DEVELOPMENT OF EYE

Corneal stroma, keratocytes and endothelium is derived from the Neural crest.

B i.e. Sclera

• Neural crest cells form the mesenchyme of head & neck and contribute to most of the eye including endothelium of cornea & trabecular meshworkQ & stroma of cornea, iris, ciliary body and choroid; melanocytes of conjunctiva & uvea; ciliary muscle ganglion & nerves (Schwann cells); Orbital bones & connective tissue; connective sheath & muscle layer of orbital blood vessels; meningeal sheath of optic nerve, sclera & part of vitreous.
• All Epithelia (except that of iris & ciliary body), the lens and the Lacrimal & Tarsal glands are derived from the surface ectoderm.Q
• Melanocytes present in iris stroma develop from neural crest.
• Sclera is of neural crest and mesodermal originQ

Ans. Substantia propria of the cornea

Ans. Optic nerve sheaths

Ans. 3 years

Ans. D i.e. Surface ectoderm

Embryology of eyeball

• Structures derived from mesoderm:
• Corneal stroma & endothelium,
• Only smooth muscles of iris,
• All muscles (EXCEPT iris muscle)
• Structures derived from surface ectoderm:
• Conjunctival epithelium,
• Lens

Structures derived from neuroectoderm:

• Epithelium of iris & ciliary body,
• Muscles of iris (constrictor & dilator pupillae)

Ans. is ‘b’ i.e., 6 months

Gaze Fixation starts developing in the first month and is completed in 6 months.

Macula is fully developed by 4 – 6 months.

Fusional reflexes, stereopsis and accommodation is well developed by 4 – 6 months.

Cornea attains normal adult diameter by 2 years of age.

Lens grows throughout life.

   2. Splanchnopleuric mesoderm (visceral layer)

• Smooth muscle and connective tissue of respiratory tract, gut, blood vessels and heart
• Adrenal cortex
• Mesothelium (visceral layer) of pleural, peritoneal and pericardeal cavities
• Mesenchyme surrounding pericardial coelom gives rise to myocardium and serous pericardiun
• Spleen and lymph nodes

   3.  Spetum transversum

• Diaphragm
• Fibrous pericardium

   4.  Angiogenic mesoderm

• Endocardium of heart
• Endothelium of blood and lymphatic vessels
• Microglia, tissue macrophages
• Circulating blood cells

Ans. is ‘c’ i.e., 3 years [Ref Khurana 4^th

 Eye in postnatal period

• Fixation starts developing by 4-6 weeks. Critical period for development of fixation reflex is 2-4 months. Development of fixation is completed by 6 months. So there are three points to remember : ‑
• Fixation starts developing 4-6 weeks (1-11/2 months).

Critical period for development→ 2-4 months.

1. Fixation development is completed→  6 months.
2. Macula is fully developed by 4-6 months.
3. Fusional reflex, stereopsis and accomodation is well developed by 4-6 months.

Cornea attains normal adult diameter by 2 years of age.

• Lens grows throughout life.
• Full visual acuity (6/6) is attained by 3 years of age.

Age                          Visual acuity

New born                     6 / 240

I month                       6/180 – 6/90

4-6 months                  6/18 – 6 /9

3 Years                         6 / 6

Ans. is ‘c’ i.e., Posterior surface

Anatom^y of crystalline lens

• There are three structural elements that make up lens –

1. Lens capsule

 A transparent membrane surrounding the lens like a pocket. It is thicker over the anterior surface than the posterior surface. It is thickest at pre- equator region and thinnest at the posterior pole. When an artificial lens replaces the natural lens in cataract surgery (IOL implantation), it is placed in this same capsule.

2. Lens epithelium

It is a single layer on the anterior (front) surface of the lens. There is no epithelium on posterior surface. The epithelial cells distribute fluid, ion and glucose through the entire lens. They also create new fibers through­out a person’s life.

3. Lens fibres

These are long protein fibers that arc closely packed and parallel. They make up most of the lens volume and are laid horizontally, front to back, and concentrically like layers of an onion.As the lens fibres are formed throughout the life, these are arranged compactly as nucleus and cortex of the lens.

a) Nucleus : – It is the central part containing the oldest fibres. it consists of different zones :-

1. Embryonic nucleus :- Formed at 1-3 months of gestation, therefore consists the oldest primary fibres.
2. Fetal nucleus : – Lies around the embryonic nucleus and is formed from 3 months of gestation till birth.
3. Infantile nucleus :- Corresponding the lens from birth to puberty and surrounds the fetal nucleus.
4. Adults :- Corresponds to the lens fibres formed after puberty to rest of the life.
5. Cortex :- It is the peripheral part containg the youngest fibres.

• The ciliary zonules (Zonules of zinn or suspensory ligaments of lens) hold the lens in position and enable the ciliary muscle to act on it. These consist essentially of a series of fibres which run from the ciliary body and fuse into the outer layer of the lens capsule around the equatorial zone.