Phaco refractive surgery for the correction of ametropia: the future of lens surgery

As recommended LASIK parameters shrink to the mid-range, refractive surgery looks to lens technology to correct the higher refractive errors. errors.

---The anticipated range of correctable refractive error for LASIK/PRK in 1996. (Figure 1)

---As the limits of LASIK became more evident, the range began to be reduced and was approximately +4 D to –14 D early this year. (Figure 2)

Refractive lensectomy and replacement with a pseudophakic device was first proposed over 100 years ago by Fukala in 1890. Verzella first published the details of his technique of “clear lensectomy and IOL replacement” for the treatment of myopia in 1985. Few followed this “phaco refractive” path, however, and refractive surgical techniques have almost exclusively been the domain of the keratorefractive approaches; initially radial keratotomy (RK), then photorefractive keratectomy (PRK) and now laser in situ keratomileusis (LASIK).

The success of today’s LASIK technique is well known. Part of that success is derived from respecting the limits of LASIK and selecting patients accordingly. As we continue to gain longer-term results, it has become increasingly clear that those limits include patients with low to moderate degrees of ametropia. It has become obvious that LASIK is simply not capable of correcting high myopia or hyperopia with the accuracy that refractive patients have come to expect.

---The approximate range for LASIK for late this year. (Figure 3)

For example, as recently as 1996 it was thought that the treatment range for LASIK might extend from approximately +8 to –25 D (Figure 1). By 1998 to 1999, it was becoming increasingly clear that LASIK was not for everyone. That range had shrunk to about +4 D to –14 D (Figure 2). As we approach 2000, most of the high volume LASIK surgeons I asked are recommending the procedure for patients within a range of +3 D to –10 D (Figure 3), and are predicting that LASIK will ultimately be recommended for patients with refractive errors between approximately +2 D and –8 D.

Limitation to corneal reshaping

The limitation to corneal reshaping as a correction for refractive errors is due primarily to these two factors:

Anatomical limitation. After leaving appropriate allowances for the flap and bed, there is a limited amount of central cornea available to reshape using the laser (Figures 4a, 4b).

The limits to LASIK are in part due to a limited amount of cornea available to ablate. (Figures 4a, 4b)

Functional limitation. If the central treatment area of the cornea is not smaller than the pupil, then the quality of vision can be significantly reduced. This becomes clinically significant in young patients with active pupils, especially in dim light (Figures 5a, 5b).

The functional limits to LASIK relate to the relationship of pupil size to the treatment zone. Overlap can result in reduced quality of vision, particularly for high myopes. (Figures 5a, 5b)

Regardless of the exact range of refractive errors that LASIK will be found to effectively correct, it is increasingly clear that the keratorefractive approach alone will not answer the needs of all refractive patients. Thus the increasing interest in applying the significant refractive benefits that lens technology and techniques have provided cataract patients in recent years to those “outer” segments of the refractive spectrum that will not be treated with LASIK or other keratorefractive procedures such as the corneal rings. As that process gains momentum, some form of phaco refractive surgery will almost certainly become an established adjunct to keratorefractive surgery and complete the full spectrum of refractive surgery that may well look like that seen in Figure 6 by the early months of the new millennium.

Upcoming topics

---The spectrum of refractive surgery will almost certainly include both corneal and lens refractive procedures from this point forward. (Figure 6)

This regular monthly column will address the issues that relate to phaco refractive surgery; that is, the techniques and technology related to lens refractive surgery as distinguished from corneal refractive surgery. Here is a preview of the topics we plan to cover in the coming months:

Refractive lensectomy: How does it differ from routine cataract surgery? Patient selection, anesthesia, incision, continuous curvilinear capsulorrhexis diameter, considerations of the best phaco approach, and IOL selection (monovision or multifocal).

What about retinal detachment risks in the high myopes? We have reviewed the latest literature on this important and still controversial subject so that you can decide for yourself.

David Apple’s latest recommendations in the battle against posterior capsule opacification. The incidence has been dramatically reduced. Here are three techniques to help achieve these lower PCO rates.

Phakic IOLs. Posterior chamber? Anterior chamber? New foldables and new insertion devices on the horizon.

Achieving the most accurate refractive results. Which IOL formulas for which patients? A-scans; contact or immersion?

Next month: Refractive lensectomy — it’s been coming ever since Ridley invented the IOL and Kelman invented phaco. We’ll tell you how to begin safely and conscientiously.