OPTOMETRY

1. Contact Lens
Anatomy of Anterior Segment of the Eye -II

2. LIMBUS
 Transition zone between cornea and
conjunctiva/sclera
 An anatomical reference for surgical procedures,
bio microscopy and contact lens fitting.

3. 1mm Depth
1.5 Width (horizontal)
2.5 Width (Vertical)
LIMBUS - Dimensions

4.  Provides limited nourishment to the peripheral
cornea via the limbal vasculature.
 Site of the aqueous humor drainage system
including Schlemm’s canal. This system is
important for the maintenance of the intraocular
pressure.
LIMBUS - Functions

5. LIMBAL VASCULATURE
Terminal arteries – Peripheral Cornea Arcades
Recurrent arteries – Peripheral Conjunctiva
Arcades

6. SCLERA
Approximately spheroidal
Collagenous
Relatively avascular
Relatively inactive metabolically
Durable and tough

7. SCLERA - Composition
 65% H2O (c.f. cornea 72-82%)
Dry weight figures:
 75% Collagen
 10% other protein
*Irregular arrangement of collagen results in an opaque tissue
*In older eyes, fatty deposits may produce a yellowing of the
sclera.

8. Sclera - Dimensions
 Approximately spheroid
 22 mm diameter
>80% of eye external surface
Thickness
- 0.8 mm at limbus
- 0.6 mm at front of rectus muscle tendon
- 0.3 mm behind rectus muscle insertions
- 0.4-0.6 mm at equator of globe
- 1.0 mm at optic nerve head

9. Lacrimal Gland
 Located under supero-temporal orbit
Sits in Lacrimal Fossa
Divided by Levator Palpebrae Superioris
into:
 Orbital portion (larger, upper)
 Palpebral portion (smaller, lower)

10. Lacrimal Gland
The lacrimal gland has up to 12 ducts
two to five from the upper (orbital) portion
six to eight from the lower (palpebral) portion.
 The ducts open onto the superior palpebral
conjunctiva.

11. Accessory Lacrimal Glands
GLANDS OF WOLFRING
Similar in structure to the lacrimal gland.
Situated near the upper border of the tarsal plate
in the upper lid.
 Supplying the aqueous phase of basal tears.

12. Accessory Lacrimal Glands
GLANDS OF ZEIS
 Sebaceous glands
 Associated with lash follicles
 Partially supply lipid layer of tears

13. Accessory Lacrimal Glands
Meibomian Glands:
Sebaceous glands
Main supply of lipid layer of tears
25 in upper lid, 20 in lower lid (shorter)
Oil on the lid margins prevents tear overflow

14. ACCESSORY LACRIMAL GLANDS
GOBLET CELLS
Unicellular sero-mucous glands
In epithelium of conjunctiva
Provides mucoid layer of tears

15. TEAR FILM

16. By eyelid action
By movement of the globe
Helps form lacrimal lake
Each blink ‘resurfaces’ tear film
Tear Distribution

17. TEAR FLOW
Tear flow aided by:
capillary action
Gravity
blinking

18. Distribution of Tear Volumes
Pre-corneal: 1 μL
 Tear meniscus: 3 μL
 Cul-de-sac: 4 μL

19. Tear Film Stability
Mucin layer spread by lid action enhances
wettability of epithelium.
Evaporation leaves an oil and mucin admixture.
Admixture does not ‘wet’ epithelium causing a
break-up of tear film

20. MECHANICS OF TEAR FILM SPREADING
 Upward lid movement draws aqueous component over
the surface
 Lipid layer spreading over surface increases film
thickness and stability

21. TEAR FLOW: LID CLOSURE MOVEMENT
TOWARDS THE MEDIAL CANTHUS
Lid closure is scissor-like towards the nose
 Tears move towards the medial canthus

22. The compressive force of blinking on the tears
combined with the scissor-like action of lid
closure, gives a directional flow towards the
medial canthus.

23. Tear Drainage

24. EYELIDS

25. Modified folds of skin
 Protect eyes from foreign bodies and sudden increases
in light level
Spread tears over the ocular surface
Lid margins are shelf-like and about 2mm wide
EYELIDS

26. EYELIDS
4-LAYERED STRUCTURE
1.Cutaneous layer (the skin)
2.Muscular layer (mainly orbicularis oculi)
3.Fibrous tissue layer (tarsal plates)
4.Mucosal layer (palpebral conjuctiva)

27. EYELIDS-GLANDS
ZEIS GLANDS
•Sebaceous glands associated with lash follicle,
They contribute to the lipid layer of the tears
MOLL’S GLANDS
•Modified sweat glands open into Zeis glands,
lash follicles, lid margins
MEIBOMIAN GLANDS
•Sebaceous glands in the tarsal plate, main source
of the tear lipid layer.

28. EYELIDS-GLANDS

29. EYELIDS: BLOOD VESSELS
Supply oxygen to the cornea via palpebral
conjuctival vessels.