Ординатура / Офтальмология / Английские материалы / Modern Cataract Surgery_Kohnen_2002

recommended penetrating keratoplasty at the time of cataract surgery due to the hardness of the cataract and the extent of his endothelial changes. He came to me specifically wondering if cataract surgery alone might not be possible and avoid the difficulties in association with penetrating keratoplasty. My evaluation found profound endothelial changes; however, there were no posterior folds in Descemet’s membrane and no epithelial edema throughout the day. There was a 3 nuclear sclerosis in both eyes with best-corrected vision in the right eye of 20/60 and 20/50 in the left eye.

We proceeded with minimal ultrasound-assisted phaco aspiration using phaco chop (right eye ultrasound time of 1 s and 2 s in the left eye) and mash with a corneal scleral tunnel and retrobulbar anesthesia and use of viscoat to provide greater protection for the endothelial surface.

Both corneas showed minimal edema on the first postoperative day with 20/25 uncorrected vision in the right eye and 20/40 uncorrected vision in the left eye. Within 2 weeks both corneas had cleared completely of any edema and were easily refracted to 20/20. The patient has been followed for over 1 year without any edema or difficulty.

Case 2: A 68-year-old white male was referred for consideration of penetrating keratoplasty and cataract removal due to Fuchs’ dystrophy and a visually significant cataract. Visual acuity was 20/50 best corrected in both eyes. Although this patient had significant corneal endothelial changes, again, there was no epithelial edema throughout the day and no folds in Descemet’s membrane. It was decided to use phaco chop with mash and no ultrasound energy in either eye for his 2 nuclear sclerosis.

On the first postoperative day both corneas had epithelial edema (right eye 2 , left eye 1–2 ). Visual acuity was 20/200 uncorrected and 20/80 corrected in the right eye and 20/70 uncorrected and 20/50 corrected in the left eye. Both corneas were clear and correctable to 20/20 by 2 weeks after surgery. Further follow-up is minimal to date.

Although this series is preliminary and small, certainly these results are impressive in patients with significant cataracts and Fuchs’ corneal changes. With the evolution of this technique, the ultrasound energy is turned off and the corneas have responded with minimal changes. If such are the results in such fragile corneas, then normal corneal endothelial changes should be minimal or nonexistent. We will complete prospective specular microscopy studies.

While irrigation is an important mechanical force, its effect is generally negative in that the irrigation flow comes around our phaco needle often short circuiting the aspiration flow and moving particles away from our emulsification tip until we can get them in the central vortex of aspiration. We have developed this so that we can have a one-handed approach to phacoemulsification and to cool the tip to decrease the incidence of wound burns. With a combination of phaco chop and mashing the nucleus to largely eliminate or significantly decrease the use of ultrasound energy, there is no reason to have irrigation around our phaco needle. This has prompted a series of studies in regard to using an irrigating chopping instrument and a second bare phaco needle utilizing two stab incisions.

Any approach such as this requires careful evaluation of the risk of creating wound burns and also whether or not we can maintain a deep anterior chamber.

The phaco chopper is based upon 19-gauge tubing with four sets of irrigation holes such that if the first two are blocked in the nucleus then the second two holes will maintain the chamber. This combination easily delivered 80 ml/min of flow unimpeded.

The irrigating chopper was introduced in eye bank eyes through a slit incision, and the bare 0° phaco needle was introduced through a second slit incision both approximately 1 mm long. Using the Allergan Sovereign machine with irrigation and aspiration at 15 ml/min and ultrasound starting at 50% power and increased in 10% increments, we continuously measured the wound temperature using a thermistor and looked for evidence of any wound burn (always noted at 45–50°C). We looked at continuous phaco and burst mode both in the unoccluded and the occluded state.

Even with continuous full phaco energy, a burn could only be created in the unoccluded state at 100% energy after 160 s and in the occluded state at 80% energy in about a minute. Using a burst mode, at 100% energy, we could create a phaco burn after 42 s occluded. Intraocular pressure was monitored throughout the procedure at every 30-second interval and intraocular pressure was continuously maintained to at least 18 mm Hg showing that we had no trouble maintaining a deep chamber with good intraocular pressure in either the occluded or unoccluded states.

Using an irrigating phaco chopper, the irrigation forces are now unopposed and very powerful. Any fragments immediately go to the phaco tip without having to chase nuclear fragments around the anterior chamber. There is some fluid loss from both wounds, which helps cool the phaco needle; small particles do come into that area, however, most pieces flow to the greatest outflow which is through the phaco needle. Now, irrigation alone with exquisite safety can be used to sweep nuclear particles off the capsule or out of the fornices eliminating the need to chase such particles with the much more dangerous phaco needle. This should enhance our safety and now allow wound sizes so small that they will again depend upon the size of the intraocular lens needed for insertion! This will push the technology for ever smaller intraocular lenses. One added benefit is the ability to swap sites for the phaco needle in complicated or difficult cases.

In conclusion, we have determined that the use of mechanical forces is the single most important step in regard to our efficiency in cataract surgery. This either dramatically diminishes or eliminates ultrasound reliance in cataract surgery. This improves efficiency and safety by minimizing capsular, iris, or corneal endothelial damage. Such an approach (being able to perform cataract surgery through two small slit incisions with no or minimal ultrasound reliance) would seem to make either laser energy or phacoptemesis unimportant in the evolution of cataract extraction.

Acknowledgments

Supported in part by a grant from Research to Prevent Blindness, Inc., New York, N.Y., to the Department of Ophthalmology and Visual Sciences, University of Utah.

References

1Pingree M, Crandall AS, Olson RJ: Cataract surgery complications in one year at an academic institution. J Cataract Refract Surg 1999;25:705–708.

3Wong T, Hingorani M, Lee V: Phacoemulsification time and power requirements in phaco chop and divide and conquer nucleofractis techniques. J Cataract Refract Surg 2000;26:1374–1378.

Randall J. Olson, MD, Department of Ophthalmology and Visual Sciences,

John A. Moran Eye Center, 50 North Medical Drive, Salt Lake City, UT 84132 (USA) Tel. 1 801 585 6622, Fax 1 801 581 3357, E-Mail randall.olson@hsc.utah.edu

Fig. 1. Cortical mature white cataract. Note the white lens. Additionally, an iridodialysis can be noted to the left indicating the traumatic nature of this cataract.

Fig. 2. Nuclear mature cataract. Note absence of red reflex and firm greenish brown nucleus that extends to the lens periphery.

Cortical (Intumescent) Mature Cataracts

The etiology of the cortically mature cataract is generally unknown, but the condition is characterized by hydration of lens cortex sufficient for the cortical

lens fibers to become swollen and opaque milky white. In the extreme case the lens cortex becomes fully liquefied, leaving only a small firm floating nucleus within a sac of white fluid; this rare special condition is referred to as a morgagnian cataract. It is uncertain why certain cataracts become cortically mature unless a specific rent in the capsule can be identified. However, the likely final common pathway is the mixture of aqueous humor with lens material. Cases without demonstrable trauma or physical openings in the lens capsule have, most likely, imbibed aqueous through the ordinarily semipermeable lens capsule. In these cases the lens generally swells, inducing an increased hydrostatic or ‘intralenticular pressure’. Lens swelling may be sufficient to cause narrowing of the chamber angle and the potential for phacomorphic glaucoma.

Raised pressure within the capsular bag (or the eye) is but one factor that can complicate surgery in this group of patients. Capsulorhexis can be very difficult, given that the capsule may be very friable and readily tear to the equator, since the capsule is ‘stretched’ by the increased water content of the lens. Furthermore, the surgeon is hindered by the absence of the red reflex, making capsulorhexis yet more challenging. Finally, these case types may be problematic since the density of the nucleus is obscured and cannot be evaluated until after the anterior capsule has been opened. Should the nucleus be very hard, phacoemulsification presents added risks since no epinucleus is present and the milky cortex may tend to wash out, leaving no protective cushion for the posterior capsule during the emulsification process.

The surgical approach to the cortically mature cataract begins with the preoperative evaluation. Gross presurgical vision testing can be assessed with two-point white light discrimination, perception of color with bright light, and entoptic phenomena. Additionally, the condition of the corneal endothelium should be evaluated with specular microscopy or slit lamp examination, since it may be necessary to elevate the nucleus into the anterior chamber during surgery, should the capsulorhexis fail, the posterior capsule rupture, etc. If the nucleus is very firm and the endothelium poor, emulsification in the anterior chamber may be contraindicated. Lastly, the preoperative evaluation should rule out phacolysis with lens-induced inflammation and secondary elevation of intraocular pressure. In that case intensive topical steroids and/or ocular hypotensive agents may be necessary prior to surgery. Phacomorphic angle closure from an intumescent white lens may require laser iridotomy prior to surgery.

Anterior capsulorhexis remains the most important and the most challenging aspect of the surgery. Generally, if one can complete the capsulorhexis, all else is likely to succeed. The factors that make the capsulorhexis difficult, as discussed above, include poor visibility and the friable nature of the capsule, particularly if it is under tension from increased hydrostatic pressure within the capsular bag. The surgical ‘game plan’ must consider these issues.

Table 1 lists the presently available options for increasing visibility during the capsulorhexis. The surgeon should alter the parameters of the microscope, increasing magnification and slowing the motorized changes in magnification, zoom, and X–Y position. In that manner the cut edge of the capsule may be kept in the surgeon’s view. Additionally, reducing the ambient room lighting will eliminate glare and improve the visibility of the events occurring in the anterior chamber. Another commonly encountered problem of visibility may occur when the capsule is first punctured, as liquefied cortex may escape from the capsular bag and mix with the aqueous or the viscoagent. This may be prevented by ‘overfilling’ the anterior chamber with a highly retentive viscoagent prior to initiating the capsule tear. This also helps to avoid peripheralization of the capsulotomy by creating a tamponade against the rapid escape of milky cortex arising from high ‘intralenticular’ pressure. Additionally, when working with an intumescent white cataract, the surgeon may consider making a small circular capsulotomy initially and enlarging it later when the risks of peripheralization are reduced. Should cortex enter the chamber during capsulorhexis, and preclude an adequate view, it may be necessary to move it out of the way with additional viscoelastic or evacuate it with the I/A handpiece or cannula.

Viscoelastic agents vary in their clinical behavior according to their chemical composition. Although individual stages of the surgery may require different viscocharacteristics, the optical clarity, cohesiveness, and high viscosity of Healon 5 (Pharmacia-Upjohn) at zero shear make it an excellent agent for capsulorhexis in cases with white cataract. However, once the emulsification process is initiated, a dispersive viscoagent may be useful to protect the

endothelium and capsule if the nucleus is firm; Viscoat (Alcon) performs well under these circumstances, but might reduce visibility as it traps bubbles and liquefied lens cortex.

The key factor in determining successful completion of a circular anterior capsulotomy (capsulorhexis) in cases with white mature cataracts is visualization of the anterior capsule and the advancing torn edge of the capsule. Historically, the use of a retinal endoilluminator, held tangential to the limbus, has been helpful in aiding the capsule tear (fig. 3a, b) [1]. Nevertheless, in my own experience, the endoilluminator method succeeds in less than 100% of cases. More recently, vital staining of the anterior capsule with either indocyanine green (ICG) or trypan blue has been popularized; this method is virtually always successful. ICG is readily available as an intravenous agent for retinal angiography and renal and hepatic imaging. Horiguchi et al. [2] have developed a system for its dilution, preparation and use in cataract surgery. It is essential to follow the prescribed method, as ICG can be modestly toxic to the corneal endothelium. As initially reported by Melles et al. [3], trypan blue is an excellent stain for the anterior capsule in cases of mature cataract. It is commercially available as a liquid in sterilized unit dose vials, is less costly than ICG, safe with respect to the endothelium and provides excellent contrast between the stained capsule and the underlying opaque or milky white lens cortex, as can be noted in figure 4. Given its advantages, trypan blue has become the method of choice for management of cortically mature cataracts. Nonetheless, it is presently unavailable in the USA, as the FDA has not evaluated it or approved its use. Other dyes for capsule staining (table 1) are either more toxic or less efficacious.

Following capsule staining, the capsule tear should be initiated under a retentive viscoelastic in the center of the anterior lens capsule in order to prevent peripheralization at the outset of the capsulotomy. Furthermore, if liquefied cortex escapes from the lens and obscures an adequate view, it is wise to aspirate the material or push it aside with additional viscoagent. In rare situations, all of the liquefied cortex may exude from the capsule bag and require removal before the capsulotomy can be completed; in such cases, after evacuating the cortex, the capsule can be filled with viscoelastic, making the surgery technically feasible.

Hydrodissection is often unnecessary in cases of white cataracts, as the liquefaction process may have sufficiently eliminated cortical-capsular adhesions. The surgeon should attempt to rotate the nucleus after capsulorhexis; if the nucleus is immobile, cautious hydrodissection is necessary (fig. 5). Given the friable nature of the capsule in these cases, hydrodissection must be approached with great care in order to prevent rupture of the capsule; small aliquots of BSS should be injected very slowly to prevent elevation of lens hydrostatic pressure. Furthermore, cases with recent trauma are likely to have a

Fig. 3. a Intraoperative view of mature cataract with poor view of capsular and anterior cortical details. b Retinal endoilluminator placed tangential to the limbus creates sclerotic scatter and markedly improved view of the capsular and cortical details.

capsule rent which may be extended with aggressive hydrodissection; posterior lens dislocation is an unfortunate, but possible sequel. On the other hand, a case of old trauma may demonstrate a fibrotic lens capsule (membranous cataract) and partially absorbed lens cortex. Hydrodissection may not be possible in cases of this nature.

Fig. 4. Intraoperative view of capsulorhexis after staining of the anterior capsule with trypan blue. Note that the capsule is easily visualized and contrasts well with the underlying white cortex.

Fig. 5. Following capsulorhexis, careful hydrodissection may be performed with a blunt cannula to avoid tearing the fragile anterior capsule.