ABO NOCE Basic Opticianry Dispensing Instrumentation Questions and Answers 2 — Questions and Answers

Question 1: When using a frame tracer (frame pattern maker), what information is captured for use by an edger?

The exact shape (silhouette) of the lens opening, including its size, position, and geometric center (Correct answer)
The prescription power to be ground on the lens
The patient's PD and OC height
The lens material and coating specifications

Correct answer: The exact shape (silhouette) of the lens opening, including its size, position, and geometric center

A frame tracer digitally captures the lens shape from the frame (or demo lens), producing a data file used by the edger to cut the lens to the exact required shape.

A frame tracer (or digitizer) traces the inner groove of a spectacle frame (the bevel channel) or the edge of a demo lens to capture its precise shape as digital coordinate data. This data is transmitted to the lens edger, which uses it to grind the lens blank to exactly that shape with the required bevel profile. Modern digital edging systems integrate the tracer and edger — the tracer data combined with the patient's PD and optical center position tells the edger where to center the lens and how to cut it so the optical center lands correctly. Accurate tracing is critical: if the frame tracer gives incorrect data, the lens will not fit the frame or the OC will be misplaced.

Question 2: An optical bench is used to measure:

The focal length and optical properties of lens systems, including back vertex distance and focal power (Correct answer)
The frame pupillary distance
The lens surface curvature
The intraocular pressure

Correct answer: The focal length and optical properties of lens systems, including back vertex distance and focal power

An optical bench is a laboratory instrument for measuring lens system properties including focal lengths, vergence, and back vertex power with precision.

An optical bench is a precision instrument consisting of a calibrated rod or rail on which lens holders, light sources, screens, and measuring devices are mounted and moved along a linear scale. In opticianry and optical laboratory settings, it is used to measure focal lengths, back vertex power, front vertex power, neutralizing power, and other properties of single lenses or complete lens systems. It allows more precise measurements than a lensometer for research, quality control, and calibration purposes. The optical bench applies vergence and image formation principles directly to measure where a lens system brings parallel light to focus, revealing the true focal power of the system.

Question 3: The purpose of a segment height gauge (seg height ruler) is to:

Measure the vertical distance from the lowest point of the lens to the top of the bifocal segment (Correct answer)
Measure the distance between bifocal segments in a pair of lenses
Measure the patient's near vision PD
Check the seg width against the prescription

Correct answer: Measure the vertical distance from the lowest point of the lens to the top of the bifocal segment

A seg height gauge measures the height of the bifocal or progressive addition segment from the bottom of the lens, used to verify correct placement per the dispensing prescription.

Segment height (or seg height) is the vertical distance from the lowest point of the edged lens (or the lowest point of the frame) to the top of the bifocal segment or the fitting cross of a progressive lens. It is a critical measurement in multifocal dispensing. The seg height gauge (or progressive fitting card for PALs) measures this distance on the finished lens to verify it matches the dispensing order. If the seg is too high, near objects appear in the patient's line of sight for distance; too low, and near tasks require excessive head tilt. ANSI Z80.1 specifies vertical placement tolerances for bifocal and progressive lenses.

Question 4: What is the function of a spectacle frame warmer (frame heater)?

To heat plastic frames to make them pliable for adjustment and lens insertion (Correct answer)
To sterilize frames before fitting
To soften lens coatings for removal
To temper glass lenses for impact resistance

Correct answer: To heat plastic frames to make them pliable for adjustment and lens insertion

Frame warmers (salt pans, hot air, or bead warmers) heat plastic frames to 60–80°C, making the material soft enough to safely adjust the frame and insert or remove lenses without cracking.

Spectacle frame warmers heat plastic (zyl/acetate) and nylon frames to their softening point (approximately 60–80°C / 140–176°F), making them pliable and safe to adjust. Types include: (1) Salt pans — heated glass beads or sand that frame is dipped into; (2) Hot air warmers — a fan blows heated air; (3) Infrared warmers. Without proper heating, plastic frames are brittle and will crack during adjustment or lens insertion. The frame should be heated just long enough to become pliable, then quickly adjusted and held in position until it cools. Overheating can damage lens coatings (especially AR coating) and warp thin frame rims. Titanium and metal frames do not require warmers.

Question 5: The purpose of a thickness caliper in opticianry is to:

Measure lens center thickness and edge thickness to verify they meet ANSI Z80.1 minimum thickness requirements (Correct answer)
Measure the depth of the frame groove for bevel selection
Measure the pupillary distance
Gauge the diameter of the lens blank

Correct answer: Measure lens center thickness and edge thickness to verify they meet ANSI Z80.1 minimum thickness requirements

Thickness calipers measure the center and edge thickness of finished lenses to ensure they meet minimum thickness requirements per ANSI Z80.1 and are safe for dispensing.

Thickness calipers (or lens thickness gauges) are used in opticianry to measure the center and edge thickness of finished lenses. ANSI Z80.1 specifies minimum center thickness requirements for impact resistance: glass lenses must be at least 3.0 mm at the center; plastic lenses must meet the drop-ball test (which effectively requires adequate thickness for the specific material and power). Checking edge thickness is important for frame selection (the edge must fit within the frame groove) and for cosmetic assessment. For minus lenses, edge thickness determines how much the lens 'overhangs' the frame and affects appearance. Calipers are also used to verify lens blank center thickness before surfacing.

Question 6: During lensometer verification, 'base-in' prism is confirmed when the mire target is displaced:

Toward the nose (toward the optical center from the nasal side) (Correct answer)
Temporally (toward the ear)
Inferiorly
The mire is centered with no displacement

Correct answer: Toward the nose (toward the optical center from the nasal side)

Base-in prism displaces the mire nasally (toward the nose) when the lens is held in standard position. The prism base is opposite to the mire displacement direction.

In a lensometer (Maddox convention), the prism base direction is opposite to the direction of mire displacement. For base-in prism (base toward the nose): the mire target is displaced nasally (toward the nose, i.e., toward the center of the body when the lens is held in standard reading position). Remember: 'The prism base is toward the thick edge; the mire moves toward the thin edge.' So base-in = thick edge nasally = mire displaced nasally. This convention must be memorized for the ABO exam. Prism is prescribed to treat binocular vision disorders (convergence insufficiency, phorias) and must be verified precisely before dispensing.

ABO NOCE Basic Opticianry Dispensing Instrumentation Questions and Answers 2

When using a frame tracer (frame pattern maker), what information is captured for use by an edger?