DEVELOPMENT OF EYE
DEVELOPMENT OF EYE
- The eye is derived from 3 types of embryonic tissue:
1. Neural tube (Neuroectoderm)
2. Surface ectoderm
3. Periocular mesenchyme: Neural crest & mesoderm derivatives.
|
Precursor |
Derivatives |
| Neural ectoderm |
|
| Surface ectoderm |
|
| Mesoderm |
|
| Neural crest |
|
EYE AT BIRTH
1. Anteroposterior diameter of eyeball :
- About 16.5 mm (70% of adult size)
- Adult size is attained by 7-8 years.
2. Corneal diameter :
- About 10 mm.
- Adult size (11.7 mm ) is attained by 2 tears of age.
3. Anterior chamber is shallow & angle is narrow.
4. Lens is spherical at birth.
5. Retina:
- Apart from macular area, the retina is fully differentiated.
- Macula differentiates 4-6 months after birth.
6. Myelination of optic nerve fibres has reached the lamina cribrosa.
7. New born is usually hypermetropic by +2 to +3D.
8. Orbit is more divergent (50°) as compared to adult (45°)
9. Lacrimal gland is still underdeveloped & tears are not secreted.
EYE IN POSTNATAL
- 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 3 points to remember:
1. Fixation starts developing→ 4-6 weeks (1-1 ½ months).
2. Critical period for development→ 2-4 months.
3. Fixation development is completed → 6 months.
- Macula is fully developed by 4-6 months.
- Fusional reflex, stereopsis & accomodation os 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 |
| 1 month | 6/180- 6/90 |
| 4-6 months | 618- 6/9 |
| 3 years | 6/6 |
Exam Important
- Uveal & conjunctival melanocytes are derived from neural crest.
- Sclera is derived from mesoderm.
- Crystalline lens, corneal epithelium & lacrimal gland are derived from surface ectoderm.
- Corneal stroma is made from Mesoderm.
- Most common site for coloboma is Inferonasal.
- The lens continues to grow throughout the lifetime.
- Eye of new born is usually hypermetropic by +2 to +3D.
- Normal level of visual acuity is attained by 3 yrs of age.
- Gaze fixation starts developing in the first month & is completed in 6 months.
Don’t Forget to Solve all the previous Year Question asked on DEVELOPMENT OF EYE
