Nanophthalmia is a severe form of microphthalmia characterized by a small eye with a short axial length, severe hyperopia, an elevated lens/eye ratio, and a high incidence of angle-closure glaucoma. The exact prevalence is unknown but is likely to be below 1/2000. Typical clinical signs include an axial length inferior to 20 mm, a lens/eye ratio 4 to 8 times greater than normal, thickened and abnormally dense sclera, a thickened lens and choroids, and severe hyperopia (+7.00 D to +13.00 D). Nanophthalmia is generally bilateral. Strabism is present in most patients. The association of nanophthalmia and pigmentary retinopathy has been reported in rare cases. The condition may occur in isolation or as part of a rare syndrome. It may be inherited as an autosomal dominant or recessive trait, or may occur sporadically. Mutations in the MFRP gene (11q23.1) have been found to be responsible for the hereditary form with recessive transmission. Chromosomal anomalies involving chromosome 11p and 2q11-14 have been identified for autosomal dominant forms of nanophthalmia. Diagnosis is based on clinical findings and ophthalmologic examinations involving ocular biometry, ultrasonography, and corneal diameter and intraocular pressure measurements. Treatment may include surgery (iridotomy, iridoplasty, glaucoma filtering surgery, and lens extraction), but side effects (malignant glaucoma, uveal effusion, nonrhegmatogenous retinal detachment and expulsive hemorrhage) may occur. Complications can be prevented by performing a sclerectomy before any intraocular intervention. Angle-closure glaucoma is a constant finding in patients with nanophthalmia but the prognosis is favorable if this manifestation is correctly managed.