Here’s a recent and welcome trend that’s part of the “long tail” of ophthalmic surgical innovation: addressing mild corneal surface abnormality before cataract surgery to optimize long-term visual outcomes.
by Christopher J. Rapuano, MD
Over the past five to 10 years, there has been a steep increase in corneal specialist referral for patients preparing for cataract surgery, including those with even mild corneal surface pathology. This is a welcome trend—one that might be considered part of the “long tail” of incremental innovation and improvement in ophthalmic surgery. I believe it will and should continue to gain momentum in years to come.
Why? Because a clear, regular, smooth corneal surface is necessary to achieve excellent post-surgical visual outcomes. Meticulous assessment—including medical and surgical history and preoperative slit-lamp examination—is essential to identifying corneal problems. When necessary, treatment of the ocular surface prior to cataract surgery reduces the risk for intraoperative and postoperative problems and improves the chance for happy patients and surgeons.1
The Dawn of DEWS
The health of the cornea used to be somewhat ignored prior to cataract surgery; if it was clear enough to see through, it was generally considered adequate. There were several reasons for this. First, concern around the ocular surface did not hit the ophthalmology mainstream until the late 2000s. The Dysfunctional Tear Syndrome Delphi panel report, published in 2006, and the International Dry Eye Workshop (DEWS) report, published in 2007, marked the first major group efforts to organize and interpret an explosion of research on the subject from the preceding 10 years.2,3 Since then, appreciation for the complexity and importance of the ocular surface as it relates to all aspects of eye health has grown.
Secondly, in years past, corneal topographic instrumentation was not as sophisticated nor widely available as it is today, and so ocular surface irregularities were probably underappreciated.
Lastly, prior to the introduction and widespread use of premium intraocular lenses (IOLs), patient expectations for visual clarity following cataract surgery were lower.
Today, the landscape is different. The medical community increasingly appreciates the importance of a smooth, clear cornea as it relates to post-cataract surgery visual outcomes; ocular surface assessment technology has markedly improved; and, more than ever, we are looking for ways to satisfy patients’ high expectations, whether they are receiving a premium or monofocal IOL.
Why the Cornea Matters
Ocular surface abnormalities can affect post-surgical comfort and physical healing. Further, the ocular surface affects visual outcomes in two critical ways. First, a clear cornea contributes to good vision regardless of the state of the crystalline lens. Mild corneal irregularities are upstaged by significant cataracts prior to their removal but become more apparent and visually bothersome afterward. Even patients with mild corneal disease may be disappointed with their post-surgical visual outcome.
Secondly, some corneal conditions, such as Salzmann’s nodules or pterygium, can affect corneal curvature and lead to spurious keratometry (K) readings—and therefore imprecise IOL power selection.1
Detecting and treating these conditions prior to cataract surgery helps to ensure accurate power calculation and reduces the chances of needing a correcting procedure, such as a lens exchange, piggyback lens, or refractive surgery, later.
Astigmatism due to treatable conditions must be identified and addressed before calculating IOL power, particularly among patients who are to receive a toric IOL (placement of a toric IOL is indicated for permanent forms of astigmatism only). For example, even a mild pterygium can cause a few diopters of astigmatism. Should the pterygium later be excised and the pterygium-induced astigmatism corrected, a toric IOL may become the source of astigmatism. When placing a multifocal IOL, a pristine cornea (and a pristine retina) is also key to optimizing the chance for high patient satisfaction.1
Keeping an Eye Out
When evaluating cataract surgery candidates, I keep an eye out for the range of conditions that can affect the cornea, including dry eye disease (DED), pterygium, basement membrane dystrophies, and Salzmann’s nodular degeneration. DED is a catch-all diagnosis characterized by a breakdown in some aspect of the lacrimal functional unit—the conjunctiva, cornea, lacrimal and meibomian glands, lacrimal drainage system, preocular tear film, and reflexive neural connections.4 DED often affects the cornea, reducing quality of life and sometimes vision and potentially impeding healing following ocular surgery.5,6 Recently developed point-of-care diagnostic technologies—including tear osmolarity and inflammatory marker (ie, MMP-9) assessments—have improved our ability to detect dry eye in the office, particularly since concordance between severity of signs and symptoms is often lacking. Cleaning up the ocular surface affected by DED prior to any type of ocular surgery is advised.
Epithelial basement membrane dystrophy (EBMD)—also called anterior basement membrane dystrophy (ABMD)—is a reduplication of the epithelial basement membrane associated with loosening of the epithelium and recurrent, sometimes painful corneal erosions. Like pterygium, EBMD can also cause a mild irregularity of the ocular surface and irregular astigmatism, impairing preoperative vision and contributing to inaccurate
K readings. Following surgery, postoperative vision quality may be compromised and worsen over time.
Salzmann’s nodular degeneration is a similar disorder characterized by creamy white elevated nodules, typically located on the periphery but occasionally more centrally. Salzmann’s nodules, which may be associated with EBMD, can cause dry eye type symptoms and irregular astigmatism, also affecting K readings and IOL choice.
When to Treat
One of the roles of corneal specialists is to judge whether corneal pathology is severe enough to warrant treatment prior to surgery. Mild and peripheral corneal irregularities may not require treatment prior to surgery; moderate and severe and/or central irregularities generally do. Patients with EBMD who have an absence of “negative staining” (ie, lesions that disperse fluorescein on slit-lamp examination) and normal topography/keratography can be advised to proceed with cataract surgery. In contrast, those with an abnormality that is central, moderate to severe, or apparent on topography should undergo treatment and delay cataract surgery for perhaps 6 weeks or so. Treatment may consist of epithelial debridement, diamond burr polishing, or excimer laser phototherapeutic keratectomy (PTK).
For patients with Salzmann’s nodular degeneration or pterygium, any irregular astigmatism centrally or on topography warrants treatment and reevaluation prior to cataract surgery. Salzmann’s nodules may be treated with lamellar keratectomy with a blade (with or without diamond burr polishing), which often results in a nice smooth surface, as the nodules can sometimes be peeled right off Bowman’s layer. Alternatively, excimer laser PTK with or without mitomycin-C can be used. Pterygium is corrected by excision, most commonly with conjunctival autografting.
The bottom line: getting the corneal surface in shape prior to cataract surgery is worth the time and effort, even though it slows down the process. Patients will thank you for it in the long run.
Christopher J. Rapuano, MD, is the chief of the cornea service at Wills Eye Hospital. Medical writer Noelle Lake, MD, assisted in the preparation of this blog post.
What is your approach to the cataract surgery candidate with corneal irregularity? Has it changed in recent years?
REFERENCES
Kim P, Plugfelder S, Slomovic AR. Top 5 pearls to consider when implanting advanced-technology IOLs in patients with ocular surface disease. Int Ophthalmol Clin. 2012;52:51-8.
Behrens A, Doyle JJ, Stern L, et al for the Dysfunctional Tear Syndrome Study Group. Dysfunctional tear syndrome: a Delphi approach to treatment recommendations. Cornea. 2006;25:900-7.
The 2007 Report of the International Dry Eye WorkShop (DEWS). Ocul Surf. 2007;5:65-224.
Bron AJ, Tomlinson A, Foulks GN, et al. Rethinking Dry Eye Disease: A Perspective on Clinical Implications. Ocul Surf. 2014;12(2S):S1-S31.
The epidemiology of dry eye disease: report of the Epidemiology Subcommittee of the International Dry Eye WorkShop. Ocul Surf. 2007;5:93-107.
Miljanovic B, Dana R, Sullivan DA, et al. Impact of dry eye syndrome on vision-related quality of life. Am J Ophthalmol. 2007;143:409-15.