Anophthalmia, (Greek: ανόφθαλμος, "without eye"), is the medical term for the absence of one or both eyes. Both the globe (human eye) and the ocular tissue are missing from the orbit. The absence of the eye will cause a small bony orbit, a constricted mucosal socket, short eyelids, reduced palpebral fissure and malar prominence. Genetic mutations, chromosomal abnormalities, and prenatal environment can all cause anophthalmia. Anophthalmia is an extremely rare disease and is mostly rooted in genetic abnormalities. It can also be associated with other syndromes.

There are three classifications for this condition:

- Primary anophthalmia is a complete absence of eye tissue due to a failure of the part of the brain that forms the eye.

- Secondary anophthalmia the eye starts to develop and for some reason stops, leaving the infant with only residual eye tissue or extremely small eyes which can only be seen under close examination.

- Degenerative anophthalmia the eye started to form and, for some reason, degenerated. One reason for this occurring could be a lack of blood supply to the eye.

The presence of a small eye within the orbit can be a normal incidental finding but in most cases it is abnormal and results in blindness. The incidence is 14 per 100,000 and the condition affects 3-11% of blind children.

Microphthalmia (Greek: μικρός "micros" = small; ὀφθαλμός "ophthalmos" = eye), also referred as microphthalmos, is a developmental disorder of the eye in which one (unilateral microphthalmia) or both (bilateral microphthalmia) eyes are abnormally small and have anatomic malformations. It is different from nanophthalmos in which the eye is small in size but has no anatomical alterations.

Lenz microphthalmia syndrome (or LMS) is a very rare inherited disorder characterized by abnormal smallness of one or both eyes (microphthalmos) sometimes with droopy eyelids (blepharoptosis), resulting in visual impairment or blindness. Eye problems may include coloboma, microcornea, and glaucoma. Some affected infants may have complete absence of the eyes (anophthalmia). Most affected infants have developmental delay and intellectual disability, ranging from mild to severe. Other physical abnormalities associated with this disorder can include an unusually small head (microcephaly), and malformations of the teeth, ears, fingers or toes, skeleton, and genitourinary system. The range and severity of findings vary from case to case. Formal diagnosis criteria do not exist.

Lenz microphthalmia syndrome is inherited as an X-linked recessive genetic trait and is fully expressed in males only. Females who carry one copy of the disease gene (heterozygotes) may exhibit some of the symptoms associated with the disorder, such as an abnormally small head (microcephaly), short stature, or malformations of the fingers or toes. Molecular genetic testing of BCOR (MCOPS2 locus), the only gene known to be associated with Lenz microphthalmia syndrome, is available on a clinical basis. One additional locus on the X chromosome (MCOPS1) is known to be associated with LMS.

Lenz microphthalmia syndrome is also known as LMS, Lenz syndrome, Lenz dysplasia, Lenz dysmorphogenetic syndrome, or microphthalmia with multiple associated anomalies (MAA: OMIM 309800). It is named after Widukind Lenz, a German geneticist and dysmorphologist.

A somewhat similar X-linked syndrome of microphthalmia, called oculofaciocardiodental syndrome (OFCD) is associated with mutations in BCOR. OFCD syndrome is inherited in an X-linked dominant pattern with male lethality.