EBOD key terms

The single spherical power that best approximates a spherocylindrical refractive error, calculated as the sphere plus half the cylinder; it is used to compare refractive outcomes and to summarise astigmatic corrections.

The age-related loss of accommodative amplitude caused by increasing stiffness of the crystalline lens, producing blurred near vision that usually becomes symptomatic in the mid-forties and is managed with reading additions or multifocal options.

Computerised mapping of corneal curvature and elevation across the entire surface, used to detect irregular astigmatism such as keratoconus and to plan refractive surgery, contact lens fitting and corneal grafting.

Excimer laser refractive surgery in which surface corneal tissue is ablated after the epithelium is removed, leaving no flap; recovery is slower and early discomfort greater than with flap-based techniques.

A progressive non-inflammatory ectasia in which the cornea thins and steepens into a cone, producing irregular astigmatism and reduced vision, with risks of acute hydrops and the need for corneal grafting.

Repeated episodes of corneal epithelial breakdown, often after a previous abrasion or in basement membrane dystrophy, causing waking pain and photophobia with loose, non-adherent epithelium on examination.

The interval in seconds between a complete blink and the first dry spot appearing in fluorescein-stained tears; a short interval indicates tear film instability and supports a diagnosis of dry eye disease.

Small-incision cataract surgery in which an ultrasonic handpiece fragments and aspirates the lens nucleus through a circular anterior capsulotomy, leaving a capsular bag that supports an intraocular lens implant.

A continuous circular tear made in the anterior lens capsule during cataract surgery; a well-centred opening of appropriate size stabilises the capsular bag and allows safe nucleus removal and in-the-bag lens placement.

Clouding of the residual lens capsule months to years after cataract surgery caused by proliferation and migration of lens epithelial cells, producing reduced vision that is treated with neodymium-YAG laser capsulotomy.

An age-related condition in which fibrillar material deposits on the lens capsule and anterior segment, weakening zonules and predisposing to raised intraocular pressure, pupil instability and surgical complications.

Examination of the anterior chamber angle with a mirrored or prism contact lens, used to separate open from closed angles, identify closure mechanisms and detect neovascularisation or abnormal pigment in the trabecular meshwork.

The proportion of the optic disc occupied by the central pale cup; progressive enlargement, asymmetry between eyes and rim thinning are key structural signs of glaucomatous optic neuropathy.

A form of glaucoma in which iris apposition against the trabecular meshwork obstructs aqueous outflow, usually in eyes with shallow anterior chambers; it may present acutely with pain and haloes or chronically and silently.

A guarded filtering operation creating a fistula from the anterior chamber into the subconjunctival space, forming a bleb that lowers intraocular pressure; it remains the commonest incisional glaucoma procedure worldwide.

Separation of neurosensory retina from the retinal pigment epithelium when a full-thickness break allows vitreous fluid into the subretinal space; it threatens sight and requires urgent surgical repair.

Fluid accumulation within the macula from breakdown of the inner blood-retinal barrier in diabetes; it is a leading cause of vision loss in working-age adults and is treated with intravitreal anti-VEGF drugs or laser.

A non-invasive imaging method using low-coherence interferometry to produce cross-sectional pictures of retinal layers in vivo, central to diagnosing and monitoring macular oedema, holes, membranes and subretinal fluid.

Scatter laser applied to peripheral retina in proliferative diabetic retinopathy to reduce ischaemic drive for new vessel growth; it stabilises disease but may cause peripheral field loss and aggravate macular oedema.

Inflammation of the iris and ciliary body causing pain, redness, photophobia and cells in the anterior chamber; most cases are idiopathic or HLA-B27 related, but infection and systemic disease must be excluded.

A layer of white blood cells settling in the inferior anterior chamber that signals severe intraocular inflammation or infection; when combined with a painful red eye it demands urgent exclusion of endophthalmitis.

Adhesions between the pupillary margin and the anterior lens capsule formed during intraocular inflammation; they distort the pupil, may cause iris bombé with angle closure and complicate cataract surgery.

Bilateral granulomatous panuveitis arising after penetrating injury or surgery to one eye, believed to be an autoimmune reaction to exposed uveal antigen; early removal of a blind injured eye reduces the risk.

A weaker pupillary response when light is swung into one eye compared with the other; it indicates optic nerve or extensive retinal dysfunction on the affected side and is absent in purely media-related visual loss.

Bilateral optic disc swelling caused by raised intracranial pressure, with visual acuity preserved until late; it requires urgent neuroimaging and investigation for mass lesions, venous sinus thrombosis or other causes.

Inflammation of the optic nerve producing subacute unilateral visual loss, pain on eye movement, colour desaturation and an afferent pupillary defect; in many populations it is a common first feature of multiple sclerosis.

Loss of the same half of the visual field in both eyes from a lesion behind the optic chiasm; incongruous defects point to optic tract disease while highly congruous defects suggest occipital involvement.

Reduced best-corrected acuity in one or both eyes caused by abnormal visual experience during the sensitive period, without organic disease; occlusion or penalisation works best when started early.

Alternately covering each eye while the other fixates reveals manifest deviation through movement of the uncovered eye and latent deviation on uncovering; it is the cornerstone of strabismus assessment.

A white pupillary reflex in a child that requires urgent assessment for retinoblastoma, congenital cataract, retinopathy of prematurity, persistent fetal vasculature or Coats disease; it is the commonest sign of retinoblastoma.

A vasoproliferative disorder of the developing retina in preterm infants, graded by zone and extent of extraretinal proliferation; screening with timely laser or anti-VEGF treatment prevents tractional detachment and blindness.

Surgical creation of a passage between the lacrimal sac and the nasal cavity to bypass a blocked nasolacrimal duct in watering eyes; it can be done externally or endonasally, with or without silicone stents.

Drooping of the upper eyelid, classified as aponeurotic, myogenic, neurogenic or mechanical; levator function and fatigability help distinguish involutional change from myasthenia and third nerve palsy.

An autoimmune orbitopathy in which antibodies stimulate orbital fibroblasts, causing extraocular muscle enlargement, proptosis, lid retraction, restrictive strabismus and sometimes compressive optic neuropathy.

Infection of tissues behind the orbital septum causing proptosis, painful eye movement, fever and risk to vision; it must be distinguished from preseptal cellulitis and needs urgent intravenous antibiotics and imaging.

The commonest primary intraocular malignancy in adults, arising from choroidal or ciliary melanocytes; plaque brachytherapy, proton beam therapy or enucleation are used, with metastatic risk linked to tumour size and genetics.

The commonest intraocular cancer of childhood, caused by biallelic loss of the RB1 gene; it presents with leukocoria or strabismus and is treated with chemotherapy, focal therapy, radiotherapy or enucleation depending on stage.

The commonest malignant eyelid tumour, usually a pearly nodule with surface telangiectasia that tends to ulcerate; it rarely metastasises but can destroy local tissue if left untreated.

Measures of diagnostic test performance: the proportion of affected people correctly identified and the proportion of unaffected people correctly excluded; both determine predictive values in a given population.

The number of cataract operations performed per million population per year, used as a benchmark of eye care delivery to plan services and compare access between countries and regions.