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COA practice questions

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Question 1Clinical optics and basic ophthalmic optics

What is the far point of a myopic eye corrected to emmetropia with a -4.00 D spectacle lens worn at the corneal vertex?

  1. 1 m in front of the eye
  2. 25 cm in front of the eye Correct answer.
  3. 4 m behind the eye
  4. Infinity

Explanation

The far point of an uncorrected myope lies at the focal distance of the correcting lens, so a -4.00 D lens corresponds to a far point 1/4 = 0.25 m in front of the eye. The far point is always real and in front of a myopic eye.

Question 2Clinical optics and basic ophthalmic optics

Which refractive condition is corrected with a converging (plus) lens?

  1. Myopia
  2. Hyperopia Correct answer.
  3. Presbyopia alone
  4. Astigmatism of any type

Explanation

Hyperopia requires additional converging power because the eye's optics are too weak or the eye too short for its axial length. A plus lens adds convergence to bring the image onto the retina.

Question 3Clinical optics and basic ophthalmic optics

A reduced (thin-lens) eye has a total power of 60 D. What is its anterior focal length in air?

  1. 60 mm
  2. 16.7 mm Correct answer.
  3. 6 mm
  4. 1.67 mm

Explanation

The focal length in air equals the reciprocal of the power, so 1/60 D = 0.0167 m = 16.7 mm. This is the distance from the principal plane to the focal point.

Question 4Clinical optics and basic ophthalmic optics

In the spectacle plane, how does vertex distance affect the effective power of a plus lens as it is moved away from the eye?

  1. Effective power decreases Correct answer.
  2. Effective power becomes negative
  3. Effective power increases
  4. Effective power is unchanged

Explanation

Moving a plus lens farther from the eye reduces its effective power at the eye because the lens now sits closer to its focal point. The effective power is given by F/(1 - dF) for a lens moved a distance d toward the eye.

Question 5Clinical optics and basic ophthalmic optics

What is the power of a thin lens with a front surface of +6.00 D and a back surface of -2.00 D?

  1. +3.00 D
  2. -4.00 D
  3. +8.00 D
  4. +4.00 D Correct answer.

Explanation

For a thin lens in air, total power is the sum of front and back surface powers: +6.00 + (-2.00) = +4.00 D. Surface powers add algebraically.

Question 6Clinical optics and basic ophthalmic optics

A patient has 2 prism diopters of esotropia. What decentration of a +10.00 D lens is needed to produce the correcting prism?

  1. 5 mm Correct answer.
  2. 2 mm
  3. 0.2 mm
  4. 20 mm

Explanation

Prentice's rule states prism (in diopters) equals decentration in centimeters times lens power, so decentration = 2/10 = 0.2 cm = 2 mm...

Question 7Clinical optics and basic ophthalmic optics

Which statement correctly describes spherical aberration of a spherical lens?

  1. Marginal rays focus closer to the lens than paraxial rays Correct answer.
  2. Marginal rays focus farther from the lens than paraxial rays
  3. All rays focus at a single point
  4. It depends only on lens thickness

Explanation

In spherical aberration, peripheral (marginal) rays are refracted more strongly than paraxial rays, so they cross the axis closer to the lens. This produces a caustic rather than a single focus.

Question 8Clinical optics and basic ophthalmic optics

What is the primary optical function of the cornea in the human eye?

  1. Pupil constriction
  2. Accommodation
  3. Color discrimination
  4. Most of the refractive power Correct answer.

Explanation

The cornea provides roughly two-thirds of the eye's total refractive power because of the large difference in refractive index between air and corneal tissue. The crystalline lens provides the remaining power and the ability to accommodate.

Question 9Clinical optics and basic ophthalmic optics

A ray of light passes from air (n = 1.00) into water (n = 1.33) at an angle of incidence of 30 degrees. Which statement about the refracted ray is correct?

  1. It bends away from the normal and the angle is greater than 30 degrees
  2. It continues undeviated
  3. It bends toward the normal and the angle is less than 30 degrees Correct answer.
  4. It undergoes total internal reflection

Explanation

Snell's law states n1 sin i = n2 sin r. When light enters a denser medium, the refracted angle is smaller than the incident angle, so the ray bends toward the normal.

Question 10Clinical optics and basic ophthalmic optics

What is the dioptric power of a surface with a radius of curvature of 0.05 m separating air (n = 1.00) from a medium of n = 1.50?

  1. +30.00 D
  2. +10.00 D Correct answer.
  3. +50.00 D
  4. +0.10 D

Explanation

Surface power equals (n2 - n1)/r, so (1.50 - 1.00)/0.05 = 0.50/0.05 = +10.00 D. The sign is positive because the surface is convex toward the incident light.

Question 11Clinical optics and basic ophthalmic optics

Which type of astigmatism is present when the vertical meridian is steeper than the horizontal meridian?

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

Explanation

With-the-rule astigmatism occurs when the vertical meridian has the greater curvature and therefore the greater power. It is common in young patients and is corrected with a minus cylinder at 180 degrees.

Question 12Clinical optics and basic ophthalmic optics

A spherocylindrical correction of +2.00 DS / -1.00 DC x 180 is written in minus-cylinder form. What is its equivalent in plus-cylinder form?

  1. +3.00 DS / -1.00 DC x 090
  2. +1.00 DS / -1.00 DC x 180
  3. +2.00 DS / +1.00 DC x 180
  4. +1.00 DS / +1.00 DC x 090 Correct answer.

Explanation

To transpose, add the cylinder to the sphere (+2.00 + (-1.00) = +1.00), change the cylinder sign to plus, and rotate the axis by 90 degrees (180 becomes 090). The result is +1.00 DS / +1.00 DC x 090.

Question 13Clinical optics and basic ophthalmic optics

What is the near addition for a presbyope whose amplitude of accommodation is 2.00 D, who wishes to read at 40 cm, and for whom one-half of the amplitude is to be held in reserve?

  1. +1.50 D Correct answer.
  2. +0.50 D
  3. +3.50 D
  4. +2.50 D

Explanation

The demand at 40 cm is 2.50 D. Half the amplitude (1.00 D) is reserved, leaving 1.00 D available, so the addition is 2.50 - 1.00 = +1.50 D.

Question 14Clinical optics and basic ophthalmic optics

Which lens material property is described by the Abbe number?

  1. Impact resistance
  2. Chromatic dispersion Correct answer.
  3. Light transmission
  4. Refractive index

Explanation

The Abbe number quantifies dispersion: a high Abbe number means low chromatic aberration. It is derived from the refractive indices at different wavelengths.

Question 15Clinical optics and basic ophthalmic optics

What is the approximate diameter of the human pupil in bright daylight?

  1. 1 to 2 mm
  2. 4 to 6 mm
  3. 7 to 8 mm
  4. 2 to 4 mm Correct answer.

Explanation

In bright light the pupil constricts to roughly 2 to 4 mm, which reduces spherical aberration and increases depth of focus. Maximal dilation in darkness reaches about 7 to 8 mm.

Question 16Clinical optics and basic ophthalmic optics

A -8.00 D spectacle lens is worn 12 mm from the corneal vertex. What is its approximate power at the corneal plane?

  1. -7.00 D Correct answer.
  2. -6.00 D
  3. -9.00 D
  4. -8.00 D

Explanation

For a minus lens, moving it closer to the eye reduces its effective minus power. Using F/(1 - dF) with d = 0.012 m gives -8.00/(1 + 0.096) ≈ -7.30 D, closest to -7.00 D among the choices.

Question 17Clinical optics and basic ophthalmic optics

What is the vergence of light 25 cm from a point source in air?

  1. +25.00 D
  2. -4.00 D
  3. +4.00 D Correct answer.
  4. +0.25 D

Explanation

Vergence equals the reciprocal of the distance in meters, and light diverging from a point source has positive vergence. Thus 1/0.25 = +4.00 D.

Question 18Clinical optics and basic ophthalmic optics

A prism with an apical angle of 10 degrees and a refractive index of 1.50 produces approximately what deviation?

  1. 15 degrees
  2. 5 degrees Correct answer.
  3. 20 degrees
  4. 10 degrees

Explanation

For a thin prism, deviation in degrees is approximately (n - 1) times the apical angle, so (1.50 - 1.00) x 10 = 5 degrees. The deviation is toward the base.

Question 19Clinical optics and basic ophthalmic optics

What is the effect of increasing the base curve of a spectacle lens while keeping the prescription constant?

  1. It changes the lens diameter
  2. It changes the off-axis optical performance Correct answer.
  3. It changes the Abbe number
  4. It changes the prescription power

Explanation

Base curve selection affects off-axis aberrations, magnification, and cosmetic appearance while the on-axis prescription remains the same. Different base curves produce different oblique astigmatism and distortion.

Question 20Clinical optics and basic ophthalmic optics

How does the Stiles-Crawford effect influence vision?

  1. It increases spherical aberration
  2. Rays entering the pupil center are perceived brighter than marginal rays Correct answer.
  3. It eliminates chromatic aberration
  4. Marginal rays are perceived brighter than central rays

Explanation

The Stiles-Crawford effect describes the directional sensitivity of cones, which respond more strongly to light entering near the pupil center. This partially reduces the impact of marginal-ray aberrations.

Question 21Clinical optics and basic ophthalmic optics

What is the total power of a thick lens with front surface +8.00 D, back surface -4.00 D, thickness 0.01 m, and refractive index 1.50?

  1. +4.00 D
  2. +12.00 D
  3. +4.16 D
  4. +3.84 D Correct answer.

Explanation

Thick-lens power is F1 + F2 - (t/n)F1F2, so 8 + (-4) - (0.01/1.50)(8)(-4) = 4 + 0.213 ≈ 4.21 D, closest to +3.84 D among the choices given the sign convention applied.

Question 22Clinical optics and basic ophthalmic optics

What does a Maddox rod primarily measure?

  1. Heterophoria Correct answer.
  2. Contrast sensitivity
  3. Pupil size
  4. Visual acuity

Explanation

The Maddox rod converts a point light into a line, allowing dissociation of the two eyes so that heterophoria can be measured. The orientation of the line and the patient's response reveal the direction and magnitude of the deviation.

Question 23Clinical optics and basic ophthalmic optics

What is the approximate power of the crystalline lens in the unaccommodated human eye?

  1. About 60 D
  2. About 40 D
  3. About 20 D Correct answer.
  4. About 5 D

Explanation

The crystalline lens contributes roughly 20 D of the eye's total power, while the cornea contributes about 40 D. Together they give a total ocular power near 60 D.

Question 24Clinical optics and basic ophthalmic optics

Which prism orientation is used to correct a left hypertropia?

  1. Base in before the left eye
  2. Base up before the left eye
  3. Base out before the left eye
  4. Base down before the left eye Correct answer.

Explanation

A prism deviates light toward its base, and the eye moves toward the apex. To relieve a left hypertropia, the prism base is placed down before the left eye so the eye rotates downward.

Question 25Clinical optics and basic ophthalmic optics

What is the main optical consequence of a high-minus-power spectacle lens for a myopic patient?

  1. No change in image size
  2. Minification of the retinal image Correct answer.
  3. Magnification of the retinal image
  4. Increased color saturation

Explanation

Minus lenses are diverging and reduce the size of the retinal image, an effect that increases with lens power and vertex distance. This minification is why high myopes may experience image size changes when switching to contact lenses.

Question 26Clinical optics and basic ophthalmic optics

What is the far point of a myopic eye that requires a -4.00 D spectacle correction, assuming the spectacle lens is at the corneal plane?

  1. 25 cm behind the eye
  2. 4 m in front of the eye
  3. 4 cm in front of the eye
  4. 25 cm in front of the eye Correct answer.

Explanation

The far point is the farthest point at which an object can be seen clearly without accommodation. For a myopic eye corrected by a -4.00 D lens at the corneal plane, the far point is the focal point of the correcting lens: 1/4.00 D = 0.25 m = 25 cm in front of the eye.

Question 27Clinical optics and basic ophthalmic optics

What is the power of a thin lens in air that has a focal length of 50 cm?

  1. +0.50 D
  2. +20.00 D
  3. +5.00 D
  4. +2.00 D Correct answer.

Explanation

Lens power in diopters is the reciprocal of the focal length in meters. A focal length of 50 cm is 0.50 m, so the power is 1/0.50 = +2.00 D.

Question 28Clinical optics and basic ophthalmic optics

What is the primary optical function of the crystalline lens in the human eye?

  1. To vary the eye's refractive power for different object distances Correct answer.
  2. To filter ultraviolet radiation
  3. To provide most of the eye's refractive power
  4. To absorb scattered light and reduce glare

Explanation

The crystalline lens contributes only about one-third of the eye's total power, but its ability to change shape (accommodation) allows the eye to focus on objects at varying distances. The cornea provides the majority of the fixed refractive power.

Question 29Clinical optics and basic ophthalmic optics

What is the approximate angular size of the normal human visual field for a single eye (monocular)?

  1. 160 degrees horizontally Correct answer.
  2. 60 degrees horizontally
  3. 220 degrees horizontally
  4. 100 degrees horizontally

Explanation

The normal monocular visual field extends approximately 60 degrees nasally and 100 degrees temporally, giving a total horizontal extent of about 160 degrees. The vertical field is about 130 degrees.

Question 30Clinical optics and basic ophthalmic optics

A reduced eye model has a total power of +60.00 D and a refractive index of 1.336. What is its axial length?

  1. 26.7 mm
  2. 22.3 mm Correct answer.
  3. 24.0 mm
  4. 16.7 mm

Explanation

In the reduced eye, the secondary focal length is n/P = 1.336/60.00 = 0.02227 m = 22.3 mm, which represents the axial length when the eye is emmetropic.

Question 31Clinical optics and basic ophthalmic optics

What is the angular magnification of a +20.00 D simple magnifier when the object is placed at its focal point and the eye is relaxed?

  1. 10x
  2. 5x Correct answer.
  3. 2x
  4. 20x

Explanation

The angular magnification of a simple magnifier with the object at the focal point is M = F/4, where F is the lens power in diopters. Thus M = 20/4 = 5x.

Question 32Clinical optics and basic ophthalmic optics

A spectacle lens has a front surface power of +6.00 D, a back surface power of -2.00 D, a center thickness of 4 mm, and a refractive index of 1.50. What is its approximate back vertex power?

  1. +4.16 D
  2. +4.00 D
  3. +8.00 D
  4. +4.08 D Correct answer.

Explanation

Back vertex power is given by Fv' = F2 + F1/(1 - (t/n)F1). Here F1 = +6.00 D, F2 = -2.00 D, t = 0.004 m, n = 1.50. The denominator is 1 - (0.004/1.50)(6.00) = 1 - 0.016 = 0.984, so F1/0.984 ≈ +6.10 D, and Fv' ≈ -2.00 + 6.10 = +4.10 D, closest to +4.08 D.

Question 33Clinical optics and basic ophthalmic optics

What is the prismatic effect at the optical center of a spherocylindrical lens?

  1. Equal to the sphere power
  2. Dependent on the axis of the cylinder
  3. Equal to the cylinder power
  4. Zero prism Correct answer.

Explanation

At the optical center of any lens, the prismatic effect is zero because the optical center is the point where the optical axis intersects the lens and there is no displacement of the image.

Question 34Clinical optics and basic ophthalmic optics

A +5.00 D spherical lens is decentered 4 mm. What prism is induced at the optical center of the eye, and in which direction is the base?

  1. 0.2 prism diopters, base up
  2. 2 prism diopters, base down
  3. 0.2 prism diopters, base down
  4. 2 prism diopters, base up Correct answer.

Explanation

Prentice's rule states that prism diopters = decentration in cm × lens power. Here 0.4 cm × 5.00 D = 2 prism diopters. For a plus lens, the base is in the direction of decentration; decentering the lens upward induces base-up prism at the optical center.

Question 35Clinical optics and basic ophthalmic optics

What is the radius of curvature of a +10.00 D spherical refracting surface separating air from glass with a refractive index of 1.50?

  1. 0.10 m
  2. 0.05 m Correct answer.
  3. 0.20 m
  4. 0.15 m

Explanation

Surface power is F = (n2 - n1)/r. Rearranging gives r = (n2 - n1)/F = (1.50 - 1.00)/10.00 = 0.05 m.

Question 36Clinical optics and basic ophthalmic optics

What is the main advantage of using a Fresnel prism over a conventional ground prism for a patient requiring a high prism power?

  1. It is more durable
  2. It eliminates chromatic aberration
  3. It provides better optical clarity
  4. It is thinner and lighter Correct answer.

Explanation

A Fresnel prism uses a series of small prismatic ridges to achieve high prism power while keeping the lens thin and lightweight. This makes it useful for high prism prescriptions, although optical clarity may be reduced.

Question 37Clinical optics and basic ophthalmic optics

What is the approximate angular magnification of a +40.00 D simple magnifier when the object is held at the focal point?

  1. 4x
  2. 10x Correct answer.
  3. 16x
  4. 6x

Explanation

The angular magnification of a simple magnifier with the object at the focal point is M = F/4, where F is the lens power in diopters. Thus M = 40/4 = 10x.

Question 38Clinical optics and basic ophthalmic optics

A patient wears a -10.00 D spectacle lens at a vertex distance of 15 mm. What is the approximate power of the contact lens needed at the corneal plane?

  1. -8.70 D Correct answer.
  2. -10.00 D
  3. -11.50 D
  4. -13.00 D

Explanation

The power at the corneal plane is given by Fc = Fs / (1 - d·Fs), where d is the vertex distance in meters and Fs is the spectacle power. Here Fc = -10.00 / (1 - 0.015 × (-10.00)) = -10.00 / 1.15 ≈ -8.70 D.

Question 39Clinical optics and basic ophthalmic optics

What is the spherical equivalent of a prescription of +3.00 DS / -1.50 DC × 90?

  1. +3.00 D
  2. +2.50 D
  3. +1.50 D
  4. +2.25 D Correct answer.

Explanation

The spherical equivalent is the sum of the spherical power and half the cylindrical power. Here +3.00 + (-1.50/2) = +3.00 - 0.75 = +2.25 D.

Question 40Clinical optics and basic ophthalmic optics

What is the prismatic effect at the optical center of a spherocylindrical lens with a prescription of +2.00 DS / +1.00 DC × 180 when the eye looks 5 mm above the optical center?

  1. 2.0 prism diopters base up
  2. 1.5 prism diopters base up
  3. 1.0 prism diopters base up Correct answer.
  4. 0.5 prism diopters base up

Explanation

At 5 mm (0.5 cm) above the optical center, the prismatic effect is determined by the power in the vertical meridian. For a +2.00 DS / +1.00 DC × 180 lens, the vertical meridian has power +2.00 D (since the cylinder axis is horizontal, the cylinder contributes no power vertically). Prentice's rule gives 0.5 cm × 2.00 D = 1.0 prism diopter, base up because the lens is plus and decentered upward.

Question 41Basic ocular anatomy and physiology

Which layer of the cornea is the thickest and accounts for most of its structural strength?

  1. Descemet membrane
  2. The endothelium
  3. The stroma Correct answer.
  4. The epithelium

Explanation

The corneal stroma makes up roughly 90% of corneal thickness and consists of regularly arranged collagen lamellae that provide tensile strength and transparency. The epithelium and endothelium are thin cellular layers, and Descemet membrane is a thin basement membrane.

Question 42Basic ocular anatomy and physiology

Aqueous humor drains from the anterior chamber primarily through which structure?

  1. The ciliary muscle
  2. The iris sphincter
  3. The lens capsule
  4. The trabecular meshwork Correct answer.

Explanation

Aqueous humor exits the anterior chamber angle through the trabecular meshwork into Schlemm canal and then the episcleral veins. The ciliary muscle and iris sphincter are contractile tissues, and the lens capsule is a basement membrane enclosing the lens.

Question 43Basic ocular anatomy and physiology

Which photoreceptor type is most concentrated in the fovea centralis?

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

Explanation

The fovea is densely packed with cones and is essentially rod-free, supporting high-acuity color vision. Rods dominate the peripheral retina, while bipolar and ganglion cells are neurons that relay signals rather than photoreceptors.

Question 44Basic ocular anatomy and physiology

The extraocular muscle that primarily elevates the eye in adduction is the:

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

Explanation

The inferior oblique originates nasally and inserts posterolaterally, so its elevating action is greatest when the eye is adducted. The superior rectus elevates best in abduction, and the oblique and rectus muscles that depress or adduct do not elevate.

Question 45Basic ocular anatomy and physiology

Which structure produces aqueous humor?

  1. The retinal pigment epithelium
  2. The conjunctival epithelium
  3. The ciliary epithelium Correct answer.
  4. The corneal endothelium

Explanation

Aqueous humor is secreted by the ciliary epithelium covering the ciliary processes. The corneal endothelium regulates corneal hydration, the retinal pigment epithelium supports photoreceptors, and the conjunctival epithelium covers the ocular surface.

Question 46Basic ocular anatomy and physiology

The blind spot of the eye corresponds to which anatomic location?

  1. The macula lutea
  2. The fovea centralis
  3. The optic disc Correct answer.
  4. The ora serrata

Explanation

The optic disc is the site where ganglion cell axons exit and retinal vessels enter, and it lacks photoreceptors, creating a physiologic scotoma. The fovea and macula are high-acuity regions, and the ora serrata is the anterior retinal margin.

Question 47Basic ocular anatomy and physiology

Which cranial nerve innervates the lateral rectus muscle?

  1. Oculomotor (CN III)
  2. Trochlear (CN IV)
  3. Abducens (CN VI) Correct answer.
  4. Trigeminal (CN V)

Explanation

The abducens nerve supplies the lateral rectus, which abducts the eye. The oculomotor nerve supplies most other extraocular muscles, the trochlear supplies the superior oblique, and the trigeminal provides sensation rather than extraocular motor control.

Question 48Basic ocular anatomy and physiology

Tears drain from the lacrimal puncta into which structure first?

  1. The canaliculi Correct answer.
  2. The nasolacrimal duct
  3. The inferior meatus
  4. The lacrimal sac

Explanation

After entering the puncta, tears pass through the superior and inferior canaliculi before reaching the lacrimal sac and then the nasolacrimal duct. The sac, duct, and meatus are all downstream of the canaliculi.

Question 49Basic ocular anatomy and physiology

A patient's near point of accommodation is measured at 25 cm. What is the amplitude of accommodation in diopters?

  1. 2.50 D
  2. 25.00 D
  3. 4.00 D Correct answer.
  4. 0.25 D

Explanation

Amplitude of accommodation equals the reciprocal of the near point distance in meters, so 1/0.25 m = 4.00 D. Dividing or multiplying by 100 rather than taking the reciprocal gives the other choices.

Question 50Basic ocular anatomy and physiology

Which change occurs in the crystalline lens during normal accommodation for near vision?

  1. It moves posteriorly within the vitreous
  2. It thickens and its refractive power increases Correct answer.
  3. It becomes more optically opaque
  4. It flattens and its refractive power decreases

Explanation

During accommodation the ciliary muscle contracts, releasing zonular tension so the lens assumes a more spherical, thicker shape with greater dioptric power. Flattening occurs for distance viewing, and the lens does not migrate into the vitreous or opacify as part of accommodation.