Learn Chapter Optics of Lenses & Ophthalmic Instruments kanski ophthalmology mcq pdf (Section 3: Prisms, Aberrations & Optical Errors Q81–120) with detailed MCQs and answers. Covers prism principles, base directions, chromatic and spherical aberrations, astigmatism, aniseikonia, and optical errors essential for optometry students, NEET PG, NEXT, AIIMS, and MRCSEd exams. Includes ophthalmic study guide and ophthalmic assistant notes for exam preparation.
Q81. The main function of a prism is to:
A. Magnify image
B. Deviate light without refraction error
C. Reflect image
D. Scatter light
View Answer
B. Deviate light without refraction error ✅ Exp: Prism changes direction of light rays without changing their convergence.
Q82. The apex of a prism is:
A. Base junction
B. Angle between its two refracting surfaces
C. Side edge
D. Optical axis
View Answer
B. Angle between its two refracting surfaces ✅ Exp: Apex = meeting point of two refracting surfaces.
Q83. The base of a prism is the:
A. Edge opposite the apex
B. Midpoint of surface
C. Normal line
D. Refracted beam
View Answer
A. Edge opposite the apex ✅ Exp: Base is opposite to apex and denotes direction of light deviation.
Q84. The deviation produced by a prism depends on:
A. Apex angle and refractive index
B. Lens power
C. Curvature
D. Thickness
View Answer
A. Apex angle and refractive index ✅ Exp: for small angles.
Q85. The unit of prism power is:
A. Diopter
B. Prism Diopter (Δ)
C. Candela
D. Lux
View Answer
B. Prism Diopter (Δ) ✅ Exp: 1 prism diopter deflects a light ray 1 cm per meter of distance.
kanski ophthalmology mcq pdf
Q86. 1 prism diopter (1Δ) deviates light by approximately:
A. 1°
B. 0.57°
C. 0.10°
D. 2°
View Answer
B. 0.57° ✅ Exp: 1Δ = 1 cm deviation per meter = 0.57°.
Q87. The base direction of a prism is always given relative to the:
A. Lens edge
B. Patient’s eye
C. Examiner’s view
D. Optical table
View Answer
B. Patient’s eye ✅ Exp: In ophthalmic prescription, base direction is described from patient’s perspective.
Q88. When a prism is placed base-in before one eye, image appears:
A. Moved toward base
B. Moved toward apex
C. Enlarged
D. Distorted
View Answer
A. Moved toward base ✅ Exp: Prism shifts image toward its apex, but eye sees object toward base.
Q89. A base-out prism induces which fusional movement?
A. Convergence
B. Divergence
C. Torsion
D. None
View Answer
A. Convergence ✅ Exp: Base-out requires eyes to converge to maintain fusion.
Q90. A base-in prism induces:
A. Divergence
B. Convergence
C. Vertical movement
D. Cyclotorsion
View Answer
A. Divergence ✅ Exp: Base-in shifts image outward → divergence.
kanski ophthalmology mcq pdf
Q91. Yoked prisms have:
A. Bases in same direction for both eyes
B. Opposite directions
C. One eye only
D. Rotated axes
View Answer
A. Bases in same direction for both eyes ✅ Exp: Used to shift entire visual field (e.g., post-stroke).
Q92. A +5 D lens decentered 4 mm produces prism of:
A. 0.5Δ
B. 2Δ
C. 5Δ
D. 10Δ
View Answer
B. 2Δ ✅
Q93. In bifocal lenses, prismatic imbalance can cause:
A. Diplopia
B. Color vision loss
C. Myopia
D. Contrast reduction
View Answer
A. Diplopia ✅ Exp: Different prism effects between near and distance segments create diplopia.
Q94. Prisms can be used therapeutically to:
A. Relieve eye strain in phoria
B. Treat cataract
C. Improve contrast
D. Correct myopia
View Answer
A. Relieve eye strain in phoria ✅ Exp: Used to aid binocular alignment in heterophoria or strabismus.
Q95. Yoked prisms have:
A. Bases in same direction for both eyes
B. Opposite directions
C. One eye only
D. Rotated axes
View Answer
A. Bases in same direction for both eyes ✅ Exp: Used to shift entire visual field (e.g., post-stroke).
kanski ophthalmology mcq pdf
Q96. Opposing prism bases create:
A. Differential prismatic effect
B. Field shift
C. Fusion
D. Reduced field
View Answer
A. Differential prismatic effect ✅ Exp: Base-in and base-out combinations can induce vertical or horizontal disparity.
Q97. Neutralizing prism in cover test is used to measure:
A. Angle of deviation
B. Accommodation
C. Visual acuity
D. Binocular rivalry
View Answer
A. Angle of deviation ✅ Exp: Prism power that eliminates movement quantifies deviation.
Q98. The minimum angle of deviation for a prism occurs when:
A. i = r
B. r₁ ≠ r₂
C. Apex = 90°
D. None
View Answer
A. i = r ✅ Exp: Symmetrical refraction through both faces → minimum deviation.
Q99. Dispersion of a prism increases with:
A. Wavelength
B. Refractive index difference
C. Apex thickness
D. Incidence angle
View Answer
B. Refractive index difference ✅ Exp: Larger n difference → greater chromatic separation.
Q100. Prism deviation is smallest for:
A. Blue light
B. Red light
C. Green light
D. Violet light
View Answer
B. Red light ✅ Exp: Longer wavelength (red) bends least.
kanski ophthalmology mcq pdf
Q101. Chromatic aberration occurs because:
A. Refractive index varies with wavelength
B. Prism defect
C. Irregular cornea
D. Spherical surface
View Answer
A. Refractive index varies with wavelength ✅ Exp: Blue bends more than red → different focal points.
Q102. Spherical aberration occurs because:
A. Peripheral rays focus at different points
B. Different lens materials
C. Chromatic dispersion
D. Large aperture
View Answer
A. Peripheral rays focus at different points ✅ Exp: Paraxial rays and peripheral rays focus at different locations.
Q103. The human eye partially corrects spherical aberration due to:
A. Corneal shape (aspheric)
B. Iris curvature
C. Lens translation
D. Pupil dilation
View Answer
A. Corneal shape (aspheric) ✅ Exp: Cornea flattens peripherally, reducing peripheral refraction.
Q104. Coma aberration occurs due to:
A. Oblique incidence of rays
B. Central rays only
C. High refractive index
D. Lens translation
View Answer
A. Oblique incidence of rays ✅ Exp: Produces comet-shaped blur for off-axis points.
Q105. Astigmatism is an aberration due to:
A. Unequal curvature of lens meridians
B. Chromatic dispersion
C. Tear film irregularity
D. Anisometropia
View Answer
A. Unequal curvature of lens meridians ✅ Exp: Two focal lines formed instead of one point focus.
Q106. Spherical aberration increases when:
A. Pupil dilates
B. Pupil constricts
C. Lens moves forward
D. Accommodation increases
View Answer
A. Pupil dilates ✅ Exp: Larger pupil allows more peripheral rays → more aberration.
Q107. The correction of spherical aberration in lenses uses:
A. Aspheric surfaces
B. Cylindrical lenses
C. Convex meniscus
D. Thick lenses
View Answer
A. Aspheric surfaces ✅ Exp: Aspheric designs reduce peripheral power error.
Q108. Cylindrical lenses correct:
A. Astigmatism
B. Chromatic aberration
C. Distortion
D. Myopia
View Answer
A. Astigmatism ✅ Exp: Focus light differently in each meridian to correct astigmatism.
Q109. The axis of a cylindrical lens represents:
A. Meridian with maximum power
B. Meridian with no power
C. Midline of cylinder
D. Direction of refraction
View Answer
B. Meridian with no power ✅ Exp: Axis = 90° from meridian of curvature → no refraction.
Q110. The power of a cylinder acts:
A. Along the axis
B. Perpendicular to the axis
C. Randomly
D. Uniformly
View Answer
B. Perpendicular to the axis ✅ Exp: Cylinder refracts only along meridian perpendicular to its axis.
Q111. Barrel distortion occurs in:
A. Plus lenses
B. Minus lenses
C. Plane lenses
D. Prism lenses
View Answer
A. Plus lenses ✅ Exp: Image magnified more at center → barrel shape.
Q112. Pincushion distortion occurs in:
A. Minus lenses
B. Plus lenses
C. Mirrors
D. Prisms
View Answer
A. Minus lenses ✅ Exp: Image magnified more at periphery → pincushion effect.
Q113. The difference in image size between eyes is called:
A. Anisometropia
B. Aniseikonia
C. Asthenopia
D. Diplopia
View Answer
B. Aniseikonia ✅ Exp: Unequal image sizes may prevent binocular fusion.
Q114. Aniseikonia >5% may cause:
A. Diplopia
B. Myopia
C. Glare
D. Chromatic effect
View Answer
A. Diplopia ✅ Exp: Unequal retinal image sizes cause fusion difficulty → double vision.
Q115. Best correction for aniseikonia:
A. Contact lenses
B. Spectacles
C. Prism lenses
D. Over-minus lenses
View Answer
A. Contact lenses ✅ Exp: Contact lenses minimize magnification difference between eyes.
Q116. Irregular astigmatism is usually due to:
A. Corneal scars or keratoconus
B. Spherical error
C. Accommodation
D. Retinal change
View Answer
Q116. Irregular astigmatism is usually due to: Exp: Irregular corneal surface alters curvature in multiple axes.
Q117. Aberrations increase with:
A. Lens aperture and thickness
B. Pupil constriction
C. Low refractive index
D. Central rays
View Answer
A. Lens aperture and thickness ✅ Exp: Peripheral rays contribute more error with larger apertures.
Q118. Diffraction becomes significant when:
A. Pupil < 2 mm
B. Pupil > 6 mm
C. No cornea
D. Lens thickens
View Answer
Q118. Diffraction becomes significant when: Exp: Small aperture increases diffraction pattern → reduced resolution.
Q119. Chromatic aberration causes:
A. Color fringes around objects
B. Diplopia
C. Retinal burn
D. Glare
View Answer
A. Color fringes around objects ✅ Exp: Dispersion causes red-blue halos at contrast edges.
Q120. Anisometropia >3 D commonly leads to:
A. Suppression or amblyopia
B. Myopia
C. Hypermetropia
D. Diplopia only
View Answer
A. Suppression or amblyopia ✅ Exp: Large refractive difference leads to cortical suppression of one image.
