Comprehensive Ophthalmic Anatomy - Exam Preparation

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Comprehensive Ophthalmic Anatomy - Exam Preparation

1. Describe the blood supply of the visual pathway

  • Retina: central retinal artery and choroidal circulation (posterior ciliary arteries).
  • Optic nerve: central retinal artery (intraocular part), pial plexus (intraorbital), ophthalmic and internal carotid branches (intracanalicular and intracranial parts).
  • Optic chiasma: supplied by anterior cerebral and anterior communicating arteries.
  • Optic tract: branches of anterior choroidal artery.
  • Lateral geniculate body: supplied by anterior and posterior choroidal arteries.
  • Optic radiations: middle cerebral artery.
  • Visual cortex: posterior cerebral artery.

2. Give an account on the anatomy of the macula

  • Located temporal to optic disc, ~5.5 mm in diameter.
  • Center: fovea centralis (~1.5 mm), contains only cones.
  • Surrounded by parafovea and perifovea.
  • Foveal pit: depression with highest visual acuity.

3. Describe the anatomy of the lacrimal gland

  • Located in lacrimal fossa (superolateral orbit).
  • Two parts: orbital (larger) and palpebral (smaller).
  • Drains via ducts to superior conjunctival fornix.
  • Innervated by parasympathetic fibers (facial nerve).

4. Give an account on the development of the iris

  • Derived from both neuroectoderm (epithelia, muscles) and neural crest (stroma).
  • Anterior pigmented epithelium gives rise to dilator and sphincter muscles.

5. Describe the anatomy of the limbus

  • Transition zone between cornea and sclera (~1 mm wide).
  • Contains stem cells, aqueous outflow structures (trabecular meshwork, Schlemm’s canal).

6. Describe the anatomy of the inferior oblique muscle

  • Origin: anterior floor of orbit (maxilla).
  • Insertion: posterolateral inferior globe.
  • Action: extorsion, elevation, abduction.
  • Innervation: inferior division of oculomotor nerve (CN III).

7. Discuss the embryology of the lacrimal drainage system

  • Arises from surface ectoderm.
  • Solid cord forms between lateral nasal and maxillary processes → canalizes into lacrimal sac and nasolacrimal duct.

8. Enumerate the structural changes occurring at the ora serrata

  • Retina ends and ciliary body begins.
  • Neural retina becomes non-neural ciliary epithelium.
  • Choroid continues as ciliary stroma.

9. Enumerate the structures attached to the lateral orbital tubercle

  • Lateral palpebral ligament
  • Lateral check ligament
  • Lockwood’s ligament
  • Lateral horn of levator aponeurosis

10. Enumerate the arterial supply of the eyelid

  • Medial palpebral arteries (from ophthalmic artery)
  • Lateral palpebral arteries (from lacrimal artery)
  • Superficial temporal artery
  • Transverse facial artery

51. Enumerate ocular structures derived embryologically from:
a. Neuroectoderm: Retina, optic nerve, RPE, iris muscles, ciliary body epithelium
b. Mesoderm: Extraocular muscles, vascular endothelium, sclera (partly), blood vessels

52. Write the thickness of different parts of the sclera in an emmetropic eye

  • Posterior pole: ~1 mm
  • Equator: ~0.6 mm
  • Limbus: ~0.8 mm

53. Describe the anatomy of the lacrimal secretory and drainage system

  • Secretory: Main lacrimal gland (orbital & palpebral), accessory glands (Krause & Wolfring)
  • Drainage: Puncta → Canaliculi → Lacrimal sac → Nasolacrimal duct → Inferior nasal meatus

54. Describe the anatomy of the superior oblique muscle

  • Origin: Body of sphenoid above optic canal
  • Passes through trochlea, then inserts on superior posterolateral globe
  • Innervation: Trochlear nerve (CN IV)
  • Actions: Intorsion (primary), depression & abduction

55. Describe the embryology of the crystalline lens

  • Derived from surface ectoderm
  • Lens placode → invaginates → forms lens vesicle → differentiates into lens fibers and epithelium

56. Describe the anatomy of the oculomotor nerve nucleus

  • Located in midbrain at superior colliculus level
  • Has subnuclei for each muscle
  • Edinger-Westphal nucleus provides parasympathetic innervation

57. Describe the blood supply of the retina

  • Inner retina: central retinal artery
  • Outer retina: choriocapillaris (from posterior ciliary arteries)

58. Describe the anatomy of the inferior orbital fissure and its clinical significance

  • Between maxilla and greater wing of sphenoid
  • Transmits infraorbital nerve/vessels, zygomatic nerve, inferior ophthalmic vein
  • Can be site of orbital floor fractures and infections

59. Mention the roots and branches of the ciliary ganglion

  • Roots: Sensory (nasociliary), sympathetic (carotid plexus), parasympathetic (oculomotor)
  • Branches: Short ciliary nerves to eyeball (sensory, sympathetic, parasympathetic)

60. Enumerate the layers of the cornea, mentioning thickness

  1. Epithelium (~50 μm)
  2. Bowman’s layer (~10 μm)
  3. Stroma (~450 μm)
  4. Descemet’s membrane (~10–15 μm)
  5. Endothelium (~5 μm)

61. Enumerate five nerves related to the cavernous sinus (order and position)

  1. Oculomotor (superior)
  2. Trochlear
  3. Ophthalmic (V1)
  4. Maxillary (V2)
  5. Abducens (within sinus, inferomedial)

62. Mention the attachments of the vitreous to the surroundings

  • Strongest: vitreous base (ora serrata)
  • Others: optic disc, macula, retinal vessels, posterior lens capsule

63. Enumerate ocular structures derived from the neural ectoderm

  • Retina, RPE, optic nerve, ciliary epithelium, iris epithelium, iris muscles

64. Describe the anatomy of the lateral rectus muscle

  • Origin: Annulus of Zinn
  • Insertion: lateral globe (~7 mm from limbus)
  • Action: abduction
  • Innervation: abducent nerve (CN VI)

65. Describe the anatomy of the superior orbital fissure

  • Between greater and lesser wings of sphenoid
  • Transmits CN III, IV, V1, VI, ophthalmic veins
  • Divided by common tendinous ring

66. Describe the anatomy of the central retinal artery

  • Branch of ophthalmic artery
  • Enters optic nerve ~1 cm behind globe
  • Divides at optic disc into four major branches

67. Describe the anatomy of the capsule of the crystalline lens

  • Basement membrane surrounding lens
  • Thicker anteriorly than posteriorly
  • Provides site of zonular attachment

68. Enumerate 8 structures piercing the orbital septum

  • Medial/lateral palpebral arteries and veins
  • Lymphatics
  • Sensory nerves (infraorbital, supratrochlear, etc.)
  • Muscles (levator aponeurosis, Müller's muscle fibers)

69. Enumerate the branches of ophthalmic division of trigeminal nerve (V1)

  1. Nasociliary → infratrochlear, ethmoidal, long ciliary
  2. Frontal → supratrochlear, supraorbital
  3. Lacrimal nerve

70. Enumerate the posterior anatomical relations of lacrimal sac (anterior to posterior)

  • Medial palpebral ligament
  • Orbicularis oculi
  • Lacrimal fascia
  • Lacrimal bone

71. Enumerate the layers of the iris

  1. Anterior border layer
  2. Stroma
  3. Anterior pigment epithelium
  4. Posterior pigment epithelium

72. Enumerate the components of the blood-retinal barrier

  • Inner: retinal capillary endothelial tight junctions
  • Outer: RPE tight junctions

73. Enumerate the structures in the lateral wall of cavernous sinus (superior to inferior)

  1. CN III
  2. CN IV
  3. CN V1
  4. CN V2

74. Describe the microscopic appearance of Bruch’s membrane

  • Five-layered thin structure between RPE and choriocapillaris
  • Appears eosinophilic, acellular, and lamellar under microscopy

75. Enumerate ocular structures derived from the mesoderm

  • Extraocular muscles, vascular endothelium, blood, connective tissue of orbit and sclera

76. Name the bones forming the bony nasolacrimal duct

  • Maxilla
  • Lacrimal bone
  • Inferior nasal concha (contributes to bony canal)

77. Enumerate and describe conjunctival glands

  • Glands of Krause & Wolfring: accessory lacrimal glands
  • Goblet cells: mucin production
  • Located in fornices and palpebral conjunctiva

78. Describe the microscopic anatomy of the corneal epithelium

  • Stratified squamous non-keratinized
  • 5–7 layers
  • Surface cells have microvilli; tight junctions form barrier

79. Enumerate the components of suspensory ligament of the lens

  • Zonular fibers from ciliary epithelium to lens capsule
  • Support lens and mediate accommodation

80. Describe the blood supply of the eyelids

  • Medial/lateral palpebral arteries
  • Transverse facial artery
  • Superficial temporal artery
  • Arterial arcades within eyelid

81. Describe the attachments, relations, and structures piercing orbital septum

  • Attached to tarsal plates and orbital rim
  • Related to orbicularis oculi, skin, and subcutaneous tissue
  • Pierced by vessels, nerves, aponeurosis, and muscles

82. Describe the origin, course, branches of ophthalmic division (V1)

  • Origin: trigeminal ganglion
  • Course: lateral wall of cavernous sinus → superior orbital fissure
  • Branches: nasociliary, frontal, lacrimal

83. Describe the anatomy of smooth muscles of globe/orbit

  • Iris sphincter & dilator muscles (from neuroectoderm)
  • Ciliary muscle (from neural crest)
  • Orbital smooth muscle: Müller's muscle

84. Describe the bony anatomy of lacrimal fossa

  • Located in anterior medial orbital wall
  • Formed by lacrimal bone and frontal process of maxilla

85. Describe the blood supply of the conjunctiva

  • Palpebral conjunctiva: marginal/arcade vessels from eyelids
  • Bulbar conjunctiva: anterior ciliary arteries

86. Discuss the Spiral of Tillaux

  • Imaginary line connecting insertions of rectus muscles
  • Medial rectus: closest to limbus (~5.5 mm), superior/lateral/inferior farther

87. Enumerate structures derived from:
a. Surface ectoderm: lens, corneal epithelium, lacrimal gland, eyelid skin
b. Neuroepithelium: retina, RPE, iris epithelium, optic nerve

88. Enumerate structures within & in lateral wall of cavernous sinus

  • Within sinus: CN VI, internal carotid artery
  • Lateral wall: CN III, IV, V1, V2 (superior to inferior)

89. Discuss vitreous attachments

  • Strongest at vitreous base (ora serrata)
  • Other sites: optic disc, macula, retinal vessels, lens capsule

90. Describe aqueous secretion & outflow

  • Secreted by ciliary epithelium
  • Flows through pupil to anterior chamber
  • Drains via trabecular meshwork → Schlemm’s canal
  • Angle of anterior chamber critical for outflow

91. Describe the visual (occipital) cortex

  • Located in calcarine fissure of occipital lobe
  • Primary visual cortex (area 17): striate cortex
  • Receives input from lateral geniculate body

92. Describe the anatomy of the optic chiasma

  • Oval structure above pituitary gland
  • Nasal retinal fibers cross midline
  • Surrounded by circle of Willis arteries

93. Describe anatomical relations of tarsal plates and orbital septum (with diagram)

  • Tarsal plates: dense CT plates within eyelids
  • Orbital septum: fibrous sheet from orbital rim to eyelids
  • Septum fuses with tarsal plate anteriorly

94. Discuss arterial supply of anterior eye segment

  • Long posterior ciliary arteries
  • Anterior ciliary arteries
  • Together form circulus iridis major

95. Describe blood supply of retina and optic nerve head

  • Retina: central retinal artery (inner), choriocapillaris (outer)
  • Optic nerve head: circle of Zinn–Haller (short posterior ciliary arteries)

96. Describe anatomy of oblique muscles

  • Superior oblique: origin from sphenoid, passes trochlea, inserts superior-lateral globe
  • Inferior oblique: origin from maxilla, inserts posterolateral globe
  • Actions: intorsion/extorsion, elevation/depression

97. Describe Levator Palpebrae Superioris Muscle

  • Origin: lesser wing of sphenoid
  • Insertion: upper eyelid (skin, tarsal plate)
  • Elevates upper eyelid
  • Innervated by CN III

98. Describe the embryology of vitreous

  • Primary: mesenchymal origin (hyaloid vasculature)
  • Secondary: collagen + hyaluronic acid (forms main gel)
  • Tertiary: zonules (from neuroectoderm)

99. Describe the anatomy of the ophthalmic artery: origin, course, relations, and branches.

  • Origin: The ophthalmic artery arises from the internal carotid artery just after it emerges from the cavernous sinus.
  • Course: It enters the orbit through the optic canal, located inferolateral to the optic nerve. Once inside the orbit, it crosses over the optic nerve from lateral to medial and runs along the medial wall of the orbit.
  • Relations:
    • Initially: Inferolateral to the optic nerve
    • Then: Crosses superior to the optic nerve and continues medially
  • Branches:
    1. Central retinal artery – penetrates the optic nerve to supply the inner retina
    2. Lacrimal artery – supplies the lacrimal gland and lateral eyelids
    3. Posterior ciliary arteries (short and long) – supply the choroid and ciliary body
    4. Muscular branches – supply extraocular muscles
    5. Supraorbital artery – travels with supraorbital nerve to forehead
    6. Posterior and anterior ethmoidal arteries – supply ethmoid sinus and nasal cavity
    7. Medial palpebral arteries – supply the medial eyelids
    8. Supratrochlear artery – terminal branch to forehead
    9. Dorsal nasal artery – supplies the lacrimal sac and nose

100. Discuss the anatomy of the lateral rectus muscle.

  • Origin: Common tendinous ring (Annulus of Zinn) at the apex of the orbit
  • Insertion: Lateral surface of the sclera, about 7 mm from the limbus
  • Nerve Supply: Abducent nerve (cranial nerve VI)
  • Action: Abducts the eyeball (moves it laterally away from the midline)

101. Describe the anatomy of the superior orbital fissure.

  • Location: Between the greater and lesser wings of the sphenoid bone
  • Boundaries:
    • Superiorly: Lesser wing of the sphenoid
    • Inferiorly: Greater wing of the sphenoid
  • Divisions and Contents:
    • Lateral part (outside annulus of Zinn): Lacrimal nerve, frontal nerve, trochlear nerve, superior ophthalmic vein
    • Middle part (within annulus of Zinn): Superior and inferior divisions of oculomotor nerve, nasociliary nerve, abducent nerve
    • Medial part: Sometimes inferior ophthalmic vein passes through

102. Describe the anatomy of the orbital veins.

  • Superior ophthalmic vein:
    • Formed by the union of the supraorbital and angular veins
    • Travels through the superior orbital fissure
    • Drains into the cavernous sinus
  • Inferior ophthalmic vein:
    • Drains the lower part of the orbit
    • Divides into two branches:
      • One drains into the cavernous sinus
      • Another into the pterygoid venous plexus
  • Clinical Note: These veins communicate with the facial vein and angular vein, creating a potential route for infection spread to the brain (danger triangle of the face)

103. Describe the anatomy of the inferior oblique muscle.

  • Origin: Maxillary bone, lateral to the nasolacrimal duct
  • Insertion: Posterolateral aspect of the sclera, under the lateral rectus
  • Nerve Supply: Inferior division of the oculomotor nerve (cranial nerve III)
  • Actions:
    • Primary: Extorsion (external rotation)
    • Secondary: Elevation
    • Tertiary: Abduction

104. Describe the embryology of the crystalline lens.

  • Origin: Surface ectoderm
  • Development:
    • The optic vesicle induces the overlying surface ectoderm to form the lens placode
    • Lens placode invaginates to form the lens pit, which deepens and pinches off to form the lens vesicle
    • Posterior cells of the lens vesicle elongate anteriorly to become primary lens fibers, forming the embryonic nucleus
    • Anterior cells remain cuboidal and form the lens epithelium

105. Describe the relations of the lacrimal sac.

  • Anterior: Medial palpebral ligament
  • Posterior: Lacrimal part of orbicularis oculi (Horner's muscle)
  • Lateral: Lacrimal fossa (formed by the frontal process of the maxilla and the lacrimal bone)
  • Medial: Skin and subcutaneous tissue
  • Superior: Common canaliculus enters the sac
  • Inferior: Continues into the nasolacrimal duct

106. Describe the anatomy of the optic canal.

  • Location: In the lesser wing of the sphenoid bone
  • Transmits:
    • Optic nerve (cranial nerve II)
    • Ophthalmic artery
  • Surrounded by: Common tendinous ring (Annulus of Zinn)

107. Describe the blood supply of the conjunctiva.

  • Palpebral conjunctiva:
    • Supplied by the marginal and peripheral arcades from the palpebral branches of the ophthalmic artery
  • Bulbar conjunctiva:
    • Supplied by anterior ciliary arteries and posterior conjunctival arteries (from the muscular and lacrimal branches)
  • Limbal conjunctiva:
    • Supplied by a pericorneal vascular plexus formed from anterior ciliary arteries

108. Describe the anatomy of the oculomotor nerve nucleus.

  • Location: Midbrain at the level of the superior colliculus, ventral to the cerebral aqueduct
  • Components:
    • Somatic motor nucleus: Supplies the extraocular muscles (except lateral rectus and superior oblique)
    • Edinger-Westphal nucleus: Parasympathetic; sends preganglionic fibers to the ciliary ganglion to innervate sphincter pupillae and ciliary muscle

109. Describe the anatomy of the medial wall of the orbit.

  • Bones:
    1. Frontal process of the maxilla
    2. Lacrimal bone
    3. Ethmoid bone (lamina papyracea)
    4. Body of the sphenoid bone
  • Features:
    • Thinnest wall of the orbit (especially ethmoid bone)
    • Contains the lacrimal fossa anteriorly
    • Medial wall separates the orbit from the ethmoid sinus

110. Describe the anatomy of the central retinal artery.

  • Origin: Branch of the ophthalmic artery
  • Course:
    • Enters the optic nerve about 1 cm behind the eyeball
    • Travels within the optic nerve to the retina
    • Emerges at the optic disc and divides into four major branches (superior/inferior nasal and temporal)
  • Supply: Inner two-thirds of the retina (except the fovea)

111. Describe the anatomy of the glands of the eyelid.

  • Meibomian (tarsal) glands: Located in the tarsal plate, sebaceous glands secreting the oily layer of the tear film
  • Glands of Zeis: Sebaceous glands associated with eyelash follicles
  • Glands of Moll: Modified sweat glands at the eyelid margin
  • Accessory lacrimal glands:
    • Glands of Krause: Located in the conjunctival fornices
    • Glands of Wolfring: Located near the superior tarsal border

112. Describe the anatomy of the ophthalmic nerve.

  • Origin: First division of the trigeminal nerve (cranial nerve V)
  • Type: Purely sensory
  • Divisions:
    1. Lacrimal nerve: Supplies lacrimal gland, conjunctiva, lateral upper eyelid
    2. Frontal nerve: Divides into supratrochlear and supraorbital nerves; supplies forehead and scalp
    3. Nasociliary nerve: Gives off long ciliary nerves, anterior/posterior ethmoidal nerves, and infratrochlear nerve

113. Describe the anatomy of the lacrimal fossa.

  • Location: In the frontal bone at the anterolateral part of the roof of the orbit
  • Contents: Houses the lacrimal gland (orbital lobe)
  • Boundaries:
    • Lateral: Frontal bone
    • Medial: Orbital septum

114. Describe the insertion of the levator palpebrae superioris muscle.

  • Insertion:
    1. Skin of the upper eyelid (via aponeurosis)
    2. Anterior surface of the superior tarsal plate
    3. Superior conjunctival fornix (via fibers blending with Müller’s muscle)

115. Enumerate the bones forming the floor of the orbit, and discuss the related foramina and fissures.

  • Bones of the orbital floor:
    1. Maxilla (major part)
    2. Zygomatic bone
    3. Palatine bone (small posterior part)
  • Foramina and fissures:
    • Infraorbital groove and canal: Transmit the infraorbital nerve and vessels
    • Inferior orbital fissure: Communicates with the pterygopalatine and infratemporal fossae; transmits zygomatic nerve, infraorbital nerve, and vessels
  • 116. Discuss the variation in scleral thickness in the emmetropic eye and its clinical importance.
  • Thickness:
  • Thickest: At the posterior pole (around 1.0 mm)
  • Intermediate: At the equator (about 0.4–0.6 mm)
  • Thinnest: Just behind the rectus muscle insertions (as little as 0.3 mm)
  • Clinical importance:
  • Thinner areas are more susceptible to perforation during surgery or trauma
  • Posterior staphyloma tends to occur at the thinner posterior pole in pathological myopia
  • 117. Describe the blood supply of the eyelids.
  • Arterial supply:
  • Medial side: Medial palpebral branches of the ophthalmic artery
  • Lateral side: Lateral palpebral branches of the lacrimal artery
  • Form two arcades:
  • Marginal arcade (near lid margin)
  • Peripheral arcade (near superior tarsus)
  • Venous drainage:
  • Medial: Angular vein → facial vein
  • Lateral: Superficial temporal vein
  • 118. Enumerate the anatomical changes occurring at the Ora serrata.
  • Termination of the retina; neural retina ends, non-neural ciliary epithelium begins
  • Rods and cones disappear
  • Pigmented and non-pigmented layers of the ciliary epithelium start
  • Marks transition from photosensitive to non-photosensitive retina
  • 119. What are the Palisades of Vogt (rete ridges) and what is their function?
  • Radial fibrovascular ridges located at the limbus
  • Contain limbal epithelial stem cells
  • Function: Regenerate corneal epithelium; maintain corneal transparency
  • 120. Mention the structures attached to the lateral orbital tubercle.
  • Also called Whitnall’s tubercle
  • Located on the zygomatic bone
  • Structures attached:
  • Lateral palpebral ligament
  • Check ligament of lateral rectus
  • Suspensory ligament of the eyeball (Lockwood’s ligament)
  • Lateral horn of levator aponeurosis
  • 121. Enumerate the branches of the ophthalmic division of the trigeminal nerve and their divisions.
  • Lacrimal nerve: To lacrimal gland, conjunctiva, skin of upper eyelid
  • Frontal nerve: Divides into
  • Supraorbital nerve: Forehead and scalp
  • Supratrochlear nerve: Medial forehead and upper eyelid
  • Nasociliary nerve: Gives rise to
  • Long ciliary nerves
  • Posterior and anterior ethmoidal nerves
  • Infratrochlear nerve
  • Communicating branch to ciliary ganglion
  • 122. What is the End Bulb of Krause and what is its function?
  • A type of mechanoreceptor (encapsulated nerve ending)
  • Located in the conjunctiva
  • Function: Detects low-frequency vibrations and cold sensation; contributes to tear reflex and ocular surface sensation
  • 123. Enumerate the relations of the lacrimal sac.
  • Anterior: Medial palpebral ligament
  • Posterior: Lacrimal part of orbicularis oculi (Horner’s muscle)
  • Lateral: Lacrimal fossa
  • Medial: Skin and subcutaneous tissue
  • Superior: Common canaliculus
  • Inferior: Nasolacrimal duct
  • 124. Describe the anatomy of the common tendinous ring (Annulus of Zinn).
  • Fibrous ring at the apex of the orbit
  • Origin for four recti muscles (superior, inferior, medial, lateral)
  • Encircles:
  • Optic nerve
  • Ophthalmic artery
  • Oculomotor nerve (superior and inferior divisions)
  • Abducent nerve
  • Nasociliary nerve
  • 125. Enumerate the structures passing within the cavernous sinus and those embedded in the lateral wall.
  • Within the sinus:
  • Internal carotid artery
  • Abducent nerve (CN VI)
  • Lateral wall (from superior to inferior):
  • Oculomotor nerve (CN III)
  • Trochlear nerve (CN IV)
  • Ophthalmic nerve (V1)
  • Maxillary nerve (V2)

 

126. Mention the origin, insertion, and nerve supply of the inferior oblique muscle.

  • Origin: Maxillary bone just lateral to the nasolacrimal duct
  • Insertion: Posterolateral aspect of the sclera beneath the lateral rectus muscle
  • Nerve supply: Inferior division of the oculomotor nerve (cranial nerve III)
  • Action: Extorsion (primary), elevation (secondary), abduction (tertiary)

127. Enumerate the components of the suspensory ligaments of the crystalline lens.

  • Also called Zonular fibers or Zonule of Zinn
  • Components:
    1. Fibers arising from the non-pigmented epithelium of the ciliary body
    2. Fibers inserting into the equator of the lens capsule
    3. Anterior, posterior, and equatorial zonules
  • Function: Maintain lens position and allow accommodation

128. Mention the layers of Bruch’s membrane.

  1. Basement membrane of the retinal pigment epithelium (RPE)
  2. Inner collagenous layer
  3. Elastic layer
  4. Outer collagenous layer
  5. Basement membrane of the choriocapillaris

129. Mention the thickness of the sclera in different areas and the clinical importance of any variations.

  • Posterior pole: ~1.0 mm (thickest)
  • Equator: ~0.4–0.6 mm
  • Just behind rectus insertions: ~0.3 mm (thinnest)
  • Clinical importance:
    • Thinner sites are more prone to perforation
    • Posterior thinning associated with myopic staphyloma
    • Scleral thinning can affect surgical approaches and suture placement

130. Enumerate ocular structures derived from the neural ectoderm.

  • Retina (both RPE and sensory retina)
  • Optic nerve fibers
  • Ciliary epithelium (non-pigmented and pigmented)
  • Iris epithelium
  • Sphincter and dilator pupillae muscles

131. Enumerate structures derived from:

  • a. Surface ectoderm:
    • Lens
    • Corneal epithelium
    • Conjunctival epithelium
    • Lacrimal gland and ducts
    • Eyelid epidermis and associated glands
  • b. Neuro-epithelium (neural ectoderm):
    • Retina
    • Optic nerve
    • Iris epithelium
    • Ciliary body epithelium
    • Pupillary muscles

132. Name three bones that form the nasolacrimal duct.

  1. Maxilla
  2. Lacrimal bone
  3. Inferior nasal concha (contributes to the canal)

133. Enumerate the structures (in order) in the lateral wall of the cavernous sinus. From superior to inferior:

  1. Oculomotor nerve (CN III)
  2. Trochlear nerve (CN IV)
  3. Ophthalmic division of trigeminal nerve (V1)
  4. Maxillary division of trigeminal nerve (V2)

134. Enumerate three important features of the capillaries of the choriocapillaris.

  1. Fenestrated endothelium (especially facing the retina)
  2. Large lumen – allows rapid nutrient exchange
  3. Dense and flat network – lies immediately adjacent to Bruch’s membrane

135. List in order the structures visualized during gonioscopy. From posterior to anterior:

  1. Ciliary body band
  2. Scleral spur
  3. Trabecular meshwork (pigmented then non-pigmented)
  4. Schwalbe’s line

136. Consider the distance of insertion of the four recti muscles; list them from the one closest to the one farthest from the limbus.

  1. Medial rectus (~5.5 mm from limbus)
  2. Inferior rectus (~6.5 mm)
  3. Lateral rectus (~6.9–7 mm)
  4. Superior rectus (~7.7 mm)
  • This arrangement is clinically important during strabismus surgery and enucleation.

137. Discuss briefly the arrangement of the nerve fibers in the optic chiasma.

  • Nasal retinal fibers cross to the opposite optic tract (decussate)
  • Temporal retinal fibers remain uncrossed and continue on the same side
  • Inferonasal fibers cross anteriorly in the anterior chiasm (Wilbrand’s knee)
  • This arrangement leads to:
    • Bitemporal hemianopia in lesions affecting the central chiasm
    • Junctional scotoma in anterior chiasmal lesions

138. Mention the bones forming the medial wall of the orbit.

  1. Maxilla (frontal process)
  2. Lacrimal bone
  3. Ethmoid bone (lamina papyracea)
  4. Body of the sphenoid
  • The medial wall is the thinnest and separates the orbit from the ethmoid sinus.

139. Enumerate the nerves piercing the orbital septum.

  1. Supratrochlear nerve
  2. Supraorbital nerve
  3. Infratrochlear nerve
  4. External nasal nerve
  5. Lacrimal nerve
  • These nerves provide sensory innervation to the eyelids and face.

140. Mention the surface anatomy of the Ora Serrata.

  • Located ~6–7 mm behind the limbus nasally and ~7–8 mm temporally
  • Marks the anterior limit of the retina and transition to the non-photosensitive ciliary body

141. Mention (in order) the nerves at the lateral wall of the cavernous sinus. From superior to inferior:

  1. Oculomotor nerve (CN III)
  2. Trochlear nerve (CN IV)
  3. Ophthalmic nerve (V1)
  4. Maxillary nerve (V2)

142. Mention the actions of the superior oblique muscle.

  • Primary: Intorsion (inward rotation)
  • Secondary: Depression
  • Tertiary: Abduction
  • Most effective depressor when the eye is adducted

143. Mention the surface anatomy of the nasolacrimal duct.

  • Begins at the lower end of the lacrimal sac (just below the medial canthus)
  • Travels inferoposteriorly within the nasolacrimal canal (maxilla)
  • Opens into the inferior meatus of the nasal cavity
  • Length: ~18 mm

144. Describe the blood-retina barrier.

  • Outer barrier: Formed by tight junctions in the retinal pigment epithelium (RPE)
  • Inner barrier: Formed by non-fenestrated endothelium of retinal capillaries
  • Function:
    • Prevents leakage of proteins and harmful substances into the retina
    • Maintains homeostasis necessary for photoreceptor function

145. If a surgical incision is made between the transparent bluish cornea and the white sclera, where will the knife enter the eyeball relative to the canal of Schlemm?

  • The knife will enter just anterior to the canal of Schlemm
  • This region is called the limbus, the transition zone between cornea and sclera
  • Clinical relevance: In trabeculectomy or limbal incisions (e.g., cataract surgery), care is taken to avoid damage to the canal to preserve aqueous outflow

 

 

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