Ординатура / Офтальмология / Английские материалы / Retinal and Vitreoretinal Diseases and Surgery_Boyd, Cortez, Sabates_2010

While phaco tools, lenses and surgical techniques have advanced sufficiently to make cataract surgery an outpatient procedure, there has also been a creep up in some post-surgical complications. We have learned over time that certain conditions, like pseudoexfoliation, are associated with a progressive contracture of the anterior lens capsule following surgery.

Dislocated Crystalline Lenses

of it. As anterior segment surgeons become more skilled with phacoemulsification, the incidence of dislocated fragments decreases. The estimated incidence of this complication is about 0.3%.

Main Causes

Zonular Disinsertion

The loss of the cataractous lens or nuclear fragments into the vitreous is one of the most serious complication during surgery. As surgeons convert from extracapsular cataract surgery to phacoemulsification, an increased number of cases of dislocated cataract occur during the fragmentation phase of the surgical procedure. The displaced fragment may involve the entire nucleus or any fragment

Zonular disinsertion is always a risk because separation of the nucleus from the cortex is necessary. Zonular rupture may occur during rotational or see-saw mechanical manipulationsofthenucleusbythephacoemulsification tip, or by a second instrument.

During central sculpting of the nucleus too much posterior, as well as inferior pressure,

can be applied with the phacoemulsification tip, resulting in a disinsertion of zonular ligaments around the superior part of the lens. In order to avoid undue stress on the zonular ligament fibers, the phacoemulsification tip should not be advanced any faster than the rate at which it can nibble its way through the nucleus. The movements must be slower and more gentle with dense lens material than with the more typical moderate nuclear sclerosis.

Posterior Capsule Rupture

The risk of posterior capsule rupture, during deep central sculpting, is not as great with firm lenses as it is with those with moderate lens density. With a thick, soft epinucleus, the sculpting may unexpectedly break through this softer material and extend through to the posterior capsule quickly. Positive posterior (vitreous) pressure and high myopia increase the risk of posterior capsule rupture. Because of this added risk, and because deep sculpting through this soft material is unnecessary with modern techniques, one should only sculpt as deeply as is required to be able to fracture the nucleus easily.

Failure to recognize a discontinuity or actual tear in the anterior capsule, can lead to a serious complication during surgery - an anterior capsule tear, which extends around the equator to the posterior capsule. This type of tear has the greatest potential for causing loss of nuclear fragments into the vitreous (Figures 1 and 2). In the presence of an anterior capsular tear, the entire nucleus should be removed by gentle sculpting while

Figure 1: Use of Perfluorocarbon Liquid for Dislocated Lens Removal - Initial Stages. The surgical technique involves a three-port pars plana vitrectomy with removal of as much as possible of the base of the vitreous gel prior to removal of the lens. After the vitreous has been removed, perfluorocarbon liquid is injected over the optic nerve head to float the dislocated lens off the retina and into the anterior vitreous cavity. The dislocated lens is then fragmented in the anterior vitreous cavity while floating on the perfluorocarbon liquid. If small fragments of nucleus drop onto the perfluorocarbon liquid, as shown in this figure, they are then removed either by aspiration or fragmentation. Perfluorocarbon liquid (P). Lens Fragments (L). Phacofragmentation tip (A). Tissue manipulator (cannula with endoilluminator (E). Infusion cannula (I). (Art from Jaypee - Highlights Medical Publishers).

Figure 2: Use of Perfluorocarbon Liquid for Dislocated Lens Removal - Final Stages. The last lens piece (L) is shown being aspirated from the eye with the phacofragmentation tip (A) as it floats on the perfluorocarbon liquid (P). Tissue manipulator (cannula with endoilluminator (E)). If a retinal detachment is present, the perfluorocarbon liquid will displace the subretinal fluid through the pre-existing anterior retinal break and into the vitreous cavity, thereby reattaching the retina. (Art from Jaypee - Highlights Medical Publishers).

stabilizing the nucleus with a second instrument to avoid pressure against the equator of the capsule.

By utilizing the newer methods in phacoemulsification for breaking up the nucleus, the risk of posterior capsule rupture should be significantly diminished. Techniques

have evolved since the original phaco chop described by Nagahara. Some surgeons do a pre-chop, by which the nucleus is actually chopped before the phacoemulsification is begun.

These advances reduce the amount of phaco-energy that must be delivered to the eye and make the surgery safer. Because there are fewer manipulations, cracks and other complicated maneuvers inside the eye, less stress is placed on the capsule and zonules.

Indications for Removal of Dislocated Lenses

Not all dislocated cataractous lenses need to be removed. If they have been present in the vitreous cavity for a long period of time and are causing no complication, it is not necessary to remove them. However, in the mayority of cases, the material dislocated into the vitreous cavity has to be removed. The general indications for removing dislocated lenses includes impaired visual acuity, resulting either from obstruction of the visual axis by the dislocated lens or the development of complications. The latter may refer either to those already occurring or to the early signs of potential for development of complications such as phacolytic uveitis, glaucoma, corneal edema, retinal tears and detachment, vitreous hemorrhage or cystoid macular edema. The degree of intraocular inflammation usually reflects the size of the retained lens fragment, the time interval since cataract surgery, and individual inflammatory reactivity. If any of these complications has occurred or is likely to develop, the dislocated lens or fragments must be removed from the eye.

Management of Dislocated Lenses

Once posterior capsule rupture occurs, the surgeon must proceed with extreme caution, using a limbal approach to retrieve lens fragments. In this situation, placing a dense viscoelastic in the anterior chamber, and using an adequate micro forceps to handle nucleus fragments, allow removal of the fragments before they migrate to a position posterior to the capsule. Once the fragment drops toward the vitreous cavity, the maneuvers to retrieve this fragment from this location increase the risk for retinal tears and detachment, and should be avoided. The surgeon can continue the surgery by placing a posterior chamber intraocular lens if there is residual peripheral capsule that could support the lens. If the remaining capsule is insufficient, the surgeon should consider a scleral sutured-IOL, placing an anterior chamber intraocular lens in the eye, or not to place an IOL, closing the eye, and referring the patient to a retinal surgeon, within a week, for appropriate management. The anterior segment surgeon should avoid panic. We emphasize that he/she should not try to remove the dislocated crystalline lens from the vitreous cavity, because of the possible development of a giant retinal tear, retinal detachment, or hemorrhage, which could lead to permanent visual damage. The vitreoretinal surgeon can handle the patient’s eye from a posterior segment point of view, and visual results often are excellent.

Today, most highly experienced vitreoretinal surgeons use perfluorocarbon liquids in management of patients with dislocated crystalline lenses (Figures 1 and 2). The physical properties of perfluorocarbons make

them far superior and safer than previous techniques for managing dislocated lenses. Other methods have been abandoned because of their limitations, complexity and complications.

Liquid perfluorocarbons, which are heavier than water, lifts the crystalline lens from the retina into the anterior vitreous cavity (Figures 1 and 2) The high specific gravity of these liquids exerts a flattening force that reattaches the retina while the lens is being lifted in cases in which there is a concommitant retinal detachment. The viscosity of perfluorocarbons provides a cushion that supports the lens and prevents retinal damage from falling lens fragments, thus, the potential for retinal damage is significantly reduced.

Surgical Technique

The surgical technique involves a threeport pars plana vitrectomy with removal of as much as possible of the basal vitreous gel prior to the removal of the lens. Adequate initial vitrectomy avoids unintended vitreous traction during phacofragmentation. After the vitreous has been removed, perfluoro-n-octane is injected over the optic nerve head to float the dislocated lens off the retina and into the anterior vitreous cavity (Figure 1). This is an effective method that significantly reduces the inflammatory response and hastens visual recovery.

If a retinal detachment is present, the perfluorocarbon liquid will displace the subretinal fluid through the preexisting anterior

Figure 3: Perfluorocarbon Liquid used to Remove Dislocated Nucleus Fragments. If a retinal detachment is present, the perfluorocarbon liquid will displace the subretinal fluid (arrow) through the preexisting anterior retinal break (R) and into the vitreous cavity, thereby reattaching the retina. The dislocated lens (N) is then fragmented in the anterior vitreous cavity while floating on the perfluorocarbon liquid (PFC). (Art from Jaypee -Highlights Medical Publishers).

retinal break and into the vitreous cavity, thereby reattaching the retina. (Figure 3). The dislocated lens is then fragmented in the anterior vitreous cavity while floating on the perfluorocarbon liquid. The lens, or lens fragments have to be kept in position with the help of a second instrument. An illuminated hook-probe is usually sufficient for this maneuver. The intermitent pulsed ultrasound-mode, with reduced ultrasound power (5%-10%), helps to keep the fragment

Figure 4: Extraction of Nuclear Fragments. The availability of modern phacofragmentation units generally precludes the need for external incisions to extract pieces or fragments of nucleus (N). Either way, they still are options when fragmentation devices (F) are unavailable, or in cases with extremely hard nuclear fragments and in cases of dislocated intraocular lenses. Perfluorocarbon liquid (PFC). Endoillumination (L). (Art from Jaypee - Highlights Medical Publishers).

If the basal vitreous gel is not debulked priortothelensfragmentation,smallfragments of lens may become embedded in it. Retinal damage can occur when these fragments are being removed. It is therefore important to remove as much as possible of the base of vitreous gel at the beginning of the operation before the dislocated crystalline lens is removed. If the lens is very firm and difficult to fragment, mechanical crushing between two instruments may be used. If the lens is too hard and the surgeon cannot fragment it in the anterior vitreous cavity, then it must be floated with the perfluorocarbon liquid until it lies just beneath the pupillary margin. If the entire lens is being removed the retinal surgeon may employ a phacofragmentation or phacoemulsificationtechnique,wheremechanical ultrasound is used to first break up the lens.

After the vitrectomy and removal of the lens-fragments has been completed, if an IOL was not inserted during the previous cataract surgery, the placement of an IOL has to be considered. If there is sufficient capsular support, the IOL is placed in the posterior chamber; if not, suture-fixation techniques may be used. An open-loop anterior-chamber lens insertion is a viable option in the absence of an adequate capsular-support.

tive visual acuity of 20/40 or better has been reported in 42% to 88% of the patients.

Postoperative complications include cornea edema, glaucoma, persistent intraocular inflammation, and retinal detachment. Retinal detachment coexistswith retainedlensmaterial in 8.0% of reported series, and retinal detachment has been reported after vitrectomy for removal of retained lens fragments, in 8.3%. It is of critical importance to evaluate the retina throughout the perioperative course in these patients.

Combine Clear or Opaque Lens Extraction, IOL and Pars Plana Vitrectomy

When is Lensectomy Indicated

An important issue that warrants consideration is determining when a lensectomy is indicated, whether the lens is clear or opaque. During vitreoretinal surgery to repair a diabetic traction or combined traction and rhegmatogenous retinal detachment, the indications for lensectomy are limited to the following conditions:

1)A cataract that will prevent visualizing the posterior retina and reattaching the retina.

Outcome After Surgery

fragments are generally good. A postopera-

2)Eyes with fibrovascular membranes extending anteriorly on the retina, in which case the clear lens has to be removed in order to release the traction on the anterior retina.

In these cases it is better to sacrifice a clear lens than to leave persistent traction on the retina, which will eventually lead to a posterior retinal detachment and surgical failure. If a lensectomy is performed, it is extremely important to perform extensive endophotocoagulation to decrease the risk of developing neovascular glaucoma.

Implantation of Intraocular

Lens - Different Options

During combined lens removal and pars planavitrectomy,implantationofanintraocular lens can be considered. The decision is made intraoperatively after the surgeon has had the opportunity of determining whether there is good visual potential. If the retina appears relatively healthy, there is not a significant amount of fibrovascular tissue, and the surgeon believes that it is likely that the patient will have a good visual rehabilitation, then a posterior chamber intraocular lens should be considered for implantation.

Different surgical options may be used to successfully insert posterior chamber lenses during combined lens removal and pars-plana vitrectomy.

Option 1: A phacoemulsification techniques is (Figure 5) followed by standard pars-plana vitrectomy and laser endophotocoagulation. The intraocular lens implantation is done after the vitrectomy and

Figure 5: Phacoemulsification in Combined Lens

cross section view shows the phacoemulsification probe

(P) removing the nucleus (N) within the capsular bag. Note the crack (arrow) created in the nucleus. The epinucleus and cortex will then be removed with the phaco probe. In Option 1, this placo technique is followed by standard pars plana vitrectomy and laser endophotocoagulation. The intraocular lens implantation is done after the vitrectomy and endophotocoagulation is completed. (Art from Jaypee - Highlights Medical Publishers).

endophotocoagulation is completed (optional). The advantages of this technique are that it uses combined standard and commonly performed procedures and permits retention of an intact barrier of zonular fibers and

capsule separating the anterior and posterior segments of the globe, and placement of the posterior chamber intraocular lens within the capsular bag. The posterior capsule is left intact. It also has the advantage of allowing the vitrectomy procedure to be completed, the fundus examined and operative complications identified, evaluated, and corrected before the decision is made to insert an intraocular lens. The disadvantage of this technique in a relative way, include the presence of a limbal

incision that may leak during the vitrectomy procedure.

made to place a posterior chamber intraocu- lar-lens, the incision can be slightly enlarged if needed, and an intraocular lens placed in the bag.