nd: YAG capsulotomy is considered a straight-forward, efficient and safe treatment for PCO. Though rare, however, the complication profile includes IOL damage, IOL optic shift with refractive change, IOL dislocation, intraocular pressure rise, vitreous floaters, cystoid macular edema and retinal detachment. Another facet of the problem is that many of the pseudophakic patients do not present to their ophthalmologist before the second eye has also developed significant PCO. This may deprive the elderly patients for years from good binocular vision and make them even more prone to falling and resulting injuries.
In addition, sharp optic edges may cause significant dysphotopsia which has been attributed “the problem number one in modern cataract surgery”. Placing an IOL in the bag also allows the vitreous body to shift anteriorly, potentially giving rise to retinal traction, and increasing the risk of retinal detachment.
With posterior optic buttonholing (POBH), the haptics of a 3-piece IOL or a 1-piece IOL with a slim optic-haptic junction are positioned in the capsular bag fornix, while the optic is entrapped or buttoned-in through a posterior capsulorhexis opening. This not only eliminates retro-optical LEC ingrowth, but also significantly reduces anterior capsule fibrosis as POBH sandwiches the peripheral posterior capsule between the anterior capsule and the optic. This greatly reduces the area of direct contact between the anterior capsule and the optic and consecutive contact-mediated myofibroblastic metaplasia of the anterior LECs. Residual fibrosis at the haptic junctions where the anterior capsule over-crosses the optic junction can be extinguished by additional anterior capsule polishing (ACP). Unlike with in-the-bag placed IOLs where ACP compromises the barrier effect at the optic edge, ACP does not interfere with the PCO-preventing efficacy of POBH, since it does not rely on the effect of the posterior optic edge. Instead of trying to withhold equatorial LECs from overcoming the optic edge, POBH simply diverts them anteriorly unto the anterior optic surface.
Common sodium hyaluronate 1% (Healon®) is used as ophthalmic viscoelastic device (OVD) for this technique. The surgical steps are:
Collapse the capsular bag fornix and create a joint flat bi-capsular diaphragm
Gently exchange the aqueous from the anterior segment by injecting OVD through the main incision without expanding the capsular bag, then settle the anterior capsule leaf onto the posterior capsule and flatten out the joint bi-capsular diaphragm thus created. Pupillary dilatation may be enhanced by injecting OVD on top of the iris base, pushing it back- and sideward.
Incise the posterior capsular incision centrally and create a 4 to 5mm posterior capsulorhexis (PCR) centered on the 1st Purkinje reflex
Bend a 27G hypodermic needle bevel-up, enter it through a paracentesis, approach the central capsule at a flat angle, move it vertically to the entrance incision to incise it. When achieved, the conventional technique is to now slowly inject OVD through the incision to inflate Berger´s space and separate capsule and hyaloid.
Alternatively, the capsulorhexis forces may be introduced before injecting OVD through the central incision to grasp the capsule edge and perform the first quadrant of the PCR . Only then (and not before), enter the OVD cannula and gently inject OVD to push back the anterior vitreous surface and separate it from the central posterior capsule. Use of capsulorhexis forceps with smooth round jaw tips to reduce the risk of inadvertent injury of the anterior haloid. This alternative avoids that a compressed air bubble hidden in the cannula abruptly expands when exiting the tip of the cannula, thus expanding the central capsular incision into the periphery.
In some eyes Berger´s space is not patent with the hyaloid surface located in close proximity to the central posterior capsule, while in others Wieger´s attachment line is completely lacking with a preformed wide contiguous space between the posterior capsule and the anterior hyaloid. In cases with the hyaloid centrally attached, puncturing of the capsule may involve the hyaloid. OVD then injected will find its wrong way into the vitreous body, and the posterior capsulorhexis forceps with also grasp the hyaloid membrane. To exclude this, performing one quadrant of the posterior capsulorhexis before starting visco-dissecting capsule and hyaloid is my preferred routine.
For separating hyaloid and capsule, alternatingly inject OVD beneath and above the posterior capsule ring to keep the capsule diaphragm flat. Continue and finalize PCR with forceps while using the anterior capsulorhexis edge as a ruler.
Note: Performing a posterior capsulorhexis is inherently much easier and controlled compared to an anterior capsule. This is because the posterior capsule is much thinner than the anterior capsule, flattened out and free from radial traction while the anterior capsule is much thicker and convex and under radial traction when the anterior chamber flattens. If posterior capsule happens to be flaccid (large-sized capsular bag with myopic eyes, or eyes with weak zonules or pseudoexfoliation) the posterior capsule may wrinkle when flattened out. The posterior capsule will then tend to evade when trying to incise and form folds when tearing it, which may make initiating and sizing the PCR rather difficult. If this occurs, implantation of a capsular tension ring (CTR) before or at any stage during the procedure solves the problem. A CTR uniformly expands the posterior capsule and distributes the radial forces, elevating PCR very much in these eyes .
Detach anterior vitreous surface from peripheral posterior capsule (“Capsular-hyaloidal visco-dissection”)
Enter the cannula through side-port incisions to gently inject OVD beneath the posterior capsule. With the anterior hyaloid still attached to the posterior capsule, place the orifice of the OVD cannula alternatingly beneath and above the capsule edge to keep the peripheral capsule leaf flat. Ensure complete circumferential capsular-hyaloidal detachment by watching the dissection line moving peripherally.
Create a capsular pocket through the main incision and implant IOL
The OVD cannula is inserted between the attached capsular leaves and the superior-nasal- /inferior-nasal fornix (right/left eye) re-opened by gently injecting OVD, thus creating a small pocket for placement of the leading IOL loop. A looped IOL, preferably the HOYA 3-piece IOL with a continuous haptic-optic transition or an AMO One 1-piece IOL because of its slim haptic-optic junction and posterior optic offset, is injected and the leading loop directed into the prepared capsular pocket and the IOL optic slowly unfolded . While using a phaco spatula inserted through a paracentesis and positioned above the optic, the trailing loop is engaged with a Y- or Push-Pull-spatula and maneuvered through the main incision into the capsular fornix by slightly compressing it and rotating the IOL counterclockwise while gently pushing on the optic with the phaco spatula.
With both loops placed in the bag fornix, the optic is entrapped or buttonholed into the PCR by gently pushing on the optic periphery 90 degrees away from the haptic insertion, thereby slightly tilting it and allowing it to slip under the posterior capsule . As an optional step, the anterior capsulorhexis may now be secondarily enlarged to reduce the substrate for fibrosis (areas of anterior LECs contacting the anterior optic surface) if anterior LEC polishing has not been performed.
Bulging of the capsule-lens diaphragm must be avoided since this may result in optic des-enclavation and vitreous prolapse. Therefore, part of the OVD is first drained from the anterior chamber by gently depressing the bottom of the main incision. This then allows hydrating the paracenteses without overinflating the anterior chamber. A sleeved coaxial I&A probe is then introduced and the residual OVD aspirated from the anterior chamber with the orifice pointing anteriorly and then sideward. (No effort is made, of course, to aspirate the OVD trapped behind the joint optic-capsule diaphragm.) With all OVD removed, the sleeved I&A tip is abruptly retracted, allowing the main incision to lock in and prevent chamber flattening. Finally, the incisions are rehydrated and then globe pressurized as usual.
Possible intraoperative complications
Puncturing of vitreous surface
Even with utmost caution, inadvertent puncturing of the anterior hyaloid cannot be completely excluded, since the anterior vitreous surface may be in close proximity to the central capsule with Berger´s space virtually lacking. Care must be taken to only engage the posterior capsule when incising it with the needle, and to only grasp the edge of the capsule with forceps should the vitreous surface have yet been punctured. When injected through the initial capsular slit, the OVD may be misdirected beneath the anterior hyaloid membrane into the vitreous body, causing vitreous bulge. Injecting OVD on of the denuded vitreous after grasping partly opening both the posterior capsule and anterior hyaloid membrane with capsulorhexis forceps is less critical. This is why I delay OVD injection until about one quadrant of the PCR has been completed.
Too small or decentered PCR
Performing an adequately sized and shaped rhexis on a posterior capsule is much easier than on an anterior capsule because it is thinner and flattened out, and because the anterior capsulorhexis edge serves as a guideline for correct dimensioning. In the unlikely case of a definitely too small or excessively decentered PCR, it may be adjusted by tangentially incising and reshaping it with the visco-dissected anterior hyaloid surface kept at a distance to the posterior capsule by the OVD cushion.
Due to the far greater elasticity of the much thinner posterior compared to the anterior capsule, a PCR still allows for optic entrapment even when smaller than 4mm. Lack of consecutive ovalization of the anterior capsulorhexis opening demonstrates that the tensile stress is fully buffered by the elastic posterior capsule and traction forces do not reach the zonules.
Again, even with a significantly decentered PCR, the optic will perfectly center in the capsular bag since the haptics reside in the capsular equator and will per se perfectly adjust the optic position to the capsular bag.
Too large PCR
This must definitely be avoided, since the saccadic eye movement may make the vitreous eventually work itself through the gap between optic and rhexis edge. This may also secondarily occur when a scarcely overlapping capsule is retracted by capsular fibrosis. If the posterior capsulorhexis edge is judged to evade the optic edge, a tight alternative diaphragm is created by fixating the loops in the sulcus and buttonholing the optic through the anterior or both capsulorhexis openings.
Leading haptic or optic misplaced beneath PCR
The OVD cushion between capsule and vitreous allows grasping and repositioning the loop using a hook or forceps, or by injecting OVD beneath the IOL without jeopardizing the hyaloid surface.
A large vitreous prolapse would prompt the need for anterior vitrectomy. Since controlled viscodissection of peripheral capsule and hyaloid surface is no longer feasible, the IOL loops should again be positioned in the sulcus and the optic buttonholed through the anterior capsulorhexis to create a tight alternative diaphragm.
With proper understanding of the pertinent anatomical details and interplay of lens capsule and anterior hyaloid surface, and strict adherence to the surgical details outlined above, POBH is quickly learned by the experienced and dedicated surgeon to become a safe and effective routine procedurexi.
POBH can be routinely used with almost any eye. Contraindications are inadequate mydriasis and zonular deficiency.
POBH virtually eradicates after-cataract by eliminating retro-optical PCO and greatly reducing fibrosis of the anterior capsule especially when combined with ACP. LEC growth is limited to the residual peripheral capsule ring. In no case have LECs surpassed its edges to grow on the optic surface. Fibrosis was significantly decreased, particularly when additional ACP has been performed .
Postoperative pressure rise, inflammatory response and retinal or macular complications are among the most expressed concerns with PCR and POBH.
Postoperative pressure rise
IOL and capsule form a joint tight mechanical diaphragm which withholds the OVD left behind it from accessing the anterior chamber. In fact, intraocular pressure (IOP) without medication was also identical when intraindividually compared to standard in-the-bag (IB) IOL implantation, and the IOP spikes observed after PCR without POBH did not occur.
Anterior chamber flare as measured with a Lens-Flare-Meter during day 1 was even lower when compared to IB IOL implantation, and identical thereafter.
Retinal detachment (RD) and cystoid macular edema (CME)
In the first consecutive 1000 cases with a follow-up of 4 to 6 years, only two cases (0.2%) of RD were reported. In these two eyes, the hyaloid membrane was intact. One case occurred in a young patient with axial myopia. In a retrospective analysis published by Ripandelli et al., the RD rate after standard IB placement of IOLs was 0.7% and 21% depending on the absence or presence of lattice degenerations. Also, no case of clinically significant CME was presented after POBH. Macular micro-morphology as imaged by high-resolution OCT was identical with that after standard IB IOL implantation.
These favorable RD and CME rates may be explained by the fact that the IOL optic positions more posteriorly after POBH compared to IB implantation as evidenced with laser-interferometry. The more posterior located capsule-IOL diaphragm may stabilize the vitreous body, reducing its axial mobility and the traction on the retina. The trapped OVD cushion may form a diffusion barrier preventing cytokines from reaching the macula in the early postoperative period.
Advantages of POBH
Advantages of added POBH over PCR only
One advantage of additional posterior optic entrapment is that it withholds secondary closure of the PCR opening by lens epithelial cells (LECs). In the absence of the central posterior capsule, LECs may still overrun the PCR edge and migrate centrally, using the anterior hyaloid or posterior optic surface as an alternative scaffold. This may lead to partial or even total secondary closure of the PCR opening and require YAG laser treatment. One other advantage is the above-mentioned lack of postoperative pressure spikes
Additional advantages of POBH over both standard IB and PCR only
Immediate refractive stability
After POBH, the optic immediately reaches its final axial position, while axial shifting is common with IB IOLs. Thus, final glasses can be prescribed without delay.
Absolute rotational stability
Buttonholing the IOL excludes postoperative optic rotation independent upon the haptic geometry, making it ideal for the use of toric IOLs.
Ample optic-to-iris clearance
The posterior position of the diaphragm avoids iris chafe or iridocapsular synechiae and provides ample space for optional placement of an Add On-IOL.
Advantages of POBH over the “bag-in-the-lens” (BIL) technique
Though BIL is an exquisitely elegant technique and completely eradicates both PCO and ACO, it has 3 downsides: First, it requires a special IOL implant with grooves along the optic rim to accommodate the capsulorhexis edges. POBH works with any standard IOL with a slim-haptic junction. POBH thus also allows for smaller incisions than required for the bulkier BIL IOL. Second, both the anterior and posterior capsulorhexis openings must be perfectly round, 5mm in diameter, and concentric to allow for stable fixation of the BIL implant.
Inadequacies may render fixation unsafe, or even impossible. In contrast, POBH is very forgiving. Since the haptics reside in the capsular bag fornix, the IOL will center also within a decentered or incongruent PCR. Should the surgeon encounter difficulties, he may fixate the IOL alternatively, be it in the bag with optional anterior, or in the sulcus with optional posterior entrapment in the anterior capsulorhexis opening.
POBH is a well-controlled and safe surgical procedure with a steep learning curve in the hands of an experienced and well-informed surgeon. POBH permanently eradicates retro-optical PCO and significantly reduces fibrosis especially when combined with anterior capsule polishing. Efficacy of POBH is independent of IOL optic material or edge profile and may be used with any open-looped IOL with a slim haptic-optic junction. Dysphotopsia caused by truncated optic rims and secondary rotation of IOLs with toric optics can thus be avoided. POBH thus constitutes the better alternative to standard in-the-bag placement of sharp-edged IOLs as a routine procedure.
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