Posterior Vitreous Detachment and the Posterior Hyaloid Membrane.

PURPOSE: Despite posterior vitreous detachment being a common ocular event affecting most individuals in an aging population, there is little consensus regarding its precise anatomic definition. We investigated the morphologic appearance and molecular composition of the posterior hyaloid membrane to determine whether the structure clinically observed enveloping the posterior vitreous surface after posterior vitreous detachment is a true basement membrane and to postulate its origin. Understanding the relationship between the vitreous (in both its attached and detached state) and the internal limiting membrane of the retina is essential to understanding the cause of rhegmatogenous retinal detachment and vitreoretinal interface disorders, as well as potential future prophylactic and treatment strategies. DESIGN: Clinicohistologic correlation study. PARTICIPANTS: Thirty-six human donor globes. METHODS: Vitreous bodies identified to have posterior vitreous detachment were examined with phase-contrast microscopy and confocal microscopy after immunohistochemically staining for collagen IV basement membrane markers, in addition to extracellular proteins that characterize the vitreoretinal junction (fibronectin, laminin) and vitreous gel (opticin) markers. The posterior retina similarly was stained to evaluate the internal limiting membrane. Findings were correlated to the clinical appearance of the posterior hyaloid membrane observed during slit-lamp biomicroscopy after posterior vitreous detachment and compared with previously published studies. MAIN OUTCOME MEASURES: Morphologic appearance and molecular composition of the posterior hyaloid membrane. RESULTS: Phase-contrast microscopy consistently identified a creased and distinct glassy membranous sheet enveloping the posterior vitreous surface, correlating closely with the posterior hyaloid membrane observed during slit-lamp biomicroscopy in patients with posterior vitreous detachment. Immunofluorescent confocal micrographs demonstrated the enveloping membranous structure identified on phase-contrast microscopy to show positive stain results for type IV collagen. Immunofluorescence of the residual intact internal limiting membrane on the retinal surface also showed positive stain results for type IV collagen. CONCLUSIONS: The results of this study provide immunohistochemical evidence that the posterior hyaloid membrane is a true basement membrane enveloping the posterior hyaloid surface. Because this membranous structure is observed only after posterior vitreous detachment, the results of this study indicate that it forms part of the internal limiting membrane when the vitreous is in its attached state.

Deep Intronic Sequence Variants in COL2A1 Affect the Alternative Splicing Efficiency of Exon 2, and May Confer a Risk for Rhegmatogenous Retinal Detachment.

COL2A1 mutations causing haploinsufficiency of type II collagen cause type 1 Stickler syndrome that has a high risk of retinal detachment and failure of the vitreous to develop normally. Exon 2 of COL2A1 is alternatively spliced, expressed in the eye but not in mature cartilage and encodes a region that binds growth factors TGFß1 and BMP-2. We investigated how both an apparently de novo variant and a polymorphism in intron 2 altered the efficiency of COL2A1 exon 2 splicing and how the latter may act as a predisposing risk factor for the occurrence of posterior vitreous detachment (PVD)-associated rhegmatogenous retinal detachment (RRD) in the general population. Using amplification of illegitimate transcripts and allele-specific minigenes expressed in cultured cells, we demonstrate variability in exon 2 inclusion not only between different control individuals, but also between different COL2A1 alleles. We identify transacting factors that bind to allele-specific RNA sequences, and investigate the effect of knockdown and overexpression of these factors on exon 2 splicing efficiency. Finally, using a specific cohort of patients with PVD-associated RRD and a control population, we demonstrate a significant difference in the frequency of the COL2A1 intronic variant rs1635532 between the two groups.

Prevention of retinal detachment in Stickler syndrome: the Cambridge prophylactic cryotherapy protocol.

PURPOSE: The Stickler syndromes are the most common causes of inherited and childhood retinal detachment; however, no consensus exists regarding the effectiveness of prophylactic intervention. We evaluate the long-term safety and efficacy of the Cambridge prophylactic cryotherapy protocol, a standardized retinal prophylactic treatment developed to prevent retinal detachment arising from giant retinal tears in type 1 Stickler syndrome. DESIGN: Retrospective comparative case series. PARTICIPANTS: Four hundred eighty seven patients with type 1 Stickler syndrome. METHODS: Time to retinal detachment was compared between patients who received bilateral prophylaxis and untreated controls, with and without individual patient matching. Patients receiving unilateral prophylaxis (after fellow eye retinal detachment) were similarly compared with an appropriate control subgroup. Individual patient matching ensured equal age and follow-up between groups and that an appropriate control (who had not suffered a retinal detachment before the age at which their individually matched treatment patient underwent prophylactic treatment) was selected. Matching was blinded to outcome events. Individual patient matching protocols purposely weighted bias against the effectiveness of treatment. All treatment side effects are reported. MAIN OUTCOME MEASURES: Time to retinal detachment and side effects occurring after prophylactic treatment. RESULTS: The bilateral control group (n = 194) had a 7.4-fold increased risk of retinal detachment compared to the bilateral prophylaxis group (n = 229) (hazard ratio [HR], 7.40; 95% confidence interval [CI], 4.53-12.08; P<0.001); the matched bilateral control group (n = 165) had a 5.0-fold increased risk compared to the matched bilateral prophylaxis group (n = 165) (HR, 4.97; 95% CI, 2.82-8.78; P<0.001). The unilateral control group (n = 104) had a 10.3-fold increased risk of retinal detachment compared to the unilateral prophylaxis group (n = 64) (HR, 10.29; 95% CI, 4.96-21.36; P<0.001); the matched unilateral control group (n = 39) had a 8.4-fold increased risk compared to the matched unilateral prophylaxis group (n = 39) (HR, 8.36; 95% CI, 3.24-21.57; P<0.001). No significant long-term side effects occurred. CONCLUSIONS: In the largest global cohort of type 1 Stickler syndrome patients published, all analyses indicate that the Cambridge prophylactic cryotherapy protocol is safe and markedly reduces the risk of retinal detachment.

Alternative splicing modifies the effect of mutations in COL11A1 and results in recessive type 2 Stickler syndrome with profound hearing loss.

BACKGROUND: Stickler syndromes types 1, 2 and 3 are usually dominant disorders caused by mutations in the genes COL2A1, COL11A1 and COL11A2 that encode the fibrillar collagens types II and XI present in cartilage and vitreous. Rare recessive forms of Stickler syndrome exist that are due to mutations in genes encoding type IX collagen (COL9A1 type 4 Stickler syndrome and COL9A2 type 5 Stickler syndrome). Recently, recessive mutations in the COL11A1 gene have been demonstrated to result in fibrochondrogenesis, a much more severe skeletal dysplasia, which is often lethal. Here we demonstrate that some mutations in COL11A1 are recessive, modified by alternative splicing and result in type 2 Stickler syndrome rather than fibrochondrogenesis. METHODS: Patients referred to the national Stickler syndrome diagnostic service for England, UK were assessed clinically and subsequently sequenced for mutations in COL11A1. Additional in silico and functional studies to assess the effect of sequence variants on pre-mRNA processing and collagen structure were performed. RESULTS: In three different families, heterozygous COL11A1 biallelic null, null/missense or silent/missense mutations, were found. They resulted in a recessive form of type 2 Stickler syndrome characterised by particularly profound hearing loss and are clinically distinct from the recessive types 4 and 5 variants of Stickler syndrome. One mutant allele in each family is capable of synthesising a normal α1(XI) procollagen molecule, via variable pre-mRNA processing. CONCLUSION: This new variant has important implications for molecular diagnosis and counselling families with type 2 Stickler syndrome.