Strive for accuracy in refractive lensectomy patients

The best preparation is to treat each of your cataract patients as though they were the most demanding refractive lensectomy patient imaginable.

Issue: November 1, 1999

ByWilliam F. Maloney, MD

The specific indications for refractive lensectomy and IOL replacement are not yet firmly established. Nevertheless, because the limits of keratorefractive techniques — especially laser in situ keratomileusis — are becoming more fully appreciated by refractive surgeons, there is little doubt that we are about to see increasing importance placed upon the role of lens procedures in refractive surgery.

Indeed, there are many surgeons, myself included, who think that phacorefractive techniques — including phakic IOLs and lensectomy in appropriate patients — are about to become the most dynamic and fastest growing area of refractive surgery. In this column, we are going to look at the current state of the art of refractive lensectomy and IOL replacement.

History lesson

---Topical intraocular, non-injection anesthesia works well for hyperopic patients but not always for myopics, because of the tendency for excessive movement of the lens-iris diaphragm in longer eyes.

The specific techniques for refractive lensectomy and IOL replacement have been evolving since Ridley implanted the first IOL in 1949 and since Kelman introduced phacoemulsification in 1967 and with it the considerable refractive benefits of small incision surgery. Since then, ophthalmology has been steadily paving the way to refractive lensectomy by developing new techniques and technology that have dramatically improved the safety and refractive accuracy of lensectomy surgery in cataract patients. Naturally this led to a gradually increasing emphasis on the refractive benefits of lensectomy surgery, together with a steady decrease in our need for the requirement that a significant obstructive impairment from lens opacity be present in every patient in order to justify the intervention.

The result of this evolution is a state-of-the-art lensectomy procedure that is a finely tuned refractive technique capable of correcting almost any degree of pre-existing hyperopic or myopic refractive error with the accuracy that today’s refractive patients have come to expect. In most cases, lensectomy and IOL procedures, including topical anesthesia, clear corneal incision, phaco lensectomy and foldable IOLs, are completed in less than 10 minutes without pain and with almost immediate recovery of excellent uncorrected vision. As a result, the state-of-the-art lensectomy procedure is increasingly seen as a legitimate contender among refractive procedures in appropriately selected patients.

The principles of proper patient selection and careful consideration of the risks of intraocular surgery — especially retinal detachment in high myopes — are of the utmost importance in refractive lensectomy surgery, and we will consider these issues in detail in upcoming columns. Now let us take an overall look at each of the components of the technique itself. As you would expect, it builds on our experience with the technique and technology that have developed for lensectomy and IOL surgery for today’s cataract patients.

Anesthesia

---Clear corneal incision using the single plane paracentesis is ideal for refractive lensectomy. The new generation of metal blades for this type of incision generally has been excellent.

Although most agree that topical anesthesia is the procedure of choice for refractive lensectomy, it has become clear that (just as in cataract surgery) it is not for everyone. In general, the guidelines we have come to follow in cataract patients hold true for refractive patients, as well. In my experience, however, there are some important additional considerations when considering topical anesthesia in younger refractive patients:

Younger patients usually are more anxious and, therefore, typically do better with more sedation than that required in cataract patients.
Younger patients usually are more light sensitive during topical anesthesia; therefore, it is necessary to increase the microscope illumination more gradually. Photophobia also makes the intraocular component of non-injection anesthesia more important, as it seems to decrease the threshold of troublesome photophobia.
Younger patients often need more intraocular anesthetic. Consider switching from 1% to 2% non-preserved Xylocaine (lidocaine; Astra), but it must be instilled much more slowly than 1% to avoid causing discomfort.
High myopes with a long axial length (usually above 25 mm or so) often will experience pain that cannot be completely covered by topical intraocular anesthesia. This is presumably due to the stresses on the ciliary muscle caused by “trampoleening” of the lens-iris diaphragm typical of these eyes. I do not yet know how best to deal with this issue, because these long eyes are the ones most inclined to serious complications from injection anesthesia. At this point, I can only say that I have been disappointed in the effectiveness of topical intraocular anesthesia on several occasions in high myopes.

Incision

---The trend to a larger 5 to 6 mm CCC that we have seen in cataract surgery also applies to refractive lensectomy, but for different reasons.

Clear corneal is the incision best suited to refractive lensectomy due primarily to its efficiency, safety and immediate sealing, which allows rapid resumption of activity, as well as its astigmatic neutrality. In my experience, the single plane paracentesis model, originally described by I. Howard Fine, is ideal for refractive patients because it eliminates the vertical groove, which usually is the cause of the foreign-body sensation sometimes associated with the clear corneal incision.

The groove component also is responsible for corneal flattening; thus, the single-plane approach is typically more reliably astigmatically neutral. It also eliminates the need to dimple down with the blade, allowing for the easiest and most reliably self-sealing incision. Although diamond blades have traditionally been required for this single-plane paracentesis-type incision, the new generation of metal blades (Sharpoint, Beaver, Alcon, for example) that are manufactured specifically for clear corneal incisions are excellent. I have found that they work well for this single-plane approach, provided that they are limited to single use as intended by the manufacturers.

Capsulorrhexis

---Cortical cleaving hydrodissection probably is the most important step in freely mobilizing the soft clear lens for phaco aspiration.

Continuous curvilinear capsulorrhexis (CCC) for refractive lensectomy should ideally be somewhat larger. As you may know there has been a trend toward a slightly larger 5 to 6 mm CCC in cataract surgery because of its greater efficiencies. Those advantages are even more important in the refractive patient. The 5 to 6 mm CCC allows for safer phaco lensectomy options, and it tends to increase access to cortical material that can be tenacious in the clear lens.

However, the most important reason for the 5 to 6 mm CCC is related to posterior capsule opacification (PCO). David Apple will outline these issues in detail here in a future column. I simply want to mention here that in addition to a truncated edge on the IOL, Dr. Apple believes that the two most important means currently at our disposal to discourage PCO are complete cortical cleanup and the “shrink-wrap” effect seen when the anterior capsular edge just approximates but does not significantly overlap the edge of the IOL.

PCO is a very important issue with refractive lensectomy, especially in high myopes. Both of these means to minimize PCO are enhanced by the larger diameter 5 to 6 mm CCC.

Phaco lensectomy

---The first principle of refractive phaco lensectomy is protect the capsule. Therefore, the lens is removed from the bag with either hydroexpression or viscoexpression before phaco aspiration. Viscoelastic adequately protects the endothelium during the usually rapid lens removal.

Removal of the clear lens in refractive lensectomy presents a different set of challenges for the phaco surgeon. Naturally, we tend to think of our experience with a soft, posterior subcapsular cataract in a younger patient, and that is a good place to start.

There is, however, more to it than that, in my experience. I have come to approach these eyes from a completely different perspective, which has led me to the following general principles for refractive phaco lensectomy.

Utilize cortical cleaving hydrodissection

---A 6-mm foldable IOL is required for refractive lensectomy. I prefer a closed delivery system because of the efficiency of pre-loading and extra protection from contamination during insertion.

Loosening the lens from the capsular bag and freely mobilizing it is the most important and challenging step in clear lensectomy. Cortical cleavage hydrodissection as described by Dr. Fine provides for the most efficient and effective cleaving by encouraging all of the hydrodissection fluid to flow in the same plane, which is between capsule and lens.

None of the fluid is wasted by infiltrating the substance of the lens. It is accomplished by lifting the cannula and tenting the anterior capsule before injecting balanced salt solution. It is very important to prevent premature infiltration before the cannula is properly placed; therefore, be sure your thumb is not in contact with the syringe plunger until the cannula is in position and you are ready to inject.

Phaco lensectomy is best performed outside of the capsular bag

Protect the capsule above all else, including the corneal endothelium. This perpetual compromise should lean in favor of the capsule when performing lensectomy on clear lenses in these younger eyes. This is best accomplished by hydroexpression or viscoexpression of the lens up through the enlarged CCC. These soft lenses usually cannot be “flipped” out of the bag.

Phaco-assisted aspiration at or slightly above the iris plane is then easily accomplished utilizing higher aspiration and very low powered, slow pulse phaco to assist the lens evacuation. A moderately highly retentive viscoelastic maintains adequate endothelial protection for this usually very brief step, while the capsule is protected by relocation of the lensectomy.

IOL selection and delivery

Foldable IOLs are required for state-of-the-art lensectomy. Although not yet available in all powers, they will be soon enough, so I prefer to advise a patient to wait rather than use a rigid IOL requiring a 6-mm incision. A smaller optic is not ideal in younger patients.

IOL selection and insertion is predominantly a matter of surgeon preference in refractive lensectomy. I have found these guidelines to be helpful:

Foldable IOLs with a 6-mm optic are indicated especially in younger patients with active pupils.
Injector delivery systems can be pre-loaded and are, therefore, considerably more efficient. This closed delivery system also is less likely to allow for contamination during IOL insertion.
Pseudophakic photophobia can be more intense and last longer in cataract patients. The younger refractive patients should be repeatedly advised accordingly during the preop orientation. Sunglasses are almost always a necessity, particularly in lightly pigmented patients.
Presbyopic correction can be accomplished with either monovision or multifocal IOLs in many properly selected patients. In either case, the key concept is compromise. In younger pre-presbyopic patients, that is sometimes a difficult concept to grasp. In my experience, this is clearly an area to underpromise and overdeliver.

Refractive results

As with any other refractive procedure, refractive lensectomy is judged exclusively by its refractive results. Refractive lensectomy is capable of achieving the accuracy that today’s refractive patients have come to expect, but only if state-of-the-art techniques are employed during the entire IOL calculation process, in conjunction with an almost obsessive insistence on accuracy of the measurements involved, such as cycloplegic refraction, axial length and keratometry. Bruce Wallace is acknowledged as one of the world’s true experts on this topic. He will write on this here in a future column.

For now, I will only say that in my experience, the best preparation is to treat each of your cataract patients as though they were the most demanding refractive lensectomy patient imaginable. You and your entire staff will then begin to develop the much tighter tolerance necessary to achieve refractive results possible with refractive lensectomy today. Here, more than anywhere, the devil is in the details. With the possible exception of immersion A-scan techniques, there is really nothing new to learn. Success is a matter of doing the same things we have done for cataract patients, but doing them more accurately.

Next month: the single plane paracentesis clear corneal incision for refractive lensectomy — step by step.

For Your Information:

William F. Maloney, is Editor of the Cataract/IOL Section of the Ocular Surgery News Editorial Board. He is in private practice and can be reached at 2023 W. Vista Way, Ste. A, Vista CA 92083; (760) 941-1400; fax: (760) 941-9643; e-mail: 74044.2361@compuserve.com. Dr. Maloney has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.