## Parasites
<ul>
 <li>Divided into subkingdoms</li>
 <ul>
 <li>Metazoa (see below)</li>
 <li>Protozoa: unicellular organisms</li>
 </ul>
</ul>

## Acanthamoeba
<ul>
 <li>Free-living, ubiquitous protozoan</li>
 <li>
 Single celled eukaryotic microorganism and &ldquo;amoeba&rdquo;: motile eukaryotes that alter
 their shape and crawl using pseudopods
 </li>
 <li>A. castellani and A. polyphaga are the most common subtypes</li>
 <li>
 Associated with contact lens wear, ocular trauma and exposure to high levels of protozoa in
 water supplies (soil, air, swimming pools, hot tubs, tap water)
 </li>
 <li>Biphasic life cycle</li>
 <ul>
 <li>
 Active trophozoite: during this phase, ingests bacteria and fungi. These can replicate within
 the acanthamoeba and be released within the cornea as &ldquo;trojan horses&rdquo; (eg.
 Legionella, Pseudomonas, mycobacteria, chlamydia).
 </li>
 <li>
 Inert dormant cyst form. Extremely resistant to environmental agents and the immune
 system.&nbsp;
 </li>
 <ul>
 <li>Survives chlorinated water.</li>
 </ul>
 <li>The organism can convert between these states eg. convert to a cyst when under duress</li>
 </ul>
 <li>Virulence factors</li>
 <ul>
 <li>Mannose-binding protein</li>
 <li>Mannose-induced protein which has collagenase and cytopathic activity</li>
 </ul>
 <li>Attaches to epithelial surface&nbsp;</li>
 <li>Collagenases cause stromal changes</li>
 <li>Clinical features</li>
 <ul>
 <li>Presents with classic symptoms of infectious keratitis</li>
 <li>Protracted clinical course and failed therapy&nbsp;</li>
 <li>
 Initial findings may be non-specific: punctate epithelial erosions, pseudodendrites, mild
 conjunctival injection
 </li>
 <li>Ring infiltrates</li>
 <li>Perineural infiltrates (radial keratoneuritis)</li>
 <li>Progressive corneal thinning and perforation</li>
 <li>Corneal neovascularisation is rare despite the chronicity of the infection</li>
 </ul>
 <li>Diagnosis</li>
 <ul>
 <li>Visualisation with in-vivo confocal microscopy: spindle shaped trophozoites</li>
 </ul>
</ul>
<HotTopic>
 
 Acanthomoeba can be cultured on non-nutrient agar 
 with a lawn of killed E.coli for food
 
</HotTopic>
<ul>
 <li>Charcoal yeast agar</li>
 <li>PCR: sensitivity and specificity of 90%</li>
 <li>
 Corneal scrapes stained with: acridine Orange, calcofluor white, PAS, wright-giemsa,
 Wheatley-trichrome
 </li>
 <li>Corneal biopsy</li>
</ul>
<ul>
 <li>Management:&nbsp;</li>
 <ul>
 <li>
 Topical chlorhexidine (a biguanide which disrupt DNA) and a diamidine which disrupt cell
 membranes (propamidine isetionate eg. Brolene or hexamidine)
 </li>
 <li>Polyhexamethylene biguanide can also be considered (PHMB)</li>
 <li>Econazole&nbsp;</li>
 <li>Additional cover with broad spectrum antibiotics</li>
 </ul>
</ul>

## Toxoplasmosis (Toxoplasma gondii)
<ul>
 <li>Obligate intracellular protozoan</li>
 <li>Most common cause of infectious retinochoroiditis worldwide</li>
</ul>
<HotTopic>
 Causes up to 50% of posterior uveitis in some countries
</HotTopic>
<ul>
 <li>
 Mammals eg. farm animals and pets: cats are the definitive hosts as they support the sexual
 stage of the parasite in their intestinal epithelium
 </li>
 <ul>
 <li>Oocysts are excreted in faeces and spore in soil</li>
 <li>Eggs become infective after ingestion by intermediate host eg. humans</li>
 </ul>
 <li>Transmission occurs via</li>
 <ul>
 <li>Ingesting food contaminated with cat faeces</li>
 <li>Undercooked meat</li>
 <li>
 Maternal transmission especially if infected during the third trimester (however disease is
 more severe if infection occurs in first trimester)
 </li>
 <li>NB: only antibody-negative mothers are at risk of vertical transmission</li>
 </ul>
 <li>
 Toxo proteins activate toll-like receptors on monocytes and dendritic cells to produce IL-2 and
 an indirect T cell response
 </li>
 <li>The conoid facilitates cell penetration</li>
 <li>In the cell, the microbe resides in a vacuole resistant to lysosomal destruction</li>
 <li>
 The parasite survives best in cerebral neurons hence the brain and retina are the predominantly
 affected tissues
 </li>
 <li>Uveal and retinal inflammation</li>
 <ul>
 <li>Uveitis: usually self-limiting in immunocompetent patients</li>
 <li>
 Retinochoroiditis (can replicate in Muller cells and RPE): the retina is affected in
 preference to the choroid due to its lower immunoglobulin levels
 </li>
 </ul>
</ul>

Parasites Divided into subkingdoms Metazoa (see below) Protozoa: unicellular organisms Acanthamoeba Free-living, ubiquitous protozoan Single celled…

Microbiology

Protozoa

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

Posterior segment

Choroid

Vitreous

Retinal Macrostructure

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

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

Viral Infections

Bacterial Infections

Fungal Infections

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