## Embryology
<ul>
 <li>Day 25: optic vesicle formed by lateral out-pouching of the diencephalon</li>
 <ul>
 <li>Proximal constricted part: optic stalk</li>
 <li>Dilated distal part: optic cup</li>
 </ul>
 <li>Week 4-5: optic cup and stalk form choroidal fissure</li>
 <li>
 Week 5: edges of the choroidal fissure close: cup first, then stalk, from forebrain to cup
 direction.&nbsp;
 </li>
 <li>
 Thickened inner portion of the optic vesicle is known as the retinal disk:{' '}
 future neural retina
 </li>
 <ul>
 <li>Outer nuclear zone: mitosis is maximal here, completed by week 15</li>
 <li>Inner marginal zone: once mitosis completes differentiation occurs here</li>
 <li>
 Inner and outer neuroblastic layers are formed from the above by week 7, separated by the
 transient layer of Chievitz
 </li>
 <li>Inner neuroblastic layer forms ganglion cells, Muller cells and amacrine cells</li>
 <li>Outer neuroblastic layer forms bipolar cells, horizontal cells, rod and cone nuclei</li>
 <li>Photoreceptors derived from cilia in the outer nuclear/neuroblastic layer</li>
 <li>Lamination completes by 4.5 months and ora serrata formed by 6 months.</li>
 </ul>
 <li>
 Week 3: thinner outer portion of the vesicle contains pseudostratified columnar cells with
 pigment granules: future RPE
 </li>
 <ul>
 <li>The cilia disappear as melanogenesis begins</li>
 </ul>
 <li>
 These two layers are continuous at the optic cup margin (future iris and CB)
 </li>
 <li>
 The opposing surfaces of these layers is initially ciliated: the outer portion (RPE) cilia
 degenerate but the inner portion cilia contribute to photoreceptor formation (as above)
 </li>
 <li>
 4-5 months: maculogenesis: localised increase in ganglion cell density at the
 posterior pole
 </li>
 <ul>
 <li>8-9 layers of ganglion cell nuclei at month 6</li>
 <li>Peripheral displacement of ganglion cells due to axonal elongation at month 7</li>
 <li>Foveal cones increase in length and decrease in width (and increase density)</li>
 </ul>
</ul>
<HotTopic>
 
 Foveal cones are not fully developed at birth hence newborns have imperfect central fixation
 
</HotTopic>
<ul>
 <li>
 At birth: single layer of ganglion cells remain as internal nuclear layer over macular cones
 </li>
 <li>
 At 4 months of life: these ganglion cells are displaced to leave central cones
 &lsquo;uncovered&rsquo;
 </li>
</ul>

## Retinal perfusion
<ul>
 <li>Retinal vessels supply (high oxygen exchange, low flow: 25mm/s):</li>
 <ul>
 <li>Nerve fibre layer</li>
 <li>Ganglion cell layer</li>
 <li>Inner plexiform layer</li>
 <li>Inner third of the inner nuclear layer</li>
 </ul>
 <li>Choroid vasculature supplies (low oxygen exchange, high flow: 150mm/s):</li>
 <ul>
 <li>Outer two thirds of the inner nuclear layer&nbsp;</li>
 <li>Outer plexiform layer</li>
 <li>Outer nuclear layer</li>
 <li>Photoreceptors</li>
 <li>RPE</li>
 </ul>
</ul>
<HotTopic>
 
 15% of people have a cilioretinal artery supplying the macular region. 30% have a cilioretinal
 artery supplying some portion of the retina. Note these are branches of the choroidal vessels
 hence they are spared in CRAO
 
</HotTopic>
<ul>
 <li>Retinal capillaries are surrounded by</li>
 <ul>
 <li>Astrocyte foot processes</li>
 <li>Contractile pericytes</li>
 <li>Thick basal lamina</li>
 </ul>
 <li>
 Retinal blood flow in the central retinal artery is autoregulated (same for iris and ciliary
 body perfusion) so does not vary with changing perfusion pressures (ie. is constant between
 ocular perfusion pressures of 45-145mmHg)
 </li>
 <ul>
 <li>Responsive to hyperoxia (vasoconstriction) and hypercapnia (vasodilation)</li>
 <li>Responsive to eicosanoids and nitric oxide</li>
 </ul>
</ul>
<Note className="mb-4">
 
 The retinal arterioles have no internal elastic lamina and the smooth muscle
 outer layer is lost near the entrance to the retina. Therefore there is no autoregulation in the
 retinal vasculature itself.
 
</Note>
<ClinicalCorrelate>
 
 Branch retinal veins occlusions occur at arteriovenous crossings especially where the vein lies
 more posterior to the artery. The superotemporal quadrant is most often affected because there
 are more crossings here
 
</ClinicalCorrelate>

Embryology Day 25: optic vesicle formed by lateral out-pouching of the diencephalon Proximal constricted part: optic stalk Dilated distal part: optic cup…

Posterior segment

Retinal Macrostructure

Intro

FRCOphth Part 1 Study Notes

Orbit and ocular adnexae

Orbit

Extraocular Muscles

Orbital Blood Vessels

Paranasal Sinuses

Lacrimal Glands

Tear Film

Eyelids

Blinking

Anterior segment - ocular surface

Conjunctiva

Conjunctivitis

Sclera

Cornea

Corneal Structure And Development

Corneal Physiology

AC to Lens

Angle

Ciliary Body

Aqueous Humour Dynamics

Iris

Pupil

Lens

Choroid

Vitreous

Neurosensory Retina

Retinal Pigment Epithelium

Neuroanatomy

Venous Sinuses

Cerebral Ventricles

Cerebral Blood Supply

Supranuclear Gaze Pathways

Head And Neck Autonomic Nervous Supply

Head And Neck Glands

Osteology

Nerves

Muscles And Pharyngeal Arches

Extraocular Nerves

Sensory Nerves

Physiology

Physics Of Blood Flow

Neuronal Control Of Blood Vessels

Oxygen-Haemoglobin Dissociation Curve

Cytochrome p450

Pituitary Gland

Thyroid Hormone Production

Insulin

Glucagon

Parathyroid Hormone

Corticosteroids

Catecholamines

Cardiac Cycle

Renal Physiology

Fluid Balance

Acid-Base Balance

Muscle Physiology

Sensory Fibres

Cutaneous Receptors

Endocytosis

Glycosaminoglycans

Condensed Ocular Biochemistry

Eye Movements

Accomodation

Vision

Visual Cycle And Phototransuction

Visual Pathway

Visual Acuity

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Collagen

Tissue Damage

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Thrombosis / Atherosclerosis

Cell Growth

Neoplasia

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Immunology

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Protozoa

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Genetics

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Mitosis

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Genes

Polypeptide Synthesis

Histones

MicroRNA

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Mutations

Chromosome Defects

Autosomal Inheritance

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