DOC-20240623-WA0002..pptx nirmal Kumar Lodha

Ab

1. The eyeball

2. The eyeball Lies in the anterior aspect of the orbit Is separated from the posterior aspect of the orbit by pad of fat and extrinsic muscles of the eyeball Poles & axises of the eyeball: Has anterior & posterior poles that are points of greatest curvatures Axis of the eyeball is an imaginary circumferential line connecting the poles Optic axis (visual axis) is an imaginary line that passes through the point of fixation & fovea centralis, area of most acute vision Equator of the eyeball - is a circumferential line equidistant from the poles Adult dimensions of the eyeball: Vertical diameter ( S to I)~ 23.5 mm Sagittal (AP) diameter ~ 24 mm In myopia (near sightedness), the AP diameter is greater than 24mm In hypermetropia (far sightedness), the AP diameter is less than 24 mm Anterior pole Posterior pole

3. Fascial sheath and adipose tissue Fascial sheath of the eyeball ( Tenon’s capsule/bulbar sheath) Extends – from optic nerve to ̃1.5 mm behind sclero -corneal junction Function – Separates eyeball from periorbital pad of fat Forms a socket for the eyeball for free movement Structures derived from periorbita (periosteum of the orbit) Fascial sheath of eyeball Tubular sheath around each tendon Lateral check lig . – Medial check lig . – Suspensory lig . – Periorbital pad of fat (Tenon’s capsule/ Bulbar sheath)

4. Suspensory & check ligaments (Hammock-like sling) Lateral Medial

5. Layers (coats) of the eyeball The three layers of the eyeball are: Fibrous outer layer (avascular) Pigmented middle layer (vascular & pigmented) Nervous (retinal) inner layer

6. Fibrous outer layer Outer fibrous layer has two parts: - Sclera - Cornea Sclera: Is the opaque, posterior 5/6 part of the fibrous layer of the eyeball; ‘ white’ of the eyeball Is posteriorly pierced by the optic nerve and ophthalmic vessels at the lamina cribrosa , a weak area of the sclera Scleral venous sinus – is a venous sinus that lies near sclerocorneal junction, and receives the drainage of aqueous humour sclera Position of lamina cribrosa cornea Optic nerve

7. Fibrous outer layer cont.. Cornea: It is the transparent anterior 1/6 part of the outer fibrous layer Is a part of the refractive media of the eyeball Anteriorly, cornea is covered by bulbar conjunctiva, a thin mucous membrane N supply: long ciliary branches of nasociliary N, branch of V1

8. Middle pigmented layer The middle pigmented layer: Lies deep to the outer fibrous coat It has three parts: Choroid ( uveal tract) Ciliary body iris iris choroid

9. Middle pigmented layer cont… The choroid: Choroid has dark brown color (wine-colored) It has: inner highly vascular layer (the choroid proper) that is firmly adherent to retina up to ora serrata ; it supplies the layer of cones & rods of the retina Mostly made-up of capillary plexuses, branches of ciliary arteries 2. an outer avascular (suprachoroid) pigmented layer that is loosely adherent to sclera Choroid Is continuous anteriorly with the ciliary body Inner vascular layer (choroid proper) Outer avascular layer ( suprachoroid ) )

10. Middle pigmented layer cont… The ciliary body consists of: 1. Ciliary ring is continuous with the choroid posteriorly 2. Ciliary processes (70-80) secrete aqueous humor and give attachment to the suspensory ligament of the lens 3. Ciliary ( ciliaris ) muscle Is the muscle of accommodation . It is attached to the suspensory ligament of the lens. Nerve supply: short ciliary N (Parasympathetic fibers of oculomotor nerve) lens

11. The ciliary body Position of ciliary ring

12. The iris (colored part of the eyeball) (L: rainbow) Is a thin, contractile diaphragm that lies anterior to the outer circumference of the lens surrounding the pupil Projects medially in front of the lens between the anterior & posterior chambers It circumscribes a central aperture, the pupil Consists of two muscles: 1. sphincter pupillae constricts pupil (in high intensity of light & during parasympathetic stimulation) N supply: parasympathetic fibers of oculomotor via short ciliary N 2. dilator pupillae dilates pupil (in low intensity of light & in response to sympathetic stimulus) N supply: ( sympathetic fibers from sup. cervical ganglion; pass along long ciliary N) iris

13. Inner layer of the eyeball The retina: Is the inner coat of the eyeball The retina has three parts: optic part (receptive to light) Extends from the optic disc to the ora serrata contains rods and cons, receptor cells of light. It has two parts: Outer pigmented layer (in contact with the choroid proper) Inner nervous layer (in contact with the hyaloid membrane of the vitreous body) retina Color of fresh retina is purple due to the p resence of coloring material, rhodopsin On exposure to light, it becomes opaque & bleached

14. The retina cont… 2. Ciliary part: (non-receptive to light) Is an anterior continuation of the pigmented part of the optic retina deep to the ciliary processes 3. Iridial part: (non-receptive to light) Is an anterior continuation of the pigmented part of the optic retina deep to the iris

15. Special features of the retina Fundus: The posterior part of the retina is known as the fundus Optic disc (papilla): ( Blind spot ) is where the axons of the ganglionic cells merge to form the optic nerve It has a slight depression in the center where the central retinal A & V exit the nerve It is insensitive to light because there are no rods and cones at the disc; thus also known as the “blind spot” Macula lutea : ( yellow spot) An oval area of the retina lateral to the optic disc Has a central depression, the fovea centralis , which is the area of most acute vision

16. Contents of the eyeball The eyeball contains: Aqueous humor (in anterior & posterior chambers) Lens Vitreous body (enclosed by hyaloid membrane)

17. Contents of the eyeball

18. Aqueous humor A clear fluid secreted into posterior chamber by diffusion of plasma from capillaries of ciliary processes Pass into anterior chamber through pupil It drains into the scleral venous sinus through the canal of Schlemm Function: nourishes the cornea and lens that are avascular removes by-products of metabolism Anterior chamber Posterior chamber

19. Vitreous body A transparent gel that fills the posterior part of the eyeball; prevents collapse of the wall It is traversed by the hyaloid canal that extends from the posterior surface of the lens to the optic disc The canal transmits hyaloid artery in the fetus Hyaloid canal

20. Lens A transparent biconvex structure enclosed in the lens capsule Attached at the circumference to the ciliary processes and muscle (ciliaris) by suspensory ligaments of the lens Contraction of the ciliary muscles allow the lens to assume more convexity by moving towards the lens and relaxing the suspensory ligaments bringing about accommodation for near objects Convexity and elasticity of lens decreases with age Suspensory lig. of the lens Ciliaris muscle

21. Refractive media of the eye The refractive media of the eye consists of: Cornea Aqueous humor Lens Vitreous humor These refract light so that the light impulses fall on the retina Aqueous humor in anterior and posterior chambers Vitreous humor

22. Arterial supply of the eyeball The eyeball is supplied by branches of the ophthalmic artery Central artery supplies the retina except the layer of rods & cones which is supplied by the choroid proper Structures near the orbital floor are supplied by infra-orbital A Branches of ophthalmic artery are: Central artery – end arteries; blockage leads to instant blindness Posterior ciliary branches : long and short Short post. ciliary branches (6-8) - supply the choroid Long post. ciliary branches (2) - pass anteriorly, anastomose with anterior ciliary arteries (continuation of muscular branches) & form a major iridial arterial circle This gives several radial branches which join at the free border of the iris to form a minor iridial arterial circle . The long posterior ciliary arteries supply the anterior part of the eyeball.

23. Arterial supply of the eyeball Minor iridial arterial circle

24. Vorticose veins Vortex (vorticose) veins begin from the vascular layer of the choroid. The veins are arranged in whorls and drain into the ophthalmic veins

25. Venous drainage of the eyeball The central retinal vein may drain into the cavernous or into one of the ophthalmic veins Superior ophthalmic V Passes through the superior orbital fissure to drain into cavernous sinus Communicates with supraorbital V Receives vorticose veins of the eyeball Inferior ophthalmic V Passes through the inferior orbital fissure into the infratemporal region to drain into pterygoid plexus, which also communicates with the cavernous sinus. Inferior ophthalmic vein communicates with facial vein and receives vorticose veins of the eyeball

26. Applied - eyeball Glaucoma: Is rise in intraocular pressure; seen as a cupped disc, an outward bulge at the lamina cribrosa May be due to decrease in drainage of aqueous humor ( eg ., due to blockage of its drainage) which can lead to build up of pressure in the anterior and posterior chambers of the eye, causing damage to the optic disc If pressure is not corrected in good time, may lead to blindness resulting from compression of neural layer of retina and retinal blood vessels Papilledema: Bulging of the optic disc inwards as a result of increase in cerebrospinal fluid (CSF) pressure causing collapse of retinal veins & edema of retina Presbyopia: Reduced ability to focus on near objects due to decreased elasticity of the lens . Occurs in old age as the lens becomes more flat Cataract: Loss of transparency of the lens commonly seen in old age