Neurofibromatosis 2 (NF2) is characterized by bilateral vestibular schwannomas with associated symptoms of tinnitus, hearing loss, and balance dysfunction. The average age of onset is 18 to 24 years. Almost all affected individuals develop bilateral vestibular schwannomas by age 30 years. Affected individuals may also develop schwannomas of other cranial and peripheral nerves, meningiomas, ependymomas, and, very rarely, astrocytomas. Because NF2 is considered an adult-onset disease, it may be underrecognized in children, in whom skin tumors and ocular findings (retinal hamartoma, thickened optic nerves, cortical wedge cataracts, third cranial nerve palsy) may be the first manifestations. Mononeuropathy that occurs in childhood is an increasingly recognized finding; it frequently presents as a persistent facial palsy or hand/foot drop.

Mutation in the CRYGS gene has been identified in multiple types of cataract, which have been described as progressive polymorphic anterior, posterior, peripheral cortical, sutural, and lamellar.

Mutations in the BFSP1 gene have been found to cause multiple types of cataract, which have been described as cortical, nuclear, and progressive punctate lamellar. Both autosomal dominant and autosomal recessive modes of inheritance have been reported.

Mutations in the MIP gene have been found to cause multiple types of cataract, which have been described as 'polymorphic,' progressive punctate lamellar, cortical, anterior and posterior polar, nonprogressive lamellar with sutural opacities, embryonic nuclear, and pulverulent cortical.

Familial exudative vitreoretinopathy is a hereditary disorder that can cause vision loss that worsens over time. This condition affects the retina, the specialized light-sensitive tissue that lines the back of the eye. In people with this disorder, blood vessels do not fully develop at the outer edges (periphery) of the retina, which reduces the blood supply to this tissue. This prolonged reduction in blood supply (chronic ischemia) causes continued damage to the retina and can lead to worsening of the condition. \n\nThe signs and symptoms of familial exudative vitreoretinopathy vary widely, even within the same family. In many affected individuals, the retinal abnormalities never cause any vision problems. Other people with this condition develop abnormal vessels that leak. This  causes chronic inflammation which, over time, can lead to fluid under the retina (exudate). A reduction in the retina's blood supply causes the retina to fold, tear, or separate from the back of the eye (retinal detachment). The resulting retinal damage can lead to vision loss and blindness. Other eye abnormalities are also possible, including eyes that do not look in the same direction (strabismus) and a visible whiteness (leukocoria) in the normally black pupil.\n\nSome people with familial exudative vitreoretinopathy also have a condition known as osteoporosis-pseudoglioma syndrome, which is characterized by reduced bone density. People with this condition have weakened bones and an increased risk of fractures.

Knobloch syndrome-1 (KNO1) is an autosomal recessive developmental disorder primarily characterized by typical eye abnormalities, including high myopia, cataracts, dislocated lens, vitreoretinal degeneration, and retinal detachment, with occipital skull defects, which can range from occipital encephalocele to occult cutis aplasia (summary by Aldahmesh et al., 2011). Genetic Heterogeneity of Knobloch Syndrome KNO2 (618458) is caused by mutation in the PAK2 gene (605022) on chromosome 3q29.

Retinitis pigmentosa-86 (RP86) is characterized by night blindness followed by progressive narrowing of visual fields and decline in visual acuity, with typical findings of RP on fundus examination, including attenuated retinal vessels, waxy pallor of the optic disc, and bone spicule-like pigmentation (de Bruijn et al., 2018). For a general phenotypic description and a discussion of genetic heterogeneity of retinitis pigmentosa, see 268000.

Microphthalmia/coloboma-11 (MCOPCB11) is characterized by ocular coloboma and related phenotypes such as inferior chorioretinal hypoplasia and/or optic disc hypoplasia, with occasional microphthalmia or high myopia. Incomplete penetrance as well as intrafamilial and intraindividual phenotypic variability have been observed (Liu et al., 2016; Aubert-Mucca et al., 2021; Jiang et al., 2021; Holt et al., 2022). For a discussion of genetic heterogeneity of colobomatous microphthalmia, see MCOPCB1 (300345).