ABO PRACTICAL EXAMINATION, AMERICAN BOARD OF OPTICIANRY, 2026 –
CERTIFIED OPTICIAN SKILLS AND ABILITIES COMPETENCY ASSESSMENT
### 1. When neutralizing a pair of single vision lenses using a manual lensometer,
you see thick, parallel lines moving *against* the reticle motion. What is the lens?
**Answer:** Minus sphere.
**Rationale:** Against motion indicates a minus lens (diverging light). Thick
parallel lines mean spherical power only—no cylinder.
---
### 2. While measuring a bifocal add, you focus the distance power, then read the
near power. The near mires are clear at +2.00 D more plus than distance. What is
the add?
**Answer:** +2.00 D.
**Rationale:** Add = near power minus distance power. The difference in plus
power is the add.
---
### 3. A patient’s right lens shows 2Δ base down in the vertical meridian. If the
patient complains of vertical imbalance, what prism direction should be placed
before the left eye to compensate?
**Answer:** 2Δ base up.
**Rationale:** Vertical imbalance is corrected by equal opposite prism. Base up
opposite base down.
---
### 4. You verify a progressive addition lens (PAL) in the lensometer. Where should
the distance reference point (DRP) be aligned?
**Answer:** At the reticle center (target center).
, **Rationale:** The DRP is the point providing the distance Rx; lensometer must
measure there for accurate distance power.
---
### 5. Using a lens clock on a +4.00 D spherical lens (n=1.523), you read +4.00 D.
What would you read on a polycarbonate lens (n=1.586) of same true power?
**Answer:** Approximately +3.75 D.
**Rationale:** Lens clock calibrated for n=1.523. For higher n (poly), actual
sagitta reads lower: true power × (1.523−1) / (n_lens −1) factor? Actually formula:
indicated power = true power × (1.523−1)/(n_lens −1). Or quicker: poly gives ~6%
less reading.
---
### 6. A frame has an A measurement of 52 mm and DBL of 18 mm. What is the
ED (effective diameter)?
**Answer:** Not enough info—need B measurement or shape. ED is twice longest
radius from geometric center. Typically ED ≥ largest diagonal. For practice: if B=42,
ED ≈ √(52²+42²) ≈ 67 mm.
**Rationale:** ED crucial for lens blank size selection.
---
### 7. In a manual lensometer, you see mires that are not aligned and focus at
two different drum readings: −1.00 and −3.00. What is the cylinder axis?
**Answer:** Cannot determine without seeing mire orientation; axis is the direction
of the *clearer* (less minus) mires when focusing.
**Rationale:** Reticale lines aligned at one meridian (axis) and perpendicular
meridian (power). Difference = cylinder power.
---
CERTIFIED OPTICIAN SKILLS AND ABILITIES COMPETENCY ASSESSMENT
### 1. When neutralizing a pair of single vision lenses using a manual lensometer,
you see thick, parallel lines moving *against* the reticle motion. What is the lens?
**Answer:** Minus sphere.
**Rationale:** Against motion indicates a minus lens (diverging light). Thick
parallel lines mean spherical power only—no cylinder.
---
### 2. While measuring a bifocal add, you focus the distance power, then read the
near power. The near mires are clear at +2.00 D more plus than distance. What is
the add?
**Answer:** +2.00 D.
**Rationale:** Add = near power minus distance power. The difference in plus
power is the add.
---
### 3. A patient’s right lens shows 2Δ base down in the vertical meridian. If the
patient complains of vertical imbalance, what prism direction should be placed
before the left eye to compensate?
**Answer:** 2Δ base up.
**Rationale:** Vertical imbalance is corrected by equal opposite prism. Base up
opposite base down.
---
### 4. You verify a progressive addition lens (PAL) in the lensometer. Where should
the distance reference point (DRP) be aligned?
**Answer:** At the reticle center (target center).
, **Rationale:** The DRP is the point providing the distance Rx; lensometer must
measure there for accurate distance power.
---
### 5. Using a lens clock on a +4.00 D spherical lens (n=1.523), you read +4.00 D.
What would you read on a polycarbonate lens (n=1.586) of same true power?
**Answer:** Approximately +3.75 D.
**Rationale:** Lens clock calibrated for n=1.523. For higher n (poly), actual
sagitta reads lower: true power × (1.523−1) / (n_lens −1) factor? Actually formula:
indicated power = true power × (1.523−1)/(n_lens −1). Or quicker: poly gives ~6%
less reading.
---
### 6. A frame has an A measurement of 52 mm and DBL of 18 mm. What is the
ED (effective diameter)?
**Answer:** Not enough info—need B measurement or shape. ED is twice longest
radius from geometric center. Typically ED ≥ largest diagonal. For practice: if B=42,
ED ≈ √(52²+42²) ≈ 67 mm.
**Rationale:** ED crucial for lens blank size selection.
---
### 7. In a manual lensometer, you see mires that are not aligned and focus at
two different drum readings: −1.00 and −3.00. What is the cylinder axis?
**Answer:** Cannot determine without seeing mire orientation; axis is the direction
of the *clearer* (less minus) mires when focusing.
**Rationale:** Reticale lines aligned at one meridian (axis) and perpendicular
meridian (power). Difference = cylinder power.
---
