EMBRYONIC DEVELOPMENT & STEM CELL COMPENDIUM
EMBRYONIC DEVELOPMENT & STEM CELL COMPENDIUM
169. Congenital Malformations of The Eye
Review of MEDICAL EMBRYOLOGY Book by BEN PANSKY, Ph.D, M.D.
- Introduction: gross malformations of the eye are formed during the period of organogenesis, approximately between days 20 and 60. However, the eye is vulnerable to teratogenic agents even after this period, especially at the time of histogenesis
- Disorders of basic organogenesis
- CYCLOPIA: rare malformation; is the presence of a single median eye or 2 eyes, more or less fused on the midline
- This condition is never a single isolated malformation, but is usually a part of a complex syndrome associating ethmocephaly and arrhinencephaly, in varying degrees
- ANOPHTHALMIA refers to the uni- or bilateral absence of the eyes
- The eyelids and motor muscles usually are present, since the origin of these structures is independent of that of the eye
- This malformation generally is accompanied by other craniocerebral anomalies
- This malformation can be produced experimentally by pantothenic acid deficiency, hypervitaminosis A, hypoglycemia-producing sulfamides, as well as other agents
- MICROPHTHALMIA: the eyeball and the lens are small and more or less malformed
- This malformation frequently is associated with coloboma
- This condition can be produced experimentally by the use of the same substances listed under B (3) above
- The etiology of this malformation in humans is uncertain, but a genetic origin is probable, and irradiation during the first few weeks of pregnancy has been implicated
- RETINOCELE is a herniation of the retina into the sclera, caused by failure of the optic choroid tissue to close. If the hernia is severe, it can result in protrusion of the eyeball
- CONGENITAL CATARACT: in this condition, the structure of the lens is altered and becomes opaque during intrauterine life
- Cataract can be produced experimentally by the administration of chemicals or drugs (thyroxine, for example) to the mother
- In humans, rubella, certain other viral infections, and toxoplasmosis are frequent causes of this malformation when they are contracted by the mother during her first 2 months of pregnancy
- If the mother is infected after week 7 of pregnancy, the lens escapes damage, but the child may be deaf as a result of imperfect development of the cochlea
- Some cases of congenital cataract are thought to be of genetic origin
- COLOBOMA represents the persistence of the optic (choroid) fissure after week 7 of development. The coloboma may involve the retina and the iris
- Its cause is unknown, and visual problems vary with the severity of the malformation
- Secondary disorders
- BUPHTHALMOS OR CONGENITAL GLAUCOMA is due to a problem of venous circulation (drainage of the aqueous humor), usually related to dysgenesis of the venous system circumscribing the iris
- It has been produced experimentally by giving glucagon to a pregnant rat
- INCOMPLETE REGRESSION OF THE HYALOID ARTERY causes problems of vision only if the remnants of the artery are considerable
- PERSISTENCE OF THE PUPILLARY MEMBRANE causes only minor problems
- ANOMALIES OF EYE DIMENSIONS may be the cause of myopia (the optic axis is too long) or hyperopia (the optic axis is too short)
- An irregularity of curvature of the lens or cornea results in astigmatism
- RETROLENTAL FIBROPLASIA is fibrosis of the vitreous body with folding of the retina
