Lecture Embryology of the Eye

							Lecture 41. Embryology of the Eye




 Lecture 41. Embryology of the Eye
 S. David

 Reference
 Moore & Persaud, 5th ed., pp. 423-433.

 Development of the Eye
 The eye develops from: (1) Neuroectoderm (retina, iris, optic nerve); (2) Surface ectoderm (lens,
 eye-lids); (3) Mesoderm (sclera, cornea, choroid).




Fig. 1. 22 days




Fig. 2. 27 days




Lecture 41. Embryology of the Eye
Lecture 41. Embryology of the Eye



 Between 28 and 35 days the following changes occur:




Fig. 3. 29 days

 Retina




Fig. 4. 33 days

 Mesenchyme in optic fissure differentiates into hyaloid vessels which supply the optic cup and
 developing lens. Between 45-50 days the fissure fuses, distal part of hyaloid vessels degenerate,
 and remainder then lie in centre of retina (central retinal artery and vein).

  

 Optic Nerve
 Develops from the optic stalk, which has 2 layers because of the invagination of the optic fissure.
 The neural layer of retina is continuous with the inner layer of optic stalk.


Lecture 41. Embryology of the Eye
Lecture 41. Embryology of the Eye



 As neurons develop, ganglion cells in the retina project their axons into the inner layer of optic
 stalk by 45 days.
  
 Cells in the inner layer differentiate into the non-neuronal cells (glial) cells in the optic nerve.




Fig. 5. Cross sections through the developing optic stalk-optic nerve.




Lecture 41. Embryology of the Eye
Lecture 41. Embryology of the Eye




 Ciliary Body, Iris and Lens




Fig. 6. 6 weeks

 CILIARY BODY:
 Lies anterior to retina.
 Extending from it are finger-like processes called ciliary processes.
 Pigment epithelium of the CB derived from outer layer of optic cup.
 Non-pigmented portion of CB continuous with the neural retina.
 Ciliary muscles and connective tissue develop from mesenchyme.

 IRIS:
 Derived from rim of optic cup.
 Partially covers lens.
 The double layered epithelium is continuous with that of the CB and retina, and is deeply
 pigmented.
 Outer layer of optic cup gives rise to dilator and sphincter pupillae muscles.
 Mesenchyme anterior to rim of optic cup gives rise to vascular connective tissue of iris.

 LENS:

 Derived from surface ectoderm

 Anterior wall: low columnar cells.

 Posterior wall: cells elongate by 40 days (lens fibers) to gradually obliterate the cavity of lens
 vesicle.

 Developing lens covered by Vascular mesenchymal layer - Tunica vasculosa lentis. Its anterior
 portion (pupillary membrane). Degenerates in late fetal period.




Lecture 41. Embryology of the Eye
Lecture 41. Embryology of the Eye




 Cornea and Anterior Chamber

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Fig. 8. 45 days (eyelids open)                                                               id
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 Mesenchyme invades the region between the lens and surface ectoderm. A space appears in this
 mesenchyme to form the anterior chamber.

 Mesenchyme anterior to this space forms the substantia propria of the cornea. This induces the
 surface ectoderm to differentiate into the corneal epithelium




Lecture 41. Embryology of the Eye
Lecture 41. Embryology of the Eye




 Sclera and Choroid
 Develop from mesenchyme around the optic cup.




Fig. 10

 Sclera: Outer layer, continuous with substantia propria of cornea anteriorly, and dura of optic
 nerve posteriorly.

 Choroid: Inner vascular layer. Toward rim of optic cup, the choroid becomes modified to form
 the cores of the ciliary processes.

 Eyelids
 Develop from 2 ectodermal folds with cores of mesenchyme.
 Folds are open before 10 weeks (see figure on page 5).
 Folds remain fused between 10 - 26 weeks (see figure on page 5).
 Opens after 26 weeks.
 When fused: conjunctival sac
 When open: conjunctiva lines exposed parts of sclera and inner parts of eyelids.




Lecture 41. Embryology of the Eye
Lecture 41. Embryology of the Eye




 Congenital Malformations
     1.    COLOBOMA:
 Inferior defect of iris (key hole defect).
 May involve ciliary body and retina
 Results from persistence of optic fissure.
 If in involves retina, could lead to herniation of retina into sclera (Retinocele).
 Causes: genetic, environmental.
     2.    CONGENITAL GLAUCOMA:
 Results from abnormal development of sinus venosus sclera
 High intraocular pressure
 Causes: genetic, maternal rubella during early pregnancy.
     3.    ANOPHTHALMIA:
 Unilateral or bilateral absence of eyes.
 Eye-lids and muscles form.
 Often accompanied by other cranio-cerebral anomalies
 Results from failure of optic vesicle to form.
 Causes: Unknown
     4.    MICROPHTHALMIA:
 Eye are small and malformed.
 Frequently associated with colobomas.
 Results from abnormal development of optic vesicles and related structures.
 Causes: genetic, intrauterine infections such as cytomegalovirus and toxoplasma gondii.
     5.    CYCLOPIA:
 Single median eye.
 The 2 eyes are partially or completely fused.
 Tubular nose above eye.
 Associated with other severe cranio-cerebral abnormalities.
 Results from failure of midline structures to develop from cranial part of neural plate.




Lecture 41. Embryology of the Eye
Lecture 41. Embryology of the Eye




Lecture 41. Embryology of the Eye