Arab Board Ophthalmology Part 1 key terms

Spongy tissue at the iridocorneal angle through which aqueous humour drains into Schlemm's canal. Its resistance to outflow is the main determinant of intraocular pressure.

Circular venous channel in the sclera at the limbus that collects aqueous humour from the trabecular meshwork and delivers it to episcleral veins.

The balance between production by the ciliary epithelium and outflow through trabecular and uveoscleral routes that sets intraocular pressure; drugs and surgery target either side of this balance.

Clinical examination of the anterior chamber angle using a mirrored or prism contact lens that overcomes total internal reflection at the cornea, allowing angle structures to be graded and closure to be detected.

Glaucoma caused by obstruction of the trabecular meshwork by the peripheral iris, producing acute or chronic pressure rise; management relieves the block with laser iridotomy or lens extraction.

Non-invasive imaging using low-coherence light interference to produce cross-sectional images of retina, optic nerve and anterior segment; used to quantify nerve fibre layer thinning and macular oedema.

Imaging technique in which intravenous fluorescein is excited by blue light and retinal and choroidal vascular filling, leakage, pooling and non-perfusion are recorded photographically.

Functional barrier formed by tight junctions of retinal capillary endothelium (inner) and retinal pigment epithelium (outer) that limits fluid and macromolecule movement into the retina.

Monolayer of pigmented cells between photoreceptors and Bruch's membrane that phagocytoses shed outer segments, regenerates visual pigment and forms the outer blood-retinal barrier.

Cascade in photoreceptors whereby absorbed light activates rhodopsin or cone opsin, triggering transducin and phosphodiesterase to lower cyclic GMP and close cation channels, generating a hyperpolarising signal.

Slow increase in visual sensitivity after transfer from bright to dim illumination, reflecting regeneration of rhodopsin and the shift from cone to rod function over roughly 20 to 30 minutes.

Enlargement and excavation of the central optic nerve head as retinal ganglion cell axons are lost, assessed by cup-to-disc ratio, neuroretinal rim thinning and disc haemorrhages.

Asymmetry in the pupillary light reflex detected by the swinging flashlight test, indicating a unilateral or asymmetric lesion of the afferent visual pathway anterior to the chiasm.

Inflammation of the optic nerve, typically demyelinating and associated with painful subacute visual loss, colour desaturation, an afferent pupillary defect and often later optic atrophy.

Bilateral optic disc swelling caused by raised intracranial pressure, transmitted along the optic nerve sheath; visual acuity is usually preserved until late.

Refractive state in which parallel light from infinity focuses exactly on the retina with accommodation relaxed, giving clear distance vision without correction.

Refractive error in which parallel rays focus in front of the retina, usually from excessive axial length, causing blurred distance vision that concave lenses correct.

Refractive error in which parallel rays would focus behind the retina with accommodation relaxed, requiring convex lenses and sustained accommodation that may cause asthenopia or accommodative esotropia.

Refractive error in which power varies across meridians so that light is not focused at a single point; corrected with cylindrical lenses and commonly caused by corneal toricity.

Measurement of corneal curvature and astigmatism by assessing the reflected image size from the anterior corneal surface, used for contact lens fitting and intraocular lens power calculation.

Estimation of the implant power needed to achieve a target refraction using corneal power, axial length and predicted lens position, refined by formulas such as SRK/T or Barrett.

Cataract surgery technique in which the crystalline lens nucleus is emulsified by ultrasonic energy through a small incision and removed by aspiration before intraocular lens implantation.

Late complication of cataract surgery in which residual lens epithelial cells proliferate and migrate onto the posterior capsule, causing visual reduction treated by neodymium:YAG laser capsulotomy.

Severe inflammation of intraocular fluids and tissues, usually bacterial after surgery or trauma, presenting with pain, hypopyon and profound visual loss and requiring urgent intravitreal antibiotics.

Layer of white blood cells settled in the inferior anterior chamber, indicating active intraocular inflammation from infection, uveitis or tumour.

Inflammation of the iris and ciliary body producing pain, photophobia, ciliary flush, cells and flare in the anterior chamber and often posterior synechiae.

Human leukocyte antigen allele strongly associated with seronegative spondyloarthropathies and with acute anterior uveitis, guiding systemic investigation in recurrent cases.

Bilateral granulomatous panuveitis occurring after penetrating injury or surgery to one eye, believed to be immune sensitisation to uveal antigens; prevented by early enucleation of a blind injured eye.

Single layer of non-regenerating cells on the posterior cornea that actively pumps fluid out of the stroma; loss of cells causes oedema and loss of transparency.

Non-contact imaging of the corneal endothelial mosaic that measures cell density, polymegathism and pleomorphism to assess endothelial reserve before surgery.

Immune-mediated destruction of a corneal transplant, most often endothelial rejection with a Khodadoust line; a leading cause of late graft failure despite corneal privilege.

Property of sites such as the anterior chamber and cornea in which foreign tissue survives longer because of absent lymphatics, local immunosuppressive factors and altered antigen presentation.

Measurement of intraocular pressure, most commonly by Goldmann applanation, with accuracy influenced by central corneal thickness and ocular rigidity.

White pupillary reflex in a child, a red flag for retinoblastoma, congenital cataract, persistent fetal vasculature or retinal detachment, requiring urgent evaluation.

Malignant intraocular tumour of childhood arising from retinal precursor cells, often presenting with leukocoria or strabismus and sometimes caused by germline RB1 mutation.

Manifest outward deviation of one eye, which may be intermittent or constant and is assessed with cover testing and control of accommodation.

Manifest inward deviation of one eye; accommodative types relate to uncorrected hyperopia and are treated with plus lenses, while infantile types require early surgery.

Reduced best-corrected visual acuity in one or both eyes from abnormal visual experience during the critical period, without organic cause, treated by correcting refractive error and penalising the better eye.

Age-related loss of accommodative amplitude from lens sclerosis, causing difficulty with near vision that is managed with reading addition, multifocal lenses or surgical options.

Active increase in the refractive power of the eye produced by ciliary muscle contraction, zonular relaxation and lens rounding, allowing focus on near objects.

Dilatation of the pupil, produced physiologically by sympathetic action or pharmacologically by antimuscarinic drugs such as tropicamide, with risk of angle closure in predisposed eyes.