Vitreous Changes in Myopia
The vitreous has a transparent gel-like structure with 4 ml of volume. The vitreous gel is covered by the vitreous cortex which consists of densely packed collagen. The Cloquet’s canal arises from Martegiani space at the optic disc and traverses the centr
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11
Shoji Kishi
11.1
Introduction
The vitreous has a transparent gel-like structure with 4 ml of volume. The vitreous gel is covered by the vitreous cortex which consists of densely packed collagen. The Cloquet’s canal arises from Martegiani space at the optic disc and traverses the central vitreous to retrolental space known as Berger’s space. Although the vitreous appears inert, it plays a major role in various fundus diseases including rhegmatogenous retinal detachment, macular hole, epiretinal membrane, and progression of proliferative diabetic retinopathy. Recently vitreous surgery expands its indication in vitreoretinal diseases such as diabetic macular edema and myopic foveoschisis [1, 2]. The vitreous is not a homogeneous tissue which is the subject for resection in vitrectomy. The vitreous has its own structure which has been elucidated by biomicroscopy of postmortem eyes. Recent advance of optical coherent tomography greatly improved our understanding on vitreous anatomy and vitreoretinal interface diseases. In myopic eyes, vitreous liquefaction develops at an early age which results in earlier posterior vitreous detachment (PVD). There is a strong statistical relation between axial myopia and rhegmatogenous retinal detachment [3]. Vitreous surgeons frequently encounter a membranous structure on the retina in eyes with myopic foveoschisis despite the apparent PVD with Weiss ring. In this chapter, the vitreous anatomy and its age-related change are described in normal eyes as well as vitreous changes in myopic eyes.
S. Kishi, MD Department of Ophthalmology, Gunma University School of Medicine, Gunma University Hospital, 3-39-15 Showamachi, Maebashi, Gunma 371-8511, Japan e-mail: [email protected]
11.2
Anatomy of the Vitreous
11.2.1 Embryology of the Vitreous [4] 11.2.1.1 Formation of Primary Vitreous (Fourth to Sixth Week; 4–13 mm Stage) The primary vitreous first appears in the narrow space between the surface and neural ectoderm during the fourth week of gestation, when the embryo is 4–5 mm in length. It derived mostly from the surface and neural ectoderm and partly from the mesoderm invaded through the embryonic choroidal fissure. The condensed fibrils of the primary vitreous form the capsula perilenticularis fibrosa around the lens. At the 5–7 mm stage, the hyaloid artery enters the distal part of optic stalk through the fetal fissure. It reaches the capsula perilenticularis fibrosa at 7 mm stage. The capsula is then vascularized by hyaloid artery and develops the tunica vasculosa lentis by the 13 mm stage. 11.2.1.2 Formation of Secondary Vitreous (Sixth Week to Third Month; 13–70 mm Stage) The secondary vitreous is the major component of the adult vitreous body which is derived from the neural ectoderm. At the end of the sixth week or 13 mm stage, the secondary vitreous emerges between the developing retina and the primary vitreous. It grows around the primary vitreous and crowds it axially. An intravitreous limiting membrane develops as a condensation layer between the primary and second
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