Familial Exudative Vitreoretinopathy

Familial Exudative Vitreoretinopathy (FEVR) is a rare, inherited eye condition that affects the development of blood vessels in the retina, the light-sensitive tissue at the back of the eye. In people with FEVR, the blood vessels do not grow all the way to the edges of the retina. This lack of blood supply can cause the edges of the retina to become starved of oxygen. To compensate, the eye may grow new, abnormal blood vessels. However, these new vessels are fragile and can leak fluid or bleed, leading to scarring and pulling on the retina. The symptoms and severity of FEVR can vary greatly, even among members of the same family. Some people may have very mild changes in their blood vessels and never experience any vision problems. Others may develop severe complications in childhood, such as the retina detaching from the back of the eye, which can cause significant vision loss or blindness. Because the condition can be silent in its early stages, it is crucial for family members of someone diagnosed with FEVR to have a thorough eye examination, even if they have no symptoms. While there is no cure for the underlying genetic cause of FEVR, treatments are available to manage the complications and protect vision. If abnormal blood vessels or leaking fluid are detected early, doctors can use laser therapy or special injections to stop the damage. In more advanced cases where the retina has detached, surgery may be necessary to reattach it. Regular, lifelong monitoring by an eye specialist is essential for anyone with FEVR to catch and treat any changes before they cause permanent vision loss.

Condition category: Vitreoretinal Disorder

Prevalence: 1 in 10,000

Inheritance patterns: Autosomal Dominant, Autosomal Recessive, X-Linked

Age of onset: Birth to early childhood

Clinical overview: Familial Exudative Vitreoretinopathy (FEVR) is a rare, inherited disorder of retinal angiogenesis characterized by the incomplete or abnormal vascularization of the peripheral retina. First described by Criswick and Schepens in 1969, the condition leads to a hypoxic environment in the avascular peripheral retina, which can trigger a cascade of secondary complications including neovascularization, subretinal exudation, fibrovascular proliferation, and retinal detachment. The clinical presentation of FEVR is highly variable, ranging from completely asymptomatic individuals with only mild peripheral avascularity to severe cases presenting with total retinal detachment and blindness in infancy. FEVR is genetically heterogeneous and can be inherited in autosomal dominant, autosomal recessive, or X-linked recessive patterns. The disease is primarily caused by mutations in genes that encode components of the Wnt/β-catenin signaling pathway, which is crucial for normal retinal vascular development. The most commonly implicated genes include FZD4, LRP5, TSPAN12, and NDP. Despite its familial nature, the variable expressivity and incomplete penetrance of FEVR mean that family members carrying the same mutation may exhibit vastly different clinical severities, making diagnosis and genetic counseling challenging. The clinical significance of FEVR lies in its potential to cause severe, irreversible vision loss, particularly in pediatric patients. It is a lifelong condition that requires careful monitoring, as complications can arise at any age. Early diagnosis through dilated fundus examination and wide-field fluorescein angiography is critical. Identifying asymptomatic family members is also essential for early intervention and prevention of vision-threatening complications. The relevant OMIM numbers for FEVR include 133780 (EVR1), 601813 (EVR4), 616468 (EVR6), 605750 (EVR3), and 613310 (EVR5), and the Orphanet number is 891.

Patient and family guide: Familial Exudative Vitreoretinopathy (FEVR) is a rare, inherited eye condition that affects the development of blood vessels in the retina, the light-sensitive tissue at the back of the eye. In people with FEVR, the blood vessels do not grow all the way to the edges of the retina. This lack of blood supply can cause the edges of the retina to become starved of oxygen. To compensate, the eye may grow new, abnormal blood vessels. However, these new vessels are fragile and can leak fluid or bleed, leading to scarring and pulling on the retina. The symptoms and severity of FEVR can vary greatly, even among members of the same family. Some people may have very mild changes in their blood vessels and never experience any vision problems. Others may develop severe complications in childhood, such as the retina detaching from the back of the eye, which can cause significant vision loss or blindness. Because the condition can be silent in its early stages, it is crucial for family members of someone diagnosed with FEVR to have a thorough eye examination, even if they have no symptoms. While there is no cure for the underlying genetic cause of FEVR, treatments are available to manage the complications and protect vision. If abnormal blood vessels or leaking fluid are detected early, doctors can use laser therapy or special injections to stop the damage. In more advanced cases where the retina has detached, surgery may be necessary to reattach it. Regular, lifelong monitoring by an eye specialist is essential for anyone with FEVR to catch and treat any changes before they cause permanent vision loss.

Symptoms and clinical features: The clinical presentation of FEVR is highly variable, and the disease is often classified into five stages based on severity. In the early stages (Stage 1 and Stage 2), patients are typically asymptomatic. The primary finding is an avascular peripheral retina, which can only be detected through a dilated fundus examination or wide-field fluorescein angiography. In Stage 2, neovascularization (the growth of new, abnormal blood vessels) begins to occur at the junction between the vascular and avascular retina, but without any exudation (leakage of fluid) or retinal detachment. As the disease progresses to the intermediate stage (Stage 3), the abnormal blood vessels begin to leak fluid and lipid exudates into or under the retina. This can lead to the formation of fibrovascular tissue that exerts traction on the retina. Patients may start to experience visual symptoms such as decreased visual acuity, visual field defects, or floaters. The traction can cause the macula (the central part of the retina) to be dragged from its normal position, leading to distortion of central vision. Strabismus (misalignment of the eyes) may also be an early sign of visual impairment in children. In the advanced stages (Stage 4 and Stage 5), the tractional forces from the fibrovascular proliferation lead to retinal detachment. Stage 4 involves a partial retinal detachment, which may be macula-sparing (4A) or macula-involving (4B). Stage 5 is characterized by a total retinal detachment. Patients at these stages often present with severe vision loss or blindness. In infants and young children, a total retinal detachment or extensive exudation can present as leukocoria (a white pupillary reflex). If left untreated, advanced FEVR can lead to secondary complications such as cataracts, glaucoma, and phthisis bulbi (shrinkage and atrophy of the eye).

Molecular pathology: The molecular pathology of FEVR is primarily centered around defects in the canonical Wnt/β-catenin signaling pathway, which is essential for the normal development and angiogenesis of the retinal vasculature. The proteins encoded by the FEVR-associated genes—NDP, FZD4, LRP5, and TSPAN12—are key components of this pathway. Norrin, the protein product of the NDP gene, acts as a specific ligand that binds to the Frizzled-4 (FZD4) receptor on the surface of retinal endothelial cells. LRP5 functions as a crucial co-receptor in this complex, while TSPAN12, an auxiliary transmembrane protein, enhances the multimerization and clustering of FZD4, thereby facilitating the binding of Norrin. When this ligand-receptor complex is successfully formed and activated, it prevents the phosphorylation and subsequent degradation of cytoplasmic β-catenin. The stabilized β-catenin then translocates to the nucleus, where it binds to lymphoid enhancer factor/T-cell factor (LEF/TCF) to promote the transcription of target genes necessary for proper retinal angiogenesis and the maintenance of the blood-retina barrier. Mutations in any of these genes disrupt the Norrin/β-catenin signaling pathway, leading to a failure in the transcription of these critical target genes. This disruption results in premature arrest of retinal vascular development, leaving the peripheral retina avascular and hypoxic. The resulting ischemia triggers the upregulation of angiogenic factors like VEGF, leading to pathological neovascularization, increased vascular permeability, and the subsequent complications of exudation, fibrovascular proliferation, and retinal detachment characteristic of FEVR.

Genetics: FEVR exhibits significant genetic heterogeneity, with multiple inheritance patterns reported: autosomal dominant, autosomal recessive, and X-linked recessive. The autosomal dominant form is the most common. To date, mutations in several genes have been identified as causative for FEVR, accounting for approximately 50% of cases. These genes include FZD4, LRP5, TSPAN12, NDP, ZNF408, and KIF11. The FZD4 (frizzled-4) gene, located on chromosome 11, is associated with autosomal dominant and recessive FEVR. The LRP5 (low-density lipoprotein receptor-related protein 5) gene, also on chromosome 11, can cause both autosomal dominant and recessive forms. TSPAN12 (tetraspanin-12), located on chromosome 7, is linked to autosomal dominant and recessive FEVR. The NDP (Norrie disease pseudoglioma) gene, located on the X chromosome, is responsible for the X-linked recessive form. ZNF408 and KIF11 are associated with autosomal dominant FEVR. Genotype-phenotype correlations exist but are complex due to variable expressivity and incomplete penetrance. For instance, patients with mutations in NDP and LRP5 tend to have more severe disease presentations (stages 4 and 5), while TSPAN12 mutations are often associated with milder forms. Furthermore, individuals with homozygous mutations or multiple mutations (e.g., in FZD4) may exhibit more severe phenotypes than those with heterozygous single mutations. Despite these correlations, significant intrafamilial variability is common, with family members carrying the same mutation displaying vastly different clinical severities.

Diagnostic evaluation: The diagnosis of FEVR is primarily based on clinical findings, particularly the lack of peripheral retinal vascular development in at least one eye, without a history of prematurity or supplemental oxygen therapy. A dilated funduscopic examination is essential to detect peripheral retinal avascularity, which classically occurs in the temporal periphery but may extend to all quadrants. Wide-field fluorescein angiography is crucial for confirming the diagnosis, as it can reveal avascular areas, arterial tortuosity, fluorescein leakage, and peripheral neovascularization. Optical coherence tomography (OCT) is utilized to visualize common complications of FEVR, such as cystoid macular edema, intraretinal exudation, and vitreomacular distortion or traction. In young children who cannot cooperate with a standard examination, an examination under anesthesia may be necessary. Genetic testing can also support the diagnosis by identifying mutations in known FEVR-associated genes (e.g., FZD4, LRP5, TSPAN12, NDP, ZNF408, KIF11), though a negative genetic test does not rule out the condition due to genetic heterogeneity. The differential diagnosis for FEVR includes other pediatric vitreoretinopathies and conditions presenting with similar retinal findings. Retinopathy of prematurity (ROP) is a primary consideration, but FEVR patients are typically born full-term with normal birth weight. Other conditions to differentiate include Coats disease (usually unilateral and non-genetic), Norrie disease (which shares NDP mutations but typically presents with congenital blindness and systemic features), persistent fetal vasculature, and retinoblastoma. Careful clinical history and examination are vital for accurate differentiation.

Differential diagnosis: Differential diagnosis of FEVR includes: (1) Retinopathy of prematurity — history of prematurity and oxygen exposure; similar peripheral avascular retina. (2) Norrie disease — X-linked, congenital blindness with hearing loss and intellectual disability; NDP mutations. (3) Coats disease — unilateral, male predominance, telangiectatic vessels with exudation, no family history. (4) Persistent fetal vasculature — unilateral, microphthalmos, retrolental fibrovascular tissue. (5) Incontinentia pigmenti — X-linked dominant, skin lesions, peripheral retinal avascularity; IKBKG mutations. (6) Toxocariasis — unilateral, peripheral granuloma, positive serology.

Natural history: The natural history of FEVR is highly variable, ranging from lifelong asymptomatic peripheral avascularity to rapid progression leading to total retinal detachment and blindness in early childhood. The disease is characterized by a failure of the peripheral retina to vascularize properly during development. This initial avascularity creates a hypoxic environment that can remain stable or trigger a cascade of pathological events. When the disease progresses, the hypoxic peripheral retina stimulates the production of angiogenic factors, leading to neovascularization at the junction of the vascular and avascular zones. This newly formed vasculature is often leaky and fragile, resulting in subretinal exudation and hemorrhage. Over time, fibrovascular proliferation occurs, creating tractional forces on the retina. This traction can lead to macular dragging, radial retinal folds, and eventually tractional or rhegmatogenous retinal detachment. The timeline of progression is unpredictable. While many severe cases present in infancy or early childhood (average age of onset ranges from 3 to 7 years depending on the genetic mutation), some individuals may remain asymptomatic until adulthood, when they might suddenly develop complications such as vitreous hemorrhage or retinal detachment. Prognostic factors include the specific genetic mutation (with NDP and LRP5 mutations often indicating a more severe course) and the extent of peripheral avascularity. Early detection and intervention are critical in altering the natural history and preventing severe visual loss.

Management and treatment research: ### Current management and standard of care Management of familial exudative vitreoretinopathy (FEVR) is individualized based on retinal findings, age, vision, and the risk of retinal detachment. The goals are to monitor the retina closely, treat abnormal blood vessels or leakage when needed, and preserve vision. - **Observation and regular retinal examinations:** Mild or early FEVR, including areas of peripheral retina without normal blood vessels (avascular retina), may be monitored closely. Young children may need wide-field retinal imaging or an examination under anesthesia to fully assess the retina. - **Laser photocoagulation or cryotherapy:** Laser treatment can target avascular retina, abnormal new blood vessels, or leaking areas. Cryotherapy uses freezing to treat targeted retinal tissue and may be used when laser cannot adequately reach the affected area. These approaches can reduce signals that promote abnormal vessel growth and may lower the risk of exudation, scarring, and retinal detachment. - **Anti-VEGF injections:** Some retinal specialists use medicines that block vascular endothelial growth factor (VEGF), a protein involved in abnormal blood-vessel growth and leakage. Injections may be used with laser, cryotherapy, or surgery in selected eyes with active abnormal vessel growth or significant exudation. Close follow-up is important because traction from scar tissue can worsen in some eyes. - **Surgery for advanced disease:** Tractional or rhegmatogenous retinal detachment, vitreous scarring, or severe macular dragging may require vitreoretinal surgery. Procedures may include vitrectomy (removal of the eye’s vitreous gel), removal of tractional membranes, scleral buckling, and retinal repair techniques. Surgery can be complex because abnormal vessels and scar tissue may be firmly attached to the retina. Supportive care may include glasses or other refractive correction, treatment for amblyopia (“lazy eye”) in children, low-vision rehabilitation, and educational support. Genetic counseling and eye examinations for relatives may be recommended because FEVR can affect family members differently, including relatives with few or no symptoms. ### Approved therapies There are no therapies approved specifically to correct the underlying genetic cause of FEVR. Laser treatment, cryotherapy, anti-VEGF injections, and retinal surgery are used to manage retinal complications. ### Investigational therapies and research There are no FEVR-specific investigational gene therapies, cell therapies, or drug treatments listed in the current treatment pipeline. Research continues to examine genes and signaling pathways involved in retinal blood-vessel development, including Wnt signaling. This research may help guide future targeted treatments, but these approaches are not established clinical therapies for FEVR. ### Clinical trial participation One recruiting study may be relevant for children who need vitreoretinal surgery: - **NCT06520410** — A Phase 4 study evaluating the safety and effectiveness of an 18 mm short vitrectomy probe for pediatric vitreoretinal surgeries. The study is being conducted by Chang Gung Memorial Hospital. This study evaluates a surgical instrument rather than a treatment that corrects the genetic cause of FEVR. Eligibility may depend on age, retinal findings, the need for surgery, prior treatment, and location. A pediatric retinal or vitreoretinal specialist can help families determine whether participation may be appropriate.

Outlook: The prognosis for patients with FEVR is highly variable and depends largely on the severity of the disease at presentation and the specific genetic mutation involved. Patients with mild, asymptomatic disease (stages 1 and 2) generally have a good visual prognosis, provided they undergo regular monitoring and receive timely prophylactic treatment, such as laser photocoagulation, if neovascularization develops. However, patients presenting with advanced disease (stages 3 to 5), characterized by extensive exudation, macular dragging, or retinal detachment, face a much poorer visual prognosis. Even with successful surgical intervention, visual outcomes in these advanced stages are often limited due to pre-existing damage to the macula or recurrent retinal detachments. Quality of life considerations for individuals with FEVR include the psychological impact of living with a chronic, potentially blinding condition and the need for lifelong ophthalmic surveillance. For those with significant vision loss, early intervention with low vision rehabilitation and educational support is crucial to maximize independence and quality of life. Additionally, because FEVR is a hereditary condition, genetic counseling is an important component of care, helping families understand the risks of transmission and the importance of screening asymptomatic relatives to prevent severe outcomes in affected family members.

Epidemiology: The exact prevalence of FEVR is not well-established, partly due to the variable expressivity of the disease, which leads to many mild or asymptomatic cases going undiagnosed. However, a large multicenter study in China involving nearly 200,000 newborns found FEVR in 1.19% of all detected ocular abnormalities, suggesting an incidence of approximately 0.11% in the general population. This indicates that FEVR may be more common than previously recognized. There are no significant gender differences in the prevalence of FEVR overall, except for the X-linked recessive form caused by NDP mutations, which predominantly affects males. The disease has been reported in various ethnic groups worldwide. The average age of onset varies depending on the specific genetic mutation, with NDP-associated FEVR presenting earliest (average 3.0 years) and FZD4-associated FEVR presenting later (average 7.4 years).

Selected references: 1. Sızmaz S, Yonekawa Y, Trese MT. Familial Exudative Vitreoretinopathy. Turk J Ophthalmol. 2015;45(4):164-168. PMID: 27800225 2. Luvisi JR, et al. Familial Exudative Vitreoretinopathy (FEVR). StatPearls [Internet]. 2025. PMID: 32809576 3. Kondo H. Complex genetics of familial exudative vitreoretinopathy and related pediatric retinal detachments. Taiwan J Ophthalmol. 2015;5(2):56-62. PMID: 29018668 4. Scruggs BA, et al. NDP-Related Retinopathies. GeneReviews. 2023. PMID: 20301504 5. Toomes C, et al. Familial Exudative Vitreoretinopathy, Autosomal Dominant. GeneReviews. 1993. PMID: 20301326