OCANZ COE key terms

The sharpness of central vision, measured by identifying the smallest letters or symbols a person can resolve at a standard distance, usually recorded as a fraction such as 6/6 or 20/20.

A wall chart of letters arranged in rows of decreasing size, used to measure distance visual acuity. Each row is calibrated so a person with normal acuity reads it at a set distance.

A scoring scale where the logarithm of the minimum angle of resolution is recorded for each line. It gives evenly spaced, statistically analysable acuity values and is preferred in clinical research.

Any mismatch between the eye's focusing power and its length that prevents light from converging clearly on the retina, producing blurred vision unless corrected with lenses or surgery.

A refractive condition in which parallel light focuses in front of the retina, so distant objects appear blurred while near objects remain relatively clear. Usually caused by an eye that is too long or too powerful.

A refractive condition in which parallel light would focus behind the retina when the eye is unaccommodated. Young patients may compensate by accommodating, so distance vision can seem normal until effort fails.

A refractive error in which the eye's optical power differs across meridians, so light is focused as two lines rather than a point. It causes blurred or distorted vision at all distances.

The age-related loss of accommodative amplitude that makes near focusing difficult, typically noticed in the forties. It is managed with reading additions, multifocal lenses, or contact lens strategies.

The increase in the eye's optical power produced by contracting the ciliary muscle, which lets the crystalline lens become rounder so near objects stay in focus.

The maximum change in optical power the eye can achieve through accommodation, measured by pushing a near target toward the patient until it blurs. It declines steadily with age.

The positive lens power added to a distance correction to restore comfortable near vision, chosen from the patient's accommodative demand, working distance, and symptoms rather than age alone.

An objective technique in which the examiner sweeps a streak of light across the pupil and observes the reflex movement to estimate refractive error, especially useful when subjective responses are unreliable.

The process of refining a lens prescription using the patient's responses, typically with sphere, cylinder, and axis checks plus duochrome or Jackson cross-cylinder tests to confirm the endpoint.

A lens with equal and opposite cylinder powers at right angles, flipped in front of the eye to compare two meridians and refine the strength and axis of a correcting cylinder.

Refraction performed after paralysing the ciliary muscle with drops, removing accommodation so the true refractive error is revealed. It is standard in young children and in suspected accommodative excess.

Measurement of the curvature of the anterior cornea, giving radius and power in two principal meridians. It underpins contact lens fitting and helps detect irregular astigmatism such as keratoconus.

A mapping technique that records curvature or elevation across the whole cornea, producing colour maps that reveal irregularity, ectasia, or distortion not visible with central keratometry alone.

A progressive condition in which the cornea thins and steepens into a cone, causing increasing irregular astigmatism and reduced best-corrected acuity. Rigid lenses or cross-linking may be required.

The total area a person can see while the eye is fixed on a central point, including peripheral regions. Field testing detects patterns of loss caused by retinal, optic nerve, or brain disease.

The systematic measurement of visual sensitivity across the field, using static or kinetic targets. Modern automated tests compare each point with age-matched normal values to flag defects.

A group of optic neuropathies characterised by progressive loss of retinal ganglion cells and characteristic field defects, often but not always associated with raised intraocular pressure.

The fluid pressure inside the eye, maintained by the balance of aqueous production and outflow. It is measured by tonometry and is a major modifiable risk factor for glaucomatous damage.

The clinical measurement of intraocular pressure, commonly by applanation or non-contact methods. Correct technique and corneal thickness both influence the reading obtained.

Enlargement of the central pale depression of the optic nerve head relative to the disc rim. Progressive cupping, especially with rim thinning, suggests glaucomatous damage and needs monitoring.

Microvascular damage to the retina caused by diabetes, ranging from microaneurysms and haemorrhages to macular oedema and proliferative new vessels that threaten sight.

Fluid accumulation within the central retina that thickens the macula and blurs vision. It complicates diabetic retinopathy, vascular occlusion, and inflammation and is detected by imaging or slit-lamp inspection.

A non-invasive imaging method using low-coherence light to produce cross-sectional pictures of the retina and optic nerve, showing layer thickness and fluid that cannot be seen on clinical examination.

Inspection of the interior of the eye, including the retina, vessels, macula, and optic disc, using an ophthalmoscope or slit-lamp lens to detect disease and record baseline findings.

Reduced vision in one or both eyes caused by abnormal visual experience during development, such as strabismus or anisometropia, not explained by structural abnormality of the eye.

A misalignment of the eyes in which the visual axes do not point at the same object, classified by direction and by whether the deviation is constant or intermittent.

A significant difference in refractive error between the two eyes. It can cause unequal retinal images, poor binocular function, and amblyopia in children if left uncorrected.

A standard test of ocular alignment in which one eye is covered while the other fixates, and any movement on uncovering reveals a manifest or latent deviation.

The coordinated use of both eyes so that images from each are fused into a single percept with depth perception. It depends on alignment, similar image clarity, and intact fusion.

The perception of depth derived from small horizontal differences between the images received by the two eyes. It is tested with polarised or vectographic targets and requires good binocular function.

Treatment for amblyopia in which the better-seeing eye is patched or blurred to force use of the weaker eye. Dose is balanced against the risk of reverse amblyopia.

A structured slit-lamp assessment of the lids, conjunctiva, cornea, anterior chamber, iris, and lens, using magnification, illumination, and stains to detect and grade disease.

Examination of the eye using a magnifying microscope paired with an adjustable slit of light, allowing optical sectioning of tissue and the choice of direct, indirect, or retroillumination techniques.

Application of fluorescein dye, viewed under blue light, to reveal corneal epithelial defects, assess tear film stability, and check contact lens fit. It is a core clinical skill.

A handheld examination of the fundus giving an upright, magnified view of the optic disc, vessels, and macula. It is quick but provides a narrow field and no stereopsis.

A technique using a head-mounted or handheld light with a condensing lens to view an inverted, wider, stereoscopic image of the peripheral retina, valuable for detecting tears and detachment.

Instillation of a mydriatic drug to enlarge the pupil so the peripheral retina and optic nerve can be examined. Mydriasis is contraindicated in some angle-closure risks.

A clinical technique using a mirrored contact lens and topical anaesthetic to view the anterior chamber angle, essential for identifying angle closure and assessing outflow structures.