ABO Study Guide 2025 | Topics & Prep

ABO Exam Overview

Format

Computer-based, multiple choice

Questions

150 (125 scored + 25 pretest)

Time Limit

3 hours

Passing Score

Scaled score of 300+

Topic 1: Ophthalmic Optics (~30%)

This is the largest and most math-heavy section. Master these concepts:

Lens Power & Prescriptions

• Sphere, cylinder, and axis notation
• Plus and minus cylinder transposition
• Reading and interpreting prescriptions
• Add power for multifocals

Prism

• Prism diopters and base direction
• Prentice's Rule: Δ = dF (prism = decentration × power)
• Induced prism from decentration
• Compounding and resolving prism

Vertex Distance

• Why vertex distance matters for high powers
• Compensated power formula
• When to apply vertex distance corrections

Essential Formulas

• Prentice's Rule: Δ = d × F (d in cm)
• Vertex Distance: F' = F / (1 - dF) (d in meters)
• Transposition: Add cyl to sphere, change cyl sign, add 90° to axis
• Resultant Prism: √(H² + V²)

Sample Question

A lens with power +4.00D is decentered 8mm from the optical center. What is the induced prism?

Answer: Using Prentice's Rule: Δ = 0.8 × 4.00 = 3.2Δ

Topic 2: Lens Types & Materials (~25%)

Single Vision Lenses

• Spherical vs. aspheric designs
• Base curve selection
• Optical center placement

Multifocal Lenses

• Bifocal types: FT-28, FT-35, Executive, Round
• Trifocal designs and intermediate powers
• Segment height and inset measurements
• Image jump and how to minimize it

Progressive Addition Lenses (PALs)

• Corridor length options (short, standard, long)
• Fitting height requirements
• Peripheral distortion zones
• Measuring and marking PALs

Lens Materials

Material	Index	Abbe	Best For
CR-39	1.498	58	Low Rx, best optics
Polycarbonate	1.586	30	Safety, kids, sports
Trivex	1.532	43	Light weight + optics
Hi-Index 1.67	1.67	32	High Rx, thin lenses
Hi-Index 1.74	1.74	33	Very high Rx

Topic 3: Frames & Fitting (~20%)

Frame Measurements

• Eye size (A measurement)
• Bridge size (DBL)
• Temple length
• Frame PD = A + DBL
• Effective diameter (ED)
• B measurement (vertical)

Frame Materials

• Zyl (Cellulose Acetate): Most common plastic, adjustable with heat
• Titanium: Lightweight, hypoallergenic, strong
• Memory Metal: Flexible, returns to shape
• Monel: Corrosion-resistant metal alloy
• Stainless Steel: Durable, affordable metal

Fitting Measurements

• Monocular PD (distance and near)
• Segment height for bifocals/trifocals
• Fitting height for progressives
• Pantoscopic tilt (8-12° ideal)
• Face form/wrap angle
• Vertex distance (typically 12-14mm)

Topic 4: Lens Treatments & Coatings (~15%)

Anti-Reflective (AR) Coatings

• Reduces reflections from 8% to less than 1%
• Improves visual clarity and cosmetics
• Essential for high-index lenses
• Multi-layer coatings for best performance

Scratch-Resistant Coatings

• Hard coat applied to plastic lenses
• Does not make lenses scratch-proof
• Applied before AR coating

UV Protection

• UVA (320-400nm) and UVB (280-320nm)
• Polycarbonate blocks UV naturally
• CR-39 requires UV coating
• 100% UV protection = blocks up to 400nm

Photochromic Lenses

• Darken in UV light, clear indoors
• Temperature affects activation
• Don't darken well in cars (UV blocked by windshield)
• Available in gray and brown tints

Topic 5: Dispensing & Patient Care (~10%)

Frame Adjustments

• Temple spread and pantoscopic tilt
• Nose pad adjustments
• Temple length and bend point
• Face form adjustment

Troubleshooting Common Complaints

• "Things look tilted" → Check axis alignment
• "Headaches" → Check PD, seg height, or add power
• "Can't read" → Verify add power, seg height
• "Frames slide down" → Adjust temples, nose pads
• "Double vision" → Check prism, PD

Verification

• Using a lensometer to verify Rx
• Checking optical center placement
• Measuring segment height
• Inspecting for defects

Most Commonly Missed Topics

1.Cylinder transposition—practice until it's automatic
2.Prentice's Rule calculations with induced prism
3.Progressive lens fitting heights and corridor lengths
4.Material properties (index, Abbe value, impact resistance)
5.Vertex distance corrections for high prescriptions

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Our comprehensive course covers every ABO topic with interactive lessons, practice questions, and detailed explanations.

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Study Tips for Success

Focus on calculations: Practice Prentice's Rule and transposition daily until they're second nature.

Know your materials: Create flashcards for lens material properties (index, Abbe, applications).

Understand progressives: This is a heavily tested area—know fitting heights, corridor lengths, and troubleshooting.

Take practice tests: Simulate exam conditions with timed practice tests.

ABO Study Guide 2025: Topics, Practice Questions & Tips

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