Eyeworld

117 EW CORNEA February 2018 by Maxine Lipner EyeWorld Senior Contributing Writer W hile anterior kera- toconus is widely recognized, posterior keratoconus may hide under the radar. Its incidence and prevalence are un- known, according to Asim Farooq, MD, assistant professor of ophthal- mology, University of Chicago. Dr. Farooq took a closer look at this condition in a recent study. 1 After seeing a couple of patients with the condition, including a mid- dle-aged patient who had previously gone undiagnosed with posterior keratoconus, Dr. Farooq felt com- Posterior keratoconus front and center Eye with posterior keratoconus Research highlight pelled to look into this. "I decided that it would be useful to perform a comprehensive review of the litera- ture in order to help ophthalmolo- gists recognize this entity," he said. The hallmarks of posterior ker- atoconus are relatively clear cut. "It is characterized by an abnormally steep posterior corneal curvature, usually associated with a deep stro- mal opacity and at times pigment deposits on the posterior corneal surface," Dr. Farooq said. It is different from the more widely recognized anterior keratoco- nus, which is marked by a pro- gressive steepening of the anterior corneal surface, leading to irregular astigmatism and decreased vision, he noted, adding that the anterior variety is often diagnosed in ado- lescence or early adulthood and has been associated with a number of genetic mutations. Posterior kerato- conus may or may not have anterior curvature abnormalities and in most cases is a congenital or developmen- tal anomaly. "It may be diagnosed in childhood or later in life, depend- ing on the amount of stromal opaci- ty and/or the impact on vision," Dr. Farooq said, adding that so far there are no associated genetic mutations with the posterior condition. Also with posterior keratoconus comes the potential for amblyopia. Honing in on the literature Investigators performed a literature search for articles with "posteri- or keratoconus" or "keratoconus posticus" in the title and included all of the relevant articles that were available in English. After sifting through these studies, investigators identified several key findings. "We found that posterior keratoconus may be localized or diffuse, and there may be associated anterior curvature ab- normalities including steepening or flattening overlying the area of pos- terior steepening," Dr. Farooq said. "Posterior stromal opacification is a common feature." Investigators also determined that in cases of posterior keratoconus, there was a significant number of associated ocular and systemic anomalies reported. In some cases, there was some similarity to anterior keratoconus. "We were surprised to learn that progressive anterior steepening has been reported in posterior kerato- conus," Dr. Farooq said. Having one condition did not necessarily preclude having the other as well. "There has been a case in which a patient had posterior keratoconus in one eye and (anterior) keratoconus in the other," he said. Gaining clinical perspective These findings have a number of im- plications, Dr. Farooq thinks. "First, pediatric patients with posterior keratoconus should be promptly referred to a pediatric ophthalmol- ogist for amblyopia evaluation and management," he said. Since poste- rior keratoconus is usually congeni- tal, amblyopia evaluation and man- agement is important, Dr. Farooq stressed, adding that an eye may develop amblyopia due to depriva- tion in the case of a dense posterior stromal opacity, or anisometropia, especially in unilateral cases of the condition. "Second, these eyes may have a number of other anomalies," he said. A comprehensive eye exam, complete with gonioscopy, assess- ment of the crystalline lens, a dilat- ed fundus exam, and axial length measurement are all indicated. A third clinical implication is the need to continue to watch these eyes over time. "Patients should be followed to ensure disease stability," he said. "Finally, patients should be referred for a systemic evaluation." Practitioners also need to think about posterior keratoconus in cases of cataract removal. "Intraocular lens power calculation for cataract surgery should take into account the posterior corneal curvature to obtain a more accurate estimation of total corneal power," Dr. Farooq said. Dr. Farooq hopes that practi- tioners come away from the study with a greater understanding of this unusual condition and how to identify it. "Posterior keratoconus is a rare corneal disorder that requires careful slit lamp examination to make the diagnosis," he said. "Imag- ing, such as anterior segment optical coherence tomography, can be a useful tool." Overall, the condition is one that once on the radar should not be difficult to spot. "One of the great things about ophthalmology is that we can often make diagnoses through direct observation," Dr. Fa- rooq said, concluding that posterior keratoconus is one such diagnosis. Even if a physician has never seen it before, he or she can recognize it from having seen a photograph. EW Reference 1. Silas MR, et al. Posterior keratoconus. Br J Ophthalmol. 2017 Nov 9. Epub ahead of print. Editors' note: Dr. Farooq has no finan- cial interests related to his comments. Contact information Farooq: asimfarooq@uchicago.edu Posterior keratoconus as seen at the slit lamp Source (all): Asim Farooq, MD

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