Ординатура / Офтальмология / Английские материалы / Modern Cataract Surgery_Kohnen_2002

Nuclear emulsification may be carried out with the most appropriate strategy for the given case; nuclear chopping methods reduce the total amount of ultrasound necessary for lens disassembly. Care must be taken to avoid damage to the anterior capsule rim, the equatorial capsule, and the posterior capsule. Occasional addition of viscoelastic during the emulsification process can be very protective. Also, the nuclear fragments and sharp edges should be brought away from the posterior capsule and into the central aspect of chamber before emulsification; the center offers the furthest distance from both the posterior capsule and the corneal endothelium. If the lens nucleus is particularly dense and no cortex remains, anterior chamber or iris plane emulsification should be considered, although the presurgical status of the corneal endothelium must be factored. In very rare circumstances, it might be safest to remove the nucleus manually, particularly if capsular integrity is compromised.

Cortex removal following nuclear emulsification is rarely challenging in cases with white cataracts. Nevertheless, it is common to encounter resistant fibrotic plaques on the posterior capsule. These may be left alone, or, in rare circumstances, a posterior capsulorhexis may be performed. Following ‘cortical clean-up’, lens implantation can be performed routinely. Postoperative management should present no unusual hurdles unless preoperative lens induced inflammation or elevation of IOP continue after surgery.

What to Do When Things Go Wrong

The most frequent complication, as it were, is failure to complete a smoothedged continuous tear anterior capsulotomy. The capsulotomy may be completed by the ‘can-opener’ method or by starting another capsulorhexis in the opposite direction, if possible. Added care must be taken when carrying out nuclear emulsification in cases without continuous capsulotomy. Given generally poor visibility, a friable capsule, little to no cortical or epinuclear cushion, my preference is to bring the nucleus into the anterior chamber with a ‘tire-iron’maneuver, using the viscoelastic agent with its cannula. Anterior chamber emulsification is performed unless the lens is extraordinarily dense and/or the endothelium significantly compromised preoperatively. Under those circumstances, manual removal of the nucleus is a safer option. In that case, it may be wise to abandon the temporal clear corneal incision and prepare a sclerocorneal incision superiorly for best wound and astigmatism management. Also, removal of the nucleus, in this situation, is properly managed with a vectis, loop, or spoon rather than by expression since the firm, large nucleus may tear the capsule or rupture zonules during the expression maneuver. In fact, cases of this nature are at added risk for posterior dislocation of the nucleus during attempted expression.

The Nuclear Mature (Brunescent) Cataract

Brunescent nuclear cataracts can progress to very advanced stages while producing little apparent loss of visual function. Most patients with nuclear cataract experience reduced distance vision, notice difficulty seeing at night and complain of glare symptoms. These cases generally have increased nuclear opalescence mixed with other forms of cataract. However, in some eyes the nucleus changes very gradually from clear to dark brown or black, passing through stages of yellow to deep red. In some of these cases, particularly those without nuclear opalescence, there is little distortion, glare, or relative loss of night vision; the patients are often tolerant of the slowly evanescent reduction in contrast sensitivity and color perception associated with this cataract type. The net result is that the surgeon may be confronted with the paradox of a very advanced cataract and a relatively asymptomatic patient. On one hand, cataract extraction should be performed before the surgery becomes extraordinarily risky, yet the patient may perceive little need for the proposed surgery, even though visual function may be significantly reduced.

A nuclear cataract may be considered as mature when an epinucleus cannot be defined with routine hydrodelineation. Additionally, the maturation process may advance to where lens cortex is minimal, or, nearly nonexistent. These cases present added challenges intraoperatively with regard to the capsulorhexis, hydrodissection, and lens emulsification in particular. Furthermore, even in cases without surgical complication, there is the potential for prolonged recovery of vision postoperatively, owing to an increased likelihood for transient corneal edema following prolonged phacoemulsification.

Surgical Management

Surgical treatment for cases with nuclear mature cataracts begins with careful presurgical evaluation and planning. Certain factors must be considered. These include the depth of the anterior chamber and the preoperative condition of the corneal endothelium. Prolonged emulsification time, almost unavoidable with advanced brunescent cataracts, will place a significant burden on the survival of the cornea, should the chamber be shallow or the endothelium already compromised. Likewise, lengthy emulsification might be accompanied by significant zonular traction with an attendant potential for long-term complications, particularly if the presurgical condition of the zonules is compromised, as in some cases with pseudoexfoliation. Therefore, in light of these few examples alone, preoperative examination should be considered as an integral part of the surgical management of nuclear mature cataracts.

Capsulorhexis can be challenging should the red reflex be obscured by the extraordinary density of the lens nucleus. In that case, it is advisable to consider any or all of the ‘tricks’ for enhanced visibility of the capsulotomy in cases with white mature cataracts (see above). The capsulotomy should be generous in size, perhaps larger than usual in order to avoid damage to the anterior capsular rim during emulsification and to facilitate removal of the nucleus from the capsule bag should it be necessary for any reason (ruptured posterior capsule, etc.). I generally aim for a centered anterior circular capsulorhexis of 6.0 mm or more with these cases, whereas in the routine situation I prefer the capsulotomy to be roughly 5.0–5.5 mm.

Hydrodissection must be carried out with great caution. In the ‘garden variety’ cataract case, the epinucleus and cortex can act as a reservoir for the injected fluid during the hydrodissection. However, in the situation of a mature nuclear cataract, there is little more than a thin lens capsule and a firm nucleus (fig. 2). As a result, there is no cushion or ‘sponge’ to absorb excess fluid as it is injected during hydrodissection; a bolus of BSS, having no opportunity to be absorbed, can ‘blow out’ the thin posterior capsule. Alternatively, if the BSS is injected slowly and in judicious amounts, the fluid can cleave the nucleus from the cortex and capsule without incident.

Nuclear emulsification will take added time, care, and patience when compared with the routine situation. When planning the surgical day, one should recognize that phacoemulsification of mature cataracts potentially takes longer than for typical cases. Recognizing and planning for the needed extra time will relieve, to some extent, the added stress of dealing with cases of this nature.

While there has been a general trend toward nuclear chopping and away from traditional ‘divide and conquer’ sculpting methods for nuclear disassembly, chopping of very dense nuclear cataracts can be difficult and potentially dangerous, given that most chopping instruments are not sharp enough or long enough to adequately penetrate a very dense nucleus. Furthermore, the added torque needed to chop a large ‘rock-hard’ nucleus is likely to add undesirable stress on the zonules. Therefore, I prefer to sculpt and hemidivide nuclear mature cataracts before chopping the segments (fig. 2). Sculpting is facilitated by using a tip with an increased cutting angle for greater efficiency. Also, use of increased emulsification energy will facilitate the sculpting process which should be carried out deeply into the central nucleus. The latter maneuver allows the nucleus to be ‘cracked’ for disassembly. Furthermore, when sculpting a firm nucleus, only a small amount of tissue should be removed with each pass in order to avoid zonular stress. A worthwhile adage suggests that ‘nuclear tissue should be removed rather than moved’ during sculpting. Finally, I add a highly retentive dispersive viscoagent (Viscoat, Alcon) to the chamber on several occasions during the emulsification process. This technique yields added

protection to the cornea and capsule during surgery, but increases the risks for incisional burns.

During nuclear sculpting I partially debulk the center of the lens and create a central trough which is used for the initial crack, creating two heminuclei. Should the nucleus fail to crack, it is generally necessary to sculpt deeper. Hard cataracts are notoriously difficult to divide as the lens is noted to have ‘leathery’ posterior bridges and adhesions when cracking is attempted. Surgeons attempt a variety of personal tricks when confronted with a ‘noncracking’ nucleus.

Following successful hemidivision of the nucleus, the two pieces may be sculpted and divided or chopped, varying with conditions, equipment, and the surgeon’s experience. For very dense cataracts I prefer to sculpt and divide into four or more equal size pieces before removing any of the segments, since it is easier to rotate the lens as a single unit. Prior to removing the fragments I add viscoelastic to the chamber. The segments are brought forward with a spatulated instrument through a paracentesis. I attempt to raise the sharp angulated portion of the nuclear piece away from the posterior capsule rather than have it sweep against the capsule and risk capsule rupture. I employ high vacuum fluidics to facilitate aspiration and I bring the free nuclear piece into the center of the chamber, so that emulsification can be carried out in the deepest portion of the chamber, giving the greatest possible protection to the cornea and the posterior capsule. In order to prevent wound burn during this case type, it is necessary to work with an incision of adequate width, allow adequate BSS (chilled) exchange, clear a path through the viscoagent (with irrigation and aspiration) prior to emulsification, and avoid (prolonged) tip occlusion by using ‘pulsed phaco’ when removing the quadrants. As a rule, newer, reduced dimension microtips are not ideal for emulsification of cases of this type since the tip occludes readily, potentially risking wound burn, and the small internal diameter of the tip prolongs removal of the bulky, dense cataract. Following nuclear emulsification, cortex removal and lens implantation should be routine.

Small incision cataract surgery provides rapid and stable optical recovery [4]. Advantages accrue to the patient, to the surgeon, and to society. Fortunately, by adhering to the above guidelines and suggestions, patients with mature cataract of both types may, in many cases, be managed as routine and can expect excellent return of visual function after surgery.

References

1Mansour AM: Anterior capsulorhexis in hypermature cataracts (letter). J Cataract Refract Surg 1993;19:116–117.

2Horiguchi M, Miyake K, Ohta I, Ito Y: Staining of the lens capsule for circular continuous capsulorrhexis in eyes with white cataract. Arch Opthalmol 1998;116:535–537.

3Melles GRJ, de Waard PWT, Pameyer JH, Beekhuis WH: Trypan blue capsule staining to visualize the capsulorhexis in cataract surgery. J Cataract Refract Surg 1999;25:7–9.

4Masket S, Tennen DG: Astigmatic stabilization of 3.0 mm temporal clear corneal cataract incisions. J Cataract Refract Surg 1996;22:1451–1455.

Prof. Dr. Samuel Masket, Private Office, 2080 Century Park East, Suite 911, Los Angeles, CA 90067 (USA)

Tel. 1 310 229 1220, Fax 1 310 229 1222, E-Mail sammasket@aol.com

Fig. 1. Dislocated hard nucleus in the vitreous cavity.

Fig. 2. Dislocated nucleus and cortical material in the vitreous cavity.

technique, there being 6 men and 6 women. Those patients who presented only dislocation of cortex material have been excluded. In no case had an intraocular lens been implanted.

The time lapse between the cataract surgery and vitrectomy varied between 1 and 24 days (average 13 10). Six of the patients presented a dislocation of more than 80% of the nucleus according to our exploration with indirect ophthalmoscopy and 6 of them between 80 and 50% of the nucleus (fig. 1, 2).

On previous evaluation, 9 patients presented an increase of intraocular pressure, 7 inflammatory reactions from mild to severe, 1 case presented a mild corneal edema and in no case was there a vitreous hemorrhage. In all cases the nucleus or its fragments were visible by indirect ophthalmoscopy.

Indications for Surgery

The primary indication for vitrectomy was in all cases the decrease of visual acuity due to vitreous opacification generated by the presence of the nucleus and the inflammatory reaction. The cases with a rise in the intraocular pressure were treated by topical medication as was the associated inflammatory reaction in some of them. In 1 case a mild corneal edema existed which did not enable a detailed visualization of the fundus eye, delaying the vitrectomy surgery for 24 days, the date by which the cornea had recovered sufficient transparency to perform the vitreous surgery without problems.

Surgical Technique

We performed three-port pars plana vitrectomy under local anesthesia (peribulbar) on an outpatient basis. At the same time we used a 30° light pipe pick to help us in the manipulation of the nucleus within the vitreous cavity and a wide field visualization system.

As a first step we performed a complete vitrectomy starting it by completely eliminating the residual cortical lens material and prolapsed vitreous in the anterior chamber cleaning thoroughly all the vitreous fibers which might have remained attached to the corneal incision. After that we filled the anterior chamber with viscoelastic material to protect the corneal endothelium. We paid special attention to thoroughly cleaning the remains of the cortical material from under the iris and in the capsular remains, trying to preserve these as much as possible for the implantation of a posterior chamber intraocular lens. A complete vitrectomy is mandatory to avoid the incarceration of vitreous strands in the phacoemulsification tip with tractions on the retina and interferences with its aspiration.

The second step consisted in lifting the nucleus and the residual cortical material (on occasion the cortical material mixed with the vitreous has been eliminated with the vitrectomy tip) by means of the injection of perfluorocarbon liquid, to place the nucleus in the center of the vitreous cavity (fig. 3). The use of this product offers us two advantages: the first protects the retina from possible impacts produced by the projection of hard nuclear fragments during its phacoemulsification and protects the retina reflecting at the surface of the perfluorocarbon bubble the ultrasound energy, provided that the sound probe is not immersed in the liquid [12]. We then proceeded to phacoemulsify the nucleus (fig. 4, 5) by means of the ultrasound tip ‘Micro Tip’ (the diameter of the same without infusion is 0.9 mm) using a bimanual technique with the 30° endoillumination pipe pick, with low ultrasound energy, pulsed mode, employing the following parameters: energy 75% in lineal mode, aspiration 200 mm Hg and 10 pps. During this step we avoided the appearance of burns in the sclerotomy by means of the continuous escape of infusion liquid by the same, since its size (1.4 mm, 20 G) is greater than the size of the Micro Tip needle (0.9 mm), allowing the escape of the liquid through it.

The third and last step of surgery consists in the implantation of an intraocular lens (foldable if possible) by the reopening of the corneal incision (clear cornea) on the capsular

Fig. 3. Injection of a bubble of perfluorocarbon liquid in the vitreous (arrows).

Fig. 4. Phacoemulsification of the nucleus by means of the ultrasound tip ‘Micro Tip’ using bimanual technique with the 30° endoillumination pipe pick, with low ultrasound energy.

remains (fig. 6, 7), if they permit a sufficiently stable base. Subsequently we eliminated the perfluorocarbon liquid and carried out a minute exploration of the peripheral retina by indentation (the use of wide field during surgery gives complete control of the whole vitreous cavity). On finding a retinal tear, we proceed to its endophotocoagulation and fluid gas exchange.

Fig. 5. Phacoemulsification of the nucleus in the vitreous cavity.

Fig. 6. Implantation of a foldable posterior chamber intraocular lens on the capsular remains.

Results

Of the 12 cases we reached a final best corrected visual acuity (BCVA) of 5/10 or better in 5. In 6 cases the final BCVA obtained varied between 4/10 and 1/10. Only in 1 case was the final BCVA of 0.05 due to the existence of high myopic atrophic maculopathy. One case required treatment with