Ophthalmology Revision Flashcards - Eye Anatomy, Cornea & Sclera

Vocabulary practice flashcards covering Basic Anatomy of the Eye, Cornea, and Sclera based on lecture transcript and diagrams.

Eyeball Shape

Aspherical (Oblate spheroid).

Eyeball Volume

$$6\,mL$$

Blow out fracture sign

Tear drop sign seen on imaging.

Thinnest Orbital Wall

Medial wall of the orbit.

Weakest Orbital Wall

Floor of the orbit.

Most Common Orbital Fracture

Blow out fracture.

Orbital Base Shape

Quadrangular.

Orbital Apex Shape

Conical.

Angle of Muscle Cone

$$45^\circ$$

Angle Between Medial Walls of Orbit

$$90^\circ$$

Annulus of Zinn

Common tendinous ring that serves as the origin for Extraocular Muscles (EOM).

Retrobulbar Anesthesia Route

Local anesthesia administered into the intraconal space.

Peribulbar Anesthesia Route

Local anesthesia administered into the extraconal space, associated with fewer complications.

Outermost Layer of Eyeball - Cornea

Transparent anterior $1/6\text{th}$ of the eyeball that is convex and refracts light.

Outermost Layer of Eyeball - Sclera

Opaque (white) posterior $5/6\text{th}$ of the eyeball covered by conjunctiva.

Limbus

The corneoscleral junction containing limbal stem cells.

Specific Limbal Stem Cell Marker

ABCG2.

Universal Limbal Stem Cell Marker

CD34.

Middle Layer of Eyeball (Uvea)

Vascular layer consisting of the Iris, Ciliary body, and Choroid.

Sphincter Pupillae

Iris muscle responsible for pupil constriction (miosis).

Dilator Pupillae

Iris muscle responsible for pupil dilation (mydriasis).

Pars Plicata

Anterior part of the ciliary body containing ciliary projections that secrete aqueous humor.

Pars Plana

Posterior, relatively avascular part of the ciliary body that serves as the point of entry into the vitreous/fundus.

Choroid

Posteriormost highly vascular portion of the uvea.

Inner Layer of Eyeball (Retina)

Neurosensory layer that converts light sensory impulses into neural signals.

Fovea Centralis

Retinal region containing the maximum concentration of cones, responsible for the best image quality at the centre of the visual field.

Foveal Fixation Development

Develops by $3\text{--}4\text{ months}$ of age.

Optic Disc

Anatomical blind spot lacking photoreceptors, composed of a central optic cup and peripheral neuroretinal rim.

Limbal Dermoid

Benign congenital choristomatous tumor at the limbus containing tissue such as bone, cilia, and hair follicles.

Pterygium Cause

Limbal stem cell deficiency causing conjunctiva to grow over the cornea.

Corneal Epithelium Type

Non-keratinized stratified squamous epithelium.

Superficial Corneal Epithelial Cells

Squamous cells with microvilli that aid in the adhesion of the tear film.

Basal Corneal Epithelial Cells

Columnar cells capable of mitosis and regeneration.

Bowman's Layer Characteristics

Acellular false basement membrane (PAS negative) that cannot regenerate and heals by scar formation.

Corneal Stroma Composition

Composed primarily of Type 1 collagen and keratan sulphate glycosaminoglycan (GAG).

Thickest Corneal Layer

Corneal Stroma ($490\,\mu m$).

Dua's Layer

Strongest corneal layer, measuring $6.5\text{--}13.9\,\mu m$ in thickness.

Descemet's Membrane (DM)

Innermost basement membrane that can regenerate; its peripheral termination forms Schwalbe's line.

Schwalbe's Line

Peripheral termination of Descemet's membrane.

Corneal Endothelium

Innermost monolayer of cells ($5\,\mu m$) that is most metabolically active and maintains corneal transparency.

Normal Endothelial Cell Count

$$2400\text{--}3000\text{ cells/mm}^2$$

Corneal Compensation Threshold

Endothelial cell count falling below $2400\text{ cells/mm}^2$.

Corneal Decompensation Critical Point

Endothelial cell count falling below $500\text{ cells/mm}^2$, leading to corneal edema and hazy cornea.

Specular Microscopy

Specialized technique used to count corneal endothelial cells.

Corneal Sensory Innervation Pathway

Trigeminal nerve (CN V) -> Ophthalmic branch ($V_1$) -> Nasociliary nerve.

Corneal Sensation Test Arc

Cotton wisp touches cornea -> Afferent CN V -> Brain -> Efferent CN VII -> Orbicularis oculi contraction (Blink).

Most Common Cause of Corneal Anaesthesia

Herpes simplex viral infection.

Corneal Refractive Power Range

$+43\text{ D}$ to $+44\text{ D}$ (Converging lens).

Nebular Corneal Opacity

Faintest opacity involving Bowman's layer & superficial stroma; pupillary margin and iris details remain visible.

Macular Corneal Opacity

Intermediate opacity involving $\le 1/2$ of the stroma; pupillary margin is visible but iris details are not seen.

Leucoma Corneal Opacity

Most opaque lesion involving $\ge 1/2$ of the stroma; neither pupillary margin nor iris details are visible.

Opacity Causing Maximum Discomfort

Nebular opacity (due to irregular astigmatism induction).

Opacity Causing Maximum Visual Loss

Leucoma.

Pachymetry

Investigation used to measure central corneal thickness (Normal CCT $\sim 540\,\mu m$ or $0.54\,mm$).

Keratometry

Measurement of corneal curvature to quantify astigmatism.

Placido Disc Topography

Diagnostic examination of the anterior corneal surface curvature.

Fluorescein Dye Properties

Orange dye that fluoresces green under Cobalt blue filter; stains base of corneal ulcers (broken epithelium).

Diagnostic Uses of Fluorescein Dye

Goldmann applanation tonometry, Seidel's test (perforation site), Tear film break-up time (TBUT for dry eye).

Rose Bengal Dye

Stains necrotic tissue red (characteristically highlights ulcer margins).

Lissamine Green Dye

Non-toxic dye staining cornea and conjunctiva; preferred for dry eye evaluation over corneal ulcers.

Corneal Abrasion vs Corneal Ulcer

Abrasion is loss of epithelium alone (regenerates); Ulcer is loss of epithelium WITH necrosis of underlying stroma.

Most Common Bacterial Cause of Corneal Ulcer in India

Pneumococcus (Streptococcus pneumoniae).

Ulcus Serpens

Snake-shaped hypopyon corneal ulcer caused by S. pneumoniae.

Pneumococcal Hypopyon Character

Mobile and sterile collection of pus in the anterior chamber.

Nocardia Corneal Ulcer

Trauma-related bacterial ulcer presenting in a wreath or pinhead pattern.

Most Common Corneal Ulcer Cause in Contact Lens Users

Pseudomonas aeruginosa.

Organisms Penetrating Intact Cornea (High Level CNS)

Haemophilus aegyptius, Listeria, Corynebacterium diphtheriae, Neisseria gonorrhoeae, Neisseria meningitidis, Shigella.

Bacterial Corneal Ulcer Management (5S)

Scrape base (15 blade), Staining (Gram) & culture, Start fortified antibiotics, Supportive therapy (Atropine cycloplegia), Steroids avoidance.

Most Common Cause of Fungal Corneal Ulcer

Aspergillus (septate, filamentous fungus).

Clinical Features of Fungal Corneal Ulcer

Dry ulcer with feathery margins, satellite lesions, Wessley immune ring, and an immobile, unsterile hypopyon.

Drug of Choice for Fungal Corneal Ulcer

5% Natamycin eye drops.

Progression of Epithelial Herpetic Keratitis

Superficial punctate keratitis -> Dendritic ulcer -> Geographic ulcer.

Treatment of Epithelial Herpetic Keratitis

3% Acyclovir eye ointment (Topical steroids are strictly contraindicated).

Necrotising Stromal Herpetic Keratitis Rx

Topical steroids (given intact epithelium) + Oral acyclovir.

Metaherpetic Keratitis Cause

CN V nerve atrophy/palsy leading to corneal anaesthesia (neurotrophic ulcer).

Neuroparalytic Ulcer Mechanism

CN VII palsy -> Loss of blinking (Lagophthalmos) -> Exposure keratitis -> Neuroparalytic corneal ulcer.

Conditions Associated with Lagophthalmos

Leprosy and Bell's palsy.

Acanthamoeba Keratitis Etiology

Contact lens wearers exposing lenses to tap water or swimming in contaminated water.

Classic Signs of Acanthamoeba Keratitis

Severe pain out of proportion to signs, radial keratoneuritis, ring abscess, and pseudodendrites.

Culture Medium for Acanthamoeba

Non-nutrient agar enriched with Escherichia coli.

Drug of Choice for Acanthamoeba Keratitis

Polyhexamethylene biguanide (PHMB) 0.02%.

Corneal Dystrophy Definition

Bilateral, non-inflammatory, autosomal dominant opacifying corneal disorder.

Most Common Epithelial Corneal Dystrophy

Cogan's epithelial basement membrane dystrophy.

Meesmann's Epithelial Dystrophy Etiology

Mutations in keratin genes.

Lisch Epithelial Dystrophy Inheritance

Autosomal dominant > X-linked dominant.

Reis-Bucklers Dystrophy Location

Bowman's layer.

Thiel-Behnke Dystrophy Feature

Honeycomb pattern opacities in Bowman's layer.

Schnyder Central Crystalline Dystrophy Etiology

Disorder of corneal lipid metabolism.

Lattice Corneal Dystrophy Staining

Amyloid deposits stained by Congo red.

Granular Corneal Dystrophy Staining

Hyaline deposits stained by Masson trichrome.

Macular Corneal Dystrophy Inheritance & Frequency

Autosomal Recessive (AR); least common stromal dystrophy.

Fuchs' Endothelial Dystrophy Hallmark

Cornea guttata (wart-like excrescences on posterior cornea/Descemet's).

Posterior Polymorphous Corneal Dystrophy

Autosomal recessive endothelial dystrophy with perinatal onset.

Keratoconus

Ectatic disorder leading to a cone-shaped protrusion of the central cornea.

Munson's Sign

V-shaped indentation of the lower eyelid by the ectatic cornea on downgaze.

Vogt's Striae

Vertical fine lines in deep stroma/Descemet's layer due to corneal stretching in keratoconus.

Fleischer's Ring

Iron deposition at the base of the cone in keratoconus.

Kayser-Fleischer Ring

Copper deposition in Descemet's membrane seen in Wilson's disease.

Rizzuti's Sign

Conical refraction arrowhead light reflection on nasal limbus when illuminated laterally.

Investigation of Choice for Keratoconus

Corneal Topography.