RANZCO Ophthalmic Sciences flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Snell's law

n1 sin i = n2 sin r, where n1 and n2 are refractive indices of the two media and i and r are the angles of incidence and refraction measured from the normal.

Thin lens power

The power of a thin lens in dioptres equals 1/f, where f is the focal length in metres; a shorter focal length corresponds to a higher power.

Aqueous outflow pathway

Aqueous humour flows from the anterior chamber through the trabecular meshwork into Schlemm canal, then collector channels and episcleral veins; obstruction raises intraocular pressure.

Phototransduction cascade

Light isomerises 11-cis-retinal to all-trans-retinal, activating rhodopsin and transducin, reducing cGMP, closing cation channels, and hyperpolarising the photoreceptor.

Apoptosis versus necrosis

Apoptosis is ATP-dependent, caspase-mediated, and non-inflammatory; necrosis involves membrane rupture, cell swelling, and inflammation.

Topical drop bioavailability

Only about 1-5% of a topically applied eye drop reaches intraocular tissues; punctal occlusion reduces nasolacrimal drainage and systemic absorption.

Relative afferent pupillary defect

A relative afferent pupillary defect is detected with the swinging flashlight test and indicates asymmetric optic nerve or severe retinal dysfunction.

Optic neuritis features

Optic neuritis causes painful subacute monocular visual loss, reduced colour vision, a relative afferent pupillary defect, and often a swollen optic disc; it is associated with multiple sclerosis.

Bitemporal hemianopia

Bitemporal hemianopia is loss of both temporal visual fields and localises to the optic chiasm, often from a pituitary lesion compressing the crossing nasal fibres.

Horner syndrome

Horner syndrome consists of ptosis, miosis, and anhidrosis from sympathetic pathway interruption; postganglionic lesions may cause ipsilateral facial flushing.

Third nerve palsy

A pupil-involving third nerve palsy suggests a compressive lesion such as a posterior communicating artery aneurysm; a pupil-sparing palsy is more often microvascular.

Papilloedema

Papilloedema is bilateral optic disc swelling caused by raised intracranial pressure; it is usually painless and may cause transient visual obscurations.

Cover-uncover test

The cover-uncover test detects heterotropia by observing the uncovered eye's movement; the alternate cover test detects heterophoria and the total deviation.

Esotropia and exotropia

Esotropia is inward deviation of the eye and exotropia is outward deviation; hypertropia is upward deviation of one eye.

Amblyopia causes

Amblyopia results from visual deprivation, strabismus, or anisometropia during the critical period and is treated with refractive correction, occlusion, or atropine penalisation.

Extraocular muscle innervation

The oculomotor nerve supplies the medial rectus, inferior rectus, superior rectus, and inferior oblique; the trochlear supplies the superior oblique and the abducens the lateral rectus.

Incomitant strabismus

In paralytic strabismus the deviation varies with direction of gaze and is greatest in the field of action of the paretic muscle, a pattern called incomitance.

Bacterial keratitis

Bacterial keratitis presents with a corneal infiltrate, often a hypopyon, and risk factors include contact lens wear and trauma; urgent scrapings and fortified antibiotics are indicated.

Acanthamoeba keratitis

Acanthamoeba keratitis occurs in contact lens wearers with water exposure, causes severe pain and a ring infiltrate, and is diagnosed by culture on non-nutrient agar with Escherichia coli.

Dendritic ulcer

A dendritic corneal ulcer with terminal bulbs indicates herpes simplex keratitis; topical corticosteroids are contraindicated during epithelial disease.

Keratoconus

Keratoconus is progressive corneal thinning and ectasia causing irregular astigmatism; management includes rigid gas-permeable lenses and corneal collagen cross-linking.

Acute angle-closure glaucoma

Acute angle-closure glaucoma causes severe pain, halos, nausea, and a mid-dilated fixed pupil; treatment is pressure-lowering medication followed by laser peripheral iridotomy.

Glaucomatous optic disc cupping

Glaucomatous cupping shows an increased cup-to-disc ratio, neuroretinal rim thinning, and sometimes disc haemorrhage, reflecting progressive optic nerve damage.

Prostaglandin analogues

Prostaglandin analogues lower intraocular pressure by increasing uveoscleral outflow and can cause iris darkening, eyelash lengthening, and periorbital skin pigmentation.

Open-angle glaucoma risk factors

Primary open-angle glaucoma risk factors include age, African ancestry, family history, elevated intraocular pressure, myopia, and thin central corneal thickness.

Cherry-red spot

A cherry-red spot appears when retinal pallor surrounds the preserved fovea, classically in central retinal artery occlusion, and is accompanied by sudden painless visual loss.

Retinal detachment

Rhegmatogenous retinal detachment occurs when a retinal break allows vitreous fluid to separate the neurosensory retina from the retinal pigment epithelium.

Diabetic retinopathy signs

Non-proliferative diabetic retinopathy shows microaneurysms, dot-blot haemorrhages, hard exudates, and cotton-wool spots; proliferative disease shows neovascularisation.

Orbital cellulitis

Orbital cellulitis causes proptosis, pain, restricted eye movement, and fever; it is an emergency requiring intravenous antibiotics and imaging, unlike preseptal cellulitis.

Basal cell carcinoma

Basal cell carcinoma is the most common eyelid malignancy; it is locally invasive, rarely metastasises, and is treated by complete surgical excision.

Leukocoria

Leukocoria is a white pupillary reflex requiring urgent evaluation for retinoblastoma, congenital cataract, and other causes of visual axis opacity.

Retinopathy of prematurity screening

Retinopathy of prematurity screening is indicated for infants with birth weight under 1500 g or gestational age under 32 weeks, with examinations starting a few weeks after birth.