Practice 40 high-yield MCQs on corneal physiology, aqueous humor dynamics, and intraocular pressure. Includes answers and explanations for NEET PG, NEXT, AIIMS, and MRCSEd and ophthalmic officer DHS preparation.

The main reason for corneal transparency is:
A. High water content
B. Regular arrangement of collagen fibrils ✅
C. Absence of blood vessels
D. Thin epithelium
Exp: Corneal transparency depends on the uniform spacing of collagen fibres in stroma (Maurice’s lattice theory).

Normal corneal hydration is maintained at:
A. 100%
B. 78% ✅
C. 50%
D. 90%
Exp: Cornea stays relatively dehydrated (~78% water) for transparency.

Which corneal layer is responsible for maintaining dehydration?
A. Epithelium
B. Endothelium ✅
C. Bowman’s membrane
D. Stroma
Exp: Endothelial pump (Na+/K+ ATPase) regulates stromal hydration.

The main ion transported by corneal endothelial pump is:
A. Sodium ✅
B. Potassium
C. Chloride
D. Calcium
Exp: Active Na+ transport drives fluid out of stroma.

The corneal epithelium contributes to transparency by:
A. Tight junctions preventing fluid entry ✅
B. Producing aqueous humor
C. Secreting collagen
D. Forming trabecular meshwork
Exp: Epithelial barrier stops excess fluid absorption.

Most oxygen to cornea is supplied from:
A. Aqueous humor
B. Tear film ✅
C. Conjunctival vessels
D. Limbal vessels
Exp: Oxygen diffuses from atmosphere via tears.

During sleep, corneal oxygen is mainly derived from:
A. Palpebral conjunctiva
B. Palpebral vessels ✅
C. Tear film
D. Limbal capillaries
Exp: Closed eye → oxygen from palpebral conjunctival vessels.

Corneal nutrition (glucose) comes primarily from:
A. Tear film
B. Aqueous humor ✅
C. Limbal vessels
D. Conjunctiva
Exp: Glucose diffuses from aqueous humor.

Normal corneal thickness (central) is about:
A. 250 µm
B. 500–550 µm ✅
C. 700 µm
D. 1000 µm
Exp: Central cornea ~520 µm, periphery thicker.

Which corneal layer is non-regenerating?
A. Epithelium
B. Stroma
C. Bowman’s membrane ✅
D. Endothelium
Exp: Bowman’s does not regenerate after injury.

Aqueous humor is formed mainly by:
A. Simple diffusion
B. Ultrafiltration
C. Active secretion ✅
D. Osmosis
Exp: 70% secretion by ciliary epithelium; rest diffusion & ultrafiltration.

Aqueous humor is secreted by:
A. Non-pigmented ciliary epithelium ✅
B. Pigmented ciliary epithelium
C. Iris stroma
D. Lens epithelium
Exp: Non-pigmented layer actively secretes aqueous.

Normal aqueous humor production rate is:
A. 1 µl/min
B. 2–3 µl/min ✅
C. 5 µl/min
D. 0.5 µl/min
Exp: Average rate ~2.5 µl/min.

Aqueous humor flow direction is:
A. Posterior → Anterior chamber → Trabecular meshwork ✅
B. Anterior → Posterior chamber
C. Posterior → Vitreous
D. Anterior → Retina
Exp: Formed in posterior chamber → anterior chamber → outflow.

Major pathway of aqueous drainage:
A. Uveoscleral outflow
B. Trabecular (conventional) pathway ✅
C. Episcleral vessels only
D. Retinal veins
Exp: 85–90% via trabecular meshwork → Schlemm’s canal.

Percentage of aqueous humor drained via uveoscleral pathway:
A. 10–15% ✅
B. 50%
C. 90%
D. 2%
Exp: Minor pathway, important for prostaglandin drugs.

Aqueous humor contains the highest concentration of:
A. Protein
B. Ascorbate (vitamin C) ✅
C. Sodium
D. Albumin
Exp: Aqueous has 20× higher vitamin C than plasma.

Aqueous humor has very low:
A. Protein content ✅
B. Ascorbate
C. Lactate
D. Sodium
Exp: Protein is <1% of plasma → maintains transparency.

Aqueous humor turnover time is approximately:
A. 30 minutes
B. 90 minutes ✅
C. 12 hours
D. 1 day
Exp: Complete turnover ~100 minutes.

Circadian rhythm of aqueous secretion shows:
A. Higher at night
B. Higher during day ✅
C. Constant
D. Random
Exp: Production highest in morning, least at night.

Normal IOP range is:
A. 5–15 mmHg
B. 10–21 mmHg ✅
C. 15–30 mmHg
D. 20–25 mmHg
Exp: Normal range = 10–21 mmHg (mean ~16).

Goldmann applanation tonometry is based on:
A. Indentation principle
B. Imbert-Fick law ✅
C. Rebound principle
D. Fluorescence
Exp: Measures pressure by flattening corneal surface.

IOP is lowest:
A. Early morning
B. Afternoon ✅
C. Evening
D. Night
Exp: Peaks in early morning; lowest in afternoon.

Valsalva maneuver causes:
A. IOP increase ✅
B. IOP decrease
C. No effect
D. IOP fluctuation only at night
Exp: Increased venous pressure → ↑ IOP.

Normal diurnal variation of IOP is:
A. 0–2 mmHg
B. 2–6 mmHg ✅
C. 8–10 mmHg
D. 10–15 mmHg
Exp: Normal variation within 6 mmHg.

IOP increases in:
A. Supine position ✅
B. Upright position
C. After general anesthesia
D. Hypotension
Exp: Venous congestion in supine raises IOP.

Aqueous outflow resistance is greatest at:
A. Trabecular meshwork ✅
B. Schlemm’s canal
C. Episcleral veins
D. Uveoscleral pathway
Exp: Main site of resistance in trabecular meshwork.

Normal episcleral venous pressure is:
A. 5 mmHg ✅
B. 10 mmHg
C. 15 mmHg
D. 20 mmHg
Exp: IOP cannot be lower than EVP.

Drugs that increase uveoscleral outflow:
A. Beta-blockers
B. Prostaglandin analogues ✅
C. Carbonic anhydrase inhibitors
D. Alpha-agonists
Exp: PG analogues increase unconventional outflow.

Carbonic anhydrase inhibitors reduce IOP by:
A. Increasing outflow
B. Decreasing aqueous secretion ✅
C. Increasing EVP
D. Enhancing corneal pump
Exp: Inhibit bicarbonate formation → less secretion.

Most accurate tonometry method is:
A. Schiotz tonometer
B. Goldmann applanation ✅
C. Air puff tonometer
D. Perkins tonometer
Exp: Goldmann = gold standard.

Ocular hypertension is defined as:
A. IOP > 18 mmHg
B. IOP > 21 mmHg with normal optic disc & fields ✅
C. Raised IOP with glaucoma
D. IOP < 10 mmHg
Exp: High pressure without glaucomatous damage.

Hypotony is defined as IOP:
A. <10 mmHg
B. <6 mmHg ✅
C. <15 mmHg
D. <20 mmHg
Exp: Low IOP (<6 mmHg) can cause retinal folds & edema.

Steroids cause glaucoma mainly by:
A. Increasing aqueous production
B. Decreasing trabecular outflow ✅
C. Increasing episcleral pressure
D. Increasing uveoscleral flow
Exp: Steroids alter TM cells, reducing outflow.

Which factor reduces IOP?
A. Exercise ✅
B. Supine posture
C. Valsalva
D. Steroids
Exp: Exercise transiently lowers IOP.

Which systemic drug reduces IOP?
A. Acetazolamide ✅
B. Atropine
C. Steroids
D. Epinephrine
Exp: Carbonic anhydrase inhibitor.

Which drug can cause transient rise in IOP?
A. Mydriatics (e.g., atropine) ✅
B. Beta-blockers
C. Prostaglandins
D. CAIs
Exp: Pupil dilation may block angle in narrow angles.

Tonography measures:
A. Aqueous outflow facility ✅
B. Aqueous secretion
C. Retinal circulation
D. Corneal hydration
Exp: Assesses facility of outflow.

Normal aqueous humor turnover per day:
A. 1–2 times
B. 12–13 times ✅
C. 20 times
D. 3–4 times
Exp: With ~100 min turnover → ~12/day.

IOP rises transiently after:
A. Coughing, sneezing, straining ✅
B. Sleep
C. Exercise
D. Hyperventilation
Exp: All Valsalva-like maneuvers transiently increase IOP.

41. The primary source of corneal ATP is:
A. Anaerobic glycolysis ✅
B. Oxidative phosphorylation
C. Pentose phosphate pathway
D. Citric acid cycle
Exp: The avascular cornea derives 85% of energy from anaerobic glycolysis.

42. Endothelial cell density at birth is:
A. 2500–3000 cells/mm² ✅
B. 1000 cells/mm²
C. 4000–5000 cells/mm²
D. <1500 cells/mm²
Exp: Normal density declines with age; <1000/mm² risks edema.


43. The main antioxidant in cornea protecting from UV damage:
A. Vitamin A
B. Vitamin C (ascorbate) ✅
C. Glutathione
D. Catalase
Exp: Ascorbate in aqueous and cornea absorbs UV rays.


44. Corneal edema develops when endothelial cells fall below:
A. 2500/mm²
B. 1500/mm²
C. 500/mm² ✅
D. 2000/mm²
Exp: Critical threshold for pump failure.


45. The corneal deturgescence (relative dehydration) is maintained by:
A. Endothelial Na+/K+ pump ✅
B. Osmotic gradient only
C. Lacrimal drainage
D. Limbal vessels
Exp: Endothelial pumps remove water from stroma.


46. Most common cause of corneal hypoxia is:
A. Contact lens wear ✅
B. Vitamin A deficiency
C. Trauma
D. Sleep
Exp: Contact lenses reduce oxygen diffusion.


47. Which corneal layer contributes most to rigidity?
A. Stroma ✅
B. Epithelium
C. Endothelium
D. Descemet’s membrane
Exp: Stroma forms ~90% of thickness, providing tensile strength.


48. Corneal swelling first affects:
A. Epithelium
B. Posterior stroma ✅
C. Anterior stroma
D. Descemet’s membrane
Exp: Swelling begins in posterior stroma where lamellae are loose.


49. Corneal deturgescence failure causes:
A. Hydrops ✅
B. Coloboma
C. Microcornea
D. Glaucoma
Exp: Endothelial decompensation → corneal edema/hydrops.


50. Lattice theory of corneal transparency was proposed by:
A. Maurice ✅
B. Goldman
C. Vogt
D. Duke-Elder
Exp: Maurice explained uniform fibril spacing → transparency.




—

Aqueous Humor Physiology

51. Enzyme critical for aqueous secretion:
A. Carbonic anhydrase ✅
B. Aldolase
C. ATPase
D. Glucose-6-phosphatase
Exp: Produces bicarbonate, drives ion transport.


52. Which drug inhibits aqueous humor formation?
A. Acetazolamide ✅
B. Pilocarpine
C. Prostaglandin analogues
D. Timolol
Exp: Acetazolamide inhibits carbonic anhydrase.


53. Hyperosmotic agents reduce IOP by:
A. Drawing fluid from vitreous ✅
B. Blocking trabecular meshwork
C. Inhibiting aqueous secretion directly
D. Enhancing uveoscleral outflow
Exp: They increase plasma osmolality → dehydrate vitreous.


54. Aqueous humor turnover occurs approximately every:
A. 1–2 hours ✅
B. 6 hours
C. 12 hours
D. 24 hours
Exp: Turnover ~100 minutes.


55. Protein content of aqueous compared to plasma is:
A. Similar
B. 1/10
C. 1/20–1/30 ✅
D. Higher
Exp: Very low protein maintains clarity.


56. Main nutrient in aqueous for lens metabolism:
A. Glucose ✅
B. Vitamin A
C. Protein
D. Lactate
Exp: Lens gets glucose from aqueous humor.


57. Which prostaglandin analogue increases uveoscleral outflow?
A. Latanoprost ✅
B. Timolol
C. Acetazolamide
D. Pilocarpine
Exp: Latanoprost → ↑ uveoscleral outflow.


58. Adrenergic agonists (α2, e.g., brimonidine) reduce IOP by:
A. Decreasing aqueous formation ✅
B. Blocking Schlemm’s canal
C. Increasing lens transparency
D. Inhibiting corneal epithelium
Exp: Reduce secretion + modestly ↑ uveoscleral outflow.


59. Pilocarpine reduces IOP by:
A. Opening trabecular meshwork via ciliary muscle contraction ✅
B. Decreasing aqueous formation
C. Increasing episcleral venous pressure
D. Blocking uveoscleral flow
Exp: Parasympathomimetic → improves conventional outflow.


60. Beta-blockers (e.g., timolol) lower IOP by:
A. Decreasing aqueous humor production ✅
B. Increasing trabecular outflow
C. Increasing episcleral venous pressure
D. Reducing vitreous volume
Exp: Reduce secretion at ciliary epithelium.




—

Intraocular Pressure

61. Normal mean IOP in adults:
A. 10 mmHg
B. 16 mmHg ✅
C. 20 mmHg
D. 22 mmHg
Exp: Mean ~16 mmHg, range 10–21.


62. IOP is highest:
A. Early morning ✅
B. Afternoon
C. Evening
D. Night
Exp: Peak at 6–8 am.


63. IOP decreases with:
A. Alcohol intake ✅
B. Supine posture
C. Valsalva
D. Mydriatics
Exp: Alcohol transiently lowers IOP.


64. IOP increases in:
A. Supine posture ✅
B. Exercise
C. Hyperventilation
D. Alcohol
Exp: Supine → venous congestion.


65. Which factor has least effect on IOP?
A. Age
B. Sex ✅
C. Circadian rhythm
D. Posture
Exp: Sex has minimal influence.

66. Thin cornea in tonometry causes:
A. Underestimation of IOP ✅
B. Overestimation
C. No effect
D. Random error
Exp: Thin corneas → falsely low IOP.

67. Thick cornea in tonometry causes:
A. Overestimation of IOP ✅
B. Underestimation
C. No effect
D. Hypotony
Exp: Opposite effect to thin cornea.

68. Manometric method measures IOP by:
A. Direct cannulation of anterior chamber ✅
B. Applanation
C. Indentation
D. Non-contact
Exp: Gold standard but invasive.

69. Rebound tonometry (iCare) is useful in:
A. Children ✅
B. Only adults
C. Aniridia
D. Coloboma
Exp: Handheld, no anesthesia required → pediatric use.

70. Dynamic contour tonometry is less affected by:
A. Corneal thickness ✅
B. IOP fluctuation
C. Aqueous secretion
D. Outflow resistance
Exp: Measures true IOP independent of corneal rigidity.

71. The most common cause of secondary raised EVP is:
A. Carotid-cavernous fistula ✅
B. Diabetes
C. Hypertension
D. Retinitis pigmentosa
Exp: Arteriovenous shunt → ↑ episcleral pressure.

72. In which condition is aqueous production reduced?
A. Uveitis ✅
B. Angle-closure glaucoma
C. Ocular hypertension
D. Steroid use
Exp: Inflammation damages ciliary body → ↓ secretion.

73. Drugs increasing aqueous production:
A. Epinephrine ✅
B. Acetazolamide
C. Timolol
D. Pilocarpine
Exp: Adrenergics stimulate ciliary body.


74. The facility of outflow is measured in:
A. µl/min/mmHg ✅
B. µl/sec
C. mmHg
D. µl/hr
Exp: Expressed as volume/time/pressure.

75. Uveoscleral outflow increases with:
A. Prostaglandins ✅
B. Steroids
C. Beta-blockers
D. Mydriatics
Exp: PG analogues enhance unconventional pathway.

76. Laser trabeculoplasty lowers IOP by:
A. Remodeling trabecular meshwork ✅
B. Decreasing aqueous production
C. Increasing episcleral pressure
D. Increasing vitreous drainage
Exp: Improves trabecular outflow.

77. Aqueous misdirection (malignant glaucoma) is due to:
A. Posterior misdirection of aqueous ✅
B. Overproduction
C. Trabecular blockage
D. Uveitis
Exp: Fluid trapped behind vitreous.

78. Normal aqueous humor pH is:
A. 7.2 ✅
B. 6.8
C. 7.5
D. 7.8
Exp: Slightly alkaline relative to plasma.

79. After cataract surgery, IOP transiently rises due to:
A. Retained viscoelastic material ✅
B. Decreased trabecular outflow
C. Increased aqueous secretion
D. Increased EVP
Exp: OVD remnants block meshwork temporarily.

80. The main site of resistance to aqueous outflow:
A. Juxtacanalicular trabecular meshwork ✅
B. Schlemm’s canal
C. Episcleral veins
D. Iris root
Exp: JCT is key site of resistance.