ICO Clinical Ophthalmology (Advanced) key terms

A visual acuity scale in which each line of the chart represents an equal 0.1 log unit step, so scores can be averaged and compared statistically. Lower values indicate better vision; 0.0 equals 6/6.

A notation expressing vision as the distance at which a patient reads a line relative to the distance a normal observer would read it, such as 6/12. Lines are not evenly spaced, limiting statistical use.

The resolving power of the eye, measured as the smallest detail that can be identified at a standard distance under specified lighting and contrast conditions, with best spectacle correction in place.

A quick assessment using a small aperture that narrows the effective pupil, reducing blur from uncorrected refractive error. Improvement suggests refractive cause; no improvement suggests media, retinal, or neural disease.

An asymmetric pupillary response detected with the swinging flashlight test, where the affected pupil dilates when light moves from the healthy eye to it. It indicates unilateral or asymmetric optic nerve or extensive retinal dysfunction.

A bedside technique alternating light between eyes to compare the direct pupillary response. A pupil that dilates rather than constricts when illuminated indicates reduced afferent input from that eye.

A screening method in which the examiner compares the patient's peripheral detection of a moving target with their own, tested one eye at a time. It detects gross field loss but is insensitive to subtle defects.

An automated static perimetry test measuring threshold sensitivity at fixed grid locations, summarized by mean deviation and pattern standard deviation. It is used to detect and monitor glaucoma and neuro-ophthalmic field loss.

A region of reduced or absent sensitivity within the field of vision. Patterns such as altitudinal, hemianopic, or arcuate loss help localize damage along the visual pathway.

Examination using a stereoscopic microscope with an adjustable slit beam to illuminate and magnify anterior segment structures layer by layer, allowing assessment of depth, cells, flare, and corneal integrity.

Findings on slit-lamp examination indicating intraocular inflammation: cells are leukocytes suspended in aqueous, while flare is light scatter from increased protein. Both are graded and used to monitor uveitis activity.

A technique using a mirrored or prismatic contact lens to view the anterior chamber angle, which is otherwise hidden by total internal reflection. It distinguishes open from closed angles and identifies synechiae or neovascularization.

The pressure within the eye, determined mainly by aqueous humor production and outflow resistance. Measured in millimetres of mercury, it is a major modifiable risk factor for glaucoma but is not diagnostic alone.

The reference method for measuring intraocular pressure, using a calibrated force to flatten a fixed area of cornea. Accuracy depends on central corneal thickness and is affected by corneal curvature and rigidity.

The thickness of the cornea at its centre, typically around 540 micrometres. Thicker corneas cause applanation tonometry to overestimate pressure and thinner corneas to underestimate it.

A non-invasive imaging technique using low-coherence interferometry to produce cross-sectional images of the retina, optic nerve, and anterior segment at near-histological resolution, quantifying layer thickness and detecting fluid.

An extension of OCT that detects motion of red blood cells to image retinal and choroidal vasculature without dye injection, showing capillary non-perfusion and abnormal new vessels.

A dye-based imaging test in which intravenous fluorescein is photographed as it passes through retinal and choroidal vessels, revealing leakage, staining, non-perfusion, and neovascularization by their temporal filling patterns.

Examination of the fundus using a condensing lens held at arm's length with a head-mounted light, producing an inverted, magnified view with a wide field that is essential for detecting retinal tears and detachments.

A technique during indirect ophthalmoscopy in which a depressor pushes the sclera inward to bring the peripheral retina, ora serrata, and pars plana into view, revealing anterior tears and lattice degeneration.

A mismatch between the eye's optical power and its axial length so that images of distant objects are not focused on the retina, causing blurred vision correctable by lenses or surgery.

A refractive state in which parallel rays focus in front of the retina, giving clear near but blurred distance vision. Axial elongation raises the risk of retinal detachment, myopic maculopathy, and glaucoma.

A refractive condition in which the cornea or lens has unequal curvature in different meridians, so light is focused at two different planes and vision is blurred at all distances without cylindrical correction.

A progressive non-inflammatory corneal ectasia causing thinning and conical protrusion, producing irregular astigmatism and reduced best-corrected acuity. Corneal topography and tomography are central to diagnosis and monitoring.

Mapping of corneal surface curvature and elevation using reflected rings or scanning slit and Scheimpflug imaging, used to detect ectasia, irregular astigmatism, and to fit contact lenses.

Opacification of the crystalline lens that reduces light transmission and increases scatter, causing progressive painless visual loss, glare, and altered colour perception. Surgery is the only definitive treatment.

Cataract surgery using ultrasound energy delivered through a small corneal incision to emulsify and aspirate the lens nucleus, followed by implantation of an intraocular lens in the capsular bag.

A common late complication of cataract surgery in which residual lens epithelial cells proliferate and migrate across the posterior capsule, causing glare and reduced acuity. It is treated with neodymium-YAG laser capsulotomy.

A group of optic neuropathies characterized by progressive retinal ganglion cell loss and characteristic optic disc cupping with corresponding field defects. Raised intraocular pressure is the main treatable risk factor.

A form of glaucoma in which the iris obstructs the trabecular meshwork, obstructing aqueous outflow and causing acute or chronic pressure rise. Acute attacks present with pain, haloes, and a fixed mid-dilated pupil.

Microvascular retinal disease from chronic hyperglycaemia, classified as non-proliferative or proliferative. Features include microaneurysms, haemorrhages, exudates, macular oedema, and neovascularization.

Fluid accumulation within the macula from breakdown of the blood-retinal barrier, causing central visual loss. It complicates diabetic retinopathy, vein occlusion, and uveitis and is detected by OCT as intraretinal cysts.

Separation of the neurosensory retina from the retinal pigment epithelium, causing painless field loss that may progress to involve the macula. Rhegmatogenous cases arise from a retinal break with vitreous fluid ingress.

Degeneration of the macula in older adults, divided into dry atrophic and wet neovascular forms. Wet disease causes sudden distortion and haemorrhage and is treated with intravitreal anti-VEGF injections.

A printed grid used for home monitoring of central vision in macular disease. Patients report distortion, missing areas, or lines appearing wavy, which may signal new or recurrent choroidal neovascularization.

Inflammation of the uveal tract, classified by anatomical site as anterior, intermediate, posterior, or panuveitis. It causes pain, photophobia, cells and flare, and may lead to synechiae and vision loss.

Damage to the optic nerve from ischaemic, inflammatory, compressive, or toxic causes, producing reduced acuity, colour desaturation, field loss, and an afferent pupillary defect when unilateral.

Misalignment of the visual axes so the eyes are not simultaneously directed at the same object, described by direction, comitance, and whether it is constant or intermittent. It may cause amblyopia in children.

Reduced best-corrected acuity in one or both eyes caused by abnormal visual experience during the sensitive period, such as strabismus, anisometropia, or deprivation. It is treatable if detected early.

A method of detecting manifest and latent strabismus by alternately covering each eye and observing the uncovered eye's movement. Recovery movement on uncovering reveals a heterophoria.