ANATOMY OF THE EYE

ANATOMY OF THE EYEANATOMY OF THE EYE

• THE WALL OF THE EYE BALL IS COMPOSED OF A DENSE, IMPER-FECTLY ELASTIC SUPPORTING MEMBRANE

• THE ANTERIOR PART OF THE MEM-BRANE IS TRANSPARENT THE CORNEA

• THE ANTERIOR PART OF THE SCLERA IS COVERED BY MUCOUS MEMBRANE THE CONJUNGTIVA

THE CORNEA CONSIST OF FIVE LAYERS : - EPITHELIUMEPITHELIUM - - BOWMAN’S MEMBRANEBOWMAN’S MEMBRANE - - STROMA OR SUBSTANTIA PROPIASTROMA OR SUBSTANTIA PROPIA - - DESCEMET’S MEMBRANEDESCEMET’S MEMBRANE - - ENDOTHELIUMENDOTHELIUM

• THE EPITHELIUM REGARDED AS THE CONTINUATION OF THE CONJUNGTIVA OVER THE CORNEA

• THE SUBSTANTIA PROPIA REGARDED AS THE CONTINUATION FORWARD OF THE SCLERA

• THE STROMA FORMING 90 % OF THE TOTAL CORNEAL THICKNESS

• DESCEMET’S MEMBRANE IS A THIN ELASTIC MEMBRANE, COVERED ON ITS POSTERIOR BY ENDOTHELIUM

• THE PRIMARY MECHANISME CONTROLLING STROMAL HYDRATION IS A FUNCTION OF THE CORNEAL ENDOTHELIUM

• ENDOTHELIAL CELLS BECOME LESS IN NUMBER WITH AGE AND INDIVIDUAL CELL ENLARGE TO COMPENSATE

• THE CORNEA IS SET INTO THE SCLERA LIKE A WATCH GLASS SO THAT THE LATTER OVER- LAPS THE CORNEA ALL AROUND THE PERI- PHERY; THE JUNCTION OF THE TWO TISSUES IS KNOWN AS THE LIMBUS

•THE CORNEA IS VERY RICHLY SUPPLIED WITH NERVE FIBERS DERIVED FROM THE TRIGEMINAL AND IT HAD NO BLOOD VESSEL

LINING THE INNER ASPECT OF THE SCLERA ARE TWO STRUCTURES :

• THE HIGHLY VASCULAR UVEAL TRACT CONCERNED CHIEFLY IN NUTRITION OF THE EYE

• A NERVOUS LAYER, THE TRUE VISUAL NERVE ENDING ONCERNED IN THE RECEPTION AND TRANSFORMING OF LIGHT STIMULL CALLED THE RETINA

THE UVEAL TRACT CONSIST OF THREE PARTS, WHICH THE TWO POSTERIOR, THE CHOROID, AND CILIARY BODY, WHILE THE ANTERIOR FORMS A FREE CIRCULAR DIAPHRAGM : THE IRIS

THE APERTURE OF THE DIAPHRAGM IS THE PUPIL

SITUATED BEHIND THE IRIS AND IN CONTACT WITH THE PUPILLARY MARGIN IS THE CRYSTALLINE LENS

THE ANTERIOR CHAMBER IS A SPACE FILLED WITH FLUID, THE AQUEOUS HUMOR; IT IS BOUNDED IN FRONT BY THE CORNEA, BEHIND BY THE IRIS AND THE PART OF THE ANTERIOR SURFACE OF THE LENS WHICH IS EXPOSED IN THE PUPIL

ITS PERIPHERAL RECESS IS KNOWN AS THE ANGLE OF THE ANTERIOR CHAMBER, BOUNDED POSTERIORLY BY THE ROOT OF THE IRIS AND THE CILIARY BODY AND ANTERIORLY BY THE CORNEOSCLERA

IN THE INNER LAYER OF THE SCLERA AT THIS PART THERE IS A CIRCULAR VENOUS SINUS, SOME TIMES BROKEN UP INTO MORE THAN ONE LUMEN CALLED THE CANALIS SCHLEMM - GREAT IMPORTANT - IN THE DRAINAGE OF THE AQUEOUS HUMOR

AT THE PERIPHERY OF THE ANGLE BETWEEN THE CANAL SCHLEMM AND THE RECESS OF THE ANTERIOR CHAMBER THERE LIES A LOOSELY CONSTRUCTED MESHWORK OF TISSUES, THE CORNEO-SCLERAL TRABECULAE

THERE ARE TWO UNSTRIPED MUSCLE WHICH CONTROL THE MOVEMENTS OF THE PUPIL

• THE SPHINCTER PUPILAE A CIRCULAR BUNDLE RUNNING ROUND THE PUPILLARY MARGIN; IS SUPPLIED BY MOTOR NERVE FIBERS DERIVED FROM THE OCULOMOTOR NERVE

•THE DILATATOR PUPILLAEARRANGED RADIALLY NEAR THE ROOT OF THE IRIS. THE MOTOR NERVE FIBRES ARE DERIVED FROM THE CERVICAL SIMPHATHETIC CHAIN

THE INNER SURFACE OF THE CILLIARY BODY IS DIVIDED INTO TWO REGION

• THE PARS PLICATATHE ANTERIOR PART WHICH IS CORRUGATED WITH A NUMBER OF FOLDS

• THE PARS PLANATHE POSTERIOR PART WHICH IS SMOOTH

THE CHIEF MASS OF THE CILLIARY BODY IS COMPOSED OF THE UN-STRIPED MUSCLE FIBERS - CALLED - THE CILLIARY MUSCLE

THE CILLIARY BODY EXTENDS BACK WARD AS FAR AS THE ORA SERRATA, AT WHICH POINT THE RETINA BEGINS ABRUPTLY

THE CHOROID IS EXTREMELY VASCULAR MEMBRANE IN CONTACT EVERY WHERE WITH THE SCLERA. ALTHOUGH NOT FIRMLY ADHERENT TO IT SO THERE IS A POTENTIAL SPACE BETWEEN THE TWO STRUCTURE - CALLED - THE EPICHOROIDAL SPACEON THE INNER SIDE THE CHOROID IS COVERED BY A THIN ELASTIC MEMBRANE - CALLED- THE LAMINA VITERA OR MEMBRANA OF BRUCH

THE RETINA CONSISTS OF 10 LAYERS

1. PIGMEN EPITHELIUM2. LAYER OF ROD AND CONES3. EXTERNAL LIMITING MEMBRANE4. OUTER NUCLEAR LAYER5. OUTER PLEXIFORM LAYER6. INNER NUCLEAR LAYER7. INNER PLEXIFORM LAYER8. GANGLION CELL LAYER9. OPTIC NERVE FIBER LAYER10. INTERNAL LIMITING MEMBRANE

AT THE POSTERIOR POLE OF THE EYE WHICH IS SITUATED ABOUT 3 MM TO THE TEMPORAL SIDE OF THE OPTIC DISC, A SPECIALLY DIFFEREN-TIATED SPOT IS FOUND IN THE RETINA, THE FOVEA CENTRALIS, A DEPRESSION OR PIT, AND IN HERE ONLY CONES ARE PRESENT IN THE NEURO EPITHELIAL LAYER

THE FOVEA IS THE MOST SENSITIVE PART OF THE RETINA, AND IT IS SURROUNDED BY A SMALL AREAS, THE MACULA LUTEA OR YELLOW SPOT. WHICH ALTHOUGH NOT SO SENSITIVE, ITS MORE SENSITIVE THAN OTHER PARTS OF THE RETINA

AT THE OPTIC DISC THE FIBERS OF THE NERVE-FIBER LAYER PASS INTO THE OPTIC NERVE

THE LENS IS A BICONVEX MASS OF PECULIARLY DIFFERENTIATED EPITHELIUM, IT IS SURROUNDED BY A HYALINE MEMBRANE, THE LENS CAPSULE, IT IS HELD IN PLACE BY THE SUSPENSORY LIGAMENT OR ZONULES OF ZINNI CONSISTS BUNDLE OF STRANDS WHICH PASS FROM THE SURFACE OF THE CILLIARY BODY TO THE CAPSULE

THERE IS A TRIANGULAR SPACE BETWEEN THE BACK OF THE IRIS AND THE ANTERIOR SURFACE OF THE LENS AND ITS BOUNDED ON THE OUTER SIDE BY THE CILLIARY BODY - CALLED - THE POSTERIOR CHAMBER AND CONTAINS AQUEOUS HUMOR

BEHIND THE LENS THERE IS LARGE VITREUS CHAMBER CONTAINING THE VITREUS HUMOR, A JELLY LIKE MATERIAL, CHEMICALLY OF THE NATURE OF INNERT GEL CONTAINING A FEW CELLS AND WANDERING LEUCOCYTES

THE EXTRA OCULAR MUSCLES

A TEAM OF SIX MUSCLES CONTROLS THE MOVE-MENT OF EACH EYE• THE RECTUS MUSCLE

- THE MEDIAL RECTUS- THE LATERAL RECTUS- THE SUPERIOR RECTUS- THE INFERIOR RECTUS

• THE OBLIQUE MUSCLE- THE SUPERIOR OBLIQUE- THE INFERIOR OBLIQUE

THE RECTUS MUSCLES HAVE THE GENERAL ACTION OF ROTATING THE EYE IN FOUR CARDINAL DIRECTIONS : UP, DOWN, OUT AND IN

THE OBLIQUE MUSCLES HAVE THE PRIMARY FUNCTION OF ROTATION OF THE GLOBE

THE MEDIAL RECTUS IS INSERTED INTO THE SCLERA, ABOUT 5 MM TO THE NASAL SIDE OF THE CORNEO-SCLERAL MARGIN.

THE INFERIOR RECTUS 6 MM BELOW

THE LATERAL RECTUS 7 MM TO THE TEMPORAL SIDE

THE SUPERIOR RECTUS 8 MM ABOVE

THE LIDS

THE LIDS ARE COVERED ANTERIORLY BY SKIN ANDPOSTERIORLY BY MUCOUSMEMBRANE - THE CON-JUNGTIVA TARSI. THEYCONTAIN MUSCLES,GLANDS, BLOOD VESSELS,AND NERVES. ALL BOUNDTOGETHER BY CONNECTIVE TISSUE WHICH IS PARTI-CULARY DENSE AT THEPOSTERIOR PART WHERE IT FORMS A STIFF PLATE - THE TARSUS

THE SKIN OF THE LIDS IS PECULIAR IN ITS THINNES AND ITS LOOSE ATTACH-MENT

THE CILIA OR EYELASHES ARE STRONG SHORT CURVED HAIRS, ARRANGED IN TWO OR MORE CLOSELY SET ROWS

THE SEBACEOUS GLANDS ARE CALLED ZEISS’S GLANDS AND THE SWEAT GLANDS ARE KNOWN AS MOLL’S GLANDS

THE TARSUS CONSISTS OF DENSE FIBROUS TISSUE; IT CONTAINS NO CARTILAGE, EMBEDDED IN IT ARE SOME ENORMOUSLY DEVELOPED SEBACEOUS GLAND : THE MEIBOMIAN GLANDS

THE ORBICULARIS PALPEBARUM OCCUPIES THE SPACE BETWEEN THE TARSUS AND THE SKIN

THE MAIN CENTRAL BOND OF THE LEVATOR PALPEBRAE SUPERIORIS IS INSERTED INTO THE UPPER BORDER OF THE TARSUS

THE THIRD NERVE SUPPLIES THE LEVATOR PALPEBRAE

THE SEVENTH SUPPLIES THE ORBICULARIS

THE LACRIMAL APPARATUS

THE LACRIMAL APPARATUS CONSISTS OF•THE LACRIMAL GLANDS•THE LACRIMAL PASSAGES

THE LACRIMAL GLAND OF EACH EYE CONSISTS OF :

• THE SUPERIOR OR ORBITAL GLAND• THE INFERIOR OR PALPEBRAE GLAND• THE ACCESSORY LACRIMAL GLANDS OR KRAUSE’S GLANDS

THE LACRIMAL PASSAGES CONSISTS OF :

• THE LACRIMAL PUNCTA• THE CANALICULI• THE LACRIMAL SAC• THE NASAL DUCT

PHYSIOLOGY OF THE EYE

BLOOD - AQUEOUS BARRIER The System of semipermeable membranes separating the blood from the ocular cavity

IN THE IN THE POSTERIOR POSTERIOR SEGMENTSEGMENT

IT IS FORMED BY THE WALLS OF THE RETINAL CAPILLARIES AND BY BRUCH’S MEMBRANE AND THE RE- TINAL EPITHELIUM

IN THE CILLIARY IN THE CILLIARY REGIONREGION

IT IS FORMED BY THE TWO-LAYERED CILLIARY EPITHELIUM

IN THE IRISIN THE IRIS

BY THE WALL OF THE CAPILLARIES IN THIS TISSUE WHICH ARE FREELY EXPOSED TO THE ANTERIOR CHAMBER

THE PECULIAR IMPERMEABILITY OF THE RETINAL CAPILLARIES AND THE BRUCH’S MEMBRANE PIGMENT EPITHELIAL BARRIER, WHILE NECESSARY FROM OPTICAL POINT OF VIEW, FORBIDS THE READY PASSAGE OF LARGE SIZE MOLECULES INTO THE EYE

SUCH THERAPEUTIC SUBSTANCES AS PENICILLIN WHEN ADMINISTERED SYSTEMICALLY HAVE LITTLE VALUE IN OCULAR THERAPEUTICS

SUBSTANCES WITH A HIGH LIPOID-SOLUBILITY WHICH EASLY PENETRATE LIVING CELLS, TRANSVERSE THE BARRIER MUCH MORE RAPIDLY (SULPHONAMIDES, CHLORAMPHE-NICOL, ETC)

THE INCREASE IN PERMEABILITY MAY BE BROUGHT BY INFLAMMATORY CONDITIONS, SUCH AS IRIDOCYCLITIS OR CHOROIDITIS, AND ALSO IF THE CAPILLARY WALLS ARE MECHANICALLY STRETCHED BY SUDDENLY LOWERING THE INTRA OCULAR PRESSURE

SUCH A TWO-WAY TRANSVERENCE OF FLIUD ACROSS THE CAPILLARY WALLS WOULD TEND TO STAGNATION

TO IT IS ADDED A SECRETORY PROCESS CONDUCTED BY THE METABOLIC ACTIVITY OF THE CELLS OF THE CILLIARY EPITHELLIUM.

95 % OF TOTAL QUANTITY OF AQUEOS

CIRCULATION OF THE CIRCULATION OF THE AQUEOUS HUMORAQUEOUS HUMOR

AS THE GREATER PART OF FLUIDS IS FORMED IN THE CILLIARY REGION, IT IS SECRETED INTO POSTERIOR CHAMBER, IT FLOWS FROM THE POSTERIOR CHAMBER THROUGH THE PUPIL INTO THE ANTERIOR CHAMBER AND ESCAPES THROUGH THE DARINAGE CHANNELS AT THE ANGLE, AND THEN INTO THE EPISCLERAL VEIN

THE INTRA OCULAR THE INTRA OCULAR PRESSURE (IOP)PRESSURE (IOP)

PROLONGED CHANGES ARE ESSENTIALLY CAUSED BY TWO FACTORS : • AN ALTERATION IN THE FORCES

DETERMINING THE FORMATION OF THE AQUEOUS

• ALTERATIONS IN THE RESISTANCE TO ITS OUTFLOW

FROM THE CLINICAL POINT OF VIEW, THE LATTER IS THE MORE IMPORTANT

A RISE IN THE IOP MAY BE CAUSED BY AN INCREASE IN THE PRESSURE IN THE EPISCLERAL VEIN OR BY ANY PROCESS WHICH BLOCKS THE SEEPAGE OF AQUEOUS INTO THE CANAL OF SCHLEMM, SUCH AS SCLEROSIS OF THE TRABECULAE OR THEIR OBSTRUCTION BY EXUDATES OR ORGANIZED TISSUE GLAUCOMA

THE PRINCIPAL FACTORS THE PRINCIPAL FACTORS DETERMINING PROLONGED DETERMINING PROLONGED

CHANGES IN THE IOPCHANGES IN THE IOP

1. VARIATION IN THE HIDROSTATIC PRESSURE IN THE CAPILLARIES

2. AN INCREASE IN PERMEABILITY OF THE CAPILLARIES3. A CHANGE IN OSMOTIC PRESSURE OF THE BLOOD4. VOLUMETRIC CHANGES5. A BLOCKAGE IN CIRCULATION OF THE AQUEOUS

a. AT THE PUPILb. AT THE ANGLE OF THE ANTERIOR CHAMBER

THE IOP NORMALLY THE IOP NORMALLY VARIES FROM 10 TO VARIES FROM 10 TO 20 MM HG20 MM HG

•IT IS ACCURATELY MEASURED BY A MANOMETER•CLINICALLY BY TONOMETRY

THE IOP PRESSURE