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NOCE / ABO Basic practice questions

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Question 1Ocular Anatomy, Physiology, and Refractive Conditions

Which layer forms the outermost surface of the cornea?

  1. Stroma
  2. Endothelium
  3. Epithelium Correct answer.
  4. Descemet membrane

Explanation

The corneal epithelium is the outermost layer and is continuous with the conjunctival epithelium at the limbus. It is a stratified, non-keratinized squamous epithelium that provides a smooth optical surface and a barrier to tears.

Question 2Ocular Anatomy, Physiology, and Refractive Conditions

Aqueous humor is actively secreted into the posterior chamber by which structure?

  1. Trabecular meshwork
  2. Ciliary epithelium Correct answer.
  3. Lens capsule
  4. Corneal endothelium

Explanation

The double-layered ciliary epithelium covering the ciliary processes secretes aqueous humor by active transport. The fluid then passes through the pupil into the anterior chamber.

Question 3Ocular Anatomy, Physiology, and Refractive Conditions

A patient reports clear near vision but blurred distance vision without correction. Which condition does this describe?

  1. Astigmatism
  2. Myopia Correct answer.
  3. Hyperopia
  4. Presbyopia

Explanation

In myopia the eye's refracting power exceeds its axial length, so parallel light from a distant object focuses in front of the retina, blurring distance vision. Near objects diverge and can be focused clearly, which is why uncorrected myopes often read comfortably.

Question 4Ocular Anatomy, Physiology, and Refractive Conditions

Which photoreceptors are responsible for vision in dim light?

  1. Cones
  2. Ganglion cells
  3. Rods Correct answer.
  4. Bipolar cells

Explanation

Rods contain rhodopsin, are highly sensitive to low light levels, and mediate scotopic vision. They do not provide color discrimination and are absent from the foveal center.

Question 5Ocular Anatomy, Physiology, and Refractive Conditions

Which muscle is the primary elevator of the upper eyelid?

  1. Inferior rectus
  2. Superior rectus
  3. Orbicularis oculi muscle
  4. Levator palpebrae Correct answer.

Explanation

The levator palpebrae superioris, innervated by the oculomotor nerve, is the main elevator of the upper lid. The superior tarsal muscle provides only a small amount of additional elevation.

Question 6Ocular Anatomy, Physiology, and Refractive Conditions

What happens during accommodation for near vision?

  1. Relaxation of the ciliary muscle tightens the zonular fibers and flattens the lens
  2. Ciliary muscle contraction makes the lens more convex Correct answer.
  3. The lens flattens and its power decreases
  4. The pupil constricts and the lens moves back

Explanation

Contraction of the ciliary muscle moves the ciliary body inward, relaxing tension on the zonular fibers. The lens then assumes a rounder, more convex shape with increased dioptric power.

Question 7Ocular Anatomy, Physiology, and Refractive Conditions

Which glands secrete the lipid layer of the tear film?

  1. Meibomian glands Correct answer.
  2. Goblet cells
  3. Accessory lacrimal glands of Krause
  4. Lacrimal gland

Explanation

Meibomian glands within the tarsal plates release meibum, which forms the superficial lipid layer of the tear film and slows evaporation.

Question 8Ocular Anatomy, Physiology, and Refractive Conditions

The corneal endothelium maintains corneal transparency chiefly by doing what?

  1. Secreting the lipid layer of the tear film
  2. Actively pumping fluid out of the stroma Correct answer.
  3. Producing new stromal collagen
  4. Generating aqueous humor

Explanation

The endothelium uses metabolic pumps to move fluid and ions from the stroma into the anterior chamber, keeping the stroma partially dehydrated and uniformly spaced. Loss of endothelial cells leads to stromal edema and haze.

Question 9Ocular Anatomy, Physiology, and Refractive Conditions

Which description best characterizes regular astigmatism?

  1. Equal refractive power in all meridians
  2. Meridians 90 degrees apart with unequal power Correct answer.
  3. Progressive loss of accommodation with age
  4. Irregular corneal surface after trauma or infection

Explanation

In regular astigmatism the two principal meridians are perpendicular and have different refractive powers, producing two focal lines. It can be corrected with a cylindrical lens.

Question 10Ocular Anatomy, Physiology, and Refractive Conditions

Which ocular condition produces axial myopia?

  1. Lens power weaker than normal for the axial length
  2. Axial length longer than the eye's optical power requires Correct answer.
  3. Corneal power weaker than the axial length requires
  4. Axial length shorter than the eye's optical power requires

Explanation

In axial myopia the globe is too long for its total refracting power, so distant images focus anterior to the retina. Corneal curvature and lens power may also contribute in refractive myopia.

Question 11Ocular Anatomy, Physiology, and Refractive Conditions

Which structure creates the physiologic blind spot?

  1. Ora serrata
  2. Macula lutea
  3. Fovea
  4. Optic disc Correct answer.

Explanation

The optic disc is the exit point for ganglion cell axons and contains no photoreceptors, so light falling on it is not perceived. This produces a scotoma in the corresponding visual field.

Question 12Ocular Anatomy, Physiology, and Refractive Conditions

The consensual pupillary light response depends on which arrangement?

  1. Decussation of fibers at the optic chiasm alone
  2. Ipsilateral projections from retinal ganglion cells only
  3. Pretectal input to both Edinger-Westphal nuclei Correct answer.
  4. Direct sympathetic innervation of the iris sphincter

Explanation

Afferent pupillary fibers synapse in the pretectal nucleus, which sends bilateral projections to both Edinger-Westphal nuclei. Because of this bilateral link, light in one eye constricts both pupils.

Question 13Ocular Anatomy, Physiology, and Refractive Conditions

Aqueous humor leaving the anterior chamber through the trabecular meshwork enters which structure next?

  1. Canal of Schlemm Correct answer.
  2. Lacrimal drainage canaliculi
  3. Central retinal vein
  4. Suprachoroidal space

Explanation

Aqueous passes through the trabecular meshwork into the canal of Schlemm, then via collector channels into episcleral veins. Resistance at this outflow pathway is a major determinant of intraocular pressure.

Question 14Ocular Anatomy, Physiology, and Refractive Conditions

Presbyopia is caused by which age-related change?

  1. Weakness of the ciliary muscle only
  2. Increased lens elasticity
  3. Excessive corneal curvature
  4. Loss of lens elasticity with age Correct answer.

Explanation

With age the crystalline lens hardens and loses elasticity, so it can no longer steepen enough for near focusing. The condition is corrected with reading additions or multifocal lenses.

Question 15Ocular Anatomy, Physiology, and Refractive Conditions

Which muscle depresses the eye when it is in the adducted position?

  1. Inferior oblique
  2. Lateral rectus
  3. Superior oblique Correct answer.
  4. Inferior rectus

Explanation

The superior oblique's tendon passes through the trochlea, so its depressor action is greatest when the eye is adducted. The inferior rectus is the main depressor when the eye is abducted.

Question 16Ocular Anatomy, Physiology, and Refractive Conditions

Anisometropia is best defined as which of the following?

  1. Unequal pupil diameters in dim light
  2. Complete loss of the eye's accommodation
  3. Unequal refractive error between the two eyes Correct answer.
  4. Absence of the crystalline lens from the eye

Explanation

Anisometropia is a clinically significant difference in refractive error between fellow eyes, which can cause aniseikonia and amblyopia. Small differences are common and usually asymptomatic.

Question 17Ocular Anatomy, Physiology, and Refractive Conditions

Which range represents normal intraocular pressure in most adults?

  1. 5 to 10 mmHg
  2. 10 to 21 mmHg Correct answer.
  3. 22 to 30 mmHg
  4. 31 to 40 mmHg

Explanation

Intraocular pressure in healthy adults typically falls between about 10 and 21 mmHg, with a mean near 15 to 16 mmHg. Values above this range raise concern for glaucoma but do not by themselves define it.

Question 18Ocular Anatomy, Physiology, and Refractive Conditions

A patient has a spectacle correction written as a minus cylinder with axis 180. Which type of astigmatism does this indicate?

  1. Oblique astigmatism
  2. With-the-rule astigmatism Correct answer.
  3. Against-the-rule astigmatism
  4. Irregular astigmatism

Explanation

With-the-rule astigmatism has the steeper meridian near 90 degrees, which is corrected by a minus cylinder at or near 180. Against-the-rule astigmatism is corrected with a minus cylinder near 90 degrees.

Question 19Ocular Anatomy, Physiology, and Refractive Conditions

Photoreceptor outer segment discs are continually renewed. Which cells remove the shed discs?

  1. Photoreceptor inner segments
  2. Müller cells
  3. Retinal pigment epithelium Correct answer.
  4. Ganglion cells

Explanation

The retinal pigment epithelium phagocytoses outer segment discs shed at the tips of photoreceptors, completing the renewal cycle. This process is essential for photoreceptor survival and retinal health.

Question 20Ocular Anatomy, Physiology, and Refractive Conditions

Which statement about the fovea centralis is accurate?

  1. Contains no photoreceptors at all
  2. Contains a high density of rods and gives poor acuity
  3. Contains only cones and gives the sharpest vision Correct answer.
  4. Lies at the optic nerve head

Explanation

The fovea contains a dense array of cones and lacks rods, and overlying retinal layers are displaced so light reaches the receptors directly. This arrangement gives the highest visual acuity.

Question 21Ocular Anatomy, Physiology, and Refractive Conditions

A tightly fitting rigid contact lens reduces corneal oxygenation mainly by limiting oxygen obtained from which source?

  1. Palpebral conjunctival vessels
  2. Atmospheric oxygen Correct answer.
  3. Limbal vasculature
  4. Aqueous humor

Explanation

With the eye open, most corneal oxygen comes directly from the atmosphere dissolved in the tear film. A poorly fitting lens traps a stagnant post-lens tear layer and reduces this exchange, which can cause edema.

Question 22Ocular Anatomy, Physiology, and Refractive Conditions

A lesion compressing the optic chiasm typically produces which visual field defect?

  1. Central scotoma
  2. Homonymous hemianopia
  3. Bitemporal hemianopia Correct answer.
  4. Binasal hemianopia

Explanation

Crossing fibers from the nasal portion of each retina carry the temporal visual fields and are damaged at the chiasm. Their loss produces a bitemporal hemianopia.

Question 23Ocular Anatomy, Physiology, and Refractive Conditions

Horner syndrome results from disruption of which neural pathway?

  1. Sympathetic fibers to the iris dilator Correct answer.
  2. Trigeminal sensory fibers
  3. Parasympathetic fibers in the oculomotor nerve
  4. Optic nerve fibers

Explanation

Loss of sympathetic input to the eye produces miosis, mild ptosis, and reduced facial sweating on the affected side. The dilator pupillae fails to act, so the pupil remains small.

Question 24Ocular Anatomy, Physiology, and Refractive Conditions

What is the palpebral conjunctiva?

  1. The layer covering the back of the cornea
  2. The covering of the sclera up to the limbus
  3. The membrane lining the anterior chamber
  4. The lining of the inside of the eyelids Correct answer.

Explanation

The palpebral conjunctiva lines the inner surface of the eyelids and reflects at the fornices to continue as the bulbar conjunctiva over the globe. It is thin, highly vascular, and firmly adherent to the tarsal plates.

Question 25Geometric and Physical Optics

The refractive index of an optical medium is defined as the ratio of the speed of light in vacuum to the speed of light in that medium. Which expression states this correctly?

  1. frequency in the medium ÷ frequency in vacuum
  2. speed of light in vacuum ÷ speed in the medium Correct answer.
  3. speed of light in the medium ÷ speed in vacuum
  4. wavelength in vacuum ÷ wavelength in the medium

Explanation

Refractive index n compares the vacuum speed of light c with the speed v in the material, so n = c/v. Because light is slower in any material than in vacuum, n is always greater than 1 for real optical media. Frequency is unchanged when light enters a medium; only speed and wavelength change.

Question 26Geometric and Physical Optics

A ray of light strikes a plane mirror at 30° to the normal. What is the angle between the reflected ray and the normal?

  1. 30° Correct answer.
  2. 60°
  3. 15°
  4. 90°

Explanation

The law of reflection states that the angle of incidence equals the angle of reflection, both measured from the normal. Since the incident ray makes 30° with the normal, the reflected ray also makes 30° with the normal. The 60° figure is the angle measured from the mirror surface, not from the normal.

Question 27Geometric and Physical Optics

A person stands 2 m in front of a plane mirror. How far is the person from the image of themselves?

  1. 8 m
  2. 1 m
  3. 4 m Correct answer.
  4. 2 m

Explanation

A plane mirror forms a virtual image as far behind the mirror as the object is in front of it. The image is therefore 2 m behind the mirror, and the total separation between person and image is 2 m + 2 m = 4 m.

Question 28Geometric and Physical Optics

A concave spherical mirror has a radius of curvature of 20 cm. What is its focal length?

  1. 10 cm Correct answer.
  2. 40 cm
  3. 5 cm
  4. 20 cm

Explanation

For a spherical mirror the focal length is half the radius of curvature, f = R/2. With R = 20 cm the focal point lies 10 cm from the vertex, on the same side as the incoming light.

Question 29Geometric and Physical Optics

A thin lens has a focal length of +0.25 m. What is its power in dioptres?

  1. +0.40 D
  2. +2.50 D
  3. +4.00 D Correct answer.
  4. +0.25 D

Explanation

Lens power in dioptres is the reciprocal of the focal length in metres, P = 1/f. Here P = 1/0.25 = +4.00 D. The positive sign indicates a converging lens.

Question 30Geometric and Physical Optics

Which statement describes the image formed by a converging lens when the object is placed beyond twice the focal length?

  1. virtual, erect, and located behind the lens
  2. real, inverted, and able to be projected Correct answer.
  3. erect and located exactly at the focal point
  4. virtual, inverted, and always magnified

Explanation

For an object beyond 2F of a converging lens, the refracted rays actually converge, producing a real image that is inverted and reduced, located between F and 2F on the far side. Because the rays converge, the image can be caught on a screen.

Question 31Geometric and Physical Optics

Which list orders visible light correctly from longest to shortest wavelength?

  1. blue, green, red, violet
  2. red, green, blue, violet Correct answer.
  3. violet, blue, green, red
  4. green, red, violet, blue

Explanation

Within the visible spectrum, red light has the longest wavelength (about 700 nm) and violet the shortest (about 400 nm). The order from longest to shortest is red, orange, yellow, green, blue, violet. Wavelength decreases as the colour moves toward the violet end.

Question 32Geometric and Physical Optics

A light ray in air enters a transparent medium of higher refractive index at an angle. What happens to the ray?

  1. It travels along the normal without bending.
  2. It bends away from the normal and speeds up.
  3. It bends away from the normal with no change in speed.
  4. It bends toward the normal and slows down. Correct answer.

Explanation

Entering an optically denser medium, light slows and the ray refracts toward the normal, as predicted by Snell's law with n₂ greater than n₁. The degree of bending increases with the index difference. Bending away from the normal occurs only on leaving a denser medium.

Question 33Geometric and Physical Optics

A ray in air (n = 1.00) strikes a glass surface (n = 1.50) at an angle of incidence of 30°. What is the angle of refraction?

  1. about 30.0°
  2. about 48.6°
  3. about 13.0°
  4. about 19.5° Correct answer.

Explanation

Snell's law gives n₁ sin θ₁ = n₂ sin θ₂, so sin θ₂ = (1.00 × sin 30°)/1.50 = 0.333. The angle whose sine is 0.333 is about 19.5°, smaller than the incidence angle as expected when entering a denser medium.

Question 34Geometric and Physical Optics

What is the critical angle for light travelling from glass (n = 1.50) toward air (n = 1.00)?

  1. 41.8° Correct answer.
  2. 90.0°
  3. 48.6°
  4. 30.0°

Explanation

At the critical angle the refracted ray grazes the surface at 90°, so sin θc = n₂/n₁ = 1.00/1.50 = 0.667. The corresponding angle is about 41.8°. Beyond this angle, total internal reflection occurs.

Question 35Geometric and Physical Optics

An object is placed 30 cm from a converging lens of focal length 10 cm. Where does the image form?

  1. 7.5 cm from the lens
  2. 15 cm from the lens Correct answer.
  3. 10 cm from the lens
  4. 30 cm from the lens

Explanation

Using the thin lens equation, 1/f = 1/v − 1/u, with u = −30 cm and f = +10 cm, gives 1/v = 1/10 − 1/30 = 2/30. Therefore v = +15 cm, a real image 15 cm on the far side of the lens.

Question 36Geometric and Physical Optics

An object 20 cm in front of a converging lens produces a real image 40 cm on the opposite side. What is the lateral magnification?

  1. −0.5
  2. +2.0
  3. −2.0 Correct answer.
  4. +0.5

Explanation

Lateral magnification is m = −v/u; with v = +40 cm and u = −20 cm, m = −(40)/(−20) = −2.0. The negative sign shows the image is inverted, and the magnitude 2 shows it is twice the object size.

Question 37Geometric and Physical Optics

Light with a vacuum wavelength of 600 nm travels through a medium of refractive index 1.50. What is its speed in the medium?

  1. 1.5 × 10⁸ m/s
  2. 4.5 × 10⁸ m/s
  3. 3.0 × 10⁸ m/s
  4. 2.0 × 10⁸ m/s Correct answer.

Explanation

The speed in a medium is v = c/n. Dividing 3.0 × 10⁸ m/s by 1.50 gives 2.0 × 10⁸ m/s. The wavelength shortens by the same factor, but the frequency stays the same.

Question 38Geometric and Physical Optics

A converging wavefront in air has a radius of curvature of 0.50 m. What is its vergence?

  1. +0.25 D
  2. +2.00 D Correct answer.
  3. +0.50 D
  4. −2.00 D

Explanation

Vergence is L = n/r, where r is the radius of curvature in metres. In air with n = 1, L = 1/0.50 = +2.00 D, and the positive sign denotes a converging wavefront.

Question 39Geometric and Physical Optics

Unpolarized light of intensity I₀ passes first through a polarizing filter and then through a second filter whose axis is at 60° to the first. What intensity emerges?

  1. I₀/2
  2. I₀/16
  3. I₀/4
  4. I₀/8 Correct answer.

Explanation

The first filter transmits half of unpolarized light, giving I₀/2. The second filter then transmits cos²60° = 0.25 of that, so the final intensity is I₀/2 × 0.25 = I₀/8.

Question 40Geometric and Physical Optics

An object is placed well beyond the centre of curvature of a concave mirror. Which description fits the image?

  1. real, inverted, and reduced Correct answer.
  2. virtual, inverted, and reduced
  3. real, erect, and the same size
  4. virtual, erect, and magnified

Explanation

For a concave mirror, an object beyond C produces a real image located between C and F. That image is inverted and smaller than the object. Virtual erect images from a concave mirror occur only when the object is inside the focal length.

Question 41Geometric and Physical Optics

A myopic eye has excess converging power. Which spectacle lens corrects this condition?

  1. A diverging lens of negative power Correct answer.
  2. A converging lens of positive power
  3. A cylinder lens with no spherical power
  4. A plano lens with no refractive power

Explanation

In myopia the eye focuses parallel light in front of the retina, so the correction must weaken the system with a diverging, negative-power lens. This pushes the focal point back onto the retina. Positive lenses are used for hyperopia, not myopia.

Question 42Geometric and Physical Optics

When white light passes through a glass prism, which colour is deviated the most?

  1. Green
  2. Red
  3. Yellow
  4. Violet Correct answer.

Explanation

Deviation increases with refractive index, and the index of glass is highest at short wavelengths. Violet, at the short-wavelength end of the visible spectrum, is therefore deviated most and red least. This wavelength dependence is called dispersion.

Question 43Geometric and Physical Optics

What is the energy of a photon whose wavelength is 500 nm? (h = 6.63 × 10⁻³⁴ J·s, c = 3.00 × 10⁸ m/s)

  1. 1.99 × 10⁻¹⁹ J
  2. 7.96 × 10⁻¹⁹ J
  3. 3.98 × 10⁻¹⁹ J Correct answer.
  4. 2.50 × 10⁻¹⁹ J

Explanation

Photon energy is E = hc/λ. Substituting gives (6.63 × 10⁻³⁴ × 3.00 × 10⁸)/(5.00 × 10⁻⁷) ≈ 3.98 × 10⁻¹⁹ J, which is about 2.5 eV. Shorter wavelengths correspond to higher photon energies.

Question 44Geometric and Physical Optics

A single-layer antireflection coating on glass works best when its optical thickness (index times physical thickness) equals which fraction of the design wavelength?

  1. One half wavelength
  2. One eighth wavelength
  3. One quarter wavelength Correct answer.
  4. One full wavelength

Explanation

A quarter-wave optical thickness makes the front-surface and glass-surface reflections differ by half a wavelength, causing destructive interference in reflection. That is why the coating suppresses reflected light at the design wavelength.

Question 45Geometric and Physical Optics

A biconvex lens is made of glass with n = 1.50, with front surface radius +10 cm and back surface radius −30 cm. Using the lensmaker's equation, what is the focal length?

  1. +7.5 cm
  2. +10.0 cm
  3. +15.0 cm Correct answer.
  4. +30.0 cm

Explanation

The lensmaker's equation gives 1/f = (n − 1)(1/R₁ − 1/R₂). Here 1/f = 0.50 × (1/10 + 1/30) = 0.50 × 0.1333 = 0.0667 cm⁻¹, so f = +15 cm.

Question 46Geometric and Physical Optics

A telescope objective has an aperture of 0.10 m and operates at 550 nm. Using the Rayleigh criterion, what is its angular resolution limit?

  1. 1.2 × 10⁻⁵ rad
  2. 5.5 × 10⁻⁶ rad
  3. 6.7 × 10⁻⁵ rad
  4. 6.7 × 10⁻⁶ rad Correct answer.

Explanation

The Rayleigh criterion gives θ = 1.22 λ/D. Substituting 1.22 × 550 × 10⁻⁹ m ÷ 0.10 m gives about 6.7 × 10⁻⁶ rad. A larger aperture reduces this angle and improves resolution.

Question 47Geometric and Physical Optics

A diffraction grating has 500 lines per millimetre. For light of 500 nm, at what angle does the first-order maximum appear?

  1. 45.0°
  2. 30.0°
  3. 7.2°
  4. 14.5° Correct answer.

Explanation

The grating spacing is d = 1/500 mm = 2.0 × 10⁻⁶ m. For the first order, sin θ = λ/d = 5.0 × 10⁻⁷/2.0 × 10⁻⁶ = 0.25, giving θ ≈ 14.5°.

Question 48Geometric and Physical Optics

What does a low Abbe number indicate about an optical glass?

  1. A low refractive index
  2. A high refractive index
  3. Low chromatic dispersion
  4. High chromatic dispersion Correct answer.

Explanation

The Abbe number is V = (n_d − 1)/(n_F − n_C), so a small denominator means a large difference in index across the spectrum. A low Abbe number therefore signals strong chromatic dispersion, which is why high-dispersion flint glasses have low V values.

Question 49Geometric and Physical Optics

An optical fibre has a core index of 1.50 and a cladding index of 1.48. What is its numerical aperture?

  1. 1.50
  2. 0.49
  3. 0.02
  4. 0.24 Correct answer.

Explanation

For a step-index fibre, NA = √(n_core² − n_clad²). Computing √(2.2500 − 2.1904) = √0.0596 gives approximately 0.24, which sets the acceptance cone half-angle.

Question 50Geometric and Physical Optics

A small object is placed 12 cm in front of a plane mirror. What is the distance between the object and its image?

  1. 12 cm
  2. 6 cm
  3. 36 cm
  4. 24 cm Correct answer.

Explanation

A plane mirror forms a virtual image that lies as far behind the mirror as the object lies in front of it. With the object 12 cm in front, the image is 12 cm behind, so the object-to-image separation is 12 + 12 = 24 cm.