Retina class 7th semester

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  • 1. Dr.Narang Retina
  • 3. Gross Anatomy
    • Retina extends from the optic disc to the ora serrata.
    • It is divided into two distinct regions:
    • posterior pole and
    • peripheral retina separated by the so called retinal equator.
  • 4. Posterior pole
    • It refers to the area of the retina posterior to the retinal equator.
    • The posterior pole of the retina includes two distinct areas:
    • optic disc and
    • macula lutea
  • 5. Macula lutea .
    • It is also called the yellow spot .
    • It is comparatively deeper red than the surrounding fundus and is situated at the posterior pole temporal to the optic disc.
    • Fovea centralis is the central depressed part of the macula. It is about 1.5 mm in diameter and is the most sensitive part of the retina. In its Center is a shining pit called foveola .
    • An area about 0.8 mm in diameter (including foveola and some surrounding area) does not contain any retinal capillaries and is called foveal avascular zone (FAZ).
    • Surrounding the fovea are the parafoveal and perifoveal areas.
  • 6. Structure of fovea centralis
    • In this area, there are no rods.
    • Cones are tightly packed and other layers of retina are very thin.
    • Its central part (foveola) largely consists of cones and their nuclei covered by a thin internal limiting membrane.
    • All other retinal layers are absent in this region.
    • In the foveal region surrounding the foveola, the cone axons are arranged obliquely (Henle’s layer or outer plexiform layer) to reach the margin of the fovea.
  • 7. Fovea centralis
  • 8. Peripheral retina
    • It refers to the area bounded posteriorly by the retinal equator and anteriorly by the ora serrata.
  • 9. Optic disc
    • It is a pink coloured , well-defined circular area of 1.5-mm diameter.
    • At the optic disc all the retinal layers terminate except the nerve fibres, which pass through the lamina cribrosa to run into the optic nerve.
    • A depression seen in the disc is called the physiological cup . The central retinal artery and vein emerge through the centre of this cup.
  • 10.  
  • 12. Internal limiting membrane
    • It is the innermost layer and separates the retina from vitreous.
    • It is formed by the union of terminal expansions of the Muller’s fibres.
    • It is essentially a basement membrane.
  • 13. Nerve fibre layer (stratum opticum)
    • It consists of axons of the ganglion cells, running parallel to retinal surface.
    • The layers increase in depth as it converges to optic disc.
    • The nerve fibers are fine and non-medullated
    • It pass through the lamina cribrosa to form the optic nerve
  • 14. Ganglion cell layer
    • It mainly contains the cell bodies of ganglion cells (the second order neurons of visual pathway).
    • There are two types of ganglion cells:
    • - The midget ganglion -cells are present in the macular region. each such cell synapses with single bipolar cell.
    • - Polysynaptic ganglion - cells lie predominantly in peripheral retina .Each such cell may synapse with upto a hundred bipolar cells
  • 15. Inner plexiform layer
    • It essentially consists of connections of bipolar cells with the ganglion cells and amacrine cells.
  • 16. Inner nuclear layer
    • It mainly consists of nuclei of bipolar cells.
    • It also contains nuclei of amacrine and Muller’s cells
    • Capillaries of central artery of retina, but outer layers are avascular.
    • The bipolar cells constitute the first order neurons.
  • 17. Outer plexiform layer
    • The Innermost portion of each rod and cone cell is swollen with lateral processes known as spherules and pedicles respectively.
    • This layer consists of connections of rod spherules and cone pedicles with the dendrites of bipolar cells and horizontal cells.
  • 18. Outer nuclear layer
    • It consists of nuclei of the rods and cones.
    • Cone nuclei are larger and more oval and carry a layer of cytoplasm
  • 19. External limiting membrane
    • It is a fenestrated membrane, on which rods and cones rest and their processes pierce
  • 20. Photoreceptor layer
    • Rods and cones are the end organs of vision and are also known as photoreceptors .
    • Rods contain a photosensitive substance visual purple (rhodopsin) and subserve the peripheral vision and vision of low illumination ( scotopic vision).
    • Cones also contain a photosensitive substance and are primarily responsible for highly discriminatory central vision ( photopic vision ) and colour vision.
  • 21. Pigment epithelium.
    • It is the outermost layer of retina.
    • It consists of a single layer of cells containing pigment.
    • The cells of RPE contain varying amount of melanin.
    • Cells are taller at fovea and contain more pigment.
    • Around the Optic disc they are heaped up as ‘ choroidal ring ’
    • It is firmly adherent to the underlying basal lamina (Bruch’s membrane) of the choroid.
  • 22. Blood supply
    • Outer four layers of the retina- choroidal vessels
    • Inner six layers- central retinal artery, which is a branch of the ophthalmic artery.
  • 23. CRAO
    • C entral retinal artery emerges from centre of the physiological cup of the optic disc and divides into four branches.
    • These are end arteries i.e., they do not anastomose with each other.
  • 24. Predisposing factors:
    • Hypertension
    • Cardiovascular diseases
  • 25. Etiology
    • Thrombophilic disorders.
    • Emboli from the carotid artery and those of cardiac origin(20%)
    • Atherosclerosis-related thrombosis at the level of lamina cribrosa(75%).
    • Arteritis with obliteration.
    • Angiospasm
    • Raised intraocular pressure
  • 26. Symptoms :
    • Sudden,painless loss of vision.
    • Amaurosis fugax
  • 27. Sign’s
    • Red reflex absent.
    • Marked narrowing of large arteries, arterioles invisible.
    • Within few hours retina become milky white because of oedema.
    • Within a day or two macular area show cherry red spots because of choroid shining through thin retina.
    • When obstruction is incomplete, column of venous blood has cattle tract appearance.
    • After few weeks oedema subsides , atrophic changes occur(optic nerve atrophy/attenuated thread like arteries).
    • No PL/PR
  • 28. Treatment
    • Immediate lowering of IOP –massage /IV mannitol /A.C. paracentesis .
    • Vasodilator and inhalation of mixture of 5%CO2 and 95%O2.
    • Anticoagulants –IV heparin
    • IV steroids –giant cell arteritis
  • 29. Prognosis:
    • >6 hours –No return of central vision.
  • 30. CRVO
    • The retinal veins: These follow the pattern of the retinal arteries.
    • The central retinal vein drains into the cavernous sinus directly or through the superior ophthalmic vein
  • 31. Predisposing Factors
    • Age :6 th /7 th decade(2 nd decade in case of non ischaemic)
    • Systemic hypertension
    • Raised IOP
    • Diabetes
    • Hyperviscosity syndrome
    • Periphlebitis
  • 32. Pathogenesis
    • External compression on the vein
    • Venous stasis
    • Degenerative disease of venous endothelium
  • 33. Types:
    • Non Ischaemic/Venous stasis retinopathy/Partial CRVO=75%
    • Ishchaemic CRVO/haemorrhagic CRVO/Complete CRVO=25%
  • 34. Non Ischaemic Symptom:
    • Vague U/L fogginess of vision initially.
    • V/A remains good.
    • Vitreous hemorrhage never present
    • Mild pupillary defect
  • 35. Signs:
    • Mild tortuosity and dilatation of retinal veins.
    • Dot and blot and flame shaped haemorrhage.
    • Optic disc swelling
    • Macular oedema may or not- permanent impaired vision but normally 50% regain VA as Macular oedema resolves.
    • Circulating IgM raised in most,leading to phlebitis of central vein in optic head ,hence fundus picture resemble venous thrombosis
  • 36. Ischaemic CRVO Symptoms :
    • VA- marked reduced
  • 37. Signs
    • Marked tortuosity and engorged retinal veins.
    • Massive superficial and deep haemorrhages.
    • Cotton wool exudates.
    • Optic disc swelling and hyperaemia.
    • Macular oedema and haemorrhage.
    • Bunches of tortuous new vessels formed upon optic disc.
    • Eventual atrophy of affected retina.
    • Fundus described as BLOOD AND THUNDER FUNDUS
    • Obstruction of central vein just behind lamina cribrosa ,peripheral at bifurcation as in arterisclerotic
  • 38. Prognosis:
    • 50% develop rubeosis and neovascular glaucoma within 3 months of initial occlusion aka 90 days glaucoma.
    • Pre-retinal or vitreous haemorrhage secondary to NVD
  • 39. Management
    • It is usually not required.
    • The condition resolves with almost normal vision in about 50 percent cases.
    • Visual loss in rest of the cases is due to chronic cystoid macular oedema, for which no treatment is effective.
    • However, a course of oral steroids for 8-12 weeks may be effective.
    • Patient should be followed up closely for rubeosis iridis, as prompt treatment in early cases by PRP.