Prevention of Iatrogenic Keratectasia

 

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Abstract

Iatrogenic corneal ectasia is a rare but devastating complication after refractive surgery. While its incidence appears to be declining, it has not been eliminated. Its cause is probably related to a combination of an intrinsic predisposition to ectasia and an additional anatomical destabilising effect from the refractive surgery. Determining which eyes are intrinsically “weak” and exactly how much additional “weakening” an eye can withstand before developing progressive thinning and protrusion are both difficult tasks. The essentially universal availability of corneal topography and the increasing use of corneal tomography have significantly improved our ability to preoperatively diagnose early forms of corneal ectasias, especially keratoconus and pellucid marginal degeneration. Advanced software algorithms have also enhanced the sensitivity and specificity of these technologies. Newer technologies, such as measuring corneal biomechanics and corneal epithelial distribution, will hopefully continue to help us to differentiate normal from abnormal corneas preoperatively. In addition to abnormalities in anterior and posterior corneal curvature, a number of other risk factors for the development of post-refractive surgery ectasia have been proposed, including younger patient age, thinner central corneal thickness, thinner residual stromal bed thickness and high myopia. If the percentage of altered tissue is > 40 %, this is an extremely accurate predictor of corneal ectasia after refractive surgery. While there are a number of effective treatments for iatrogenic corneal ectasia, such as contact lenses, corneal crosslinking, intracorneal rings and corneal transplantation, prevention should be the goal. With newer and better corneal imaging technology to help screen out patients with abnormal corneas along with an improved understanding of exactly how much weakening a given cornea can take, we should be able to minimize this vision threatening complication.

Zusammenfassung

Die iatrogene Hornhautkeratektasie ist eine seltene, aber verheerende Komplikation, die nach einem refraktiv-chirurgischen Eingriff auftreten kann. Obwohl die Häufigkeit rückläufig ist, kann die iatrogen bedingte Hornhautkeratektasie nicht vollkommen ausgeschlossen werden. Die wahrscheinlichste Ursache ist eine Kombination aus einer patientenspezifischen Veranlagung und der destabilisierenden Auswirkung einer Augen-Laser-Behandlung. Die Schwierigkeit besteht darin, vor einer Operation festzustellen, welche Augen eine inhärente „Schwäche“ besitzen und wieviel zusätzliche „Schwächung“ das Auge verträgt, bevor es zu einer progressiven Ausdünnung und Vorwölbung der Hornhaut kommt. Die allgemeine Verfügbarkeit von Hornhauttopografie und die zunehmende Verbreitung dieser Untersuchungsmethode haben wesentlich dazu beigetragen, dass frühe Formen der Hornhautektasie, insbesondere Keratokonus und pelluzide marginale Degeneration, vor einem chirurgischen Eingriff entdeckt werden. Hochentwickelte Software-Algorithmen haben die Sensitivität und Spezifität dieser Technologien zusätzlich erhöht. Neue Technologien, z. B. die Messung der Biomechanik der Hornhaut und der Epithelschicht der Hornhaut, werden hoffentlich dazu beitragen, dass normale Augenhornhaut präoperativ besser von abnormaler Hornhaut unterscheiden werden kann. Neben Anomalien der vorderen und hinteren Hornhautkrümmung werden eine Reihe weiterer Risikofaktoren für die Entwicklung einer Hornhautektasie nach refraktiver Chirurgie aufgezählt, darunter jüngeres Patientenalter, dünnere zentrale Hornhautdicke, dünnere stromale Restdicke sowie starke Kurzsichtigkeit. Falls der Prozentsatz an verändertem Gewebe mehr als 40 % beträgt, stellt dies einen äußerst genauen Prädiktor für das Auftreten einer Hornhautektasie nach refraktiver Chirurgie dar. Obwohl es wirksame Behandlungen der iatrogen bedingten Hornhautektasie gibt, z. B. das Tragen von Kontaktlinsen, das Crosslinking der Hornhaut, die Implantation von intrakornealen Ringsegmenten und die Hornhauttransplantation, sollte das Ziel die Vermeidung dieser Komplikation sein. Neue und bessere Bildgebungsverfahren zur Darstellung der Hornhaut, welche Patienten mit Hornhautanomalien frühzeitig erfassen, sowie bessere Kenntnisse über das Ausmaß der Schwächung, die eine Hornhaut verträgt, könnten zur Minimierung dieser visusbedrohenden Komplikation beitragen.

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