Pars plana injection of viscoelastic after posterior crystalline lens dislocation results in good visual acuity

Issue: March 15, 2000

ByRolando Sorcinelli, MD

The complete loss of a lens in the vitreous is quite a rare complication of eye contusions. In these cases, a posterior vitrectomy can be performed using perfluorocarbon liquid (PFL) to lift the lens up. But in most cases, the lens is dislocated in the middle of the vitreous because the break in the zonular fibers is incomplete. Surgical treatment should be considered, but controversy exists as to the most effective mode of treatment for these patients with incomplete lens dislocation into the vitreous. Many surgical techniques and approaches have been devised to treat lens subluxation.

Preoperative assessment

A new and appropriate surgical procedure was studied, together with its complications and other aspects. The guidelines for optimal management are presented.

The author conducted a retrospective study over 21 months (from April 1997 to January 1999) of the charts of five consecutive patients with a posterior subluxated crystalline lens in the middle of the vitreous (four men and one woman), ranging in age from 62 to 84 years. Three patients had a post-contusive dislocation of their lenses, and two patients presented a spontaneous lens subluxation. In the post-trauma cases, there were no significant alterations on the iris.

In one case, the trauma had occurred 35 years before; in others, it occurred 2 years before. In no case was glaucoma or hypotony present, and the observation of the fundus was possible in all cases, before the operation, by indirect ophthalmoscopy. It was not necessary to make an ultrasound evaluation in order to exclude retinal detachment or choroidal detachment. In all patients, the corrected visual acuity was less than 0.1.

Surgical technique

The patients were managed by a surgical technique comprised of a limbal and pars plana approach with a simplified method using viscoelastic infusion. All operations were carried out by the same surgeon. When the lens is dislocated posteriorly in the middle of the vitreous, it is important to pay attention on which meridian the zonular fibers are still good: an evaluation of the lens must be performed after mydriasis under the operative microscope while the patient is supine. This can presumably be established by drawing a straight line perpendicular to the apex of the convexity of the lens, which can be observed in the pupillary field (Figures 1, 2).

Second, we make conjunctival flaps with a fornix base by exposing the sclera where the zonular fibers are still good, then perform an accurate coagulation of the episcleral vessels. Then a sclerotomy is performed in pars plana 3 mm from the limbus with a microvitreoretinal blade (20-gauge shank, 1.4-mm blade width, lance and tip) while avoiding the horizontal meridian that corresponds to the long posterior ciliary artery.

Before the incision, the parallel limbal 6-0 silk suture is placed onto the surface of the sclera in order to imbricate the cannula. It is advisable to use a 6-mm cannula, which has a better chance of fully penetrating through the pars plana and into the vitreous cavity, in an eye that might have choroidal detachment from trauma, and to inspect the tip of the cannula, which can be visualized by using an operating microscope (this is very easy if the lens is clear; otherwise, it is not).

The cannula is connected with a manual infusion of the viscoelastic. We used a sodium hyaluronate of middle viscosity in a 1.2% solution; its molecular weight is 1,000,000 daltons, and its pseudoplasticity (cps, 2 sec-1) is 6,000 to 11,600. Viscoelastics with high viscosity are not recommended, as they are seldom aspirable with a vitreous cutter. The anterior chamber was opened with a 30° blade at the limbus, and a limbal incision was effected of sufficient size for lens extraction.

A monomanual anterior vitrectomy was performed (Figure 3). As much of the anterior vitreous face as possible was excised, putting the opening of the vitreous cutter as far behind the iris as possible, depending on good microscope observation. The adjustment of the vitreous cutter was based according to the following parameters: maximum opening of port, suction 100 to 120 mm Hg, flow rate of 20 mL/minute and cutting of 250 cuts/minute.

The anterior vitreous was removed and, at the same time, the viscoelastic infusion restored the volume of the eye to maintain a normal intraocular pressure (IOP). The flow of the viscoelastic toward the anterior chamber lifted the lens up to the center of the pupil (Figure 4). Then the lens was removed across the limbus using the “intracapsular cataract extraction” technique using a cryoprobe, or it could have been delivered spontaneously. This is possible because there is not too much vitreous above the lens, and a slow viscoelastic infusion makes it possible to keep the anterior lens capsule at a level plane with the iris.

Finally, after having replaced the infusion with balanced salt solution, the anterior vitrectomy was kept to remove the remaining anterior vitreous and to aspirate the viscoelastic as much as possible (Figure 5). The basal iridectomy, even if not necessary, was carried out to reduce the risk of ocular hypertension. A strong suture of the corneal incision and sclerotomy is advised when faced with an incidental ocular hypertensive pressure. No one received an IOL at the end of the procedure for fear of retinal detachment.

After surgery, the patients were examined at 1 day, 1 week, 1 month, 3 months, 6 months and 1 year. All patients received the following tests after surgery: visual acuity with and without correction; measurement of IOP; slit lamp examination; and dilated fundus examination, including scleral-depressed peripheral retinal examination.

Results

In four out of five eyes (80%), final visual acuity was better than 0.8 with lens spectacles depending on the condition of the macula, which is related to older age. A visual acuity outcome of less than 0.1 occurred in a patient with retinitis sclopetaria. The mean postoperative spherical equivalent was +10 D with a range of +8 D to +12 D. No intraoperative complications were observed. None of the following conditions occurred after the procedure: intraocular inflammation, elevated IOP above 21 mm Hg, corneal edema or retinal detachment. The follow-up period was 1 year.

Conclusion

The extraction of a lens is necessary due to the danger of a complete luxation, which would require a far more complex operation of removal with perfluorocarbon. This procedure takes less time than with perfluorocarbon because it avoids making a three-port system of sclerotomies. It also is safer because it is not important to remove all the viscoelastic, as opposed to the perfluorocarbon, which, in some cases, is not easy to do. The rationale behind the use of a middle-viscosity viscoelastic is to keep easy aspiration during the vitrectomy. It is known, however, that great difficulty is found in the removal of the viscoelastic at high viscosity from the vitreous even in a fully vitrectomized eye. In addition, a viscoelastic at middle viscosity and at low molecular weight leaves the eye more quickly through the trabeculum, compared with a viscoelastic at high viscosity and at high molecular weight. It is manifest that a viscoelastic, even though left inside the eye, is a lesser danger for eye pressure if it is removed quickly, therefore avoiding irreversible damage to the optic nerves.

Kidokoro tried to deliver luxated lenses using a stream of vitreous infusion fluid. The luxated lenses appeared at the pupillary area and were extracted through the corneoscleral wound. The infusion of the viscoelastic was preferred to the infusion of the fluid because the lens sinks into fluid more easily than into viscoelastic. Another reason is because during extraction with a cryoprobe, a larger ice ball can be formed with fluid and, therefore, touching the cornea becomes easier.

The extraction of the lens with a loop opposite to the cryoprobe is more dangerous for the corneal endothelium. This technique should be considered safer than the others when compared with simple cryoextraction without a pars plana approach where a lump of ice develops. This causes a great loss of vitreous and a danger of tractions on the retina. In fact, some authors report that 8% of retinal detachments are due to complications arising from this operation. Through this series of operations, though small, no cases of retinal detachment were observed after the operation. Perhaps this is because the vitreous cutter was used before the extraction to make less traction of the vitreous, which may be the way to retinal tears. Instead, the loss of vitreous following the single cryoextraction may be more dangerous for the retina, and the retinal detachment could be more frequent. Therefore, most patients managed by pars plana injection of viscoelastic had good visual acuity outcomes. The author believes this technique can be recommended after posterior crystalline lens dislocation to prevent complications and to preserve visual acuity.

Operative microscope observation. (Figure 1)
Dislocated lens in the middle vitreous. (Figure 2)	Anterior vitrectomy and viscoelastic infusion performed at the same time. (Figure 3)
Anterior lens capsule at level of the plane with the iris. (Figure 4)	Exchange of the viscoelastic with fluid. (Figure 5)

For Your Information:

Rolando Sorcinelli, MD, is the Director of Vision Electrophysiology, University of Cagliari, Italy. Fax: (70) 6092318. Dr. Sorcinelli can be reached at Via Mameli 106, 09123 Cagliari, Italy. Dr. Sorcinelli has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.

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