Anatomy Of Retina

ANATOMY OF RETINA


ANATOMY OF RETINA

  • Retina is the innermost tunic of eye.
  • Major component , clinically viewed as the fundus.
  • Retina extends from the optic disc to ora serrata & has a surface area of 266 mm2.
  • Retina is thickest at posterior pole in the peripapillary region (0.56 mm).
  • Thinnest at ora serrata (0.1mm).

Retina is divided into two distinct regions:

A) POSTERIOR POLE

  • It is the part of retina posterior to the retinal equator.
  • Examined most commonly by direct ophthalmoscopy.
  • When additional magnification or binocular vision is required, by slit lamp indirect biomicroscopy.

Posterior pole includes two distinct areas:-

1. Optic disc (optic nerve head)

  • Vertically oval area.
  • Average dimension of 1.76 mm horizontally & 1.88mm vertically.
  • The optic disc is placed 3-4 mm nasal to the fovea (fovea is temporal to optic disc).
  • There is a central depression in the optic disc called physiological cup.
  • Optic nerve head (optic disc) in a normal human eye carries 1-1.2 million neurons from the eye towards the brain.
  • Optic disc is also the entry point for the major BV’s (CRA & CRV) that supply the retina.
  • CRA & CRV emerge thriugh the physiological cup.

2. Macula lutea (Yellow spot)

  • Small yellowish area 5.5 mm in diameter.
  • Situated at the posterior pole of the eyeball , temporal to the optic disc.
  • Fovea centralis is the central depressed part of the macula & has a diameter of 1.5 mm.
  • It is situated about 2 disc diameter (3 mm) temporal to temporal margin of optic disc.
  • Most sensitive part of retina.
  • Lowest threshold for light & highest visual acquity  because it contains only cones.

Following parts are related to fovea centralis:

  1. Foveola:Forms the central floor of the fovea (0.35 mm in diameter)
  2. Umbo: Is a tiny depression in the very centre of foveola.
  3. Foveal avascular zone (FAZ): Located inside the fovea but outside the foveola.

B) PERIPHERAL RETINA

  • It is the area bounded posteriorly by the retinal equator & anteriorly by the ora serrata.
  • Peripheral retina is visualised by indirect ophthalmoscopy, or 
  • with more magnified view by use of Goldmann three mirror contact lens.

Nutrition & blood supply of Retina

  • Retina receives nutrition from two discrete circulatory system:-
  1. Retinal vascular system: Through central retinal artery.
  2. Choroidal vascular system: Anterior ciliary artery & posterior ciliary artery.

Exam Important

  • The junction between Retina & Ciliary body is Ora serrata.
  • The retina is an out growth of the Diencephalon.
  • Retina is part of CNS.
  • Broadest neuroretinal rim is seen in Inferior pole.
  • Macula lutea is the most sensitive part of retina.

Layers of the retina, from the outside inwards:

  1. Retinal Pigment Epithelium
  2. Layer of rods and cones
  3. External (Outer) limiting membrane
  4. Outer nuclear layer
  5. Outer plexiform layer
  6. Inner nuclear layer
  7. Inner plexiform layer
  8. Ganglion cell layer
  9. Layer of optic nerve fibres
  10. Internal (Inner) limiting membrane
  • Photosensitive layer of retina is Layers of rods and cones.
  • Visual axis of the eye meets the retina at a point which coincides with the fovea centralis.
  • The optical axis of the eye meets the retina at a point which is nasal to the fovea centralis.
  • Peripheral retina is visualised by indirect ophthalmoscopy.
  • The most common site of obstruction in central retinal artery is at the lamina cribrosa.
  • Normal A: V ratio of retinal blood vessels is 2 : 3.
  • Major retinal vessels are present in the nerve fibre layer.
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