Although initially the primary goal of cataract surgery was removal of an opacified crystalline lens—restoring visual acuity and relieving patients' feelings of social isolation—it has lately become more about postoperative quality of vision. Patients no longer accept mediocre results but rather demand excellent quality vision. In other words, visual results must exceed the patient's expectations of image quality after lens removal. Luckily, cataract surgeons can obtain better visual results than were previously possible. One reason for this revolution in cataract surgery is the tremendous progress we have made in understanding physiologic optics. We now have the ability to apply better IOLs with refractive properties, thus creating the notion of refractive cataract surgery.
But how do we teach residents about this new era of cataract surgery? This article outlines the importance of guiding our fellows in the hopes that future cataract operations will be even more successful than the ones we perform today.
FOCUS ON QUALITY OF VISION
For a long time, the evolution of cataract surgery was limited by its most common complication, posterior capsular opacification (PCO); however, the incidence of this major complication is not nearly as high today. In the future, PCO may even be eradicated thanks to new IOL designs and lens implantation techniques. In the meantime, physicists working in close collaboration with refractive surgeons draw attention to a new line of thinking: Cataract surgeons must focus on the fact that visual acuity is no longer the major criterion to evaluate patient's vision. Rather, quality of vision should be the ideal consideration, including the correction of wavefront aberrations, glare, and contrast sensitivity.
As this new approach to cataract surgery took shape, suddenly concepts, including modulation transfer function, point spread function, and contrast sensitivity in mesopic or scotopic conditions, were introduced as parameters to evaluate quality of vision after surgery. Based on these factors, it was evident that correcting refractive errors at the corneal level was possible only within the frame of low to moderate myopia and low hyperopia. Limits of tolerance for reshaping the cornea were then defined accordingly.
THE LENTICULAR PLANE OR THE CORNEA?
These new concepts introduced the question: Was the lenticular plane better to correct refractive errors, with or without crystalline lens opacification? Compared with the cornea, the lenticular plane has the advantage of being more tolerant for slight decentrations or misalignments; however, three major issues still remain unresolved: capsular healing, lens power calculations, and restoration of accommodation. Do we have full control over these parameters? The answer is indisputably negative. Therefore, ophthalmologists are still reluctant to investigate refractive lens exchange.
Why is capsular healing still an issue? Even now that PCO rates have been drastically reduced, the contraction forces exerted by the capsular healing process after uneventful cataract surgery define the final position of the IOL in the capsular bag. Current formulas used to calculate the IOL power are based on the presumption that the final position of the IOL can be deduced from preoperative measurements; however, accepting this presumption means that certain errors—such as refractive outliers—are unavoidable. Patients who come to our practice seeking alternative methods to corneal refractive surgery must be considered refractive outliers. In these patients, capsular healing has a great potential of influencing the final position of the IOL in the eye. As a consequence, refractive cataract surgery for outliers can be considered as an alternative refractive correction; however, the surgeon must consider all restrictions, such as patients with a capsular bag that is too big or small or patients with macular degeneration.
We do not have full control over the patient's healing process unless we destroy all lens epithelial cells (LECs). Even if they are all destroyed, we are still unsure whether the capsular bag can survive because the role of LECs is to rejuvenate the capsular bag. It is clear that in addition to classic lens-in-the-bag implantation, other implantation techniques (eg, bag-in-the-lens) should be proposed to achieve this goal.
CURRENT TECHNOLOGY LACKING
When considering restoration of accommodation after cataract surgery, current technologies are not at the level to promote refractive lens exchange. Multifocal lens implantation, monovision, and dual-optic IOLs, are all alternatives proposed to correct accommodation—but with the caveat that one must choose candidates carefully. We must clearly suggest to our residents, as well as our colleagues who are exploring the idea of refractive lens exchange, that these IOLs are useful only in a small number of patients. Ideally, those patients should not be too demanding or have high expectations with regard to quality of vision.
The blurring lines between cataract and refractive surgery are in fact becoming clearer. Before refractive cataract surgery can replace or take over laser vision correction where its indication stops, a few obstacles still remain to be solved. First, manufacturers must develop an IOL that adapts its spherical aberrations to those of the cornea. Such an IOL should be made of a biomaterial having blue-blocking properties, should not reduce scotopic vision, and should be centered along the visual axis to include spherical and toric correction. Additionally, the anterior curvature should be changeable in response to the accommodative reflex. All these parameters are coming closer to possibility. It will not take long before the ideal IOL will be available; however, in the meantime, refractive lens exchange must only be proposed with proper patient selection. Too many restrictions currently remain for it to be a common practice among all patients.
CONCLUSION
When educating our residents about refractive cataract surgery, it is best to be upfront about the indications for refractive lens exchange. Be sure they understand that refractive lens exchange is not suited for all patients, and urge them to select candidates who are willing to be patient with the process.
Marie-José Tassignon, MD, PhD, FEBO, is Head of the Department of Ophthalmology at the Antwerp University Hospital, Belgium. She is also President of the European Board of Ophthalmology and initiator of a network of educational programs. Dr. Tassignon states that she has a patent ownership or part ownership with Morcher GmbH. She may be reached at tel: +32 3 821 33 77; fax +32 3 825 19 26; e-mail: Marie-Jose.Tassignon@uza.be.
