ABO Practice Test: NOCE Questions With Worked Answers by Exam Domain

The ABO exam, officially the National Opticianry Competency Examination (NOCE), is a 2-hour computer-based test of 125 multiple-choice questions. The content outline scores 100 of them: Ophthalmic Optics 25, Ophthalmic Products 20, Dispensing Procedures 20, Instrumentation 15, Ocular Anatomy, Physiology, Pathology, and Refraction 10, and Laws, Regulations, and Standards 10. ABO-NCLE sells an official practice exam. This page gives you something different: 24 original questions weighted like the real exam, with every calculation shown, and a short CLRE set at the end.

“ABO” here means the American Board of Opticianry, not the American Board of Optometry. For eligibility, fees and scoring, see ABO and NCLE certification.

These questions are written for practice in the style of the official outline. They are not real exam items, and none are taken from ABO-NCLE or any prep site. Cover the answer and try each question first, then read the working. The domain names and scored-question counts come from the ABO-NCLE Basic Exam Handbook (February 2025).

How This Practice Set Maps to the NOCE

Ophthalmic Optics (25 of 100 scored questions)

This domain covers prescriptions, transposition, lens powers and materials, prism, and the ophthalmic formulas. It is the largest share of the exam and the one where arithmetic errors cost the most points.

Question 1: Transposing to plus cylinder

A prescription reads +2.25 -1.75 x 085. Which is the equivalent plus-cylinder form?

• A. +0.50 +1.75 x 085
• B. +0.50 +1.75 x 175
• C. +4.00 +1.75 x 175
• D. +0.50 -1.75 x 175

Answer: B. Transposition takes three steps. Add the sphere and cylinder to get the new sphere: +2.25 + (-1.75) = +0.50 D. Change the sign of the cylinder: -1.75 becomes +1.75 D. Move the axis 90 degrees: 85 + 90 = 175. Option A forgets to rotate the axis. Option C subtracts the cylinder from the sphere instead of adding it. Option D forgets to flip the cylinder sign. Check your own examples with the transposition calculator.

Question 2: Spherical equivalent

What is the spherical equivalent of -3.50 -1.50 x 020?

• A. -5.00 D
• B. -4.25 D
• C. -3.50 D
• D. -2.75 D

Answer: B. Spherical equivalent is the sphere plus half the cylinder: -3.50 + (-1.50 / 2) = -3.50 + (-0.75) = -4.25 D. The axis does not enter the calculation. Option A adds the full cylinder, C ignores it, and D has the wrong sign on the half-cylinder.

Question 3: Decentration for prescribed prism

A right lens is +4.00 D and the prescription calls for 2.00 prism diopters base in. Where should the optical center sit relative to the patient’s pupil?

• A. 5 mm out (temporal)
• B. 5 mm in (nasal)
• C. 0.5 mm in (nasal)
• D. 8 mm in (nasal)

Answer: B. Prentice’s rule: prism (Δ) = lens power (D) × decentration (cm). Rearranged, decentration = prism / power = 2.00 / 4.00 = 0.50 cm = 5 mm. In a plus lens the prism base points toward the optical center, so base in means the optical center sits nasal to the pupil. Option A gets the direction wrong, C stops at 0.5 without converting centimeters to millimeters, and D multiplies power by prism (2 × 4 = 8) instead of dividing. See Prentice’s rule and induced prism and the Prentice’s rule calculator.

Question 4: Vertical prism imbalance at the reading level

A patient wearing OD -2.00 D sphere and OS -4.00 D sphere reads through a point 8 mm below the optical center of each lens. What is the vertical prism imbalance between the eyes?

• A. 4.80 Δ
• B. 3.20 Δ
• C. 1.60 Δ
• D. 0.80 Δ

Answer: C. Work each eye with Prentice’s rule, converting 8 mm to 0.8 cm. OD: 2.00 × 0.8 = 1.60 Δ. OS: 4.00 × 0.8 = 3.20 Δ. Both are minus lenses viewed below the optical center, so both prisms are base down and they subtract: 3.20 – 1.60 = 1.60 Δ, with the left eye seeing more base-down prism. Option A adds the two values, B is the left eye alone, and D uses 4 mm instead of 8 mm for the difference. Anisometropia like this is the classic reason to consider slab-off or separate reading glasses.

Question 5: Effective power of a high-plus lens

A +8.00 D lens sits 12 mm from the cornea. What is its effective power at the corneal plane, to two decimals?

• A. +7.30 D
• B. +8.00 D
• C. +8.85 D
• D. +8.96 D

Answer: C. Effective power Fe = F / (1 – d × F), with d in meters and the sign of F kept. Here d = 0.012 m, so d × F = 0.012 × 8.00 = 0.096. Then 1 – 0.096 = 0.904, and Fe = 8.00 / 0.904 = +8.85 D. A plus lens gains power as it moves away from the eye. Option A divides by 1.096, which is the formula with the sign flipped. B ignores vertex distance. D adds 12 percent to the power, a shortcut that overstates the change. Use the vertex distance calculator and read vertex distance compensation for the minus-lens case.

Question 6: Hand neutralization

You move an unknown lens up and down in front of a distant vertical target, and the target appears to move in the same direction as the lens. What do you have?

• A. A plus lens (“with” motion)
• B. A minus lens (“with” motion)
• C. A plus lens (“against” motion)
• D. A minus lens (“against” motion)

Answer: B. Apparent target motion in the same direction as the lens is “with” motion, which indicates a minus lens. Motion in the opposite direction is “against” motion and indicates a plus lens. You then add trial lenses of the opposite sign until the motion stops, which neutralizes the lens. Options A and D pair the wrong sign with the motion, and C mislabels the observed motion.

Ocular Anatomy, Physiology, Pathology, and Refraction (10 of 100 scored questions)

Expect straightforward structure-and-function items here, plus refractive errors and how they are corrected.

Question 7: Controlling the light that enters the eye

Which structure changes the size of the pupil and so controls how much light enters the eye?

• A. Ciliary body
• B. Sclera
• C. Iris
• D. Choroid

Answer: C. The National Eye Institute describes it this way: “The iris (the colored part of the eye) controls how much light the pupil lets in.” The ciliary body changes the shape of the lens for focusing, the sclera is the white outer wall, and the choroid is the vascular layer beneath the retina.

Question 8: A new near-vision complaint

A 48-year-old patient has a long-standing -2.00 D spherical prescription and sees well at distance. They now hold menus at arm’s length and ask for help with close work. What is the most likely explanation, and what corrects it?

• A. Presbyopia, corrected with added plus power for near
• B. Hyperopia, corrected with added minus power
• C. Presbyopia, corrected with added minus power for near
• D. Astigmatism, corrected with a stronger distance sphere

Answer: A. The National Eye Institute says that “As you age, the lens in your eye gets harder and less flexible, and it stops focusing light correctly on the retina,” and that everyone gets presbyopia with age, “usually after age 45.” Because the lens can no longer add plus power on demand, the correction is added plus power at near (reading glasses, bifocals or progressives). Minus power would push near vision further out of focus, and nothing in the history points to astigmatism or uncorrected hyperopia.

Ophthalmic Products (20 of 100 scored questions)

This domain tests lens materials, designs, coatings and tints, and what each is good and bad at.

Question 9: Material for a child’s glasses

A parent wants lenses for a 9-year-old who plays soccer. The prescription is -1.50 D OU. Which material is the best fit?

• A. CR-39 (standard 1.50 plastic)
• B. Untreated crown glass
• C. Polycarbonate
• D. High-index 1.74

Answer: C. Polycarbonate (along with Trivex) is the impact-resistant standard for children and sports. Untreated glass is the least suitable for a child, CR-39 is more fragile than polycarbonate, and 1.74 is chosen for thinness at high powers, which a -1.50 D prescription does not need. For a side-by-side of index, Abbe value and impact rating, see the lens material comparison.

Question 10: What a low Abbe value means

A patient complains of color fringes around lights when looking toward the edge of a new lens. The lens material has a low Abbe value. Which statement is correct?

• A. A low Abbe value means less chromatic aberration
• B. A low Abbe value means more chromatic aberration
• C. Abbe value measures impact resistance
• D. Abbe value measures how much the lens weighs

Answer: B. The Abbe value expresses how much a material disperses white light into colors. The lower the Abbe value, the more dispersion, and the more color fringing a wearer can see away from the optical center, especially in stronger prescriptions. It has nothing to do with impact resistance or weight, which rules out C and D.

Question 11: Lens design for computer work

A 56-year-old with a +2.00 D add works at a monitor 60 cm away and reads documents at 40 cm. They rarely need distance vision at work. Which lens is the best choice for a dedicated work pair?

• A. Single vision, distance
• B. Standard flat-top 28 bifocal
• C. Occupational (office) progressive
• D. Single vision, high-wrap sport design

Answer: C. An occupational progressive gives clear vision from near through intermediate, which matches both the 40 cm and 60 cm tasks. A distance single vision lens leaves both blurred, and a standard bifocal has no intermediate zone, so the monitor sits in the blurry gap between the distance and reading portions. A wrap sport design addresses a different need entirely.

Question 12: Polarized lens orientation

A fishing guide wants polarized sunglasses to cut glare off the water. How should the polarizing filter be oriented in the lens?

• A. Transmission axis horizontal
• B. Transmission axis vertical
• C. Transmission axis at 45 degrees
• D. Orientation does not matter

Answer: B. Glare reflected off flat horizontal surfaces such as water or a wet road is mostly horizontally polarized. A filter with a vertical transmission axis blocks it and passes vertically polarized light. A horizontal axis would pass the glare, and a 45 degree axis would only partly block it.

Question 13: Reading progressive lens engravings

The ink layout is gone from a progressive lens. You find the two permanent alignment engravings. Which statement is correct?

• A. The engravings are 17 mm apart and the add power is under the nasal mark
• B. The engravings are 34 mm apart and the add power is under the temporal mark
• C. The engravings are 34 mm apart and the add power is under the nasal mark
• D. The engravings are 17 mm apart and the add power is under the temporal mark

Answer: B. The Vision Council’s Lens Marking Guidelines call for “two alignment reference markings comprising two marks with their centers separated by a distance of 34 mm ±0.5 mm,” and for the add power to “appear directly below the temporal alignment reference marking.” The manufacturer and design code sits under the nasal mark. The prism reference point is the midpoint between the two marks, 17 mm from each, which is where the 17 mm in A and D comes from. See progressive lens markings for the full layout.

Instrumentation (15 of 100 scored questions)

Lensmeter reading, lens measurement devices, and dispensing instruments are in scope.

Question 14: Writing a lensmeter reading in minus cylinder

A lensmeter shows +1.00 D in the 30 degree meridian and +3.00 D in the 120 degree meridian. Write the prescription in minus-cylinder form.

• A. +1.00 +2.00 x 030
• B. +3.00 -2.00 x 030
• C. +3.00 -2.00 x 120
• D. +1.00 -2.00 x 120

Answer: C. In minus-cylinder form, the sphere is the most plus meridian: +3.00 D. The cylinder is the other meridian minus the sphere: +1.00 – (+3.00) = -2.00 D. The axis is the meridian that carries the sphere power alone, with no cylinder effect, which is 120. Check: along 120 the power is +3.00; along 30 it is +3.00 – 2.00 = +1.00. Option A is a correct plus-cylinder prescription for the same lens but is not in the form asked for. B has the axis on the wrong meridian, and D takes the wrong sphere.

Question 15: Lens clock reading on a different index

A lens clock calibrated for index 1.523 reads +6.00 D on the front surface of a lens made of index 1.586. What is the true surface power?

• A. +5.36 D
• B. +6.00 D
• C. +6.38 D
• D. +6.72 D

Answer: D. A lens clock measures curvature and shows power for its calibration index. The true power scales by (n – 1) ratios: 6.00 × (1.586 – 1) / (1.523 – 1) = 6.00 × 0.586 / 0.523 = +6.72 D. Check from the radius: r = 0.523 / 6.00 = 87.2 mm, then 0.586 / 0.0872 m = 6.72 D. Option A inverts the ratio, B skips the correction, and C scales by the index difference (0.063) instead of by (n – 1). The stem states the calibration index so the question is self-contained. Check the index printed on your own clock, since models differ.

Question 16: Measuring vertex distance

Which instrument is used to measure the distance from the back of the lens to the front of the patient’s eye?

• A. Lens clock
• B. Distometer
• C. Circumference gauge
• D. Corneal reflex pupilometer

Answer: B. A distometer measures vertex distance. The lens clock measures surface curvature, the circumference gauge measures the frame’s lens opening, and the corneal reflex pupilometer measures PD. All four appear in the Instrumentation domain of the handbook outline.

Dispensing Procedures (20 of 100 scored questions)

This domain covers measuring, fitting, and adjusting: monocular PD, fitting heights, lens blank size, tilt, and frame measurements.

Question 17: Which PD for a progressive order

A patient has a binocular distance PD of 64 mm, with a monocular PD of 30.5 mm (OD) and 33.5 mm (OS). They are ordering progressive lenses. What should you send to the lab?

• A. 32 / 32
• B. 30.5 / 33.5
• C. 64 (binocular only)
• D. 30.5 / 33.5 near PD

Answer: B. Progressives place the fitting cross over each pupil, so each eye needs its own value. Splitting 64 into 32 / 32 builds a 1.5 mm error into each eye. That is more than the tolerance in the ANSI Z80.1-2015 quick reference, which says the fitting cross “shall be within ± 1.0mm of the specified monocular interpupillary distance.” A binocular number alone gives the lab nothing to work with, and near PD is a different value used for near-only or occupational lenses. See monocular vs binocular PD for more.

Question 18: Bifocal segment height

For a flat-top bifocal your shop places the segment line at the lower lid margin. Measured from the lowest point of the lens opening, the pupil center is 23 mm up and the lower lid margin is 18 mm up. What is the segment height?

• A. 5 mm
• B. 18 mm
• C. 20.5 mm
• D. 23 mm

Answer: B. Segment height is measured up from the bottom of the lens opening to the segment line, so with the line at the lower lid the answer is 18 mm. Option D is the pupil height, which is the reference for a progressive’s fitting height, not for a bifocal line. A is the difference between the two, and C averages them. Practices differ on whether the line sits at the lid or slightly above it, so use the rule your lab or shop follows. The fitting height calculator and segment height in progressive lenses cover the progressive case.

Question 19: Minimum blank size

A frame has an eyesize (A) of 50 mm and a distance between lenses (DBL) of 20 mm, and the chosen lens shape has an effective diameter (ED) of 54 mm. The patient’s PD is 66 mm. What is the minimum blank size?

• A. 52 mm
• B. 58 mm
• C. 60 mm
• D. 64 mm

Answer: C. Minimum blank size = ED + total decentration + 2 mm, where total decentration is frame PD minus patient PD. From the boxing system, frame PD (distance between centers) = A + DBL = 50 + 20 = 70 mm. Total decentration = 70 – 66 = 4 mm. MBS = 54 + 4 + 2 = 60 mm. Option A subtracts the decentration instead of adding it, B forgets the 2 mm allowance, and D uses 8 mm of decentration, which is what you get by doubling a value that is already the total. Practice it with the MBS calculator and read minimum block size and the boxing system frame measurements.

Question 20: Near PD from distance PD

Use near PD = distance PD × l / (l + s), where l is the working distance and s is 27 mm, the distance from the spectacle plane to the eye’s center of rotation. A patient has a distance PD of 66 mm and reads at 250 mm. What is the near PD?

• A. 62.0 mm
• B. 59.6 mm
• C. 73.1 mm
• D. 57.5 mm

Answer: B. Near PD = 66 × 250 / (250 + 27) = 16,500 / 277 = 59.6 mm. Option A is the “subtract 4 mm” shortcut, which drifts at short working distances. C inverts the ratio, and D uses s = 37 mm instead of 27 mm. The near PD calculator runs the same formula for any working distance.

Question 21: Pantoscopic tilt and optical center position

A frame is adjusted to 10 degrees of pantoscopic tilt. Using the rule of thumb of 1 mm of drop per 2 degrees of tilt, where should the optical center sit relative to the distance viewing center?

• A. 5 mm below
• B. 5 mm above
• C. 10 mm below
• D. At the distance viewing center

Answer: A. The National Academy of Opticianry course material states: “As a rule-of-thumb, for each 2 degrees of pantoscopic tilt, the optical center of the lenses should be placed 1mm below the distance viewing center.” At 10 degrees that is 10 / 2 = 5 mm below. Option B has the direction reversed, C applies 1 mm per degree, and D ignores the tilt. See pantoscopic tilt for the optical effects.

Optogrid captures monocular PD and fitting height (segment height) from a photo on a phone or tablet: the monocular PD behind question 17 and the pupil height in question 18. The walkthrough is in how to measure PD, dual PD and SH with Optogrid.

Measure PD, monocular PD and fitting height from a photoNo pupillometer needed, straight from the browser.Try it free

Laws, Regulations, and Standards (10 of 100 scored questions)

The outline lists product performance, national standards and regulations (OSHA, ANSI, FDA, EPA, HIPAA), universal precautions, and coding.

Question 22: ANSI Z80.1 tolerance check

A single-vision lens was ordered as -2.00 -1.00 x 180. Using ANSI Z80.1 power and axis tolerances, which of these finished lenses passes?

• A. -2.00 -1.25 x 180
• B. -2.25 -1.00 x 180
• C. -2.12 -1.00 x 180
• D. -2.00 -1.00 x 172

Answer: C. In the Vision Council’s ANSI Z80.1-2015 quick reference, sphere meridian power is held to ±0.13 D up to ±6.50 D, cylinder up to 2.00 D is held to ±0.13 D, and the axis tolerance for a cylinder over 0.75 D up to 1.50 D is ±3 degrees. Option C moves each meridian by only 0.12 D and leaves the cylinder and axis alone, so it passes. A has a cylinder 0.25 D off. B is 0.25 D off in both meridians. D has an axis 8 degrees off, well beyond ±3 degrees. These numbers are from the 2015 edition; confirm the edition your lab verifies against. Try the ANSI lens tolerance checker and the eyeglass prescription tolerances guide.

Question 23: The FDA drop-ball test

Under 21 CFR 801.410, which description matches the impact test for eyeglass lenses?

• A. A 1-inch steel ball dropped from 50 inches
• B. A 5/8-inch steel ball dropped from 20 inches
• C. A 5/8-inch steel ball dropped from 50 inches
• D. A 1/2-inch steel ball dropped from 100 inches

Answer: C. The regulation says: “a 5/8-inch steel ball weighing approximately 0.56 ounce is dropped from a height of 50 inches upon the horizontal upper surface of the lens.” To pass, the lens must not fracture. Each finished impact-resistant glass lens for prescription use is tested individually, while plastic lenses are tested on a statistically significant sample from each production batch. The rule allows a physician or optometrist to direct other lenses in writing and notify the patient in writing when impact-resistant lenses will not meet the patient’s visual needs. Source: 21 CFR 801.410 at eCFR.

Question 24: The Eyeglass Rule and prescription release

Under the FTC Eyeglass Rule (16 CFR Part 456), when must a prescriber give the patient a copy of the prescription?

• A. Only if the patient asks for it
• B. After the patient buys glasses from the prescriber
• C. Immediately after the refractive exam is completed, before offering to sell glasses, whether or not the patient asks
• D. Within seven days of the exam

Answer: C. Section 456.2 makes it an unfair act or practice for an ophthalmologist or optometrist to “fail to provide to the patient one copy of the patient’s prescription immediately after the refractive eye examination is completed and before offering to sell the patient ophthalmic goods, whether or not the prescription is requested by the patient.” The copy may be on paper, or in a digital format after the prescriber obtains verifiable affirmative consent, and the 2024 amendment (89 FR 60774) added a requirement to confirm release. A prescriber may withhold it only until the exam is paid for, and only if immediate payment would have been required even if no eyewear were needed. Source: 16 CFR Part 456 at eCFR.

NOCE Answer Key

CLRE Practice Questions

The Contact Lens Registry Examination (CLRE) is the NCLE Basic exam. Its outline has eight domains, with Dispensing and Follow-Up carrying 20 of 100 scored questions each. Four items follow.

CLRE Question 1: Spectacle power to contact lens power

A patient’s spectacle prescription is -10.00 D sphere at a vertex distance of 12 mm. Which contact lens power, to the nearest 0.25 D, is closest?

• A. -11.25 D
• B. -10.00 D
• C. -9.00 D
• D. -8.00 D

Answer: C. Use Fc = F / (1 – d × F) with d = 0.012 m: Fc = -10.00 / (1 – 0.012 × (-10.00)) = -10.00 / 1.12 = -8.93 D. The nearest 0.25 D is -9.00 D. A minus prescription needs less minus power at the cornea. Option A uses the wrong direction (-10.00 / 0.88), B skips the conversion, and D applies the formula twice. The contact lens power converter does the same calculation.

CLRE Question 2: Toric lens rotation

A toric soft lens ordered as -3.00 -1.25 x 090 settles with its axis mark rotated 15 degrees to the right, as seen from the examiner’s side of the slit lamp. Using LARS, what axis should you order?

• A. 105
• B. 090
• C. 075
• D. 015

Answer: C. LARS stands for Left Add, Right Subtract, judged from the examiner’s view. Rotation to the right means subtract the rotation from the ordered axis: 90 – 15 = 75. Option A adds when it should subtract, B ignores the rotation, and D is the size of the rotation, not an axis. Always confirm the direction convention with the lens manufacturer before ordering.

CLRE Question 3: Base curve in millimeters

Which statement compares an 8.40 mm base curve and an 8.80 mm base curve correctly? Use K (D) = 337.5 / r (mm).

• A. 8.40 mm is steeper by about 1.83 D
• B. 8.80 mm is steeper by about 1.83 D
• C. 8.40 mm is steeper by about 0.40 D
• D. 8.80 mm is steeper by about 0.40 D

Answer: A. 337.5 / 8.40 = 40.18 D and 337.5 / 8.80 = 38.35 D. The smaller radius is the steeper curve, and the difference is 40.18 – 38.35 = 1.83 D. Options C and D confuse the 0.40 mm radius difference with a power difference in diopters. B reverses which curve is steeper.

CLRE Question 4: Follow-up fit assessment

At a soft lens follow-up, the lens does not move on blink and resists the push-up test. Which assessment and change are appropriate?

• A. Tight (steep) fit, so try a flatter base curve
• B. Tight (steep) fit, so try a steeper base curve
• C. Loose (flat) fit, so try a steeper base curve
• D. Loose (flat) fit, so try a flatter base curve

Answer: A. A lens with little or no movement that resists the push-up test is fitting too tightly, which means it is too steep for the cornea. The change is to a flatter base curve (a larger radius). A steeper curve would tighten the fit further, and the movement findings rule out a loose fit.

Frequently Asked Questions

Using the Official Resources

The outline in the handbook is the most reliable study map. Match your weakest domain to its scored-question count and spend time in proportion. The handbook includes five NOCE sample questions, and ABO-NCLE sells a full practice exam if you want its own item style. For the arithmetic domains, drill with the calculators linked above until you can reproduce each answer without them.

Saulo Garcia

I grew up inside an optical shop. My mother likes to tell how, as a kid, I would watch eyeglasses being assembled, play with the tools, and draw on the back of service order slips. The family business taught me early what a precise measurement and work done right are worth.
I went on to spend more than twenty years as a software engineer, always keeping an eye on the optical world. Optogrid was born where the two meet: digital measurement technology (pupillary distance and fitting heights) built by someone who knows the dispensing counter from the inside.