ophthalmology

• Conjunctivitis, also known as pink eye, is an inflammation of the conjunctiva that can cause redness, itching, and discharge.
• Embryology:

  • The eye ball is developed from the primary optic vesicle formed by neural groove and mesoderm and ectoderm
• Position:

  • The eyeball lies in a quadrilateral pyramid-shaped bony orbital cavity situated on either side of the root of the nose
  • It is suspended by extraocular muscles and protected by adipose tissue
• Diameter:

  • At birth, the axial length is 17.5 mm and reaches ± 24 mm in adults
  • Horizontal diameter is 23.5 mm and vertical diameter is 23 mm
• Blood and nerve supply:

  • Blood supply is from the ophthalmic artery with drainage through the ophthalmic vein
  • Innervation is through the ophthalmic division of the trigeminal nerve
• The adnexa:

  • Consists of eyelids and lacrimal apparatus
  • The upper lid is longer, covers 2/3 of the palpebral fissure, and has long lashes
  • The lower lid is shorter, covers 1/3 of the palpebral fissure, and has shorter lashes
  • Lacrimal apparatus consists of the lacrimal gland, 2 punctums, lacrimal canaliculi, lacrimal sac, and nasolacrimal duct
• Eye globe layers:

  • Refractive layer: cornea, anterior chamber, lens, vitreous, retina
  • Uveal tissue layer: iris, ciliary body, choroid
  • Connective tissue layer: sclera
• Cornea:

  • The outermost 1/6 coat of the eye
  • Convex transparent lens with anterior and posterior surfaces
  • Axial length is 500-600 micrometers, vertical diameter is 10.5 mm, horizontal diameter is 11 mm
  • Has 42 ± dioptric power and 5 layers
• Anterior chamber:

  • 2-3 mm depth, filled with aqueous humor between the cornea and the iris
  • Low refractivity produced by the ciliary body
  • Contains 95% water with other components like glucose and proteins
  • Aqueous humor passes through the iridocorneal angle
• Lens:

  • Biconvex transparent lens between the iris and vitreous body
  • Axial length is 3.5-4 mm, dioptric power is ± 17
  • Composed of epithelial cells with a central nucleus and palpebral cortex
  • Covered by a semi-permeable elastic membrane and suspended by ligaments called "zonule of Zinn"
• Vitreous:

  • Jelly-like material filling the vitreous chamber
  • Axial length is 11 mm, attached to the lens and the retina
  • Contains 95% water and a loose framework of collagenous fibrous with protein
• Retina:

  • Consists of 10 layers formed by three layers of nerve cells and their synapses, visual cells, bipolar cells, ganglion cells, and the axons forming the optic nerve
  • Landmarks include the optic nerve, macula with central depression named fovea, and ora serrata in the anterior area
• Uveal tissue:

  • Circular diaphragm richly supplied with blood vessels and a central aperture named pupil
  • Iris composed of stroma containing branched connective tissue cells, pigmented epithelium layers, and muscles sphincter and dilator pupillae
  • Ciliary body has a ciliary muscle and two layers of pigment epithelium with a rich blood supply
• Choroid:

  • Extremely vascular membrane in contact with sclera externally and the retina internally
  • Stroma with branched pigmented connective tissue cells
• Sclera:

  • The outermost layer covering 5/6 of the eyeball up to the optic nerve
  • Consists of dense fibrous tissue forming the skeleton of the eye
  • Covered by a mucous conjunctival membrane from the limbus reflecting the lids, forming palpebral and bulbar conjunctiva
• • Contains the accessory lacrimal glands and the goblet cell
• Anatomy of the conjunctiva:

  • The conjunctiva is a thin mucous membrane lining the posterior surface of the lid, from which is reflected on the anterior aspect of the eyeball as far as the limbus
  • Divided into:
  • The palpebral conjunctiva: lines the under surface of the eyelids and extends to the fornix
  • The fornix conjunctiva: formed by the reflection of the palpebral conjunctiva onto the anterior portion of the eyeball
  • The bulbar conjunctiva: covers the anterior portion of the eyeball until the corneo-scleral junction (limbus)
• Subconjunctival haemorrhage:

  • Bleeding from the conjunctival vessels usually takes the form of extravasation of blood into the subconjunctival tissue
  • Usually symptomless
  • Causes include trauma, acute inflammation of the conjunctiva, spontaneous rupture of a weak vessel in old people, increased intra-abdominal pressure, local manifestation of systemic vascular diseases, blood disorders, and idiopathic
  • No treatment needed as the blood takes 2-4 weeks to absorb
• • Oedema of the conjunctiva (chemosis) may occur in acute inflammation, obstruction to the orbital circulation, or abnormal blood conditions
  • Membrane and pseudomembrane formation, papillary hypertrophy, follicle formation, scar formation, corneal infiltration, and lymphadenopathy
• Inflammation of the conjunctiva (conjunctivitis):

  • Clinical features for diagnosis include type of conjunctival discharge, type of conjunctival reaction, and lymphadenopathy
  • Type of conjunctival discharge:
  • Watery discharge: viral conjunctivitis
  • Mucoid or mucopurulent discharge: bacterial conjunctivitis
  • Purulent discharge: gonococcal infection and other virulent micro-organisms
  • Blood-stained discharge: diphtheric conjunctivitis
  • Type of conjunctival reaction:
  • Redness of the conjunctiva, most intense at the fornices and fading towards the limbus
• Trachoma:

  • Chronic inflammation of the conjunctiva and cornea caused by Chlamydia trachomatis
  • Symptoms include foreign body sensation, mucopurulent discharge, and itching
  • WHO classification includes Trachoma follicle (TF), Trachoma intense (TI), Trachoma scarring (TS), Trachoma trichiasis (TT), and Corneal opacity (CO)
  • Risk factors (5 F's): Flies, Fomites, Fingers, Faces, and Feaces
  • Treatment involves the SAFE strategy: Surgery, Antibiotic treatment, Facial cleanliness, and Environmental changes
• Vernal keratoconjunctivitis (spring catarrh):

  • Chronic recurrent allergic seasonal conjunctivitis
  • Aetiology involves exogenous allergens and physical factors
  • Symptoms include itching, photophobia, lacrimation, discolouration of the conjunctiva, and ropy discharge
  • Treatment includes dark glasses, cold compresses, local antihistamine and mast cell stabilizer, and local steroids
• Phlyctenular conjunctivitis:

  • Acute nodular affection of the conjunctiva commonly at the limbus
  • Mainly occurs in children as an allergic response to endogenous toxins
  • Symptoms include irritation, photophobia, blepharospasm, and lacrimation
  • Treatment involves local application of steroids and local antibiotics if there is a secondary bacterial infection
• Pterygium:

  • Triangular fold of the conjunctiva invading the cornea
  • Symptoms include no symptoms when small, but may cause irritation when larger
  • Treatment involves medical treatment with NSAIDs, and surgical removal for symptomatic, large, or cosmetic pterygium
• Pinguecula:

  • Common, innocuous, bilateral, asymptomatic condition
  • Usually seen in elderly people exposed to sunlight, dust, and wind
  • Signs include a yellowish triangular patch of bulbar conjunctiva near the limbus
  • Treatment is usually unnecessary as growth is slow