<ul>
 <li>Single layer of cuboidal epithelial cells</li>
 <li>Outermost retinal layer</li>
 <ul>
 <li>Between the choriocapillaris and the photoreceptor outer segments</li>
 </ul>
 <li>4-6 million RPE cells per eye</li>
 <li>45:1 photoreceptors:RPE</li>
 <li>
 Embryologically from the same tissue as the neural retina but differentiates into a secretory
 epithelium
 </li>
 <li>Cell bases face Bruchs, apices face neurosensory retina</li>
 <li>Long microvillous processes interdigitate with the photoreceptor outer segments</li>
</ul>
<HotTopic>
 
 Tight junctions between cells at the apical side contribute to the{' '}
 blood retinal barrier
 
</HotTopic>
<ul>
 <li>Numerous melanin granules to absorb light</li>
 <li>RPE cells are more flattened in the periphery than in the centre</li>
</ul>

## Biochemistry
<ul>
 <li>RPE contain enzymes for all 3 major energy producing pathways</li>
 <ul>
 <li>Glycolysis</li>
 <li>Kreb&rsquo;s</li>
 <li>Pentose-phosphate pathway</li>
 </ul>
 <li>80% water</li>
 <li>The Na/K ATPase is located on the apical surface (unique)</li>
 <ul>
 <li>Maintains the ionic balance in the subretinal space</li>
 </ul>
</ul>
<ClinicalCorrelate>
 
 A transepithelial electrical potential exists across the RPE apical membrane and can be measured
 using the EOG.
 
</ClinicalCorrelate>
<ul>
 <li>
 RNA is constantly synthesised for the production of enzymes for metabolism, phagocytosis of shed
 outer segment discs, maintenance of the retinoid cycle and transport
 </li>
</ul>

## Function
<ul>
 <li>Metabolic</li>
 <ul>
 <li>Regeneration of visual pigment</li>
 <ul>
 <li>RPE stores high concentrations of vitamin A</li>
 <ul>
 <li>Recycles vitamin A after rhodopsin bleaching</li>
 <li>Uptake from the circulation</li>
 <li>From phagocytosed discs releasing vitamin A</li>
 </ul>
 <li>Generates 11-cis-retinaldehyde, which forms rhodopsin</li>
 <li>
 Converts retinol (product of the visual cycle) to a retinyl ester and then to 11-cis-retinol
 and finally back to 11-cis-retinal. This is returned to the photoreceptors by
 interphotoreceptor retinoid-binding protein (IRBP)
 </li>
 </ul>
 <li>
 Disposal/phagocytosis/detoxification of waste products and shed discs from the visual cycle
 </li>
 <ul>
 <li>Shed discs enter the cell in phagosome and fuse with lysosomes</li>
 <li>Disc components are recycled</li>
 <li>Each RPE disposes of more than 4000 discs per day</li>
 <li>Rod phagocytosis peaks just after light exposure</li>
 <li>Cone phagocytosis is more random and occurs at the onset of darkness</li>
 </ul>
 <li>Transports nutrients to the photoreceptors</li>
 </ul>
 <li>Physical/structural&nbsp;</li>
 <ul>
 <li>Maintenance of adhesion between the retinal layers</li>
 <ul>
 <li>Hydrostatic forces</li>
 <li>Interdigitation of the outer segments by RPE microvilli</li>
 <li>Active transport of subretinal fluid/water via ocular dipole</li>
 <li>Maintenance/synthesis of the IPM</li>
 </ul>
 <li>Maintenance of the blood-retinal barrier</li>
 <li>Embryogenesis of photoreceptors</li>
 </ul>
 <li>Optical</li>
 <ul>
 <li>Absorption of scattered light</li>
 <ul>
 <li>Pigment granules are numerous within the RPE cytoplasm</li>
 <li>
 Triggering of melanogenesis is the key step in the embryological differentiation of the
 neuroectoderm into RPE
 </li>
 <li>
 There is age-related fusion of melanin granules with lysosomes so that older RPE is less
 pigmented
 </li>
 </ul>
 </ul>
</ul>

## Melanin
<ul>
 <li>Derived from tyrosine (itself from phenylalanine)</li>
 <ul>
 <li>Rate determining step is the conversion of tyrosine to dopa by tyrosine hydroxylase</li>
 <li>Dopa is then converted by a non-enzymatic reaction</li>
 </ul>
 <li>Anti-oxidant properties and contains stable free radicals</li>
 <ul>
 <li>Effective free radical scavenger in the RPE which it protects&nbsp;</li>
 </ul>
 <li>Melanin is lost with age: may contribute to ARMD</li>
</ul>

## RPE pathology
<ul>
 <li>Sorsby fundus dystrophy</li>
 <li>Autosomal recessive retinitis pigmentosa</li>
 <li>Vitelliform macular degeneration (Best disease)</li>
 <li>Malattia leventinese (dominant drusen)</li>
 <li>ARMD</li>
 <li>Stargardt disease</li>
</ul>

Posterior segment

Retinal Pigment Epithelium

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

Retinal Macrostructure

Neurosensory Retina

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

Colour Vision

Binocular Vision

Pathology

Collagen

Tissue Damage

Inflammation

Disease Entities

Wound Healing

Thrombosis / Atherosclerosis

Cell Growth

Neoplasia

Histopathology

Nystagmus

Free Radicals And Antioxidants

Immunology

Ocular Immunology

Microbiology

Viral Infections

Bacterial Infections

Fungal Infections

Protozoa

Nematodes

Antimicrobials

Genetics

Chromosomes

Mitosis

Meiosis

Genes

Polypeptide Synthesis

Histones

MicroRNA

Hardy-Weinberg Equilibrium

Mutations

Chromosome Defects

Autosomal Inheritance

X-Linked Inheritance

Mitochondrial Inheritance

Multifactorial Inheritance