ABO Optician — All Questions

Transpose the Rx: +2.00 -1.00 x 090 into plus-cylinder form.

• a.+1.00 -1.00 x 090
• b.+2.00 +1.00 x 090
• c.+1.00 +1.00 x 180✓
• d.+3.00 -1.00 x 180

To transpose: add the sphere and cylinder for the new sphere (+2.00 + -1.00 = +1.00), change the cylinder sign (+1.00), and rotate the axis 90 degrees (090 becomes 180). Result: +1.00 +1.00 x 180.

Transpose the Rx: -3.00 +2.00 x 045 into minus-cylinder form.

• a.-5.00 +2.00 x 135
• b.-1.00 +2.00 x 045
• c.-1.00 -2.00 x 135✓
• d.-3.00 -2.00 x 045

New sphere = -3.00 + 2.00 = -1.00; change cylinder sign to -2.00; rotate axis 90 degrees (045 to 135). Result: -1.00 -2.00 x 135.

In the Rx -2.50 -0.75 x 180, what does the 180 represent?

• a.The sphere power
• b.The prism base
• c.The add power
• d.The axis of the cylinder✓

The number after the 'x' is the cylinder axis, expressed 1 to 180 degrees, indicating the orientation of the cylinder correction. Here the axis is 180 degrees.

A patient has Rx OD -1.00 DS. What does 'DS' indicate?

• a.Decentration standard
• b.Distance seg
• c.Double segment
• d.Diopters sphere with no cylinder✓

DS stands for diopters sphere, meaning the lens is spherical only with no cylinder or axis. The prescription is simply -1.00 D of sphere.

Per ANSI Z80.1 tolerances, verifying a finished single-vision lens checks that the measured power falls within what?

• a.Half the prescribed power
• b.Exactly the prescribed power with zero deviation
• c.Twice the prescribed power
• d.An allowed tolerance range of the prescribed power✓

ANSI Z80.1 defines acceptable tolerances for sphere, cylinder, axis, add, and prism. A lens passes if its measured values fall within the standard's allowed range, not necessarily an exact match.ANSI Z80

A lens is decentered 4 mm from the optical center for a +5.00 D lens. How much prism results (Prentice's rule)?

• a.5.0 prism diopters
• b.1.0 prism diopter
• c.2.0 prism diopters✓
• d.0.4 prism diopters

Prentice's rule: prism = decentration in cm x power. 4 mm = 0.4 cm; 0.4 x 5.00 = 2.0 prism diopters.

When reading an Rx, which value is always a plus number on a bifocal?

• a.The sphere
• b.The add✓
• c.The axis
• d.The cylinder

The add power on a multifocal is always additional plus power for near vision, so it is written as a positive value regardless of the distance prescription.

Segment height is best defined as what?

• a.The pantoscopic tilt
• b.The horizontal distance between segments
• c.The width of the bifocal
• d.The vertical distance from the lowest point of the lens to the top of the segment line✓

Segment height is measured vertically from the lowest edge of the lens (or the deepest part of the eyewire) up to the top of the segment line, positioning the reading area correctly.

Monocular PD is measured from what to what?

• a.The center of the bridge of the nose to the center of each pupil✓
• b.Pupil to pupil
• c.Ear to ear
• d.Lens edge to lens edge

Monocular PD is the distance from the center of the nasal bridge to the center of each pupil individually. It accounts for facial asymmetry better than a single binocular PD.

A binocular distance PD of 64 mm typically corresponds to what near PD range?

• a.66 to 68 mm
• b.64 mm exactly
• c.70 mm
• d.60 to 62 mm✓

Because the eyes converge for near tasks, the near PD is smaller than the distance PD, usually by about 3 to 4 mm total. A 64 mm distance PD is roughly 60 to 61 mm at near.

Compensated (effective) power differs from the prescribed power mainly due to what?

• a.Bridge size
• b.Vertex distance and lens tilt✓
• c.Frame color
• d.Lens tint

When a high-powered lens sits at a vertex distance or tilt different from where it was refracted, its effective power on the eye changes, so a compensated power is calculated to preserve the intended correction.

A -8.00 D lens is moved closer to the eye. Its effective minus power does what?

• a.Decreases (less minus effect)✓
• b.Stays exactly the same
• c.Increases (more minus effect)
• d.Becomes plus power

For a minus lens moved closer to the eye, the effective power decreases; moved farther away, the effective minus power increases. Vertex compensation adjusts for this in high prescriptions.

Neutralizing a lens with a lensmeter finds what point?

• a.The point where the target is clear with no prism, the optical center✓
• b.The bevel apex
• c.The frame temple
• d.The segment top

On a lensmeter, the operator centers the lens so the mires (target) are clear and centered, identifying the optical center where there is no prismatic deviation, then reads sphere, cylinder, axis, and add.

Hand neutralization of an unknown lens uses what technique?

• a.Weighing the lens
• b.Reading the frame stamp
• c.Measuring edge thickness
• d.Moving the lens and observing target movement to add opposite power✓

In hand neutralization, an optician moves the lens across a target line; the direction of apparent movement indicates plus or minus, and trial lenses of opposite power are added until movement stops.

With-the-rule astigmatism typically has the cylinder axis oriented near what?

• a.Axis 135
• b.Axis 180 in minus cylinder✓
• c.Axis 45
• d.Axis 90 in plus cylinder

With-the-rule astigmatism has the steeper corneal meridian vertical, corrected with minus cylinder axis at or near 180 degrees. This is the most common form of astigmatism.

An Rx reads OD +1.50 -0.50 x 090, OS +1.50 -0.50 x 090, Add +2.25. What is the near power in each eye?

• a.+3.75 -2.75 x 090
• b.+2.25 -0.50 x 090
• c.+3.75 -0.50 x 090✓
• d.+1.50 -0.50 x 090

Near sphere = distance sphere + add = +1.50 + 2.25 = +3.75. The cylinder and axis carry through unchanged. Near Rx: +3.75 -0.50 x 090 in each eye.

Prism prescribed as '2 base out' in each eye is used to help with what?

• a.Reading add
• b.Convergence or divergence problems (horizontal)✓
• c.Vertical alignment
• d.Color vision

Base out and base in prism address horizontal deviations of the eyes, aiding fusion for esophoria or exophoria. Vertical deviations use base up or base down prism.

A patient needs 3 prism diopters base down in the right lens. If the lens is +2.00 D, how much decentration achieves this (Prentice's rule)?

• a.6.0 cm down
• b.1.5 cm (raise the OC 15 mm)✓
• c.0.67 cm up
• d.3.0 cm down

Prentice's rule solved for decentration: cm = prism / power = 3 / 2.00 = 1.5 cm. To create base-down prism with a plus lens, the optical center is raised 15 mm relative to the pupil.

Slab-off prism is used to correct what condition in a multifocal wearer?

• a.Excess add power
• b.Horizontal PD error
• c.A scratched segment
• d.Vertical imbalance at near between the two eyes✓

Slab-off grinds prism into one lens to compensate for the vertical prism imbalance created at the reading level when the two eyes have unequal Rx (anisometropia), restoring comfortable near fusion.

The written Rx 'OU' means what?

• a.Left eye only
• b.Over-refraction
• c.Both eyes (oculus uterque)✓
• d.Right eye only

OU is the Latin abbreviation oculus uterque, meaning both eyes. OD refers to the right eye and OS to the left eye.

Compensated power calculations are most critical when the fitted vertex distance differs from what?

• a.The seg height
• b.The frame PD
• c.The refracted vertex distance✓
• d.The base curve

The refraction is done at a specific vertex distance; when the dispensed frame sits at a different vertex distance, the effective power shifts, so compensation restores the intended power at the eye.

A spherical equivalent of the Rx -2.00 -1.00 x 180 is what?

• a.-2.00 D
• b.-3.00 D
• c.-1.50 D
• d.-2.50 D✓

Spherical equivalent = sphere + one-half the cylinder = -2.00 + (-1.00 / 2) = -2.00 + (-0.50) = -2.50 D. It represents the average dioptric power of the lens.

When both eyes require decentration for a smaller PD than the frame, the optical centers are moved which way?

• a.Nasally (inward)✓
• b.Temporally (outward)
• c.Vertically only
• d.Not at all

When the patient's PD is smaller than the frame's distance between lens centers, the optical centers must be decentered inward (nasally) to line up with the pupils and avoid unwanted prism.

Reading an Rx that lists 'BO' after a prism value indicates the base is oriented how?

• a.Base in
• b.Base down
• c.Base out✓
• d.Base up

BO stands for base out, meaning the thick base of the prism points toward the ear (temporal side). BI means base in (toward the nose), BU base up, and BD base down.