Ocular Anatomy

1. Ocular Anatomy G. Wollstein, MDAssociate Professor

3. The eye Diameter: 24mm • Anterior chamber: 3mm deep, volume of 250μL • Posterior chamber: 60μL • Vitreous: 6.5mL • Diameter: 24mm • Anterior chamber: 3mm deep, volume of 250μL • Posterior chamber: 60μL • Vitreous: 6.5mL

4. Tear Film • Superficial oily layer • Made by Meibomianglands • Function: anti-evaporative agent • Aqueous layer • Made by lacrimal and accessory lacrimal glands • Function: provides smooth optical surface, nutrients, immunoglobulins, oxygen • Mucin layer • Made by goblet cell • Function: wetting agent

5. Cornea • Oval shape • 12 mm wide • 11 mm high • Varying thickness • Center: 0.55mm • Limbus: 1mm • Radius of curvature: 8mm

6. Cornea • Average power: 43 diopters • Steepest centrally, flatter peripherally • More curved posteriorly then anteriorly

7. Corneal Layers OCT Histology Epithelium Bowman Stroma Descement Endothelium

8. Corneal Epithelium • Constant turnover of cells • Stem cells located in crypts adjacent to limbus • Move centripetally and anteriorly • Anchored to basement membrane by hemidesmosomes

9. Bowman’s layer • Anterior most stroma • Thickness: 8-14μm • Randomly dispersed collagen fibrils • Cannot regenerate [

10. Stroma • Composition: • Collagen fibers • Ground substance • Keratocytes

11. Fibrils arranged in oblique and parallel lamellae Individual fibrils run the entire diameter of the cornea Spatial organization of the fibrils allows for transparency Stroma

12. Descemet’s Membrane • Basement membrane of the corneal endothelium • Made of type IV collagen • Thickens with age [

13. Corneal Endothelium • A monolayer of hexagonal cells • Cell density: 3000 cells/mm2 • Decreases with age • Cannot regenerate • Loss of cells results in corneal edema

14. Anterior Chamber Angle • Formed between the posterior aspect of the cornea and anterior aspect of iris • Opening of the drainage system • Trabecular meshwork • Schlemm’s canal • Collector channels • Ant. ciliary v.

15. Uvea • Iris • Ciliarybody • Choroid

16. Iris • Anterior border layer • Stroma • Dilator muscle • Posterior pigmented layer • Two layers of heavily pigmented epithelial cells • Melanin

17. Iris Innervation • Dilator muscle: Primarily sympathetic autonomic system • Sphincter muscle: Parasympathetic system

18. Base inserts into the sclera spur via the longitudinal muscle fibers Gives rise to the iris Apex is bordered by the oraserrata of the retina CiliaryBody

19. Ciliary Body - Functions • Accommodation • Controlling the lens curvature through the zonules • Aqueous humor formation • Ciliarybody epithelium • Trabecular and uveoscleraloutflow

20. Diameter: 9-10mm Ant.-post. width: 6mm Power: 20 Diopters Cornea: 40D The actively dividing lens epithelial cells are located just anterior to the equator of the lens Lens

21. The high refractive index of the lens results from a high concentration of alpha, beta and gamma crystalins in lens fibers

22. Choroid • Thickness: 0.25mm • Highly vascularized layer • Fenestrated vessels • Primary metabolic source for the RPE

23. Choroid • “Spaghetti bowl”

24. Choroid - Vasculature • Arterial supply: Long and short posterior ciliarya. and anterior ciliarya. • Venous drainage: Channeled toward equator vortex veins -> ophthalmic v.

25. Bruch’s Membrane • Separating between the choroid and retina • Created from the fusion of basement membranes of the choriocapillarisand RPE • Play a critical role in preventing penetration of abnormal vasculature into the retina

26. Retina • Converts light stimuli into electrical impulse • Clinical macula: Bounded by the vascular arcade • Histological macula: >1 ganglion cell body

27. Retina • Fovea: Avascular center of the macula • “Center of vision”

28. Multilevel connections between photoreceptors and optic nerve Retina

29. RPE • A monolayer of hexagonal cells • RPE cells in the macula are taller, thinner and contain more and larger melanosomes • Functions include: • Vitamin A metabolism • Maintenance of the outer blood retina barrier • Phagocytosis of the photoreceptor outer segments • Absorption of light • Heat exchange • Formation of matrix around the photoreceptors • Active transport of materials

30. Photoreceptors • The outer segment consists of discs connected to the inner segment by the cilium • Constant shedding of discs as exposed to light • High concentration of mitochondria in the inner segment to provide the energy requirements

31. Photoreceptors • Photoreceptor density is greater in the fovea than elsewhere in the retina • The only layers of the retina present in the fovea are the photoreceptors and Henle’s layer (outer plexiform layer in the fovea)

32. Nuclei in the outer nuclear layer Axons (cone pedicle and rod spherule) in the outer plexiform layer Photoreceptors

33. Made up of the cell bodies of the bipolar, horizontal and amacrinecells Interconnect photoreceptors with each other and with ganglion cells Initial steps of image processing Inner Nuclear Layer

34. Extend from the internal to external limiting membranes Nuclei in the inner nuclear layer Provide support and structural functions for the retina Muller cells

35. Ganglion cell layer Cell bodies Inner plexiform layer Ganglion cells dendrites Nerve fiber layer Ganglion cell axons Inner Retina

36. Retina – Blood Supply • CRA enter the eye through the optic nerve and bifurcate into 4 main branches • Supply inner retina down to the inner nuclear layer • Outer retina supplied by the choroidal vasculature

37. Cool picture!

38. Vitreous • Constitutes 95% of the eye volume • Main component: water (98%) • The component that make vitreous viscous is hyaluronic acid

39. No time to cover other important ocular and orbital structures • Assembly of other important slides follows

40. Eyelids

41. Extraocular Muscles

42. Orbit

43. Orbital base

44. Arterial Supply

45. Venous Drainage

46. Orbital Cranial Nerves

47. The End