Glaucoma Essentials: Anatomy, Physiology, and Clinical Classifications

A collection of vocabulary flashcards covering the anatomy of the eye relative to glaucoma, aqueous humor dynamics, clinical grading systems, and classifications of primary and developmental glaucomas.

Glaucoma

A group of disorders characterized by progressive optic neuropathy resulting in characteristic optic disc appearance and specific irreversible visual field defects, frequently associated with raised intraocular pressure ($IOP$).

Schwalbe's line

The prominent peripheral end of Descemet's membrane of the cornea, serving as a boundary for the angle of the anterior chamber.

Trabecular meshwork

The circular spongework of connective tissue through which aqueous humour leaves the eye, consisting of uveal, corneoscleral, and juxtacanalicular layers.

Schlemm's canal

An endothelial-lined oval channel present circumferentially in the scleral sulcus that receives aqueous from the trabecular meshwork.

Shaffer's Grade 4

An angle width of $40^{\circ}$ where closure is impossible and structures visible include Schwalbe's line ($SL$), trabecular meshwork ($TM$), scleral spur ($SS$), and ciliary body band ($CBB$).

Aqueous humour

A clear watery fluid with a refractive index of $1.336$ that fills the anterior ($0.25\,mL$) and posterior ($0.06\,mL$) chambers.

Active secretion

The process responsible for $70\%$ of aqueous humor production, utilizing the $Na^{+}-K^{+}$ activated ATPase pump and carbonic anhydrase enzyme system.

Uveoscleral outflow

The unconventional drainage route responsible for $20\%$ to $30\%$ of total aqueous outflow, passing between ciliary muscle bundles into the suprachoroidal space.

Intraocular pressure ($IOP$)

Pressure exerted by intraocular fluids on the eyeball coats, normally ranging from $10$ to $21\,mm\,Hg$ with a mean of $16 \pm 2.5\,mm\,Hg$.

Ocular hypertension

A condition where the $IOP$ is constantly above $21\,mm\,Hg$ but no optic disc or visual field changes are present.

Normal tension glaucoma ($NTG$)

Glaucomatous disc changes and visual field defects associated with an $IOP$ constantly below $21\,mm\,Hg$.

Buphthalmos

A 'bull-like' enlargement of the eyeball occurring in developmental glaucoma when the disease manifests prior to the age of $3$ years.

Haab's striae

Opaque, concentric lines with double contours representing peripheral tears in Descemet's membrane due to corneal enlargement.

Bayonetting sign

An advanced sign of glaucomatous cupping where retinal vessels shift nasally and appear broken off at the disc margin.

Bjerrum's area

An arcuate zone of the visual field between $10^{\circ}$ and $20^{\circ}$ of fixation where early glaucomatous field defects typically appear.

Seidel's scotoma

A sickle-shaped visual field defect formed when a paracentral scotoma joins with the blind spot.

Roenne's central nasal step

A sharp right-angled defect at the horizontal meridian created when two arcuate scotomas of unequal size meet.

ISNT rule

The clinical observation that the neuro-retinal rim is normally thickest in the Inferior region, then Superior, then Nasal, and thinnest Temporally.

Water drinking test

A provocative test where a rise in $IOP$ of $8\,mm\,Hg$ or more after drinking one litre of water indicates primary open-angle glaucoma.

Prostaglandin analogues

A class of drugs used as first-line therapy (e.g., latanoprost $0.005\%$) that lowers $IOP$ by increasing unconventional uveoscleral outflow.

Laser peripheral iridotomy ($LPI$)

A procedure that creates a communication between the posterior and anterior chambers to bypass pupillary block in angle-closure disease.

Trabeculectomy

A filtration surgery that provides a new channel for aqueous outflow into the subconjunctival space to control uncontrolled glaucoma.

Glaukomflecken

Small anterior subcapsular lenticular opacities that serve as a clinical sign of a previous attack of acute primary angle-closure.

Vogt's triad

A sequela of acute primary angle-closure consisting of glaukomflecken, patches of iris atrophy, and a fixed, semidilated pupil.

Primary Angle-Closure Suspect ($PACS$)

An eye with irido-trabecular contact in greater than $270^{\circ}$ of the angle but with normal $IOP$, disc, and visual fields.

Van Herick method

A slit-lamp grading system for angle width; Grade 1 represents peripheral anterior chamber depth ($PACD$) less than $\frac{1}{4}$ of corneal thickness ($CT$).

Target pressure

The intended $IOP$ level determined to prevent further damage, such as $< 18\,mm\,Hg$ for mild glaucoma or $< 14\,mm\,Hg$ for severe cases.