RANZCO Ophthalmic Sciences key terms

Distance from the anterior corneal surface to the fovea along the visual axis, measured by ultrasound or optical biometry. It is the strongest predictor of refractive error and a key input for intraocular lens power calculation.

Non-contact technique using partial coherence interferometry or low-coherence reflectometry to measure axial length and other ocular dimensions. It is more accurate and reproducible than applanation ultrasound and is standard before cataract surgery.

The refractive state in which parallel light rays from infinity focus exactly on the retina with the eye at rest. Such an eye needs no optical correction for distance vision.

A refractive error in which parallel rays focus in front of the retina, usually because the eye is too long or the cornea too steep. Distance vision is blurred while near vision is relatively preserved.

A refractive condition in which the eye's optical power differs between meridians, so a point object forms a line rather than a point image. It is commonly caused by toroidal corneal curvature and corrected with cylindrical lenses.

Active increase in the eye's refractive power achieved by ciliary muscle contraction, which relaxes zonules and allows the elastic crystalline lens to become more convex. It permits clear near vision and declines with age.

Age-related loss of accommodative amplitude caused by increasing lens stiffness and altered lens capsule elasticity. It typically becomes symptomatic in the fifth decade, requiring reading glasses or multifocal correction.

Interval, measured in seconds after a complete blink, until the first dry spot appears in the fluorescein-stained tear film. Shortened values indicate unstable tears and support a diagnosis of dry eye disease.

Chronic abnormality of the lid margin glands that supply the lipid layer of tears, producing obstructed or altered secretions. It causes evaporative dry eye, blepharitis, and tear film instability.

Inflammation of the eyelid margins, often involving the lash follicles and meibomian glands. It produces crusting, redness, irritation, and secondary tear film instability, and is usually chronic and bilateral.

Closure of the lacrimal punctum with a silicone plug or cautery to reduce tear drainage. It is used in moderate to severe dry eye to conserve the patient's own tears and topical medications.

Progressive non-inflammatory corneal ectasia with central or inferior thinning and conical protrusion. It causes irregular astigmatism, reduced vision, and characteristic topographical and slit-lamp signs.

Procedure combining riboflavin with ultraviolet-A light to create new chemical bonds within corneal collagen. It stiffens the cornea and slows or halts progression of keratoconus and other ectatic disorders.

Single layer of non-regenerating cells on the posterior corneal surface that actively pumps fluid out of the stroma. Loss of cell density causes stromal oedema and corneal decompensation.

Non-invasive imaging of the corneal endothelial mosaic using reflected light. It quantifies endothelial cell density, size variation, and morphology before surgery or in suspected endothelial disease.

Excess fluid within the corneal stroma that disrupts collagen spacing and causes haze, thickening, and halos. Common causes include endothelial failure, raised intraocular pressure, and intraocular surgery.

Spongy tissue at the anterior chamber angle through which aqueous humour drains into Schlemm canal. Increased outflow resistance here is the main mechanism of primary open-angle glaucoma.

Clear fluid produced by the ciliary epithelium that fills the anterior and posterior chambers. Its balanced secretion and drainage determine intraocular pressure and nourish avascular anterior segment structures.

Fluid pressure within the eye, normally between about 10 and 21 mmHg in adults. It reflects the balance between aqueous production and outflow and is the major modifiable risk factor for glaucoma.

Clinical examination of the anterior chamber angle using a mirrored or prismatic contact lens. It distinguishes open from closed angles and identifies peripheral anterior synechiae and angle neovascularisation.

Ocular condition in which apposition between the iris and trabecular meshwork obstructs aqueous outflow, often in eyes with a shallow anterior chamber. It may be asymptomatic or present acutely with pain and raised pressure.

Creation of a small hole in the peripheral iris with laser to equalise pressure between the posterior and anterior chambers. It relieves pupillary block and is used in angle closure and its prevention.

Enlargement and excavation of the central optic nerve head depression with thinning of the neuroretinal rim. Progressive cupping with corresponding field loss is characteristic of glaucomatous optic neuropathy.

Non-invasive imaging technique using low-coherence light interference to produce cross-sectional images of ocular tissue. It quantifies retinal layers, macular thickness, and peripapillary nerve fibre layer thickness.

Imaging of the retinal and choroidal circulation after intravenous fluorescein dye, capturing vessel filling and leakage. It identifies neovascularisation, capillary non-perfusion, and breakdown of the blood-retinal barrier.

Microvascular retinal disease caused by chronic hyperglycaemia, characterised by microaneurysms, haemorrhages, exudates, and capillary loss. Proliferative disease adds neovascularisation with risk of vitreous haemorrhage and tractional detachment.

Accumulation of fluid within the macula causing retinal thickening and distorted or reduced central vision. It arises from breakdown of the blood-retinal barrier in diabetes, vein occlusion, uveitis, and after surgery.

Abnormal proliferation of vessels from the choroid through Bruch membrane into the subretinal space. It leaks and bleeds, causing rapid central visual loss, most often in age-related macular degeneration.

Intravitreal injection of antibodies or fusion proteins that bind vascular endothelial growth factor. It reduces vascular permeability and neovascular growth in macular degeneration, diabetic retinopathy, and vein occlusion.

Separation of neurosensory retina from retinal pigment epithelium caused by a full-thickness retinal break allowing fluid into the subretinal space. It requires prompt surgical repair to prevent permanent visual loss.

Separation of the vitreous cortex from the internal limiting membrane, usually age-related. It commonly causes floaters and photopsia and may produce retinal tears or haemorrhage.

Asymmetric pupillary constriction when light is swung from one eye to the other, indicating reduced afferent conduction in the affected eye. It points to optic nerve or extensive retinal disease on that side.

Reflex constriction of both pupils to light, mediated by retinal ganglion cells, the optic nerve, chiasm, pretectal nuclei, and the Edinger-Westphal nucleus. It is tested to localise lesions in the afferent and efferent pathways.

Inflammation of the optic nerve, typically producing subacute unilateral visual loss, pain on eye movement, and impaired colour vision. It is strongly associated with demyelinating disease and often recovers spontaneously.

Bilateral optic disc swelling caused by raised intracranial pressure transmitted along the optic nerve sheath. It usually preserves central vision until late and demands urgent investigation for its cause.

Reduced best-corrected vision in one or both eyes caused by abnormal visual experience during the sensitive period, without structural abnormality. It results from strabismus, anisometropia, or deprivation and responds best to early treatment.

Misalignment of the visual axes so that the eyes are not simultaneously directed at the same object. It may be constant or intermittent, comitant or incomitant, and can cause diplopia or amblyopia.

Estimation of ocular deviation by observing the position of the corneal light reflection relative to the pupil centre. Each millimetre of displacement corresponds to roughly 15 prism dioptres of deviation.

Alternating occlusion of each eye while the patient fixates a target, used to detect manifest and latent deviation. Movement of the uncovered eye reveals the type and size of strabismus.

Patching or otherwise penalising the better-seeing eye to force use of the amblyopic eye. It is the mainstay of amblyopia treatment and is most effective during early childhood.