OP10.1-7 | Miscellaneous Skills, Emergencies and Community Ophthalmology — Glossary

Accommodative convergence to accommodation ratio: the amount of convergence (in prism dioptres) driven per unit of accommodation (per dioptre); high AC/A predisposes to esotropia at near.

The process of increasing lens curvature (via ciliary muscle contraction and zonular relaxation) to bring near objects into focus on the retina.

Esotropia driven by excessive accommodative convergence in a hypermetropic child; fully or partially corrected by spectacles.

Ophthalmic emergency caused by sudden blockage of aqueous drainage at the trabecular meshwork by the iris; presents with severe headache, red eye, haloes, and markedly elevated IOP.

The extra plus lens power added to a presbyope's distance prescription to restore near vision; typically +1.00 DS at age 45, increasing to +2.50–3.00 DS by age 60.

Malignant tumour of the lacrimal gland with a tendency for perineural spread; may require exenteration for locoregional control.

Test measuring total deviation (tropia + phoria) by alternately covering each eye without allowing binocular fusion.

Reduced best-corrected visual acuity in one eye without detectable structural anomaly; caused by cortical suppression during the critical period of visual development.

Difference between the visual axis and pupillary axis; positive angle kappa causes temporal displacement of the corneal reflex in a straight eye, mimicking exotropia.

Ocular fatigue and discomfort, often with headache, arising from sustained visual effort; typical of uncorrected refractive error or binocular vision anomalies.

Refractive error caused by unequal curvature of the cornea (or lens) in different meridians, producing two focal planes and causing sustained accommodative effort.

Blindness that is either preventable (e.g., vitamin A deficiency, trachoma) or treatable with available interventions (e.g., cataract, uncorrected refractive error); constitutes approximately 80% of global blindness.

Two-dimensional ocular ultrasound used to image intraocular structures through opaque media; essential before evisceration to exclude an intraocular solid mass.

Standardised classification system for mechanical ocular injuries distinguishing closed globe from open globe (penetrating, perforating, IOFB).

Foamy, cheesy-white triangular plaques on the TEMPORAL BULBAR CONJUNCTIVA caused by squamous metaplasia of the conjunctival epithelium in vitamin A deficiency; a CONJUNCTIVAL lesion — not corneal.

Visual acuity <3/60 (20/1200) in the better eye with best available correction, OR a visual field of <10° around the point of fixation.

Number of individuals with visually significant cataract who have not yet received surgery; the gap between cataract incidence and surgical output.

Number of cataract surgeries performed per million population per year; a key NPCBVI monitoring indicator; target >6,000 per million to reduce cataract backlog.

Intraocular copper toxicity from a copper or high-copper alloy IOFB; causes sunflower cataract, corneal deposits, and retinal degeneration.

Most common primary intraocular malignancy in adults; arising from uveal melanocytes; may require enucleation or vision-sparing radiotherapy depending on size.

Blunt or lamellar ocular trauma with intact eyewall integrity; includes contusion and partial-thickness laceration.

Deviation equal in all positions of gaze; typically of childhood onset with no underlying muscle or nerve pathology.

Strabismus in which the angle of deviation is equal in all positions of gaze; associated with full ductions and childhood onset.

Retinal whitening from disruption of the outer photoreceptor layers after concussive blunt trauma; usually self-limiting.

Non-invasive technique pressing filter paper on the bulbar conjunctiva to obtain a cellular impression; in VAD, shows absent goblet cells and squamous metaplasia.

Dry, lusterless, non-wettable bulbar conjunctiva due to goblet cell depletion and mucin loss; stage X1A of xerophthalmia.

Inability to maintain adequate binocular convergence for near work; near point of convergence is receded (>10 cm); causes near headache and asthenopia not correctable by spectacles.

Dryness and haziness of the cornea due to vitamin A deficiency; the critical threshold at which corneal involvement begins and urgent treatment is mandatory.

Test detecting heterotropia by covering one eye and watching the uncovered fellow eye for a corrective fixation movement.

The developmental window (approximately birth to age 7–8 years) during which the visual cortex remains plastic and amblyopia treatment is most effective.

In large-angle infantile esotropia, using the adducting (nasal) eye to fixate in the contralateral field; can mimic abduction palsy.

Refraction performed after instillation of cycloplegic drops (cyclopentolate or atropine) to paralyse accommodation and reveal the full underlying refractive error.

Standardised psychophysical test measuring the recovery of visual sensitivity (especially rod function) after exposure to a bright adapting light; the gold-standard functional test for night blindness.

Public health metric measuring disease burden as years of healthy life lost; childhood blindness carries a greater DALY burden than adult blindness due to long duration of disability.

Upward drifting of an eye when it is covered or under reduced illumination; associated with infantile esotropia.

The operational unit of NPCBVI at the district level; coordinates cataract surgery targets, outreach camps, school screening, and eye banking activities.

Monocular rotation of one eye; tested with the fellow eye occluded to isolate individual muscle action.

Surgical removal of the entire globe (cornea, sclera, and all intraocular contents) by dividing the extraocular muscles and optic nerve; used for intraocular tumours and sympathetic ophthalmia prevention.

Manifest convergent (inward) deviation of one or both eyes.

Surgical removal of the intraocular contents (uvea, retina, lens, vitreous) while leaving the scleral shell, optic nerve, and extraocular muscles intact; used for blind painful eyes without suspected tumour.

Surgical removal of the entire orbital contents including the globe, extraocular muscles, orbital fat, lacrimal gland, and eyelids; used for orbital malignancy and uncontrolled orbital mucormycosis.

Manifest divergent (outward) deviation of one or both eyes.

The gaze direction in which a particular extraocular muscle contributes maximally; deviation is greatest in the field of a paretic muscle.

Test performed under topical anaesthesia by grasping the conjunctiva with forceps and attempting to rotate the globe; positive (resistance) indicates mechanical restriction rather than nerve palsy.

Rigid protective shield placed over the orbit (not touching the eye) for transport of an open globe patient; prevents inadvertent pressure on the globe.

Mucin-secreting cells of the conjunctival epithelium; their loss in vitamin A deficiency causes mucin deficiency, tear film instability, and ocular surface keratinisation.

Law of equal and simultaneous innervation: yoke muscles receive equal neural innervation during conjugate gaze movements.

Latent tendency for ocular misalignment controlled by fusion; only revealed when binocular fusion is disrupted (alternate cover test).

Manifest misalignment of the visual axes present during binocular viewing; detected by cover/uncover test.

Objective test using the corneal light reflex position to estimate angle of strabismus; 1 mm decentration ≈ 7°.

Refractive error in which the eye is too short; parallel rays focus behind the retina; requires accommodation even for distance vision.

Blood in the anterior chamber after blunt trauma; graded I–IV by proportion of anterior chamber filled; risk of secondary haemorrhage on days 2–5.

International Agency for the Prevention of Blindness; international alliance of NGOs and professional bodies co-leading the Vision 2020 initiative with WHO.

International Intraocular Retinoblastoma Classification (Groups A–E); Groups D and E represent advanced tumours with poor visual prognosis, typically requiring enucleation.

Deviation that varies with direction of gaze; indicates palsy of a specific muscle or mechanical restriction.

Comprehensive population-based national survey of blindness prevalence and causes in India; conducted 2015–2019; provides current burden data for NPCBVI planning.

Large-angle constant esotropia presenting within the first 6 months of life; non-accommodative; typically requires surgical treatment.

Exodeviation that is intermittently manifest (on distance fixation or inattention) but controlled by fusion much of the time; the commonest exodeviation in childhood.

Foreign material retained inside the globe after penetrating injury; can cause siderosis (iron) or chalcosis (copper) if not removed promptly.

Liquefactive necrosis of the corneal stroma due to severe vitamin A deficiency; X3A involves <1/3 of the corneal area, X3B involves ≥1/3; rapid progression to perforation and total blindness.

Refinement of Hirschberg using prisms in front of the fixing eye to neutralise and quantify the deviation.

Component of hypermetropia masked by involuntary accommodation; only revealed under cycloplegic refraction; a common under-diagnosed cause of refractive headache.

Dense white corneal opacity caused by corneal scarring; the XS stage sequela of healed keratomalacia.

White pupillary reflex; a key presenting sign of retinoblastoma (also: cataract, PHPV, toxocariasis); requires urgent ophthalmic investigation.

Interruption of the limbal vasculature in chemical burns; limbal stem cell destruction prevents corneal epithelial regeneration, leading to persistent epithelial defects and scarring.

VA between 6/18 and 3/60 (or restricted field <20°) in the better eye despite best optical correction and treatment; managed with optical/non-optical low vision aids and rehabilitation.

Mnemonic: Lateral Rectus = CN VI; Superior Oblique = CN IV; all other extraocular muscles = CN III.

Invasive fungal infection by Mucorales species (Rhizopus, Mucor); angioinvasive; occurs in immunocompromised patients (especially DKA); orbital invasion may require emergency exenteration.

Refractive error in which the eye is too long; parallel rays focus in front of the retina; near vision is naturally clear without accommodation.

Nearest point to the nose at which both eyes can maintain convergence; normal ≤10 cm from the nose.

Systematic test of conjugate eye movements in primary position plus eight other positions (right, left, up, down, and four oblique directions) to assess all muscle pairs.

National Programme for Control of Blindness and Visual Impairment — the Indian national programme that includes childhood vitamin A supplementation (100,000 IU at 6 months; 200,000 IU every 6 months until 5 years).

Impaired vision in low light due to depletion of rhodopsin in rod photoreceptors; the earliest functional stage of vitamin A deficiency.

Patching of the better eye to force the amblyopic eye to work; primary treatment for strabismic and anisometropic amblyopia.

Custom-made painted acrylic shell placed over a spherical orbital implant after evisceration or enucleation to restore cosmetic appearance.

Full-thickness wound of the cornea and/or sclera; includes penetrating, perforating, and IOFB injuries; requires emergency surgical repair.

Fracture of the orbital floor (or medial wall) from blunt orbital trauma, with herniation of orbital fat and inferior rectus into the maxillary sinus; causes diplopia on upward gaze and enophthalmos.

Spherical implant (typically hydroxyapatite or porous polyethylene) placed in the orbit after evisceration/enucleation to maintain orbital volume and restore socket motility.

Swelling of the optic disc due to raised intracranial pressure; a red flag finding on fundus examination mandating urgent neuroimaging.

A systematic three-step test to identify the paretic muscle in cyclovertical palsy, particularly CN IV palsy.

UV radiation keratitis causing punctate corneal epithelial erosions; presents 6–8 hours after unprotected exposure to UV (welding arc, snow); severe pain and photophobia.

End-stage blind, shrunken, disorganised, often calcified globe resulting from severe ocular disease or trauma; a common indication for evisceration or enucleation.

Simple bedside test using a disc with small holes to reduce blur from uncorrected refractive error; VA improvement with pinhole indicates a refractive cause.

Age-related (40+ years) reduction in accommodative amplitude due to progressive stiffening of the crystalline lens; presents as difficulty with near vision and near headache.

Quantitative version of the alternate cover test using prisms to neutralise the deviation in prism dioptres.

Apparent squint in a straight-eyed child caused by prominent epicanthal folds or a wide nasal bridge; confirmed by symmetric Hirschberg reflex and negative cover test.

Most common intraocular malignancy of childhood, arising from the retina; presents as leukocoria (white pupil); IIRC Group D/E = advanced disease requiring enucleation.

Carrier protein synthesised in the liver that transports vitamin A in the circulation; its synthesis requires zinc; acute-phase response reduces RBP even when liver stores are adequate.

Abnormal retinal vascular development in premature low-birth-weight infants; a growing cause of childhood blindness as neonatal survival improves; screened by NPCBVI in eligible NICUs.

Visual pigment in rod photoreceptors formed by 11-cis retinal (derived from vitamin A) bound to the protein opsin; essential for scotopic (dim-light) vision.

Grading system for chemical ocular burns (Grades I–IV) based on corneal clarity and extent of limbal ischaemia; Grade IV carries a very poor prognosis.

WHO strategy for trachoma elimination: Surgery (for trichiasis), Antibiotics (azithromycin mass distribution), Facial cleanliness, Environmental improvement.

Rebleed into the anterior chamber, typically on days 2–5 after initial hyphaema; often larger than the primary bleed and associated with IOP spikes and corneal bloodstaining.

Application of fluorescein to a suspected corneal wound; a positive Seidel test shows streaming aqueous diluting the fluorescein, confirming a full-thickness wound (open globe).

Blood test measuring vitamin A status; normal ≥0.70 μmol/L; <0.35 μmol/L = deficiency; unreliable during acute illness (negative acute-phase reactant).

Law of reciprocal innervation: when an agonist muscle contracts, its antagonist in the same eye simultaneously relaxes.

Progressive intraocular damage from an iron IOFB; iron ions stain all uveal structures, causing pigment deposition, ERG changes, and eventual visual loss.

Transformation of normal columnar mucus-secreting conjunctival epithelium to flat, keratinised squamous epithelium; the cellular basis of xerophthalmia.

Active cortical inhibition of the image from the deviating eye in a child with strabismus; prevents diplopia but can lead to amblyopia.

Bilateral granulomatous panuveitis occurring weeks to months after penetrating uveal injury to one eye (exciting eye), affecting the fellow (sympathising) eye; caused by autoimmune sensitisation to sequestered uveal antigens.

Fibrous fascial sheath surrounding the globe; surgical plane used in both evisceration and enucleation for implant placement.

Headache reaching maximum intensity within seconds to minutes of onset; a red flag symptom for subarachnoid haemorrhage requiring urgent CT head.

Disconjugate binocular movement (convergence or divergence) that maintains single vision as target depth changes.

Conjugate binocular eye movement in the same direction; tests coordinated yoke muscle pairs.

'Right to Sight' — global initiative launched by WHO and IAPB in 1999 to eliminate avoidable blindness; India is a partner nation; strategies include disease control, human resource development, and infrastructure strengthening.

Loss of vision not fully correctable with spectacles; categorised as mild (6/12–6/18), moderate (6/18–6/60), severe (6/60–3/60), and blind (<3/60) per WHO ICD-11.

Dryness of the conjunctiva and cornea due to vitamin A deficiency; encompasses all stages from night blindness to corneal scarring.

A pair of muscles (one from each eye) that act together in conjugate gaze in a given direction (e.g. right lateral rectus and left medial rectus for dextroversion).