Secondary Vitreous Research Articles

The Ultrastructural Localization of Type II, IV, and VI Collagens at the Vitreoretinal Interface.

BackgroundThe vitreoretinal interface is the border of the cortical vitreous and the inner surface of the retina. The adhesion of the cortical vitreous to the ILM, namely vitreoretinal adhesion, involves a series of complex molecular adhesion mechanisms and has been considered as an important pathogenic factor in many vitreoretinal diseases. The presence of type VI collagen at the vitreoretinal interface and its possible interaction with collagens and glycoproteins indicates that type VI collagen may contribute to the vitreoretinal adhesion.PurposeTo clarify the ultrastructural location of type VI collagen and its relationship to type II and IV collagens at the vitreoretinal interface.MethodsThe ultrastructural localization of type II, IV and VI collagens in the adult human vitreoretinal interface of five donor eyes was evaluated by transmission electron microscopy using immunogold labeling.ResultsIn the pre-equatorial region, we observed densely packed vitreous lamellae with a partly intraretinal course containing type II and VI collagens, reticular structures containing type IV and VI collagens and a thin inner limiting membrane (ILM) containing type IV and VI collagens in a linear distribution pattern. From the anterior to the posterior retina, the linear pattern of type IV and VI collagen labeling gradually became more diffusely present throughout the entire thickness of the ILM.ConclusionsThe presence of type VI collagen in vitreous lamellae penetrating the ILM into the superficial retina suggests that type VI collagen may be involved in the organization of vitreous fibers into lamellae and in the adhesion of the vitreous fibers to the retina. The close relation of type VI to type IV collagen in the ILM suggests that type VI collagen is an important collagen type in the ILM. The topographic variations of type IV and VI collagens in the different regions of the ILM suggest a regional heterogeneity of the ILM. The reticular labeling pattern of type IV and VI collagens observed in the anterior vitreous are highly similar to labeling patterns of blood vessel walls. In the anterior vitreous, they may represent remnants of the regressed embryonic hyaloid blood vessel system. Their presence is in support of the theory on interactive remodeling of the developing vitreous as opposed to the main stream theory of displacement and compression of the primary by the secondary vitreous.

Remodelling of the human vitreous and vitreoretinal interface – A dynamic process

The highly hydrated, almost acellular vitreous body of the human eye consists of only 0.1% macromolecules, of which collagens are the most important for its matrix structure. During embryological development, the human vitreous body is a highly dynamic matrix, in which the primary (vascular) vitreous is gradually replaced by the secondary (avascular) vitreous. With aging, the human vitreous undergoes a slowly progressive remodelling, characterized by the gradual formation of collagenous condensations and liquefied spaces in the gel structure. The former is probably the result of collagen synthesis and the deposition of newly formed collagen into the matrix, while the latter is probably due to collagen breakdown. Therefore, remodelling of the vitreous matrix starts at a very early age and continues into old age, albeit at a slower pace. Older theories and concepts of a strict spatial separation between the primary and secondary vitreous during embryonic development, and morphological changes in the aging vitreous being due to a simple aggregation of collagen fibrils are questioned. This review describes the embryological and postnatal remodelling of the human vitreous matrix and vitreoretinal interface, in addition to the mechanisms and cells that are potentially involved in this process.

Uncommon cause of juvenile cataract: Adenoma of the nonpigmented ciliary epithelium

Adenoma of the nonpigmented ciliary epithelium developed in a 36-year-old woman, causing decreased visual acuity and a total cataract in the involved eye. Ultrasound biomicroscopy disclosed associated persistent hyperplasic primary vitreous (PHPV). Sectoral cyclectomy with removal of the mass and intracapsular cataract extraction were performed, and the tumor was submitted for histological examination. Although ciliary adenomas arising in adults are considered to be acquired, the associated PHPV suggests a congenital origin in view of the tumor's possible interference in the normal replacement of the primary vitreous by the secondary vitreous.

Histogenesis of the Intravitreal Membrane and Secondary Vitreous in the Mouse

The intravitreal membrane (IVM) is a membranous structure between the primary and secondary vitreous bodies in developing mammalian eyes. In this study, for the first time the histogenesis of the IVM and the relationship between the hyaloid vasculature and the IVM was characterized in newborn mice. Eyes of mice less than 12 days old were fixed and embedded. From these, serial paraffin-embedded sections were made for lectin histochemistry, immunohistochemistry, and picrosirius red (PSR) staining, and ultrathin sections were made for transmission electron microscopy (TEM). Eight biotinylated lectins and antibodies for laminin and type IV collagen were used. Among the eight lectins tested, concanavalin A (Con A) agglutinin, Ricinus communis agglutinin I, and wheat germ agglutinin demonstrated strong positive staining in the IVM and vitreous fibrils of the primary and secondary vitreous bodies. They also bound to the internal limiting membrane (ILM) of the retina. At postgestational day 4, the secondary vitreous first appeared between the ILM and the vasa hyaloidea propria (VHP). Immunohistochemical staining revealed that the IVM consists of extracellular matrix components including laminin and type IV collagen, whereas PSR staining and TEM showed that collagen fibrils in the IVM are bundled and continuous with the basement membrane of hyaloid capillaries or the VHP. Lectin histochemistry and immunohistochemistry provided good methods for visualizing the structures of the IVM and vitreous fibrils. These results suggest that the IVM is separated from the basement membrane of the retinal ILM along with the vascular network of the VHP when the secondary vitreous begins to form.

Vascular Remnants in the Rabbit Vitreous Body. I. Morphological Characteristics and Relationship to Vitreous Embryonic Development

Using light and transmission electron microscopy, we observed novel structures in the rabbit vitreous body. They were found in 18 out of 27 eyes from rabbits 0.5–36 months of age. These structures are scattered throughout the entire vitreous matrix. By light and transmission electron microscopy, they appear to be made up of the same structural components. Based upon their morphological appearance, they can be subdivided into two groups which we provisionally named ‘intravitreal structure type 1 and 2’ or ‘IVS-1’ and ‘IVS-2’. IVS-1 has a highly variable morphology (e.g. star-shaped, round, oval), whereas IVS-2 is tubular. The dimensions of IVS-1 vary in relation to the mesh diameters of the collagen matrix, while those of IVS-2 do not. In adult rabbit eyes, we observed transitions between IVS-1 and intravitreal ghost vessels (acellular remnants of blood vessels), and between IVS-1 and IVS-2. In very young rabbits (14 days) we observed intravitreal ghost vessels consisting of tightly-packed IVS-1. Therefore, we concluded that IVS-1 and 2 are related structures presumably of vascular origin. It appears that they represent fragmented and non-fragmented acellular remnants of hyaloid blood vessels. The presence of vascular remnants throughout the entire vitreous matrix of adult rabbit eyes is in conflict with existing theories on the embryonic development of the vitreous body, which describe a strict spatial separation between the primary (vascular) and secondary (avascular) vitreous. However, it strongly supports an alternative theory that explains the formation of the secondary vitreous by a process of continuous remodelling of the primary vitreous.

Glycosaminoglycan and collagen distribution in the developing human vitreous.

We determined the distribution of glycosaminoglycans and collagens in the developing human vitreous. Eighty human eyes from 5 gestational weeks to 2 postnatal years of age were used. Glycosaminoglycan components were determined by enzyme digestion with hyaluronidase or chondroitinase AC and ABC and immunohistochemistry for chondroitin, chondroitin-4-sulfate, chondroitin-6-sulfate, and dermatan sulfate. Collagen distribution was determined by immunohistochemistry for types I, II, and III collagens. Enzyme digestion showed that throughout development hyaluronic acid is the main glycosaminoglycan in the vitreous and in the extraocular space at 5-7 gestational weeks. Both areas were filled with mesenchymal cells. Immunohistochemistry showed chondroitin-6-sulfate in the vitreous between 6 and 40 gestational weeks, and chondroitin-4-sulfate between 12 and 40 gestational weeks. Hyaluronic acid and chondroitin sulfate appeared in the retina and around the hyaloid vessels at 12-40 weeks. Immunohistochemistry showed type III collagen in the vitreous and around the mesenchymal cells at 5-7 weeks that was replaced by type II collagen after 8 weeks. Hyaluronic acid is the major glycosaminoglycan in the vitreous throughout development, except for the transient appearance of chondroitin sulfate at 6-40 gestational weeks. Type III is the main collagen in the early developing vitreous that converts to type II collagen at 8 weeks. The primary and secondary vitreous has the same components as these macromolecules. These vitreous glycosamino-glycans and collagens seem to be produced by mesenchymal cells at an early stage and by the retina and hyaloid vessels during middle and late development.

Topography of the “vitreous structures” (tractus; membranelles) with respect to the layers of embryonal blood vessels

It is believed that the vascular or primary vitreous, with the exception of the later Cloquet's canal, gradually disappears and is substituted by the avascular or secondary vitreous. It is known that it is possible topographically to objectify mats of fibril concentrations (membranelles or tractus) of stronger light reflection inside the adult vitreous. These concentrations open up in the shape of a funnel from the papilla or Cloquet's canal towards the front of the vitreous. This was a light microscopy investigation on human eyes between the embryonal stage of 3.2 cm and the fetal stage of 12.5 cm and eyes 8 months and 2 years old with persistent vessels of the vitreous. The investigation showed that at the embryonal stage, the vitreous body is threaded from behind by branches (mats) of the hyaloid artery and from in front by vessels (mats) that go over the rim of the optic cup, i.e., the later vitreous base. Vitreous structures, in the form of horsetail-shaped fibril concentrations, could already be observed histologically in the fetal stage with the disappearance of embryonal blood vessels. These structures begin in the vitreous base, go into the vitreous, run parallel to the retina, and then go to the back of the vitreous and towards the lens. The physiological mats of vitreal fibril concentrations (membranelles or tractus) and the pathological branches of the persistent hyaloid artery, topographically correspond to the mats of the obliterated embryonal blood vessels of the vitreous. These mats grow in relation to the bulbous growth. In these investigations an attempt has been made to clarify the question of which embryonal blood vessels. which embryonal and fetal lengths, which different physiological tractus of the vitreous body and which different pathological features of the persistent hyaloid artery correspond.

Complex Microphthalmos

Forty patients were diagnosed as having complex microphthalmos on the basis of a malformed globe with a total axial length measurement at least 2 SDs below the mean for age-similar controls. Three had anterior segment dysgenesis; 4, congenital lens abnormalities; 14, chorioretinal colobomas; 12, persistent hyperplastic primary vitreous; 4, retinal dysplasia; and 3, complex malformations due to ipsilateral facial malformations. Measurements of total axial length indicated that complex microphthalmos was congenital and that postnatal growth of the malformed eye was similar to that of normal eyes. In most patients the anterior segment length was normal, while in all patients the posterior segment length was at least 2 SDs below the mean. Corneal diameter correlated significantly with total axial length (r2 = .57) and decreased linearly as total axial length decreased. In most patients in whom measurements were obtained, the lens and corneal power were increased, thereby compensating for decreased total axial length. We propose that inadequate production of secondary vitreous is the cause of the microphthalmos, given that the posterior segment was disproportionately reduced in size and the secondary vitreous is its predominant component. Evidence that each of the various ocular malformations can influence the production of secondary vitreous is presented.

Histochemical study on glycosaminoglycans in the developing mouse vitreous.

The distribution of polyanionic glycosaminoglycans (GAGs) in the developing mouse vitreous was studied histologically by P.A.S. reaction, metachromatic staining by toluidin blue at various pH's, alcian blue at pH 0.5 and alcian blue at various pH's, alcian blue at pH 0.5 and alcian blue C.E.C. stainings, modified Hale's method with colloidal iron, and enzymatically with bovine testicular hyaluronidase. A subdivision of the vitreous developmental period into four phases and an early distinction between, the posterior and equatorial vitreous portions are suggested on basis of the results. The early vitreous, during the first developmental phase, exhibits a high content in GAGs. This property gradually vanishes in the posterior part during the second phase of development, while acid GAGs including possibly hyaluronate are present in the equatorial zone. During this second phase, the lens capsule present a strong P.A.S.-reactivity, especially positive in it's posterior part. During the third phase, sulphated GAGs reappear in the posterior vitreous while non-sulphated material remains present in the equatorial zone. During the first two postnatal weeks (fourth developmental phase), acid GAG's disappear in the equatorial part of the vitreous but the maturing zonular fibres display the properties of sulphated GAGs. It is suggested that the histochemical maturation of the secondary vitreous starts around the 16th or 17th fetal day, i.e. much earlier than its morphological differentiation.

Morphological study on glycosaminoglycans in the developing human vitreous.

The vascular and the avascular vitreous in 7th- and 8th-week human embryos and 9th-week fetuses were stained strongly by alcian blue, while marked decrease in staining by alcian blue was observed in 12th- and 13th-week human fetuses. The nature of alcian blue positive materials was identified as hyaluronic acid and chondroitin sulfate or dermatan sulfate by enzymatic digestion methods and the Scott-Dorling method. The results suggest that distinction between primary and secondary vitreous is difficult by classical histochemical techniques and electron microscopy, and that the vitreous glycosaminoglycans concentration seems to be high at 7th- and 8th-week embyonic stages and decreases at later fetal stages.

Gross anatomy of the vitreous body (author's transl)

The anatomical arrangement of vitreous structures in human and animal eyes is described on the basis of coinciding findings of histological examinations, biomicroscopy and the "optical dissection" of unfixed vitreous specimens. The "funnel" of the primary vascular vitreous disappears completely during development. The vitreous cavity is filled with secondary vitreous. Its structure in nearly homogeneous, containing "holes" of low density at all sites where the structure of a normal inner retinal surface is altered. During postnatal development the secondary vitreous forms a new funnel system, consisting of zones of different density and of membranelles (vitreous tracts). Before completion of this funnel system, destruction of the vitreous gel begins and confuses the typical arrangement. Postnatal vitreous structures include: zones of different density: preretinal zone, intermediary zone, retrolental zone; holes (of low density): prepapillary hole, prefoveal hole, prevascular fissures, vitreous tracts (of high density): preretinal tract, median tract, coronary tract, retrolental tract ("hyaloid" tract). The pattern of the "holes" strongly suggests that the framework is formed by retinal elements.