Retina | An Introduction | Part 1
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▬▬▬▬▬▬▬▬▬▬ Contents of this video ▬▬▬▬▬▬▬▬▬▬
(0:00-3:40)
Delicate membranous light-sensitive part of the eye, location in the eye ball;
Outermost protective layer= Sclera & Cornea.
Middle layer (Uveal Tract) = Choroid, Ciliary body & Iris.
Innermost layer= Retina; pigmented epithelium, Innermost Neuronal layer of Retina.
(3:41-9:30)
Exact location of Retina; sandwiched between Vitreous Body inside (Vitreous aspect of retina) and Choroid outside (Choroidal part of retina).
Ora Serrata; Wavy margins where light sensitive part of retina terminates anteriorly.
(9:35-13:20)
Through the Ophthalmoscope: Only posterior part of retina i.e., Optic Disc and part around it visible; Ocular Fundus.
Non-light sensitive part of retina; continuing beyond Ora Serrata.
(13:22-23:20)
Embryological Development of Eye: CNS development; Neural Tube; Optic Vesicle to Optic Cup; Outer and Inner layers differentiate into outer pigmented & inner neuronal retinal layers.
Retina, therefore is the only part of CNS visible through ophthalmoscope.
(23:25-29:10)
Fundoscopy: Posterior pole of fundus(yellowish) [Macula Lutea]; Optic Disc nasally/medially (pale colored).
Macula Lutea in detail: Has undefined margins, slight depressed area in center; Fovea Centralis.
(29:15-34:25)
Optic Disc in detail: Highly vascular (Central Retinal Artery coming out of it), Optic Disc; point of Retina from where all optic nerve fibers are moving out of retina through lamina cribrosa as Optic Nerve.
Technically Optic Nerve is a CNS tract and not a nerve per say.
(34:30-38:40)
Optic Disc continued: Central Retinal Artery, branches after passing through the Optic Disc & its Nasal & Temporal branches then supply inner parts of Retina.
Outer part of Retina supplied by Choriocapillaris.
(38:41-41:30)
Optic Disc continued; Central Retinal Artery (CRA) continued: Fovea Centralis (FC); the area of maximal visual acuity, depends only on Choriocapillaris for nutrition & not CRA, therefore NO Blood Vessels: Avascular.
Further comparison of Macula Lutea and Optic Disc.
(41:31-43:44)
Clinical Co-relate of Optic Disc (OD): Physiological Cup: Depression in OD; In Glaucoma when ICP is very high, this cup is pushed backwards; pathologically cupped/depressed. No rods & cones here so; Blind Spot.
Comparison continued: In Fovea Centralis (FC), cones are packed very tightly & blood vessels basically pushed aside to reveal FC; hence thinnest area of the retina; sharpest acuity.
(43:48-45:30)
Summary of comparison b/w OD & Macula Lutea (ML); 1- OD nasally situated, ML central but inferolateral to OD.
2-OD = 1.5mm, while ML = 5-6mm.
3-OD is pale, ML yellowish.
4- OD = Blood vessels coming in & out; highly vascular, while ML = Avascular.
5- OD is a blind spot while ML has point of maximal visual acuity.
6-OD has 'Physiological cupping' while ML has Fovea Centralis.
7-OD has sharper margins, while ML much diffused, undefined margins.
(45:31-51:00)
Blood supply of Fovea Centralis. Descriptive schematic diagram of OD, ML, Optic Nerves and Retinal Arteries, along with their positions in eyeball from above.
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