Ocular Embryology, Anatomy & Development – OPT 027 Pediatric Optometry

A comprehensive set of question-and-answer flashcards covering germ-layer origins, timelines, tissue derivatives, ocular milestones, and clinically relevant facts from the lecture on ocular embryology and pediatric eye development.

Ectoderm and Mesoderm (including neural crest-derived mesenchyme).

Which two primary germ layers contribute to the developing ocular structures?

Day 25.

On what embryonic day do the optic pits enlarge to form the optic vesicles?

The optic stalk.

What structure connects the optic vesicle to the forebrain and later becomes the optic nerve sheath?

Day 33

At what embryonic day is the lens vesicle fully separated from the surface ectoderm?

Proximity of the optic vesicle (inductive influence).

What induces the surface ectoderm to form the lens placode?

Primary lens fibres that form the embryonic nucleus.

What will the posterior epithelial cells of the lens vesicle become?

The intraretinal space.

What separates the apices of the inner and outer layers of the optic cup?

1) Retinal pigment epithelium (RPE) 2) Pigmented epithelium of the ciliary body 3) Anterior iris epithelium.

List three derivatives of the outer layer of the optic cup.

1) Neural retina 2) Non-pigmented ciliary body epithelium 3) Posterior iris epithelium.

List three derivatives of the inner layer of the optic cup.

Corneal stroma & endothelium, uveal stroma & melanocytes, ciliary muscle, most of the sclera (also meninges of optic nerve and lid/orbital connective tissue).

Name four ocular tissues formed by neural crest–derived mesenchyme.

The hyaloid artery (branch of the internal carotid).

Which vascular structure enters the optic cup through the fetal fissure during week 5?

By birth.

When is the hyaloid vasculature completely reabsorbed?

The retinal pigment epithelium (RPE).

What is the first retinal layer to differentiate?

Proliferative (outer) zone and marginal (anuclear) zone.

During weeks 4-6, what are the two zones evident in the proliferating neural retina?

The transient fibre layer of Chievitz.

What transient, nucleus-free zone separates the inner and outer neuroblastic layers at week 7?

Retinal ganglion cells (RGCs).

Which retinal cells undergo apoptosis to refine retinal circuitry?

1) Displacement of inner retinal layers forming the depression 2) Centripetal migration & packing of cones 3) Photoreceptor maturation.

State the three stages of foveal development.

Because cones are centrally packed while rods remain peripheral; cone migration later narrows the rod-free zone.

Why is the foveola rod-free before birth?

4th month; they emerge from the hyaloid artery near the optic disc into the nerve fibre layer.

When do primitive retinal vessels first appear and where do they originate?

Bowman’s layer forms in the 4th month.

Which corneal layer is last to appear prenatally and at what month?

Approximately 55 dioptres at birth; flattens to about 44 D by 6 months.

What is the neonatal corneal curvature and how does it change by 6 months?

The first wave of neural crest mesenchyme between surface ectoderm and lens.

What embryologic ‘wave’ of mesenchyme forms corneal endothelium?

5th month.

Which month marks full differentiation of the sclera, including the scleral spur?

4th month.

At what month does Bruch’s membrane first appear?

Between 4 and 6 months gestation (as ciliary processes fenestrate).

When does aqueous humour production begin?

Iris sphincter in the 5th month; the dilator follows in the 6th month.

Which iris muscle differentiates first and in which month?

The anterior tunica vasculosa lentis (from the annular vessel).

What transient vascular structure replaces the hyaloid vasculature on the anterior lens surface in week 7?

Secondary vitreous enclosing the regressing hyaloid system within the primary vitreous.

What forms Cloquet’s canal?

It develops in the tertiary vitreous between lens equator and ciliary body.

What is the embryologic origin of the zonule (suspensory ligament) of the lens?

1 to 3 months after birth.

By what age does myelination of optic nerve fibres normally reach the lamina cribrosa?

During the 3rd month.

When do eyelid folds meet and fuse during development?

Why do the fetal eyelids remain fused until the 6th month?

To protect developing ocular surfaces from amniotic fluid and allow internal structures to mature.

Mesoderm (connective tissue sheaths are neural crest).

Which germ layer gives rise to extraocular muscle cells?

Name two ocular structures that surface ectoderm forms after birth continues.

Lacrimal gland epithelium and epithelium lining the nasolacrimal drainage system.

Retinal pigment epithelium, neural retina, optic nerve fibres (also ciliary & iris epithelium, sphincter/dilator muscles).

Give three examples of neural ectoderm derivatives in the eye.

Hyperopic by approximately +2 to +3 dioptres.

What is the usual refractive status of a newborn?

Between 4 and 6 months postnatal.

When is the macula considered fully developed?

About 2 years (≈11.7 mm).

At what age does the cornea reach adult diameter?

Around 6 months, indicating improving eye-hand coordination.

Which postnatal milestone corresponds to accurate reaching for toys?

The mucin layer.

What layer of tear film adheres the film to the hydrophobic corneal surface?

The hyaloid (vitreous) membrane.

Which membrane holds the vitreous body in place?

Bruch’s membrane.

Which part of the choroid is avascular and directly adjacent to the RPE?

The ora serrata.

Which retinal landmark marks the transition to the ciliary body?

Aqueous humour (via diffusion across the lens capsule).

What nourishes the avascular lens in the adult eye?

Meibomian gland (tarsal gland).

Which gland secretes meibum (lipid) into the tear film?

The collarette (junction of sphincter and dilator muscles).

What is the thickest region of the iris called?

Posterior scleral fibres crossing the scleral foramen during the 4th month.

Which embryonic structure becomes the connective tissue strands of the lamina cribrosa?

All adult-type layers are present (basal, wing, and superficial squamous).

How many cellular layers does the corneal epithelium have by the 5th-6th month?

Buckling and fusion of the inferior walls of the optic vesicle and stalk after cup formation.

What developmental event creates the optic (fetal) fissure?

Differentiation starts in the central retina and spreads outward, facilitating early fixation capability.

State one reason retinal development is more advanced centrally than peripherally.

Müller (glial) cells.

Which cells provide a scaffold for retinal cell migration and development?

Basal lamina secreted by corneal endothelium at 4 months gestation.

What is the first evidence of Descemet’s membrane and when does it appear?

Anastomosis of the long posterior ciliary arteries in the 4th month, replacing the annular vessel.

Which structure forms the major arterial circle of the iris and when?

The choriocapillaris (not the central retinal artery).

What is the main source of nourishment for photoreceptors?

About 6 months.

What postnatal age marks completion of fixation development?

Extraocular muscles are still maturing and early visual experience is needed to refine binocular control.

Give two reasons why the newborn exhibits poorly coordinated eye movements.

Approximately 7-8 years (anteroposterior diameter achieved).

By what age does the globe reach its adult axial length?

The crystalline lens (due to lifelong addition of secondary lens fibres).

Which ocular tissue continues to grow throughout life?

Cells of the inner layer of the stalk (future optic nerve).

What layer of the optic stalk undergoes programmed cell death to allow ganglion axon passage?

In the last few weeks before birth, contributing to anterior chamber maturation.

When do programmed splits in the pupillary membrane enhance aqueous outflow?

Bowman’s layer.

Which corneal stromal layer is acellular and produced by anterior stromal fibroblasts?

Neural crest mesenchyme.

What is the embryologic origin of orbital fat and connective tissue?

After week 6.

At what gestational week does the retinal pigment epithelium become a single cell layer?

Nasal retinal vessels complete first; temporal vessels finish ≈3 months after birth.

Which vessels finish development first – nasal or temporal retinal vasculature?

First wave – endothelium; Second wave – stromal fibroblasts/collagen; Third wave – pupillary membrane.

Name the three ‘waves’ of neural crest mesenchyme entering the cornea in order.

Emergence of binocular vision and coordinated eye movements responsive to smiles.

What postnatal visual milestone typically appears at 3 months?