ABO Cheat Sheet 2026

The 30 highest-yield ABO facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. Which contact lens care solution component is responsible for killing microorganisms? → Disinfectant (such as hydrogen peroxide or polyquaternium)
2. Anisometropic amblyopia develops primarily because: → A significant refractive difference between the two eyes causes chronic blur in one eye
3. A patient whose exophoria is significantly greater at distance than at near most likely has which binocular vision condition? → Divergence excess (or simulated divergence excess)
4. Topical carbonic anhydrase inhibitors (e.g., dorzolamide) lower IOP by: → Reducing aqueous humor production
5. What effect do variations in vertex distance have on a high-minus lens's effective power? → Increasing the vertex distance decreases the effective power
6. Which of the following mistakes will a four-point touch test miss? → Skewing
7. What is the function of the "add power" in bifocal lenses? → To provide additional magnification for near tasks in presbyopic patients
8. A hypertropia is defined as a vertical deviation in which the deviating eye turns: → Upward
9. In retinoscopy, a 'with' motion of the reflex indicates what type of refractive error? → Hyperopia or insufficient minus correction
10. Which structure of the eye is primarily responsible for focusing light at different distances? → Crystalline lens
11. What is the primary risk factor for open-angle glaucoma in the United States? → Elevated intraocular pressure
12. What does a myopic patient experience without corrective lenses? → Blurred distance vision
13. What theory explains why moving a plus lens away from the eye reduces its effective power? → The effective focal length (EFL) principle
14. The base curve of a spectacle lens primarily affects: → Cosmetic appearance and peripheral optics
15. A contact lens prescription of -3.00 D corresponds to a spectacle prescription of -3.25 D at a 12mm vertex distance. Why is the contact lens power less minus? → The contact lens sits closer to the eye, requiring less minus power
16. Chromatic aberration in spectacle lenses produces: → Color fringing around objects
17. A prescription reads -2.50 -1.00 x 180. What type of correction does this represent? → Compound myopic astigmatism
18. Which lens material has the highest index of refraction among common ophthalmic materials? → High-index 1.74 plastic
19. The Worth 4-Dot test uses red and green filters to evaluate: → Suppression and the quality of binocular fusion
20. What is the main way that astigmatism affects the retinal image quality? → By creating multiple focal points within the eye
21. Why are UV-blocking compounds added to the materials used to make contact lenses? → To reduce the risk of developing cataracts and other UV-related ocular conditions
22. The primary mechanism of action of latanoprost (Xalatan) is: → Prostaglandin F2α analog increasing uveoscleral outflow
23. When is it appropriate to use a slab-off prism? → To correct vertical imbalance in anisometropic patients wearing multifocals
24. Lenticular lens design is most commonly used when: → Very high plus powers are needed
25. A positive result on the Randot Stereotest indicates: → Bifoveal fixation and intact binocular vision
26. What is the impact of a lens's increased base curve on its optical power in ophthalmic optics? → It increases the lens's optical power
27. Add power in a bifocal lens is defined as: → Near power minus distance power
28. In minus cylinder notation, the cylinder axis meridian has: → The least minus (most plus) power of the two principal meridians
29. When comparing silicone hydrogel contact lenses to conventional hydrogel lenses, what is the main mechanism that enhances oxygen permeability? → By incorporating silicone into the lens material
30. A patient's vertex distance changes from 12mm to 14mm. How does this affect the effective power of a minus lens? → The effective power decreases