NCLE Practice Test: Free CLRE Sample Questions

15 NCLE Practice Questions with Answers

1. Question 1

   Easy

   During sleep the closed lids cut the cornea off from the air. Where does the front of the cornea get most of its oxygen while the eyes are closed?

   1. A. Oxygen stored in the corneal stroma during waking hours
   2. B. Capillaries of the palpebral conjunctiva, through the tear layer
   3. C. The aqueous humor, diffusing forward through the stroma
   4. D. Limbal blood vessels that grow into the central cornea at night
   Show answer to question 1

   Answer: B. Capillaries of the palpebral conjunctiva, through the tear layer

   With the eyes open, the tear film takes up oxygen from the air at about 155 mmHg. With the lids closed, the supply comes from the capillaries of the palpebral conjunctiva at only about 55 mmHg, roughly a third as much, and even a cornea with no lens on it swells slightly overnight. That is why a lens worn during sleep needs far higher oxygen transmissibility (Dk/t) than a daily-wear lens.

   Study this topic: Pre-Fitting Evaluation

2. Question 2

   Medium

   Keratometry reads 43.25 @ 180 / 43.25 @ 090, and the spectacle refraction is -2.50 -1.25 x 090 (at these powers the vertex effect is small enough to ignore). Which lens is most likely to give this patient clear, stable vision?

   1. A. A spherical GP lens, since its tear lens will neutralize the 1.25 D of cylinder
   2. B. A back-toric GP lens whose back-surface toricity matches the 1.25 D of cylinder
   3. C. A soft toric lens ordered from the refraction, since the cylinder is internal
   4. D. A spherical soft lens set to the spherical-equivalent power, treating 1.25 D of cylinder as too little to matter
   Show answer to question 2

   Answer: C. A soft toric lens ordered from the refraction, since the cylinder is internal

   Equal K readings mean the front corneal surface is spherical, so all 1.25 D of the refractive cylinder is internal: mostly from the crystalline lens, with a small share from the back surface of the cornea. The tear layer behind a rigid lens evens out only toricity of the front corneal surface, so a spherical GP would leave about -1.25 x 090 uncorrected. A back-toric GP is no better, because on a round cornea nothing holds its orientation and the tears filling its toric back surface cancel most of that surface's cylinder. A soft toric lens ordered from the refraction corrects the full cylinder, whereas a sphere-only soft lens would leave all 1.25 D of it, half the sphere power, as blur.

   Study this topic: Pre-Fitting Evaluation

3. Question 3

   Hard

   A patient's glasses read -6.25 -1.50 x 180 and sit 13 mm from the cornea. Converting each principal meridian with Fc = F / (1 - dF), which soft toric power is closest (sphere and cylinder to the nearest 0.25 D)?

   1. A. -5.75 -1.25 x 180
   2. B. -6.25 -1.50 x 180
   3. C. -6.75 -1.75 x 180
   4. D. -5.75 -1.50 x 180
   Show answer to question 3

   Answer: A. -5.75 -1.25 x 180

   Treat each principal meridian as a sphere, with d in meters. The 180 meridian is -6.25 / (1 - 0.013 × -6.25) = -6.25 / 1.08125 = -5.78 D, and the 90 meridian is -7.75 / 1.10075 = -7.04 D. Recombined, that is -5.78 -1.26 x 180, which rounds to -5.75 -1.25 x 180. The cylinder shrinks too, because the stronger meridian changes more with vertex distance.

   Study this topic: Pre-Fitting Evaluation

4. Question 4

   Easy

   After settling for 15 minutes, a soft lens barely moves on the blink or in upgaze, resists the push-up test and recenters slowly, and leaves an impression ring on the conjunctiva when removed. The patient says vision is clearest right after each blink. What change is most appropriate?

   1. A. Order a steeper base curve so the lens grips the cornea more evenly
   2. B. Keep this fit, because a lens that barely moves gives the most stable vision
   3. C. Order a larger diameter so lid pressure is spread over more of the lens
   4. D. Order a flatter base curve or a smaller diameter to reduce sagittal depth
   Show answer to question 4

   Answer: D. Order a flatter base curve or a smaller diameter to reduce sagittal depth

   Little movement, a sluggish push-up, a conjunctival impression ring and vision that clears for a moment after each blink are classic signs of a tight (steep) soft lens. Reducing sagittal depth, with a flatter base curve or a smaller diameter, loosens the fit and restores tear exchange under the lens. Left in place, a tight lens can lead to limbal redness, hypoxia and an acute red eye, even though it often feels comfortable at first.

   Study this topic: Diagnostic Fitting & Evaluation

5. Question 5

   Medium

   A -3.00 D spherical GP lens with a 7.95 mm base curve rocks and drops after each blink. With fluorescein, the area over the corneal apex stays black, while a wide green band collects under the lens edge. The fitter reorders with a 7.90 mm base curve. What power keeps the patient's correction the same?

   1. A. Order -3.25 D, adding -0.25 D for the more plus tear lens
   2. B. Order -2.75 D, adding +0.25 D because the new lens is steeper
   3. C. Keep -3.00 D, since a base curve change does not alter power on the eye
   4. D. Order -3.50 D, adding -0.50 D because each 0.05 mm equals 0.50 D
   Show answer to question 5

   Answer: A. Order -3.25 D, adding -0.25 D for the more plus tear lens

   Black over the apex with green collecting under the edge means the lens is resting on the corneal apex: it is too flat, so steepening the base curve is the right change. Going from 7.95 mm (42.45 D) to 7.90 mm (42.72 D) steepens the base curve by about 0.25 D, which makes the tear lens about 0.25 D more plus. By SAM (Steeper Add Minus), order about -3.25 D so the total power on the eye stays the same.

   Study this topic: Diagnostic Fitting & Evaluation

6. Question 6

   Hard

   Keratometry: 42.25 @ 180 / 43.75 @ 090. Spectacle Rx: -1.25 -1.50 x 180 (vertex effect negligible). A spherical GP with a 42.75 D (7.89 mm) base curve is chosen. Which lens power belongs on the order?

   1. A. -0.75 D
   2. B. -1.75 D
   3. C. -2.00 D
   4. D. -3.25 D
   Show answer to question 6

   Answer: B. -1.75 D

   The vertical corneal meridian is 43.75 - 42.25 = 1.50 D steeper than the horizontal, the same as the refractive cylinder, so the tears under a spherical GP will cancel it and a sphere power is all the lens needs. Work in the flat meridian, which needs -1.25 D: the 42.75 D base curve is 0.50 D steeper than that meridian, which creates a +0.50 D tear lens, so SAM gives -1.25 - 0.50 = -1.75 D. Check the vertical meridian: the tear lens there is 42.75 - 43.75 = -1.00 D, and -1.75 - 1.00 = -2.75 D, exactly what the Rx needs along 090.

   Study this topic: Diagnostic Fitting & Evaluation

7. Question 7

   Easy

   A soft toric lens has settled, and its scribe mark has clearly turned away from 6 o'clock. Which method measures the amount of rotation most precisely?

   1. A. Turn a narrow slit beam until it lies along the marks, then read the beam's angle scale
   2. B. Compare the mark with the lower lid margin, using the lid as a horizontal reference
   3. C. Trace the lens edge against the limbus with a wide diffuse beam to see how far it turned
   4. D. Count the clock hours the mark has moved from 6 o'clock and multiply by 30° per hour
   Show answer to question 7

   Answer: A. Turn a narrow slit beam until it lies along the marks, then read the beam's angle scale

   Many slit lamps let the slit beam rotate against a degree scale, so lining a thin beam up with the scribe marks gives the rotation directly, with the patient's head level and eyes straight ahead. Counting clock hours at 30° each is a quick estimate, good to about half an hour (15°); the lid margin curves and tilts, so it is no reference, and a round lens edge shows nothing about rotation. Check the position over several blinks before applying LARS.

   Study this topic: Instrumentation

8. Question 8

   Hard

   A diagnostic soft toric lens with its cylinder axis at 170, the same as the refraction, is placed on the eye. Seen from the examiner's chair, its 6 o'clock scribe mark has turned 15° clockwise, to the left, and it returns there after every blink. Which axis should be ordered?

   1. A. 170
   2. B. 155
   3. C. 080
   4. D. 005
   Show answer to question 8

   Answer: D. 005

   LARS is read from the examiner's side: a mark that turns left (clockwise) means add, so 170 + 15 = 185, and because axes stop at 180, 185 - 180 = 005. The new lens will turn the same 15° clockwise on this eye, carrying its axis from 005 back to 170, where the refraction needs it. Subtracting instead (155) would leave the lens 30° off axis, and compensating like this works only because the rotation is the same after every blink.

   Study this topic: Diagnostic Fitting & Evaluation

9. Question 9

   Medium

   Lens A is made from a Dk 100 material with a 0.14 mm center thickness; Lens B from a Dk 70 material with a 0.07 mm center thickness. Using Dk/t = Dk ÷ thickness in cm, which lens has the higher central oxygen transmissibility, and how does it compare with the Holden-Mertz overnight figure of about 87 × 10⁻⁹?

   1. A. Lens A, at about 71 × 10⁻⁹, which meets the overnight figure
   2. B. Lens A, because its material has the higher Dk value
   3. C. Lens B, at about 100 × 10⁻⁹, which meets the overnight figure
   4. D. Lens B, at about 10 × 10⁻⁹, which falls short of the overnight figure
   Show answer to question 9

   Answer: C. Lens B, at about 100 × 10⁻⁹, which meets the overnight figure

   Dk/t describes the finished lens, so thickness matters as much as the material. Lens A: 100 × 10⁻¹¹ ÷ 0.014 cm ≈ 71 × 10⁻⁹; Lens B: 70 × 10⁻¹¹ ÷ 0.007 cm = 100 × 10⁻⁹. Only Lens B reaches the Holden-Mertz figure of about 87 × 10⁻⁹ for overnight wear, even though its material Dk is lower. Whether a lens may be slept in still depends on its FDA approval and the prescriber, not on Dk/t alone.

   Study this topic: Lens Materials & Design

10. Question 10

    Easy

    A 50-year-old emmetrope (no distance prescription) with a +1.75 D add wants to stop using his reading glasses and agrees to try monovision. Which lens setup matches that plan?

    1. A. A +1.75 D lens in the dominant eye only, since that eye leads when reading
    2. B. About +1.75 D in the non-dominant eye only, with no lens on the other eye
    3. C. +1.75 D lenses in both eyes, taken out whenever he needs to see far away
    4. D. A +1.00 D lens in each eye, as a compromise between distance and near
    Show answer to question 10

    Answer: B. About +1.75 D in the non-dominant eye only, with no lens on the other eye

    Monovision sets the dominant eye for distance and the other eye for near. An emmetrope already sees clearly far away, so only the non-dominant eye needs a lens, usually close to the add (some fitters use slightly less to keep more intermediate vision). Confirm the setup with diagnostic lenses before ordering, checking his distance and near vision with both eyes open during the tasks he does every day.

    Study this topic: Lens Materials & Design

11. Question 11

    Medium

    A patient's one-step hydrogen peroxide system uses a special cup with a platinum disc. She cracks the cup, so she soaks her soft lenses overnight in the peroxide solution in an ordinary flat lens case. In the morning both eyes sting and burn intensely as soon as the lenses go in. What is the most likely explanation?

    1. A. The lenses soaked longer than the minimum 6 hours, which concentrated the peroxide
    2. B. Flat-case wells hold too little solution, so the lenses dried out overnight
    3. C. Both lenses were inside out, which commonly causes burning on insertion
    4. D. The flat case has no catalyst, so the peroxide was never neutralized
    Show answer to question 11

    Answer: D. The flat case has no catalyst, so the peroxide was never neutralized

    In a disc-type system, 3% hydrogen peroxide is broken down into water and oxygen only inside the system's own vented cup, because the platinum disc is the catalyst. In an ordinary case the lenses soaked in full-strength peroxide all night, and a soft lens absorbs enough of it to burn the eye. She should remove the lenses and flush her eyes with sterile saline, not reinsert those lenses until they have been through a full cycle in a new disc cup (or replace them), and seek care if pain or redness persists.

    Study this topic: Patient Education & Handling

12. Question 12

    Medium

    A patient's contact lens prescription names a brand-name monthly lens. Her online retailer offers two cheaper choices: its own store-label lens, which is the identical lens made by the same manufacturer, and a similar silicone hydrogel lens from another maker in the same power and base curve. Under the FTC Contact Lens Rule, what may the retailer ship without the prescriber's authorization?

    1. A. Only the other maker's lens, since its power and base curve are the same as prescribed
    2. B. Either lens, as long as the patient agrees to the switch in writing first
    3. C. Only the store-label lens, because it is the prescribed lens under another name
    4. D. Neither lens, because a change of label also needs the prescriber's approval
    Show answer to question 12

    Answer: C. Only the store-label lens, because it is the prescribed lens under another name

    Federal law bars a seller from altering a contact lens prescription, with one narrow exception: when a manufacturer sells the very same lens under several labels, the seller may fill the order with that manufacturer's lens under a different name. A lens from another maker is a different device even when its power and base curve match, so it needs the prescriber's authorization, and the patient's consent does not replace that.

    Study this topic: Regulations & Standards

13. Question 13

    Medium

    A patient who has worn PMMA hard lenses for years has recently started wearing them about 14 hours a day for a new job. Late in the day, lights now have colored rings around them and her vision looks misty, and both effects linger for a while after the lenses come out. The lenses center and move as they did before. What is the most likely cause?

    1. A. Swelling of the central corneal epithelium from too little oxygen
    2. B. Light passing through the peripheral curves around a small optic zone
    3. C. A film of deposits building up on the front lens surface over the day
    4. D. Flexure of the lens on the eye as the material warms during wear
    Show answer to question 13

    Answer: A. Swelling of the central corneal epithelium from too little oxygen

    PMMA is practically impermeable to oxygen, so the cornea depends on tears pumped under the lens by each blink; after long hours the central epithelium swells, scatters light into colored halos and shows as a gray central haze with sclerotic scatter at the slit lamp. This central corneal clouding, known as Sattler's veil, outlasts lens removal, which rules out the lens-borne causes (optic-zone flare, deposits, flexure), since those stop as soon as the lens is out. The remedy is more oxygen: refit in a high-Dk GP material that moves well on the blink, and check the cornea again after the change.

    Study this topic: Follow-Up & Problem Solving

14. Question 14

    Medium

    A soft lens wearer of six years says her lenses have felt more noticeable over the past few months. The same lens that centered well a year ago now rides high and moves too much, as if the upper lid drags it up with each blink, and she mentions mild itching after taking the lenses out. Which examination step is most likely to show the cause?

    1. A. Checking the lower lid margin for blocked meibomian glands
    2. B. Staining the superior cornea to look for an arc near the lens edge
    3. C. Everting the upper lid to inspect the tarsal conjunctiva
    4. D. Repeating keratometry to look for a change in corneal curvature
    Show answer to question 14

    Answer: C. Everting the upper lid to inspect the tarsal conjunctiva

    A lens that once centered but is now hauled upward by the lid, together with itching, suggests a roughened upper tarsal surface catching the lens edge: the mechanical side of giant papillary conjunctivitis (GPC). The papillae are on the underside of the upper lid, so they stay hidden unless the lid is turned over: with the patient looking down, hold the lashes, press a cotton-tipped applicator gently at the upper border of the tarsal plate, and fold the lid back over it. Fluorescein helps, because the dye collects between the papillae and outlines them.

    Study this topic: Follow-Up & Problem Solving

15. Question 15

    Hard

    A patient has worn thick, low-Dk hydrogel lenses about 16 hours a day for 12 years, and new vessels now extend about 2 mm past the superior limbus into the clear cornea. She is refit into high-Dk silicone hydrogel lenses for shorter days, never slept in. When she returns months later, what should the fitter expect to see where the vessels were?

    1. A. They fade over a few weeks until the cornea looks as it did before
    2. B. They empty of blood but remain visible as faint ghost vessels
    3. C. They keep advancing toward the pupil at the same rate as before
    4. D. They stay filled and red for as long as she wears contact lenses
    Show answer to question 15

    Answer: B. They empty of blood but remain visible as faint ghost vessels

    New vessels grow into the cornea in response to a long-term oxygen shortage, here from a thick, low-Dk lens worn long hours. When the refit ends that shortage, blood stops flowing through them, but the empty channels stay in the stroma as ghost vessels, usually for years, rather than disappearing. They can refill quickly if the cornea is starved of oxygen again, so note their extent in the record and recheck them at every visit.

    Study this topic: Follow-Up & Problem Solving

What the NCLE (CLRE) Exam Covers

The CLRE is a computer-based exam of 125 multiple-choice questions with a 2-hour time limit. Only 100 questions are scored; the other 25 are unscored pretest items, and you cannot tell which is which. Passing takes a scaled score of 70, which is not the same as 70% correct. You must be at least 18 with a high school diploma or GED, and the exam is offered in quarterly testing windows at Prometric test centers or by remote proctoring. Fees and dates change, so check abo-ncle.org before you register.

ABO-NCLE's published content outline for the CLRE divides the 100 scored questions into eight domains: dispensing (20), follow-up (20), pre-fitting (15), ocular anatomy, physiology and pathology (12), instrumentation (12), diagnostic fitting (11), refractive errors (5), and regulatory and administrative topics (5). Pre-fitting, diagnostic fitting, dispensing and follow-up together account for 66 of the 100, so the exam leans toward clinical decisions: judging a fit, choosing a care system, recognizing a complication and knowing when to refer.

On this site the material is organized into seven NCLE study guides that map onto those eight domains. If you are deciding between exams, the ABO vs. NCLE guide explains how the CLRE differs from the ABO basic exam.

How to Use the Sample Questions

Answer each question before you read the explanation, and note why you chose your answer. A guess that happens to be right teaches you nothing, so count guesses as misses.

Treat each miss as a pointer to a topic, not a score. Fifteen questions show how the CLRE asks about the material, but they are too few to predict your result. Look up every miss in the matching study guide: fit evaluation and toric rotation in Diagnostic Fitting & Evaluation, oxygen and Dk/t in Lens Materials & Design, and complications in Follow-Up & Problem Solving.

Some questions involve math, such as converting a spectacle prescription to the corneal plane with Fc = F / (1 - dF), where d is the vertex distance in meters. Work these by hand first, then check yourself with the vertex distance calculator.

How to Prepare for the CLRE

Start with the heaviest domains. Dispensing and follow-up are 40 of the 100 scored questions: care systems, wearing schedules, insertion and removal, complications and troubleshooting. Then cover pre-fitting and anatomy, diagnostic fitting and instrumentation, using the free NCLE study guides.

Practice scenarios, not just definitions. Be ready for questions that describe a lens that lags, a fluorescein pattern or a red eye and ask what to change or what to do next. Learn the signs of a steep or flat fit for soft and rigid gas-permeable lenses, the LARS rule for toric lens rotation, and which signs mean the patient must be referred to the eye doctor.

Pace yourself for 125 questions in 120 minutes, just under a minute each. In the last two weeks, take full-length timed tests so the format feels routine on exam day.

When you want more practice than the samples, the NCLE plan adds mock tests of 25, 50, 75 or 100 questions drawn to the eight domain weights, practice by study topic, and a 125-question exam simulation on a 2-hour clock. It also includes the full ABO Basic prep. New customers get a 7-day free trial (card required; cancel before day 7 and pay nothing). If you are also sitting the ABO basic exam, the free ABO practice test gives you one test a day without a card.

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