Pars plicata

Abstract: Scanning electron microscopic studies of the zonular apparatus in 10 human and 17 monkey eyes revealed two functionally different sets of zonular fibers: the "main fiber" and the "tension fiber" system. The two systems are connected, forming a broad, sagittally oriented "zonular plexus" within the pars plicata of the ciliary body. The zonular plexus is attached to the ciliary epithelium by the tension fibers, which leave the main system and run obliquely forward to the epithelium deep in the valleys of the ciliary processes. Anteriorly, the zonular plexus splits into the two branches of the "zonular fork," which run respectively to the anterior and posterior aspect of the lens. Thus the zonular plexus can act as a fulcrum. The three-dimensional architecture of the zonular apparatus is consistent with a new concept of accommodation.

Abstract: Twenty-two eyes of 11 cynomolgus monkeys were subjected to contact transscleral cyclophotocoagulation with a continuous-wave Nd:YAG laser. The right eye of each monkey was coagulated at the pars plicata region by the contact probe placed 1.0 mm from the limbus, while the left eye of each monkey was coagulated at the pars plana region by the contact probe placed 3.0 mm from the limbus. Physiological and morphological studies were carried out up to 6 months after the treatment. The postoperative intraocular pressure showed a significant decrease within 1 week, corresponding to the inflammation of the anterior chamber. A gradual increase of the intraocular pressure occurred from the 2nd week on and returned to the preoperative value 8 weeks after pars plicata coagulation. The pars plana coagulation group maintained the intraocular pressure lower than the preoperative value until the end of the observation period. Histopathological examinations were carried out by the use of tracer particle perfusion into the anterior chamber. The pathologic features of pars plicata coagulation were necrosis, followed by atrophy of the ciliary process. The tracer particles accumulated at the anterior portion of the space between the bundles of ciliary muscle. The pathologic features of pars plana coagulation were necrosis followed by extension of proliferative tissue into the vitreous. The surrounding extracellular space of the stroma was enlarged, and the ciliary muscles were separated from the sclera. The tracer particles accumulated at the enlarged extracellular space of the stroma and the opened suprachoroidal space. These results suggest that the decrease of the intraocular pressure after pars plicata cyclocoagulation resulted from the reduction of aqueous secretion, whereas that after pars plana cyclocoagulation resulted from enhancement of the uveoscleral outflow through the enlarged extracellular space from the anterior chamber into the suprachoroidal space.

Abstract: • Lensectomy is routinely performed in infant eyes undergoing vitreoretinal surgery. Using a two-port system, we performed pars plicata vitrectomy and membrane peeling without removal of the crystalline lens. Surgical manipulations were done in the postequatorial region in eyes with areas of attached peripheral retina. Eight of 10 eyes showed no evidence of postoperative cataract formation. In no instance was a peripheral retinal break created. In selected cases, vitreoretinal surgery can be performed in infant eyes without the need for lens removal.