1. EYE & EAR ALL CONTENT IS COPYRIGHT © OF DR. STEEVNS M.B KISAKA
THIS CONTENT MAY ONLY BE USED FOR EDUCATIONAL PURPOSES BY CURRENT STUDENTS OF MAKERERE

2. Objectives
Recognise and describe a section of neural retina, identifying areas of histogenesis with lamination/stratification and the adjacent choroid and scleral layers.
Recognise and describe a section of cornea, distinguishing areas of limbus-like character, as well as Descemet’s and Bowman’s membranes.
Be able to describe and recognise various stages in the development of optic vesicles, the differentiation of the optic cup, lens and adjacent structures, including : developing ciliary body and anterior and posterior chambers of the eye.
Distinguish between otic vesicles at various stages of their development and their spatial relationship with portions of the pharynx and developing cochlea in histological section.

3. SLIDE 200 Retina dog
Examine this section at low magnification and identify :
Cornea Non- neural retina Anterior chamber.
Iris Neural retina Posterior chamber.
Ciliary apparatus Choroid Cavity of vitreous humor.
Corneal limbus Sclera.
1.0 mm

4. SLIDE 200 Retina dog
Examine this section at low magnification and identify :
Cornea Non- neural retina Anterior chamber.
Iris Neural retina Posterior chamber.
Ciliary apparatus Choroid Cavity of vitreous humor.
Corneal limbus Sclera. 2 11 3 6 10 9 5 1 4 7 8
1.0 mm

5. SLIDE 200 Retina dog
Examine this section at low magnification and identify :
Cornea Non- neural retina Anterior chamber.
Iris Neural retina Posterior chamber.
Ciliary apparatus Choroid Cavity of vitreous humor.
Corneal limbus Sclera. 2 11 3 6 10 9 5 1 4 7 8
1.0 mm

6. SLIDE 200 Cornea dog Identify : Cornea. 4. Anterior chamber.
Iris Posterior chamber.
Corneal limbus.
External eye – Dog
▪ Left eye. Note pigmented epidermis of eyelids.
▪ Identify : Medial canthus
Lateral canthus
3rd eyelid
Cornea
Iris
Pupil
250 µm

7. SLIDE 200 Cornea dog Identify : Cornea. 4. Anterior chamber.
Iris Posterior chamber.
Corneal limbus.
posterior chamber
iris
corneal limbus
anterior chamber
cornea
250 µm

8. SLIDE 200 Cornea dog Examine the cornea at higher magnification.
The function of the cornea is …….
100 µm

9. SLIDE 200 Cornea dog Examine the cornea at higher magnification.
The function of the cornea is …….
The cornea has an important role in image formation, it forms a primary refractive
element in the eye.
anterior
posterior
100 µm

10. SLIDE 200 Cornea dog Five layers can be identified in the cornea :
1. anterior epithelium anterior sub-epithelial membrane (lamina)
3. stroma posterior limiting membrane (Descemet’s)
5. posterior epithelium (corneal endothelium)
100 µm

11. SLIDE 200 Cornea dog Five layers can be identified in the cornea :
1. anterior epithelium anterior sub-epithelial membrane (lamina)
3. stroma posterior limiting membrane (Descemet’s)
5. posterior epithelium (corneal endothelium)
anterior
epithelium
posterior
epithelium
stroma
posterior
limiting
lamina
Descemet’s
anterior
lamina
100 µm

12. SLIDE 200 Cornea dog
Identify : Anterior epithelium and anterior sub-epithelial basement membrane.
What type of epithelium covers this surface?
25 µm

13. SLIDE 200 Cornea dog
Identify : Anterior epithelium and anterior sub-epithelial basement membrane.
What type of epithelium covers this surface?
Non-keratinised stratified squamous epithelium.
Identify : Anterior epithelium and anterior sub-epithelial basement membrane.
What type of epithelium covers this surface?
anterior epithelium
stroma
sub-epithelial
basement membrane
25 µm

14. SLIDE 200 Cornea dog
Identify : Anterior epithelium and anterior sub-epithelial basement membrane.
What type of epithelium covers this surface?
Non-keratinised stratified squamous epithelium.
Consider the cellularity and the extent of the extracellular matrix in these compartments
and the cornea ‘proper’.
Identify : Anterior epithelium and anterior sub-epithelial basement membrane.
What type of epithelium covers this surface?
anterior epithelium
stroma
sub-epithelial
basement membrane
25 µm

15. SLIDE 200 Cornea dog
Identify : Posterior epithelium (corneal endothelium) and posterior limiting membrane
(Descemet’s membrane).
What type of epithelium covers this surface?
25 µm

16. SLIDE 200 Cornea dog
Identify : Posterior epithelium (corneal endothelium) and posterior limiting membrane
(Descemet’s membrane).
What type of epithelium covers this surface?
Simple squamous epithelium.
Note the lack of vasculature in the cornea.
Identify : Posterior epithelium (corneal endothelium) and posterior limiting membrane
(Descemet’s membrane).
What type of epithelium covers this surface?
Descemet’s membrane
stroma
posterior epithelium
or corneal endothelium
25 µm

17. What is the corneal limbus?
SLIDE 200 Cornea dog
What is the corneal limbus?
posterior chamber
iris
corneal limbus
anterior chamber
corneal stroma
250 µm

18. What is the corneal limbus?
SLIDE 200 Cornea dog
What is the corneal limbus?
The corneo-scleral junction.
Here the collagen fibres of the corneal stroma become irregular and blood vessels
supplying nutrients to the cornea are seen.
The anterior epithelium becomes the conjunctival epithelium.
What is the corneal limbus?
posterior chamber
posterior chamber
sclera
iris
iris
corneal limbus
corneal limbus
anterior chamber
anterior chamber
conjunctival
epithelium
posterior epithelium
corneal stroma
corneal stroma
anterior epithelium
250 µm

19. SLIDE 200 Iris dog
The iris is the most anterior part of the vascular tunic (uvea) a continuation of
the choroid layer.
posterior chamber
iris
corneal limbus
anterior chamber
cornea
250 µm

20. SLIDE 200 Iris dog
The iris is the most anterior part of the vascular tunic (uvea) a continuation of
the choroid layer.
posterior chamber
iris
corneal limbus
anterior chamber
cornea
250 µm

21. Examine the iris at higher magnification.
SLIDE 200 Iris dog
Examine the iris at higher magnification.
50 µm

22. The iris at higher magnification.
SLIDE 200 Iris dog
The iris at higher magnification.
posterior chamber
pars iridica retinae
myoepithelial cells
connective tissue stroma BV BV
BV : blood vessels M
M : melanocytes
anterior surface of iris
sphincter muscle
anterior chamber
50 µm

23. SLIDE 200 Retina dog
Through examination observe whether different areas of the retina exhibits
neural (thicker) and non neural (thinner) organisation approaching the iris.
100 µm

24. SLIDE 200 Retina dog
Through examination observe whether different areas of the retina exhibits
neural (thicker) and non neural (thinner) organisation approaching the iris.
towards iris
close to
edge of neural retina
non-neural retina
edge of neural retina
neural retina
100 µm

25. SLIDE 200 Retina dog
This non neural portion of the retina approaching the iris consists of two layers
of non-light sensitive epithelium.
This epithelium is continuous with that covering the ciliary body and iris.
50 µm

26. SLIDE 200 Retina dog
This non neural portion of the retina approaching the iris consists of two layers
of non-light sensitive epithelium.
This epithelium is continuous with that covering the ciliary body and iris.
epithelium of non-neural retina
choroid
50 µm

27. SLIDE 200 Retina dog
This area shows the sudden increase in thickness of the retina as it becomes the
neural retina.
The junction is called the ora ciliaris retinae.
50 µm

28. SLIDE 200 Retina dog
This area shows the sudden increase in thickness of the retina as it becomes the
neural retina.
The junction is called the ora ciliaris retinae (arrowed).
retina
choroid
sclera
space artefact
50 µm

29. SLIDE 200 Retina dog
A comparison of the neural retina close to the periphery (left)
and at its full thickness (right).
Larger blood vessels may be seen in the nerve ganglion cell layer towards the edge of the retina.
The individual layers are more easily recognised (right).
Note the much thicker layer of rods and cones.
50 µm

30. SLIDE 200 Retina dog
A comparison of the neural retina close to the periphery (left)
and at its full thickness (right).
Larger blood vessels may be seen in the nerve ganglion cell layer towards the edge of the retina.
The individual layers are more easily recognised (right).
Note the much thicker layer of rods and cones.
BV : blood vessel BV
layer of
rods & cones
choroid
sclera
50 µm

31. SLIDE 200 Retina dog Examine the neural retina in more detail
Observe a full depth portion of this area
and identify the different zones.
Inner limiting membrane.
Nerve fibre layer.
Ganglion cell layer.
Inner plexiform layer.
Inner nuclear layer.
Outer plexiform layer.
Outer nuclear layer.
Outer limiting membrane.
Layer of rods and cones.
Pigmented epithelium.
Choroid layer.
Scleral layer.
50 µm

32. SLIDE 200 Retina dog Examine the neural retina in more detail
Observe a full depth portion of this area
and identify the different zones. 1 2 3
Inner limiting membrane.
Nerve fibre layer.
Ganglion cell layer.
Inner plexiform layer.
Inner nuclear layer.
Outer plexiform layer.
Outer nuclear layer.
Outer limiting membrane.
Layer of rods and cones.
Pigmented epithelium.
Choroid layer.
Scleral layer. 4 5 6 7 8 9 10 11 12
50 µm

33. SLIDE 11 Developing head coronal section at level of diencephalon and developing eyes.
Identify at low magnification :
Oral cavity.
Tongue.
Developing eyes.
Developing nasal cavity.
Mandible.
Other bones of skull.
Developing enamel organs.
Developing brain.
Eye-lids.
1.0 mm

34. SLIDE 11 Developing head coronal section at level of diencephalon and developing eyes.
Identify at low magnification :
Oral cavity.
Tongue.
Developing eyes.
Developing nasal cavity.
Mandible.
Other bones of skull.
Developing enamel organs.
Developing brain.
Eye-lids. 8 6 6 9 4 3 3 9 1 7 7 2 5 5
1.0 mm

35. SLIDE 11 Developing head coronal section at level of diencephalon and developing eyes.
Identify the main regions of the eye.
Care should be taken to distinguish between eye chambers and ‘space artefacts’.
Identify : 1. Lens.
2. Cornea.
3. Iris.
4. Developing retinal layers.
5. Ciliary body.
6. Eye-lid.
7. Anterior chamber.
8. Vitreous humor.
9. Optic nerve,
(may not be visible in all sections).
250 µm

36. SLIDE 11 Developing head coronal section at level of diencephalon and developing eyes.
Identify the main regions of the eye.
Care should be taken to distinguish between eye chambers and ‘space artefacts’.
Identify : 1. Lens.
2. Cornea.
3. Iris.
4. Developing retinal layers.
5. Ciliary body.
6. Eye-lid.
7. Anterior chamber.
8. Vitreous humor.
9. Optic nerve,
(may not be visible in all sections). 6 A 3* 2 1 8 7 9 5* A 4 6
A : space artefacts
* Unclear due to distortion of tissue during fixation.
250 µm

37. SLIDE 11 Developing head coronal section at level of diencephalon and developing eyes.
At a higher magnification identify:
Equator of developing lens Developing retina.
Lens anterior surface epithelium Cornea.
Optic nerve (may not be visible on all sections).
100 µm

38. SLIDE 11 Developing head coronal section at level of diencephalon and developing eyes.
At a higher magnification identify:
Equator of developing lens Developing retina.
Lens anterior surface epithelium Cornea.
Optic nerve (may not be visible on all sections).
E : equator of lens
developing
retina A
anterior epithelium of lens E
optic nerve
cornea
A : space artefacts A
100 µm

39. How is the diameter of the lens controlled?
SLIDE 11 Developing head coronal section at level of diencephalon and developing eyes.
How is the diameter of the lens controlled?
100 µm

40. SLIDE 11 Developing head coronal section at level of diencephalon and developing eyes.
How is the diameter of the lens controlled?
By the contraction and relaxation of the ciliary muscle.
cornea
lens capsule
cuboidal lens epithelium
proliferating cells at equator of lens
distortion due to fixation;
developing iris and ciliary body displaced
developing retina
artefact
100 µm

41. SLIDE 11 Developing head coronal section at level of diencephalon and developing eyes.
At high magnification identify: note the spatial differentiation of the lens fibre cells.
The surrounding lens capsule is composed of
basal lamina and collagen fibres.
The cuboidal epithelial cells on the anterior
surface have their bases facing the lens capsule
and their apices facing the lens fibres.
At the equator of the lens the cells elongate and
differentiate into lens fibres forming the body of
the lens.
These run in an anterior-posterior direction.
The fully differentiated fibres are hexagonal in
cross section and have lost their nucleus and
most cell organelles.
50 µm

42. Demonstration slides with green labels This set of slides is available during classes from the front bench in the teaching lab (or by request). These slides are serial sections through the the head region of developing embryos. They show stages in the early development of the eye and the ear. In the set can be found : 1. Very early stage in development of the eye. 2. Slightly later stage of eye development. 3. Very early stage in development of ear. 4. Slightly later stage in ear development. Remember; if you look at the slides, you will need to search for the section which shows best either the eye or ear. Try also to recognise some of the other developing structures sectioned.

43. SLIDE (green label) Early stage of developing eye
In the early embryo, the eyes are
first seen as diverticulae developing
laterally from the diencephalon.
In this section only the optic
diverticulum on the right side can be
seen.
These specimens are often cut at an
oblique angle, so the eye on one
side will appear before its partner.
At this stage of development, the
prominent flexure of the head region
can result in the section going
through both hind-brain and fore-
brain (and sometimes the spinal
cord).
250 µm

44. SLIDE (green label) Early stage of developing eye
In the early embryo, the eyes are
first seen as diverticulae developing
laterally from the diencephalon.
In this section only the optic
diverticulum on the right side can be
seen.
These specimens are often cut at an
oblique angle, so the eye on one
side will appear before its partner.
At this stage of development, the
prominent flexure of the head region
can result in the section going
through both hind-brain and fore-
brain (and sometimes the spinal
cord).
spinal cord
diocoel*
diencephalon
developing
optic vesicle
pharyngeal pouch
250 µm
* diocoel ═ lumen of diencephalon

45. SLIDE (green label) Early stage of developing eye
A few sections along on the same
slide and both developing optic
vesicles can be seen.
250 µm

46. SLIDE (green label) Early stage of developing eye
A few sections along on the same
slide and both developing optic
vesicles can be seen.
diencephalon
optic vesicle
optic vesicle
blood vessels
250 µm

47. SLIDE (green label) Early stage of developing eye
Two adjacent sections from another of the slides showing the early stages in the
development of the eye.
The optic vesicles are well developed and due to the flexure in the head an area of
mid-hind brain can be seen.
Note the embryonic membranes.
100 µm

48. SLIDE (green label) Early stage of developing eye
Two adjacent sections from another of the slides showing the early stages in the
development of the eye.
The optic vesicles are well developed and due to the flexure in the head an area of
mid-hind brain can be seen.
Note the embryonic membranes.
branches of vitelline vein
wall of
diencephalon
optic vesicles
amnion
amniotic cavity
100 µm

49. SLIDE (green label) Later stage of developing eye
The diverticulae (seen in the previous
slide), invaginate to form the optic cup.
Producing the retina, ciliary layers and
iris.
The lens is formed from modified
epithelial cells; the surface ectoderm
overlying the optic cup.
The apparent discontinuity between
the diencephalon and the retinal layer
of the optic cup is because of the shape
of the cup and the plane of the section.
250 µm

50. SLIDE (green label) Later stage of developing eye
The diverticulae (seen in the previous
slide), invaginate to form the optic cup.
Producing the retina, ciliary layers and
iris.
The lens is formed from modified
epithelial cells; the surface ectoderm
overlying the optic cup.
amniotic cavity
diencephalon
retina
diocoel
lens
optic cup
anterior cardinal vein
choroid layer
The apparent discontinuity between
the diencephalon and the retinal layer
of the optic cup is because of the shape
of the cup and the plane of the section.
myelencephalon
(with thin roof)
250 µm

51. SLIDE (green label) Early stage of developing ear
The otic vesicles arise from otic (auditory) placodes (areas of thickened ectoderm)
level with the posterior part of the brain.
These sink below the surface to form auditory pits becoming auditory or otic vesicles.
100 µm

52. SLIDE (green label) Early stage of developing ear
The otic vesicles arise from otic (auditory) placodes (areas of thickened ectoderm)
level with the posterior part of the brain.
These sink below the surface to form auditory pits becoming auditory or otic vesicles.
myelencephalon OV
OV : otic vesicles OV
amniotic cavity
neural tube
developing heart
100 µm

53. SLIDE (green label) Early stage of developing ear
Again see how the appearance of the otic vesicles can vary in these serial sections.
100 µm

54. SLIDE (green label) Early stage of developing ear
Previous section at a slightly higher magnification showing some of the associated
structures.
100 µm

55. SLIDE (green label) Early stage of developing ear
Previous section at a slightly higher magnification showing some of the associated
structures.
myelencephalon
with thin roof
vesicle closing
otic vesicle
anterior
cardinal vein
notochord
internal
carotid artery
pharynx
100 µm

56. SLIDE (green label) Later stage of developing ear
The auditory or otic vesicles, have lost their connection to the surface and are now
forming the inner portion of the ear.
The first pharangeal (hyomandibular) pouch will give rise to the Eustachian tube and
the chamber of the middle ear.
0.5 mm

57. SLIDE (green label) Later stage of developing ear
The auditory or otic vesicles, have lost their connection to the surface and are now
forming the inner portion of the ear.
The first pharangeal (hyomandibular) pouch will give rise to the Eustachian tube and
the chamber of the middle ear.
OV : otic vesicles
myelencephalon OV OV OV OV
pharyngeal
pouch
visceral arch
pharyngeal
pouch
0.5 mm

58. SLIDE (green label) Later stage of developing ear
Note the close proximity of the first pharyngeal pouch to the otic vesicle.
Also note developing nerve fibres in the vicinity of the otic vesicle.
250 µm
100 µm

59. SLIDE (green label) Later stage of developing ear
Note the close proximity of the first pharyngeal pouch to the otic vesicle.
Also note developing nerve fibres in the vicinity of the otic vesicle.
N : nerve fibre
P : pharyngeal pouch
otic vesicle N P N
250 µm
100 µm

60. SLIDE (green label) Later stage of developing ear
The same specimen, but a few sections along the slide.
Note the change in shape of the otic vesicle; early stages in the formation of the
semicircular canals.
Also note the more prominent nervous tissue/ganglia (arrowed).
250 µm
100 µm

61. Lecturer: Dr. MBS Kisaka Slides and Stains: Monica Nambi