Chapter 20: Eye Clinical correlates

Coloboma

What eye abnormality occurs when the choroid fissure fails to close, leaving a persistent cleft?

Seventh week of development

During what week does the choroid fissure normally close?

Persistent cleft/ cleft

What remains when the choroid fissure fails to close?

Coloboma iridis

What is a coloboma that is limited to the iris called?

Ciliary body, retina, choroid, and optic nerve

Into what structures may a coloboma extend if it is not limited to the iris?

PAX2 mutation

Mutation in which gene has been linked with optic nerve colobomas?

Renal coloboma syndrome

What syndrome includes renal defects associated with PAX2 mutations?

Colobomas of the eyelids

What type of coloboma can occur as clefts of the eyelids?

Persistent iridopupillary membrane

What abnormality occurs when the iridopupillary membrane fails to be resorbed during formation of the anterior chamber?

Congenital cataract

What abnormality causes the lens to become opaque during intrauterine life?

Rubella (German measles)

What maternal infection between the fourth and seventh weeks of pregnancy is associated with congenital cataracts?

Fourth to seventh weeks of pregnancy

During what period can maternal rubella infection result in congenital cataracts?

Hearing loss

What may occur if the mother is infected with rubella after the seventh week of pregnancy due to cochlear abnormalities?

MMR (measles, mumps, and rubella) vaccine

What vaccine has contributed to the near eradication of congenital rubella syndrome in the United States?

Hyaloid artery persistence

What abnormality occurs when the hyaloid artery fails to completely degenerate and persists as a cord or cyst?

Central artery of the retina

What does the proximal part of the hyaloid artery normally develop into after the distal portion degenerates?

Cord or cyst

What forms when the hyaloid artery persists instead of completely degenerating?

Microphthalmia

What abnormality occurs when the eye is too small and the eyeball may be only two-thirds of its normal volume?

Intrauterine infections, such as cytomegalovirus and toxoplasmosis

What can cause microphthalmia?

Anophthalmia

What is the congenital absence of the eye called?

Severe cranial abnormalities

What type of abnormalities usually accompany anophthalmia?

Congenital aphakia

What is the congenital absence of the lens called?

Aniridia

What is the congenital absence of the iris called?

Disturbances in induction and development of tissues responsible for lens and iris formation

What causes congenital aphakia and aniridia?

PAX6 mutations

Mutations in which gene result in aniridia and may also contribute to anophthalmia and microphthalmia?

Cyclopia

What defect is characterized by a single eye?

Synophthalmia

What defect is characterized by fusion of the eyes?

Cyclopia and synophthalmia

What spectrum of defects involves the eyes being partially or completely fused?

Loss of midline tissue

What causes cyclopia and synophthalmia?

Days 19-21 of gestation

As early as what days of gestation can loss of midline tissue causing cyclopia and synophthalmia occur?

Underdevelopment of the forebrain and frontonasal prominence

What results from the loss of midline tissue associated with cyclopia and synophthalmia?

Holoprosencephaly

What brain defect is invariably associated with cyclopia and synophthalmia?

Partial or complete merging of the cerebral hemispheres into a single telencephalic vesicle

What occurs in holoprosencephaly?

Alcohol, maternal diabetes, mutations in SHH, and abnormalities in cholesterol metabolism

What factors are associated with holoprosencephaly?

SHH signaling

What signaling pathway may be disrupted by abnormalities in cholesterol metabolism associated with holoprosencephaly?