Enhance your knowledge with our comprehensive guide and curated study materials.
The eyeball is the organ of sight, structurally similar to a camera. It is almost spherical, measuring about 2.5 cm in diameter. It has three concentric coats:
Outer (fibrous) coat: Sclera + Cornea
Middle (vascular/uveal) coat: Choroid, Ciliary body, Iris
Inner (nervous) coat: Retina
Light enters through refracting media: cornea → aqueous humour → lens → vitreous.
The outer coat includes sclera (posterior 5/6) and cornea (anterior 1/6).
Opaque, tough, dense fibrous coat forming posterior five-sixths of eyeball.
Thickest near optic nerve entry; thinnest 6 mm behind limbus where recti insert; weakest at optic nerve entrance.
Region at optic nerve perforations = Lamina cribrosa.
Outer surface: smooth, white, covered by Tenon’s capsule; anterior part visible as “white of eye”.
Inner surface: brown, grooved for ciliary vessels/nerves; separated from choroid by perichoroidal space with lamina fusca.
Meets cornea at the sclerocorneal junction/limbus.
Deep part contains canal of Schlemm, draining aqueous humour.
Optic nerve (slightly inferomedial).
Ciliary nerves & arteries.
Anterior ciliary arteries.
4 vortex veins (vorticose veins).
Sclera is almost avascular.
Episclera (loose connective tissue between conjunctiva and sclera) is vascular.
Recti → anterior to equator
Obliques → posterior to equator
Use a fresh goat eyeball.
Remove fascial sheath, clean posterior ciliary nerves/vessels, identify vortex veins.
Incise sclera at equator and strip it off from choroid.
Transparent, forms anterior one-sixth.
Junction with sclera = limbus.
More convex than sclera.
Separated from iris by anterior chamber.
Avascular.
Nourished by:
Lymph in corneal spaces
Lacrimal fluid
Branches of ophthalmic nerve
Short ciliary nerves via ciliary ganglion
Pain is the only sensation from cornea
Incise around limbus to remove cornea.
Expose iris, ciliary body, choroid.
Strip iris, remove lens (floats in water).
Vitreous escapes on removing lens.
Cornea can be grafted (avascular → immune privilege).
Injury causes opacities → visual disturbance.
Highly sensitive; even dust causes pain.
Conjunctival inflammation → conjunctivitis; palpebral conjunctiva used to assess HB level.
Shape, curvature & AP diameter determine refractive errors (myopia, hypermetropia).
The middle coat consists of:
Choroid
Ciliary body
Iris
The choroid is a thin, pigmented, vascular layer lying between sclera and retina.
Separates posterior sclera from retina.
Anterior end: merges with ciliary body at ora serrata.
Posterior end: pierced by optic nerve and attached firmly to it.
Outer surface: separated from sclera by suprachoroidal lamina, containing ciliary nerves and vessels.
Attachments: loose to sclera; firm to retina.
Suprachoroid lamina
Vascular lamina
Choriocapillary lamina
Bruch’s membrane (basal lamina)
The ciliary body is a thickened part of the uveal tract posterior to the corneal limbus.
Continuous with iris anteriorly and choroid posteriorly.
Suspends the lens and helps in accommodation.
Triangular in cross section.
Pars plana: smooth posterior part.
Pars plicata: anterior part with ~70 ciliary processes.
The iris is the coloured diaphragm of the eye forming the pupil.
Anteriorly covered by mesothelium, posteriorly by deeply pigmented double-layered epithelium.
Iris stroma contains connective tissue, blood vessels, pigment cells.
Major arterial circle at periphery; minor arterial circle near pupil.
Eye colour depends on pigment density; fewer pigment cells → blue iris.
Sphincter pupillae – parasympathetic supply
Dilator pupillae – sympathetic supply
Looking far → ciliary muscle relaxed, suspensory ligament tense, lens flat.
Near vision → ciliary muscle contracts, ligament relaxed, lens becomes round.
Normal vision is binocular and 3D.
Convergent squint: one eye turns inward.
Thin delicate inner layer, continuous with optic nerve.
Outer retinal surface (pigment layer) attached to choroid.
Inner surface contacts hyaloid membrane of vitreous.
Optic disc: inferomedial to posterior pole, 1.5 mm diameter.
Optic part: light-sensitive; extends from optic disc to ora serrata.
Ciliary and iridial parts: thin, non-nervous layers anterior to ora serrata.
Physiological cup: central depression of optic disc; no rods or cones → blind spot.
Macula lutea: lateral to optic disc, yellow, avascular.
Fovea centralis: centre of macula; cones only; highest visual acuity; thinnest part of retina.
(Directly covered under Clinical Anatomy section of middle coat; retina-specific clinical notes appear later in chapter.)
■ Key points from retrieved content
Accommodation defects → myopia, hypermetropia
Squint arises due to misalignment of visual axes
The aqueous humour is a clear fluid filling the space between cornea (in front) and lens (behind) in the anterior segment of the eye.
The iris divides this segment into anterior and posterior chambers, which communicate freely via the pupil.
Secreted into the posterior chamber by capillaries of ciliary processes.
Flows through pupil → anterior chamber.
Drains via:
Iridocorneal angle (spaces in ligamentum pectinatum)
Canal of Schlemm
→ Anterior ciliary veins
Maintains intraocular pressure and thereby the optical dimensions of the eyeball.
Rich in ascorbic acid, glucose, amino acids → nourishes avascular cornea and lens.
Obstruction of outflow (or excess production) → raised intraocular pressure = glaucoma.
Glaucoma leads to:
Cupping of optic disc
Pressure atrophy of retina
Blindness
Glaucoma must be treated urgently.
Transparent, biconvex structure between anterior and posterior segments.
Diameter ≈ 1 cm.
Poles: central points of anterior and posterior surfaces.
Axis: line joining the poles.
Equator: marginal circumference.
Contributes 15 dioptres to the total ~58 D of the eye.
Posterior surface is more convex than anterior.
Anterior surface kept flattened by tension of suspensory ligament.
When ligament relaxes (ciliary muscle contracts), lens becomes more convex.
Enclosed in thick elastic capsule (thickest anteriorly).
Anterior surface has cubical epithelium centrally; at periphery, cells elongate → lens fibres.
Nucleus: central, oldest, firm fibres.
Cortex: peripheral, softer, newer fibres.
Attaches to:
Ciliary processes
Furrows between processes
Ora serrata
Fibres attach to lens mostly in front of equator, some behind.
Make an incision on anterior surface.
Apply gentle pressure to express the lens from its capsule.
Lens becomes opaque with age → cataract, requiring replacement.
Central retinal artery is an end artery; blockage → sudden blindness.
Third nerve paralysis → partial ptosis, dilated pupil, eye deviated down and out.
Horner’s syndrome → partial ptosis + miosis.
Brainstem death → pupils fixed and dilated.
Ophthalmoscopy allows observation of:
Diabetic/hypertensive retinal changes
Papilloedema (raised intracranial pressure)
The vitreous body is the transparent, gel-like substance that fills the posterior four-fifths of the eyeball.
It lies behind the lens and ciliary processes, which indent the vitreous anteriorly.
Occupies the vitreous chamber.
Maintains the shape of the eyeball.
Supports the retina by pressing it against the choroid.
Composed of:
Water
Hyaluronic acid
Collagen fibrils
Enclosed by a thin membrane called the hyaloid membrane (not directly in this snippet but referenced in adjacent retina content).
The development information appears as a consolidated section under “DEVELOPMENT,” which applies to lens, retina, vitreous region, sclera, choroid, cornea, and related structures.
Optic vesicle → forms optic cup, an outpouching from forebrain.
Lens → develops from the lens placode (ectodermal).
Retina:
Pigmented layer → from outer layer of optic cup
Nervous layers → from inner layer of optic cup
Choroid & sclera → from mesoderm
Cornea:
Epithelium → surface ectoderm
Remaining layers → mesoderm
(The vitreous body itself forms largely from secondary mesenchyme surrounding the optic cup; although this specific line is not fully visible in the retrieved page, the adjoining description confirms the region.)
The molecular signals controlling eye development are clearly described:
WNT, BMP, TGF-β, FGF → regulate optic vesicle formation
PAX6 → essential for lens vesicle differentiation
Sonic hedgehog (SHH) has two critical roles:
Inhibition of SHH + expansion of PAX2 → failure of eye separation → cyclopia
Overexpression of SHH → loss of eye structures
Vitamin A deficiency in pregnancy → anterior segment defects (cornea, eyelids)
A patient reports sudden flashes of light, floaters, and a curtain-like shadow descending over the visual field.
The retina has two layers with different embryological origins.
The outer pigmented layer adheres firmly to the choroid.
The inner nine nervous layers are loosely attached and can separate.
When the inner layers pull away, photoreceptors lose blood supply from choroid and central retinal artery branches.
This produces visual field defects.
Immediate ophthalmologic evaluation with urgent retinal reattachment, such as pneumatic retinopexy, scleral buckle, or vitrectomy, to prevent permanent loss of photoreceptor function.
An elderly patient has painless progressive blurring of vision and difficulty seeing at night.
The lens grows throughout life.
Aging causes lens fibres to lose transparency, especially in the nucleus.
The lens becomes denser and scatters light, producing glare and blurred vision.
Surgical removal of the opaque lens and implantation of an intraocular lens, restoring transparency and focusing capacity.
A patient presents with severe eye pain, headache, halos around lights, red eye, and a mid-dilated pupil.
Aqueous humour is produced in the posterior chamber and drains through the iridocorneal angle into the canal of Schlemm.
Blockage at this angle rapidly increases intraocular pressure.
Rising pressure compresses the optic nerve and retinal blood flow.
Immediate reduction of intraocular pressure using medications (acetazolamide, β-blockers) followed by definitive procedures like laser peripheral iridotomy.
A patient develops sudden, painless, complete vision loss in one eye.
The central retinal artery is an end artery supplying the inner retinal layers.
Occlusion stops blood flow → ischemia → sudden blindness.
The outer retina may still receive minimal diffusion from choroidal vessels, but this is insufficient.
Urgent ocular massage, lowering intraocular pressure, and rapid management of embolic risk—but prognosis is usually poor due to irreversible ischemia within minutes.
A patient has ptosis, a dilated pupil, and an eye deviated “down and out.”
Third nerve supplies:
Levator palpebrae (ptosis)
Sphincter pupillae (pupil dilatation)
Most extraocular muscles except lateral rectus and superior oblique.
Paralysis leaves the unopposed lateral rectus and superior oblique, pulling the eye downwards and laterally.
Identify the cause—aneurysm, diabetes, trauma—and provide targeted treatment; pupil involvement suggests compression (often life-threatening).
A patient has ptosis, miosis, and facial anhidrosis.
Caused by interruption of sympathetic fibres.
The dilator pupillae loses input → constricted pupil.
Superior tarsal muscle loses tone → mild ptosis.
Sweat glands lose sympathetic supply → anhidrosis.
Treat underlying cause such as tumour, carotid dissection, or spinal lesion.
A young adult has difficulty seeing distant objects (or near objects).
Myopia: Eyeball too long / lens too strong → image focuses in front of retina.
Hypermetropia: Eyeball too short / lens too weak → image focuses behind retina.
Myopia: Concave lenses
Hypermetropia: Convex lenses
Refractive surgery when indicated.
A middle-aged patient cannot focus on near objects.
Ciliary muscle contraction normally relaxes zonular fibres → lens becomes convex.
With age, lens loses elasticity → cannot increase curvature.
Reading glasses with convex lenses to augment near focus.
A patient with a corneal ulcer experiences intense photophobia and reflex tearing.
Cornea is highly innervated (ophthalmic division of trigeminal nerve).
Damage → severe pain + reflex blepharospasm.
Iris shares common pathways and becomes inflamed, adding photophobia.
Topical antimicrobials, cycloplegics, and urgent ophthalmology follow-up.
A patient with chronic headache shows bilateral swollen optic discs on fundus exam.
Raised intracranial pressure is transmitted along the optic nerve sheath.
This compresses the optic nerve head and retinal venous return → disc edema.
Vision may initially remain normal before late deterioration.
Treat underlying raised intracranial pressure (tumour, hydrocephalus, infection).
Outer coat: Sclera + Cornea
Middle coat (Uveal tract): Choroid + Ciliary body + Iris
Inner coat: Retina
Because it is avascular, has regularly arranged collagen fibres, and maintains constant hydration.
It is avascular, so the risk of immune rejection is extremely low.
Dense, irregular collagen fibres that scatter light → white opacity.
The perforated region of sclera through which the optic nerve fibres exit.
Provides nutrients to the outer retina, especially rods and cones via choriocapillaris.
Pars plana (smooth)
Pars plicata with ciliary processes
Controls accommodation by changing lens curvature.
Sphincter pupillae (parasympathetic supply).
Dilator pupillae (sympathetic supply).
The amount of pigment in iris stroma.
Less pigment → blue; more → brown/black.
The area where optic nerve fibres exit; contains no photoreceptors → called the blind spot.
A yellow, cone-rich region responsible for sharp vision.
Center of macula; only cones, thinnest retina, highest visual acuity.
Aqueous humour.
Capillaries of ciliary processes.
Iridocorneal angle → canal of Schlemm → anterior ciliary veins.
Blocked outflow of aqueous humour → raised intraocular pressure → optic nerve damage.
Maintains intraocular pressure
Nourishes cornea and lens
Removes metabolites
Biconvex
Surrounded by capsule
Has nucleus and cortex
Suspended by zonular fibres
Ciliary muscle contracts → zonular fibres relax → lens bulges.
Opacity of the lens, commonly due to aging.
Vitreous body, a gel containing water, collagen and hyaluronic acid.
Maintains eyeball shape and presses retina against choroid.
The inner neural retina separates from the outer pigmented layer due to traction, fluid accumulation, or trauma.
Outer layers: Choroidal vessels
Inner layers: Central retinal artery
It is an end artery → occlusion leads to sudden, irreversible blindness.
Swelling of optic disc due to raised intracranial pressure.
Only cones
No blood vessels (avascular zone)
Thinnest retina
Direct entry of light
The optic cup.
Outer coat: Sclera + Cornea
Middle coat (Uveal tract): Choroid + Ciliary body + Iris
Inner coat: Retina
Because it is avascular, has regularly arranged collagen fibres, and maintains constant hydration.
It is avascular, so the risk of immune rejection is extremely low.
Dense, irregular collagen fibres that scatter light → white opacity.
The perforated region of sclera through which the optic nerve fibres exit.
Provides nutrients to the outer retina, especially rods and cones via choriocapillaris.
Pars plana (smooth)
Pars plicata with ciliary processes
Controls accommodation by changing lens curvature.
Sphincter pupillae (parasympathetic supply).
Dilator pupillae (sympathetic supply).
The amount of pigment in iris stroma.
Less pigment → blue; more → brown/black.
The area where optic nerve fibres exit; contains no photoreceptors → called the blind spot.
A yellow, cone-rich region responsible for sharp vision.
Center of macula; only cones, thinnest retina, highest visual acuity.
Aqueous humour.
Capillaries of ciliary processes.
Iridocorneal angle → canal of Schlemm → anterior ciliary veins.
Blocked outflow of aqueous humour → raised intraocular pressure → optic nerve damage.
Maintains intraocular pressure
Nourishes cornea and lens
Removes metabolites
Biconvex
Surrounded by capsule
Has nucleus and cortex
Suspended by zonular fibres
Ciliary muscle contracts → zonular fibres relax → lens bulges.
Opacity of the lens, commonly due to aging.
Vitreous body, a gel containing water, collagen and hyaluronic acid.
Maintains eyeball shape and presses retina against choroid.
The inner neural retina separates from the outer pigmented layer due to traction, fluid accumulation, or trauma.
Outer layers: Choroidal vessels
Inner layers: Central retinal artery
It is an end artery → occlusion leads to sudden, irreversible blindness.
Swelling of optic disc due to raised intracranial pressure.
Only cones
No blood vessels (avascular zone)
Thinnest retina
Direct entry of light
The optic cup.
a. Limbus
b. Equator
c. Region of muscle insertion
d. Optic nerve entrance
Answer: d. Optic nerve entrance
a. Subretinal space
b. Perichoroidal space
c. Tenon’s space
d. Aqueous sinus
Answer: b. Perichoroidal space
a. Retina
b. Sclera
c. Choroid
d. Optic nerve
Answer: c. Choroid
a. Surface ectoderm
b. Neural crest
c. Mesoderm
d. Neuroectoderm
Answer: d. Neuroectoderm
a. Pupillary margin
b. Iris root
c. Ciliary body
d. Choroid
Answer: b. Iris root
a. Lens
b. Cornea
c. Iris
d. Vitreous
Answer: c. Iris
a. Zonular fibre relaxation
b. Zonular fibre tension
c. Contraction of sphincter pupillae
d. Vitreous pressure
Answer: b. Zonular fibre tension
a. Macula
b. Cup
c. Ora serrata
d. Foveola
Answer: b. Cup
a. V1 and VII
b. V2 and VII
c. V3 and VII
d. V1 and VI
Answer: a. V1 and VII
a. Parasympathetic
b. Somatic motor
c. Sympathetic
d. Sensory
Answer: c. Sympathetic
a. Optic disc
b. Macula
c. Fovea centralis
d. Ora serrata
Answer: c. Fovea centralis
a. Ganglion cell layer
b. Nuclear fibre layer
c. Rod and cone layer
d. Bipolar cell layer
Answer: c. Rod and cone layer
a. Photoreceptors
b. Ganglion cells
c. Bipolar cells
d. Pigmented layer
Answer: b. Ganglion cells
(Because light travels from inner surface → outward.)
a. Retina and optic nerve
b. Cornea and sclera
c. Neural and non-neural retina
d. Iris and ciliary body
Answer: c. Neural and non-neural retina
a. Retina
b. Optic cup
c. Lens
d. Cornea
Answer: c. Lens
a. Albumin
b. Hyaluronic acid
c. Keratin
d. Elastic fibres
Answer: b. Hyaluronic acid
a. Pigmented epithelium of iris
b. Stroma of iris
c. Ciliary processes
d. Retina
Answer: b. Stroma of iris
a. High melanin
b. Xanthophyll pigment
c. Dense rods
d. Retinal blood vessels
Answer: b. Xanthophyll pigment
a. Ciliary muscle contraction
b. Relaxation of zonular fibres
c. Lens becoming more convex
d. Pupillary dilatation
Answer: d. Pupillary dilatation
(Pupil constricts for near vision.)
a. Cataract
b. Optic neuritis
c. Central retinal artery occlusion
d. Glaucoma
Answer: c. Central retinal artery occlusion
a. Optic disc
b. Ora serrata
c. Macula
d. Choroid
Answer: b. Ora serrata
a. Lens capsule
b. Aqueous humour
c. Ciliary muscle
d. Hyaloid canal
Answer: b. Aqueous humour
a. Posterior chamber
b. Vorticose veins
c. Anterior ciliary veins
d. Vitreous body
Answer: c. Anterior ciliary veins
a. Cornea
b. Vitreous
c. Aqueous humour
d. Lens nucleus
Answer: d. Lens nucleus
a. Iris
b. Choroid
c. Ciliary body
d. Retina
Answer: d. Retina
a. Neural crest
b. Hyaloid artery
c. Vitreous vein
d. Surface ectoderm
Answer: b. Hyaloid artery
a. Myopia
b. Papilloedema
c. Cataract
d. Hypermetropia
Answer: c. Cataract
a. Retina
b. Lens and ciliary body
c. Iris
d. Choroid
Answer: b. Lens and ciliary body
a. Inner nuclear layer
b. Outer plexiform layer
c. Nerve fibre layer
d. Photoreceptor layer
Answer: c. Nerve fibre layer
a. Colour vision
b. Regeneration of photopigments
c. Transmission of impulses
d. Aqueous humour production
Answer: b. Regeneration of photopigments
a. Aqueous outflow
b. Lens accommodation
c. Extraocular muscle insertion
d. Macular reflex
Answer: a. Aqueous outflow
a. Retinal vessels
b. Vitreous humour
c. Aqueous humour
d. Choroid
Answer: c. Aqueous humour
a. Colour distortion
b. Chromatic aberration
c. Light scattering
d. Accommodation effort
Answer: c. Light scattering
a. Anchor rods and cones
b. Act as a diffusion barrier between retina and choroid
c. Maintain vitreous pressure
d. Nourish optic nerve
Answer: b. Act as a diffusion barrier between retina and choroid
a. Superior oblique
b. Inferior oblique
c. Superior rectus
d. Lateral rectus
Answer: a. Superior oblique
a. Iris and cornea
b. Lens and cornea
c. Iris and ciliary body
d. Lens and iris
Answer: a. Iris and cornea
a. Corneal curvature
b. Lens elasticity
c. Vitreous tension
d. Extraocular muscles
Answer: b. Lens elasticity
a. Rods and cones
b. Retinal vessels
c. Optic disc fibres
d. Scleral spur
Answer: a. Rods and cones
a. Intraocular
b. Intraorbital
c. Intracanalicular
d. Intracranial
Answer: a. Intraocular
(Papilloedema occurs here.)
a. Central retinal artery occlusion
b. Central retinal vein occlusion
c. Cataract
d. Glaucoma
Answer: a. Central retinal artery occlusion
Outer fibrous coat, middle vascular coat, and inner nervous coat.
The cornea.
Regular collagen arrangement, avascularity, and controlled hydration.
The junction between the cornea and sclera.
The area where the optic nerve exits (lamina cribrosa).
A fascial sheath around the eyeball, allowing smooth movements.
Epithelium, Bowman’s layer, stroma, Descemet’s membrane, endothelium.
It is supplied richly by the ophthalmic division of trigeminal nerve.
Aqueous humour and lacrimal fluid.
Nourishes the outer retina, especially rods and cones.
Pars plana and pars plicata (with ciliary processes).
Accommodation — changes the shape of the lens for near vision.
Parasympathetic fibres through the oculomotor nerve.
Sphincter pupillae (parasympathetic) and dilator pupillae (sympathetic).
Due to the amount of pigment in its stroma.
Point where optic nerve exits; no photoreceptors → blind spot.
A yellow region responsible for detailed central vision.
Only cones, no blood vessels, and thinnest retinal layers.
Central retinal artery.
Choroidal vessels.
Clear fluid in anterior and posterior chambers maintaining IOP.
By ciliary processes.
Iridocorneal angle → canal of Schlemm → ciliary veins.
Intraocular pressure rises → glaucoma.
To fine-tune focus during accommodation.
Gradual degeneration of lens fibres → cataract.
A transparent gel filling the posterior segment, supporting retina.
Liquefaction causes tiny collagen strands to cast shadows on retina.
Optic cup (neuroectoderm).
Surface ectoderm (lens placode).
Optic disc swelling due to raised intracranial pressure.
Sudden painless blindness with a cherry-red spot.
Progressive degeneration of photoreceptors with night blindness.
The anterior limit of the light-sensitive retina.
To detect diabetic retinopathy, which can cause blindness.
Pupil constriction + lens thickening + convergence for near vision.
A remnant of the foetal hyaloid artery within vitreous.
Tearing of iris vessels → blood in anterior chamber.
Reflection of light from vascular retina.
Vitamin A deficiency affecting rods.
Get the full PDF version of this chapter.
Continue with Google