22 Lens Products & Materials Practice Questions & Answers

1. 1. A patient has no useful vision in the left eye and wears a plano "balance" lens on that side. The right eye is -3.25 -0.75 x 180. What material should both lenses be made in, and why?

   • A.Polycarbonate or Trivex in both eyes, to protect the one seeing eye from impact injury✓ Answer
   • B.Crown glass in both eyes, because its hard surface resists scratching over years of wear
   • C.CR-39 in both eyes, because its Abbe value gives the seeing eye the sharpest image
   • D.Index 1.67 in both eyes, because matching thin edges keep the pair cosmetically even

   A patient with only one seeing eye must have that eye protected first, so both lenses — including the plano balance lens — are ordered in a high-impact material such as polycarbonate or Trivex. Abbe value, scratch resistance and cosmetic edge thickness all rank behind impact safety for a monocular wearer.

   Source: ABO-NCLE NOCE Basic test specifications, Ophthalmic Products — lens material selection; ANSI Z87.1 high-impact materials (polycarbonate and Trivex)Report a problem with this question

2. 2. A 9-year-old who plays soccer needs -1.50 DS in each eye, and the parent asks for "the thinnest lens you have." How should the optician respond?

   • A.Index 1.67, because the parent asked for the thinnest lens and the child's power is low
   • B.Polycarbonate, because impact resistance matters more than the slight thinning of 1.67✓ Answer
   • C.CR-39 with a hard coat, because children scratch lenses and CR-39 holds coatings well
   • D.Crown glass, because it stays clear longest and a child's lenses take heavy surface abuse

   At -1.50 D the thickness difference between 1.586 polycarbonate and 1.67 is negligible, while the impact difference is not: children and sports wearers are dispensed polycarbonate or Trivex as a matter of practice, and glass and CR-39 are not high-impact materials. The optician answers the underlying need — safety — rather than the product word the parent used.

   Source: ABO-NCLE NOCE Basic test specifications, Ophthalmic Products — material selection for children and sports; ANSI Z87.1 high-impact lens materialsReport a problem with this question

3. 3. A wearer wants a three-piece rimless mounting with holes drilled through the lenses, Rx -2.00 DS. Which material is appropriate and why?

   • A.CR-39, because it machines cleanly and its edge holds a drilled hole without stress
   • B.Trivex or polycarbonate, because both resist chipping and cracking at a drilled hole✓ Answer
   • C.Crown glass, because its rigidity keeps the drilled lens from flexing in the mounting
   • D.Index 1.74, because the thinner edge makes the drilled hole less visible to onlookers

   A drilled rimless lens carries stress concentrated at the hole, so the material must tolerate point loading: Trivex and polycarbonate deform rather than fracture, while CR-39 is brittle at a drill hole and glass is unsuitable for drilled mountings. Thin edges do not help if the lens cracks around the bushing.

   Source: ABO-NCLE NOCE Basic test specifications, Ophthalmic Products — edge treatments and special processes; impact behaviour of CR-39 versus polycarbonate and TrivexReport a problem with this question

4. 4. A high myope orders 1.74 lenses and later reports colored fringes around headlights when he looks through the edge of the lens. What explains this?

   • A.The 1.74 has a high Abbe value, and high Abbe materials disperse more in the periphery
   • B.The lens base curve is too flat, which splits white light into colors at the lens edge
   • C.The 1.74 has a low Abbe value, so chromatic dispersion is worst away from the optical center✓ Answer
   • D.The antireflective coating separates white light, which is why the fringes appear at night

   Abbe value measures a material's resistance to chromatic dispersion, and it generally falls as refractive index rises — 1.74 sits near the bottom of the common materials. Dispersion grows with the prismatic effect at the point of gaze, so the color fringing is worst peripherally and absent at the optical center.

   Source: Ophthalmic optics: Abbe value (constringence) and its inverse relationship with refractive index; ABO-NCLE NOCE Basic test specifications, Ophthalmic Optics — index of refractionReport a problem with this question

5. 5. Why does antireflective treatment become more important as lens index increases?

   • A.Surface reflection falls with index, so AR is added mainly to improve the lens cosmetically
   • B.Surface reflection rises with index, so an untreated 1.67 lens loses more light than CR-39✓ Answer
   • C.High-index materials transmit more ultraviolet light, and the AR stack is what blocks it
   • D.High-index lenses are softer, and the AR stack is what supplies their scratch resistance

   The proportion of light reflected at each lens surface increases as the refractive index increases, so a high-index lens transmits less light and shows stronger surface ghosts than CR-39 before treatment. Antireflective layers restore that transmission, which is why 1.6x lenses are usually dispensed with AR and 1.7x essentially always are.

   Source: Reflectance at an air–lens interface increases with refractive index (Fresnel relationship); ABO-NCLE NOCE Basic test specifications, Ophthalmic Products — lens coatingsReport a problem with this question

6. 6. A wearer at -6.00 DS asks whether switching from CR-39 to Trivex will noticeably thin his lens edges. What is the accurate answer?

   • A.Yes — Trivex is about 1.60, so the edges come out roughly a third thinner than CR-39
   • B.Yes — Trivex has a lower specific gravity, and lower density always yields thinner edges
   • C.No — Trivex edges come out thicker than CR-39 because the material is surfaced flatter
   • D.No — Trivex is 1.53, so edge thickness is close to CR-39; the gain is weight and impact✓ Answer

   Thickness is governed by refractive index, and Trivex at 1.53 is only marginally higher than CR-39 at about 1.50, so the edge change is slight. Trivex is chosen for its low specific gravity (about 1.11, the lightest standard material) and its high-impact performance, not as a thinning material.

   Source: Refractive indices of ophthalmic materials: CR-39 n ≈ 1.498–1.50, Trivex n = 1.53; ABO-NCLE NOCE Basic test specifications, Ophthalmic Optics — index of refraction and lens thicknessReport a problem with this question

7. 7. Two pairs are made to the same Rx and frame size, one in Trivex (specific gravity about 1.11) and one in polycarbonate (about 1.20). What will the wearer notice?

   • A.The polycarbonate pair weighs less, since a higher index always means a lighter lens
   • B.Both pairs weigh the same, since specific gravity describes surface hardness, not density
   • C.The Trivex pair weighs less, since specific gravity compares the material's density to water✓ Answer
   • D.The Trivex pair weighs more, since its thicker edge outweighs any density difference

   Specific gravity is the ratio of a material's density to that of water, so at equal volume the material with the lower figure weighs less; Trivex at about 1.11 is the lightest of the standard ophthalmic materials. Index governs thickness, not weight, and the two properties must be judged separately.

   Source: Specific gravity of ophthalmic lens materials (Trivex ≈ 1.11, polycarbonate ≈ 1.20); ABO-NCLE NOCE Basic test specifications, Ophthalmic Optics — material propertiesReport a problem with this question

8. 8. A -9.00 DS wearer complains that the edges of his CR-39 lenses are thick and heavy in a large frame. Which combination addresses the complaint?

   • A.Index 1.67 with AR in a smaller frame fitted to his PD, keeping decentration minimal✓ Answer
   • B.Polycarbonate in the same large frame, since poly gives the thinnest edge of any material
   • C.Index 1.74 in a larger frame, because more decentration pulls the thick edge out of view
   • D.CR-39 in the same large frame with a flatter base curve, which thins the edge directly

   In a minus lens a larger eyewire opening always produces a thicker edge, so the frame must shrink and be centered on the wearer's PD to limit decentration before any material change helps. A higher index then reduces the remaining edge, and AR offsets the extra surface reflection that higher index brings.

   Source: ABO-NCLE NOCE Basic test specifications, Ophthalmic Optics — effect of eyewire opening and decentration on lens thickness; Ophthalmic Products — high-index lenses and ARReport a problem with this question

9. 9. Four bifocal styles carry the same +2.00 add. Which produces essentially no image jump, and why?

   • A.Flat top 35, because a wider segment lowers the prism at the top of the segment
   • B.Round 22, because a curved segment top spreads the prism across a wider area
   • C.Flat top 28, because its segment optical center lies below the dividing line
   • D.Executive, because the segment's optical center sits on the dividing line itself✓ Answer

   Image jump is the prism encountered at the segment top, and by Prentice's rule that prism equals the add times the distance from the segment top down to the segment's optical center. The Executive design places the segment optical center on the dividing line, so that distance is zero and jump is essentially eliminated; a round segment places it farthest below and jumps most.

   Source: Image jump = add power × distance from segment top to segment optical center (Prentice's rule); ABO-NCLE NOCE Basic test specifications, Ophthalmic Products — multifocal segment stylesReport a problem with this question

10. 10. An optician explains image jump and image displacement to a student. Which statement distinguishes them correctly?

    • A.Jump comes from the add power alone; displacement comes from the segment width
    • B.Jump is prism at the segment top; displacement is total prism when reading✓ Answer
    • C.Jump occurs only in plus lenses, while displacement occurs only in minus lenses
    • D.Jump is noticed at near; displacement is what the wearer notices in distance gaze

    Jump is a discontinuity: the sudden prism met as the line of sight crosses the segment top, set by the segment style. Displacement is the net prism actually present at the reading point, the vector sum of the distance lens prism and the segment prism, so a minus distance lens and a plus segment can partly cancel.

    Source: Ophthalmic optics of multifocals: image jump versus image displacement (Prentice's rule applied at the segment top and at the reading point); ABO-NCLE NOCE Basic test specifications, Ophthalmic OpticsReport a problem with this question

11. 11. A prescription specifies an 8 x 35 trifocal with a +2.40 add. What do the two numbers mean, and what is the intermediate power?

    • A.Intermediate height 8 mm, segment width 35 mm, intermediate +1.20✓ Answer
    • B.Segment width 8 mm, intermediate height 35 mm, intermediate +1.20
    • C.Intermediate height 8 mm, segment width 35 mm, intermediate +2.40
    • D.Segment drop 8 mm, segment height 35 mm, intermediate +1.60

    In trifocal notation the first number is the vertical height of the intermediate zone and the second is the overall segment width, which reverses the single-number bifocal convention where ST 28 means a 28 mm width. The intermediate of a standard trifocal is half the add, so +2.40 gives +1.20.

    Source: Trifocal segment designation (intermediate height × segment width) and 50% intermediate add; ABO-NCLE NOCE Basic test specifications, Ophthalmic Products — segment styles and sizesReport a problem with this question

12. 12. An optician is ordering a progressive lens. Which set of measurements must be taken on the patient in the adjusted, chosen frame?

    • A.Binocular distance PD and a segment height measured to the lower lid margin
    • B.Monocular distance PDs and a fitting height to pupil center in the chosen frame✓ Answer
    • C.Monocular near PDs and a fitting height measured to the lower orbital rim
    • D.Binocular near PD and a seg height to the lower rim, as for a flat top bifocal

    A progressive has no line, so the fitting cross must be placed in front of the pupil center of each eye individually: monocular distance PDs handle facial asymmetry, and the fitting height is measured from the pupil center to the lowest point of the finished lens. Both must be taken with the frame already adjusted, since tilt and vertex change where the pupil sits in the opening.

    Source: ABO-NCLE NOCE Basic test specifications, Dispensing Procedures — positioning of optical centers and major reference points for progressive lensesReport a problem with this question

13. 13. Two progressive designs carry the same add, but one has a much shorter corridor. What does Minkwitz's theorem predict for the shorter design?

    • A.Lateral astigmatism is unchanged, and only the height of the near zone moves up
    • B.Lateral astigmatism falls as the corridor shortens, widening the usable near zone
    • C.Lateral astigmatism rises about twice as fast as the power along the corridor✓ Answer
    • D.Lateral astigmatism appears in the distance zone only, leaving near vision clear

    Minkwitz's theorem states that close to the umbilical line the rate of change of unwanted astigmatism sideways is about twice the rate of change of power along the corridor. A shorter corridor forces the same add to build over less distance, so the lateral blur gradient steepens and the usable intermediate and near zones narrow.

    Source: Minkwitz's theorem (rate of unwanted astigmatism ≈ twice the rate of power change near the umbilic); ABO-NCLE NOCE Basic test specifications, Ophthalmic Products — progressive designsReport a problem with this question

14. 14. A patient chooses a small, shallow frame for progressive lenses. Why must the optician check the B measurement before ordering?

    • A.The frame must let the segment clear the lower rim by at least 5 mm
    • B.A shallow frame forces a longer corridor, which delays the power buildup
    • C.The frame must allow the design's minimum fitting height above the lower rim✓ Answer
    • D.A shallow B measurement changes the add power reaching the near zone

    Every progressive design specifies a minimum fitting height: the vertical distance from the fitting cross down to the lowest edge of the lens needed for the full near zone to survive edging. If the B measurement of the frame is shallower than that, the near zone is cut away, so the frame must be checked before the lens is ordered rather than after.

    Source: ABO-NCLE NOCE Basic test specifications, Ophthalmic Products — progressive lens availability parameters (minimum fitting height) and boxing-system B measurementReport a problem with this question

15. 15. A first-time progressive wearer says the floor seems to move and the sides of the room look curved when she turns her head. What is the correct first response?

    • A.Explain the peripheral blur and verify fitting height and monocular PDs✓ Answer
    • B.Reorder the lenses with a stronger add so the near zone is easier to locate
    • C.Assume a lab error and reorder immediately on a much flatter base curve
    • D.Have her drop her chin and scan with her eyes instead of turning her head

    Swim and peripheral curvature are the expected consequence of the lateral astigmatism every progressive carries, but they are made far worse by a fitting cross that sits too low or off the monocular PD. The correct sequence is to counsel the wearer about eye-and-head coordination and verify the as-worn measurements, before concluding that the lens itself is wrong.

    Source: ABO-NCLE NOCE Basic test specifications, Dispensing Procedures — non-adapt troubleshooting and coordination of eye and head movements with progressive lensesReport a problem with this question

16. 16. An aphakic patient needs +12.00 DS. Why is an aspheric design specified?

    • A.Steepening the periphery deepens the lens and widens the wearer's field of view
    • B.The aspheric surface adds plus power toward the edge and extends the reading range
    • C.Asphericity raises the Abbe value, which removes color fringes in high plus power
    • D.Flattening the periphery cuts center thickness, weight and off-axis astigmatism✓ Answer

    An aspheric surface flattens progressively away from its center, which lets a high plus lens be made on a flatter base curve with less center thickness and less weight. The changing curvature also controls the oblique astigmatism a steeply curved high plus lens would otherwise produce, and it reduces the magnification the wearer's eyes appear to have.

    Source: ABO-NCLE NOCE Basic test specifications, Ophthalmic Products — aspheric lens designs for high plus prescriptions and aphakiaReport a problem with this question

17. 17. A +16.00 DS lens is ordered in a lenticular form. What does that design do?

    • A.It grinds a weaker second segment below to give the wearer an intermediate zone
    • B.It spreads the power evenly across the whole blank to keep the edge uniform
    • C.It puts the full power on the back surface and leaves the front surface plano
    • D.It carries the power in a central aperture with a thin flat carrier around it✓ Answer

    A lenticular confines the prescription to a limited central aperture and surrounds it with a thin, low-power carrier, which is the only practical way to keep an extreme plus or extreme minus lens from becoming impossibly thick and heavy. The trade-off is a visible aperture edge and a restricted field beyond it.

    Source: ABO-NCLE NOCE Basic test specifications, Ophthalmic Products — lenticular and myodisc designs for extreme prescriptionsReport a problem with this question

18. 18. A driver says her photochromic lenses barely darken in the car although they work well outdoors. Why?

    • A.Laminated windshield glass absorbs most ultraviolet, and UV drives the darkening✓ Answer
    • B.Visible light activates photochromics, and the windshield reduces visible light
    • C.The car's interior is warm, and heat alone is what triggers photochromic darkening
    • D.Photochromics need moving air and cooling to reach their full dark state

    Conventional photochromic molecules are switched by ultraviolet radiation, and a laminated automobile windshield absorbs almost all of it, so very little activation reaches the lens inside the car. Heat works the other way: higher temperature makes photochromics lighten, which is why they also reach a lighter maximum on hot days.

    Source: ABO-NCLE NOCE Basic test specifications, Ophthalmic Products — photochromic lens behaviour (UV activation, temperature dependence, windshield attenuation)Report a problem with this question

19. 19. A boat angler complains of glare off the water. How does a polarized lens help, and what is its limitation?

    • A.It blocks vertically polarized light, but cannot reduce glare from wet pavement
    • B.It scatters reflected light evenly, but makes distance judgment harder on water
    • C.It absorbs all ultraviolet light, but does nothing to reduce visible brightness
    • D.It blocks horizontally polarized light, but may darken some liquid-crystal displays✓ Answer

    Light reflected from a horizontal surface such as water or a road becomes largely horizontally polarized, so the laminated filter is oriented to absorb that plane and the glare disappears while the rest of the scene stays bright. The same filter also attenuates liquid-crystal displays, which are themselves polarized, so dashboards and phone screens can go dark at certain head positions.

    Source: ABO-NCLE NOCE Basic test specifications, Ophthalmic Products — polarized lenses; polarization of light reflected from horizontal surfacesReport a problem with this question

20. 20. A wearer orders a dark gray tint in CR-39, a material with no inherent absorption out to 400 nm, for beach use. What else must be specified?

    • A.A darker tint, since transmission below 20 percent blocks ultraviolet by itself
    • B.A mirror coating, since a reflective front surface is what stops ultraviolet light
    • C.A separate UV treatment, since a dark tint alone leaves ultraviolet largely unfiltered✓ Answer
    • D.A polarized filter, since the polarizing layer is what absorbs ultraviolet in a tint

    Tint density controls visible transmission, not ultraviolet transmission, so an untreated CR-39 lens can look very dark while passing UV. That is actively harmful at the beach, because the dark lens dilates the pupil and lets more UV into the eye — hence a UV treatment is ordered, which polycarbonate, Trivex and high-index materials already provide inherently.

    Source: ABO-NCLE NOCE Basic test specifications, Ophthalmic Products — tints and ultraviolet protection; inherent UV absorption of polycarbonate, Trivex and high-index versus CR-39Report a problem with this question

21. 21. A laboratory tests a finished glass dress lens for impact resistance under the FDA regulation. What does that test use?

    • A.A 5/8-inch steel ball of about 0.56 oz dropped 50 inches onto the upper surface✓ Answer
    • B.A 1-inch steel ball dropped from 50 inches onto the upper surface of the finished lens
    • C.A 5/8-inch steel ball fired at 150 feet per second at the front surface of the lens
    • D.A 1/4-inch steel ball fired at 150 feet per second at the center of the front surface

    The federal impact-resistance rule for eyeglass and sunglass lenses specifies a drop-ball test: a 5/8-inch steel ball weighing approximately 0.56 ounce is dropped from 50 inches onto the upper surface, striking within a 5/8-inch circle centered on the geometric center, and the lens must not fracture. The 1-inch ball belongs to the ANSI basic-impact safety test and the velocity-driven 1/4-inch ball to the ANSI high-impact test.

    Source: 21 CFR 801.410 — Use of impact-resistant lenses in eyeglasses and sunglasses (drop-ball test: 5/8-inch steel ball, approx. 0.56 oz, 50 inches)Report a problem with this question

22. 22. A machinist needs prescription safety eyewear rated high impact under ANSI Z87.1. Which specification is correct?

    • A.Minimum 3.0 mm thickness, marked with a plus sign, in any available lens material
    • B.Minimum 2.0 mm thickness, marked with a plus sign, in polycarbonate or Trivex✓ Answer
    • C.Minimum 2.0 mm thickness, no lens marking needed, with the frame alone marked Z87
    • D.Minimum 1.5 mm thickness, marked with a plus sign, in glass or high-index plastic

    Under the occupational eye-protection standard, high-impact prescription lenses must not be under 2.0 mm thick, must pass a high-velocity test with a 1/4-inch ball, and must carry the manufacturer's mark followed by a plus sign; in practice only polycarbonate and Trivex pass. The 3.0 mm minimum belongs to the basic-impact category, which is the thickness rule candidates most often misapply.

    Source: ANSI Z87.1 occupational eye protection standard — high-impact prescription lenses: minimum 2.0 mm thickness, 1/4-inch ball at 150 ft/sec, '+' markingReport a problem with this question

Practice questions based on the American Board of Opticianry Basic Certification exam content outline, standard ophthalmic dispensing references, and the federal rules that govern eyewear (the FDA impact-resistance requirement and the FTC Eyeglass and Contact Lens Rules). ABO and NCLE are marks of the American Board of Opticianry and National Contact Lens Examiners; this site is not affiliated with or endorsed by them. Opticianry is licensed in only some states and the requirements differ — confirm your own state board's practice act and the current exam format before testing. About the ABO exam →