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Physio: 6# Eye & Retina
Q1. The greatest refraction of light in the eye occurs at the:
Lens–vitreous interface
Aqueous humor
Air–cornea interface
Posterior lens surface
Explanation:
Most refraction occurs at the air–cornea interface due to the largest change in refractive index.
Q2. If the eye is considered a single optical system, its total refractive power is approximately:
+40 D
+59 D
+34 D
+70 D
Explanation:
Refractive power ≈ 1 / 0.017 m ≈ +59 diopters.
Q3. Myopia is best corrected by concave lenses because they:
Diverge light rays
Increase axial length
Increase refractive power
Increase corneal curvature
Explanation:
Concave lenses diverge light rays, moving the image from in front of the retina onto it.
Q4. Astigmatism occurs due to:
Weak lens power
Long eyeball
Short eyeball
Uneven corneal curvature
Explanation:
Astigmatism is caused by non-uniform curvature of the cornea causing unequal refraction in different planes.
Q5. During accommodation, increased refractive power of the lens occurs because:
Suspensory ligaments tighten
Lens becomes more convex
Ciliary muscles relax
Pupil dilates
Explanation:
Contraction of ciliary muscles releases ligament tension, making the lens more convex.
Q6. The parasympathetic fibers mediating accommodation originate from:
Superior cervical ganglion
Lateral geniculate body
Edinger–Westphal nucleus
Oculomotor nucleus proper
Explanation:
Preganglionic PSNS fibers arise from the Edinger–Westphal nucleus.
Q7. Presbyopia develops mainly due to:
Loss of lens elasticity
Weak ciliary muscle contraction
Increased axial length
Corneal flattening
Explanation:
Age-related lens hardening and reduced capsule elasticity reduce accommodation.
Q8. A 30-fold change in light entry into the eye is mainly due to:
Lens curvature
Retinal adaptation
Blinking
Change in pupil diameter
Explanation:
Light entry ∝ (pupil diameter)²; 1.5² vs 8² gives ~30-fold difference.
Q9. The sphincter pupillae muscle is supplied by:
Sympathetic fibers
Parasympathetic fibers
Somatic motor fibers
Optic nerve
Explanation:
Parasympathetic stimulation causes pupil constriction (miosis).
Q10. Aqueous humor is primarily drained through:
Uveal tract
Ciliary veins
Trabecular meshwork → Schlemm canal
Choroid plexus
Explanation:
Aqueous humor drains via trabeculae into Schlemm canal then venous circulation.
Q11. Normal mean intraocular pressure (IOP) is approximately:
15 mmHg
5 mmHg
25 mmHg
40 mmHg
Explanation:
Mean IOP is ~15 mmHg; elevation causes glaucoma.
Q12. The most common cause of irreversible blindness worldwide mentioned is:
Cataract
Macular degeneration
Diabetic retinopathy
Glaucoma
Explanation:
Increased IOP in glaucoma damages retina and optic nerve.
Q13. The fovea centralis contains:
Only rods
Only cones
Equal rods and cones
No photoreceptors
Explanation:
Fovea centralis has cones only, giving highest visual acuity.
Q14. High visual acuity at the fovea is due to all EXCEPT:
High cone density
Absence of blood vessels
High rod density
Low cone–ganglion ratio
Explanation:
Fovea has few rods; cones dominate.
Q15. Inner two-thirds of the retina is supplied by:
Central retinal artery
Posterior ciliary arteries
Choroidal vessels only
Venous diffusion
Explanation:
Outer third is supplied by choroid; inner two-thirds by central retinal artery.
Q16. Horizontal cells primarily function to:
Transmit color
Transmit motion
Excite bipolar cells
Enhance contrast
Explanation:
Horizontal cells inhibit bipolar cells and enhance edge contrast.
Q17. Rods differ from cones by having:
Higher visual acuity
Higher sensitivity to light
Color discrimination
Low receptor–ganglion ratio
Explanation:
Rods are highly sensitive and mediate night vision.
Q18. Rod signals reach ganglion cells through:
Direct bipolar pathway
Horizontal cells
Amacrine cells
Interplexiform cells
Explanation:
Rods → bipolar → amacrine → ganglion.
Q19. The photopigment of rods is:
Rhodopsin
Photopsin
Melanopsin
Iodopsin
Explanation:
Rhodopsin consists of scotopsin + 11-cis-retinal.
Q20. Vision involves conversion of light energy into neural signals by:
Refractive adaptation
Neural summation
Electrical coupling
Phototransduction
Explanation:
Phototransduction converts light energy into electrical signals.