BLOG: Expect the unexpected: Complex corneas are out there
This is the first installment in a blog series on the implications of the complex cornea on cataract surgery and how to identify these patients preoperatively.
Welcome to the first blog in a series on the complex cornea patient. “Complex Cornea” describes a patient population that presents with diverse ocular histories, corneal shapes and irregularities that are not typical and can affect many aspects of cataract surgery. Patients with these irregular corneas present unique challenges when it comes to postoperative visual results, and these scenarios may be more common than what is currently recognized.
We can think about these complex cornea patients as falling into one of three categories:
Those with surgically induced corneal irregularities such as post-LASIK, PRK, radial keratotomy, astigmatic keratotomy, pterygium surgery, corneal transplants and trabeculectomy.
Genetically derived or dystrophic corneal aberrations in which the individual naturally presents with corneal higher-order aberrations of 0.5 µm or more. These include ectasias such as keratoconus or pellucid marginal degeneration. These can also include subtle irregularities that are not easily identified on standard topography mapping. Epithelial basement membrane dystrophy (EBMD) among other corneal dystrophies is also included here.
Disease or trauma-induced corneal shape irregularities. Examples include Terrien’s marginal degeneration, Salzmann nodular degeneration and immune-related alterations of the cornea such as peripheral ulcerative keratitis. Trauma like a fully or partially penetrating eye injury can cause an irregular cornea, as well as surgery performed to repair the trauma. These can result in scarring, edema and other abnormalities.
Although these patient groups can vary in terms of their baseline optical quality, they all have elevated complexity involved with their case when it comes to lens selection, IOL power calculation and postoperative visual results that allow for a continuous range of focus. Post-refractive patients likely have good baseline optical quality, for example, whereas a keratoconus patient would typically have a poorer baseline level of optical quality.
Market research has revealed that around 12% to 14% of patients presenting for cataract surgery have a complex cornea. A recent panel convened to create consensus on corneal irregularity reported that approximately 24% of the members’ preoperative cataract patients have irregular corneas. A review of 200 eyes of 400 patients found that approximately one-fourth of patients scheduled for cataract surgery had abnormal corneal topography, yet they did not have a history of corneal surgery. Ten percent of these patients had irregular astigmatism or dry eye disease, 9% had borderline pellucid marginal degeneration, forme fruste keratoconus or superior steepening, and the remaining 6% had topographic findings consistent with forme fruste keratoconus, pellucid marginal corneal degeneration or keratoconus.
As surgeons, it is important that we identify these patients before surgery as their corneal irregularities will influence the subsequent cataract procedure as well as the type of IOL technology appropriate for their situation. Some types of irregular corneas such as EBMD can be treated before cataract surgery for better postoperative visual outcomes and others cannot. Some of these patients may not be candidates for traditional premium technology, and it is crucial that we take the time to educate this group about their individual situation and set the appropriate expectations for their postoperative vision.
Corneal irregularities are not uncommon and have consequences with regard to cataract surgery, so surgeons should aggressively seek out abnormalities. We look forward to exploring the best practices when it comes to identifying, treating and counseling these patients.
References:
- AcuFocus data on file.
- Frank B, et al. Invest Ophthalmol Vis Sci. 2014; 55(13):2477.
- 2020 global consensus on corneal irregularity: Expert panel offers recommendations for defining, diagnosing, and treating irregular corneas. Accessed April 29, 2021.
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