This document provides an overview of the anatomy and structures of the human eye. It describes the dimensions and layers of the eyeball, including the outer fibrous layer (cornea and sclera), middle vascular layer (iris, ciliary body, and choroid), and inner neural layer (retina). It also discusses the anterior chamber, posterior chamber, lens, vitreous humour, blood supply, and nerve supply to the eye.

1. Anatomy of Eye GS Shrestha, M. Optom Teaching Assistant

2. Learning Objective Describe dimensions and gross anatomical structure of eye Describe different coats of eye Describe the spaces in eye Describe the functions of eye

3. The Eyeball Eyeball is a cystic structure kept distended by the pressure inside it It is not a spherical but consists of two modified spheres fused together. The anterior cornea of smaller radius(7.8mm) & The posterior sclera (12mm)

6. EOM

8. Dimensions of an adult eyeball/new born infant. ADULT INFANT Antero-posterior diameter - 24mm 16.4 Vertical diameter -23mm 16 Lateral diameter -23.5mm 16.4 Circumference -75mm Volume -6.5ml Weight -7gm

9. Three coat or tunica 1 Outer fibrous layer of connective tissue (Cornea and sclera) 2. Middle vascular layer UVEA ( Iris , Ciliary body and choroid) 3. Inner neural layer (Retina)

10. Outer fibrous layer of connective tissue Anterior 1/6 th transparent- Cornea . Posterior 5/6 th opaque- Sclera . Junction of cornea & sclera – Limbus Function Protection for structure within maintain globe’s shape Provide resistance to the pressure of the fluids inside Transmittance of light from cornea to retina

12. Middle vascular layer UVEA Iris , Ciliary body and choroid Functions acts as diaphragm to regulate the amount of light Control shape and diameter of pupil Production of aqueous humour Control accommodation of crystalline lens Supply nutrient to outer layer of retina

14. Inner neural layer Retina Change light energy in to a visual signal for processing in brain via neural pathway

15. Cornea Cornea Corneal epithelium Bowman’s layer Stroma Descemet’s membrane Endothelium

16. Sclera It opaque and porcelain white Consists of indistinct 3 layers: outer episclera to inner layer scleral stroma Thinnest 0.3mm at insertion of rectus muscles, thickest 1.0mm at post pole, 0.4-0.5mm at equator

18. Limbus Transition zone between peripheral cornea & anterior sclera 1.5mm-horizontal & 2mm at vertical meridian Structures included Conjunctiva Tenon’s capsule Episclera Corneoscleral stroma Aqueous outflow apparatus

19. Globe is covered behind the limbus by tenon’s fascia and above tenon is covered by bulbar conjunctiva

20. Iris A thin, circular structure located anterior to the lens Central aperture is called PUPIL Collarette: transition (land mark) to pupillary zone and Ciliary zone Divide anterior chamber with posterior chamber

21. Iris Anterior limiting membrane Stroma and spincter muscle Anterior non-pigmented epithelium and dilator muscle Posterior pigmented epithelium A. Pigment frill

22. Ciliary body Ring shaped structure Width 5.9mm nasal side 6.7mm on temporal side Extend from root of iris at scleral spur to ora serrata Divided in to two parts Pars plicata containing ciliary processes Pars plana: a transition b/w pars plicata and ora serrata

24. Ciliary body 1. Supraciliaris (supraciliary lamina) 2. Stroma of ciliary body Ciliary muscles Smooth muscle of longitudinal, radial and circular orientation 3. Outer pigmented ciliary epithelium 4. Inner non-pigmented ciliary epithelium 5. Internal limiting membrane

25. 1 2 3 4 5

26. Choroid Extend from ora serrata to optic disc Primarily made up of blood vessels and covered both side by connective tissue Layers Suprachoroidal Lamina Choroidal stroma Choriocapillaries Bruch’s membrane

27. Retina

28. Retina Inner most and transparent layer Extend from optic disc to ora serrata Two basic layers: pigment layer and neural layer Function Transformation of light energy to neural signal by photoreceptor, bipolar cells and ganglion cells Its thickness at posterior pole in peripapillary region is approx 0.5mm, at equator 0.18-0.2mm & at ora serrata approx 0.1mm

30. Retina Retinal pigment epithelium Photoreceptor layer Outer limiting membrane Outer nuclear layer Outer plexiform layer Inner nuclear layer Inner plexiform layer Ganglion cell layer Nerve fibre layer Internal limiting membrane Provide blood retinal barrier Phagocytosis of dead and shedding photoreceptor Metabolize and store vit A Absorb light and reduce light scattering Provide nutrition to photoreceptor

32. Anterior chamber Bounded anteriorly by back of cornea & posteriorly by iris, lens in pupillary region & part of ciliary body. 3.0mm (2.5-4.4)deep in centre. Contains 0.25ml of aqueous humour.

33. Posterior chamber Triangular space. Boundary anteriorly by posterior surface of iris, part of ciliary body posteriorly by anterior vitreous face centrally by lens with its zonules

34. Lens A transparent biconvex, crystalline structure between iris & vitreous in a saucer-shaped depression, the patellar fossa It has anterior & posterior surface which meets at equator. Birth Adult Equatorial diameter 6.5mm 9-10mm Thickness 3.5mm 5mm Weight 90mg 255mg Accommodative power 14-16D 1-2 D(50yrs) Refractive index cortex: 1.39 nucleus: 1.41 Refractive power 16-20 D

36. Lens Lens consists of -lens capsule -anterior lens epithelium -lens fibres Lens is hold in position by ciliary zonules, which extends from ciliary body to outer layer of lens capsule in equatorial zone.

38. Vitreous humour It is an inert, transparent, colourless, jellylike structure. Vitreous cavity is bounded anteriorly by lens & ciliary body ; posteriorly by retina. Space of berger Wieger’s ligament Weight-4gm

39. Vitreous humour Vitreous attached firmly to retina at 4 sites: At ora serrata At peripapillary region At fovea At retinal vasculatures.

40. Blood supply to eye Internal carotid artery Central retinal artery Lacrimal artery Posterior ciliary artery Long and short Ethmoidal artery Supraorbital artery Muscular artery Medial palpebral artery Supratrochlear artery Dorsonasal artery External carotid artery Facial artery Superficial temporal artery Maxillary artery

41. Blood supply

42. Blood supply

44. Vein Superior ophthalmic vein Angular vein Supraorbital vein Ethmoidal vein Muscular vein Lacrimal vein Anterior ciliary vein Central retinal vein Upper vortex vein Inferior ophthalmic vein lower eyelids, lateral muscles, inferior conjunctiva, lacrimal sac, lower vortex veins pterygoid venous plexus

45. Nerve supply Cranina nerves II, III, IV, V, VI, VII Optic nerve-visual signal and afferent fibers Oculomotor nerves to extraocular muscles Trochlear nerve to superior oblique muscle Trigeminal nerves Ophthalmic (lacrimal, frontal and nasociliary nerves) maxillary division Abducent nerve Facial nerve (secretomotor fibres)

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