Between the first days (day 22) and the fifth week of gestation,
lateral to the neural groove,
the neuroectoderm of the diencephalon develops the optic grooves.
The optic grooves evolves to optic diverticulum and later to optic vesicle.
The optic vesicle by apposition with the surface ectoderm induces the formation of the lens.
Later,
the optic vesicle is transformed into an optic stalk and an optic cup.
- Anophthalmia: It is the complete absence of the eye due to alteration in its development.
It is extremely weird. Frequently,
there is a small cystic remnant with hypoplasia of the visual tract.
The muscles,
lacrimal glands,
eyelids and bone orbit are present (alteration only of the neuroectoderm).
The stalk and the optical cup are a tubular structure that closes in its lower portion.
- Coloboma (Greek "mutilation"): there is an error in the lower closure of the optic stalk and the optical cup,
forming a lower indentation.
This cleavage is in the inferior pole of the eye and it can extend to the optic disc.
10% is associated with other malformations: heart disease,
slow growth and development,
choanal atresia,
atrial malformations and cerebellar vermis hypoplasia.
Unilateral = bilateral.
Hereditary = acquired.
PAX 2 mutation (dominant) - gene expressed in kidneys,
uterus,
ureters,
ear and CNS.
All patients with coloboma should have a renal echo to rule out malformations (hypoplasia,
VUR and CKD).
The lens vesicle induces the formation of the cornea.
The optic stalk and the eyeball are completely closed.
There is an internal neuronal layer,
the retina and two more external layers of mesenchyme,
the choroid and the sclera.
The lens are irrigated in embryonic life by the hyaloid artery through the Coquet channel.
These structures involute and disappear.
Later the irrigation of the eye is given by the central artery of the retina.
The eyeball is formed by two superimposed spheres.
In the newborns it measures 1/3 of its final size and finishes growing at 5 years of age.
Its approximate volume in the adult is 6.5cc.
- Microphthalmia:
Axial diameter <21 mm in adult and <19 mm in children under 1 year.
Congenital: isolated or associated with hypoplasia of the orbit.
Acquired (ptisis bulbi): secundary to trauma,
surgery,
inflammation,
radiation,
among others,
result in disorganization and calcification of the eye.
- Macrophtalmia
Enlarged eye> 30 mm (adult normal 24 mm).
Buftalmo - "bull's eye".
Myopia,
congenital glaucoma (<3-4 years),
Sturge Weber syndrome (30%),
Neurofibromatosis (50%).
Staphyloma: It´s a thinning of the sclera and choroids with secondary deformity of the eye.
It is frequent in the posterior region of the eye. Causes: scleritis,
subsequent to necrotizing infections,
postsurgical and trauma
The eye can be divided into:
Anterior segment:
- Anterior chamber: cornea,
iris and ciliary body
- Posterior chamber: posterior to the iris and ciliary body,
anterior to the lens.
Posterior segment: Lens,
Vitreous,
Sclera,
Choroid and Retina.