Certified Ophthalmic Medical Technologist (COMT) Practice Exam

Which type of spectacle lenses might require slab off adjustment?

1. Progressive lenses

2. Bifocal lenses

3. Single vision lenses

4. Lenses with near add power

The correct answer is: Lenses with near add power

Slab-off adjustment is a specific technique used primarily in glasses that correct for significant differences in lens power between the two eyes, particularly in cases of anisometropia, where one eye has a significantly different refractive error compared to the other. Lenses with near add power are especially relevant in this context because they often have a difference in prescription between the distance vision and the near vision zones. When a person requires a segment of the lens for near vision, such as in bifocal or progressive lenses, and there is a significant difference in the power of the lenses for each eye, slab-off can be employed to reduce prism in the more powerful lens. This adjustment ensures that the glasses provide proper alignment for both eyes, improving visual comfort and function. This adjustment technique mitigates issues such as double vision or discomfort during viewing, which can occur when the prismatic effect caused by differing lens powers is not addressed. Thus, lenses with near add power are the correct context for slab-off adjustments, as they are most often needed in cases involving bifocal or progressive designs where such disparities can arise.