Ophthalmology Flashcards
External Anatomy of the Eye
• Average length 24mm; Discrepancies in length lead to Refractory Errors
• Cornea – 78% refractive power; Highly Innervated, Avascular
o Layers of the Cornea – Epithelium, Bowman’s Membrane, Stroma, Descemet’s
Membrane, Endothelium (Responsible for maintaining clarity by continuously
pumping fluid out of tissue; Disruption leads to Corneal Oedema and Blurred vision)
• Sclera – White opaque structure, covers 4/5ths of globe, continuous with Cornea at Limbus;
Attachment of six extraocular muscles and perforation of Optic nerve
• Conjunctiva – Anterior surface of the Sclera; Richly vascularised, innervated mucous
membrane; Stretched from Limbus, over Anterior Sclera (= Bulbar Conjunctiva) and reflected onto undersurface of eyelids (Tarsal Conjunctiva)
Internal Anatomy of the Eye
• Anterior Segment comprises Anterior (In front of Iris) and Posterior Chambers (Behind Iris)
• The Uveal Tract comprises Iris anteriorly, Ciliary Body and Choroid
o Aqueous Humour is produced by Ciliary Body at 2Ul/min; ULN pressure 21mmHg
o Aqueous Humour provides nutrients and oxygen for the avascular Cornea
• The Lens – Immediately posterior to pupil; 22% of refractive power; Anterior to Vitreous
humour; Transparent, Biconvex structure; Shape starts to decline by fourth decade, becomes
less transparent and develop cataracts
• Contraction of Ciliary muscles relaxes Suspensory Ligaments, Increasing the Refractive Power
of the Lens (for Accommodation)
• Three Layers – Retinal (Neural), Choroid (Vascular) and Sclera (Fibrous)
• Macula and Fovea Centralis – Recession of Choroid layer and lack of overlying vessels; Point
of highest Visual Acuity and concentration of Cone cells for Colour vision
• Optic Disc – CN II; Accounts for visual blind spot
Neurovascular Supply
• Ophthalmic Artery – Divides into Central Retinal Artery to supply inner retinal layers; Venous
return through Central Retinal/Ophthalmic Veins; LN Drainage to Preauricular and Submental
• Sensory innervation through Trigeminal (CN V1) Ophthalmic br
Refractive Error
Abnormalities of focusing mechanism of the eye;
Myopic or Hyper-metropic
o Myopia is usually inherited, discovered in
childhood; Progresses throughout teenage
years when body is growing
o Hypermetropia also inherited
Astigmatism
Refractory error which there is a different degree of refraction in different meridians of curvature (i.e. Defect in another plane)
Presbyopia
Normal ageing of the lens resulting in
change in refractory state; Lens less able to alter
curvature, resulting in difficulties in near-vision
Keratoconus
Non-inflammatory Degenerative disorder resulting in Cornea thinning and
change into Conical shape; Unknown Aetiology
Treatment of Refractory Errors
• Spectacles (Negative Lenses for Myopia, Positive Lenses for Hypermetropia) or Contact lenses
(better quality vision but risk of infection)
• Surgical Techniques – Excimer laser to reprofile Corneal Curvature (e.g. PRK. LASIK, LASEK);
Either removal of Central Corneal tissue to flatten in Myopia, or steepen in Hypermetropia
Eyelids
Eyelids protect the eyes and help distribute tear over front surface of globe; Excess tears
drained by Punctae and Lacrimal System
Entropion
Lid margin rolls inwards, causing lashes to be against globe, causing irritation
o Can mimic conjunctivitis; Occasionally constant rubbing leads to Corneal Abrasion
o Commonly due to ageing; Surgery is usually required
Ectropion
Lid margin rolls outwards, no apposition to globe; Puncta are in poor position to
drain tears, patient complains of watery eye; RF: Age, CN VII Palsy, Skin conditions; Surgery usually required for repair
Dacryocystitis
Inflammation of Lacrimal Sac; Tender lump on medial side (Nasal) adjacent to
lower eyelid; Oral Broad-spectrum Abx and watched carefully for signs of Cellulitis
o Referred to Ophthalmology – Mucocoele or dilated sac requiring surgical repair
Blepharitis
Inflammation of Lid Margins ± Lashes and Follicles;
Results in Stye (= Hordeolum, Inflammation/Blockage of Meibomian
gland); Itchy, burning eyes (Tear Film instability)
o Commonly due to Meibomian gland dysfunction,
Seborrhoea, S aureus (Frequently responsible for Chronic
Blepharo-conjunctivitis
o Lid Hygiene, Short course Topical Chloramphenicol or
Fusidic acid; If Acne Rosacea suspected, Oral Doxycycline required
o Chalazion – Residual cystic lump; Requires Incision/Curettage for cosmesis
Conjunctivitis
• Commonest cause for Red Eye (=Pink Eye); Can arise from Viral, Bacterial and Allergic causes
commonly; Soreness, Redness, Discharge without disruption to Visual Acuity
• Hx – Speed of onset, Colour and Consistency of discharge, Recent Hx Cold or Sore Throat; In
Neonate important to exclude Gonococcal or Chlamydial conjunctivitis
Conjunctivitis Red Flags
Severe pain, Photophobia, Sudden Visual Acuity loss, Coloured Halos, Proptosis,
Smaller Pupil in affected eye, High IOP, Keratitis, Shallow Anterior Chamber depth
Bacterial Conjunctivitis
• 5% of cases; Sore and Gritty eye in presence of good vision; Invariably bilateral, suspected
with purulent discharge
o Gonococcal – Rapid onset, copious discharge, ocular inflammation includes
Conjunctival Oedema (Chemosis) and Lid Oedema; Palpable preauricular LN
▪ Gram Stain of Conjunctival Swab – Presence of Gram -ve Diplococci
o Less acute Purulent Conjunctivitis with moderate discharge – HiB, S pneumo
• Chronic Conjunctivitis – Mild injection with scanty discharge; S aureus and Moraxella
• Oral and Topical Penicillin for Gonococcal to reduce rate of Corneal Perforation
• Topic Broad-Spectrum (E.g. Chloramphenicol) for other causes
Chlamydial Conjunctivitis
• C trachomatis; Direct or indirect contact with genital secretions; Shared eye cosmetics
o Trachoma – Same organism but usually not sexually transmitted; Tropics and Middle
East; Common cause of blindness in the world; Chronic inflammation leads to
Progressive Scarring, Trichiasis, Entropion and Corneal Scarring; Blindness from
Opacification or Ulceration
• Slow onset; Scanty mucopurulent discharge in some; Preauricular LN
o In Neonates – 2/52 onset (C/f Gonococcal, which occurs within days); Swabs taken
and NAAT performed to confirm before starting treatment
• Topical Erythromycin BD; Referral to GUM; Neonates referred to Paediatrician; Assoc with
Otitis Media or Pneumonitis
Viral Conjunctivitis: Adenovirus
Highly Contagious, Epidemics; Direct or Indirect contact; May have prodromal
symptoms; Inflammation associated with Chemosis, Lid Oedema and Palpable Preauricular LN
o Some develop membrane on Tarsal conjunctiva, and Haemorrhage on Bulbar
o Can cause deterioration in visual acuity due to focal Corneal Inflammation
o Self-limiting, Eye Lubricants, Cold Compress, Strict Hygiene; Topical steroids for
Inflammation or Corneal Involvement
Viral Conjunctivitis: HSV
Typically unilateral; Palpable Preauricular LN, Cutaneous Eyelid Vesicles; 50% develop
Dendritic Corneal Ulcers; Typically, self-limiting; Topical Aciclovir to reduce risk of Corneal
Epithelial involvement
Phthiriasis Palpebrarum
Infestation with Phthirus pubis (crab lice); Leads to Blepharitis with marked Conjunctival
Inflammation, Preauricular LN, and rarely secondary infections
• Mechanical removal with fine forceps, Physostigmine 1.25%, and Pilocarpine 4% gel