Clinical Description
VCAN-related vitreoretinopathy comprises the phenotypic continuum of Wagner vitreoretinal degeneration (Wagner syndrome) and erosive vitreoretinopathy (ERVR).
Vitreoretinal degeneration. The hallmark of VCAN-related vitreoretinopathy is progressive degenerative changes of the vitreous (syneresis) and the vitreoretinal interface beginning at a young age. Syneresis can lead to massive liquefaction of the vitreous such that on slit-lamp examination the vitreous cavity appears optically empty ("empty vitreous") with pockets of liquefied vitreous that are usually lined by avascular strands and veils. Preretinal vitreous membranes that span the whole equator of the eye are characteristic. Ocular changes show considerable inter- and intrafamilial variability.
The first signs usually become apparent during early adolescence, but onset can be as early as age two years [Miyamoto et al 2005].
No sex-specific difference in the occurrence or frequency of any particular ocular features has been observed.
The vitreous degeneration, which is assumed to be the primary pathology, leads to a number of secondary changes, including presenile cataract, degeneration and atrophy of the retina and the underlying retinal pigment epithelium (RPE) and choroid, and retinal detachment [Wagner 1938, Jansen 1962, Graemiger et al 1995, Zech et al 1999, Miyamoto et al 2005, Mukhopadhyay et al 2006, Meredith et al 2007].
Common Ocular Features (≤60% of Affected Individuals)
Myopic refractive error (nearsightedness) results from axial myopia (a developmental mismatch of the refractive power and length of the globe) and/or index myopia (a change in the refractive index of the progressively cataractous lens). Axial myopia is common, although severity varies. In the family reported by Wagner, most affected members had mild myopia and only a few had moderate to severe myopia. In contrast, in the Dutch family all members had high myopia with astigmatism [Jansen 1962].
Presenile cataract (progressive loss of transparency of the ocular lens) is a common finding and a common cause of decline in visual acuity over time. The types of cataract vary. Small spherical opacities and posterior subcapsular cataract affected 43% of eyes in the original family reported by Wagner [Graemiger et al 1995]. In the Dutch families, cataract types included moderate cortical cataract, anterior and posterior cortical cataract, and posterior subcapsular cataract [Mukhopadhyay et al 2006]. Nuclear cataract without any posterior subcapsular opacity was described in a British family [Meredith et al 2007].
In a Japanese family, approximately 50% of affected individuals underwent cataract surgery; the oldest was age 35 years [Miyamoto et al 2005]. In a French family, cataract affected 55% of individuals [Zech et al 1999]. Of note, even after cataract extraction and correction of the refractive error, visual acuity was not normal, typically ranging from 6/12 (20/40) to 6/24 (20/80).
Nonspecific reactive changes of the retinal pigment epithelium and overlying retina (pigment condensation, vascular sheathing, pigmented lattice degeneration, and later chorioretinal atrophy in the retinal periphery) occur. Affected individuals may experience nyctalopia (night blindness) and visual field constriction that are not as severe as those seen in retinitis pigmentosa. Nyctalopia may or may not progress. In some individuals the chorioretinal atrophy is so severe that it resembles choroideremia. Diffuse retinal pigmentary changes and patchy chorioretinal atrophy are observed in some (but not all) family members affected by Wagner syndrome [Meredith et al 2007, Ronan et al 2009].
The full-field electroretinogram (ERG) becomes attenuated. Typically both the amplitudes of the a-waves (response of the photoreceptor layer) and the b-waves (response of the bipolar cell layer) are reduced. The rod and cone systems (as measured by the scotopic and photopic response, respectively) are affected to varying degrees but in a family-specific manner, as demonstrated by the Swiss family originally reported by Wagner, the Japanese family, and the British family [Graemiger et al 1995, Miyamoto et al 2005, Meredith et al 2007].
Abnormal retinal vessels or poor vascularization of the peripheral retina were found in approximately 50% of individuals from the family reported by Wagner [Graemiger et al 1995], but only in a few individuals of the Dutch families [Mukhopadhyay et al 2006].
Retinal detachment was initially found to be associated with increasing age; however, a later report indicated that detachments can occur earlier (average age 9.5 years) [Ronan et al 2009]. Caused by shrinkage of the preretinal membranes and the vitreous strands and veils, retinal detachment is either tractional or rhegmatogenous.
Tractional retinal detachment is caused by tangential shortening of the adhering membranes. The detached retina is rigid; successful surgical repair requires meticulous removal of the membranes and vitreoretinal adhesions and, most often, extensive retinotomies to relieve the traction. Tractional retinal detachment is not a particularly common feature of Wagner syndrome.
Rhegmatogenous retinal detachment is caused by retinal breaks associated with the preretinal membranes. Liquefied vitreous fluid enters the potential subretinal space through one or more retinal tears caused by shrinking membranes. The retinal detachment is typically bullous; surgical repair primarily relies on closure of all retinal breaks. Of note, in a considerable number of young individuals, rhegmatogenous retinal detachment associated with hereditary vitreoretinal degeneration presents with only minor changes of the vitreous. Consequently, large retinal tears in young persons should raise the suspicion of a hereditary disease, and should prompt examination of other family members and eventually molecular genetic analysis.
In the original publication by Wagner the incidence of retinal detachment at age 20 years was one in four, whereas in the Dutch pedigrees published by Jansen bilateral retinal detachment was a frequent finding at a young age. Of note, follow-up publications of the original Wagner pedigree reported an incidence of retinal detachment of greater than one in two. Of the few retinal detachments described in the Swiss family reported originally by Wagner and in the Dutch families reported by Jansen, some were peripheral tractional [Graemiger et al 1995, Mukhopadhyay et al 2006]. Further tractional effects were observed as situs inversus [Wagner 1938]. Recently, affected individuals were described with inversion of the papilla as a possible consequence of tractional forces [Ronan et al 2009].
In the Japanese family reported by Miyamoto et al [2005], most of the retinal detachments were rhegmatogenous. No retinal detachments were observed in the only two affected individuals reported in a British family [Meredith et al 2007].
Occasional Ocular Features
The following features have been reported rarely. Some may not be part of VCAN-related vitreoretinopathy but rather occur coincidentally.
Spherophakia, a spherical deformation of the ocular lens, has been observed sporadically in persons with VCAN-related vitreoretinopathy [Graemiger et al 1995].
Cataract can induce a change of the refractive index of the lens nucleus, further attenuating the myopic refractive error (index myopia).
Posterior vitreous detachment (PVD), detachment of the posterior vitreous membrane from the retinal surface, is caused by shrinkage of the vitreous body and the pathologic vitreoretinal interface. In contrast to the usual age-related PVD, the PVD in VCAN-related vitreoretinopathy initially affects the peripheral rather than the central posterior vitreous. None of the individuals from the original family described by Wagner or the French family showed PVD [Graemiger et al 1995, Zech et al 1999].
Ectopic fovea, manifesting as an increased angle kappa (the angle between the visual axis and the pupillary axis), has occasionally been reported [Graemiger et al 1995, Miyamoto et al 2005, Meredith et al 2007].
Phthisis bulbi (painful shrinking of the ocular globe as a result of loss of intraocular pressure) can occur and may require enucleation of the eye. Retinal detachment that has not been repaired successfully and retinal detachment associated with proliferative retinal vitreoretinopathy (PVR) are risk factors for phthisis bulbi. The decrease in intraocular pressure is caused by decreased aqueous production by the ciliary body epithelium, which becomes compromised by the pathologic vitreoretinal membranes because of the primary vitreal changes, the PVR, or both.
Synchysis scintillans (bilateral accumulation of cholesterol crystals in the vitreous, which may or may not be associated with recurrent vitreous hemorrhage), may or may not occur with increased frequency in VCAN-related vitreoretinopathy, as it was only observed in a few older affected individuals [Graemiger et al 1995, Zech et al 1999].
Optic atrophy was found in only a few of the older individuals from the original Wagner family. These individuals had advanced chorioretinal atrophy, suggesting that optic atrophy is secondary to the massive loss in retinal ganglion cells [Graemiger et al 1995].
Glaucoma may be an occasional feature of Wagner syndrome, or a sequela of the disease such as aphakia glaucoma or rubeotic glaucoma. In the original pedigree, ten individuals out of the sixty family members exhibited a dysgenetic chamber angle [Graemiger et al 1995]; one individual had congenital glaucoma. Three individuals with congenital glaucoma were reported by Jewsbury et al [2014].
Exudative vitreoretinopathy with vascular abnormalities has been reported in one French family [Brézin et al 2011]; in fact, familial exudative vitreoretinopathy (FEVR) was the initial diagnosis suspected in this family.
Uveitis is a rare clinical feature of VCAN-related vitreoretinopathy that has come to attention only recently. Uveitis was reported in a French [Brézin et al 2011] and a British [Meredith et al 2007] family as spontaneous anterior uveitis, and otherwise unexplained severe and prolonged intraocular inflammation after uneventful cataract surgery, respectively [Rothschild et al 2011, Rothschild et al 2013b]. Given versican's role in inflammation and cancer that was increasingly elucidated during the last decade, the occurrence of uveitis in individuals with VCAN-related vitreoretinopathy is likely related to the causative genetic defect [Du et al 2013, Wight et al 2014].
Systemic findings. No systemic abnormalities associated with VCAN-related vitreoretinopathy have been reported to date, and consequently VCAN-related vitreoretinopathy is considered an isolated vitreoretinal degeneration.