ANATOMY OF EYE

                      ANATOMY OF EYE

INTRODUCTION:

• IT IS NOT A TRUE SPHERE, BUT CONSISTS OF THE SEGMENTS OF TWO MODIFIED SPHERES, ONE IN FROM OF THE OTHER.
• THE CORNEA IS MORE CONVEX THAN THE REST OF THE GLOBE.{7.8 mm radius as opposed to 12mm}
• THE ANTEROPOSTERIOR DIAMETER IS ABOUT 24 mm, WHILE THE VERTICAL IS 23mm AND THE HORIZONTAL IS 23.5mm.
• THE EYEBALL IS SHORTER IN HYPERMETROPES BUT LONGER IN MYOPES.

THE GLOBE :

• THREE CONCENTRIC LAYERS OR TUNICS:

                   1. OUTER SUPPORTING LAYER: IT CONSISTS OF TRANSPARENT CORNEA, OPAQUE SCLERA, AND THEIR JUNCTION, THE LIMBUS.

                   2. MIDDLE VASCULAR LAYER: IT IS CALLED UVEA & CONSISTS OF CHOROID, CILIARY BODY & THE IRIS.

                  3. INNER NEUTRAL LAYER: IT IS CALLED RETINA, COMPOSED OF TWO PARTS (a) A SENSORY PORTION & (b) A LAYER OF PIGMENT EPITHELIUM. 

            

• A CRYSTALLINE LENS: THE TRANSPARENT STRUCTURE IS LOCATED IMMEDIATELY BEHIND THE IRIS, AND IS SUPPORTED BY FINE FIBERS, CALLED ZONULES.
• THREE CHAMBERS : 

                        1. ANTERIOR CHAMBERS: IT IS LOCATED BETWEEN THE IRIS AND THE POSTERIOR SURFACE OF THE CORNEA.

                         2. POSTERIOR CHAMBER: IT IS BOUNDED BY LENS & ZONULES BEHIND, AND THERE IS IN FRONT.

                         3. VITREOUS CAVITY: IT IS THE LARGEST AND LOCATED BEHIND THE LENS AND ZONULES, AND ADJACENT TO THE RETINA THROUGHOUT.

THE CORNEA:

• AVASCULAR TRANSPARENT ORGAN;
• CLEAR/ TRANSPARENT;
• DOME-LIKE STRUCTURE;
• CONVEX STRUCTURE WITH HORIZONTAL DIAMETER 12 mm & VERTICAL DIAMETER 10-11mm.
• AVERAGE DIOPTRIC VALUE 43-45D
• THICKNESS of (540 T0 560)micrometer.

LAYERS OF CORNEA:

1. ANTERIOR EPITHELIUM
2. BOWMAN'S LAYER: IT DOES NOT REGENERATE & LEAVES BEHIND A SUPERFICIAL CORNEAL SCAR.
3. CORNEAL STROMA: COMPRISING 90% OF CORNEAL THICKNESS.
4. DESCEMET'S MEMBRANE: IT READILY REGENERATES AFTER AN INJURY.
5. ENDOTHELIUM: IT DOES NOT REGENERATE IN HUMAN BEING.

COLLAGEN FIBRILS ARE MAIN COMPONENTS FOR MADE THIS LAYER.

IN THE CORNEA BLOOD SUPPLY BY ANTERIOR CILIARY ARTERIES.

THE SCLERA:

IT IS A DENSE TOUGH FIBROUS ENVELOPE THAT COVERS POSTERIOR FIVE-SIXTHS OF THE EYE.

• SCLERA FORMS THE POSTERIOR 5/6ths OF THE GLOBE.
• THE TISSUE IS AVASCULAR AND APPEARS WHITE.
• THICK- 1mm; thin- 0.6 mm
• SCLERA MAINTAIN THE SHAPE OF THE GLOBE.

STRUCTURES:

1. EPISCLERA: IT IS THE LOOSE FIBROUS TISSUE, CONTAINING NUMEROUS FINE CAPILLARIES.

2. SCLERA PROPER: IT IS DENSE NETWORK OF COLLAGEN FIBERS. THE SCLERA IS WHITE.

3. LAMINA FUSCA: IT IS THE INNER LAYER, LOCATED ADJACENT TO THE CHOROID.

LIMBUS: 

SCLERA FORMS A JUNCTION WITH CORNEA 0.8 mm THICK.

THE UVEA

THE MIDDLE COAT OF THE EYEBALL IS CALLED UVEA.

UVEA HAS THREE PARTS:

1. ANTERIOR- IRIS;

2. INTERMEDIATE: CILIARY BODY.

3. POSTERIOR: CHOROID.

1. IRIS: THE COLORED PART OF THE EYE.

FORMS A DIAPHARM IN FRONT OF THE CRYSTALLINE LENS.

CONTROLS PUPIL SIZE, REGULATES THE AMOUNT OF LIGHT ENTERING THE EYE.

INFLUENCE SHARPNESS OF RETINAL IMAGE.

2. CILIARY BODY:

PRODUCES AQUEOUS HUMOR.

CILIARY MUSCLE PLAYS A MAJOR ROLE IN ACCOMMODATION(CHANGE IN THE LENS SHAPE TO FOCUS AT DISTANCE OR NEAR).

THE CILIARY BODY EXTENDS FROM THE BASE OF THE IRIS AND BECOMES CONTINUOS WITH THE CHOROID AT THE ORA SERRATA.

IT IS APPROXIMATELY 6-6.5 mm

IT IS DIVIDED INTO TWO PARTS:

(i) PARS PLICATA:

PRODUCE AQUEOUS IN THE CILIARY PROCESSES. THESE ARE SMALL FINGERLIKE PROJECTIONS IN THE POSTERIOR CHAMBER BEHIND THE IRIS.

PARS PLICATA PROMOTING ACCOMMODATION.

(ii) PARS PLANA: 

POSTERIOR PART OF THE CILIARY BODY. IT ATTACHES TO THE ORA SERRATA OF THE RETINA AND REPRESENTS AN ANATOMIC LANDMARK FOR MICROSURGICAL INSTRUMENTS TO ACCESS THE POSTERIOR SEGMENT OF THE GLOBE.

3.CHOROIDS:

THE CHOROIDS HAS FOUR LAYERS:

a. LAMINA FUSA

b. STROMA

c. CHORIOCAPILLARIS

d. BRUCH'S MEMBRANE.

LARGE VASCULAR & PIGMENTED TISSUE THAT FORMS THE MIDDLE COAT OF THE POSTERIOR PART OF THE EYE & EXTEND FROM THE ORA SERRATA TO THE OPTIC NERVE.

OPHTHALMIC ARTERY AS THE MAJOR BLOOD OF THE CHOROIDS.

CHOROIDS PROVIDES NOURISHMENT TO THE RETINA.

CONJUNCTIVA:

IT IS A MUCOUS MEMBRANE COVERING THE INNER SURFACE OF THE EYELIDS & REFLECTED TO COVER THE INTERIOR PART OF THE EYEBALLOVER THE SCLERA, UP TO THE CORNEAL MARGIN.

PARTS

PALPEBRAL- IT CONSISTS OF MARGINAL, TARSAL AND ORBITAL PART. IT IS FIRMLY ADHERENT TO THE DEEPER TISSUE.

BULBAR- IT LIES OVER THE SCLERA AND IT IS FREELY MOBILE.

FORNIX- IT IS THE CUL-DE-SAC AT THE JUNCTION OF PALPEBRAL AND BULBAR CONJUNCTIVA.

LIMBAL- IT IS THE CONJUNCTIVA AT THE CORNEAL JUNCTION WHICH IS ADHERE.

LENS:

THE LENS IS A TRANSPARENT BICONVEX BODY OF CRYSTALLINE STRUCTURE.
IT IS ABOUT 9 mm DIAMETER & 4mm IN THICKNESS WHEN THE SUSPENSORY LIGAMENT IS RELAYED.

RADIUS OF CURVATURE OF ANTERIOR SURFACE IS 10mm & THAT OF POSTERIOR SURFACE IS 6mm.

RETINA:

THE RETINA IS THE MEMBRANOUS LIGHT-SENSITIVE COAT OF EYEBALL. IT IS TRANSPARENT.
RETINA HAS TEN LAYERS-

1. RETINAL PIGMENT EPITHELIUM.
2. LAYERS OF ROD AND CONES
3. EXTERNAL LIMITING MEMBRANE.
4. OUTER NUCLEAR LAYER
5. OUTER PLEXIFORM LAYER
6. INNER NUCLEAR LAYER
7. INNER PLEXIFORM LAYER
8. GANGLION CELL LAYER
9. NERVE-FIBER LAYER
10. INTERNAL LIMITING MEMBRANE.

EYELIDS:-

THE EYELIDS ARE THIN CURTAINS OF SKIN, MUSCLES, FIBROUS TISSUE AND MUCOUS MEMBRANE.

THE UPPER EYELID IS LIMITED ABOVE BY THE EYEBROW, AND THE LOWER EYELID MERGES WITH THE CHEEK.

LAYERS OF EYELIDS--

(a) CUTANEOUS LAYER: IT IS THIN SMOOTH DELICATE, ELASTIC, HAVING CREASES AND WITHOUT ANY LONG HAIR.

(b) subcutaneous layer

(c) MUSCULAR LAYER- 

1. ORBICULAR OCULI
2. LEVATOR PALPEBRAE SUPERIORIS IN THE UPPER LID ONLY.
3. MULLER'S MUSCLE.

(d) FIBROUS LAYER-

1. ORBITAL SEPTUM IN THE UPPER PART
2. TARSAL PLATE IN THE LOWER PART.

(e) PALPEBRAL CONJUNCTIVAL LAYER.

GLANDS:- 

1. MEIBOMIAN GLAND: THEY ARE MODIFIED SEBACEOUS GLAND OF LARGER IN SIZE & RESPONSIBLE FOR OILY SECRETION OF THE TEAR FILM.                                   NUMBER> 30-40 IN UPPER LID & 20-30 IN THE LOWER LID.
2. GLANS OF ZEIS
3. GLANDS OF MOLL
4. GLANDS OF KRAUSE & WOULFRING

LACRIMAL APPARATUS: 

PARTS OF LACRIMAL APPARATUS-

1. LACRIMAL GLAND
2. PUNCTUM
3. COMMON CANALICULUS
4. LACRIMAL SAC
5. NASOLACRIMAL DUCT

THE LACRIMAL APPARATUS CONSISTS OF TWO PARTS:

• SECRETORY PORTION: LACRIMAL GLAND & ACCESSORY LACRIMAL GLAND OF KRAUSE & WOULFRING
• DRAINAGE PORTION: VIA WHICH THE TEARS DRAIN INTO THE INFERIOR MEATUS OF THE NOSE.

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