How do our eyes develop?

Have you ever wonder while looking into the sky , road , birds , trees , nature , people , faces etc if you were not able to see them what type of lifestyle you would have! We humans are so bankrupt in gratitude that we don’t take out time in our day for thanking the lord who gave  us so much that we don’t even deserve. 

 

Have you ever wonder how do we see ?

What are the basic changes that occur in the embryo that leads to the development of human eye ? 

 

I will try to cover all in brief!

 

CONTENT 

 

1. General embryology
2. Basic ocular embryology 
3. Eye derivatives 
4. Genetics in eye developments 

 

 

General embryology

 

• 3 Germinal layers -  Ectoderm , mesoderm , endoderm
• Ectoderm  give rise to    surface ectoderm,  neuro - ectoderm,  neural crest
• Mesoderm give rise to mesenchyme ( mesoderm + neural crests)
• Endoderm - no contribution to ocular development 

 

 

EVENTS

 

• Formation of zygote 
• Formation of blastocysts
• Formation of bilaminar  disc - 2nd wk

       - the two important  layers of cell - epiblast and hypoblast 

        -  the two cavities - amniotic cavity and yolk sac cavity

 

• Formation of Trilaminar disc - 3rd wk ( bilaminar disc to trilaminar)  - 

      Formation of 3 layers( ectoderm , mesoderm , endoderm).  - Gastrulation 

• Neural tube formation 

 

BASIC OCULAR EMBRYOLOGY

 

 

• Formation of optic stalk and optic vesicle

 

Neural plate - thickening-  formation of optic sulcus - formation of optic vesicle

 

• Formation of lens vesicle 

 

Optic vesicle grow - come in contact with surface ectoderm - 

Surface ectoderm thickens - lens placode formation 

 

• Formation of optic cup 

 

          Developing lens invaginate the optic vesicle - margin of optic  

        cup cover the upper and lower part to enclose to lens . 

 

         Inferior part of lens  not enclosed -  inferior surface of optic stalk- 

        a deficiency or hollow path - CHOROIDAL FISSURE

 

• Then there occur changes in mesenchyme 
• Layer development of ocular structures like retina, lens , cornea , sclera, choroid , cilliary body , vitreous, conjunctiva , the lacrimal  apparatus , extra ocular muscle 

 

DERIVATIVES OF EYE

 

Derivative of the neuroectoderm

 

1. Retinal pigment epithelium 
2. Neurosensory retina 
3. Neuroglia of optic nerve
4.  Epithelia of cilliary body and iris
5. Sphincter and dilator muscle of iris 
6. Secondary vitreous 

 

Derivatives of the surface ectoderm 

 

1. Lens 
2. Primary and tertiary vitreous
3. Epithelium of the cornea , lids , conjunctiva , nasolacrimal drainage apparatus including goblet cells 
4. Epithelial derivatives : eyelash follicles, Meibomian glands, 

           Lacrimal gland, glands of Krause and Wolfring

 

Derivatives of the Neural crest

 

1. Stroma of cornea , ciliary body , iris , choroid and sclera 
2. Corneal endothelium
3. Trabecular meshwork, 
4. Tenons capsule 
5. Orbital cartilage, bone adipose and connective tissues.

 

Derivatives of the mesoderm 

 

1. Vascular endothelium 
2. Temporal portion of the sclera 
3. Extra ocular muscles 
4. Skeletal muscles of the eye lids.

 

 

GENETICS OF THE EYE DEVELOPMENT 

 

Most important genes in eye development:

 

1. Master gene - switch for eye development-  

            PAX6 = PAIRED BOX6 

        

            Mutation of PAX6

• Coloboma
• Micropthalmia

 

1. Eye ball split into two , the formation of two eyeball

 SHH = SONIC HEDGEHOG 

 

Mutation of SHH

 

• Holoprosencephaly

 

 

          Hope you have a brief knowledge of embryology of eye now .

 

 

 

 

 

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