Phakic refractive lenses and vitreous dislocationписьмо
Аннотация: In their case report describing luxation of a phakic refractive lens (PRL) in vitro 2 months postoperatively, Eleftheriadis et al.1 attribute the complication to a possible zonular defect associated with extreme myopia, a previously forgotten and unrecognized ocular trauma, or intraoperative manipulations that may have resulted in the spontaneous dislocation of the PRL. In my opinion, the position of the lens in the anterior chamber and the design of the lens could also play a role in triggering this complication. Phakic refractive lenses have a continuous posterior curvature and do not have knees (unlike the implantable contact lens in which the knees are supported by the zonula and this complication has not been reported).2 Because of this and their relative rigidity, PRLs should adapt to the space available in the posterior chamber. This adaptability and according to the relationship between the diameter of the posterior chamber and the diameter of the PRL, these lenses are able to adopt different positions. If the lens is relatively large with respect to the diameter of the posterior chamber, the haptics will position themselves on the sulcus. If the size is relatively small, the haptics will settle on the zonula or in the area anterior to the crystalline lens. Intermediate sizes will adopt mixed positions; for example, 1 haptic on the sulcus and the other in the ciliary body or 1 haptic on the sulcus and the other in the zonula.3,4 It is the lenses that have adopted a mixed position that may favor the transmission of the elastic force of the PRL toward the zonular fibers; that is, lenses that are not fully at rest (they are, in fact, slightly bent or “squeezed,” unlike the smaller lenses that rest on the zonula). This does not not occur with lenses that fit tightly between 2 sturdy “walls”; ie, lenses with both haptics positioned on the sulcus. In these latter cases, the elastic force is evenly distributed between the 2 walls, although the possibility of alterations above the iris root or anterior displacement of the inner surface of the lens exists. The intermediate lenses, as mentioned above, may have 1 haptic resting against a resistant surface (the sulcus) and the other against a fragile surface (the zonula). Therefore, if all the elastic force is directed against the zonular fibers, which could give way over time, the lens could easily be displaced toward the vitreous. Such a displacement could be sudden, with the “snap” that might occur at the moment the fibers give way. In the case reported by Eleftheriadis et al., this may not be the sole mechanism. As the authors point out, due to the intrinsic weakness of the zonula in myopic patients and in situations in which surgical factors come into play, the risk for luxation of the posterior chamber phakic lens in the vitreous is increased. However, these factors are present when other types of posterior chamber phakic IOLs are implanted, yet they have not presented this complication. Julián García-Feijoó MD, PhD Madrid, Spain
Год издания: 2005
Авторы: J. García–Sánchez
Издательство: Lippincott Williams & Wilkins
Источник: Journal of Cataract & Refractive Surgery
Ключевые слова: Corneal surgery and disorders, Intraocular Surgery and Lenses, Ocular Infections and Treatments
Другие ссылки: Journal of Cataract & Refractive Surgery (HTML)
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Открытый доступ: bronze
Том: 31
Выпуск: 12
Страницы: 2245–2246