Retina Anatomy and Biochemistry PDF

EPISCLERITIS AND RETINAL ANATOMY AND BIOCHEMISTRY EPISCLERETIS Episcleretis is an inflammation of the episclera ,a thin layer of vascular layer of connective tissues that lies between the conjunctiva and the sclera Episcleretis is a benign recurrent inflammation involving inflammation of...

EPISCLERITIS AND RETINAL ANATOMY AND BIOCHEMISTRY EPISCLERETIS Episcleretis is an inflammation of the episclera ,a thin layer of vascular layer of connective tissues that lies between the conjunctiva and the sclera Episcleretis is a benign recurrent inflammation involving inflammation of the Tenon's capsule but not the underlying sclera Most affects young adults female than male EPISCLERITIS ETIOLOGY Not yet known Found in association with gout and psoariasis Has been considered hypersensitivity reaction to endogenous tubecular Congestion of overlaying of Tenon's capsule and conjunctiva SYMPTOMS OF EPISCLERETIS Redness Blurred vision thou its less common but can happen in some cases Mild ocular discomfort described as gritty , burning ,foreign sensation Many a times ,not accomplained by Any discomfort Photophobia and lacrimation may occurs  PATHOLOGY There occurs localised lymphocytic infiltration of episcleral tissues associated, associated with oedema Also congestion of overlaying of Tenon's capsule and conjunctiva  Signs Examinations, two clinical types of episcleral are diffuse and nodular Episclera is seen acutely inflamed in the involved area In diffuse episcleritis the whole eye may be involved to some extent.Maximum inflammation is confined to one or two quadrants In nodular episcleritis a pink or purple nodule surrounded by injection is seen, usually situated 2-3mm away from the limbus SIGNS Nodule is a firm ,tender and the overlying conjunctiva moves freely Clinical course ; episcleritis runs a limited course of 10 days resolving spontaneously Recurrence are common and tend to occur in bouts..A fleeting type of disease (episcleritis periodical may occurs) May be confused with inflamed pinguela swelling, congestion due to foreign body lodged in bulbar conjunctiva and very rarely with scleritis  RETINAL ANATOMY Retina is a thin delicate transparent membrane that is the innermost tunic of the eye back -It is a highly developed tissues of the eye appears purplish red because of virtual of the rods and vascular choroid -Retina extends from the optic disc to the ora setta, grossly it is into 2 distinct regions which is the posterior pole and peripheral retina separated by the retina -Retinal equator is an imaginary which is considered to lie in line with the exit of the four vena verticose -posterior pole refers to the area of the retina posterior to the retinal equator.The posterior pole of the retina includes distinct area ,the optic disc and macula lutea. -It can be examined slit lamp indirect biomicroscopy using +78D and +90D lens and direct ophthalmoscope  Optic disk is a pink coloured defined area of 1.5mm diameter.At the optic disk ,all the retinal layers expect the nerve fibres which pass through the lamina cribosa to run into the optic nerve A depression seen in a disc called physiological cup The central retinary artery and vein emerge through the centre of this cup Macula lutea ,is called yellow spot.It is comparatively deeper red than the surrounding fundus is situated at the posterior pole temporal to the optic disk about 5 ,5 mm in diameter It is most sensitive part of the retina,in it's centre is a shining pit is called the fovea 0.35mm diameter which is situated 3mm from temporal margin MICROSCOPIC STRUCTURE Pigmented epithelium Outer most layer of the retina,consists of a single layer of cell containing pigment firmly adherent to underlying basal lamina(Brunch membrane of the choroid Plays important role in photoreceptor renewal and recycling of vitamin A Probably RPE cells have phagocytic action Provides mechanical support to the processes of photoreceptors They manufacture pigment which presumably has an optical function in absorbing light  LAYER OF RODS AND CONES Rods and cones are the end organs of the vision are also photoreceptors.Layers of rods and cones contains only the outer segments of the photoreceptors cells arranged in a palisade manner There are 120 million rods and6.5 million conea..Rods contains a photosensitive substance visual purple rhodopsina and subserve the peripheral vision. Cones also contain are photosensitive substance and are primarily responsible for highly discrimination central vision.Photopoc vision and color vision  MICROSCOPIC STRUCTURE 3.External limiting membrane-it is a fenestrated membrane through which pass processes of the rods and cornea 4.outer nuclear layer it consists of the nuclei of rods and cones 5..Inner nuclear layer,it mainly consists of cells bodies of bipolar bodies of bipolar cells also contains cell bodies  6.Inner plexiform layer consists of connection between the axons of bipolar cells and dendrite of the ganglion cells and processes of amacrine cells This layer disappears at fovea and in rest of retina consists of bipolar ,horizontal, amacrine , the soma of the muller’s cells and capillaries of the central retinal vessels 7.Ganglion cell layer ,mainly contains the cell bodies of ganglion cells(the second order neurons of visual pathway)..There are 2 types of ganglion cells are present in the macula region and the dendrite of each such as cell synapses with the axon of single bipolar cells.The midget ganglion are present in.macular region and the dendrite of each such a synapses with the axons of single bipolar cells  8.Nerve fibre layer consists of axons of the ganglion which pass through the lamina cribosa to form optic nerve 9.Interal limiting membrane ,it is the innermost layer and separates the retina from vitreous..It is formed by the union of terminal expansions of the Mullet fibres and to essentially basement INTERNAL LIMITING MEMBRANE It consist of PAS positive true basement membrane that forms the interface between retina and vitreous Consist of collagen fibrils , proteoglycans of the vitreous , the basement membrane and the plasma membrane of the Muller cells and possibly other glial cells off the retina STRUCTURE OF FOVEAL CENTRALLS There are no rods , cones are tightly packed and the other layer of the retina are very thin.Central part (foveola) largely consists of cones covered by a thin internal limiting membrane All other retinal layer are absent in this region.In the foveal region surrounding of foveola ;the cone axons are arranged obliquely (henle layer) to reach the margin of the fovea FUNCTIONS DIVISIONS OF RETINA -divided into temporal retina and nasall by a line drawn vertically through the centre of fovea Nerve fibres arising from the temporal retina pass through the optic nerve and optic tract of the same side to terminate in the geniculate body while the nerve fibres originating from the nasal retina after passing through the optic nerve cross in the optic chiasma and travel through optic tract to terminate in the contralateral geniculate  BLOOD SUPPLY -outer four layers of the retina pigment epithelium,layer of rods and cones,external limiting membrane and outer nuclear layer to get their nutrition from the choroidal vessels -Inner six layers get their supply from the central retinal artery ,which is a branch of opthalmic artery  Central retinary artery energy from the centre physiological cup of the optic disk and divides into 4 branches namelythe superior nasal, superior temporal,, inferior nasal and inferior temporal.These are end arteries. Retinal veins ,these follow the pattern of retinal arteries.The central retinal veins drain into cavernous sinus directly or through the superior opthalmic vein BIOCHEMISTRY OF THE RETINA The retina’s biochemistry involves light detection, signal transduction, energy metabolism, and protection from oxidative damage. The following sections outline the key biochemical processes: -Phototransduction is the process by which photoreceptor cells (rods and cones) convert light into an electrical signal. PHOTO TRANSDUCTION Rhodopsin and Cone Opsins: Photoreceptors contain visual pigments: rhodopsin (in rods) and cone opsins (in cones). Rhodopsin consists of opsin (a transmembrane protein) and 11-cis-retinal (a chromophore derived from vitamin A). 1. Light Activation: Light converts 11-cis-retinal to all-trans-retinal, causing a conformational change in rhodopsin. 2. Signal Amplification: Activated rhodopsin stimulates transducin, a G-protein.  Activated rhodopsin stimulates transducin, a G-protein. 3. cGMP Reduction: Transducin activates phosphodiesterase (PDE), which hydrolyzes cyclic GMP (cGMP). cGMP levels decrease, leading to closure of cGMP-gated sodium channels. 4. Membrane Hyperpolarization: Closure of sodium channels hyperpolarizes the photoreceptor, reducing neurotransmitter release and initiating a neural signal. VISUAL PATHWAY The visual cycle regenerates 11-cis-retinal for continuous photoreceptor function. 1. Release of All-Trans-Retinal: After phototransduction, all-trans-retinal is reduced to all-trans-retinol. 2. Transport to the RPE: All-trans-retinol is transported to the retinal pigment epithelium (RPE).  3. Isomerization: RPE enzymes, particularly RPE65, convert all-trans-retinol back to 11- cis-retinol, then to 11-cis-retinal. 4. Recycling to Photoreceptors: 11-cis-retinal is transported back to photoreceptors to recombine with opsins. ENERGY METABOLISM Energy Metabolism The retina has one of the highest energy demands of any tissue. Glycolysis and Oxidative Phosphorylation: Despite sufficient oxygen supply, the retina relies heavily on aerobic glycolysis (Warburg effect). Mitochondria in the inner retina also perform oxidative phosphorylation for ATP production. GLUCOSE SUPPLY Glucose Supply: Glucose is transported into the retina by GLUT1 transporters in the blood-retina barrier. The pentose phosphate pathway (PPP) is active, providing NADPH for antioxidant defense. NEUROTRANSMITTERS 4. Neurotransmitters in the Retina Neurotransmitters mediate signal transmission between retinal neurons. Glutamate: Released by photoreceptors and bipolar cells. Acts as the primary excitatory neurotransmitter. Inhibitory Neurotransmitters: GABA and glycine are released by horizontal and amacrine cells, modulating signal flow.